>10%:

Central nervous system: Headache (33%)

Dermatologic: Photosensitivity

Gastrointestinal: Anorexia, nausea, vomiting, diarrhea (33%), gastric distress

Genitourinary: Reversible oligospermia (33%)

<3%:

Dermatologic: Urticaria/pruritus (<3%)

Hematologic: Hemolytic anemia (<3%), Heinz body anemia (<3%)

<0.1%: Alopecia, anaphylaxis, aplastic anemia, ataxia, convulsions, crystalluria, depression, drowsiness, epidermal necrolysis, exfoliative dermatitis, granulocytopenia, hallucinations, hearing loss, hematuria, hepatitis, insomnia, interstitial nephritis, jaundice, leukopenia, Lyell's syndrome, myelodysplastic syndrome, nephropathy (acute), neutropenic enterocolitis, pancreatitis, peripheral neuropathy, photosensitization, rhabdomyolysis, serum sickness-like reactions, skin discoloration, Stevens-Johnson syndrome, thrombocytopenia, thyroid function disturbance, tinnitus, urine discoloration, vasculitis, vertigo

Additional events reported with sulfonamides and/or 5-ASA derivatives: Cholestatic jaundice, eosinophilia pneumonitis, erythema multiforme, fibrosing alveolitis, hepatic necrosis, Kawasaki-like syndrome, SLE-like syndrome, pericarditis, seizure, transverse myelitis

Azathioprine, mercaptopurine, sulfasalazine: May increase the risk of myelosuppression (due to TPMT inhibition).

Cyclosporine concentrations may be decreased; monitor levels and renal function

Digoxin's absorption may be decreased

Folic acid's absorption may be decreased

Hydantoin levels may be increased; monitor levels and adjust as necessary

Hypoglycemics: Increased effect of oral hypoglycemics (rare, but severe); monitor blood sugar

Methenamine: Combination may result in crystalluria; avoid use

Methotrexate-induced bone marrow suppression may be increased

NSAIDs and salicylates: May increase sulfonamide concentrations

PABA (para-aminobenzoic acid - may be found in some vitamin supplements): Interferes with the antibacterial activity of sulfonamides; avoid concurrent use

Sulfinpyrazone: May increase sulfonamide concentrations

Thiazide diuretics: May increase the incidence of thrombocytopenia purpura

Thiopental's effect may be enhanced; monitor for possible dosage reduction

Uricosuric agents: Actions of these agents are potentiated

Warfarin and other oral anticoagulants: Anticoagulant effect may be increased; decrease dose and monitor INR closely

Food: May impair folate absorption.

Herb/Nutraceutical: Avoid dong quai, St John's wort (may also cause photosensitization)

Absorption: 10% to 15% as unchanged drug from small intestine

Distribution: Small amounts enter feces and breast milk

Metabolism: Via colonic intestinal flora to sulfapyridine and 5-aminosalicylic acid (5-ASA); following absorption, sulfapyridine undergoes N-acetylation and ring hydroxylation while 5-ASA undergoes N-acetylation

Half-life elimination: 5.7-10 hours

Excretion: Primarily urine (as unchanged drug, components, and acetylated metabolites)

Children 2 years: Ulcerative colitis: Initial: 40-60 mg/kg/day in 3-6 divided doses; maintenance dose: 20-30 mg/kg/day in 4 divided doses

Children 6 years: Juvenile rheumatoid arthritis: Enteric coated tablet: 30-50 mg/kg/day in 2 divided doses; Initial: Begin with ¹/4 to ¹/3 of expected maintenance dose; increase weekly; maximum: 2 g/day typically

Adults:

Ulcerative colitis: Initial: 1 g 3-4 times/day, 2 g/day maintenance in divided doses; may initiate therapy with 0.5-1 g/day

Rheumatoid arthritis: Enteric coated tablet: Initial: 0.5-1 g/day; increase weekly to maintenance dose of 2 g/day in 2 divided doses; maximum: 3 g/day (if response to 2 g/day is inadequate after 12 weeks of treatment)

Dosing interval in renal impairment:

Clcr 10-30 mL/minute: Administer twice daily

Clcr<10 mL/minute: Administer once daily

Dosing adjustment in hepatic impairment: Avoid use

Tablet (Azulfidine®): 500 mg

Tablet, delayed release, enteric coated (Azulfidine® EN-tabs®): 500 mg

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