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Pronunciation: sull-fih-SOX-uh-zole
Class: Sulfonamide

Trade Names:
Gantrisin Pediatric
- Suspension 500 mg per 5 mL


Exerts bacteriostatic action by competing with PABA, an essential component in folic acid synthesis, thus preventing synthesis of folic acid, needed by bacteria for growth.



Sulfisoxazole is rapidly and completely absorbed. The major site of absorption is the small intestine, but some drug is absorbed from the stomach. Steady-state plasma concentrations are about 49 to 89 mcg/mL. C max is approximately 169 mcg/mL.


Sulfisoxazole is approximately 85% bound to plasma proteins and is only distributed in extracellular body fluids. The drug readily crosses the placental barrier and enters into fetal circulation. Sulfisoxazole crosses the blood-brain barrier.


N 1 -acetyl sulfisoxazole is metabolized to sulfisoxazole and is absorbed as sulfisoxazole.


Sulfisoxazole is excreted primarily by the kidneys through glomerular filtration. Drug concentrations are higher in urine than in blood. Sulfisoxazole t ½ is 4.6 to 7.8 h after oral administration.

Special Populations


Elimination has been shown to be slower in the elderly (63 to 75 years of age) with diminished renal function (CrCl 37 to 68 mL/min).

Indications and Usage


Treatment of UTI, chancroid, inclusion conjunctivitis, malaria, meningitis caused by Haemophilus influenzae or meningococci, nocardiosis, acute otitis media, toxoplasmosis, and trachoma.


Treatment of conjunctivitis, corneal ulcer, and superficial ocular infections, adjunct to systemic sulfonamide therapy of trachoma.

Unlabeled Uses


Treatment of recurrent otitis media.


Hypersensitivity to sulfonamides or chemically related drugs (eg, sulfonylureas, thiazide and loop diuretics, carbonic anhydrase inhibitors, sunscreens containing PABA, local anesthetics); hypersensitivity to salicylates; porphyria; children younger than 2 mo of age; pregnancy at term.

Dosage and Administration


PO 2 to 4 g initially, then 4 to 8 g/day in 4 to 6 divided doses. Ophthalmic Instill 1 to 2 drops into lower conjunctival sac every 1 to 3 h daily.

Children and Infants older than 2 mo of age

PO 75 mg/kg initially, then 120 to 150 mg/kg/day in 4 to 6 divided doses (max, 6 g/day).


Store oral suspension in refrigerator. Store at room temperature and protect from light.

Drug Interactions

Anticoagulants, oral

May enhance anticoagulant action.


Reduced concentration of cyclosporine and reduced efficacy; may have additive nephrotoxicity.


May increase hydantoin serum levels.


May enhance risk of methotrexate-induced bone marrow suppression.


May increase sulfonylurea half-life and produce hypoglycemia.

Laboratory Test Interactions

May produce false-positive urinary glucose test results when performed by Benedict method; may interfere with Urobilistix test; may produce false-positive results with sulfosalicylic acid tests for urinary protein.

Adverse Reactions


Headache; peripheral neuropathy; depression; convulsions; dizziness; ataxia.


Nausea; vomiting; abdominal pain; diarrhea; anorexia; pancreatitis; impaired folic acid absorption; pseudomembranous enterocolitis.


Crystalluria; hematuria; proteinuria; elevated creatinine; nephrotic syndrome; toxic nephrosis with oliguria and anuria.


Agranulocytosis; aplastic anemia; thrombocytopenia; leukopenia; hemolytic anemia; purpura; hypoprothrombinemia; anemia; methemoglobinemia; megaloblastic (macrocytic) anemia.


Hepatitis; hepatocellular necrosis.


Browache; local irritation; transient epithelial keratitis; reactive hyperemia; conjunctival edema; burning; stinging; sensitivity to bright light.


Pulmonary infiltrates.


Drug fever; chills; pyrexia; arthralgia; myalgia; periarteritis nodosum; lupus erythematosus phenomenon. Hypersensitivity reactions may present as erythema multiforme of Stevens-Johnson type, generalized skin eruptions, allergic myocarditis, epidermal necrolysis with or without corneal damage, urticaria, serum sickness; pruritus, exfoliative dermatitis, anaphylactoid reactions, periorbital edema, photosensitization, arthralgia, and transient pulmonary changes with eosinophilia and decreased pulmonary function.



Category C . Sulfonamides cross placenta and can produce jaundice, hemolytic anemia, and kernicterus in newborn; therefore, they are contraindicated at term.


Excreted in breast milk in low concentrations. Do not nurse premature infants or those with hyperbilirubinemia or G-6-PD deficiency.


Contraindicated in infants younger than 2 mo of age.

Renal Function

Use drug with caution.

Hepatic Function

Use drug with caution.


Photosensitization may occur.

Allergy or asthma

Use drug with caution in patients with severe allergy or bronchial asthma.

Dry eye (ophthalmic)

Use with caution in patients with severe dry eye.

Group A beta-hemolytic streptococcal infections

Do not use drug for these infections.

Hemolytic anemia

May occur in G-6-PD-deficient individuals.


Drug may precipitate acute attack of porphyria.

Severe reactions

Reactions, including deaths, have been associated with hypersensitivity reactions, agranulocytosis, aplastic anemia, other blood dyscrasias, and renal and hepatic damage. Irreversible neuromuscular and CNS changes and fibrosing alveolitis may occur.


Have chemical similarities to some goitrogens, diuretics (acetazolamide and the thiazides), and oral hypoglycemic agents. Goiter production, diuresis, and hypoglycemia have occurred rarely in patients receiving sulfonamides. Cross-sensitivity may exist.



Anorexia, nausea, vomiting, abdominal cramping, dizziness, headache, drowsiness, coma.

Patient Information

  • Oral
  • Advise patient to administer medication around the clock.
  • Advise patient to notify other health care providers/dentists of this drug therapy prior to other treatments or surgery.
  • Instruct patient to report these symptoms to health care provider immediately: difficulty breathing, skin rash, fever, chills, mouth sores, sore throat, ringing in ears or unusual bleeding/bruising.
  • Caution patient to avoid exposure to sunlight and to use sunscreen or wear protective clothing to avoid photosensitivity reaction. Inform patient that photosensitivity may persist for several months after therapy is completed.
  • Advise patient not to take OTC medications without consulting health care provider.
  • Ophthalmic
  • Instruct patient/family in correct instillation of drops. Inform patient that stinging, burning, and blurred vision may occur after instillation of ophthalmic preparations. Advise patient to avoid hazardous activities until vision clears. Emphasize need for patient to contact health care provider immediately if patient notices a change in vision, eye pain, increased redness, itching, swelling, loss of sight, inability to breath, or flushing after ophthalmic application of this medication.
  • Advise patient to note color change or precipitate in container and to discard if these are present.
  • Tell patient to notify health care provider if improvement is not noted within 7 days.

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