EFFECT OF PHYSOSTIGMINE ON MORPHINE-INDUCED POSTOPERATIVE PAIN AND SOMNOLENCE

The effects of physostigmine 1 mg I v were studied on the analgesia, sedation and reduction in respiratory rate induced by morphine 10mg/60kg I v in 10 panents recovering from surgery. Within 5-10min, physostigmine abolished the somnolent effect of morphine and restored the respiratory rate to pre-drug values Analgesia, assessed by an independent observer and by the patient was, if anything, increased by physostigmine. The analepuc effect of physostigmine lasted 40-60 mm An important factor limiting the use of morphine in acutely painful conditions is the well documented danger of significant respiratory depression. Som-nolence, while less of a problem, may be a trouble-some side-effect. Our previous studies in experi-mental animals have shown that physostigmine, an anticholinesterase agent that readily penetrates the central nervous system, can reverse the respiratory depressant effect of morphine without reducing the analgesic activity (Weinstock et al., 1980). Physo-stigmine was also found to antagonize the respirat-ory depressant effect of morphine given as part of the pre-anaesthetic medication to human subjects (Snir-Mor, Weinstock and Davidson, 1981). These findings suggest that physostigmine may be of value in antagonizing the side-effects of mor-phine after surgery. However, a possible role for physostigmine in such patients would be largely vitiated if the analgesic effect of morphine was reversed. The present study was undertaken to determine the effect of physostigmine on the somnolence in-duced by morphine and to clarify if it alters the level of analgesia in the postoperative period