Daniel Repplinger, MD

Case

A 34-year-old man with a history of polysubstance abuse presented to the ED after he had a seizure during his regular methadone-treatment program meeting. While at the clinic, attendees witnessed the patient experience a loss of consciousness accompanied by generalized shaking movements of his extremities, which lasted for several minutes.

Upon arrival in the ED, the patient stated that he had a mild headache; he was otherwise asymptomatic. Initial vital signs were: blood pressure, 126/80 mm Hg; heart rate, 82 beats/minute; respiratory rate, 16 breaths/minute; and temperature, 97.3°F. Oxygen saturation was 98% on room air, and a finger-stick glucose test was 140 mg/dL. 

Physical examination revealed a small right-sided parietal hematoma. The patient had no tremors and his neurological examination, including mental status, was normal. When reviewing the patient’s medical history and medications in the health record, it was noted that the patient had a prescription for alprazolam for an anxiety disorder. On further questioning, the patient admitted that he had sold his last alprazolam prescription and had not been taking the drug for the past week.

What characterizes the  benzodiazepine withdrawal syndrome?

Although introduced into clinical practice in the 1960s, the potential for dependence and a withdrawal syndrome was not appreciated until the early 1980s. This clinical syndrome can manifest with a wide variety of findings, most commonly with what are termed “rebound effects” or “rebound hyperexcitability.” These effects include anxiety, insomnia or sleep disturbance, tremulousness, irritability, sweating, psychomotor agitation, difficulty in concentration, nausea, weight loss, palpitations, headache, muscular pain and stiffness, or generalized weakness.² More severe manifestations include delirium, seizures, or psychosis. Often, these symptoms and signs may be confused with the very manifestations that prompted the initial use of the BZD, a reemergence of which can exacerbate the withdrawal syndrome.

When does benzodiazepine withdrawal occur?

The exact time course of BZD withdrawal can vary considerably and, unlike alcohol withdrawal (which occurs from a single compound, ethanol), can be difficult to characterize. The onset of withdrawal symptoms is dependent on a number of factors, including the half-life of the BZD involved. For example, delayed onset withdrawal symptoms of up to 3 weeks after cessation of the medication are described with long-acting BZDs such as chlordiazepoxide and diazepam. Conversely, symptoms may present as early as 24 to 48 hours after abrupt termination of BZDs with shorter half-lives, alprazolam and lorazepam. This variable time of onset differs considerably from other withdrawal syndromes, notably ethanol withdrawal. While both syndromes correlate to the individual patient’s severity of dependence, alcohol withdrawal follows a more predictable time course.

Some authors distinguish a rebound syndrome from a true withdrawal syndrome, the former of which is self-limited in nature and the result of cessation of treatment for the primary disease process. In this model, rebound symptoms begin 1 to 4 days after the abrupt cessation or dose reduction of the BZD, and are relatively short-lived, lasting 2 to 3 days.²

What is the appropriate treatment for benzodiazepine withdrawal?

The standard therapy for almost all withdrawal syndromes is reinstitution of the causal agent. A number of non-BZD-based treatment strategies have been investigated, and all have met with limited success. Of these, anticonvulsant drugs such as carbamazepine and valproic acid were initially considered promising based on case reports and small case series.⁴ These medications ultimately proved ineffective in randomized, placebo-controlled studies.⁵ β-Adrenergic antagonists, such as propranolol, have been studied as a method to normalize a patient’s vital signs but also proved nonbeneficial in managing withdrawal.^5,6

The safest and most effective management approach for patients with BZD withdrawal is reinstitution of the BZD followed by a prolonged and gradual tapering until cessation, if that is desired.^1,2,5,6 While all BZDs share structural and mechanistic similarities, there are subtle variations within this class that can affect their pharmacologic effects. These structural differences may result in incomplete cross-tolerance, which may lead to inadequate mitigation of the withdrawal syndrome. For example, previous reports suggest that alprazolam and clonazepam are structurally unique and bind to the BZD receptor with higher affinity than other BZDs. Therefore, while in general any BZD can be used to treat withdrawal from another BZD, it is recommended to treat withdrawal from these two agents with the implicated BZD.

There are, however, limitations to this approach. Namely, some BZDs are only available in oral formulations (eg, alprazolam and clonazepam) or the BZD of choice may not be readily available or on formulary within a given institution. In a patient with a severe withdrawal syndrome where it is not feasible or potentially harmful to administer an oral medication, it is reasonable to provide parenteral (preferably intravenous [IV]) BZD therapy. The optimal approach is to start with a small “standard” dose and titrate to effect while monitoring for adverse effects (eg, oversedation, ventilatory depression). Redosing should be triggered by symptoms or signs, and not performed in a timed or standing-order fashion. If this approach proves ineffective and withdrawal symptoms persist despite adequate BZD therapy, a direct GABA agonist such as propofol is a sensible alternative or adjuvant treatment. This may sound similar to the management of patients with ethanol withdrawal; indeed, this approach is essentially the same, with the exception of the more drawn-out time course.

Case Conclusion

After arrival in the ED, the patient received diazepam 10 mg IV and was subsequently admitted to the hospital for further evaluation. During his hospitalization, the patient was re-started on his usual dose of oral alprazolam.  No further withdrawal syndrome was observed, and he was discharged on hospital day 2 with a plan to slowly taper his alprazolam dose with his outpatient psychiatrist.

Dr Repplinger is a senior medical toxicology fellow in the department of emergency medicine at New York University Langone Medical Center. Dr Nelson, editor of “Case Studies in Toxicology,” is a professor in the department of emergency medicine and director of the medical toxicology fellowship program at the New York University School of Medicine and the New York City Poison Control Center. He is also associate editor, toxicology, of the EMERGENCY MEDICINE editorial board.

Case

A 34-year-old man with a history of polysubstance abuse presented to the ED after he had a seizure during his regular methadone-treatment program meeting. While at the clinic, attendees witnessed the patient experience a loss of consciousness accompanied by generalized shaking movements of his extremities, which lasted for several minutes.

Upon arrival in the ED, the patient stated that he had a mild headache; he was otherwise asymptomatic. Initial vital signs were: blood pressure, 126/80 mm Hg; heart rate, 82 beats/minute; respiratory rate, 16 breaths/minute; and temperature, 97.3°F. Oxygen saturation was 98% on room air, and a finger-stick glucose test was 140 mg/dL. 

Physical examination revealed a small right-sided parietal hematoma. The patient had no tremors and his neurological examination, including mental status, was normal. When reviewing the patient’s medical history and medications in the health record, it was noted that the patient had a prescription for alprazolam for an anxiety disorder. On further questioning, the patient admitted that he had sold his last alprazolam prescription and had not been taking the drug for the past week.

What characterizes the  benzodiazepine withdrawal syndrome?

Although introduced into clinical practice in the 1960s, the potential for dependence and a withdrawal syndrome was not appreciated until the early 1980s. This clinical syndrome can manifest with a wide variety of findings, most commonly with what are termed “rebound effects” or “rebound hyperexcitability.” These effects include anxiety, insomnia or sleep disturbance, tremulousness, irritability, sweating, psychomotor agitation, difficulty in concentration, nausea, weight loss, palpitations, headache, muscular pain and stiffness, or generalized weakness.² More severe manifestations include delirium, seizures, or psychosis. Often, these symptoms and signs may be confused with the very manifestations that prompted the initial use of the BZD, a reemergence of which can exacerbate the withdrawal syndrome.

When does benzodiazepine withdrawal occur?

The exact time course of BZD withdrawal can vary considerably and, unlike alcohol withdrawal (which occurs from a single compound, ethanol), can be difficult to characterize. The onset of withdrawal symptoms is dependent on a number of factors, including the half-life of the BZD involved. For example, delayed onset withdrawal symptoms of up to 3 weeks after cessation of the medication are described with long-acting BZDs such as chlordiazepoxide and diazepam. Conversely, symptoms may present as early as 24 to 48 hours after abrupt termination of BZDs with shorter half-lives, alprazolam and lorazepam. This variable time of onset differs considerably from other withdrawal syndromes, notably ethanol withdrawal. While both syndromes correlate to the individual patient’s severity of dependence, alcohol withdrawal follows a more predictable time course.

Some authors distinguish a rebound syndrome from a true withdrawal syndrome, the former of which is self-limited in nature and the result of cessation of treatment for the primary disease process. In this model, rebound symptoms begin 1 to 4 days after the abrupt cessation or dose reduction of the BZD, and are relatively short-lived, lasting 2 to 3 days.²

What is the appropriate treatment for benzodiazepine withdrawal?

The standard therapy for almost all withdrawal syndromes is reinstitution of the causal agent. A number of non-BZD-based treatment strategies have been investigated, and all have met with limited success. Of these, anticonvulsant drugs such as carbamazepine and valproic acid were initially considered promising based on case reports and small case series.⁴ These medications ultimately proved ineffective in randomized, placebo-controlled studies.⁵ β-Adrenergic antagonists, such as propranolol, have been studied as a method to normalize a patient’s vital signs but also proved nonbeneficial in managing withdrawal.^5,6

The safest and most effective management approach for patients with BZD withdrawal is reinstitution of the BZD followed by a prolonged and gradual tapering until cessation, if that is desired.^1,2,5,6 While all BZDs share structural and mechanistic similarities, there are subtle variations within this class that can affect their pharmacologic effects. These structural differences may result in incomplete cross-tolerance, which may lead to inadequate mitigation of the withdrawal syndrome. For example, previous reports suggest that alprazolam and clonazepam are structurally unique and bind to the BZD receptor with higher affinity than other BZDs. Therefore, while in general any BZD can be used to treat withdrawal from another BZD, it is recommended to treat withdrawal from these two agents with the implicated BZD.

There are, however, limitations to this approach. Namely, some BZDs are only available in oral formulations (eg, alprazolam and clonazepam) or the BZD of choice may not be readily available or on formulary within a given institution. In a patient with a severe withdrawal syndrome where it is not feasible or potentially harmful to administer an oral medication, it is reasonable to provide parenteral (preferably intravenous [IV]) BZD therapy. The optimal approach is to start with a small “standard” dose and titrate to effect while monitoring for adverse effects (eg, oversedation, ventilatory depression). Redosing should be triggered by symptoms or signs, and not performed in a timed or standing-order fashion. If this approach proves ineffective and withdrawal symptoms persist despite adequate BZD therapy, a direct GABA agonist such as propofol is a sensible alternative or adjuvant treatment. This may sound similar to the management of patients with ethanol withdrawal; indeed, this approach is essentially the same, with the exception of the more drawn-out time course.

Case Conclusion

After arrival in the ED, the patient received diazepam 10 mg IV and was subsequently admitted to the hospital for further evaluation. During his hospitalization, the patient was re-started on his usual dose of oral alprazolam.  No further withdrawal syndrome was observed, and he was discharged on hospital day 2 with a plan to slowly taper his alprazolam dose with his outpatient psychiatrist.

Dr Repplinger is a senior medical toxicology fellow in the department of emergency medicine at New York University Langone Medical Center. Dr Nelson, editor of “Case Studies in Toxicology,” is a professor in the department of emergency medicine and director of the medical toxicology fellowship program at the New York University School of Medicine and the New York City Poison Control Center. He is also associate editor, toxicology, of the EMERGENCY MEDICINE editorial board.

Case

A 34-year-old man with a history of polysubstance abuse presented to the ED after he had a seizure during his regular methadone-treatment program meeting. While at the clinic, attendees witnessed the patient experience a loss of consciousness accompanied by generalized shaking movements of his extremities, which lasted for several minutes.

Upon arrival in the ED, the patient stated that he had a mild headache; he was otherwise asymptomatic. Initial vital signs were: blood pressure, 126/80 mm Hg; heart rate, 82 beats/minute; respiratory rate, 16 breaths/minute; and temperature, 97.3°F. Oxygen saturation was 98% on room air, and a finger-stick glucose test was 140 mg/dL. 

Physical examination revealed a small right-sided parietal hematoma. The patient had no tremors and his neurological examination, including mental status, was normal. When reviewing the patient’s medical history and medications in the health record, it was noted that the patient had a prescription for alprazolam for an anxiety disorder. On further questioning, the patient admitted that he had sold his last alprazolam prescription and had not been taking the drug for the past week.

What characterizes the  benzodiazepine withdrawal syndrome?

Although introduced into clinical practice in the 1960s, the potential for dependence and a withdrawal syndrome was not appreciated until the early 1980s. This clinical syndrome can manifest with a wide variety of findings, most commonly with what are termed “rebound effects” or “rebound hyperexcitability.” These effects include anxiety, insomnia or sleep disturbance, tremulousness, irritability, sweating, psychomotor agitation, difficulty in concentration, nausea, weight loss, palpitations, headache, muscular pain and stiffness, or generalized weakness.² More severe manifestations include delirium, seizures, or psychosis. Often, these symptoms and signs may be confused with the very manifestations that prompted the initial use of the BZD, a reemergence of which can exacerbate the withdrawal syndrome.

When does benzodiazepine withdrawal occur?

The exact time course of BZD withdrawal can vary considerably and, unlike alcohol withdrawal (which occurs from a single compound, ethanol), can be difficult to characterize. The onset of withdrawal symptoms is dependent on a number of factors, including the half-life of the BZD involved. For example, delayed onset withdrawal symptoms of up to 3 weeks after cessation of the medication are described with long-acting BZDs such as chlordiazepoxide and diazepam. Conversely, symptoms may present as early as 24 to 48 hours after abrupt termination of BZDs with shorter half-lives, alprazolam and lorazepam. This variable time of onset differs considerably from other withdrawal syndromes, notably ethanol withdrawal. While both syndromes correlate to the individual patient’s severity of dependence, alcohol withdrawal follows a more predictable time course.

Some authors distinguish a rebound syndrome from a true withdrawal syndrome, the former of which is self-limited in nature and the result of cessation of treatment for the primary disease process. In this model, rebound symptoms begin 1 to 4 days after the abrupt cessation or dose reduction of the BZD, and are relatively short-lived, lasting 2 to 3 days.²

What is the appropriate treatment for benzodiazepine withdrawal?

The standard therapy for almost all withdrawal syndromes is reinstitution of the causal agent. A number of non-BZD-based treatment strategies have been investigated, and all have met with limited success. Of these, anticonvulsant drugs such as carbamazepine and valproic acid were initially considered promising based on case reports and small case series.⁴ These medications ultimately proved ineffective in randomized, placebo-controlled studies.⁵ β-Adrenergic antagonists, such as propranolol, have been studied as a method to normalize a patient’s vital signs but also proved nonbeneficial in managing withdrawal.^5,6

The safest and most effective management approach for patients with BZD withdrawal is reinstitution of the BZD followed by a prolonged and gradual tapering until cessation, if that is desired.^1,2,5,6 While all BZDs share structural and mechanistic similarities, there are subtle variations within this class that can affect their pharmacologic effects. These structural differences may result in incomplete cross-tolerance, which may lead to inadequate mitigation of the withdrawal syndrome. For example, previous reports suggest that alprazolam and clonazepam are structurally unique and bind to the BZD receptor with higher affinity than other BZDs. Therefore, while in general any BZD can be used to treat withdrawal from another BZD, it is recommended to treat withdrawal from these two agents with the implicated BZD.

There are, however, limitations to this approach. Namely, some BZDs are only available in oral formulations (eg, alprazolam and clonazepam) or the BZD of choice may not be readily available or on formulary within a given institution. In a patient with a severe withdrawal syndrome where it is not feasible or potentially harmful to administer an oral medication, it is reasonable to provide parenteral (preferably intravenous [IV]) BZD therapy. The optimal approach is to start with a small “standard” dose and titrate to effect while monitoring for adverse effects (eg, oversedation, ventilatory depression). Redosing should be triggered by symptoms or signs, and not performed in a timed or standing-order fashion. If this approach proves ineffective and withdrawal symptoms persist despite adequate BZD therapy, a direct GABA agonist such as propofol is a sensible alternative or adjuvant treatment. This may sound similar to the management of patients with ethanol withdrawal; indeed, this approach is essentially the same, with the exception of the more drawn-out time course.

Case Conclusion

After arrival in the ED, the patient received diazepam 10 mg IV and was subsequently admitted to the hospital for further evaluation. During his hospitalization, the patient was re-started on his usual dose of oral alprazolam.  No further withdrawal syndrome was observed, and he was discharged on hospital day 2 with a plan to slowly taper his alprazolam dose with his outpatient psychiatrist.

Dr Repplinger is a senior medical toxicology fellow in the department of emergency medicine at New York University Langone Medical Center. Dr Nelson, editor of “Case Studies in Toxicology,” is a professor in the department of emergency medicine and director of the medical toxicology fellowship program at the New York University School of Medicine and the New York City Poison Control Center. He is also associate editor, toxicology, of the EMERGENCY MEDICINE editorial board.

Case

An 8-month-old boy with a history of hypotonia, developmental delay, and seizure disorder refractory to multiple anticonvulsant medications, was presented to the ED with a 2-week history of intermittent fever and poor oral intake. His current medications included sodium bromide 185 mg orally twice daily for his seizure disorder.

On physical examination, the boy appeared small for his age, with diffuse hypotonia and diminished reflexes. He was able to track with his eyes but was otherwise unresponsive. No rash was present. Results of initial laboratory studies were: sodium 144 mEq/L; potassium, 4.8 mEq/L; chloride, 179 mEq/L; bicarbonate, 21 mEq/L; blood urea nitrogen, 6 mg/dL; creatinine, 0.1 mg/dL; and glucose, 63 mg/dL. His anion gap (AG) was −56.

What does the anion gap represent?

The AG is a valuable clinical calculation derived from the measured extracellular electrolytes and provides an index of acid-base status.¹ Due to the necessity of electroneutrality, the sum of positive charges (cations) in the extracellular fluid must be balanced exactly with the sum of negative charges (anions). However, to routinely measure all of the cations and anions in the serum would be time-consuming and is also unnecessary. Because most clinical laboratories commonly only measure one relevant cation (sodium) and two anions (chloride and bicarbonate), the positive and negative sums are not completely balanced. The AG therefore refers to this difference (ie, AG = Na – [Cl + HCO₃]).

Of course, electroneutrality exists in vivo, and is accomplished by the presence of unmeasured anions (UA) (eg, lactate and phosphate) and unmeasured cations (UC) (eg, potassium and calcium) not accounted for in the AG (ie, AG = UA – UC). In other words, the sum of measured plus the unmeasured anions must equal the sum of the measured plus unmeasured cations.

What causes a low or negative anion gap?

While most healthcare providers are well versed in the clinical significance of an elevated AG (eg, MUDPILES [methanol, uremia, diabetic ketoacidosis, propylene glycol or phenformin, iron or isoniazid, lactate, ethylene glycol, salicylates]), the meaning of a low or negative AG is underappreciated. There are several scenarios that could potentially yield a low or negative AG, including decreased concentration of UA, increased concentrations of nonsodium cations (UC), and overestimation of serum chloride.

Decreased Concentration of Unmeasured Anions. This most commonly occurs by two mechanisms: dilution of the extracellular fluid or hypoalbuminemia. The addition of water to the extracellular fluid will cause a proportionate dilution of all the measured electrolytes. Since the concentration of measured cations is higher than the measured anions, there is a small and relatively insignificant decrease in the AG.

Alternatively, hypoalbuminemia results in a low AG due to the change in UA; albumin is negatively charged. At physiologic pH, the overwhelming majority of serum proteins are anionic and counter-balanced by the positive charge of sodium. Albumin, the most abundant serum protein, accounts for approximately 75% of the normal AG. Hypoalbuminemic states, such as cirrhosis or nephrotic syndrome, can therefore cause low AG due to the retention of chloride to replace the lost negative charge. The albumin concentration can be corrected to calculate the AG.²

Nonsodium Cations. There are a number of clinical conditions that result in the retention of nonsodium cations. For example, the excess positively charged paraproteins associated with IgG myeloma raise the UC concentration, resulting in a low AG. Similarly, elevations of unmeasured cationic electrolytes, such as calcium and magnesium, may also result in a lower AG. Significant changes in AG, though, are caused only by profound (and often life-threatening) hypercalcemia or hypermagnesemia.

Overestimation of Serum Chloride. Overestimation of serum chloride most commonly occurs in the clinical scenario of bromide exposure. In normal physiologic conditions, chloride is the only halide present in the extracellular fluid. With intake of brominated products, chloride may be partially replaced by bromide. As there is greater renal tubular avidity for bromide, chronic ingestion of bromide results in a gradual rise in serum bromide concentrations with a proportional fall in chloride. However, and more importantly, bromide interferes with a number of laboratory techniques measuring chloride concentrations, resulting in a spuriously elevated chloride, or pseudohyperchloremia. Because the measured sodium and bicarbonate concentrations will remain unchanged, this falsely elevated chloride measurement will result in a negative AG.

What causes the falsely elevated chloride?

All of the current laboratory techniques for measurement of serum chloride concentration can potentially result in a falsely elevated value. However, the degree of pseudohyperchloremia will depend on the specific assay used for measurement. The ion-selective electrode method used by many common laboratory analyzers appears to have the greatest interference on chloride measurement in the presence of bromide. This is simply due to the molecular similarity of bromide and chloride. Conversely, the coulometry method, often used as a reference standard, has the least interference of current laboratory methods.³ This is because coulometry does not completely rely on molecular structure to measure concentration, but rather it measures the amount of energy produced or consumed in an electrolysis reaction. Iodide, another halide compound, has also been described as a cause of pseudohyperchloremia, whereas fluoride does not seem to have significant interference.⁴ 

How are patients exposed to bromide salts?

Bromide salts, specifically sodium bromide, are infrequently used to treat seizure disorders, but are generally reserved for patients with epilepsy refractory to other, less toxic anticonvulsant medications. During the era when bromide salts were more commonly used to treat epilepsy, bromide intoxication, or bromism, was frequently observed.

Bromism may manifest as a constellation of nonspecific neurological and psychiatric symptoms. These most commonly include headache, weakness, agitation, confusion, and hallucinations. In more severe cases of bromism, stupor and coma may occur.^3,5

Although bromide salts are no longer commonly prescribed, a number of products still contain brominated ingredients. Symptoms of bromide intoxication can occur with chronic use of a cough syrup containing dextromethorphan hydrobromide as well as the brominated vegetable oils found in some soft drinks.⁵ 

How is bromism treated?

The treatment of bromism involves preventing further exposure to bromide and promoting bromide excretion. Bromide has a long half-life (10-12 days), and in patients with normal renal function, it is possible to reduce this half-life to approximately 3 days with hydration and diuresis with sodium chloride.³ Alternatively, in patients with impaired renal function or severe intoxication, hemodialysis has been used effectively.⁵

Case Conclusion

The patient was admitted for observation and treated with intravenous sodium chloride. After consultation with his neurologist, he was discharged home in the care of his parents, who were advised to continue him on sodium bromide 185 mg orally twice daily since his seizures were refractory to other anticonvulsant medications.

Dr Repplinger is a medical toxicology fellow in the department of emergency medicine at New York University Langone Medical Center. Dr Nelson, editor of “Case Studies in Toxicology,” is a professor in the department of emergency medicine and director of the medical toxicology fellowship program at the New York University School of Medicine and the New York City Poison Control Center. He is also associate editor, toxicology, of the EMERGENCY MEDICINE editorial board.

Case

An 8-month-old boy with a history of hypotonia, developmental delay, and seizure disorder refractory to multiple anticonvulsant medications, was presented to the ED with a 2-week history of intermittent fever and poor oral intake. His current medications included sodium bromide 185 mg orally twice daily for his seizure disorder.

On physical examination, the boy appeared small for his age, with diffuse hypotonia and diminished reflexes. He was able to track with his eyes but was otherwise unresponsive. No rash was present. Results of initial laboratory studies were: sodium 144 mEq/L; potassium, 4.8 mEq/L; chloride, 179 mEq/L; bicarbonate, 21 mEq/L; blood urea nitrogen, 6 mg/dL; creatinine, 0.1 mg/dL; and glucose, 63 mg/dL. His anion gap (AG) was −56.

What does the anion gap represent?

The AG is a valuable clinical calculation derived from the measured extracellular electrolytes and provides an index of acid-base status.¹ Due to the necessity of electroneutrality, the sum of positive charges (cations) in the extracellular fluid must be balanced exactly with the sum of negative charges (anions). However, to routinely measure all of the cations and anions in the serum would be time-consuming and is also unnecessary. Because most clinical laboratories commonly only measure one relevant cation (sodium) and two anions (chloride and bicarbonate), the positive and negative sums are not completely balanced. The AG therefore refers to this difference (ie, AG = Na – [Cl + HCO₃]).

Of course, electroneutrality exists in vivo, and is accomplished by the presence of unmeasured anions (UA) (eg, lactate and phosphate) and unmeasured cations (UC) (eg, potassium and calcium) not accounted for in the AG (ie, AG = UA – UC). In other words, the sum of measured plus the unmeasured anions must equal the sum of the measured plus unmeasured cations.

What causes a low or negative anion gap?

While most healthcare providers are well versed in the clinical significance of an elevated AG (eg, MUDPILES [methanol, uremia, diabetic ketoacidosis, propylene glycol or phenformin, iron or isoniazid, lactate, ethylene glycol, salicylates]), the meaning of a low or negative AG is underappreciated. There are several scenarios that could potentially yield a low or negative AG, including decreased concentration of UA, increased concentrations of nonsodium cations (UC), and overestimation of serum chloride.

Decreased Concentration of Unmeasured Anions. This most commonly occurs by two mechanisms: dilution of the extracellular fluid or hypoalbuminemia. The addition of water to the extracellular fluid will cause a proportionate dilution of all the measured electrolytes. Since the concentration of measured cations is higher than the measured anions, there is a small and relatively insignificant decrease in the AG.

Alternatively, hypoalbuminemia results in a low AG due to the change in UA; albumin is negatively charged. At physiologic pH, the overwhelming majority of serum proteins are anionic and counter-balanced by the positive charge of sodium. Albumin, the most abundant serum protein, accounts for approximately 75% of the normal AG. Hypoalbuminemic states, such as cirrhosis or nephrotic syndrome, can therefore cause low AG due to the retention of chloride to replace the lost negative charge. The albumin concentration can be corrected to calculate the AG.²

Nonsodium Cations. There are a number of clinical conditions that result in the retention of nonsodium cations. For example, the excess positively charged paraproteins associated with IgG myeloma raise the UC concentration, resulting in a low AG. Similarly, elevations of unmeasured cationic electrolytes, such as calcium and magnesium, may also result in a lower AG. Significant changes in AG, though, are caused only by profound (and often life-threatening) hypercalcemia or hypermagnesemia.

Overestimation of Serum Chloride. Overestimation of serum chloride most commonly occurs in the clinical scenario of bromide exposure. In normal physiologic conditions, chloride is the only halide present in the extracellular fluid. With intake of brominated products, chloride may be partially replaced by bromide. As there is greater renal tubular avidity for bromide, chronic ingestion of bromide results in a gradual rise in serum bromide concentrations with a proportional fall in chloride. However, and more importantly, bromide interferes with a number of laboratory techniques measuring chloride concentrations, resulting in a spuriously elevated chloride, or pseudohyperchloremia. Because the measured sodium and bicarbonate concentrations will remain unchanged, this falsely elevated chloride measurement will result in a negative AG.

What causes the falsely elevated chloride?

All of the current laboratory techniques for measurement of serum chloride concentration can potentially result in a falsely elevated value. However, the degree of pseudohyperchloremia will depend on the specific assay used for measurement. The ion-selective electrode method used by many common laboratory analyzers appears to have the greatest interference on chloride measurement in the presence of bromide. This is simply due to the molecular similarity of bromide and chloride. Conversely, the coulometry method, often used as a reference standard, has the least interference of current laboratory methods.³ This is because coulometry does not completely rely on molecular structure to measure concentration, but rather it measures the amount of energy produced or consumed in an electrolysis reaction. Iodide, another halide compound, has also been described as a cause of pseudohyperchloremia, whereas fluoride does not seem to have significant interference.⁴ 

How are patients exposed to bromide salts?

Bromide salts, specifically sodium bromide, are infrequently used to treat seizure disorders, but are generally reserved for patients with epilepsy refractory to other, less toxic anticonvulsant medications. During the era when bromide salts were more commonly used to treat epilepsy, bromide intoxication, or bromism, was frequently observed.

Bromism may manifest as a constellation of nonspecific neurological and psychiatric symptoms. These most commonly include headache, weakness, agitation, confusion, and hallucinations. In more severe cases of bromism, stupor and coma may occur.^3,5

Although bromide salts are no longer commonly prescribed, a number of products still contain brominated ingredients. Symptoms of bromide intoxication can occur with chronic use of a cough syrup containing dextromethorphan hydrobromide as well as the brominated vegetable oils found in some soft drinks.⁵ 

How is bromism treated?

The treatment of bromism involves preventing further exposure to bromide and promoting bromide excretion. Bromide has a long half-life (10-12 days), and in patients with normal renal function, it is possible to reduce this half-life to approximately 3 days with hydration and diuresis with sodium chloride.³ Alternatively, in patients with impaired renal function or severe intoxication, hemodialysis has been used effectively.⁵

Case Conclusion

The patient was admitted for observation and treated with intravenous sodium chloride. After consultation with his neurologist, he was discharged home in the care of his parents, who were advised to continue him on sodium bromide 185 mg orally twice daily since his seizures were refractory to other anticonvulsant medications.

Dr Repplinger is a medical toxicology fellow in the department of emergency medicine at New York University Langone Medical Center. Dr Nelson, editor of “Case Studies in Toxicology,” is a professor in the department of emergency medicine and director of the medical toxicology fellowship program at the New York University School of Medicine and the New York City Poison Control Center. He is also associate editor, toxicology, of the EMERGENCY MEDICINE editorial board.

Case

An 8-month-old boy with a history of hypotonia, developmental delay, and seizure disorder refractory to multiple anticonvulsant medications, was presented to the ED with a 2-week history of intermittent fever and poor oral intake. His current medications included sodium bromide 185 mg orally twice daily for his seizure disorder.

On physical examination, the boy appeared small for his age, with diffuse hypotonia and diminished reflexes. He was able to track with his eyes but was otherwise unresponsive. No rash was present. Results of initial laboratory studies were: sodium 144 mEq/L; potassium, 4.8 mEq/L; chloride, 179 mEq/L; bicarbonate, 21 mEq/L; blood urea nitrogen, 6 mg/dL; creatinine, 0.1 mg/dL; and glucose, 63 mg/dL. His anion gap (AG) was −56.

What does the anion gap represent?

The AG is a valuable clinical calculation derived from the measured extracellular electrolytes and provides an index of acid-base status.¹ Due to the necessity of electroneutrality, the sum of positive charges (cations) in the extracellular fluid must be balanced exactly with the sum of negative charges (anions). However, to routinely measure all of the cations and anions in the serum would be time-consuming and is also unnecessary. Because most clinical laboratories commonly only measure one relevant cation (sodium) and two anions (chloride and bicarbonate), the positive and negative sums are not completely balanced. The AG therefore refers to this difference (ie, AG = Na – [Cl + HCO₃]).

Of course, electroneutrality exists in vivo, and is accomplished by the presence of unmeasured anions (UA) (eg, lactate and phosphate) and unmeasured cations (UC) (eg, potassium and calcium) not accounted for in the AG (ie, AG = UA – UC). In other words, the sum of measured plus the unmeasured anions must equal the sum of the measured plus unmeasured cations.

What causes a low or negative anion gap?

While most healthcare providers are well versed in the clinical significance of an elevated AG (eg, MUDPILES [methanol, uremia, diabetic ketoacidosis, propylene glycol or phenformin, iron or isoniazid, lactate, ethylene glycol, salicylates]), the meaning of a low or negative AG is underappreciated. There are several scenarios that could potentially yield a low or negative AG, including decreased concentration of UA, increased concentrations of nonsodium cations (UC), and overestimation of serum chloride.

Decreased Concentration of Unmeasured Anions. This most commonly occurs by two mechanisms: dilution of the extracellular fluid or hypoalbuminemia. The addition of water to the extracellular fluid will cause a proportionate dilution of all the measured electrolytes. Since the concentration of measured cations is higher than the measured anions, there is a small and relatively insignificant decrease in the AG.

Alternatively, hypoalbuminemia results in a low AG due to the change in UA; albumin is negatively charged. At physiologic pH, the overwhelming majority of serum proteins are anionic and counter-balanced by the positive charge of sodium. Albumin, the most abundant serum protein, accounts for approximately 75% of the normal AG. Hypoalbuminemic states, such as cirrhosis or nephrotic syndrome, can therefore cause low AG due to the retention of chloride to replace the lost negative charge. The albumin concentration can be corrected to calculate the AG.²

Nonsodium Cations. There are a number of clinical conditions that result in the retention of nonsodium cations. For example, the excess positively charged paraproteins associated with IgG myeloma raise the UC concentration, resulting in a low AG. Similarly, elevations of unmeasured cationic electrolytes, such as calcium and magnesium, may also result in a lower AG. Significant changes in AG, though, are caused only by profound (and often life-threatening) hypercalcemia or hypermagnesemia.

Overestimation of Serum Chloride. Overestimation of serum chloride most commonly occurs in the clinical scenario of bromide exposure. In normal physiologic conditions, chloride is the only halide present in the extracellular fluid. With intake of brominated products, chloride may be partially replaced by bromide. As there is greater renal tubular avidity for bromide, chronic ingestion of bromide results in a gradual rise in serum bromide concentrations with a proportional fall in chloride. However, and more importantly, bromide interferes with a number of laboratory techniques measuring chloride concentrations, resulting in a spuriously elevated chloride, or pseudohyperchloremia. Because the measured sodium and bicarbonate concentrations will remain unchanged, this falsely elevated chloride measurement will result in a negative AG.

What causes the falsely elevated chloride?

All of the current laboratory techniques for measurement of serum chloride concentration can potentially result in a falsely elevated value. However, the degree of pseudohyperchloremia will depend on the specific assay used for measurement. The ion-selective electrode method used by many common laboratory analyzers appears to have the greatest interference on chloride measurement in the presence of bromide. This is simply due to the molecular similarity of bromide and chloride. Conversely, the coulometry method, often used as a reference standard, has the least interference of current laboratory methods.³ This is because coulometry does not completely rely on molecular structure to measure concentration, but rather it measures the amount of energy produced or consumed in an electrolysis reaction. Iodide, another halide compound, has also been described as a cause of pseudohyperchloremia, whereas fluoride does not seem to have significant interference.⁴ 

How are patients exposed to bromide salts?

Bromide salts, specifically sodium bromide, are infrequently used to treat seizure disorders, but are generally reserved for patients with epilepsy refractory to other, less toxic anticonvulsant medications. During the era when bromide salts were more commonly used to treat epilepsy, bromide intoxication, or bromism, was frequently observed.

Bromism may manifest as a constellation of nonspecific neurological and psychiatric symptoms. These most commonly include headache, weakness, agitation, confusion, and hallucinations. In more severe cases of bromism, stupor and coma may occur.^3,5

Although bromide salts are no longer commonly prescribed, a number of products still contain brominated ingredients. Symptoms of bromide intoxication can occur with chronic use of a cough syrup containing dextromethorphan hydrobromide as well as the brominated vegetable oils found in some soft drinks.⁵ 

How is bromism treated?

The treatment of bromism involves preventing further exposure to bromide and promoting bromide excretion. Bromide has a long half-life (10-12 days), and in patients with normal renal function, it is possible to reduce this half-life to approximately 3 days with hydration and diuresis with sodium chloride.³ Alternatively, in patients with impaired renal function or severe intoxication, hemodialysis has been used effectively.⁵

Case Conclusion

The patient was admitted for observation and treated with intravenous sodium chloride. After consultation with his neurologist, he was discharged home in the care of his parents, who were advised to continue him on sodium bromide 185 mg orally twice daily since his seizures were refractory to other anticonvulsant medications.

Dr Repplinger is a medical toxicology fellow in the department of emergency medicine at New York University Langone Medical Center. Dr Nelson, editor of “Case Studies in Toxicology,” is a professor in the department of emergency medicine and director of the medical toxicology fellowship program at the New York University School of Medicine and the New York City Poison Control Center. He is also associate editor, toxicology, of the EMERGENCY MEDICINE editorial board.