The Influence of Drugs Used in Therapeutics on the Action of Muscle Relaxants.

When one considers the many types of chemical compound used in modern therapeutics, it is not surprising that some of these modify the action of muscle relaxants. In general such substances may interfere with neuromuscular transmission, or may influence relaxants by actions at other sites. Some such side effects are well known. Others, based on animal experiments on many different species and under varying conditions, are more difficult to assess precisely. Nevertheless, it would be unwise for the anaesthetist to ignore the possible risks they suggest. Although it is difficult to classify drugs accurately according to their pharmacological action at the neuromuscular junction, they may be grouped under the following headings. It must, however, be remembered that one drug may have several effects. (1) Drugs influencing the release or metabolism of acetylcholine. (2) Drugs altering the sensitivity of the motor endplate. (3) Drugs affecting the metabolism and excretion of muscle relaxants.