Anticonvulsants, antidepressants, and opioids are the most frequently prescribed medications for neuropathic pain.1 But some patients are unable to tolerate the adverse effects of these drugs, and others achieve only partial pain relief. What can you offer them?
Combinations of prescription medications are generally considered more effective than monotherapy for painful peripheral neuropathy,1 but it is unclear which combinations are best. Alternative therapies—several of which have some evidence of safety and efficacy in treating peripheral neuropathy—are another option. Yet trials with alternative therapies, alone or in combination with prescription drugs, are rarely considered.
In fact, physicians are often unfamiliar with these therapies. Many are concerned about the absence of US Food and Drug Administration approval for alternative therapies and the variability in quality control associated with the lack of oversight, as well. Making recommendations about the duration of therapy also presents a challenge because most studies of supplements are relatively short. What’s more, alternative treatments are rarely covered by third-party payers.
Nonetheless, the therapies detailed in the text and TABLE2-12 that follow are generally well tolerated and appear to be safe. Adding them to your arsenal of therapeutic choices for patients with painful peripheral neuropathy may increase your ability to provide successful treatment.
Acetyl-L-carnitine (ALC)
ALC occurs naturally in the body as L-carnitine and acetyl-carnitine esters, which are converted to carnitines by intracellular enzymes and cell membrane transporters.2 ALC has been studied in patients with neuropathy associated with human immunodeficiency virus (HIV), cancer, and diabetes. Potential mechanisms of action include the correction of a deficiency that may be causing the neuropathy (which sometimes occurs in HIV-positive patients13 or those taking anticonvulsants14), a direct antioxidant effect, or an enhanced response to nerve growth factor.13
ALC can be given intramuscularly (IM) or orally in doses of 2000 to 3000 mg/d. In one randomized placebo-controlled trial (N=333), patients with diabetic neuropathy received 1000 mg IM followed by an oral dose of 2000 mg every day for a year.6 Mean pain scores decreased by 39%, with 67% of those receiving ALC vs 23% of those on placebo showing moderate to marked improvement.
In a pooled analysis (N=1257) of 2 randomized controlled trials (RCTs), patients with diabetes took 1000 mg ALC 3 times daily or placebo for a year.7 Cohort pain scores improved by 40% from baseline in the ALC group compared with a 24% improvement for those in the placebo group.
THE BOTTOM LINE ALC is well tolerated, with minor adverse effects such as headache and nausea reported.6,7 It should not be given to patients taking acenocoumarol or warfarin, however. A major interaction causing an elevated international normalized ratio has been found to occur when either agent is combined with L-carnitine2 and could theoretically occur with ALC, as well. No other drug-drug interactions have been documented.2
Alpha lipoic acid (ALA)
Both a fat- and a water-soluble vitamin that is usually obtained from the diet, ALA regenerates endogenous antioxidants like vitamins C and E and glutathione. It is this regenerative mechanism that it is believed to alleviate diabetic neuropathy.2 ALA 600 mg/d appears to be effective, although studies suggest that intravenous (IV) use is more effective than oral administration.
A meta-analysis of 4 RCTs (N=653), 2 with ALA taken orally and 2 involving IV administration, is a case in point.3 The pooled standardized mean difference estimated from all trials showed a reduction in total symptom scores of −2.26 (95% confidence interval [CI], −3.12 to −1.41; P=.00001), with 0 indicating no symptoms, 3 indicating severe symptoms, and a maximum score of 14.64 if all symptoms were severe and continuous. Subgroup analyses revealed a reduction of −1.78 (95% CI, −2.45 to −1.10; P=.00001) for oral ALA and −2.81 (95% CI, −4.16 to −1.46; P=.0001) for IV administration. Doses >600 mg/d did not improve efficacy, but did increase adverse effects such as nausea, vomiting, and dizziness.
In a multicenter RCT (N=460) of ALA 600 mg/d for 4 years, however, no improvement in the primary endpoint (a composite of neuropathy impairment scores and 7 neurophysiologic tests) was found.15 Although there was a statistically significant improvement in symptoms of neuropathy (−0.68 with ALA compared with +0.61 with placebo), the change was too small to be considered clinically significant.
ALA did slow the progression of neuropathy, however, with 29% of patients in the treatment group experiencing worsening symptoms compared with 38% of those on placebo. There was no difference in tolerability or discontinuation of treatment between the 2 groups.