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SULFONAMIDES, INCLUDING SULFISOXAZOLE, SHOULD BE DISCONTINUED AT THE FIRST APPEARANCE OF SKIN RASH OR ANY SIGN OF AN ADVERSE REACTION. In rare instances, a skin rash may be followed by more severe reactions such as Stevens-Johnson syndrome, toxic epidermal necrolysis, hepatic necrosis and serious blood disorders (see PRECAUTIONS).

Clinical signs such as rash, sore throat, fever, arthralgia, pallor, purpura or jaundice may be early indications of serious reactions.

Cough, shortness of breath and pulmonary infiltrates are hypersensitivity reactions of the respiratory tract that have been reported in association with sulfonamide treatment.

The sulfonamides should not be used for the treatment of group A beta-hemolytic streptococcal infections. In an established infection, they will not eradicate the streptococcus and, therefore, will not prevent sequelae such as rheumatic fever.

Pseudomembranous colitis has been reported with nearly all antibacterial agents, including sulfisoxazole, and may range in severity from mild to life-threatening. Therefore, it is important to consider this diagnosis in patients who present with diarrhea subsequent to the administration of antibacterial agents.

Treatment with antibacterial agents alters the normal flora of the colon and may permit overgrowth of clostridia. Studies indicate that toxin produced by Clostridium difficile is one primary cause of “antibiotic-associated colitis.”

After the diagnosis of pseudomembranous colitis has been established, therapeutic measures should be initiated. Mild cases of pseudomembranous colitis usually respond to drug discontinuation alone. In moderate to severe cases, consideration should be given to management with fluids and electrolytes, protein supplementation, and treatment with an antibacterial drug clinically effective against C. difficile colitis.


General: Sulfonamides should be given with caution to patients with impaired renal or hepatic function and to those with severe allergy or bronchial asthma. In glucose-6-phosphate dehydrogenase-deficient individuals, hemolysis may occur; this reaction is frequently dose-related.

The frequency of resistant organisms limits the usefulness of antibacterial agents, including the sulfonamides, as sole therapy in the treatment of urinary tract infections. Since sulfonamides are bacteriostatic and not bactericidal, a complete course of therapy is needed to prevent immediate regrowth and the development of resistant uropathogens.

Laboratory Tests: Complete blood counts should be done frequently in patients receiving sulfonamides. If a significant reduction in the count of any formed blood element is noted, sulfonamide therapy should be discontinued. Urinalyses with careful microscopic examination and renal function tests should be performed during therapy, particularly for those patients with impaired renal function. Blood levels should be measured in patients receiving a sulfonamide for serious infections (see INDICATIONS AND USAGE).

Carcinogenesis, Mutagenesis and Impairment of Fertility

Carcinogenesis: Sulfisoxazole was not carcinogenic to mice in either sex when administered by gavage for 103 weeks at dosages up to approximately 18 times the highest recommended human daily dose or to rats at 4 times the highest recommended human daily dose. Rats appear to be especially susceptible to the goitrogenic effects of sulfonamides and long-term administration of sulfonamides has resulted in thyroid malignancies in this species.

Mutagenesis: There are no studies available that adequately evaluate the mutagenic potential of Gantrisin (acetyl sulfisoxazole pediatric suspension) . Ames mutagenic assays have not been performed with sulfisoxazole. However, sulfisoxazole was not observed to be mutagenic in E. coli Sd-4-73 when tested in the absence of a metabolic activating system.

Impairment of Fertility: Gantrisin (acetyl sulfisoxazole pediatric suspension) has not undergone adequate trials relating to impairment of fertility. In a reproduction study in rats given 7 times the highest recommended human dose per day of sulfisoxazole, no effects were observed regarding mating behavior, conception rate or fertility index (percent pregnant).


Teratogenic Effects: Pregnancy Category C. At dosages 7 times the highest recommended human daily dose, sulfisoxazole was not teratogenic in either rats or rabbits. However, in two other teratogenicity studies, cleft palates developed in both rats and mice, and skeletal defects were also observed in rats after administration of 9 times the highest recommended human daily dose of sulfisoxazole.

There are no adequate and well-controlled studies of Gantrisin (acetyl sulfisoxazole pediatric suspension) in pregnant women. It is not known whether Gantrisin (acetyl sulfisoxazole pediatric suspension) can cause fetal harm when administered to a pregnant woman prior to term or can affect reproduction capacity. Gantrisin (acetyl sulfisoxazole pediatric suspension) should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Nonteratogenic Effects: Kernicterus may occur in the newborn as a result of treatment of a pregnant woman at term with sulfonamides (see CONTRAINDICATIONS).

Nursing Mothers

Gantrisin (acetyl sulfisoxazole pediatric suspension) is excreted in human milk. Because of the potential for the development of kernicterus in neonates due to the displacement of bilirubin from plasma proteins by sulfisoxazole, a decision should be made whether to discontinue nursing or discontinue the drug taking into account the importance of the drug to the mother (see CONTRAINDICATIONS).

Pediatric Use

Gantrisin (acetyl sulfisoxazole pediatric suspension) is not recommended for use in infants less than 2 months of age except in the treatment of congenital toxoplasmosis as adjunctive therapy with pyrimethamine (see CONTRAINDICATIONS).

This monograph has been modified to include the generic and brand name in many instances.

Last reviewed on RxList: 9/16/2008


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