sulfamethoxazole (Gantanol)

Sulfamethoxazole is an anti- bacterial sulfonamide. It prevents the formation of dihydrofolic acid, a compound that bacteria must be able to make in order to survive. Although it was once a very useful antibiotic, it is almost obsolete as a single agent today due to the development of bacterial resistance to its effects. Sulfamethoxazole is now used primarily in combination with trimethoprim, a combination product known as Bactrim or Septra.

Sulfamethoxazole may be used to treat acute, recurrent or chronic urinary tract infections (primarily pyelonephritis, pyelitis and cystitis) due to susceptible organisms (usually E. coli, Klebsiella-Enterobacter, staphylococcus, Proteus mirabilis and, less frequently, Proteus vulgaris) in the absence of obstructive uropathy or foreign bodies.

Meningococcal meningitis prophylaxis when sulfonamide-sensitive group A strains are known to prevail in family groups or larger closed populations. (The prophylactic usefulness of sulfonamides when group B or C infections are prevalent has not been proven and in closed population groups may be harmful.)

Acute otitis media due to Haemophilus influenzae when used concomitantly with adequate doses of penicillin.

Trachoma. Inclusion conjunctivitis. Nocardiosis. Chancroid. Toxoplasmosis as adjunctive therapy with pyrimethamine. Malaria due to chloroquine-resistant strains of Plasmodium falciparum, when used as adjunctive therapy.

Sulfamethoxazole was approved by the FDA in 1961. According to the FDA database, all brand and generic formulations of sulfamethoxazole have been discontinued.

: Common side effects of sulfamethoxazole are:

• dizziness,
• headache,
• lethargy,
• diarrhea,
• anorexia,
• nausea,
• vomiting, and
• rash.

Sulfamethoxazole should be stopped at the first appearance of a skin rash since the rash may become severe. Serious rashes include Stevens-Johnson syndrome (aching joints and muscles; redness, blistering, and peeling of the skin); toxic epidermal necrolysis (difficulty in swallowing; peeling, redness, loosening, and blistering of the skin). Sulfamethoxazole therapy also can cause extensive sunburn, following exposure to sunlight. Patients receiving sulfamethoxazole should avoid excessive exposure to sunlight and should wear sunscreen.

Other important rare side effects include:

• liver damage,
• low white blood cell count,
• low platelet count (thrombocytopenia), and
• anemia.

Sulfamethoxazole may form crystals in the urine which may damage the kidney and cause bleeding into the urine. It is important to drink additional liquids during sulfonamide therapy to prevent these side effects.

Sulfamethoxazole usually is taken two or three times daily, with or without meals. It should be taken with 6 to 8 ounces of liquid to prevent crystals from forming in the urine. Persons with advanced kidney diseases may require lower doses.

Sulfamethoxazole can enhance the blood-thinning effects of warfarin, possibly leading to bleeding. Sulfonamides such as sulfamethoxazole can increase the metabolism (break-down and elimination) of cyclosporine (causing loss of effectiveness of cyclosporine), and can add to the kidney damage caused by cyclosporine. All sulfonamides can crystallize in urine when the urine is acidic. Since methenamine (Hiprex, Urex, Mandelamine) causes an acidic urine, it should not be used with sulfonamides.

The effects of the sulfonamide class of antibiotics on the fetus have not been adequately studied. Therefore, physicians may use them if the benefits are deemed to outweigh potential risks. On the other hand, use of sulfonamides near term (that is, near the ninth month of pregnancy) may cause bilirubin to be displaced from proteins in the infant's blood. Displacement of bilirubin can lead to a dangerous condition called kernicterus in which the bilirubin damages the brain. For this reason, sulfonamides should not be used near term birth.

Sulfamethoxazole is excreted in breast milk and should not be used in women who are breastfeeding. Sulfonamides can cause kernicterus in nursing newborns.

What preparations of sulfamethoxazole are available?

Tablets: 500 mg and 1 gm.

How should I keep sulfamethoxazole stored?

The tablets should be kept at room temperature, 15 C - 30 C (59 F - 86 F).