[Analgesic effects of an oral dose of clonidine]

Experimental data and anecdotal clinical observations have shown that clonidine, an alpha 2-agonist, has a marked analgesic effect. We investigated clonidine-induced analgesia in response to nociceptive stimuli. On 2 different days 7 normal volunteers received either placebo or clonidine (200 micrograms) orally according to a cross-over, double-blind, randomized, placebo-controlled design. Analgesia was assessed by measurement of the subjective (VAS) and objective (R III reflex) pain thresholds. A close correlation was observed between subjective and objective pain thresholds (r = 0.88, y = 0.2 + 1.2 x). Clonidine increased the objective threshold by 21% (+6.2 mA, SEM 2.4) and the subjective threshold by 10% (+2.4 mA, SEM 1.3). Drug effect was rapid (peak between 90 and 120 min) and overall analgesia lasted up to 4 hours. Side effects were a moderate fall in blood pressure, sedation and dryness of the mouth. A single oral dose of clonidine induces significant analgesia. These results suggest that clonidine is potentially a worthwhile drug for pain treatment which deserves further clinical investigation.