A comparison of the hypoalgesic effect of paracetamol in slow-release and plain tablets on laser-induced pain.

1. In a double-blind, three way, cross-over study 15 volunteers received plain paracetamol tablets 1000 mg every 6th hour, paracetamol slow-release tablets 2000 mg every 12th hour, and placebo. Steady state conditions were established over a 5 day period preceding each test session. 2. Plain paracetamol was given twice in the 12h test session, initially and after 6 h, and the slow-release formulation was given once at the start of the session. 3. Hypoalgesia, measured by experimentally laser-induced pain (pain threshold), and plasma concentrations of paracetamol were measured hourly for 12 h. 4. Both formulations of paracetamol were significantly superior (P = 0.0003) to placebo, but not difference in analgesic efficacy was found between the two regimens.