David Charles, MD, and Thomas Davis, MD, on updates on levodopa-induced dyskinesia treatment and research

David Charles, MD, and Thomas Davis, MD, of the Vanderbilt University Department of Neurology, recently spoke with Neurology Reviews about the treatment pipeline and latest research in levodopa-induced dyskinesia in Parkinson's disease.

How is the treatment pipeline advancing for different types of levodopa-induced dyskinesia (LID)?
 
Dr. Thomas Davis: Dyskinesia has traditionally been hard to quantify, and we have been lacking any US Food and Drug Administration (FDA)-approved anti-dyskinesia drugs. The pipeline has historically been strongest for wearing-off because it is easier to measure on time than to quantify involuntary movements.

The Unified Dyskinesia Rating Scale (UDysRS), released in 2008 by the Movement Disorder Society, provided a standardized scale that allowed dyskinesia clinical trials to move forward. The UDysRS was used as the primary outcome for the extended release amantadine capsule study. This was important because it demonstrated the possibility of a successful clinical trial design to get a drug approved for dyskinesia, which will encourage others to test more potential new treatments.
 
What is the status of research on deep brain stimulation (DBS) for Parkinson's disease, and when might it be considered?
 
Dr. David Charles: This is one of the areas of research that we're focused on here at Vanderbilt. All 3 of the FDA-approved device manufacturers have been conducting research in technology refinement and improvements. These advances include not only patient programmers and physician programmers, but also new sensing capability and lead designs. Some of the manufacturers now have leads that allow the physician to steer the current in one direction or another, where traditionally the current has been delivered in a circumferential contact that's shaped like a cylinder, where the energy is transmitted 360 degrees from the lead. The new designs allow you to steer the current hopefully toward areas that provide more efficacy and away from areas that cause side effects. Even more exciting is the emerging sensing capability that may allow the development of stimulating technology that is responsive to fluctuating symptoms. There is keen research interest in understanding whether a device could detect a specific neuronal firing pattern and then respond with an individually tailored stimulation to improve symptoms as needed. Will the next generation of deep brain stimulating devices detect the pattern and deliver energy in a more targeted and precise way, responsive to what it's sensing from the patient's brain? I think that's an area of research that's really exciting.
 
In regard to when it might be considered: The ability to steer the current is already available in 2 of the 3 systems that are on the market today. Having current that is steerable in all 3 will be coming in the not too distant future. The available devices already have improved programming platforms for health care providers as well.
 
Our research at Vanderbilt is focused on DBS in early-stage Parkinson's disease. There is a paper published in Neurology that reports Class II evidencet hat DBS applied in early-stage Parkinson's disease slows the progression of tremor. This is exciting because none of the available treatments change the progression of disease—they're currently accepted as symptomatic therapies only. In this publication, we report that participants receiving DBS in the very earliest stages of Parkinson's disease it may slow the progression of rest tremor. We now have approval from the FDA to conduct a large-scale phase 3, multicenter, clinical trial of DBS in early-stage Parkinson's disease, with the primary endpoint focused on slowing progression of tremor, a cardinal feature of the disease. This upcoming trial is approved by the FDA as a pivotal trial, meaning that the findings could potentially be used to change the labeling of DBS devices. Our goal is to obtain Class I evidence of slowing the progression of tremor or other elements of the disease.
 
Dr. Thomas Davis: If you are a device manufacturer for DBS it is natural for you to aim to make better devices, better batteries, better programming, and better electrodes than your competitor. That's really where the industry-based research is right now. Clinicians are still determining which device is the best candidate, where the best target in the brain is, and when to use DBS.

When would a health care practitioner decide to try frequent smaller dosages or immediate-release formulations of dopaminergic drugs to control levodopa-induced dyskinesia (LID), compared with non-dopaminergic treatments that are available? What are some pros and cons of each approach?
 
Dr. David Charles: If you have a patient who's already on levodopa, it's not uncommon that—separate from the way we prescribe the medicine—the patients experiment with their medicine to some degree. At the very least, people occasionally forget to take a dose and they feel the effect of a missed dose. They may take an extra dose or an extra half dose, particularly if they feel that the last dose isn't working as well, or in the event they have some special occasion coming up. 
 
Over time, patients and physicians learn that sometimes smaller, more frequent dosing of levodopa can be a helpful strategy for certain individuals. One advantage is that it's the medication that the patient is already taking, and they're just simply breaking tablets. Many pharmacies will break tablets for patients so they can take some smaller doses more frequently. Obviously, there can be downsides to that, such as it becoming harder to remember to take more frequent doses.
 
Dr. Thomas Davis: I would agree that the biggest advantage of taking more frequent, smaller doses is that it's cheaper than adding an adjunct or moving to a more invasive therapy.  More frequent smaller doses of levodopa also generally has no side effects because if you're taking 2 carbidopa/levodopa 3 times a day and you're tolerating it, but you're having peak dose problems, you can then switch to 1.5 tablets 4 times a day. It involves more work and planning, but it's no more total medication than the patient is taking already, so this strategy usually does not have any unexpected side effects. It really boils down to how much work the patient wants to put in, how adherent they are to medication dosing, and whether they want to add another medication.
 
Most of the adjunctive medications to treat motor fluctuations are approved to improve on-time in Parkinson's disease patients with wearing off. These include the monoamine oxidase inhibitors, COMT inhibitors, and adenosine A2A antagonists. For treatment of dyskinesia, only the extended release capsule formulation of amantadine has FDA approval, although all formulations are approved for Parkinson's disease and are used clinically to dampen dyskinesia. How long to try these strategies before moving to one of the more advanced therapies, like DBS or jejunal infusion of levodopa, is not clear. It's great to have options, but it makes the decisions a lot harder.
 
Dr. David Charles: Dr. Davis raised the question of what medicine to choose, and what's your next choice in a patient who's having wearing-off dyskinesia or LID and so forth. There is an increasing number of options for those mid-stage patients. The pitfall is feeling that you have to try every available medication and combination before moving to a more advanced therapy.  The physician risks churning through the various combinations for so long that the benefit of an advanced therapy becomes shortened or lost altogether. 
 
Take epilepsy, for example. In operative candidates, surgery is often more beneficial when applied earlier. There's solid data to support that adding on multiple anti-epileptics medications is not always helpful. Continuing to add or change medications can actually diminish returns, particularly in a person who could receive benefit from surgery for epilepsy. 
 
I get the sense that the same may be true for dyskinesia. In clinical practice, we often receive DBS referrals when a patient's community-based physician has tried various medications and combination therapies until the point that the patient and the physician have become totally frustrated. By the time they are referred, the patient may benefit from DBS, but not nearly as well and as for long as they could have if they had received it earlier. We as physicians have to be mindful that while we have these increasing number of options—which is a good thing for both patients and physicians—that we don't continue to use them to the point that it takes away the option of more advanced therapies for appropriate candidates.
 
Metabotropic glutamate (mGlu) receptors have been receiving attention as potential therapeutic targets for LID. How do these compare with other receptors such as N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid (AMPA)?
 
Dr. Thomas Davis: NMDA and AMPA are traditional ionotropic receptors, meaning that they are ligand gated, that they are almost exclusively excitatory, and that they generally have to do with the flow of potassium. 
 
mGlu receptors are protein coupled receptors. They have more elaborate action and may be either excitatory or inhibitory. Though mGlu, NMDA, and AMPA are completely different, they are all activated by glutamate. Pharmacologically utilizing the mGlu receptors is a relatively new and novel idea. Specifically, mGlu-5 receptors have received the most attention as potentially having an anti-parkinsonian effect and possibly dampening dyskinesia. The mGlu-5 receptors are an attractive target because they are concentrated in the striatum, as opposed to other glutamatergic receptors that are more diffusely located. It was felt that mGlu-5 modulators would be more specific and have less of the potential adverse effects of other glutamates. Most drugs that we think of affecting glutamate, like amantadine and memantine (used for Alzheimer's disease), have some NMDA antagonist effect, but this is relatively mild. 

David Charles, MD, and Thomas Davis, MD, of the Vanderbilt University Department of Neurology, recently spoke with Neurology Reviews about the treatment pipeline and latest research in levodopa-induced dyskinesia in Parkinson's disease.

How is the treatment pipeline advancing for different types of levodopa-induced dyskinesia (LID)?
 
Dr. Thomas Davis: Dyskinesia has traditionally been hard to quantify, and we have been lacking any US Food and Drug Administration (FDA)-approved anti-dyskinesia drugs. The pipeline has historically been strongest for wearing-off because it is easier to measure on time than to quantify involuntary movements.

The Unified Dyskinesia Rating Scale (UDysRS), released in 2008 by the Movement Disorder Society, provided a standardized scale that allowed dyskinesia clinical trials to move forward. The UDysRS was used as the primary outcome for the extended release amantadine capsule study. This was important because it demonstrated the possibility of a successful clinical trial design to get a drug approved for dyskinesia, which will encourage others to test more potential new treatments.
 
What is the status of research on deep brain stimulation (DBS) for Parkinson's disease, and when might it be considered?
 
Dr. David Charles: This is one of the areas of research that we're focused on here at Vanderbilt. All 3 of the FDA-approved device manufacturers have been conducting research in technology refinement and improvements. These advances include not only patient programmers and physician programmers, but also new sensing capability and lead designs. Some of the manufacturers now have leads that allow the physician to steer the current in one direction or another, where traditionally the current has been delivered in a circumferential contact that's shaped like a cylinder, where the energy is transmitted 360 degrees from the lead. The new designs allow you to steer the current hopefully toward areas that provide more efficacy and away from areas that cause side effects. Even more exciting is the emerging sensing capability that may allow the development of stimulating technology that is responsive to fluctuating symptoms. There is keen research interest in understanding whether a device could detect a specific neuronal firing pattern and then respond with an individually tailored stimulation to improve symptoms as needed. Will the next generation of deep brain stimulating devices detect the pattern and deliver energy in a more targeted and precise way, responsive to what it's sensing from the patient's brain? I think that's an area of research that's really exciting.
 
In regard to when it might be considered: The ability to steer the current is already available in 2 of the 3 systems that are on the market today. Having current that is steerable in all 3 will be coming in the not too distant future. The available devices already have improved programming platforms for health care providers as well.
 
Our research at Vanderbilt is focused on DBS in early-stage Parkinson's disease. There is a paper published in Neurology that reports Class II evidencet hat DBS applied in early-stage Parkinson's disease slows the progression of tremor. This is exciting because none of the available treatments change the progression of disease—they're currently accepted as symptomatic therapies only. In this publication, we report that participants receiving DBS in the very earliest stages of Parkinson's disease it may slow the progression of rest tremor. We now have approval from the FDA to conduct a large-scale phase 3, multicenter, clinical trial of DBS in early-stage Parkinson's disease, with the primary endpoint focused on slowing progression of tremor, a cardinal feature of the disease. This upcoming trial is approved by the FDA as a pivotal trial, meaning that the findings could potentially be used to change the labeling of DBS devices. Our goal is to obtain Class I evidence of slowing the progression of tremor or other elements of the disease.
 
Dr. Thomas Davis: If you are a device manufacturer for DBS it is natural for you to aim to make better devices, better batteries, better programming, and better electrodes than your competitor. That's really where the industry-based research is right now. Clinicians are still determining which device is the best candidate, where the best target in the brain is, and when to use DBS.

When would a health care practitioner decide to try frequent smaller dosages or immediate-release formulations of dopaminergic drugs to control levodopa-induced dyskinesia (LID), compared with non-dopaminergic treatments that are available? What are some pros and cons of each approach?
 
Dr. David Charles: If you have a patient who's already on levodopa, it's not uncommon that—separate from the way we prescribe the medicine—the patients experiment with their medicine to some degree. At the very least, people occasionally forget to take a dose and they feel the effect of a missed dose. They may take an extra dose or an extra half dose, particularly if they feel that the last dose isn't working as well, or in the event they have some special occasion coming up. 
 
Over time, patients and physicians learn that sometimes smaller, more frequent dosing of levodopa can be a helpful strategy for certain individuals. One advantage is that it's the medication that the patient is already taking, and they're just simply breaking tablets. Many pharmacies will break tablets for patients so they can take some smaller doses more frequently. Obviously, there can be downsides to that, such as it becoming harder to remember to take more frequent doses.
 
Dr. Thomas Davis: I would agree that the biggest advantage of taking more frequent, smaller doses is that it's cheaper than adding an adjunct or moving to a more invasive therapy.  More frequent smaller doses of levodopa also generally has no side effects because if you're taking 2 carbidopa/levodopa 3 times a day and you're tolerating it, but you're having peak dose problems, you can then switch to 1.5 tablets 4 times a day. It involves more work and planning, but it's no more total medication than the patient is taking already, so this strategy usually does not have any unexpected side effects. It really boils down to how much work the patient wants to put in, how adherent they are to medication dosing, and whether they want to add another medication.
 
Most of the adjunctive medications to treat motor fluctuations are approved to improve on-time in Parkinson's disease patients with wearing off. These include the monoamine oxidase inhibitors, COMT inhibitors, and adenosine A2A antagonists. For treatment of dyskinesia, only the extended release capsule formulation of amantadine has FDA approval, although all formulations are approved for Parkinson's disease and are used clinically to dampen dyskinesia. How long to try these strategies before moving to one of the more advanced therapies, like DBS or jejunal infusion of levodopa, is not clear. It's great to have options, but it makes the decisions a lot harder.
 
Dr. David Charles: Dr. Davis raised the question of what medicine to choose, and what's your next choice in a patient who's having wearing-off dyskinesia or LID and so forth. There is an increasing number of options for those mid-stage patients. The pitfall is feeling that you have to try every available medication and combination before moving to a more advanced therapy.  The physician risks churning through the various combinations for so long that the benefit of an advanced therapy becomes shortened or lost altogether. 
 
Take epilepsy, for example. In operative candidates, surgery is often more beneficial when applied earlier. There's solid data to support that adding on multiple anti-epileptics medications is not always helpful. Continuing to add or change medications can actually diminish returns, particularly in a person who could receive benefit from surgery for epilepsy. 
 
I get the sense that the same may be true for dyskinesia. In clinical practice, we often receive DBS referrals when a patient's community-based physician has tried various medications and combination therapies until the point that the patient and the physician have become totally frustrated. By the time they are referred, the patient may benefit from DBS, but not nearly as well and as for long as they could have if they had received it earlier. We as physicians have to be mindful that while we have these increasing number of options—which is a good thing for both patients and physicians—that we don't continue to use them to the point that it takes away the option of more advanced therapies for appropriate candidates.
 
Metabotropic glutamate (mGlu) receptors have been receiving attention as potential therapeutic targets for LID. How do these compare with other receptors such as N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid (AMPA)?
 
Dr. Thomas Davis: NMDA and AMPA are traditional ionotropic receptors, meaning that they are ligand gated, that they are almost exclusively excitatory, and that they generally have to do with the flow of potassium. 
 
mGlu receptors are protein coupled receptors. They have more elaborate action and may be either excitatory or inhibitory. Though mGlu, NMDA, and AMPA are completely different, they are all activated by glutamate. Pharmacologically utilizing the mGlu receptors is a relatively new and novel idea. Specifically, mGlu-5 receptors have received the most attention as potentially having an anti-parkinsonian effect and possibly dampening dyskinesia. The mGlu-5 receptors are an attractive target because they are concentrated in the striatum, as opposed to other glutamatergic receptors that are more diffusely located. It was felt that mGlu-5 modulators would be more specific and have less of the potential adverse effects of other glutamates. Most drugs that we think of affecting glutamate, like amantadine and memantine (used for Alzheimer's disease), have some NMDA antagonist effect, but this is relatively mild. 

David Charles, MD, and Thomas Davis, MD, of the Vanderbilt University Department of Neurology, recently spoke with Neurology Reviews about the treatment pipeline and latest research in levodopa-induced dyskinesia in Parkinson's disease.

How is the treatment pipeline advancing for different types of levodopa-induced dyskinesia (LID)?
 
Dr. Thomas Davis: Dyskinesia has traditionally been hard to quantify, and we have been lacking any US Food and Drug Administration (FDA)-approved anti-dyskinesia drugs. The pipeline has historically been strongest for wearing-off because it is easier to measure on time than to quantify involuntary movements.

The Unified Dyskinesia Rating Scale (UDysRS), released in 2008 by the Movement Disorder Society, provided a standardized scale that allowed dyskinesia clinical trials to move forward. The UDysRS was used as the primary outcome for the extended release amantadine capsule study. This was important because it demonstrated the possibility of a successful clinical trial design to get a drug approved for dyskinesia, which will encourage others to test more potential new treatments.
 
What is the status of research on deep brain stimulation (DBS) for Parkinson's disease, and when might it be considered?
 
Dr. David Charles: This is one of the areas of research that we're focused on here at Vanderbilt. All 3 of the FDA-approved device manufacturers have been conducting research in technology refinement and improvements. These advances include not only patient programmers and physician programmers, but also new sensing capability and lead designs. Some of the manufacturers now have leads that allow the physician to steer the current in one direction or another, where traditionally the current has been delivered in a circumferential contact that's shaped like a cylinder, where the energy is transmitted 360 degrees from the lead. The new designs allow you to steer the current hopefully toward areas that provide more efficacy and away from areas that cause side effects. Even more exciting is the emerging sensing capability that may allow the development of stimulating technology that is responsive to fluctuating symptoms. There is keen research interest in understanding whether a device could detect a specific neuronal firing pattern and then respond with an individually tailored stimulation to improve symptoms as needed. Will the next generation of deep brain stimulating devices detect the pattern and deliver energy in a more targeted and precise way, responsive to what it's sensing from the patient's brain? I think that's an area of research that's really exciting.
 
In regard to when it might be considered: The ability to steer the current is already available in 2 of the 3 systems that are on the market today. Having current that is steerable in all 3 will be coming in the not too distant future. The available devices already have improved programming platforms for health care providers as well.
 
Our research at Vanderbilt is focused on DBS in early-stage Parkinson's disease. There is a paper published in Neurology that reports Class II evidencet hat DBS applied in early-stage Parkinson's disease slows the progression of tremor. This is exciting because none of the available treatments change the progression of disease—they're currently accepted as symptomatic therapies only. In this publication, we report that participants receiving DBS in the very earliest stages of Parkinson's disease it may slow the progression of rest tremor. We now have approval from the FDA to conduct a large-scale phase 3, multicenter, clinical trial of DBS in early-stage Parkinson's disease, with the primary endpoint focused on slowing progression of tremor, a cardinal feature of the disease. This upcoming trial is approved by the FDA as a pivotal trial, meaning that the findings could potentially be used to change the labeling of DBS devices. Our goal is to obtain Class I evidence of slowing the progression of tremor or other elements of the disease.
 
Dr. Thomas Davis: If you are a device manufacturer for DBS it is natural for you to aim to make better devices, better batteries, better programming, and better electrodes than your competitor. That's really where the industry-based research is right now. Clinicians are still determining which device is the best candidate, where the best target in the brain is, and when to use DBS.

When would a health care practitioner decide to try frequent smaller dosages or immediate-release formulations of dopaminergic drugs to control levodopa-induced dyskinesia (LID), compared with non-dopaminergic treatments that are available? What are some pros and cons of each approach?
 
Dr. David Charles: If you have a patient who's already on levodopa, it's not uncommon that—separate from the way we prescribe the medicine—the patients experiment with their medicine to some degree. At the very least, people occasionally forget to take a dose and they feel the effect of a missed dose. They may take an extra dose or an extra half dose, particularly if they feel that the last dose isn't working as well, or in the event they have some special occasion coming up. 
 
Over time, patients and physicians learn that sometimes smaller, more frequent dosing of levodopa can be a helpful strategy for certain individuals. One advantage is that it's the medication that the patient is already taking, and they're just simply breaking tablets. Many pharmacies will break tablets for patients so they can take some smaller doses more frequently. Obviously, there can be downsides to that, such as it becoming harder to remember to take more frequent doses.
 
Dr. Thomas Davis: I would agree that the biggest advantage of taking more frequent, smaller doses is that it's cheaper than adding an adjunct or moving to a more invasive therapy.  More frequent smaller doses of levodopa also generally has no side effects because if you're taking 2 carbidopa/levodopa 3 times a day and you're tolerating it, but you're having peak dose problems, you can then switch to 1.5 tablets 4 times a day. It involves more work and planning, but it's no more total medication than the patient is taking already, so this strategy usually does not have any unexpected side effects. It really boils down to how much work the patient wants to put in, how adherent they are to medication dosing, and whether they want to add another medication.
 
Most of the adjunctive medications to treat motor fluctuations are approved to improve on-time in Parkinson's disease patients with wearing off. These include the monoamine oxidase inhibitors, COMT inhibitors, and adenosine A2A antagonists. For treatment of dyskinesia, only the extended release capsule formulation of amantadine has FDA approval, although all formulations are approved for Parkinson's disease and are used clinically to dampen dyskinesia. How long to try these strategies before moving to one of the more advanced therapies, like DBS or jejunal infusion of levodopa, is not clear. It's great to have options, but it makes the decisions a lot harder.
 
Dr. David Charles: Dr. Davis raised the question of what medicine to choose, and what's your next choice in a patient who's having wearing-off dyskinesia or LID and so forth. There is an increasing number of options for those mid-stage patients. The pitfall is feeling that you have to try every available medication and combination before moving to a more advanced therapy.  The physician risks churning through the various combinations for so long that the benefit of an advanced therapy becomes shortened or lost altogether. 
 
Take epilepsy, for example. In operative candidates, surgery is often more beneficial when applied earlier. There's solid data to support that adding on multiple anti-epileptics medications is not always helpful. Continuing to add or change medications can actually diminish returns, particularly in a person who could receive benefit from surgery for epilepsy. 
 
I get the sense that the same may be true for dyskinesia. In clinical practice, we often receive DBS referrals when a patient's community-based physician has tried various medications and combination therapies until the point that the patient and the physician have become totally frustrated. By the time they are referred, the patient may benefit from DBS, but not nearly as well and as for long as they could have if they had received it earlier. We as physicians have to be mindful that while we have these increasing number of options—which is a good thing for both patients and physicians—that we don't continue to use them to the point that it takes away the option of more advanced therapies for appropriate candidates.
 
Metabotropic glutamate (mGlu) receptors have been receiving attention as potential therapeutic targets for LID. How do these compare with other receptors such as N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid (AMPA)?
 
Dr. Thomas Davis: NMDA and AMPA are traditional ionotropic receptors, meaning that they are ligand gated, that they are almost exclusively excitatory, and that they generally have to do with the flow of potassium. 
 
mGlu receptors are protein coupled receptors. They have more elaborate action and may be either excitatory or inhibitory. Though mGlu, NMDA, and AMPA are completely different, they are all activated by glutamate. Pharmacologically utilizing the mGlu receptors is a relatively new and novel idea. Specifically, mGlu-5 receptors have received the most attention as potentially having an anti-parkinsonian effect and possibly dampening dyskinesia. The mGlu-5 receptors are an attractive target because they are concentrated in the striatum, as opposed to other glutamatergic receptors that are more diffusely located. It was felt that mGlu-5 modulators would be more specific and have less of the potential adverse effects of other glutamates. Most drugs that we think of affecting glutamate, like amantadine and memantine (used for Alzheimer's disease), have some NMDA antagonist effect, but this is relatively mild.