Procainamide

What it is used for

Procainamide hydrochloride injection is indicated for the treatment of documented ventricular arrhythmias, such as sustained ventricular tachycardia, that, in the judgement of the physician, are life-threatening. Because of the proarrhythmic effects of procainamide, its use with lesser arrhythmias is generally not recommended. Treatment of patients with asymptomatic ventricular premature contractions should be avoided.

Initiation of procainamide treatment, as with other antiarrhythmic agents used to treat life-threatening arrhythmias, should be carried out in the hospital.

Antiarrhythmic drugs have not been shown to enhance survival in patients with ventricular arrhythmias.

Because procainamide has the potential to produce serious hematological disorders (0.5 percent) particularly leukopenia or agranulocytosis (sometimes fatal), its use should be reserved for patients in whom, in the opinion of the physician, the benefits of treatment clearly outweigh the risks. (see WARNINGS and Boxed Warning.)

How to take it

Procainamide Hydrochloride Injection is useful for arrhythmias which require immediate suppression and for maintenance of arrhythmia control. Intravenous therapy allows most rapid control of serious arrhythmias, including those following myocardial infarction; it should be carried out in circumstances where close observation and monitoring of the patient are possible, such as in hospital or emergency facilities. Intramuscular administration is less apt to produce temporary high plasma levels but therapeutic plasma levels are not obtained as rapidly as with intravenous administration. Oral procainamide dosage forms are preferable for less urgent arrhythmias as well as for long-term maintenance after initial parenteral PA therapy. Intramuscular administration may be used as an alternative to the oral route for patients with less threatening arrhythmias but who are nauseated or vomiting, who are ordered to receive nothing by mouth preoperatively, or who may have malabsorptive problems. An initial daily dose of 50 mg per kg body weight may be estimated. This amount should be divided into fractional doses of one-eighth to one-quarter to be injected intramuscularly every three to six hours until oral therapy is possible. If more than three injections are given, the physician may wish to assess patient factors such as age and renal function (see below), clinical response and, if available, blood levels of PA and NAPA in adjusting further doses for that individual. For treatment of arrhythmias associated with anesthesia or surgical operation, the suggested dose is 100 to 500 mg by intramuscular injection. Intravenous administration of Procainamide Hydrochloride Injection should be done cautiously to avoid a possible hypotensive response (see PRECAUTIONS and OVERDOSAGE ). Initial arrhythmia control, under ECG monitoring, may usually be accomplished safely within a half-hour by either of the two methods which follows:

• Direct injection into a vein or into tubing of an established infusion line should be done slowly at a rate not to exceed 50 mg per minute. It is advisable to dilute either the 100 mg/mL or the 500 mg/mL concentrations of procainamide hydrochloride prior to intravenous injection to facilitate control of dosage rate. Doses of 100 mg may be administered every 5 minutes at this rate until the arrhythmia is suppressed or until 500 mg has been administered, after which it is advisable to wait 10 minutes or longer to allow for more distribution into tissues before resuming.
• Alternatively, a loading infusion containing 20 mg of Procainamide Hydrochloride per mL (1 g diluted to 50 mL with 5% Dextrose Injection, USP) may be administered at a constant rate of 1 mL per minute for 25 to 30 minutes to deliver 500 to 600 mg of PA. Some effects may be seen after infusion of the first 100 or 200 mg; it is unusual to require more than 600 mg to achieve satisfactory antiarrhythmic effects. The maximum advisable dosage to be given either by repeated bolus injections or such loading infusion is 1 g.

To maintain therapeutic levels, a more dilute intravenous infusion at a concentration of 2 mg/mL is convenient (1000 mg procainamide HCl in 500 mL of 5% Dextrose Injection, USP), and may be administered at 1 to 3 mL/minute. If daily total fluid intake must be limited, a 4 mg/mL concentration (1 g of Procainamide Hydrochloride Injection in 250 mL of 5% Dextrose Injection, USP) administered at 0.5 to 1.5 mL/minute will deliver an equivalent 2 to 6 mg per minute. The amount needed in a given patient to maintain the therapeutic level should be assessed principally from the clinical response, and will depend upon the patient's weight and age, renal elimination, hepatic acetylation rate, and cardiac status, but should be adjusted for each patient based upon close observation. A maintenance infusion rate of 50 mcg/min/kg body weight to a person with a normal renal PA elimination half-time of three hours may be expected to produce a plasma level of approximately 6.5 mcg/mL.

Since the principal route for elimination of PA and NAPA is renal excretion, reduced excretion will prolong the half-life of elimination and lower the dose rate needed to maintain therapeutic levels. Advancing age reduces the renal excretion of PA and NAPA independently of reductions in creatinine clearance; compared to normal young adults, there is approximately 25 percent reduction at age 50 and 50 percent at age 75.

Intravenous therapy should be terminated if persistent conduction disturbances or hypotension develop. As soon as the patient's basic cardiac rhythm appears to be stabilized, oral antiarrhythmic maintenance therapy is preferable, if indicated and possible. A period of about three to four hours (one half-time for renal elimination, ordinarily) should elapse after the last intravenous dose before administering the first dose of Procainamide Hydrochloride tablets or capsules.

DILUTIONS AND RATES FOR INTRAVENOUS INFUSIONS* Procainamide Hydrochloride Injection, USP

Parenteral drug products should be examined visually for particulate matter and discoloration ( see HOW SUPPLIED ) prior to administration.

Side effects, and when to stop

Cardiovascular System: Hypotension and serious disturbances of cardiorhythm such as ventricular asystole or fibrillation are more common with intravenous administration of PA than with intramuscular administration. Because PA is a peripheral vasodilator in concentrations higher than the usual therapeutic range, transient high plasma levels which may occur especially during intravenous administration may produce temporary but at times severe lowering of blood pressure (see OVERDOSAGE and PRECAUTIONS ).

Multisystem: A lupus erythematosus-like syndrome of arthralgia, pleural or abdominal pain, and sometimes arthritis, pleural effusion, pericarditis, fever, chills, myalgia, and possibly related hematologic or skin lesions (see below) is fairly common after prolonged PA administration, perhaps more often in patients who are slow acetylators (See Boxed Warning and PRECAUTIONS ). While some series have reported less than 1 in 500, others have reported the syndrome in up to 30 percent of patients on long term oral PA therapy. If discontinuation of PA does not reverse the lupoid symptoms, corticosteroid treatment may be effective.

Hematologic: Neutropenia, thrombocytopenia, or hemolytic anemia may rarely be encountered. Agranulocytosis has occurred after repeated use of PA, and deaths have been reported. (See Boxed Warning, WARNINGS section.)

Skin: Angioneurotic edema, urticaria, pruritus, flushing, and maculopapular rash have also occurred.

Gastrointestinal System: Anorexia, nausea, vomiting, abdominal pain, diarrhea or bitter taste may occur in 3 to 4 percent of patients taking oral procainamide.

Nervous System: Dizziness or giddiness, weakness, mental depression and psychosis with hallucinations have been reported.

Elevated Liver Enzymes: Elevations of transaminase with and without elevations of alkaline phosphatase and bilirubin have been reported. Some patients have had clinical symptoms (e.g., malaise, right upper quadrant pain). Deaths from liver failure have been reported.

Other medicines and interactions

If other antiarrhythmic drugs are being used, additive effects on the heart may occur with PA administration, and dosage reduction may be necessary (see WARNINGS ).

Anticholinergic drugs administered concurrently with PA may produce additive antivagal effects on A-V nodal conduction, although this is not as well documented for PA as for quinidine.

Patients taking PA who require neuromuscular blocking agents such as succinylcholine may require less than usual doses of the latter, due to PA effects on reducing acetylcholine release.

General

Immediately after initiation of PA therapy, patients should be closely observed for possible hypersensitivity reactions. In conversion of atrial fibrillation to normal sinus rhythm by any means, dislodgement of mural thrombi may lead to embolization, which should be kept in mind. After achieving and maintaining therapeutic plasma concentrations and satisfactory electrocardiographic and clinical responses, continued frequent periodic monitoring of vital signs and electrocardiograms is advised. If evidence of QRS widening of more than 25 percent or marked prolongation of the Q-T interval occurs, concern for overdosage is appropriate, and interruption of the PA infusion is advisable if a 50 percent increase occurs. Elevated serum creatinine or urea nitrogen, reduced creatinine clearance or history of renal insufficiency, as well as use in older patients (over age 50), provide grounds to anticipate that less than the usual dosage or infusion rate may suffice, since the urinary elimination of PA and NAPA may be reduced, leading to gradual accumulation beyond normally- predicted amounts. If facilities are available for measurement of plasma PA and NAPA, or acetylation capability, individual dose adjustment for optimal therapeutic levels may be easier, but close observation of clinical effectiveness is the most important criterion.