Ethambutol adverse effects

Retrobulbar neuritis is the major adverse effect noted in patients treated with ethambutol. Patients usually complain of a change in visual acuity and/or inability to see the color green. Vision testing should be performed on all patients who must receive ethambutol for more than 2 months. 

Hypersensitivity to ethambutol is rare. The most common serious adverse event is retrobulbar neuritis, resulting in loss of visual acuity and red-green color blindness. This dose-related adverse effect is more likely to occur at dosages of 25 mg/kg/d continued for several months. At 15 mg/kg/d or less, visual disturbances are very rare. Periodic visual acuity testing is desirable if the 25 mg/kg/d dosage is used. Ethambutol is relatively contraindicated in children too young to permit assessment of visual acuity and red-green color discrimination. 

The mechanism of ethambutol (Myambutol) is not fully understood. This drug apparently suppresses RNA synthesis in susceptible bacteria, but it is not known how this occurs. Ethambutol is primarily effective against M. tuberculosis infections and is a secondary agent in the treatment of tuberculosis.61 Adverse effects associated with this drug include joint pain, nausea, skin rash and itching, and CNS abnormalities (dizziness, confusion, hallucinations). 

Ethambutol [e THAM byoo tole] is bacteriostatic and specific for most strains of M- tuberculosis and M- kansasii. Resistance is not a serious problem if the drug is employed with other antituberculous agents. Ethambutol can be used in combination with pyrazinamide, isoniazid, and rifampin to treat tuberculosis. Absorbed on oral administration, ethambutol is well distributed throughout the body. Penetration into the central nervous system (CNS) is therapeutically adequate in tuberculous meningitis. Both parent drug and metabolites are excreted by glomerular filtration and tubular secretion. The most important adverse effect is optic neuritis, which results in... 

Retrobulbar neuritis is the major adverse effect noted in patients treated with ethambutol, Patients usually complain of a change in visual acuity and/or inability to see the color green. Vision testing should be performed on all patients who must receive ethambutol for more than 2 months. Impairment of eighth cranial nerve function is the most important adverse effect of streptomycin, Vestibular function is most frequently affected, but hearing may also be impaired. Audiometric testing should be performed in patients who must receive streptomycin for more than 2 months. Streptomycin occasionally causes nephrotoxicity. 

ETHAMBUTOL ANTIVIRALS-DIDANOSINE Possibly t adverse effects (e.g. peripheral neuropathy) with didanosine Additive side-effects Monitor closely for development of peripheral neuropathy but no dose adjustment is required... 

The adverse effects of ethambutol are mainly seen in patients taking very high doses, that is over 25 mg/kg/day. Dosages over 25 mg/kg/day should be administered for only about 2 weeks at the beginning of therapy. Treatment can then be continued with 15 mg/kg/day. If initial problems arise and ethambutol is essential, the daily dose should not exceed 10 mg/kg. 

No adverse effects during lactation have been attributed to ethambutol (24). 

Side effects caused by isoniazid, rifampin, pyrazinamide, and ethambutol are common and can include hepatotoxic-ity, peripheral neuropathy, optic neuritis, and Gl side effects. All four agents can potentially be hepatotoxic, but this side effect is most frequently associated with isoniazid and rifampin. Peripheral neuropathy is most commonly associated with isoniazid, whereas optic neuritis is associated with ethambutol. The metabolism of isoniazid is genetically predetermined. Patients of Scandinavian, European, and African descent metabolize isoniazid slower (slow acetylators) and are therefore more predisposed to hepatotoxicity and peripheral neuropathy due to isoniazid. Fast acetylators include people of Asian or American Indian descent and are less predisposed to these adverse effects. 

Nervous system The adverse effects of antituberculosis drugs on the nervous system have been reviewed [1 ]. Isoniazid is most often associated with nervous system reactions, most prominently peripheral neuropathy, psychosis, and seizures. Optic neuropathy can occur with ethambutol and ototoxicity and neuromuscular blockade with aminoglycosides. Cycloserine can cause psychosis and seizures, and the psychosis in particular limits its use. Fluoroquinolones are rare causes of seizures and delirium. Significant neurotoxicity has not been documented with newer forms of therapy under development. 

An interesting and unusual adverse effect attributed to pyrazinamide was described in a paper from the United States (54 ). A patient was described who suffered several attacks of acute intermittent porphyria whilst under treatment for tuberculosis. The first attack occurred after 18 months therapy with isoniazid and ethambutol. The second episode occurred after 14 days treatment with rifampicin, 7 days treatment with pyrazinamide and 3 days treatment with streptomycin. The patient was subsequently treated successfully with a combination of rifampicin, ethambutol and capreomycin. The compounds were investigated for their capacity to induce hepatic delta-aminolaev-ulinic acid synthesis in an in vitro preparation of rat Uver. The results showed that pyrazinamide had a greater potential for inducing the enzyme activity than any of the other compounds. It is worthy of note, however, that in this in vitro system para-aminosalicylic acid, rifampicin, cycloserine and ethionamide all induced increased delta-aminolaevulinic acid synthesis. 

Because of the dangerous adverse reactions (including the risk of death), individuals should not take methylphenidate if they have taken a class of drugs known as monamine oxidase (MAO) inhibitors within 14 days. Most MAO inhibitors are antidepressants, but some anti-tuberculosis drugs such as Ethambutol also have MAO effects. Since drug users are prone to many infectious diseases, it is not unheard of for drug abusers to come down with tuberculosis (TB). 

Ethambutol produces very few untoward reactions. Fewer than 2% of nearly 2000 patients who received daily doses of 15 mg/kg of ethambutol had adverse reactions 0.8% experienced diminished visual acuity, 0.5% had a rash, and 0.3% developed drug fever. Other side effects that have been observed are pruritus, joint pain, gastrointestinal upset, abdominal pain, malaise, headache, dizziness, mental confusion, disorientation, and possible hallucinations. Numbness and tingling of the fingers owing to peripheral neuritis are infrequent. Anaphylaxis and leukopeifia are rare. 

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