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Antimycobacterial (MDR-TB) Pregnancy: It is not known whether cycloserine can cause fetal harm; concentrations in fetal blood approach those in serum. Should be given to a pregnant woman only if clearly needed. Concentrations in mother's milk approach those in serum; decide whether to discontinue nursing or the drug.

Cycloserine

Brand names: Specialist UKHSA supply

Cycloserine is a second-line antituberculous agent used within multidrug regimens for drug-resistant tuberculosis.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 500 mg to 1 g daily in divided doses, monitored by blood level determinations; initial dose most frequently 250 mg twice daily at 12-hour intervals for the first two weeks
Route: Oral
Frequency: In divided doses (commonly twice daily at 12-hour intervals)
Max: 1 g daily should not be exceeded
Monitor by blood level determinations; adjust dosage to keep blood level below 30 mg/L (toxicity usually associated with levels >30 mg/L). Blood levels should be determined at least weekly for patients with reduced renal function, those receiving more than 500 mg daily, and those with signs of toxicity. Elderly: as adults but reduce dosage if renal function is impaired.

Paediatric dose

Dose: 10 mg/kg
Route: Oral
Frequency: Per day (usual starting dose), then adjusted
Usual starting dose is 10 mg/kg/day, then adjusted according to blood levels obtained and therapeutic response.

Dose adjustments

Renal

Contraindicated in severe renal insufficiency. Reduce dosage if renal function is impaired; determine blood levels at least weekly in patients with reduced renal function.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

Usual starting dose is 10 mg/kg/day, then adjusted according to blood levels obtained and therapeutic response.

Verify in a children's formulary

Contraindications

  • Hypersensitivity to the active substance or any excipient
  • Epilepsy
  • Depression, severe anxiety or psychosis
  • Severe renal insufficiency
  • Alcohol abuse

Side effects

  • Convulsions, drowsiness/somnolence, headache, dysarthria, vertigo
  • Confusion, disorientation with loss of memory, paraesthesia
  • Psychosis, suicidal tendencies, personality change, hyper-irritability, aggression
  • Tremor, hyper-reflexia
  • Megaloblastic anaemia; elevated serum aminotransferases; heart failure (at 1-1.5 g daily doses)

Interactions

  • Ethionamide: concurrent administration reported to potentiate neurotoxic side-effects
  • Alcohol: incompatible, especially during large-dose regimens; increases possibility and risk of epileptic episodes
  • Isoniazid: combined toxic action on CNS (monitor for dizziness and drowsiness); dosage adjustments may be necessary

Clinical monograph

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.

Reference: WHO MDR-TB guideline; BTS/SIGN; UKHSA; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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