Trade names: Isoptin®, Calan®, Verelan® among others
German: Verapamil
Verapamil is an active substance widely spread as antiarrhythmics (eg. Isoptin). It belongs to the group of calcium antagonists (subgroup: phenylalkylamines = "Verapamil type" substances).
Verapamil is the means of choice against supraventricular tachyarrhythmias. Moreover, it is applied for the therapy of coronary heart disease (CHD and angina pectoris), high blood pressure (hypertension) and hypertrophic obstructive cardiomyopathy (HOCM).
Verapamil is absorbed by over 90%; its bioavailability lies at 10-20%, on permanent therapy at up to 40%, high first-pass-effect. Its half-life period is 3-7h. The active and passive metabolites are eliminated and excreted via the kidney and bile.
Verapamil has a negative effect on the impulse formation of the heart (negatively chronotropic), it reduces the saltatory conduction (strongly negatively dromotropic), it reduces myocard contraction (negatively inotropic), and additionally, it causes a slight arterial vasodilatation (slightly arterially vasodilatative).
The adverse effects include bradycardia, AV blocks (up to AV block grade III), too much negative inotropy, hypotension, constipation, headache and dizziness.
The combination of Verapamil with beta blockers is to be avoided due to the increasingly negative inotropy. A combination with other class I to IV antiarrhythmics can cause bradycardia, AV block, and cardiodepression. The same undesired effect can be observed when combining Verapamil with inhalational anesthetics. In combination with antihypertensives and anesthetics, Verapamil causes a more powerful reduction of blood pressure. Non-steroid anti-inflammatory drugs (NSAID), in contrast, lead to a reduced blood pressure reduction (by inhibiting the prostaglandin synthesis as well as increased retention of sodium and water).
Verapamil causes an inhibition of the liver enzyme CYP3A4, as do other calcium antagonists. Thatís why some other drugs that are degraded by CYP3A4 (eg. Theophyllin, Carbamazepine etc.), given at the same time, are not metabolized that well anymore. They accumulate in the blood (elevated concentration of the affected substances measurable in the serum). Conversely, other CYP3A4 inhibitors also can inhibit the degradation of Verapamil, so that its blood level increases and the antihypertensive effect is boosted.
Verapamil must not be given in decompensated heart failure, AV block higher than grade I, atrial flutter and atrial fibrillation with pre-excitation syndrome, sick-sinus-syndrome, and cardiogenic shock that cannot be traced back to another cause than arrythmia.
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