(PZA), RMP, INH Rash: PZA, RMP, Ethambutol (EMB) Thrombocytopenia is only caused by RMP and no test dosing need be done. Regimens omitting RMP are discussed below. Please refer to the entry on rifampicin for further details. The most frequent cause of neuropathy is INH. The peripheral neuropathy of INH is always a pure sensory neuropathy and finding a motor component to the peripheral neuropathy should always prompt a search for an alternative cause. Once a peripheral neuropathy has occurred, INH must be stopped and pyridoxine should be given at a dose of 50 mg thrice daily. Simply adding high dose pyridoxine to the regimen once neuropathy has occurred will not stop the neuropathy from progressing. Patients at risk of peripheral neuropathy from other causes (diabetes mellitus, alcoholism, renal failure, malnutrition, pregnancy, etc.) should all be given pyridoxine 10 mg daily at the start of treatment. Please refer to the entry on isoniazid for details on other neurological side effects of INH. Rashes are most frequently due to PZA, but can occur with any of the TB drugs. Test dosing using the same regimen as detailed below for hepatitis may be necessary to determine which drug is responsible. Itching RMP commonly causes itching without a rash in the first two weeks of treatment: treatment should not be stopped and the patient should be advised that the itch usually resolves on its own. Short courses of sedative antihistamines such as chlorpheniramine may be useful in alleviating the itch. Fever during treatment can be due to a number of causes. It can occur as a natural effect of tuberculosis (in which case it should resolve within three weeks of starting treatment). Fever can be a result of drug resistance (but in that case the organism must be resistant to two or more of the drugs). Fever may be due to a superadded infection or additional diagnosis (patients with TB are not exempt from getting influenza and other illnesses during the course of treatment). In a few patients, the fever is due to drug allergy. The clinician must also consider the possibility that the diagnosis of TB is wrong. If the patient has been on treatment for more than two weeks and if the fever had initially settled and then come back, it is reasonable to stop all TB medication for 72 hours. If the fever persists despite stopping all TB medication, then