Cardiovascular System: Hypotension following oral PA administration is rare. Hypotension and serious disturbances of cardiorhythm such as ventricular asystole or fibrillation are more common after intravenous administration (see OVERDOSAGE, WARNINGS). Second degree heart block has been reported in 2 of almost 500 patients taking PA orally.

Multisystem Effects: 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

DESCRIPTION

: 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 System: Neutropenia, thrombocytopenia, or hemolytic anemia may rarely be encountered. Agranulocytosis has occurred after repeated use of PA, and deaths have been reported. (see WARNINGS and

DESCRIPTION

: Boxed Warning).

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

Gastrointestinal System: Anorexia, nausea, vomiting, abdominal pain, bitter taste, or diarrhea may occur in 3 to 4 percent of patients taking oral procainamide. Hepatomegaly with increased serum aminotransferase activity have been reported after a single oral dose.

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

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.