Calcium channel antagonists,

Calcium channel antagonists, or calcium channel blockers (CCBs), bind L-type calcium channels that regulate calcium entry into vascular smooth muscle, myocardial cells, and cardiac pacemaker cells. They decrease the vascular resistance of peripheral organs, cause coronary artery vasodilation, and are myocardial depressants. CCBs are distinguished by their relative affinities for cardiac versus vascular L-type calcium channels.

1. Dihydropyridine (DHP) CCBs are more selective for vascular smooth muscle and are used to treat hypertension. Their physiologic effect is largely arterial vasodilation with minimal effects on venous capacitance.
   1. Clevidipine is an ultrashort-acting antihypertensive administered by IV infusion ideal for perioperative use due to its rapid onset, titration, and elimination half-life of approximately 1 minute by serum esterases. After cessation, effects last 5 to 10 minutes, with a 90% return to baseline blood pressure by 7 minutes. Infusions are started at 1 to 2 mg/h and doubled every 90 seconds until blood pressure approaches target range. Usual doses are 4 to 8 mg/h. The maximum allowable dose is 21 mg/h.
   2. Nicardipine is another short-acting antihypertensive administered in IV infusion perioperatively. Infusions are started at 5 mg/h, increased by 2.5 mg/h every 5 to 15 min until target blood pressure is reached, up to a maximum dose of 15 mg/h. Onset is within minutes. After cessation, effects may last up to 8 hours.
   3. Nifedipine is limited to oral administration for the treatment of hypertension, including hypertension associated with pregnancy, at daily doses of 30 to 90 mg.
   4. Nimodipine is an oral CCB approved for the prevention of vasospasm in subarachnoid hemorrhage at a dose of 60 mg q4h. Dose reductions are required in hepatic insufficiency.
   5. Amlodipine is a common oral antihypertensive at daily doses of 5 to 10 mg.
2. Non-DHP CCBs are more selective for myocardial and pacemaker L-type calcium channels and are termed cardioselective. Verapamil and diltiazem are the two non-DHP CCBs in clinical use.
   1. Indications
      1. Antianginal therapy (by decreasing myocardial oxygen consumption and coronary vasospasm)
      2. Rate control (by depressing AV nodal conduction)
      3. Conversion of hemodynamically stable SVTs (by prolonging AV nodal repolarization, blocking reentry)
      4. Hypertension (by effecting vascular smooth muscle L-type calcium channels)
   2. Contraindications to CCBs are similar to those of β-blockers. CCBs are not appropriate antiarrhythmics for patients with WPW syndrome in atrial fibrillation/flutter, as they may allow for preferential conduction through the accessory pathway.
   3. Verapamil is initially dosed 2.5 to 5 mg IV over 2 minutes, with subsequent doses of 5 to 10 mg IV every 15 to 30 minutes.
   4. Diltiazem is initially dosed 10 to 20 mg IV over 2 minutes, which can be redosed up to 0.35 mg/kg after 15 minutes if needed. An infusion of 5 to 15 mg/h can be initiated in responders.