• Baron et al.9 conducted an open-label, non-inferiority study comparing a 5% lidocaine patch versus pregabalin capsules in post-herpetic neuralgia and diabetic peripheral neuropathy. The primary outcome was response rate after 4 weeks. Secondary outcomes included 30% and 50% reductions in 11-point Numerical Rating Scale (NRS-3), a change in allodynia severity, quality of life (QoL), and patient satisfaction with therapy. Ninety-six patients with post-herpetic neuralgia and 204 with painful diabetic peripheral neuropathy were analyzed. In post-herpetic neuralgia, lidocaine 5% had a 62.2% response w'hile pre- gabalin had a 46.5% response. Both treatments reduced allodynia severity, and 30-50% reductions in NRS-3 scores and QoL scores were greater with 5% lidocaine. The response to both treatments was comparable in painful diabetic neuropathy. Patients on lidocaine experienced fewer adverse events than those taking pregabalin. This study supports 5% lidocaine as a potential first-line therapy for patients with localized neuropathic pain.
- • Oral amitriptyline is currently used for neuropathic pain; however, it can be limited by dose-related anticholinergic effects.
- • Chemotherapy-induced peripheral neuropathy (CIPN) is extremely debilitating, and patients have limited options for relief. Dose reduction or the discontinuation of chemotherapy regimens may result from severe CIPN. A pilot study done by Rossignol et al.10 investigated the application of amitriptyline 10% cream on neuropathic pain. Patients who had hematological or solid tumors with CIPN of the hands and feet were given amitriptyline 10% cream twice a day. Pain intensity scores were assessed by the VAS at 1, 2, and 4 weeks, followed by monthly for up to 1 year. A total of 44 patients were enrolled in the study. The median pain score was 7 at baseline which decreased to a median of 2 after 4 weeks of topical treatment. This led to 11/44 patients with reduced initial chemotherapy doses, as well as 5 patients who discontinued chemotherapy, to resume chemotherapy after treatment w'ith topical amitriptyline 10%.
- • A double-blind, randomized, placebo-controlled crossover study compared the effectiveness of 5% lidocaine, 5% amitriptyline, and placebo gel with neuropathic pain. Thirty-five patients with postsurgical neuropathic pain, postherpetic neuralgia, or diabetic neuropathy with allodynia or hyperalgesia were instructed to apply 3-5 mL of the study drug twice a day for a week. There was a w'ashout period of 1 week following each treatment. After the washout periods, patients would be presented with a different study drug. The primary outcome of this study was to determine if either 5% lidocaine or 5% amitriptyline was effective in alleviating symptoms of neuropathic pain. The researchers found that there was a significant reduction in pain intensity in the patients treated with the lidocaine, but this result was not surprising as lidocaine has been shown to be effective as a patch in previous studies. The researchers found that there was no significant change in pain intensity score for both the placebo and amitriptyline. When comparing the treatments, the researchers found topical lidocaine and placebo reduced pain more than amitriptyline."
• Boardman et al.12 investigated the use of topical gabapentin 2% to 6% in the treatment of localized and generalized vulvodynia. A retrospective study based off a 10-point VAS was done comparing pain scores pre- and post-treatment. Between January 2001 and December 2006, 51 women with vulvodynia received topical gabapentin anywhere from 2% to 6%. After 8 weeks, the mean pain score was significantly reduced from 7.26 to 2.49 among the 35 evaluable participants. Eighty percent of evaluable women showed at least a 50% improvement in pain scores. Sexual function also improved in 17 out of 20 evaluable women. Fourteen percent of the women treated discontinued therapy. Topical gabapentin seems to offer significant pain relief in women w'ith vulvodynia.
- • Topical baclofen acts as an agonist at the GABA-B receptor. By the activation of tetraeth- ylammonium-sensitive K+ channels on GABA-B, peripheral antinociceptive effects are observed. The intracellular increase in K+ is accompanied by a decrease in calcium ions, which alter membrane permeability, leading to a slow and prolonged inhibitory transmission.13 Baclofen is used mostly in combination with other topical formulations for combined analgesia, as efficacy has not been established for monotherapy.
- • Keppel Hesselink et al.14 investigated the use of baclofen 5% and palmitoylethanolamide 400 mg TID for the treatment of idiopathic vulvodynia and proctodynia. This case consisted of a 33-year-old woman with intractable chronic vulvar and anal pain, resulting in abstinence from sexual intercourse and the inability to cycle or sit for more than 5 minutes. After 3 months of topical baclofen 5% and palmitoylethanolamide 400 mg TID, her symptoms decreased by more than 50% and she was able to have pain-free sexual intercourse. This case suggests that this formulation should be a viable treatment in patients with chronic vulvodynia and proctodynia.
- • A study was performed by Ala et al.15 that investigated the effects of topical 5% baclofen in patients after a hemorrhoidectomy. They conducted a randomized, double-blind, placebo- controlled clinical trial with 60 participants. Participants received either baclofen (5%) cream or placebo immediately after surgery and then every 12 hours for 14 days. Pain was assessed using the VAS, and analgesic requirement was measured by analgesic consumption. Pain ratings did not differ significantly between the baclofen and placebo groups at both 24 and 48 hours after the surgical procedure. The baclofen group showed a significantly lower pain score on weeks 1 and 2 post-surgery compared to the placebo group. The baclofen group also reported less concomitant use of oral systemic analgesics compared to placebo on week 1 and 2. There were reports of slight itching and bleeding from both groups, but there was no discontinuation of treatment due to adverse effects.