Calcium Channel Blockers

Ca2+-channel blockers:

  • Have affinity for L-type calcium channels
    L-type channels exist in myocardium, nodal, and vascular smooth muscle.
    • Variable affinity for each causes a preference for either nodal and inotropic, or vascular effects
  • Prevent Ca2+ entry into cells in a use-dependent fashion
Class Chemical Structure Drugs
Class I Phenylalkylamines Verapamil
Class II Dihydropyridines Nifedipine, amlodipine, nimodipine
Class III Benzothiazepines Diltiazem

Comparison of Calcium Channel Blockers

Property Verapamil Amlodipine Diltiazem
Class Phenylalkylamine Dihydropyridine Benzothiazepine
Uses SVT, excluding AF with WPW HTN, Angina Angina, HTN, SVT, Raynauds, migraine, oesophageal dysmotility
Presentation 20-240mg tablet, PO solution, IV at 2.5mg.ml-1 Tablet Tablet
Isomerism Racemic preparation. The D-isomer also has some local anaesthetic activity
Route of Administration PO/IV PO PO
Dosing 80-160mg BD/TDS 2.5-10mg daily 30-120mg TDS
Absorption 20% bioavailability 60% bioavailability 40% bioavailability
Distribution 90% protein bound 90% protein bound, lipid insoluble. 80% protein bound
Metabolism Hepatic to active norverapamil Hepatic to inactive metabolites Hepatic to active metabolites
Elimination Renal elimination of active metabolites Renal of inactive metabolites Renal of active metabolites. t1/2 2-7 hours
CVS HR via ↓ SA and ↓ AV nodal conduction, ↓ inotropy, ↓ SVR, ↓ BP, arrhythmia including HB SVR, ↓ BP, with reflexive ↑ HR, ↑ inotropy, ↑ CO ↓ AV nodal conduction but typically stable HR, ↓ SVR, ↓ CVR, ↓ MVO2, ↑ CO
CNS ↓ Cerebral vascular resistance ↓ Cerebral vascular resistance with nimodipine
GIT ↓ LOS tone
Interactions Contraindicated with concurrent β-blocker use due to profound ↓ HR, ↓ inotropy Contraindicated with concurrent β-blocker use due to profound ↓ HR, ↓ inotropy

References

  1. Peck TE, Hill SA. Pharmacology for Anaesthesia and Intensive Care. 4th Ed. Cambridge University Press. 2014.
  2. Smith S, Scarth E, Sasada M. Drugs in Anaesthesia and Intensive Care. 4th Ed. Oxford University Press. 2011.
  3. Rang HP, Dale MM, Ritter JM, Flower RJ. Rang and Dale's Pharmacology. 6th Ed. Churchill Livingstone.
Last updated 2017-09-08

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