Generic Name  : Trimethoprim + Sulfamethoxazole

Trade Name     : Septrin

Drug Class       : Sulfonamides

Forms of The Drug

  1. Injected Solution: (16mg/80mg)/mL.
  2. Oral Suspension: (40mg/200mg)/5mL.
  3. Tablet: 80mg/400mg, 160mg/800mg.

Mechanism of Action

Blocks 2 consecutive steps in the biosynthesis of nucleic acids and proteins essential to many bacteria.

  1. Trimethoprim: Inhibits dihydrofolate reductase, thereby blocking production of tetrahydrofolic acid from dihydrofolic acid
  2. Sulfamethoxazole: Inhibits bacterial synthesis of dihydrofolic acid by competing with para-aminobenzoic acid


  1. Urinary tract infections: such as Escherichia coli.
  2. Respiratory tract infections: such as acute exacerbations of chronic bronchitis, pneumonia, and sinusitis caused by susceptible bacteria.
  3. Gastrointestinal infections: such as traveler’s diarrhea caused by susceptible bacteria.
  4. Skin and soft tissue infections: such as cellulitis and impetigo caused by susceptible bacteria.
  5. Toxoplasmosis.


  1. Known hypersensitivity.
  2. Age <2 months.
  3. CrCl <15 mL/min when renal function status cannot be monitored.
  4. Documented megaloblastic or folate deficiency anemia.
  5. Significant hepatic impairment.
  6. Contraindicated in pregnant patients at term and in nursing mothers, because sulfonamides, which pass the placenta and are excreted in the milk, may cause kernicterus.
  7. History of drug-induced immune thrombocytopenia with use of trimethoprim and/or sulfonamides.
  8. Concomitant administration with dofetilide.

Side Effects

  1. Black, tarry stools.
  2. Blistering, peeling, or loosening of the skin.
  3. Changes in skin color.
  4. Chest pain or tightness.
  5. Chills.
  6. Clay-colored stools.
  7. Cough or hoarseness.
  8. Dark urine.
  9. Diarrhea.
  10. Dizziness.
  11. General feeling of tiredness or weakness.
  12. Sore throat.
  13. Loss of appetite.
  14. Itching, skin rash.

Drug Interaction

Interaction occurs when it is given with certain drugs.

  1. Amiodarone.
  2. Digoxin.
  3. Heparin.
  4. Warfarin.
  5. Methotrexate.
  6. Protamine.
  7. Phenytoin.
  8. Oral contraceptives.
  9. ACE inhibitors.


  1. Pregnancy: Category D.
  2. Lactation: It is excreted into breast milk, and there is a potential risk of adverse effects in nursing infants. Therefore, caution should be exercised when using this medication during lactation.

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