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Background: Painful polyneuropathy remains a significant clinicial problem in patients with HIV infection. Preclinical studies suggest that cannabinoids may be effective in neuropathic pain syndromes.

Methods: Open-label pilot inpatient study conducted over 9 days in the General Clinical Research Center. Eligible subjects with confirmed HIV-related neuropathies and persistent pain greater than 40/100 as assessed by a 7-day pain diary were enrolled. All subjects had prior experience smoking marijuana but had ceased for 30 days prior to admission. After a 2-day lead-in period, pts smoked one 3.56% THC containing marijuana cigarette three times daily for 7 days. A heat-capsaicin model induced experimental pain that was also evaluated. Pts experiencing a >30% reduction in their 24-hour neuropathy pain scored on a 0-100 visual analog scale were assessed as responders. The pilot study was designed to assess effect size and calculate sample size for a follow-on randomized, placebo-controlled trial if warranted.

Results: We enrolled 16 patients (14 men), median age 43 years with an average of 6 years duration of neuropathy . Neuropathy was related to HIV alone (3), nucleoside therapy (8) or both (5). Mean baseline average daily pain value of 47/100 dropped to 40/100 following the 2-day lead-in. Marijuana smoking caused a drop in mean pain score to 20/100 with 10/16 pts experiencing a > 30% reduction in average daily pain. Excellent correlation was seen in the response to the heat-capsaicin model where 14/16 patients experienced a > 30% reduction in the area of secondary hyperalgesia after smoking.

Conclusions: Findings from this open-label pilot suggest an analgesic effect of smoked marijuana in HIV neuropathy as well as the experimental pain model. A 50-subject 7-day randomized placebo-controlled trial has been initiated in an attempt to confirm these preliminary results.

Keywords: marijuana; neuropathy; pain