Effect of tricyclic antidepressants on analgesic activity in laboratory animals.

A study has been made in rodents of the interactions between a range of psychotropic drugs, narcotic agonist and partial agonist analgesics, and pain. In rodents, tricyclic antidepressants do not alone reduce pain responses but, in combination with morphine or pentazocine, clomipramine enhances analgesic activity after single doses yet increases the onset and degree of tolerance to morphine on repeated injection. The tricyclic antidepressant maprotiline, in contrast, reduced both the rate of development and extent of morphine tolerance. In morphine-dependent rats, repeated injections of clomipramine or maprotiline exerted a mixed effect upon the abstinence syndrome, some behavioural signs being potentiated whilst others were suppressed. These studies suggest that combining maprotiline with morphine will improve the control of chronic pain states.