The study by Gilron et al (2005) looked at neuropathic pain in patients with painful diabetic neuropathy and those with postherpetic neuralgia. They looked at the effects of gabapentin, morphine and a gabapentin-morphine combination compared to a placebo consisting of lorazepam, which does not cause pharmacological analgesia but mimics the adverse effects of the active treatments. The study used a randomized, double-blind, active placebo-controlled, four-period crossover trial, with patients receiving daily doses of active placebo, sustained-release morphine, gabapentin, or a combination of gabapentin and morphine, each given orally for five weeks.
The outcome measured was the mean daily pain intensity in patients while they were receiving the maximal tolerated dose of the drugs. Secondary outcomes measured were pain rated on the Short-Form McGill Pain Questionnaire, adverse effects of the drugs, maximal tolerated doses of each drug, mood changes, and quality of life estimates. A pharmacist prepared a concealed allocation schedule randomly assigning the four sequences, in blocks of four, to a consecutive series of numbers, and each consecutive patient was assigned the next consecutive number and their corresponding series of medications for the study were dispensed to them when they enrolled in the study.
To maintain the double-blind conditions of the study, the medications were placed in blue or gray gelatin capsules, with patients receiving identical blue and gray capsules during each treatment period of the study. Blue capsules were administered twice daily and gray capsules three times daily. For the morphine treatment period, blue capsules contained 30 mg sustained-release morphine and gray capsules lactose placebo; for the gabapentin treatment period, blue capsules contained lactose placebo and gray capsules contained 400 mg gabapentin; for the combined gabapentin-morphine treatment period, blue capsules contai...