[Intra- and postoperative interactions between the 2 opioids fentanyl and buprenorphine]

In order to demonstrate pharmacokinetic and pharmacodynamic interactions between fentanyl and buprenorphine, 3 groups of patients (n = 30) were compared, receiving either fentanyl (0.005 mg/kg b.w.) or buprenorphine (0.01 mg/kg b.w.) or both opioids as analgesic during surgery for disc protrusion. For a period of 4 h haemodynamic parameters were monitored and blood samples were taken for determination of the following concentrations: ADH, ACTH, cortisol, glucose, unbound glycerol, fentanyl and buprenorphine. Blood gas analyses were performed up to 2 h postoperatively. Although in all groups haemodynamic parameters were constant, there was an increase in factors related to operative stress (cortisol, glucose, unbound glycerol, postoperative acidosis) after the combination of both opioids, while postoperative ventilatory parameters in this group were not improved by the partial agonist buprenorphine. Plasma levels were not affected by combined application, except for a slight elevation of buprenorphine concentrations during additional use of fentanyl. Buprenorphine, at least in higher dosages, seems to antagonize analgesia induced by fentanyl, although respiratory depression is even more pronounced. It may be assumed, that with partial agonists the relation of agonistic and antagonistic activity may be different, depending on the dosage used and on the respective pharmacologic effect observed during investigation.