Cycloserine

How it works

As a structural analogue of D-alanine it inhibits enzymes involved in bacterial cell-wall synthesis (alanine racemase and D-alanine ligase), impairing peptidoglycan formation.

Prescribing in practice

• Central nervous system toxicity is the key concern, ranging from headache and confusion to depression, psychosis, seizures and suicidal ideation, and it should be avoided or used with great caution in epilepsy, depression or severe psychiatric illness.
• Pyridoxine is usually co-prescribed to reduce neurotoxicity, and alcohol increases the seizure risk.
• It requires dose adjustment in renal impairment as it is renally cleared.

Monitoring

Monitor mental state and neurological status closely, with plasma-concentration monitoring used in specialist practice to limit toxicity.

Counselling the patient

• Report low mood, unusual thoughts, confusion or any fit promptly.
• Take the pyridoxine prescribed alongside it and avoid alcohol.
• Do not stop abruptly without specialist advice.

Evidence & guidelines

Use is grounded in WHO and national guidance for drug-resistant tuberculosis regimens.