Methodological Issues in Conducting Pilot Trials in Chronic Pain as Randomized, Double-blind, Placebo-controlled Studies

BACKGROUND

The efficacy of tapentadol extended release (ER) for managing chronic pain has been demonstrated in large-scale, randomized, controlled, phase 3 studies (N=318-1,030) in patients with chronic osteoarthritis (OA) pain, low back pain (LBP), and pain related to diabetic peripheral neuropathy (DPN), which led to registration in many regions, including the United States and Europe. 2 pilot 12-week, randomized, double-blind, placebo-controlled phase 2 studies of tapentadol ER for chronic pain (OA knee pain or LBP, n=91; DPN or peripheral herpetic neuralgia [PHN] pain; n=91) were conducted in Japan. These small exploratory studies were substantially underpowered compared with the registration trials.

METHODS

Patients in both studies were randomized (2:1) to tapentadol ER (25-250 mg) or placebo for 12 weeks (≤6-week titration plus maintenance periods).

RESULTS

For the primary efficacy endpoint (change in pain intensity from baseline to last week of treatment; last observation carried forward), both studies failed to differentiate between tapentadol ER and placebo; least-squares mean differences (95% confidence intervals) for tapentadol ER vs. placebo were -0.1 (-1.04, 0.80) in the OA/LBP study and -0.1 (-1.10, 0.99) in the DPN/PHN study. More than 80% of patients took concomitant analgesics during these studies. Tapentadol was well tolerated.

CONCLUSIONS

Both studies were associated with methodological issues, including populations with different disease entities, small sample sizes, use of concomitant analgesics, and possible placebo effect that may have led to the failure to differentiate between tapentadol ER and placebo.

Direct conversion from tramadol to tapentadol prolonged release for moderate to severe, chronic malignant tumour-related pain

Background

A recent randomized‐withdrawal, active‐ and placebo‐controlled, double‐blind phase 3 study showed that tapentadol prolonged release (PR) was effective and well tolerated for managing moderate to severe, chronic malignant tumour‐related pain in patients who were opioid naive or dissatisfied with current treatment (Pain Physician, 2014, 17, 329–343). This post hoc, subgroup analysis evaluated the efficacy and tolerability of tapentadol PR in patients who previously received and were dissatisfied with tramadol for any reason and who had a pain intensity ≥5 (11‐point numerical rating scale) before converting directly to tapentadol PR.

Methods

In the original study, eligible patients had been randomized (2:1) and titrated to their optimal dose of tapentadol PR (100–250 mg bid) or morphine sulphate‐controlled release (40–100 mg bid) over 2 weeks. The present report focuses on results during the titration period for a subgroup of patients randomized to tapentadol PR after having been on tramadol treatment prior to randomization in the study (n = 129). Results for this subgroup are compared with results for all 338 patients who received tapentadol PR during titration (overall tapentadol PR group).

Results

Responder rates (responders: completed titration, mean pain intensity <5 [0–10 scale] and ≤20 mg/day rescue medication during last 3 days) were slightly better for the tramadol/tapentadol PR subgroup (69.8% [90/129]) vs. the overall tapentadol PR group (63.9% [214/335]). Tolerability profiles were comparable for both groups.

Conclusions

Results of this subgroup analysis indicate that patients with cancer pain could safely switch from prior treatment with the weak centrally acting analgesic tramadol directly to the strong centrally acting analgesic tapentadol PR, for an improved analgesic therapy for severe pain.

What does this study add?

Results of this post hoc analysis show that patients who had received prior tramadol therapy could switch directly to tapentadol PR, with the majority (˜70%) experiencing improved efficacy.