The efficacy of buprenorphine transdermal system has been evaluated in four 12-week double-blind, controlled clinical trials in opioid-naïve and opioid-experienced patients with moderate to severe chronic low back pain or osteoarthritis using pain scores as the primary efficacy variable. Two of these studies, described below, demonstrated efficacy in patients with low back pain. One study in low back pain and one study in osteoarthritis did not show a statistically significant pain reduction for either buprenorphine transdermal system or the respective active comparators.

12-Week Study in Opioid-Naïve Patients with Chronic Low Back Pain

A total of 1,024 patients with chronic low back pain who were suboptimally responsive to their non-opioid therapy entered an open-label, dose-titration period for up to four weeks. Patients initiated therapy with three days of treatment with buprenorphine transdermal system 5 mcg/hour. After three days, if adverse events were tolerated, the dose was increased to buprenorphine transdermal system 10 mcg/hour. If adverse effects were tolerated but adequate analgesia was not reached, the dose was increased to buprenorphine transdermal system 20 mcg/hour for an additional 10 to 12 days. Patients who achieved adequate analgesia and tolerable adverse effects on buprenorphine transdermal system 10 or 20 mcg/hour were then randomized to remain on their titrated dose of buprenorphine transdermal system or matching placebo. Fifty-three percent of the patients who entered the open-label titration period were able to titrate to a tolerable and effective dose and were randomized into a 12-week, double-blind treatment period. Twenty-three percent of patients discontinued due to an adverse event from the open-label titration period and 14% discontinued due to lack of a therapeutic effect. The remaining 10% of patients were dropped due to various administrative reasons.

During the first seven days of double-blind treatment patients were allowed up to two tablets per day of immediate-release oxycodone 5 mg as supplemental analgesia to minimize opioid withdrawal symptoms in patients randomized to placebo. Thereafter, the supplemental analgesia was limited to either acetaminophen 500 mg or ibuprofen 200 mg at a maximum of four tablets per day. Sixty-six percent of the patients treated with buprenorphine transdermal system completed the 12-week treatment compared to 70% of the patients treated with placebo. Of the 256 patients randomized to buprenorphine transdermal system, 9% discontinued due to lack of efficacy and 16% due to adverse events. Of the 283 patients randomized to placebo, 13% discontinued due to lack of efficacy and 7% due to adverse events.

Of the patients who were randomized, the mean pain (SE) NRS scores were 7.2 (0.08) and 7.2 (0.07) at screening and 2.6 (0.08) and 2.6 (0.07) at pre-randomization (beginning of double-blind phase) for the buprenorphine transdermal system and placebo groups, respectively.

The score for average pain over the last 24 hours at the end of the study (Week 12/Early Termination) was statistically significantly lower for patients treated with buprenorphine transdermal system compared with patients treated with placebo. The proportion of patients with various degrees of improvement, from screening to study endpoint, is shown in Figure 3 below.

Figure 3: Percent Reduction in Pain Intensity

12-Week Study in Opioid-Experienced Patients with Chronic Low Back Pain

One thousand one hundred and sixty (1,160) patients on chronic opioid therapy (total daily dose 30 mg to 80 mg morphine equivalent) entered an open-label, dose-titration period with buprenorphine transdermal system for up to 3 weeks, following taper of prior opioids. Patients initiated therapy with buprenorphine transdermal system 10 mcg/hour for three days. After three days, if the patient tolerated the adverse effects, the dose was increased to buprenorphine transdermal system 20 mcg/hour for up to 18 days. Patients with adequate analgesia and tolerable adverse effects on buprenorphine transdermal system 20 mcg/hour were randomized to remain on buprenorphine transdermal system 20 mcg/hour or were switched to a low-dose control (buprenorphine transdermal system 5 mcg/hour) or an active control. Fifty-seven percent of the patients who entered the open-label titration period were able to titrate to and tolerate the adverse effects of buprenorphine transdermal system 20 mcg/hour and were randomized into a 12-week double-blind treatment phase. Twelve percent of patients discontinued due to an adverse event and 21% discontinued due to lack of a therapeutic effect during the open-label titration period.

During the double-blind period, patients were permitted to take ibuprofen (200 mg tablets) or acetaminophen (500 mg tablets) every 4 hours as needed for supplemental analgesia (up to 3200 mg of ibuprofen and 4 grams of acetaminophen daily). Sixty-seven percent of patients treated with buprenorphine transdermal system 20 mcg/hour and 58% of patients treated with buprenorphine transdermal system 5 mcg/hour completed the 12-week treatment. Of the 219 patients randomized to buprenorphine transdermal system 20 mcg/hour, 11% discontinued due to lack of efficacy and 13% due to adverse events. Of the 221 patients randomized to buprenorphine transdermal system 5 mcg/hour, 24% discontinued due to lack of efficacy and 6% due to adverse events.

Of the patients who were able to be randomized in the double-blind period, the mean pain (SE) NRS scores were 6.4 (0.08) and 6.5 (0.08) at screening and were 2.8 (0.08) and 2.9 (0.08) at pre-randomization (beginning of Double-Blind Period) for the buprenorphine transdermal system 5 mcg/hour and buprenorphine transdermal system 20 mcg/hour, respectively.

The score for average pain over the last 24 hours at Week 12 was statistically significantly lower for subjects treated with buprenorphine transdermal system 20 mcg/hour compared to subjects treated with buprenorphine transdermal system 5 mcg/hour. A higher proportion of buprenorphine transdermal system 20 mcg/hour patients (49%) had at least a 30% reduction in pain score from screening to study endpoint when compared to buprenorphine transdermal system 5 mcg/hour patients (33%). The proportion of patients with various degrees of improvement from screening to study endpoint is shown in Figure 4 below.

Figure 4: Percent Reduction in Pain Intensity