Ethambutol Dosing for an 8kg Pediatric Patient
For an 8kg child with tuberculosis, ethambutol should be dosed at 20 mg/kg daily (160 mg), using the 100 mg tablet formulation with appropriate splitting or crushing to achieve the correct dose. 1
Formulation Available
- Ethambutol is available as 100 mg and 400 mg tablets 1
- For an 8kg child, the 100 mg tablet is the most practical formulation for dose preparation 1
Recommended Dosing
Daily Therapy
- Dose: 20 mg/kg daily (range 15-25 mg/kg) 1, 2
- For an 8kg child: 160 mg daily (1.5 tablets of 100 mg) 1
- This can be achieved by giving 1½ of the 100 mg tablets 1
Intermittent Therapy (if using twice-weekly DOT)
- Dose: 50 mg/kg twice weekly (maximum 4g) 1
- For an 8kg child: 400 mg twice weekly (1 tablet of 400 mg or 4 tablets of 100 mg) 1
Critical Dosing Considerations
The standard 15 mg/kg dose commonly cited produces subtherapeutic levels in young children due to different pharmacokinetics. 2, 3 Children achieve significantly lower peak serum concentrations than adults at equivalent mg/kg doses, necessitating the higher end of the dosing range. 2, 3
- Doses of 20 mg/kg (range 15-25 mg/kg) daily are safe and achieve therapeutic serum levels in children of all ages 2
- At these doses, ocular toxicity occurred in only 0.05% (2 of 3,811 children) in the largest pediatric safety review 2
- Body surface area-based dosing (867 mg/m²) may be more accurate but weight-based dosing at 20 mg/kg is simpler and effective 3
Safety Monitoring Requirements
Visual Monitoring Challenges
For an 8kg child (likely under 2 years old), standard visual acuity testing is impossible, creating a significant monitoring challenge. 4, 5
- Parental education is essential: Instruct caregivers to watch for behavioral changes suggesting vision problems (bumping into objects, difficulty reaching for items, loss of interest in visual stimuli) 5
- Monthly clinical assessment should include questioning parents about any concerning visual behaviors 4, 5
- Visual-evoked potentials (VEPs) can be used if available, though this requires specialized equipment 5
When to Use Ethambutol Despite Monitoring Limitations
Ethambutol should be included in the regimen for an 8kg child when: 4
- Drug resistance (especially isoniazid or rifampin resistance) is suspected or confirmed 4
- The child has exposure to a source case with known drug-resistant TB 4
- The child is from an area with high prevalence of drug-resistant TB 4
The risk of inadequate treatment and development of further resistance outweighs the minimal risk of ocular toxicity at appropriate doses. 4, 2
Practical Administration
- Tablets can be crushed and mixed with small amounts of food or liquid for administration to young children 1
- Administer as a single daily dose 1, 4
- Give with food to improve tolerability, though this is less critical than with other TB medications 1
Common Pitfall to Avoid
Do not underdose based on fear of toxicity. The most common error is using 15 mg/kg in young children, which produces subtherapeutic levels and risks treatment failure. 2, 3 At the recommended 20 mg/kg dose, the risk of ocular toxicity remains extremely low (0.05-0.7%) while ensuring adequate drug exposure. 2, 3