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Included in the listing that follows are adverse reactions that have not been reported with this specific drug; however, the pharmacologic similarities among the sulfonamides require that each of the reactions be considered with Gantanol (sulfamethoxazole) administration.

Hematologic: Agranulocytosis, aplastic anemia, thrombocytopenia, leukopenia, hemolytic anemia, purpura, hypoprothrombinemia, methemoglobinemia, neutropenia, eosinophilia.

Allergic Reactions: Anaphylaxis, allergic myocarditis, serum sickness, conjunctival and scleral injection, generalized allergic reactions. In addition, periarteritis nodosa and systemic lupus erythematosus have been reported.

Dermatologic: Stevens-Johnson syndrome, epidermal necrolysis, erythema multiforme, exfoliative dermatitis, photosensitivity, pruritus, urticaria, rash, generalized skin eruptions.

Gastrointestinal: Hepatitis, hepatocellular necrosis, pseudomembranous enterocolitis, pancreatitis, stomatitis, glossitis, nausea, emesis, abdominal pain, diarrhea, anorexia.

Genitourinary:Creatinine elevation, toxic nephrosis with oliguria and anuria. The frequency of renal complications is considerably lower in patients receiving the more soluble sulfonamides.

Neurologic: Convulsions, peripheral neuritis, ataxia, vertigo, tinnitus, headache.

Psychiatric: Hallucinations, depression, apathy.

Endocrine: The sulfonamides bear certain chemical similarities to some goitrogens, diuretics (acetazolamide and the thiazides) and oral hypoglycemic agents. Cross-sensitivity may exist with these agents. Diuresis and hypoglycemia have occurred rarely in patients receiving sulfonamides.

Musculoskeletal: Arthralgia, myalgia.

Respiratory: Pulmonary infiltrates.

Miscellaneous: Edema (including periorbital), pyrexia, chills, weakness, fatigue, insomnia.

In elderly patients concurrently receiving certain diuretics, primarily thiazides, an increased incidence of thrombopenia with purpura has been reported.

It has been reported that sulfamethoxazole may prolong the prothrombin time in patients who are receiving the anticoagulant warfarin. This interaction should be kept in mind when Gantanol (sulfamethoxazole) is given to patients already on anticoagulant therapy, and the coagulation time should be reassessed.

Sulfamethoxazole may inhibit the hepatic metabolism of phenytoin. At a 1.6-g dose, sulfamethoxazole produced a slight but significant increase in the half-life of phenytoin but did not produce a corresponding decrease in the metabolic clearance rate. When administering these drugs concurrently, one should be alert for possible excessive phenytoin effect.

Sulfonamides can also displace methotrexate from plasma protein-binding sites, thus increasing free methotrexate concentrations.

The presence of sulfamethoxazole may interfere with the Jaffe alkaline picrate reaction assay for creatinine, resulting in overestimations of about 10% in the range of normal values.

Last reviewed on RxList: 12/8/2004
This monograph has been modified to include the generic and brand name in many instances.