Thursday October 1, 2009
Clonidine and Bradycardia!

Clonidine is a alpha adrenergic agonist with sympatholytic activity and has been used for various clinical indications beside blood pressure control including treatment for migraines, menopausal complaints, narcotic and alcohol withdrawal symptoms, spasticity after spinal cord injury, attention-deficit hyperactivity disorder as well as rate control for atrial fibrillation.

Mechanism of action: Symptomatic bradycardia is a side effect of clonidine which many times go ignored. Clonidine's central effect results in decreased sympathetic outflow and enhanced vagal tone, lowering blood pressure and heart rate. This also cause side effects of drowsiness, lethargy and dry mouth. Clonidine acts peripherally within the heart to inhibit norepinephrine release, contributing to further reductions in heart rate.

Risk factors: Patients at higher risk for clonidine-induced bradycardia seem to be those with an already-diseased conduction system, renal failure, high doses of clonidine, concomitant therapy with medications known to cause bradycardia or heart block, (eg, beta-blockers, verapamil, diltiazem, digoxin).

Treatment: For severe, symptomatic bradycardia, atropine can be used. For refractory symptomatic cases, isoproterenol, epinephrine, dopamine, and pacing may be required.