What it's for (Indications)
- Cycloserine is primarily indicated for the treatment of active pulmonary and extrapulmonary tuberculosis caused by susceptible strains of *Mycobacterium tuberculosis*.
- It is categorized as a second-line antitubercular agent, typically reserved for cases of multi-drug resistant tuberculosis (MDR-TB) or extensively drug-resistant tuberculosis (XDR-TB) when first-line agents (such as isoniazid and rifampicin) are contraindicated, poorly tolerated, or ineffective due to microbial resistance patterns confirmed by drug susceptibility testing.
- Its use is always in combination with other effective antitubercular drugs to prevent the emergence of resistance, enhance synergistic effects, and achieve optimal therapeutic outcomes within a comprehensive treatment regimen.
- Cycloserine is not recommended as a sole agent for tuberculosis treatment due to the rapid development of resistance when used alone.
Dosage Information
| Type | Guideline |
|---|---|
| Standard | Cycloserine is administered orally. The usual adult dosage ranges from 500 mg to 1 g daily, given in divided doses and monitored by blood levels. An initial adult dosage frequently used is 250 mg twice daily at 12-hour intervals for the first 2 weeks. A daily dosage of 1 g should not be exceeded. |
Safety & Warnings
Common Side Effects
- Most adverse reactions involve the nervous system or are manifestations of drug hypersensitivity.
- Nervous system symptoms (often dose-related, especially >500 mg daily) include headache, drowsiness/somnolence, tremor, dysarthria, vertigo, confusion, disorientation with loss of memory, psychoses (possibly with suicidal tendencies), character changes, hyperirritability, aggression, paresis, hyperreflexia, paresthesia, major and minor clonic seizures, and coma.
- Cardiovascular effects such as sudden congestive heart failure have been reported (especially with 1-1.
- 5g daily).
- Other side effects include skin rash (hypersensitivity), elevated serum transaminase (especially in patients with preexisting liver disease), and Vitamin B12 deficiency.
Serious Warnings
- Black Box Warning: None
- Caution is advised in patients with kidney dysfunction and brain-related disorders such as anxiety or depression.
- Given the potential for nervous system symptoms like drowsiness, confusion, and seizures, patients should avoid driving or operating heavy machinery.
- Patients should also avoid consuming alcohol while on this medication.
- Pregnant or lactating individuals should consult their doctor before use.
- Monitor for elevated serum transaminase, especially in patients with preexisting liver disease.
- Close monitoring for severe neurological and psychiatric adverse reactions, including psychoses and suicidal tendencies, is crucial.
How it Works (Mechanism of Action)
Cycloserine exerts its bactericidal effect primarily by interfering with the synthesis of the bacterial cell wall, a crucial component for the survival and integrity of *Mycobacterium tuberculosis*. Structurally, cycloserine is an analogue of D-alanine, which allows it to competitively inhibit two key enzymes involved in the early stages of peptidoglycan formation: D-alanine racemase and D-alanine:D-alanine ligase. D-alanine racemase is responsible for converting L-alanine to D-alanine, while D-alanine:D-alanine ligase catalyzes the formation of the D-Ala-D-Ala dipeptide. By inhibiting these enzymes, cycloserine prevents the incorporation of D-alanine into the peptidoglycan precursor, thereby disrupting the subsequent cross-linking of peptidoglycan strands essential for cell wall rigidity. This leads to a defective and weakened bacterial cell wall, rendering the bacterium susceptible to osmotic lysis and ultimately causing its death. This unique mechanism contributes to its utility in combating drug-resistant strains of tuberculosis.