Paper II — 2021 February (Supplementary) (2010 Scheme) — Q3

Paper II

2021 February (Supplementary) (2010 Scheme)

Question

Cotrimoxazole

Q33 marksShort Notes★✓

Answer

Co-trimoxazole is a fixed-dose combination of trimethoprim and sulfamethoxazole.

Mechanism of action

• Sulfamethoxazole inhibits dihydropteroate synthase (blocking PABA→dihydrofolic acid); trimethoprim inhibits dihydrofolate reductase (blocking conversion to tetrahydrofolic acid) — sequential blockade of bacterial folate synthesis, producing synergistic bactericidal effect

Uses

• Urinary tract infections
• Pneumocystis jirovecii pneumonia (treatment and prophylaxis in HIV)
• Respiratory tract infections, traveller’s diarrhoea
• Nocardiosis

Adverse effects

• Hypersensitivity reactions (including Stevens-Johnson syndrome)
• Bone marrow suppression (megaloblastic anaemia, especially with folate deficiency)
• Hyperkalaemia
• Crystalluria
• Kernicterus risk if given near term in pregnancy

Related Concepts

1. 1Sulfonamides and Cotrimoxazole

Other Years Asked

1. 1Cotrimoxazole2023 July (Supplementary) (2010 Scheme)Short Note · 3 marks
2. 2Cotrimoxazole2022 May (Supplementary) (2010 Scheme)Short Note · 3 marks
3. 3Trimethoprim and Sulfamethoxazole as a combination2024 August (Supplementary) (2010 Scheme)Short Answer · 1 mark
4. 4Mechanism of action of cotrimoxazole2016 February (2010 Scheme)Short Answer · 1 mark
5. 5Treatment of pneumocystis carnii2015 February (2010 Scheme)Short Answer · 1 mark
6. 6Combination of Trimethoprim and Sulfamethoxazole.2025 March (Supplementary) (2010 Scheme)Short Answer · 1 mark
7. 7Mechanism of action of co-trimoxazole.2015 September (Supplementary) (2010 Scheme)Short Answer · 1 mark
8. 8Drugs for pneumocystis carini infection2022 February (2019 Scheme)Short Answer · 0.2 marks