Hydromorphone hydrochloride is a opioid analgesic; its principal therapeutic effect is relief of pain. The precise mechanism of action of hydromorphone hydrochloride and other opiates is not known, although it is believed to relate to the existence of opiate receptors in the central nervous system. There is no intrinsic limit to the analgesic effect of hydromorphone hydrochloride; like morphine, adequate doses will relieve even the most severe pain. Clinically, however, dosage limitations are imposed by the adverse effects, primarily respiratory depression, nausea, and vomiting, which can result from high doses.
Hydromorphone hydrochloride has diverse additional actions. It may produce drowsiness, changes in mood and mental clouding, depress the respiratory center and the cough center, stimulate the vomiting center, produce pinpoint constriction of the pupil, enhance parasympathetic activity, elevate cerebrospinal fluid pressure, increase biliary pressure, produce transient hyperglycemia.
Generally, the analgesic action of parenterally administered hydromorphone hydrochloride is apparent within 15 minutes and usually remains in effect for more than five hours. The onset of action of oral hydromorphone hydrochloride is somewhat slower, with measurable analgesia occurring within 30 minutes.