Refresher on physiology: Muscles contract because of Actin and Myosin. But we can’t have them contract indefinitely, so we have something that inhibits them from coupling: Troponin and Tropomyosin. When calcium enters the muscle cell, it inhibits troponon and tropomyosin and when those are inhibited, the muscles contract.
Why is this important? What surrounds vascular blood vessels? Smooth muscle. What causes them to contract? Calcium. When calcium enters the cells, the muscle contracts, blood vessels constrict and BP goes up.
How do we counteract it? With Calcium Channel Blockers! They block the entry of calcium into cells, causing the muscles to relax, causing the BP to go down.
Calcium Channel Blocking Agents
Looks like a long list below but it’s actually not too many cause there’s lots of duplicates. Here’s a story of what drug companies have done with naming these drugs that have confused physicians. Let’s begin with diltiazem.
Diltiazem (Cardizem) – p.o., inj. – Historically this was the first calcium channel blocker on the market almost 25 years ago. When it first came out on the market, it was a 3x a day drug. When the patent was running out for this drug, the drug company said, look doctor, put your patient on our SR version, where it’s only a 2x a day drug. When that patent ran out, they came out with a Long Acting cardizem where you have to dose only once a day. By that time there were many other cardizems and we had a hodge podge of what pharmacists could substitute.
Around that time, Verapamil came out. It was to be prescribed twice a day. When the patent ran out, they came out with the SR version where you have to dose it once a day. Here’s where the doctors are really confused. They write Diltiazem SR and think it’s supposed to be once a day but it’s supposed to be twice a day. Cardiologists won’t have this problem but other physicians might because there’s no standardized meaning to their words.
- Diltiazem (Cardizem) – p.o., inj.
- Diltiazem SR (Cardizem SR) – p.o.
- Diltiazem Long Acting (Cardizem CD, Dilitrate XR) – p.o.
- Amlodipine (Norvasc) – p.o.
- Felodipine (Plendil) – p.o.
- Nicardipine (Cardene) – p.o.
- Nifedipine (Procardia, Adalat) – p.o.
- Nifedipine XL (Procardia XL, Adalat CC) – p.o.
- Verapamil (Calan, Isoptin) – p.o., inj.
- Verapamil SR (Calan SR, Isoptin SR) – p.o.