Ethionamide warnings and precautions

# Warnings
The use of Trecator alone in the treatment of tuberculosis results in rapid development of resistance. It is essential, therefore, to give a suitable companion drug or drugs, the choice being based on the results of susceptibility testing. However, therapy may be initiated prior to receiving the results of susceptibility tests as deemed appropriate by the physician. Ethionamide should be administered with at least one, sometimes two, other drugs to which the organism is known to be susceptible. Drugs which have been used as companion agents are rifampin, ethambutol, pyrazinamide, cycloserine, kanamycin, streptomycin, and isoniazid. The usual warnings, precautions, and dosage regimens for these companion drugs should be observed.
Patient compliance is essential to the success of the antituberculosis therapy and to prevent the emergence of drug-resistant organisms. Therefore, patients should adhere to the drug regimen for the full duration of treatment. It is recommended that directly observed therapy be practiced when patients are receiving antituberculous medication. Additional consultation from experts in the treatment of drug-resistant tuberculosis is recommended when patients develop drug-resistant organisms.

# Precautions

## General
Ethionamide may potentiate the adverse effects of the other antituberculous drugs administered concomitantly . Ophthalmologic examinations (including ophthalmoscopy) should be performed before and periodically during therapy with Trecator.

## Information For Patients
Patients should be advised to consult their physician should blurred vision or any loss of vision, with or without eye pain, occur during treatment.
Excessive ethanol ingestion should be avoided because a psychotic reaction has been reported.

## Laboratory Tests
Determination of serum transaminases (SGOT, SGPT) should be made prior to initiation of therapy and should be monitored monthly. If serum transaminases become elevated during therapy, ethionamide and the companion antituberculosis drug or drugs may be discontinued temporarily until the laboratory abnormalities have resolved. Ethionamide and the companion antituberculosis medication(s) then should be reintroduced sequentially to determine which drug (or drugs) is (are) responsible for the hepatotoxicity.
Blood glucose determinations should be made prior to and periodically throughout therapy with Trecator. Diabetic patients should be particularly alert for episodes of hypoglycemia.
Periodic monitoring of thyroid function tests is recommended as hypothyroidism, with or without goiter, has been reported with ethionamide therapy.

## Drug Interactions
Trecator has been found to temporarily raise serum concentrations of isoniazid. Trecator may potentiate the adverse effects of other antituberculous drugs administered concomitantly. In particular, convulsions have been reported when ethionamide is administered with cycloserine and special care should be taken when the treatment regimen includes both of these drugs. Excessive ethanol ingestion should be avoided because a psychotic reaction has been reported.

## Carcinogenesis, Mutagenesis, Impairment of Fertility

### Pregnancy Category: C
Animal studies conducted with Trecator indicate that the drug has teratogenic potential in rabbits and rats. The doses used in these studies on a mg/kg basis were considerably in excess of those recommended in humans. There are no adequate and well-controlled studies in pregnant women. Because of these animal studies, however, it must be recommended that Trecator be withheld from women who are pregnant, or who are likely to become pregnant while under therapy, unless the prescribing physician considers it to be an essential part of the treatment.

### Labor and Delivery
The effect of Trecator on labor and delivery in pregnant women is unknown.

### Nursing Mothers
Because no information is available on the excretion of ethionamide in human milk, Trecator should be administered to nursing mothers only if the benefits outweigh the risks. Newborns who are breast-fed by mothers who are taking Trecator should be monitored for adverse effects.

### Pediatric Use
Due to the fact that pulmonary tuberculosis resistant to primary therapy is rarely found in neonates, infants, and children, investigations have been limited in these age groups. At present, the drug should not be used in pediatric patients under 12 years of age except when the organisms are definitely resistant to primary therapy and systemic dissemination of the disease, or other life-threatening complications of tuberculosis, is judged to be imminent.