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 (see INDICATIONS AND USAGE). 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 anti-tuberculosis 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 anti-tuberculous medication. Additional consultation from experts in the treatment of drug-resistant tuberculosis is recommended when patients develop drug-resistant organisms.
Severe Cutaneous Adverse Reactions
There have been reports of severe cutaneous adverse reactions (SCARs), such as Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS), and acute generalized exanthematous pustulosis (AGEP) with anti-tuberculosis drugs (see ADVERSE REACTIONS). If patients develop a skin rash they should be monitored closely and suspect drug(s) discontinued if lesions progress. Identifying the specific drug is difficult, as multiple anti-tuberculosis drugs are prescribed in association concurrently. Specifically, for DRESS, a multi-system potential life-threatening SCAR, time to onset of the first symptoms may be prolonged. DRESS is a clinical diagnosis, and its clinical presentation remains the basis for decision making. An early withdrawal of the suspect drug is essential because of the syndrome's mortality and visceral involvement (e.g., liver, bone marrow or kidney).
Prescribing Trecator in the absence of a proven or strongly suspected bacterial infection indication is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.
Ethionamide may potentiate the adverse effects of the other anti-tuberculous drugs administered concomitantly (see Drug Interactions). 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.
Patients should be counseled that antibacterial drugs including Trecator should only be used to treat bacterial infections. They do not treat viral infections (e.g., the common cold). When Trecator is prescribed to treat a bacterial infection, patients should be told that although it is common to feel better early in the course of therapy, the medication should be taken exactly as directed. Skipping doses or not completing the full course of therapy may (1) decrease the effectiveness of the immediate treatment and (2) increase the likelihood that bacteria will develop resistance and will not be treatable by Trecator or other antibacterial drugs in the future.
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 anti-tuberculosis drug or drugs may be discontinued temporarily until the laboratory abnormalities have resolved. Ethionamide and the companion anti-tuberculosis 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.
Trecator has been found to temporarily raise serum concentrations of isoniazid. Trecator may potentiate the adverse effects of other anti-tuberculous 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
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.
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.
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.