ANALGESIC EFFECTS OF LAMOTRIGINE AND PHENYTOIN ON COLD-INDUCED PAIN -A CROSSOVER PLACEBO-CONTROLLED STUDY IN HEALTHY-VOLUNTEERS

The analgesic activity of a single dose of lamotrigine (300 mg p.o.) a nd phenytoin (300 mg p.o.) was evaluated in a randomised, double-blind , placebo-controlled study in 12 healthy volunteers. A computerised co ld-presser test (CPT) was used to measure analgesia. Dihydrocodeine (9 0 mg p.o.) was used to validate the effectiveness of the CPT in measur ing analgesia in the volunteers. On each study day the volunteers perf ormed the CPT before study medication and at 1.25, 2.75, 4.25 and 5.75 h post-dose. Psychomotor tests were carried out before each CPT to de termine possible drug-induced sedation. These included digit symbol su bstitution, critical flicker fusion and choice reaction time. Subjecti ve feelings of concentration, vigilance and relaxation were also measu red using visual analogue scales. All three active drugs significantly reduced pain scores. Maximum pain relief was achieved at 1.25 h post- dose for both dihydrocodeine and lamotrigine, whereas for phenytoin it occurred at 4.25 h post-dose. There was a significant association bet ween analgesia and plasma concentrations of lamotrigine (P = 0.013) an d phenytoin (P = 0.028). There were no significant differences in the sedation produced by any of the active drugs, compared to placebo. The findings of this study suggest that lamotrigine and phenytoin could h ave a wider clinical use as analgesics. (C) 1998 International Associa tion for the Study of Pain. Published by Elsevier Science B.V.