Monday July 19, 2010
Drug interaction

Scenario: 58 years old male is admitted to ICU with atrial fibrillation with rapid ventricular rate (RVR). Patient's past medical history is significant only with BPH (prostate hypertrophy) and patient uses Tamsulosin (Flomax) for it. Patient's BP is on lower side so you decide to use Amiodarone instead of cardizem or esmolol. With Amiodarone bolus patient 's blood pressure dropped drastically and patient coded.

Answer: IV Amiodarone bolus is know to cause transient hypotension but it may cause dramatic hypotension with concurrent alpha or beta blockade use. Amiodarone (with its active metabolite, desethylamiodarone) blocks sodium, potassium, and calcium channels. Amiodarone itself is a relatively potent noncompetitive alpha and beta-blocker and with cocomitant use of alpha, beta blockers or calcium channel blockers may cause life threatening situation.

Moreover, Amiodarone itself has direct potent coronary as well as veno vasodilatory property. Amiodarone acts as a direct venodilator through the cyclooxygenase pathway, activation of nitric oxide synthase, and cyclooxygenase-dependent relaxing endothelial factors.

On side note - Hypotension from IV amiodarone (particularly bolus) is also contributed due to its solubilized vehicle called polysorbate 80 which may have histamine releasing effect.