VERAPAMIL

“Isoptin”

1) Action

• Calcium channel blocker

• Class IV antiarrhythmic

2) Mechanism

• Inhibits voltage activated inward displacement of calcium & reduce the amount of calcium available intracellularly

• Effect is more marked in tissues that fire frequently ie cardiac A-V & SA nodes, but also vasodilates

• Prolongs AV nodal conduction & effective refractory periods

• Slows SA node

• See reduction in afterload, increased coronary blood flow, negative inotropic activity, reduction in myocardial oxygen consumption

• Coronary vasospasm is often reduced

3) Indications

• Treatment & prophylaxis of supraventricular tachyarrhythmias eg atrial flutter, rapid ventricular response, extrasystoles

• May convert atrial fib into SR

• Not so effective against ventricular arrhythmias

• [is fast replacing previous treatments: beta-blockers, digoxin, cardioversion]

• Hypertension

4) Effects on organs—side effects

• Peripheral vasodilation

5) Toxic effects/ precautions with administration

• In high doses can lead to AV block leading to asystole and hypotension

• Not to be used in conjunction with beta-blockers

6) Contraindications

• Cardiogenic shock, recent MI, AV blocks, LBBB, hypotension, bradycardia

7) Reversal, antagonism or antidote

• Heart block: atropine, isoprenaline, pacing

• Cardiac failure: dobutamine, dopamine, calcium

• Hypotension: dobutamine, dopamine, adrenaline

8) Loading dose, maintenance dose, frequency & method of administration

• 5 mg/ml ampoules [2 ml]; 80 & 120 mg tablets

• IVI 5 mg continually observing patient; may be repeated after 5—10 min

• Infusion 5 — 10 mg/hr

9) Drug’s metabolism—Drug’s excretion—Half life (pharmacokinetics)

• Elimination half life: 5 hr

• % plasma protein bound: 90

• Metabolised in liver