Analgesic efficacy of immediate and sustained release paracetamol and plasma concentration of paracetamol. Double blind, placebo-controlled evaluation using painful laser stimulation.

The analgesic efficacy of single doses of immediate release paracetamol 500 mg and 1000 mg, sustained release paracetamol 2000 mg, and placebo was evaluated over a 12 h period in 10 healthy volunteers. The efficacy was related to the concurrent plasma concentrations of paracetamol. Experimental pain was induced by brief cutaneous application of argon laser pulses, and the analgesic effect was assessed as change in pricking pain threshold. Both 0.5 g and 1.0 g immediate release paracetamol had an analgesic effect superior to that of placebo from 1 to 5 h after administration. Peak analgesia was reached after 2 h. No difference was found in the analgesic effect of the two dosages. Sustained release paracetamol was not significantly superior to placebo at any time. The plasma concentration of paracetamol had peaked in the 1 h sample after of the immediate release tablet. The peak plasma concentration was reached 3-4 h after 2.0 g sustained release paracetamol. It is not known why the sustained release formulation did not produce any detectable analgesia. It is proposed, that the rate of increase in the plasma concentration of paracetamol might be important in the alleviation of acute (laser-induced) pain.

RCT Entities:   Population Interventions Outcomes