What is the recommended dosage for first-line tuberculosis medications?

First-Line Tuberculosis Medication Dosages

The recommended dosages for first-line tuberculosis medications include isoniazid 5 mg/kg daily (maximum 300 mg), rifampin 10 mg/kg daily (maximum 600 mg), pyrazinamide 15-30 mg/kg daily (maximum 2 g), and ethambutol 15 mg/kg daily. 1

Standard Treatment Regimen

The standard treatment for drug-susceptible tuberculosis consists of:

Initial Phase (2 months)

• Isoniazid (INH): 5 mg/kg daily, maximum 300 mg
• Rifampin (RIF): 10 mg/kg daily, maximum 600 mg (450 mg if <50 kg)
• Pyrazinamide (PZA): 15-30 mg/kg daily, maximum 2 g
• Ethambutol (EMB): 15 mg/kg daily

Continuation Phase (4 months)

• Isoniazid: 5 mg/kg daily, maximum 300 mg
• Rifampin: 10 mg/kg daily, maximum 600 mg (450 mg if <50 kg)

Specific Dosing Considerations

Isoniazid

• Adults: 5 mg/kg daily (typically 300 mg) 1, 2
• Children: 10-15 mg/kg daily, maximum 300 mg 1, 2
• Pyridoxine (vitamin B6) 25-50 mg/day should be given with INH to all persons at risk of neuropathy (pregnant women, breastfeeding infants, persons with HIV, patients with diabetes, alcoholism, malnutrition, chronic renal failure, or advanced age) 1

Rifampin

• Adults: 10 mg/kg daily, maximum 600 mg (450 mg if <50 kg) 1, 3
• Children: 10-20 mg/kg daily, maximum 600 mg 1, 3
• Should be administered once daily, either 1 hour before or 2 hours after a meal with a full glass of water 3

Pyrazinamide

• Adults: 15-30 mg/kg daily, maximum 2 g 1, 4
• Children: 15-30 mg/kg daily 1, 4

Ethambutol

• Adults and children: 15 mg/kg daily 1
• Accurate calculation is required to reduce the risk of toxicity, particularly ocular toxicity 1
• Should be used with caution in children whose visual acuity cannot be monitored 2

Important Clinical Considerations

1. Drug Susceptibility Testing:

   • EMB can be discontinued once susceptibility to INH and RIF is confirmed 1
   • If drug resistance is suspected, treatment should be adjusted based on susceptibility results 2

2. Administration Schedule:

   • Daily dosing is strongly preferred for both intensive and continuation phases 1
   • Fixed-dose combinations may provide a more convenient form of drug administration and help with adherence 1

3. Special Populations:

   • HIV Co-infection: Same regimen, but may require longer treatment duration and careful monitoring for drug interactions 5
   • Liver Disease: Baseline and regular monitoring of liver function is required in patients with known chronic liver disease 1
   • Pregnancy: All first-line drugs except streptomycin can be used during pregnancy 5

4. Monitoring:

   • Regular clinical evaluations to monitor for adverse effects, including hepatotoxicity, optic neuritis, and peripheral neuropathy 5
   • Rifampicin blood levels may be monitored if poor response to treatment is suspected 1

Common Pitfalls to Avoid

1. Inadequate Dosing: Underdosing can lead to treatment failure and development of drug resistance 6

2. Poor Adherence Monitoring: Directly observed therapy (DOT) is recommended to ensure adherence and prevent the emergence of drug-resistant TB 5, 7

3. Inappropriate Management of Isoniazid Resistance: Treatment of isoniazid-resistant TB with standard first-line regimens may lead to suboptimal outcomes and acquired multidrug resistance 6

4. Failure to Adjust for Body Weight: Dosages should be calculated based on patient weight, with maximum doses observed 1

5. Neglecting Pyridoxine Supplementation: Always provide pyridoxine (B6) with isoniazid to prevent peripheral neuropathy in at-risk patients 1

By following these dosage recommendations and clinical considerations, treatment success rates exceeding 95% can be achieved for drug-susceptible tuberculosis 5.