The characteristic toxicity of ethambutol is
Correct Answer: Visual field defects
Description: Ethambutol It is selectively tuberculostatic. mechanism of action:- It has been found to inhibit arabinosyl transferases (encoded by embABgenes) involved in arabinogalactan synthesis thereby interfering with mycolic acid incorporation in mycobacterial cell wall. Ethambutol Resistance:- Develops slowly and is most commonly associated with mutation in embB gene, reducing the affinity of the target enzyme for Ethambutol. No cross resistance with any other antitubercular drug has been noted. pharmacokinetics:- About 3/4 of an oral dose of Ethambutol is absorbed.It is distributed widely, but penetrates meninges incompletely and is temporarily stored in RBCs. Less than 1/2 of E is metabolized. It is excreted in urine by glomerular filtration and tubular secretion; plasma t 1/2 is ~4 hrs. Caution isrequired in its use in patients with renal disease. side effects:- Loss of visual acuity/colour vision, field defects due to optic neuritis is the most impoant dose and duration of therapy dependent toxicity. Contraindication:- Young children & patients with optic neuritis. Ref:- kd tripathi; pg num:-769
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