After oral administration, cycloserine is readily absorbed from the gastrointestinal tract, with peak blood levels occurring in 4 to 8 hours. Blood levels of 25 to 30 μg/mL can generally be maintained with the usual dosage of 250 mg twice a day, although the relationship of plasma levels to dosage is not always consistent. Concentrations in the cerebrospinal fluid, pleural fluid, fetal blood, and mother’s milk approach those found in the serum. Detectable amounts are found in ascitic fluid, bile, sputum, amniotic fluid, and lung and lymph tissues. Approximately 65% of a single dose of cycloserine can be recovered in the urine within 72 hours after oral administration. The remaining 35% is apparently metabolized to unknown substances. The maximum excretion rate occurs 2 to 6 hours after administration, with 50% of the drug eliminated in 12 hours.

Microbiology

Cycloserine inhibits cell–wall synthesis in susceptible strains of gram–positive and gram–negative bacteria and in Mycobacterium tuberculosis.

Susceptibility Tests

Cycloserine clinical laboratory standard powder is available for both direct and indirect methods1 of determining the susceptibility of strains of mycobacteria. Cycloserine MICs for susceptible strains are 25 μg/mL or lower.

      Hypersensitivity to cycloserine

      Epilepsy

      Depression, severe anxiety, or psychosis

      Severe renal insufficiency

      Excessive concurrent use of alcohol

Administration of Seromycin should be discontinued or the dosage reduced if the patient develops allergic dermatitis or symptoms of CNS toxicity, such as convulsions, psychosis, somnolence, depression, confusion, hyperreflexia, headache, tremor, vertigo, paresis, or dysarthria.

The toxicity of Seromycin is closely related to excessive blood levels (above 30 μg/mL), as determined by high dosage or inadequate renal clearance. The ratio of toxic dose to effective dose in tuberculosis is small.

The risk of convulsions is increased in chronic alcoholics.

Patients should be monitored by hematologic, renal excretion, blood level, and liver function studies.

General

Laboratory Tests

Drug Interactions

Carcinogenesis, Mutagenicity, and Impairment of Fertility

Pregnancy Category C

Nursing Mothers

Because of the potential for serious adverse reactions in nursing infants from Seromycin, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

Usage in Pediatric Patients

Safety and effectiveness in pediatric patients have not been established.

Signs and Symptoms

Acute toxicity from cycloserine can occur if more than 1 g is ingested by an adult. Chronic toxicity from cycloserine is dose related and can occur if more than 500 mg is administered daily. Patients with renal impairment will accumulate cycloserine and may develop toxicity if the dosing regimen is not modified. Patients with severe renal impairment should not receive the drug. The central nervous system is the most common organ system involved with toxicity. Toxic effects may include headache, vertigo, confusion, drowsiness, hyperirritability, paresthesias, dysarthria, and psychosis. Following larger ingestions, paresis, convulsions, and coma often occur. Ethyl alcohol may increase the risk of seizures in patients receiving cycloserine.

The oral median lethal dose in mice is 5290 mg/kg.

Treatment

To obtain up–to–date information about the treatment of overdose, a good resource is your certified Regional Poison Control Center. Telephone numbers of certified poison control centers are listed in the Physicians’ Desk Reference (PDR). In managing overdosage, consider the possibility of multiple drug overdoses, interaction among drugs, and unusual drug kinetics in your patient.

Overdoses of cycloserine have been reported rarely. The following is provided to serve as a guide should such an overdose be encountered.

Protect the patient’s airway and support ventilation and perfusion. Meticulously monitor and maintain, within acceptable limits, the patient’s vital signs, blood gases, serum electrolytes, etc. Absorption of drugs from the gastrointestinal tract may be decreased by giving activated charcoal, which, in many cases, is more effective than emesis or lavage; consider charcoal instead of or in addition to gastric emptying. Repeated doses of charcoal over time may hasten elimination of some drugs that have been absorbed. Safeguard the patient’s airway when employing gastric emptying or charcoal.

In adults, many of the neurotoxic effects of cycloserine can be both treated and prevented with the administration of 200 to 300 mg of pyridoxine daily.

The use of hemodialysis has been shown to remove cycloserine from the bloodstream. This procedure should be reserved for patients with life-threatening toxicity that is unresponsive to less invasive therapy.

Seromycin® is available as a 250 mg capsule with an opaque red cap and opaque gray body imprinted with “Lilly” and “F04” in edible black ink on both the cap and the body.

   Bottles of 40 (No.12) NDC 0002-0604-40

Store at controlled room temperature, 20° to 25°C (68° to 77°F) [see USP].