PHARMACOKINETICS AND CLINICAL EFFECTS OF INTRAMUSCULAR SCOPOLAMINE PLUS MORPHINE - A COMPARISON OF 2 INJECTION SITES

Background: Intramuscular scopolamine plus morphine premedication is t raditionally used when prominent sedative or antisialogogue effect is needed. Knowledge of the pharmacokinetics of scopolamine is limited du e to low plasma concentrations found after therapeutic doses. This inv estigation compares the pharmacokinetics and the clinical responses of this drug combination injected into two commonly used injection sites . Methods: Twelve ASA class 1 patients scheduled for minor surgery und er spinal anaesthesia received scopolamine 6 mu g/kg plus morphine 200 mu g/kg injected in either deltoid (group D, n=6) or gluteal (group G , n=6) muscle. Results: The peak plasma concentrations of scopolamine after deltoid or gluteal injection (2.2 vs 1.6 mu g/l) and the time th ey were reached (17 vs 19 min) were comparable. The absorption of morp hine was similar in both groups (T-max 16 min), but the peak plasma co ncentrations were higher after deltoid injection (71 vs 49 mu g/l). Th e individual variation in the elimination half-lives of both scopolami ne and morphine was smaller after deltoid injection (T 1/2 scopolamine 1.9+/-0.7 vs 2.1+/-1.1 h, morphine 1.3+/-0.7 vs 2.3+/-1.5 h). Moderat e slowing (25%) of heart rate was found in both soups. A heavy sedatio n and antisialogogue effect (VAS) was found in both groups with faster occurrence of maximal effect in group D (60 vs 120-180 min). Conclusi on: More predictable pharmacokinetics and clinical effects of intramus cular scopolamine plus morphine premedication can be achieved after an injection into deltoid muscle.