Antidepressants are used to treat many different conditions, including depression, panic disorder and post-traumatic stress disorder. There are several classes of antidepressants, which differ in their effect on neurotransmitters. Some antidepressants affect many different transmitters, while others affect mostly one type. Overdoses, whether accidental or intentional, can lead to serious medical complications.
Tricyclic Antidepressants
Amitriptyline and imipramine are examples of tricyclic antidepressants, or TCAs. Their toxicity is a result of their effects on several neurotransmitters and on the cells of the heart. Central nervous system effects include drowsiness, confusion, paralysis of eye movements, seizures and coma. The anticholinergic effects of an overdose are secondary to blockade of receptors for acetylcholine. Symptoms include blurry vision, dilated pupils and fever.
The most common effect on the heart, as described in an article in the Emergency Medical Journal, is a rapid heart rate. An overdose of TCAs can also cause disturbances in the heart rhythm, including potentially fatal arrhythmias, such as ventricular tachycardia and fibrillation.
SSRIs
Serotonin Specific Re-uptake Inhibitors, or SSRIs, are considered a safer class of medication than older antidepressants. An excess of serotonin is often the result of unintentionally combining several medications that increase serotonin, such as an SSRI along with tramadol, a pain medication. Symptoms include changes in the patient's mental state, with confusion, restlessness and coma. The neuromuscular system becomes excitable, leading to rigidity, myoclonus--brief muscular contractions--and increased reflexes. Clonus, which is an up and down movement of the foot as a result of rapid muscle contractions, can appear. Temperature rises, blood pressure fluctuates, and the heart rate is rapid. Seizures may occur. Serotonin syndrome is a life-threatening condition. It must be treated in a hospital's intensive-care unit.
Bupropion
Bupropion is an antidepressant also used as a smoking cessation aid. Overdose can lead to a rapid heart rate, agitation and hallucinations. In a review of 385 cases published in the Journal of Emergency Medicine, seizures occurred in 11 percent of patients. Seizures usually present within six hours of ingestion but may occur later, particularly if the other signs of toxicity persist.
Venlafaxine
Venlafaxine is an antidepressant which affects both noradrenaline and serotonin. When combined with other drugs that increase serotonin, it can cause serotonin syndrome. Overdose of venlafaxine, which according to the FDA usually occurs in combination with alcohol or other drugs, can lead to EKG changes and arrhthymias. Low blood pressure and slowed heart rate can occur. Central nervous system effects include sleepiness, coma and seizures. Necrosis--cellular death--of the liver can occur. Overdoses with venlafaxine can be fatal.
References
- "Emergency Medical Journal" ; Tricyclic antidepressant overdose: a review; G W Kerr, A C McGuYe and S Wilkie; 2001;18:236--241
- "Journal of Emergency Medicine"; Intentional bupropion overdoses.; Shepherd G, Velez LI and Keyes DC; Aug 2004
- Mayo Clinic: Serotonin Syndrome
- "Kaplan and Sadock's Comprehensive Textbook of Psychiatry": Virginia Sadock and Pedro Ruz (eds); 2009
- FDA: Effexor (venlafaxine)
