Repolarization Prolongers

Repolarization Prolongers

Mode of Action: The prolongation effect is mostly due to the blockade of K+ channels, although enhanced inward Na+ current also prolongs the action potentials increased inward current produces the QT prolongation. The cardiac block of K+ channels increases action potential duration and reduces normal automaticity.

i. Amiodarone (Cardarone, Aldarone, Amiodar)

Synthesis

Properties and uses: It is a white to cream-coloured crystalline powder, which is sparingly soluble in water, soluble in alcohol and chloroform. It is an iodinated benzofuran derivative, which is effective in maintaining rhythms in patients who has direct current shock for atrial fibrillation. It is also used as an antianginal agent.

Assay: Dissolve the sample in a mixture of 0.01 M hydrochloric acid and ethanol. Perform potentiometric titration using 0.1 M sodium hydroxide.

Storage: It should be stored in well-closed airtight containers and protected from light at a temperature not exceeding 30°C.

Dose: The usual dose is 400 mg alternating with 600 mg daily for 1 to 3 weeks orally.

Dosage forms: Amiodarone intravenous infusion B.P., Amiodarone tablets B.P.

ii. Bretylium tosylate

Synthesis

Properties and uses: It is a white crystalline powder and exhibits polymorphism. freely soluble in water, in ethanol, and in methanol. It is used as antiadrenergic, antiarrythmic, and antihypertensive agent.

Assay: Dissolve the sample in 1,4-dioxan and titrate with 0.025 M perchloric acid. Determine the end point potentiometrically.

Storage: It should be stored in well-closed airtight containers and protected from light. Dose: Administered by I.M. or by slow I.V. infusion of 5 to 10 mg/kg over 10 to 30 min. Dosage forms: Bretylium injection B.P.

iii. Acecainide

Synthesis

Uses: It is effective in suppressing a variety of treatment of ventricular arrhythmias.