What is the standard treatment regimen for tuberculosis using Isoniazid (Isoniazide)?

Standard Treatment Regimen for Tuberculosis Using Isoniazid

The standard treatment regimen for tuberculosis consists of a two-month initial phase of isoniazid, rifampicin, pyrazinamide, and ethambutol, followed by a four-month continuation phase of isoniazid and rifampicin (2HRZE/4HR). 1

Initial Phase (First 2 Months)

The initial phase of treatment includes four drugs:

• Isoniazid (H): 5 mg/kg up to 300 mg daily in a single dose 2
• Rifampicin (R): 10 mg/kg (450 mg for patients <50 kg; 600 mg for patients >50 kg) 1
• Pyrazinamide (Z): 35 mg/kg (1.5 g for patients <50 kg; 2.0 g for patients >50 kg) 1
• Ethambutol (E): 15 mg/kg 1

Important considerations for the initial phase:

• Daily dosing is strongly recommended 1
• Ethambutol may be omitted in patients with low risk of isoniazid resistance (previously untreated white patients who are HIV-negative and not contacts of cases with known drug resistance) 1
• Drug susceptibility testing should be performed on organisms initially isolated from all newly diagnosed tuberculosis patients 2

Continuation Phase (Next 4 Months)

After the initial two months, treatment continues with:

• Isoniazid: 5 mg/kg up to 300 mg daily
• Rifampicin: 10 mg/kg (450 mg for patients <50 kg; 600 mg for patients >50 kg)

Special Situations

Extended Treatment Duration

Treatment should be extended in the following situations:

1. Meningeal/CNS tuberculosis: 12 months total (2HRZE/10HR) 1
2. Cavitary pulmonary TB with positive sputum culture at 2 months: 7-month continuation phase (9 months total) 1
3. When pyrazinamide is not included in initial phase: 9 months total treatment 1

Drug Resistance Management

• Isoniazid resistance: If discovered before treatment, use rifampicin, pyrazinamide, ethambutol, and streptomycin for 2 months, followed by rifampicin and ethambutol for 7 months 1
• Rifampicin resistance: Requires extended treatment (18 months) with alternative regimens 1
• Pyrazinamide resistance or M. bovis: Rifampicin and isoniazid for 9 months, with ethambutol for initial 2 months 1

Fixed-Dose Combinations

Fixed-dose combinations may provide more convenient drug administration 1:

• Two drugs (isoniazid and rifampicin)
• Three drugs (isoniazid, rifampicin, and pyrazinamide)
• Four drugs (isoniazid, rifampicin, pyrazinamide, and ethambutol)

Monitoring During Treatment

• Liver function should be monitored if pre-existing liver disease exists or if symptoms develop (fever, malaise, vomiting, jaundice) 1
• If AST/ALT rises to five times normal or bilirubin rises, stop rifampicin, isoniazid, and pyrazinamide 1
• Sputum cultures should be monitored to confirm conversion to negative

Patient-Centered Approach

A patient-centered approach to treatment should be implemented to ensure adherence:

• Directly observed therapy (DOT) or video-observed therapy (VOT) may be necessary 1
• Treatment supporters may be identified and trained 1
• Regular follow-up to monitor for adverse effects and response to treatment

Common Pitfalls to Avoid

1. Inadequate initial regimen: Always start with four drugs in the initial phase unless there is a very low risk of resistance
2. Premature discontinuation: Complete the full course of therapy even when symptoms improve
3. Failure to monitor for adverse effects: Watch for hepatotoxicity, especially in patients with risk factors
4. Poor adherence management: Implement strategies to ensure treatment completion
5. Ignoring drug interactions: Rifampicin has numerous drug interactions that must be managed

The 6-month regimen (2HRZE/4HR) has been proven effective across various populations and health systems, with high cure rates when properly administered and completed.