Verapamil
Mechanism :
Verapamil is a calcium ion influx inhibitor (slow-channel blocker or calcium ion antagonist) that exerts its pharmacologic effects by modulating the influx of ionic calcium across the cell membrane of the arterial smooth muscle as well as in conductile and contractile myocardial cells.
Indication :
- Supraventricular tachycardia
Contraindications :
Contraindicated in severe left ventricular dysfunction, hypotension (systolic pressure less than 90 mm Hg) or cardiogenic shock, sick sinus syndrome (except in patients with a functioning artificial ventricular pacemaker), second- or third-degree AV block (except in patients with a functioning artificial ventricular pacemaker), in patients with atrial flutter or atrial fibrillation and an accessory bypass tract (e.g., Wolff-Parkinson-White) and in patients with known hypersensitivity to verapamil hydrochloride.
Dosing :
PSVT conversion:
1-15 years: 0.1-0.3 mg/kg IV over 2 mins. (Maximum: 5 mg/first dose). May give second dose up to 10 mg in 30 min.
Adverse Effect :
Constipation, dyspnea, dizziness, bradycardia, nausea, hypotension, headache, gingival hyperplasia, edema, CHF, pulmonary edema, flushing, fatigue, and elevated liver enzymes have been reported.
Interaction :
Digoxin: Enhanced effect of digoxin (AV block and bradycardia).
Beta-blockers, Anti-Arrhythmic Agents or Inhaled Anesthetics: In combination with verapamil may lead to additive cardiovascular effects (e.g. AV block, bradycardia, hypotension, heart failure).
Class 1 Antiarrhythmics (e.g. flecainide): In combination with verapamil may result in profound cardiac depression and requires expert supervision.
Amiodarone: May result in bradycardia, AV block and myocardial depression.
Carbamazepine, Cyclosporin or Theophylline: Has resulted in increased serum levels of these medications which could lead to increased side-effects.
Phenytoin and Phenobarbital: Reduce the effect of verapamil.
Cimetidine: Can cause an increase in the verapamil serum level.
Neuromuscular Blocking Agents: Employed in anaesthesia may be potentiated by verapamil.
Renal Dose :
Dose in Renal Impairment GFR (mL/min)
| 20-50 | Dose as in normal renal function. Monitor carefully |
| 10-20 | Dose as in normal renal function. Monitor carefully |
| <10 | Dose as in normal renal function. Monitor carefully |
Dose in Patients undergoing Renal Replacement Therapies
| CAPD | Not dialysed. Dose as in GFR<10 mL/min |
| HD | Not dialysed. Dose as in GFR<10 mL/min |
| HDF/High flux | Unknown dialysability. Dose as in GFR<10 mL/min |
| CAV/VVHD | Dialysability minimal. Dose as in GFR=10–20 mL/min |
Hepatic Dose :
Oral Preparation: If patient has cirrhosis, reduce dose to 1/5th – 1/3rd of normal and monitor patient’s ECG.
Injection preparation: If patient has cirrhosis, reduce dose to 1/2 and monitor ECG. In severe failure, avoid repeated injections and monitor patient’s vital parameters.
Monitor liver function as well, as the drug can cause raised aminotransferase levels.