[The clinical significance of drug interactions between opiates and calcium antagonists. A randomized double-blind study using fentanyl and nimodipine within the framework of postoperative intravenous on-demand analgesia].
It is widely accepted that the nociceptive state and opiate-induced nociception are regulated at least in part by calcium ions. Animal experiments suggest that systemically or intracerebroventricularly applied calcium antagonizes analgesic effects, whereas calcium chelating agents or calcium channel blockers enhance them. Recently, von Bormann et al. [3] reported a fentanyl-saving effect in cardiovascular patients who had received an intraoperative infusion of nimodipine; this finding was discussed as a possible synergistic analgesic interaction. Since doubts remained as to whether this interpretation was justified, the present study aimed to verify, in awake postoperative patients, whether nimodipine increased the analgesic efficacy of fentanyl. Forty ASA I-II patients (mean age 43-44 years) undergoing elective hysterectomy under standardized balanced anesthesia were investigated. In the recovery room, they were allowed to self-administer fentanyl by means of the On-Demand Analgesia Computer (ODAC). Demand dose was 34.5 micrograms, infusion rate 4 micrograms/h, lockout time 1 min, hourly maximum dose 250 micrograms. The patients were randomly and double-blindly assigned to have an additional infusion of either placebo (P) or nimodipine (N: 15 micrograms/kg/h during the first 2 h, 30 micrograms/kg/h from the 3rd to the 12th h). Fentanyl consumption, pain scores (actual and retrospective), blood pressure, heart rate, respiratory rate, and side-effects were monitored. The mean duration of patient-controlled analgesia was 16 (P) to 19 (N) h, during which time 0.64 +/- 0.46 (N) to 0.79 +/- 0.43 (P) micrograms fentanyl/kg/h was demanded. Pain relief was very satisfactory in 92.5% of the patients.(ABSTRACT TRUNCATED AT 250 WORDS)