What is the dosage of anti-tuberculosis (TB) medication, such as isoniazid and rifampin, per kilogram for a patient with a cold abscess suspected to be caused by tuberculosis?

Anti-Tuberculosis Medication Dosing Per Kilogram for Cold Abscess

For a patient with a cold abscess suspected to be caused by tuberculosis, use the standard 6-month four-drug regimen with weight-based dosing: isoniazid 5 mg/kg (max 300 mg), rifampin 10 mg/kg (max 600 mg), pyrazinamide 15-30 mg/kg (max 2000 mg), and ethambutol 15-20 mg/kg for the initial 2 months, followed by isoniazid and rifampin for 4 additional months. 1, 2, 3

Initial Phase (First 2 Months) - Four-Drug Regimen

Isoniazid Dosing

• Adults: 5 mg/kg daily, maximum 300 mg/day 3
• Children: 10-15 mg/kg daily, maximum 300 mg/day 3, 1
• Intermittent dosing (if using DOT): Adults 15 mg/kg (max 900 mg) 2-3 times weekly; Children 20-40 mg/kg (max 900 mg) 2-3 times weekly 3

Rifampin Dosing

• Adults: 10 mg/kg daily, maximum 600 mg/day 2, 1
• Children: 10-20 mg/kg daily, maximum 600 mg/day 2
• Weight-based adult dosing: <50 kg = 450 mg; ≥50 kg = 600 mg 1
• Administer 1 hour before or 2 hours after meals with full glass of water 2

Pyrazinamide Dosing

• Adults daily: 15-30 mg/kg (maximum 2000 mg/day) 1
• Weight-banded adult dosing:
  • 40-55 kg: 1000 mg daily 4
  • 56-75 kg: 1500 mg daily 4
  • 76-90 kg: 2000 mg daily 4
• Children: 15-30 mg/kg daily (maximum 2000 mg) 1
• Intermittent dosing: 50-70 mg/kg twice weekly (max 4000 mg) 4

Ethambutol Dosing

• Adults and children: 15-20 mg/kg daily 1
• Intermittent dosing: 25-30 mg/kg three times weekly 1
• Can be omitted only if primary isoniazid resistance is <4% in the community AND patient has no prior TB treatment AND no exposure to drug-resistant cases 5

Continuation Phase (Months 3-6) - Two-Drug Regimen

Isoniazid and Rifampin Only

• Continue same per-kilogram dosing as initial phase 1
• Duration: 4 additional months for total of 6 months treatment 1, 5
• For extrapulmonary TB including bone/joint involvement (which cold abscess may represent), standard 6-month regimen is appropriate 5

Critical Dosing Considerations for Cold Abscess

Extrapulmonary TB Management

• Cold abscess represents extrapulmonary TB, typically bone/joint involvement 5
• Use same drug regimen and dosing as pulmonary TB 5
• Exception: Children with bone/joint TB should receive minimum 12 months therapy 5
• Adults with bone/joint TB can receive standard 6-month regimen 1

Fixed-Dose Combination Tablets (Alternative)

• Rifater® (contains rifampin 120 mg + isoniazid 50 mg + pyrazinamide 300 mg per tablet):
  • ≤44 kg: 4 tablets daily 1
  • 45-54 kg: 5 tablets daily 1
  • ≥55 kg: 6 tablets daily 1
  • Critical pitfall: Patients >90 kg require additional pyrazinamide tablets to achieve adequate dosing 1, 4

Common Pitfalls to Avoid

Dosing Errors

• Over-dosing is more common than under-dosing in national TB programs, particularly with isoniazid and pyrazinamide 6
• Patients at upper end of weight bands should receive higher dose to ensure adequate drug exposure 4
• Do not use Rifater® in patients >90 kg without adding extra pyrazinamide 1, 4

Duration Errors

• Do not continue pyrazinamide beyond 2 months in drug-susceptible TB, even if extending total treatment duration 4
• For children with bone/joint TB, extend total treatment to 12 months (not just 6 months) 5

Monitoring Requirements

• Baseline liver function tests required 4
• If AST/ALT rises to 5 times normal or bilirubin rises, stop rifampin, isoniazid, and pyrazinamide immediately 1, 4
• Monthly monitoring for adherence and adverse effects 4

Drug Resistance Considerations

• Include ethambutol as fourth drug unless community isoniazid resistance is documented <4% 5
• If isoniazid resistance confirmed, continue rifampin, ethambutol, and pyrazinamide for full 6 months (do not drop to 2-drug continuation phase) 7

Special Populations

Pregnancy

• All four drugs (isoniazid, rifampin, pyrazinamide, ethambutol) can be used 8
• Add prophylactic pyridoxine 10 mg/day 8
• Avoid streptomycin due to fetal ototoxicity 8

Renal Impairment

• Adjust ethambutol and streptomycin doses based on creatinine clearance 8
• Rifampin and isoniazid generally do not require adjustment 2, 3

HIV Co-infection

• Use same dosing regimen as HIV-negative patients 4, 8
• Monitor closely for malabsorption and consider therapeutic drug monitoring 8
• Rifabutin-based regimens may be necessary with protease inhibitors or NNRTIs 4