The effects of intravenously administered dihydrocodeine bitartrate in anaesthetized man.

IN the past decade narcotic analgesics have been widely used to supplement thiopentone-nitrous oxide-oxygen anaesthesia. Pethidine (Neff, Mayer and Perales, 1947) and alphaprodine (Siker, Foldes, Pahk and Swerdlow, 1954) have been most frequently employed, but many other narcotics, e.g. levorphanol (Brotman, Cullen and Wilkins, 1950) and anileridine (Riffin et al., 1958) have also been used. In the dosage necessary to produce adequate operating conditions, with small doses of thiopentone and muscle relaxants, these drugs frequently cause respiratory depression of variable intensity (Foldes et al., 1956). On the other hand, little or no circulatory changes have been observed when such techniques are employed (Foldes et al., 1957). In view of the undesirable respiratory effects of narcotics when used for the supplementation of anaesthesia, the search has continued for a potent narcotic analgesic which would be free from this disadvantage. It has been reported that, in 30 mg subcutaneous doses, dihydrocodeine bitartrate produces relief of postoperative pain comparable with that given by 10" mg morphine, without causing appreciable respiratory depression (Gravenstein et aL, 1956). Other investigators (Keats et al., 1957; Wallenstein et aL, 1957) found that about 60 mg dihydrocodeine had the same analgesic potency as 10 mg morphine and that when used in this ratio the respiratory depression caused by the two analgesics was very similar (Seed et al., 1957). Eckenhoff and Helrich (1957) found relatively less respiratory depression after intramuscular injection of 50-60 mg dihydrocodeine than after comparable doses of other narcotic analgesics. In an earlier study one