Question 1

How does trimethoprim kill bacteria without harming human cells?

Accepted Answer

Trimethoprim selectively targets bacterial dihydrofolate reductase 50,000 times more effectively than human versions. Humans get folate from diet, while bacteria must synthesize it, making this pathway essential only for bacteria.

Question 2

Why is trimethoprim particularly good for urinary tract infections?

Accepted Answer

Trimethoprim concentrates 40-100 times higher in urine than blood, delivering high antibiotic levels directly to the infection site. Its chemical properties allow excellent penetration into urinary tract tissues.

Question 3

How long does trimethoprim take to start working after taking a dose?

Accepted Answer

Trimethoprim begins inhibiting bacterial enzymes within 1-2 hours, stops bacterial growth within 4-8 hours, and most patients notice symptom improvement within 24-48 hours of starting treatment.

Question 4

Can bacteria become resistant to trimethoprim's mechanism?

Accepted Answer

Yes, bacteria develop resistance through enzyme mutations, acquiring resistant genes, or increasing drug export. UK resistance rates are 25-35% for E. coli, requiring consideration of local patterns.

Question 5

How does trimethoprim differ from other UTI antibiotics like nitrofurantoin?

Accepted Answer

Trimethoprim inhibits folate synthesis, while nitrofurantoin damages multiple bacterial enzymes. Both concentrate in urine but have different resistance patterns and side effect profiles.