Recommended Doses of Tuberculosis Medications Based on Body Weight
The recommended daily doses for first-line tuberculosis medications are: isoniazid 5-10 mg/kg (maximum 300 mg), rifampicin 10-20 mg/kg (maximum 600 mg), pyrazinamide 15-30 mg/kg (maximum 2000 mg), and ethambutol 15-25 mg/kg (maximum 2500 mg). 1, 2
Standard Daily Dosing for Adults
| Drug | Daily Dose (mg/kg) | Maximum Daily Dose |
|---|---|---|
| Isoniazid | 5 mg/kg | 300 mg |
| Rifampicin | 10 mg/kg | 600 mg |
| Pyrazinamide | 15-30 mg/kg | 2000 mg |
| Ethambutol | 15 mg/kg | 2500 mg |
Standard Daily Dosing for Children
| Drug | Daily Dose (mg/kg) | Maximum Daily Dose |
|---|---|---|
| Isoniazid | 10-15 mg/kg | 300 mg |
| Rifampicin | 10-20 mg/kg | 600 mg |
| Pyrazinamide | 15-30 mg/kg | 2000 mg |
| Ethambutol | 15-25 mg/kg | 2500 mg |
Weight-Based Considerations
- For adults weighing <50 kg, rifampicin dose is typically 450 mg daily
- For adults weighing >50 kg, rifampicin dose is typically 600 mg daily 1
- For pyrazinamide, adults <50 kg typically receive 1.5 g daily, while those >50 kg receive 2.0 g daily 1
Intermittent Dosing Options
For directly observed therapy (DOT) regimens, higher doses are used less frequently:
Three Times Weekly Dosing
| Drug | Dose (mg/kg) | Maximum Dose |
|---|---|---|
| Isoniazid | 15 mg/kg | 900 mg |
| Rifampicin | 10 mg/kg | 600 mg |
| Pyrazinamide | 50-70 mg/kg | 3000 mg |
| Ethambutol | 30 mg/kg | 2500 mg |
Twice Weekly Dosing
| Drug | Dose (mg/kg) | Maximum Dose |
|---|---|---|
| Isoniazid | 15 mg/kg | 900 mg |
| Rifampicin | 10 mg/kg | 600 mg |
| Pyrazinamide | 50-70 mg/kg | 3000 mg |
| Ethambutol | 45-50 mg/kg | 2500 mg |
Special Considerations
- Hepatotoxicity risk: The risk of isoniazid-induced hepatitis increases with dose when used in combination with rifampicin. Evidence suggests that a dose of 5 mg/kg is appropriate and safe for adults 1
- Ethambutol in children: Ethambutol can be recommended for children aged ≥5 years at a dosage of 15 mg/kg daily without taking more precautions than for adults 1
- Ethambutol dosing strategy: The American Thoracic Society recommends 25 mg/kg during the intensive phase of treatment (first 8 weeks) followed by 15 mg/kg during the continuation phase 1
- Liver function monitoring: Liver function should be tested before starting therapy and monitored when clinical signs of hepatotoxicity appear (fever, malaise, vomiting, jaundice, and weight loss) 1
Drug Interactions and Side Effects
- Rifampicin is an important inducer of hepatic enzymes, which may reduce the effectiveness of other drugs metabolized in the liver, including oral contraceptives 1
- When used simultaneously, isoniazid and rifampicin can produce hepatitis in 3-4% of patients, typically appearing during the first 2 weeks of treatment 1
- Pyrazinamide may cause arthralgia related to elevated uric acid levels, which requires monitoring especially in older patients 3
Multidrug-Resistant TB (MDR-TB)
For MDR-TB (resistance to at least isoniazid and rifampicin), patients should be referred to specialized centers with appropriate expertise and laboratory services 1. Treatment requires individualized regimens based on susceptibility testing.
Remember that monitoring for adverse effects is crucial, particularly for hepatotoxicity with isoniazid, rifampicin, and pyrazinamide; optic neuritis with ethambutol; and ototoxicity with injectable agents like streptomycin.