Classifications: antibiotic; antituberculosis agent;
Therapeutic: antibiotic; antituberculosis agent

Pregnancy Category: C


250 mg capsules


Broad-spectrum antiinfective that inhibits cell wall synthesis in susceptible strains. Bacteriostatic or bactericidal depending on concentration and susceptibility of organism. It competitively interferes with the incorporation of D-alanine into the bacterial cell wall, resulting in cell death.

Therapeutic Effect

Effective against gram-positive and gram-negative bacteria and Mycobacterium tuberculosis.


In conjunction with other tuberculostatic drugs in treatment of active pulmonary and extrapulmonary tuberculosis when primary agents isoniazid, rifampin, ethambutol, streptomycin have failed. Also used in treatment of acute UTI caused by Enterobacter sp. and Escherichia coli that are unresponsive to conventional treatment.

Unlabeled Uses

Treatment of tuberculosis meningitis and nocardiosis.


Epilepsy; depression, severe anxiety, history of psychoses; severe renal insufficiency; chronic alcoholism; pregnancy (category C). Safe use in children not established.

Cautious Use

Renal impairment, lactation; anemia.

Route & Dosage

Adult: PO 250 mg q12h for 2 wk, may increase to 500 mg q12h (max: 1 g/d)

Urinary Tract Infection
Adult: PO 250 mg q12h for 2 wk


  • Pyridoxine 200–300 mg/d may be ordered concurrently to prevent neurotoxic effects of cycloserine.
  • Store in tightly closed container at 15°–30° C (59°–86° F) unless otherwise directed.

Adverse Effects (≥1%)

CV: Arrhythmias, CHF. Hematologic: Vitamin B12 and folic acid deficiency, megaloblastic or sideroblastic anemia. CNS: Drowsiness, anxiety, headache, tremors, myoclonic jerking, convulsions, vertigo, visual disturbances, speech difficulties (dysarthria), lethargy, depression, disorientation with loss of memory, confusion, nervousness, psychoses, tic episodes, character changes, hyperirritability, aggression, hyperreflexia, peripheral neuropathy, paresthesias, paresis, dyskinesias. Skin: Dermatitis, photosensitivity. Special Senses: Eye pain (optic neuritis), photophobia.


Drug: Alcohol increases risk of seizures; ethionamide, isoniazid potentiate neurotoxic effects; may inhibit phenytoin metabolism, increasing its toxicity.


Absorption: 70–90% from GI tract. Peak: 3–4 h. Distribution: Distributed to lung, ascitic, pleural and synovial fluids, and CSF; crosses placenta; distributed into breast milk. Metabolism: Not metabolized. Elimination: 60–70% in urine within 72 h; small amount in feces. Half-Life: 10 h.

Nursing Implications

Assessment & Drug Effects

  • Lab tests: Culture and susceptibility tests should be performed before initiation of therapy and periodically thereafter to detect possible bacterial resistance. Monitor plasma drug levels weekly and hematologic, renal, and hepatic function at regular intervals.
  • Maintenance of blood-drug level below 30 mg/mL considerably reduces incidence of neurotoxicity. Possibility of neurotoxicity increases when dose is 500 mg or more or when renal clearance is inadequate.
  • Observe patient carefully for signs of hypersensitivity and neurologic effects. Neurotoxicity generally appears within first 2 wk of therapy and disappears after drug is discontinued.
  • Drug should be withheld and physician notified or dosage reduced if symptoms of CNS toxicity or hypersensitivity reaction (see Appendix F) develop.

Patient & Family Education

  • Take cycloserine after meals to prevent GI irritation.
  • Notify physician immediately of the onset of skin rash and early signs of CNS toxicity (see Appendix F).
  • Avoid potentially hazardous tasks such as driving until reaction to cycloserine has been determined.
  • Take drug precisely as prescribed and to keep follow-up appointments. Continuous therapy may extend into months or years.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

© 2006-2023 Last Updated On: 02/02/2023 (0)
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