ETHAMBUTOL-Anti Tuberculosis Drug
Ethambutol is effective against mycobacteria
and has no effect on other organisms. It is probably cell wall synthesis
inhibitor. It exerts a bacteriostatic effect after a period of 24 hours.
Resistance:
Use of drug alone cause the resistance rapidly. Resistance
to ethambutol is due to mutations resulting in overexpression of emb gene
products or within the embB structural gene. Therefore, ethambutol is always
given in combination with other antituberculous drugs.
Ethambutol may be discontinued if the isolate is
determined to be susceptible to isoniazid, rifampin, and pyrazinamide.
Pharmacokinetic:
Ethambutol is given orally and is well absorbed. In
the blood, it is taken up by erythrocytes and slowly released. It can reach
therapeutic concentrations in the Cerebro Spinal Fluid in tuberculous
meningitis Ethambutol is partly metabolised and is excreted in the urine.
Unwanted effects:
Unwanted effects are not common. The most important
are optic neuritis, is more likely to occur if renal function is
decreased and is dose-related. This results in visual disturbances exhibiting
initially as red–green colour blindness progressing to a decreased visual
acuity. Colour vision should be monitored before and during prolonged treatment.
Contra indication:
Uric acid excretion is decreased by ethambutol, and
caution should be exercised in patients with gout. Ethambutol is relatively
contraindicated in children too young to permit assessment of visual acuity and
red-green color discrimination.