Non-dihydropyridine CCB — strongest cardiac (AV-nodal) effect of the class. Used for AF rate control, certain SVTs, hypertension, and migraine prophylaxis. Strong CYP3A4 + P-glycoprotein inhibitor → major DDI source. Constipation (~25%).
Half-Life (t½)
PO: 5h, IV: 2.36h
Dosing Guidelines
PO: Typical 240 mg (Range: 80–480 mg)
Target Organ Systems
nervous
cardiovascular
digestive
Interactions
Simvastatin (major): CYP3A4 inhibition. Kantola 1998 (PMID:9728898): verapamil 240 mg/d × 2 d raised simvastatin AUC 4.6×, Cmax 2.6×, simvastatin acid AUC 2.8× (n=12 crossover). Limit simvastatin dose to 10 mg/d when co-administered with verapamil.
Buspirone (caution): CYP3A4 inhibition. Lamberg 1998 (PMID:9663178) verbatim: "Verapamil and diltiazem increased the area under the buspirone plasma concentration-time curve [AUC (0-infinity)] 3.4-fold (p < 0.001) and 5.5-fold (p < 0.001), respectively". 9 healthy volunteers, randomized 3-phase crossover, verapamil 80 mg tid + 10 mg PO buspirone on d2. AUC 3.4×; Ki ≈ 0.5/2.4 = 0.208 µM. Cmax also 3.4× — substantial sedation amplification.
Midazolam (caution): CYP3A4 inhibition. Backman 1994 (PMID:8198928) verbatim: midazolam AUC "increased from 12 +/- 1 microgram ml-1 min ... to 35 +/- 5 micrograms ml-1 min by verapamil (P < 0.001)". 9 healthy volunteers, double-blind 3-phase crossover, verapamil 80 mg tid × 2d + 15 mg PO midazolam d2. AUC ratio 35/12 = 2.92×; Ki ≈ 0.5/1.92 = 0.260 µM. Cmax doubled, t½ prolonged, "profound and prolonged sedative effects" — dose reduction advised.