The use of adrenaline in anaphylaxis is complicated by chronic pre-treatment of the patient in the following situations:
patients who are taking tricyclic antidepressants or monoamine oxidase inhibitors should receive only 50% of the usual dose of adrenaline because of an interaction which is potentially dangerous. Some fluorohydrocarbons used as refrigerants as well as cocaine sensitise the heart to adrenaline and are contraindications to its use
also half doses of adrenaline (epinephrine) may be safer for patients on a beta blocker (1)
Resuscitation Council (UK). The Emergency Medical Treatment of Anaphylactic Reactions for First Medical Responders and for Community Nurses Revised January 2002, May 2005.