Ethambutol
Mechanism :
Ethambutol is an oral chemotherapeutic agent which is specifically effective against actively growing Mycobacteria, including M. tuberculosis. Ethambutol inhibits arabinosyl transferases which is involved in cell wall biosynthesis. By inhibiting this enzyme, the bacterial cell wall complex production is inhibited. This leads to an increase in cell wall permeability. No cross resistance with other available antimycobacterial agents has been demonstrated.
Indication :
- Tuberculosis
- Mycobacterium avium complex prophylaxis
Contraindications :
Ethambutol is contraindicated in patients who are known to be hypersensitive to this drug, in patients with known optic neuritis, in patients who are unable to appreciate and report visual side effects or changes in vision (e.g., young children, unconscious patients. Ethambutol should be used with caution in children until they are at least 1 years old capable of reporting symptomatic visual changes accurately. Patients should undergo a full ophthalmic examination before starting treatment.
Dosing :
Dose:
20 mg/kg orally once a day;
Max:
1000 mg/day.
Adverse Effect :
Red/green colour blindness, optic neuritis, rash, pruritus, peripheral neuritis, urticaria, thrombocytopenia, vomiting and nausea, diarrhea have been reported in patients.
Interaction :
Aluminium hydroxide: Reduction of mean serum concentrations of ethambutol.
Renal Dose :
Dose in Renal Impairment GFR (mL/min)
| 20-50 | Dose as in normal renal function |
| 10-20 | 15 mg/kg every 24–36 hours, or 7.5–15 mg/kg/day |
| <10 | 15 mg/kg every 48 hours, or 5–7.5 mg/kg/day |
Dose in Patients undergoing Renal Replacement Therapies
| CAPD | Not dialysed. Dose as in GFR<10 mL/min |
| HD | Dialysed. Dose as in GFR<10 mL/ min, or on dialysis days only give 25 mg/kg post-dialysis |
| HDF/High flux | Dialysed. Dose as in GFR<10 mL/ min, or on dialysis days only give 25 mg/kg post-dialysis |
| CAV/VVHD | Dialysed. Dose as in GFR=10– 20 mL/min |
Hepatic Dose :
No dosage adjustments are recommended. Ethambutol should be used cautiously in patients with hepatic disease as the drug itself is hepatotoxic. Severe hepatic disease including fatalities have been reported.