Which drug is a calcium channel blocker used to treat feline hypertension, and what is its mechanism?

• A. Diltiazem; inhibits L-type calcium channels causing vasodilation.
• B. Nifedipine; inhibits L-type calcium channels causing vasodilation.
• C. Amlodipine; inhibits L-type calcium channels causing vasodilation.
• D. Verapamil; inhibits L-type calcium channels causing vasodilation.

Answer: (C)

Blocking calcium entry into vascular smooth muscle lowers intracellular calcium, causing the muscle to relax and the vessels to dilate. This reduces systemic vascular resistance and lowers blood pressure.

Amlodipine fits best here because it’s a dihydropyridine calcium channel blocker that preferentially blocks L-type calcium channels in peripheral vascular smooth muscle. The result is calm, sustained vasodilation with a drop in arterial pressure, and it does so with relatively limited direct effects on the heart. That makes it particularly effective and safer for treating feline hypertension, and it often allows once-daily dosing with good clinical results.

The other drugs listed also inhibit L-type calcium channels and cause vasodilation, but their cardiac effects differ: verapamil and diltiazem affect the heart more (possible negative inotropy and conduction changes), and nifedipine can be associated with more variable or reflexive blood pressure changes. These factors make amlodipine the preferred choice for cats.