[Long-term efficacy and safety of pregabalin in patients with postherpetic neuralgia: results of a 52-week, open-label, flexible-dose study].

BACKGROUND: The efficacy of pregabalin was demonstrated in a randomized double-blind placebo-controlled 13-week trial in 371 Japanese patients with postherpetic neuralgia (PHN). In this study, we evaluated the long-term efficacy and safety of pregabalin for relief of PHN. METHODS: 126 patients were enrolled from the preceding double-blind study into the 52-week open-label study. Patients were given pregabalin 150 to 600 mg x day(-1). Pain intensity was measured using the Short-Form McGill Pain Questionnaire (SF-MPQ: total score, visual analogue scale and present pain intensity). RESULTS: The efficacy parameter SF-MPQ showed a decrease over the treatment-term. The changes of visual analogue scale and present pain intensity at the endpoint were -28.3 mm and -1.1 score, respectively. The commonly reported adverse events were dizziness, somnolence, peripheral edema and weight gain, and most of them were mild to moderate in intensity. No new adverse events were observed due to long-term pregabalin administration. CONCLUSIONS: These results suggest that long-term treatment of pregabalin may be beneficial in patients with PHN.

Pregabalin for Neuropathic Pain: Why Benefits Could Be Expected for Multiple Pain Conditions.

BACKGROUND AND OBJECTIVE: Limited research exists to support the extrapolation of the analgesic efficacy of pregabalin from one neuropathic pain condition to another. This retrospective analysis evaluated similarities in the efficacy of pregabalin for treating neuropathic pain associated with post-herpetic neuralgia (PHN), diabetic peripheral neuropathy (DPN), and spinal cord injury (SCI) in a Japanese population, as a basis for considering the extrapolation of these data to other neuropathic pain conditions. METHODS: Data were analysed across pregabalin doses within each pain condition, from three comparable 13- to 16-week, randomized, double-blind, placebo-controlled trials (RCTs) and the corresponding 52-week, open-label extension trials of pregabalin in Japanese patients with PHN, DPN or SCI. Efficacy outcomes in the RCTs included endpoint and weekly mean pain and sleep interference scores; endpoint proportions of responders in pain; Patient Global Impression of Change scores; and 36-Item Short Form Health Survey (SF-36) scores or Hospital Anxiety and Depression Scale (HADS) assessments. Study discontinuation rates were compared between treatment groups. The extension trials assessed pain intensity, using the Short-Form McGill Pain Questionnaire. RESULTS: In the RCTs for all pain conditions, significant improvements in comparison with placebo in mean pain and sleep interference scores were evident after 1 week with pregabalin and were sustained throughout the treatment periods (p < 0.05). At the study endpoint, in comparison with placebo, a significantly greater percentage of pregabalin-treated patients experienced a ≥30 % reduction in pain across the RCTs (p < 0.05), and pregabalin significantly improved six of 16 SF-36 subscale scores in the PHN and DPN trials (p < 0.05). In the SCI trial, pregabalin-treated patients had numerically better outcomes of HADS scores. In the extension trials, improvements in pain intensity were maintained over a 52-week period. CONCLUSION: Similarities in the pregabalin efficacy profiles, including time to onset and magnitude of response, were confirmed regardless of the neuropathic pain condition. These data support the potential for extrapolating analgesic efficacy to other neuropathic pain conditions. CLINICALTRIALS. GOV IDENTIFIERS: NCT00394901, NCT00553475, NCT00407745, NCT00424372, NCT00553280, NCT01202227.

An investigation of factors contributing to higher levels of placebo response in clinical trials in neuropathic pain: a systematic review and meta-analysis.

BACKGROUND: In new drug development in neuropathic pain (NeP), randomized, double-blind, placebo-controlled trials (PCTs) with long treatment durations in a parallel-group design are recommended for confirmatory trials. OBJECTIVE: This study was conducted to identify potential factors contributing to elevated placebo response in parallel-group PCTs for oral drugs with at least a 4-week treatment duration. METHODS: A literature search was conducted through MEDLINE and EMBASE, and was supplemented with data from ClinicalTrials.gov and US/Japanese regulatory approval review information. Using the 30 or 50 % responder rate (RR), logistic regression analyses were performed to investigate the relationship between the degree of placebo response and several potential influencing factors. RESULTS: The search identified 71 trials (n = 6,126). The estimated 50 % RRs (95 % confidence intervals) in the placebo group were as follows: peripheral neuropathic pain (P-NeP) 23 % (21, 26 %); central neuropathic pain (C-NeP) 14 % (10, 19 %); postherpetic neuralgia (PHN) 19 % (15, 24 %); painful diabetic peripheral neuropathy (pDPN) 26 % (23, 29 %); posttraumatic peripheral neuropathic pain (PT) 15 % (10, 20 %). From the logistic regression analyses, it was found that there was a significant association between placebo response (50 % RR and 30 % RR) and NeP classification (P < 0.05). Associations between placebo response and several factors were seen in univariate logistic regression analyses of 50 % RR. Multivariate analyses showed that age and baseline pain intensity in PHN, and treatment duration, trial design (fixed-dose/flexible-dose) and baseline pain intensity in pDPN, were associated with placebo response, suggesting that a reduced placebo response correlated with increasing age and baseline pain intensity, and a higher placebo response correlated with a longer treatment period and flexible dosing regimen. A similar pattern observed in the analysis of 50 % RR was suggested in the analysis of 30 % RR, with the exception of treatment duration. In addition, investigations of trials with at least a 12-week treatment duration in pDPN found associations with the number of patients per site, patient enrolment rate, proportion of male patients and baseline pain intensity, suggesting that a higher placebo response correlated with an increasing number of patients per site, and a reduced placebo response correlated with increasing patient enrolment rate and proportion of male patients and baseline pain intensity. CONCLUSION: The results of this study suggest that NeP condition, trial design, and demographic and baseline characteristics may contribute to elevated placebo response in clinical trials in patients with NeP. In addition, the magnitude of placebo response and the effect of treatment duration are greater in pDPN than in PHN. These facts should be considered when planning and conducting confirmatory trials in NeP.

A Comparison of the Pharmacokinetics and Drug Safety Among East Asian Populations.

Global clinical studies conducted in various countries and regions are increasing. Race and extrinsic ethnic factors are key covariates that may affect the pharmacokinetics (PK), efficacy, and safety of the drug. Genetic similarity among East Asian populations has been confirmed; thus, PK, efficacy, and safety in these populations are expected to be similar, but this has not been confirmed. This study presents a comparison of PK and safety among East Asians from clinical studies sponsored by Pfizer. Four compounds with different characteristics, including mechanism of actions and PK profiles, were selected, and retrospective PK and safety comparisons in East Asians were conducted. No distinct differences were observed in PK and safety across the 4 compounds. These results are consistent with previous reports on PK comparisons and meet the expectations based on genetic similarity among East Asians. Extrapolation of these findings to other compounds should be done with caution, but these results should support the consideration of mutual use of clinical data among East Asian countries.

Pregabalin treatment for peripheral neuropathic pain: a review of safety data from randomized controlled trials conducted in Japan and in the west.

Two well-studied conditions of peripheral neuropathic pain are postherpetic neuralgia (PHN) and painful diabetic peripheral neuropathy (DPN). Several pregabalin trials for peripheral neuropathic pain have been conducted in the West, but limited data are available for Japan. As ethnicity may influence health risks, differences may be evident in safety data from pregabalin trials in Japan and in the West. The objectives of this review were to compare large pooled safety data from randomized controlled trials evaluating pregabalin for the treatment of PHN or DPN in the West with data from two (one PHN, N = 371; one DPN, N = 314) similar trials in Japan. Longer-term safety data from Japanese open-label extension studies were also reviewed in these neuropathic pain populations. Published and unpublished Pfizer-supported pregabalin trials were identified and sourced from internal Pfizer records. A PubMed search to check for inclusiveness was conducted on 2 November 2011 using the following criteria: 'diabetic peripheral neuropathy' OR 'postherpetic neuralgia' OR 'neuropathic pain' AND 'pregabalin', with limits set for clinical and randomized controlled trials published in English. Five PHN trials (N = 1250) and nine DPN trials (N = 2554) were identified as suitable for inclusion based on methodological comparability. Descriptive safety data from the original trials were reviewed and the most commonly reported adverse events (AEs; dizziness, somnolence, peripheral oedema and weight gain) were identified to be of primary interest. The majority of AEs were of mild to moderate severity in Japanese and Western populations. The most commonly reported AE data (all-causality) with pregabalin (regardless of dose) in Japan (dizziness: PHN = 31.1%; DPN = 24.6%, and somnolence: PHN = 28.6%; DPN = 25.7%) were compared with pooled data from the Western trials (dizziness: PHN = 24.9%; DPN = 23.0%, and somnolence: PHN = 15.1%; DPN = 13.4%). Further assessment of these pooled AE (all-causality) data showed that dizziness and somnolence appeared early in the course of pregabalin treatment, but resolved before the end of the treatment in the majority of PHN and DPN patients (maximum duration of trials was 13 weeks). The slightly higher incidence of dizziness and somnolence in the two Japanese trials than that seen in the Western trials may reflect an increased exposure to pregabalin per fixed dose due to the lower mean bodyweight of the Japanese versus Western populations (on a mg/kg basis). However, of the participants who experienced these AEs (all-causality), the proportion who withdrew from the trials in Japan (dizziness: PHN = 23.5%; DPN = 18.2%, and somnolence: PHN = 10.3%; DPN = 10.9%) were comparable with the proportion who withdrew from trials in the West (dizziness: PHN = 16.0%; DPN = 29.3%, and somnolence: PHN = 19.4%; DPN = 34.2%). In Japan, 12.5% (PHN) and 15.1% (DPN) of patients experienced peripheral oedema as an AE (all-causality) compared with 8.8% (PHN) and 10.3% (DPN) in the West. Weight gain as an AE (all-causality) was experienced in 11.7% (PHN) and 13.4% (DPN) of patients in Japan compared with 3.8% (PHN) and 7.0% (DPN) in the West, but stabilized with continued treatment. Despite the lower mean bodyweight in Japanese versus Western patients, the PHN and DPN patients in Japan had stable blood glucose and HbA(1c) levels throughout the trials. The results of this review indicate safety outcomes in pregabalin trials are comparable between patients in Japan and those in the West. While managing peripheral neuropathic pain with pregabalin treatment, all patients should be observed closely for the incidence of dizziness and somnolence, especially at the beginning of treatment. These patients should also be monitored for evidence of peripheral oedema and weight gain during stable treatment, regardless of the source of neuropathic pain.

Efficacy and safety evaluation of pregabalin treatment over 52 weeks in patients with diabetic neuropathic pain extended after a double-blind placebo-controlled trial.

UNLABELLED: Aims/Introduction: Diabetic peripheral neuropathy (DPN) is often associated with pain, and thus a new treatment option is anticipated. We recently showed the efficacy of pregabalin in a randomized, double-blind, placebo-controlled, 14-week trial in Japanese patients with painful DPN. In the present study, we evaluated the long-term efficacy and safety of pregabalin for the relief of painful DPN. MATERIALS AND METHODS: A total of 123 patients were enrolled in a 52-week open-label study, from among those who participated in the preceding double-blind trial. The subjects received pregabalin 150-600 mg/day. Pain intensity was measured using the short-form McGill pain questionnaire (SF-MPQ: total score, visual analog scale and present pain intensity). RESULTS: The efficacy parameter SF-MPQ showed a decrease over the treatment period. The changes in visual analog scale and present pain intensity at the final evaluation were -25.4 mm and -0.7, respectively, suggesting an analgesic effect of pregabalin. Commonly reported adverse events were somnolence, weight gain, dizziness and peripheral edema, but most of them were mild to moderate in intensity. No new concerns about safety as a result of long-term administration of pregabalin were identified. CONCLUSIONS: The findings from this trial suggest that long-term treatment with pregabalin is beneficial for pain relief in patients with DPN. This trial was registered with ClinicalTrials.gov (no. NCT00553280). (J Diabetes Invest, doi: 10.1111/j.2040-1124.2011.00122.x, 2011).