Editing Vasospasm (section)

===Contraindications===
Organic nitrates should not be taken with [[PDE5]] inhibitors (i.e. [[sildenafil]]) since both NO and PDE5 inhibitors increase [[cyclic GMP]] levels and the sum of their pharmacodynamic effects will greatly exceed the optimal therapeutic levels. What you could see upon taking both medications at the same time, as caused by the much higher induction of relaxation of smooth muscle cells, include a severe drop in blood pressure.

Beta-receptor antagonists should be avoided in patients with reactive pulmonary disease to avoid asthma attacks. Also Beta-receptor antagonists should be avoided in patients with AV node dysfunction and/or patients on other medications which might cause bradycardia (i.e. calcium channel blockers). The potential for these contraindications and drug-drug interaction could lead to asystole and cardiac arrest.

Certain calcium channel blocker should be avoided with some beta-receptor blockers since they may cause severe bradycardia and other potential side effects.