It is also an effective preventive medication for migraine. It is a class 3 antianginal drug, and a class IV antiarrhythmic. It is a common adulterant of cocaine seized in the UK, and has been found to reduce cocaine cravings in rats, indicating it may prolong the "high" (see below). It incites minimal reflex sympathetic changes. It is based upon a 1,4-thiazepine ring.
Diltiazem is metabolized by and acts as an inhibitor of the CYP3A4 enzyme.
Diltiazem is a potent vasodilator, increasing blood flow and variably decreasing the heart rate via strong depression of A-V node conduction. Its pharmacological activity is somewhat similar to verapamil.
It is a potent vasodilator of coronary and peripheral vessels, which reduces peripheral resistance and afterload.
Because of its negative inotropic effect, diltiazem causes a modest decrease in heart muscle contractility and reduces myocardium oxygen consumption. Its negative chronotropic effect results in a modest lowering of heart rate, due to slowing of the sinoatrial node. It results in reduced myocardium oxygen consumption.
Because of its negative dromotropic effect, conduction through the AV (atrioventricular) node is slowed, which increases the time needed for each beat. This results in reduced myocardium oxygen consumption.
Nontherapeutic effects and toxicities
A reflex sympathetic response, caused by the peripheral dilation of vessels and the resulting drop in blood pressure, works to counteract the negative inotropic, chronotropic and dromotropic effects of diltiazem. Undesirable effects include hypotension, bradycardia, dizziness, and flushing.
The drug is indicated for angina:
Stable angina (exercise-induced) – diltiazem increases coronary blood flow and decreases myocardial oxygen consumption, secondary to decreased peripheral resistance, heart rate, and contractility.
Variant angina – it is effective owing to its direct effects on coronary dilation.
Unstable angina (preinfarction, crescendo) – diltiazem may be particularly effective if the underlying mechanism is vasospasm.
Because of its vasodilatory effects, diltiazem is useful for treating hypertension. Calcium channel blockers are well tolerated, and especially effective in treating low-renin hypertension.
The dose of diltiazem in supraventricular tachycardias is 0.25 mg/kg, IV bolus push over 2 minutes. Most commonly, a 20 mg IV dose is given to the average-sized patient.
Contraindications and precautions
In congestive heart failure, patients with reduced ventricular function may not be able to counteract the inotropic and chronotropic effects of diltiazem, the result being an even higher compromise of function.
With SA node or AV conduction disturbances, the use of diltiazem should be avoided in patients with SA or AV nodal abnormalities, because of its negative chronotropic and dromotropic effects.
Low blood pressure patients, with systolic blood pressures below 90 mm Hg, should not be treated with diltiazem.
Intravenous diltiazem should be used with caution with beta-blockers because, while the combination is most therapeutically beneficial, there are rare instances of dysrhythmia and AV node block.
Quinidine should not be used concurrently with calcium channel blockers because of reduced clearance of both drugs and potential pharmacodynamic effects at the SA and AV nodes.
Diltiazem and verapamil inhibit hepatic cytochromes CYP3A4, CYP2C9 and CYP2D6, possibly resulting in drug interactions.
Potential future indications
Diltiazem is prescribed off-label by doctors in the US for prophylaxis of cluster migraine. Some research on diltiazem and other calcium channel antagonists in the treatment and prophylaxis of migraine is ongoing.
Diltiazem is also being used in the treatment of anal fissures. It can be taken orally or applied topically with increased effectiveness. When applied topically, it is made into a cream form using either vaseline or Phlojel. Phlojel absorbs the diltiazem into the problem area better than the vaseline base. It has good short term success rates. Like all nonsurgical treatments of anal fissure, it does not address the long term problem of increased basal anal tone and does not decrease the subsequent recurrence rate that can vary between 40 and 60%.
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