The Pharmacodynamics of Mivacurium in Males and Females: A Study in Human Volunteers

Muscle relaxants are a type of drug used to provide muscle relaxation during induction of anesthesia and surgical treatment. Residual drug effect postoperatively (i.e. residual muscle relaxation) occurs frequently and studies have shown that this may be harmful in certain groups of patients. Of special concern is residual effect on upper airway and breathing muscles. A previous study has shown that males and females respond differently to the effect of this kind of drug. It appears that some muscle groups which are important for airway protection and breathing are more sensitive to the effect of muscle relaxants in males than females. Males may therefore be more susceptible to postoperative lung complications than females. In this study we try to determine what causes the observed sex-related difference in response to the muscle relaxant Mivacurium. We have previously shown that this sex-related difference cannot be explained by different pharmacokinetics (what the body does to the drug) in males and females. Our hypothesis is that a pharmacodynamic (what the drug does to the body) difference between sexes exists, i.e. that a lower blood concentration of Mivacurium is needed in males than females in order to obtain a predefined degree of muscle relaxation in certain muscle groups.