procainamide hydrochloride

Action

Decreases myocardial excitability by inhibiting conduction velocity. Also depresses myocardial contractility.

Availability

Injection: 100 mg/ml, 500 mg/ml

Indications and dosages

➣ Life-threatening ventricular arrhythmias

Adults: 100 mg by slow I.V. push at a rate of 50 mg/minute, repeated q 5 minutes until arrhythmia subsides, up to a maximum advisable dosage of 1 g. Alternatively, loading dose of 500 to 600 mg by I.V. infusion over 25 to 30 minutes. With either I.V. method, maximum loading dose is 1 g. When arrhythmia subsides, give continuous I.V. infusion of 2 to 6 mg/minute. Or 50 mg/kg I.M. in divided doses q 3 to 6 hours until patient can tolerate P.O. therapy.

Dosage adjustment

• Renal impairment

Contraindications

• Hypersensitivity to drug, tartrazine, procaine, or sulfites

• Complete heart block

• Torsades de pointes

• Lupus erythematosus

Precautions

Use cautiously in:

• procaine hypersensitivity, renal impairment, ischemic heart disease, heart failure, first-degree heart block, atypical ventricular tachycardia, myasthenia gravis, systemic lupus erythematosus, cytopenia

• patients receiving other antiarrhythmics concurrently

• pregnant or breastfeeding patients

• children.

Administration

See Ask patient about procaine sensitivity before giving; cross-sensitivity may occur.

• For I.V. use, dilute with dextrose 5% in water.

• Administer I.V. doses with patient in supine position to avoid hypotensive effects.

• When giving by I.V. infusion, use infusion pump to ensure that drug infuses at 50 mg/minute or less.

See Don't leave patient's bedside during I.V. administration.

Adverse reactions

CNS: headache, dizziness, confusion, psychosis, restlessness, asthenia, depression, neuropathy, seizures

CV: hypotension, bradycardia, atrioventricular block, ventricular fibrillation, ventricular asystole, cardiovascular collapse, cardiac arrest

GI: nausea, vomiting, diarrhea, anorexia Hematologic: hemolytic anemia, agranulocytosis, thrombocytopenia, neutropenia

Skin: rash, urticaria, pruritus, flushing

Other: bitter taste, lupuslike syndrome, edema

Interactions

Drug-drug. Amiodarone: increased procainamide blood level and risk of toxicity Anticholinesterase drugs: decreased anticholinesterase effects

Antihypertensives: additive hypotension

Beta-adrenergic blockers, cimetidine, ranitidine, trimethoprim: increased procainamide blood level

Lidocaine: additive cardiodepressant action, conduction abnormalities

Neuromuscular blockers: increased skeletal muscle relaxation

Other antiarrhythmics: additive or antagonistic effects, additive toxicity

Trimethoprim: increased pharmacologic effect of procainamide

Drug-herbs. Henbane: increased anticholinergic activity

Jimsonweed: adverse cardiovascular effects

Licorice: prolonged QT interval

Drug-behaviors. Alcohol use: altered drug blood level

Patient monitoring

See When giving I.V., stay at patient's bedside and monitor blood pressure and ECG continuously.

See If ECG shows prolonged QT interval and QRS complexes, heart block, or worsening arrhythmia, stop drug therapy, run rhythm strip, and contact prescriber immediately.

• Assess blood levels of procainamide and N-acetylprocainamide (drug's active metabolite).

See Monitor electrolyte levels, CBC, and antinuclear antibody titers. Watch for signs and symptoms of blood dyscrasias.

• Evaluate patient for signs and symptoms of lupuslike syndrome.

Patient teaching

See Advise patient to immediately report cardiovascular symptoms or bleeding tendency.

• Emphasize importance of taking exactly as prescribed. Advise patient to use alarm clock to help him remember to take nighttime doses.

• Advise patient to avoid alcohol.

• Instruct patient not to take herbal remedies unless prescriber approves.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, herbs, and behaviors mentioned above.