Fixcom HRZE Dosing Information
For drug-susceptible tuberculosis, the standard fixed-dose combination (HRZE) regimen consists of a 2-month intensive phase with all four drugs followed by a 4-month continuation phase with HR only, with specific weight-based dosing that differs substantially between adults and children.
Standard Treatment Regimen Structure
The recommended approach is:
- Intensive phase (2 months): Isoniazid (H) + Rifampicin (R) + Pyrazinamide (Z) + Ethambutol (E)
- Continuation phase (4 months): Isoniazid (H) + Rifampicin (R) only 1
Adult Dosing (≥18 years, ≥50 kg)
Daily dosing for adults ≥50 kg:
- Isoniazid: 300 mg
- Rifampicin: 600 mg
- Pyrazinamide: 2.0 g
- Ethambutol: 15 mg/kg 1
For adults 30-50 kg:
- Isoniazid: 300 mg (same dose)
- Rifampicin: 450 mg
- Pyrazinamide: 1.5 g
- Ethambutol: 15 mg/kg 1
Pediatric Dosing (<30 kg)
Children require higher mg/kg doses than adults:
- Isoniazid: 10-15 mg/kg daily (max 300 mg)
- Rifampicin: 10-20 mg/kg daily (max 600 mg)
- Pyrazinamide: 30-40 mg/kg daily (max 2.0 g)
- Ethambutol: 15-20 mg/kg daily 2, 3
For children, the higher per-kilogram dosing is necessary due to different pharmacokinetics and faster drug clearance 2.
Fixed-Dose Combination Tablets
Available FDC preparations simplify administration and improve compliance:
- Rifater contains: 50 mg isoniazid + 120 mg rifampicin + 300 mg pyrazinamide per tablet 1
- These should be used whenever possible to prevent accidental monotherapy and emergence of drug resistance 1
The bioavailability of FDC tablets is equivalent to separate drug administration, and rifampicin-containing preparations allow compliance monitoring through orange/pink urine discoloration 1.
Intermittent Dosing Options
Three times weekly dosing (under directly observed therapy):
- Isoniazid: 15 mg/kg (max 900 mg)
- Rifampicin: 600 mg (adults >50 kg) or 450 mg (<50 kg)
- Pyrazinamide: 2.5 g (>50 kg) or 2.0 g (<50 kg)
- Ethambutol: 30 mg/kg 1
Twice weekly dosing:
- Pyrazinamide: 3.5 g (>50 kg) or 3.0 g (<50 kg)
- Ethambutol: 45 mg/kg 1
Critical Dosing Considerations
Weight-based adjustments are mandatory - the 50 kg threshold is critical for rifampicin (450 vs 600 mg) and pyrazinamide (1.5 vs 2.0 g) dosing in adults 1.
Ethambutol requires accurate calculation to minimize ocular toxicity risk. At 15 mg/kg daily, the risk is minimal, but increases substantially above 30 mg/kg 4. In children under 5 years where visual acuity cannot be monitored, ethambutol should only be used when drug resistance is suspected 4, 2.
The fourth drug (ethambutol) can be omitted only in patients with confirmed fully sensitive organisms and low risk of isoniazid resistance 1. However, given the difficulty in ascertaining drug resistance prevalence, most experts include ethambutol in the initial phase 5.
Recent Updates
For children 3 months to 16 years with nonsevere TB, a shortened 4-month regimen (2HRZE/2HR) is now recommended as an alternative to the standard 6-month regimen 6. This applies only to children without suspected multidrug-resistant TB.
Monitoring Requirements
Baseline liver function testing is not required in patients without pre-existing liver disease 1. However, treatment should be stopped if AST/ALT rises to 5 times normal or if bilirubin rises 1. Routine uric acid monitoring is not recommended but may serve as a compliance marker 4.