Skip to Content



(sye kloe SER een)

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Capsule, Oral:

Generic: 250 mg

Pharmacologic Category

  • Antibiotic, Miscellaneous
  • Antitubercular Agent


Inhibits bacterial cell wall synthesis by competing with amino acid (D-alanine) for incorporation into the bacterial cell wall; bacteriostatic or bactericidal


~70% to 90% from GI tract (WHO 2008)


Widely to most body fluids and tissues including CSF, bile, sputum, lymph tissue, lungs, and ascitic, pleural, and synovial fluids (WHO 2008)




Urine (~65% as unchanged drug) within 72 hours; Feces (small amounts); remainder metabolized

Time to Peak

Serum: 4 to 8 hours

Half-Life Elimination

Normal renal function: 12 hours

Protein Binding

Not plasma protein bound

Use: Labeled Indications

Tuberculosis: Treatment of active pulmonary or extrapulmonary tuberculosis, in combination with other agents, when treatment with primary tuberculosis therapy has proved inadequate

Urinary tract infections: May be effective in treatment of acute urinary tract infections caused by susceptible strains of gram-positive and gram-negative bacteria, especially Enterobacter spp. and Escherichia coli. Note: Should be considered only when more conventional therapy has failed and when the organism has been demonstrated to be susceptible to the drug.


Hypersensitivity to cycloserine or any component of the formulation; epilepsy; depression, severe anxiety, or psychosis; severe renal insufficiency; excessive concurrent use of alcohol

Dosing: Adult

Tuberculosis: Oral:

Manufacturer's labeling: Initial: 250 mg every 12 hours for 14 days, then administer 500 to 1,000 mg/day in 2 divided doses (maximum: 1,000 mg/day)

Alternate dosing: 10 to 15 mg/kg/day (maximum: 1,000 mg/day), usually 500 to 750 mg/day in 2 divided doses. Note: Experienced clinicians indicate most patients are unable to tolerate this dose. Serum concentrations targeted at 20 to 35 mcg/mL are often useful in determining the optimal dose (ATS 2003).

Note: Some neurotoxic effects may be treated or prevented by concomitant administration of 200 to 300 mg of pyridoxine daily or 50 mg of pyridoxine per 250 mg of cycloserine (WHO 2008).

Urinary tract infections: Oral: There is no dosage provided in the prescribing information. Note: Should be considered only when more conventional therapy has failed and when the organism has been demonstrated to be susceptible to the drug.

Dosing: Geriatric

Refer to adult dosing.

Dosing: Pediatric

Tuberculosis (off-label use): Infants, Children, and Adolescents: Oral: 10 to 20 mg/kg/day divided every 12 to 24 hours (if tolerability issues, may divide into 2 doses); maximum daily dose: 1,000 mg/day; administer with supplemental pyridoxine to minimize neurotoxicity (ATS 2003; DHHS [pediatric 2013]; Red Book [AAP 2015]; Seddon 2012; WHO 2009). Note: Some patients may be unable to tolerate recommended doses; serum concentrations targeted at 25 to 30 mcg/mL have been suggested to minimize toxicity (DHHS [pediatric 2013]).

Dosing: Renal Impairment

There are no dosage adjustments provided in the manufacturer’s labeling; use is contraindicated in severe impairment. However, the following adjustments have been used by some clinicians:

Aronoff 2007:

CrCl >50 mL/minute: No dosage adjustment necessary.

CrCl 10 to 50 mL/minute: Administer every 24 hours.

CrCl <10 mL/minute: Administer every 36 to 48 hours.

ATS 2003: CrCl <30 mL/minute or hemodialysis: 250 mg once daily, or 500 mg 3 times per week. Note: Avoid in patients with CrCl <50 mL/minute unless the patient is receiving hemodialysis. The efficacy of 250 mg daily doses has not been established, and careful monitoring is necessary for evidence of neurotoxicity. Monitor serum concentrations to minimize toxicity.

Dosing: Hepatic Impairment

There are no dosage adjustments provided in the manufacturer’s labeling.


Administer orally in divided doses with or without food.

Dietary Considerations

May be taken with food; may increase vitamin B12 and folic acid dietary requirements.


Store at 20°C to 25°C (68°F to 77°F).

Drug Interactions

Alcohol (Ethyl): May enhance the neurotoxic effect of CycloSERINE. Specifically, the risk for seizures may be increased. Avoid combination

BCG (Intravesical): Antibiotics may diminish the therapeutic effect of BCG (Intravesical). Avoid combination

BCG Vaccine (Immunization): Antibiotics may diminish the therapeutic effect of BCG Vaccine (Immunization). Monitor therapy

Cholera Vaccine: Antibiotics may diminish the therapeutic effect of Cholera Vaccine. Avoid combination

Ethionamide: May enhance the adverse/toxic effect of CycloSERINE. Monitor therapy

Isoniazid: May enhance the adverse/toxic effect of CycloSERINE. Specifically, CNS toxicity may be enhanced. Monitor therapy

Lactobacillus and Estriol: Antibiotics may diminish the therapeutic effect of Lactobacillus and Estriol. Monitor therapy

Prothionamide: May enhance the adverse/toxic effect of CycloSERINE. Monitor therapy

Sodium Picosulfate: Antibiotics may diminish the therapeutic effect of Sodium Picosulfate. Management: Consider using an alternative product for bowel cleansing prior to a colonoscopy in patients who have recently used or are concurrently using an antibiotic. Consider therapy modification

Typhoid Vaccine: Antibiotics may diminish the therapeutic effect of Typhoid Vaccine. Only the live attenuated Ty21a strain is affected. Management: Vaccination with live attenuated typhoid vaccine (Ty21a) should be avoided in patients being treated with systemic antibacterial agents. Use of this vaccine should be postponed until at least 3 days after cessation of antibacterial agents. Consider therapy modification

Adverse Reactions

Frequency not defined.

Cardiovascular: Cardiac arrhythmia, cardiac failure

Central nervous system: Coma, confusion, dizziness, drowsiness, dysarthria, headache, hyperreflexia, paresis, paresthesia, psychosis, restlessness, seizure, vertigo

Dermatologic: Skin rash

Endocrine & metabolic: Cyanocobalamin deficiency, folate deficiency

Hepatic: Increased liver enzymes

Hypersensitivity: Hypersensitivity reaction

Neuromuscular & skeletal: Tremor


Concerns related to adverse effects:

• CNS effects: Has been associated with dose-related CNS toxicity, including seizures, psychosis, depression, and confusion; decrease dosage or discontinue use if occurs. Pyridoxine may be coadministered to prevent/treat CNS effects (ATS 2003).

• Skin reactions: Allergic dermatitis may occur; reduce dose or discontinue use if allergic dermatitis develops.

• Superinfection: Prolonged use may result in fungal or bacterial superinfection, including C. difficile-associated diarrhea (CDAD) and pseudomembranous colitis; CDAD has been observed >2 months postantibiotic treatment.

Disease-related concerns:

• Alcoholism: Use with caution in patients with a history of chronic alcoholism; increased risk of seizures.

• Mental illness: Use with caution in patients with depression, severe anxiety, and/or psychosis.

• Renal impairment: Use with caution in patients with renal impairment; dosage adjustment may be necessary. Use is contraindicated in severe renal insufficiency.

Concurrent drug therapy issues:

• Drug-drug interactions: Potentially significant interactions may exist, requiring dose or frequency adjustment, additional monitoring, and/or selection of alternative therapy. Consult drug interactions database for more detailed information.

Special populations:

• Patients with potential for vitamin deficiency: Use with caution in patients with potential vitamin B12 and/or folate deficiency (malnourished, chronic anticonvulsant therapy, or elderly).

Monitoring Parameters

Periodic renal, hepatic, hematological tests, and plasma cycloserine concentrations; assess neuropsychiatric status at monthly intervals and more frequently if symptoms occur (ATS 2003).

Pregnancy Risk Factor


Pregnancy Considerations

Adverse events have not been observed in animal reproduction studies. Cycloserine crosses the placenta and can be detected in the fetal blood and amniotic fluid. The American Thoracic Society recommends use in pregnant women only if there are no alternatives (CDC 2003).

Patient Education

• Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)

• Have patient report immediately to prescriber signs of depression (suicidal ideation, anxiety, emotional instability, or confusion), behavioral changes, aggressive behavior, fatigue, headache, change in balance, confusion, memory impairment, dizziness, seizures, muscle weakness, shortness of breath, excessive weight gain, swelling of arms or legs, severe loss of strength and energy, change in speech, tremors, or burning or numbness feeling (HCAHPS).

• Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer:Should not be printed and given to patients. This information is intended to serve as a concise initial reference for health care professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience, and judgment in diagnosing, treating, and advising patients.