Overview and uses

Sulfamethoxazole is an intermediate-acting (8-12 hr) antibiotic of the sulfonamide family of drugs.

Indication (uses)

  • Used for the treatment of infections like:
    • Nocardiosis
    • Trachoma
    • Chancroid
    • Inclusion conjunctivitis
    • As a secondary treatment in urinary tract infections
    • Toxoplasmosis encephalitis
    • Acute otitis media
    • Meningococcal meningitis
    • Rheumatic fever
    • Lymphogranuloma venerum

Pharmacological classification

Sulfonamide antibacterial

Brand names

Available only in combination with Trimethoprim. Combination brands are Gantanol, Bactrim.

Dosage form

  • Available as tablets, oral solution and injectable solution in combination with other drugs.

Mechanism of action

Sulfonamides inhibit the formation of bacterial folic acid by inhibiting folate synthase enzyme. Since sulfonamides are structurally similar to PABA, they inhibit the union of PABA with pteridine residue to form dihydropteroic acid which conjugates with glutamic acid to produce dihydrofolic acid. Also, being structurally similar to PABA, sulfonamides may get directly incorporated into the bacterial cell to form an altered folate which is metabolically injurious.


Data not available for Sulfamethoxazole.

Side effects or unwanted effects

  • Hypersensitivity reaction including urticarial rash (most common), allergic myocarditis, arthralgia, epidermal necrolysis, erythema multiforme, exfoliative dermatitis, Stevens-Johnson syndrome, urticaria, serum sickness, photosensitization and generalized skin eruptions.
    • Consult your doctor as soon as possible if you observe skin rash, red or purple colored skin rash, facial swelling, swelling of the tongue, hives on the skin, joint pain, a painful red area on the skin that spreads quickly, peeling of the skin without blistering, fever, shortness of breath during exercise at first and then at night time while lying down, abnormal heartbeat, lightheadedness, sharp or stabbing chest pain and fatigue are some of the symptoms. This may require immediate medical attention and discontinuation of the therapy.
  • Gastrointestinal side effects include nausea, vomiting, abdominal pain, diarrhea, anorexia, pancreatitis and stomatitis.
    • Ask your pharmacist to recommend a suitable medicine and consult your doctor.
  • The occurrence of hepatitis and jaundice, though rare cannot be ruled out.
    • Nausea, stomach pain, dark colored urine, yellowing of the skin and whites of the eye, light or clay-colored stools, fever and unusual tiredness are some of the symptoms. Consult your doctor as soon as possible. This may require discontinuation of the treatment with Sulfamethoxazole.
  • Aplastic anemia, hemolytic anemia, hypoprothrombinemia, leucopenia, purpura and agranulocytosis.
    • Purple-colored spots under skin, sudden fever, chills, sore throat, weakness in limbs, mouth ulcers, bleeding gums, easy bruising and prolonged bleeding are some of the symptoms of the above-mentioned condition. Consult your doctor as soon as possible as some of the above-mentioned conditions are serious and life-threatening.
  • Tremulousness, delirium and disorientation have been frequently reported
    • Shaking of a body part or even full body, anxiety, fear, hallucinations, irritability, rapid and unpredictable mood swings, difficulty in reading, writing, recalling or speaking of words are some of the symptoms of the above-mentioned condition. Consult your doctor as soon as possible.
  • The occurrence of frank psychosis is rare.
  • Ataxia, convulsions, hallucinations, headache, insomnia, mental depression, peripheral neuritis, tinnitus and vertigo have also been reported.
  • Crystalluria, lupus periarteritis nodosa, toxic nephrosis with oliguria and anuria have also been reported.
  • The occurrence of hypoglycemia has also been reported with Sulfamethoxazole use.
  • Kernicterus may be precipitated in newborn, commonly observed with premature born babies.

Pregnancy and breastfeeding warnings


Category C, which means animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.


  • Sulfamethoxazole use is contraindicated in a mother nursing a G6PD deficient breast feeding infant.
  • Sulfamethoxazole use in mothers nursing a premature baby or a baby with jaundice should be avoided as safety profile for Sulfamethoxazole use in such cases is not established.
  • Sulfamethoxazole can be used in a mother nursing a healthy and full term baby.


Drug-drug interactions

  • Concomitant use of Sulfamethoxazole with indomethacin, probenecid or aspirin (including all salicylates) may worsen the side effects of Sulfamethoxazole.
  • Anti-coagulants like warfarin increases the risk of bleeding when co-administered with Sulfamethoxazole.
  • Side effects of methotrexate and thiazide diuretics like Hydrochlorothiazide, Benzthiazide, Hydroflumethiazide and Clopamide may be increased when co-administered with Sulfamethoxazole.
  • Sulfonylurea’s like Glipizide, Glimepiride and Glyburide may increase the risk of low blood sugar when co-administered with Sulfamethoxazole.
  • Consult your doctor before taking Sulfamethoxazole with clozapine, cyclosporine, anisindione, sodium nitrite, methenamine, lomitapide, mipomersen and live cholera vaccine.

Drug-food interactions

  • Sulfamethoxazole can be taken with or without food.
  • Avoid consuming alcohol when taking Sulfamethoxazole.

Note: The sole purpose of every information shared on this article is to bring awareness. Do not use this information as a medical advice or prescription advice or as a tool for the treatment, diagnosis or prevention of the disease.