Which of the following antimicrobials needs dose reduction even in mild renal failure?
Correct Answer: Ethambutol
Description: Ethambutol (E) Ethambutol is selectively tuberculostatic and clinically as active as S. Fast multiplying bacilli are more susceptible as are many atypical mycobacteria. Added to the triple drug regimen ofRHZ it has been found to hasten the rate of sputum conversion and to prevent development of resistance. The mechanism of action of E is not fulhunderstood, but it has been found to inhibit arabinosyl transferases involved in arabinogalactan synthesis and to interfere with mycolic acid incorporation in mycobacterial cell walL Resistance to E develops slowly; in many cases it is due to alteration in the drug target gene. Io cross resistance with any other antitubercular drug has been noted. About 3 I 4 of an oral dose of E is absorbed. It is distributed widely but penetrates meninge5 incompletely and is temporarily stored in RBCs Less than liz of E is metabolized. It is excreted in urine by glomerular filtration and tubular secretion; plasma halflife is 4 hrs. Caution is required in its use in patients with renal disease. Patient acceptability of E is very good and side effects are few. Loss of visual acuity I colour vision. field defects due to optic neuritis is the most impoant dose and duration of therapy dependent toxicity. Because young children ma,be unable to repo early visual impairment, it should not be used below 6 years of age. With early recognition and stoppage of therapy, visual toxicity is largely reversible. Ethambutol produces few other symptoms: nausea, rashes, fever, neurological changes are infrequent. Hyperuricemia is due to interference with urate excretion. It a commonly used antitubercular drug.Ethambutol hydrochloride, following a single oral dose of 25 mg/kg of body weight, attains a peak of 2 to 5 mcg/mL in serum 2 to 4 hours after administration. When the drug is administered daily for longer periods of time at this dose, serum levels are similar. The serum level of Ethambutol falls to undetectable levels by 24 hours after the last dose except in some patients with abnormal renal function. The intercellular concentrations of erythrocytes reach peak values approximately twice those of plasma and maintain this ratio throughout the 24 hours. REFERENCE: www.drugs.com ESSENTIALS OF MEDICAL PHARMACOLOGY(K.D.TRIPATHI,SIXTH EDITION,PAGE NO:742)
Category:
Pharmacology
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