Sulfamethoxazole and Trimethoprim (Page 3 of 4)


The following adverse reactions associated with the use of sulfamethoxazole and trimethoprim were identified in clinical trials, postmarketing or published reports. Because some of these reactions were reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

The most common adverse reactions are gastrointestinal disturbances (nausea, vomiting, anorexia) and allergic skin reactions (such as rash and urticaria). Fatalities and serious adverse reactions, including severe cutaneous adverse reactions (SCARs), including Stevens- Johnson syndrome, toxic epidermal necrolysis, drug reaction with eosinophilia and systemic symptoms (DRESS), acute febrile neutrophilic dermatosis (AFND), acute generalized erythematous pustulosis (AGEP); fulminant hepatic necrosis; agranulocytosis, aplastic anemia and other blood dyscrasias; acute and delayed lung injury; anaphylaxis and circulatory shock have occurred with the administration of sulfamethoxazole and trimethoprim products, including sulfamethoxazole and trimethoprim (see WARNINGS).

Hematologic: Agranulocytosis, aplastic anemia, thrombocytopenia, leukopenia, neutropenia, hemolytic anemia, megaloblastic anemia, hypoprothrombinemia, methemoglobinemia, eosinophilia, thrombotic thrombocytopenic purpura, idiopathic thrombocytopenic purpura.

Allergic Reactions: Stevens-Johnson syndrome, toxic epidermal necrolysis, anaphylaxis, allergic myocarditis, erythema multiforme, exfoliative dermatitis, angioedema, drug fever, chills, Henoch-Schoenlein purpura, serum sickness-like syndrome, generalized allergic reactions, generalized skin eruptions, photosensitivity, conjunctival and scleral injection, pruritus, urticaria,rash, periarteritis nodosa, systemic lupus erythematosus, drug reaction with eosinophilia and systemic symptoms (DRESS), acute generalized erythematous pustulosis (AGEP), and acute febrile neutrophilic dermatosis (AFND) (see WARNINGS).

Gastrointestinal: Hepatitis, (including cholestatic jaundice and hepatic necrosis), elevation of serum transaminase and bilirubin, pseudomembranous enterocolitis, pancreatitis, stomatitis, glossitis, nausea, emesis, abdominal pain, diarrhea, anorexia.

Genitourinary: Renal failure, interstitial nephritis, BUN and serum creatinine elevation, renal insufficiency, oliguria and anuria, crystalluria and nephrotoxicity in association with cyclosporine.

Metabolic and Nutritional: Hyperkalemia, hyponatremia (see PRECAUTIONS: Electrolyte Abnormalities), metabolic acidosis.

Neurologic: Aseptic meningitis, convulsions, peripheral neuritis, ataxia, vertigo, tinnitus, headache.

Psychiatric: Hallucinations, depression, apathy, nervousness.

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.

Musculoskeletal: Arthralgia, myalgia, rhabdomyolysis

Respiratory: Cough, shortness of breath and pulmonary infiltrates, acute eosinophilic pneumonia, acute and delayed lung injury, interstitial lung disease, acute respiratory failure (see WARNINGS).

Cardiovascular System: QT prolongation resulting in ventricular tachycardia and torsades de pointes, circulatory shock (see WARNINGS).

Miscellaneous: Weakness, fatigue, insomnia.



The amount of a single dose of sulfamethoxazole and trimethoprim that is either associated with symptoms of overdosage or is likely to be life-threatening has not been reported. Signs and symptoms of overdosage reported with sulfonamides include anorexia, colic, nausea, vomiting, dizziness, headache, drowsiness and unconsciousness. Pyrexia, hematuria and crystalluria may be noted. Blood dyscrasias and jaundice are potential late manifestations of overdosage.

Signs of acute overdosage with trimethoprim include nausea, vomiting, dizziness, headache, mental depression, confusion and bone marrow depression.

General principles of treatment include the institution of gastric lavage or emesis, forcing oral fluids, and the administration of intravenous fluids if urine output is low and renal function is normal. Acidification of the urine will increase renal elimination of trimethoprim. The patient should be monitored with blood counts and appropriate blood chemistries, including electrolytes. If a significant blood dyscrasia or jaundice occurs, specific therapy should be instituted for these complications. Peritoneal dialysis is not effective and hemodialysis is only moderately effective in eliminating sulfamethoxazole and trimethoprim.


Use of sulfamethoxazole and trimethoprim at high doses and/or for extended periods of time may cause bone marrow depression manifested as thrombocytopenia, leukopenia and/or megaloblastic anemia. If signs of bone marrow depression occur, the patient should be given leucovorin 5 to 15 mg daily until normal hematopoiesis is restored.


Sulfamethoxazole and trimethoprim is contraindicated in pediatric patients less than 2 months of age.

Urinary Tract Infections and Shigellosis in Adults and Pediatric Patients, and Acute Otitis Media in Children

Adults : The usual adult dosage in the treatment of urinary tract infections is 4 teaspoonfuls (20 mL) of sulfamethoxazole and trimethoprim oral suspension every 12 hours for 10 to 14 days. An identical daily dosage is used for 5 days in the treatment of shigellosis.

Children: The recommended dose for children with urinary tract infections or acute otitis media is 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, given in two divided doses every 12 hours for 10 days. An identical daily dosage is used for 5 days in the treatment of shigellosis. The following table is a guideline for the attainment of this dosage:

Children 2 months of age or older:
Weight Dose-every 12 Hours
lb Kg Teaspoonfuls
22 10 1 (5 mL)
44 20 2 (10 mL)
66 30 3 (15 mL)
88 40 4 (20 mL)

For Patients with Impaired Renal Function

When renal function is impaired, a reduced dosage should be employed using the following table:

Creatinine Clearance (mL/min) Recommended Dosage Regimen
Above 30 Usual Standard Regimen
15 to 30 ½ the usual regimen
Below 15 Use not Recommended

Acute Exacerbations of Chronic Bronchitis in Adults

The usual adult dosage in the treatment of acute exacerbations of chronic bronchitis is 4 teaspoonfuls (20 mL) of sulfamethoxazole and trimethoprim oral suspension every 12 hours for 14 days.

Pneumocystis jirovecii Pneumonia


Adults and Children:

The recommended dosage for treatment of patients with documented Pneumocystis jirovecii pneumonia is 75 to 100 mg/kg sulfamethoxazole and 15 to 20 mg/kg trimethoprim per 24 hours given in equally divided doses every 6 hours for 14 to 21 days12. The following table is a guideline for the upper limit of this dosage:

Weight Dose- every 6 hours
lb kg Teaspoonfuls
18 8 1 (5 mL)
35 16 2 (10 mL)
53 24 3 (15 mL)
70 32 4 (20 mL)
88 40 5 (25 mL)
108 48 6 (30 mL)
141 64 8 (40 mL)
176 80 10 (50 mL)

For the lower limit dose (75 mg/kg sulfamethoxazole and 15 mg/kg trimethoprim per 24 hours) administer 75% of the dose in the above table.



The recommended dosage for prophylaxis in adults is 4 teaspoonfuls (20 mL) of sulfamethoxazole and trimethoprim oral suspension daily.13


For children, the recommended dose is 750 mg/m2 /day sulfamethoxazole with 150 mg/m2 /day trimethoprim given orally in equally divided doses twice a day, on 3 consecutive days per week. The total daily dose should not exceed 1600 mg sulfamethoxazole and 320 mg trimethoprim14. The following table is a guideline for the attainment of this dosage in children:

Body Surface Area Dose-every 12 hours
(m2) Teaspoonfuls
0.26 ½ (2.5 mL)
0.53 1 (5 mL)
1.06 2 (10 mL)

Traveler’s Diarrhea in Adults

For the treatment of traveler’s diarrhea, the usual adult dosage is 4 teaspoonfuls (20 mL) of sulfamethoxazole and trimethoprim oral suspension every 12 hours for 5 days.

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