Opioid clinical pharmacology and routes of administration.

Opiate prescription is based on titration to effect. This principle is supported by the difference between the laboratory and clinical pharmacologies of opiates. Clinically the presence of nociceptive pain appears to act as a counter to the respiratory depressant effect of opiates, and perhaps the dependence, which are such features in the laboratory. Factors in choosing between opiates are described; these include onset speed, duration of effect, toxic and active metabolites and specific side-effects. Side-effect comparison between opiates is only satisfactory when the drugs are compared at equianalgesic doses. The kinetic and clinical logic of alternative routes is explored. Overall there is probably more difference between the effect of the same opiate given by different routes than between the effects of different opiates given by the same route.