Miscellaneous

Question 1

Metronidazole

Answer 1

Mode of action: pro-drug, activated in low-oxygen conditions, directly toxic by interaction with DNA

• good anaerobic cover, therefore, effective against all the clostridia and bacteroides fragilis
• first line against c. diff colitis (together with oral vancomycin)
• anaerobic cover for intra-abdominal sepsis
• used together with cefuroxime as surgical prophylaxis
• oral infections (dentist)

Adverse effects: metallic taste, GI disturbance, dizziness/headache, reaction with alcohol

Question 2

Trimethoprim

Answer 2

Mode of action: bacterial dihydrofolate reductase inhibitor; prevents bacterial DNA synthese

Combined with sulfamethoxazole to form co-trimoxazole

Simple UTI
P. carinii/P. jirovecii - pneumonia in immunosuppressed
Toxoplasmosis
Nocardiosis

To be avoided in pregnancy due to folate inhibiting effect unless taken with 5mg folic acid

Question 3

Nitrofurantoin

Answer 3

Mode of action: Poorly understood; inhibition of bacterial protein synthesis and toxic to DNA

UTIs (unless pseudomonas/proteus)

DO NOT USE if septicaemia (poor serum levels)
DO NOT USE in renal impairment, insufficient levels will be filtered into the urine (less effective and increased risk of peripheral neuropathy); requires EGFR 60+

Adverse effects: Gi disturbance common, peripheral neuropathy, haemolytic anaemia, hypersensitivity reactions, pulmonary fibrosis

Caution: anaemia, diabetes mellitus, Vit B12 and folate deficiency, pulmonary disease, hepatic and renal impairment)