Known brand names include Cardizem.
A calcium channel blocker that slows the heart rate and relaxes blood vessels. Given IV in a monitored setting, it quickly slows a racing heart in atrial fibrillation or flutter and can stop PSVT; as once-daily Cardizem CD capsules, it treats high blood pressure and prevents chest pain (angina).
Diltiazem keeps calcium from flowing into the muscle cells of the heart and blood vessel walls when they are signaled to contract. In the AV node, the relay point between the heart's upper and lower chambers, this slows each signal and makes the node wait longer before passing the next one, so fewer beats get through. That slows the heart rate in atrial fibrillation or flutter and can break the looping signal that drives PSVT. In blood vessels, less calcium lets the muscle relax, which widens the arteries, including the heart's own, and lowers blood pressure and the heart's need for oxygen.
Given by IV, it usually starts slowing the heart within 3 minutes, reaches its full effect in 2 to 7 minutes, and a single dose keeps working for 1 to 3 hours. Cardizem CD releases the drug slowly through the day, and its full effect on blood pressure usually takes about 2 weeks. Because it slows the heart's electrical system and relaxes blood vessels, too strong an effect shows up as a slow heartbeat, heart block, dizziness, or low blood pressure. In people whose heart already pumps weakly, it can make heart failure worse.
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Given by IV, diltiazem slows a racing heartbeat for a short time in atrial fibrillation or atrial flutter, rhythms in which the heart's upper chambers beat chaotically or too fast and drive the lower chambers too fast. The IV form can also quickly stop paroxysmal supraventricular tachycardia (PSVT), a sudden, very fast rhythm, and return the heart to a normal beat. As Cardizem CD capsules, it lowers high blood pressure, which over time can damage the heart, brain, kidneys, and blood vessels. The capsules also help prevent chest pain (angina), both the steady kind that comes with exertion and the kind caused by spasm of the heart's arteries.
The IV form is used where the heart rhythm and blood pressure can be watched closely and emergency equipment is ready, while the capsules are taken by mouth once a day at home, alone or with other blood pressure medicines. The capsules prevent chest pain but do not stop an attack once it starts, so a separate fast-acting medicine is used for that. The IV form is not used for atrial fibrillation or flutter in people with an extra electrical pathway, as in Wolff-Parkinson-White syndrome, or for ventricular tachycardia. Its safety and effectiveness in children have not been established.
With the capsules, headache, dizziness, a slow heartbeat, swelling in the legs, and weakness are what people notice most. With the IV form, a drop in blood pressure is the most common problem, along with burning or itching where it is injected and flushing. The label treats severe heart block, a very slow heart rate, low blood pressure, worsening heart failure, liver injury, and severe skin reactions as serious.