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Introduction of Cotrimoxazole

According to WHO (World Health Organization), cotrimoxazole is a fixed-dose combination of sulphamethoxazole and trimethoprim in ratio of 5:1.

It is one of the drugs in which commonly used antimicrobial agents. The drug cotrimoxazole was introduced in late 1960.

Mechanism of action

Cotrimoxazole produces a sequential blockade, i.e two drugs interfere with two successive steps in the same metabolic pathway hence their combination of two drugs produces a supra-additive effect.

Sulphamethoxazole inhibits folate synthetase and Trimethoprim inhibits dihydrofolate reductase enzyme on the same metabolic pathway.


Pharmacokinetics of Cotrimoxazole

The pharmacokinetic properties of two drugs such as sulphamethoxazole and trimethoprim match each other almost closely, hence select for combination and two drugs have a similar half-life.

The concentration ratio of 20:1 (sulphamethoxazole and trimethoprim) shows the optimum synergistic effect in blood and tissues.

The drug cotrimoxazole is well absorbed after oral administration and is also used in the parental route. It is widely distributed to various tissues such as CSF and sputum. It is metabolized in the liver and excreted mainly through urine.

Advantages of this combination of drugs are;

Both are bacteriostatic but their combination of drugs has cidal effect and chances of development of bacterial resistance are also greatly reduced.

Adverse effects

It is well tolerated drug but their some common adverse effects of the following

  • Skin rashes
  • Gastrointestinal (GI) disturbance
  • Exfoliative dermatitis
  • Erythema multiforme
  • Stevens-Johnson syndrome
  • Nausea, vomiting, glossitis, and stomatitis.
  • Megaloblastic anemia
    • It occurs due to folate deficiency but may occur rarely, especially in malnourished persons and alcoholics persons.
  • Bone marrow suppression with leukopenia, neutropenia, and thrombocytopenia.
  • Contraindication in pregnancy

Indications of cotrimoxazole (@SEPTRAN D)

  • Sexually transmitted diseases (STD’s) such as Chancroid and Lymphogranuloma venereum (LGV).
  • Enteritis (E.coli, Shigella)
  • Pneumocystis jiroveci infection
  • Typhoid fever
  • Bacterial Respiratory tract infections
  • Acute uncomplicated lower urinary tract infection (UTIs)
  • Nocardia
  • Bacterial diarrhoeas


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