What is the appropriate treatment regimen for an 8kg child with tuberculosis, specifically the dosage of first-line antibiotics such as isoniazid (Directly Observed Therapy, Short-Course, DOTS (DSTB) treatment) in syrup form?

Treatment of Drug-Susceptible Tuberculosis in an 8kg Child

For an 8kg child with drug-susceptible tuberculosis, administer 2 dispersible fixed-dose combination (FDC) tablets daily (rifampicin/isoniazid/pyrazinamide 75/50/150 mg) for the first 2 months, followed by 2 tablets of rifampicin/isoniazid (75/50 mg) for 4 months, for a total treatment duration of 6 months. 1, 2

Standard First-Line Regimen

The treatment consists of two phases:

Intensive Phase (First 2 Months)

• Rifampicin: 150 mg daily (18.75 mg/kg) 3
• Isoniazid: 100 mg daily (12.5 mg/kg) 3
• Pyrazinamide: 300 mg daily (37.5 mg/kg) 3
• Fourth drug consideration: Add ethambutol or streptomycin if drug resistance is suspected or if isoniazid resistance rate in the community exceeds 4% 1, 4, 5

Continuation Phase (Months 3-6)

• Rifampicin: 150 mg daily 3
• Isoniazid: 100 mg daily 3

Syrup Formulation Dosing

If using individual syrups instead of FDC tablets:

• Rifampicin syrup (20 mg/mL): 7.5 mL daily (150 mg) 3
• Isoniazid: 10-15 mg/kg/day = 80-120 mg daily 3, 1
• Pyrazinamide: 30-40 mg/kg/day = 240-320 mg daily 3

Critical Considerations for the Fourth Drug

For children under 5 years who cannot cooperate with visual acuity monitoring, streptomycin 20-40 mg/kg/day IM (160-320 mg daily for this 8kg child) is preferred over ethambutol. 2, 5 However, ethambutol at 15-25 mg/kg/day (120-200 mg daily) can be used if streptomycin is unavailable, as the risk of ocular toxicity is minimal at 15 mg/kg daily. 3, 2

Important Dosing Nuances

Current WHO-recommended weight band dosing may result in suboptimal rifampicin exposures in children. 6, 7 Studies show rifampicin exposure in the 8-12 kg weight band can be up to 50% lower than adult targets. 6 Despite this pharmacokinetic limitation, the 2-tablet regimen remains the standard recommendation until new FDC formulations become available. 3, 1

Essential Supportive Measures

• Pyridoxine (vitamin B6) supplementation: Mandatory for malnourished children, breastfed infants, and HIV-infected children to prevent isoniazid-induced peripheral neuropathy 1, 8
• Directly observed therapy (DOT): Strongly recommended throughout the entire 6-month treatment course 1, 4, 5

Treatment Duration Modifications

Extend treatment to 12 months if any of the following are present:

• TB meningitis or CNS involvement 1, 8, 5
• Miliary tuberculosis 1, 5
• Bone/joint tuberculosis 1, 5

For these severe forms, use the same 4-drug intensive phase for 2 months, followed by rifampicin and isoniazid for 10 additional months. 1, 8

Common Pitfalls to Avoid

• Inadequate fourth drug inclusion: Always include ethambutol or streptomycin in the initial regimen until drug susceptibility results confirm full susceptibility, unless primary isoniazid resistance is documented to be <4% in your community 1, 4, 5
• Failure to recalculate doses with weight gain: Dosages should be recalculated as the child gains weight during treatment 1
• Premature discontinuation: The full 6-month course must be completed even if clinical improvement occurs earlier 9, 5
• Inadequate monitoring: Baseline liver function should be checked, with repeat testing if fever, malaise, vomiting, or jaundice develop 3

Drug Resistance Scenarios

If isoniazid resistance is confirmed but rifampicin susceptibility is maintained, switch to rifampicin, pyrazinamide, ethambutol, and levofloxacin for 6-12 months. 3, 1 For suspected multidrug-resistant TB (resistance to both isoniazid and rifampicin), immediate consultation with a TB specialist is mandatory, and treatment should include at least 4 drugs likely to be effective based on susceptibility patterns. 3, 1