About This Calculator

The Isoniazid Dose Calculator (TB) is a clinical support tool designed to help healthcare professionals determine appropriate Isoniazid (INH) dosages for patients being treated for active or latent tuberculosis (TB). Calculations are based on patient weight, category (adult or pediatric), and specific treatment regimen, aligning with current CDC guidelines.

Outputs Explained

After entering the required patient data, the calculator provides the following key outputs:

• Calculated Dose: The weight-based dose in milligrams (mg), presented as a specific value for adults or a range for pediatric patients (e.g., 10-15 mg/kg).
• Recommended Dose: A practical dose rounded to the nearest 50 mg for ease of administration, without exceeding the maximum recommended dose for the selected regimen.
• Suggested Tablet Combination: A possible way to achieve the recommended dose using common Isoniazid tablet strengths (e.g., 300 mg, 100 mg, 50 mg).

How to Use the Tool

Follow these simple steps to calculate an Isoniazid dose:

1. Enter Patient Weight: Input the patient's weight and select the appropriate unit (kg or lbs).
2. Select Patient Category: Choose between 'Adult' and 'Pediatric' to apply the correct dosing parameters.
3. Choose Indication & Regimen: Select the treatment context from the dropdown menu, specifying active vs. latent TB and the dosing frequency (e.g., Daily, Twice Weekly).
4. Calculate: Click the "Calculate Dose" button to generate the dosing recommendations.

Dosing Overview

Isoniazid dosing is weight-based and varies by patient age and treatment frequency. This tool uses the following standard parameters derived from CDC guidelines:

• Adults (Daily): 5 mg/kg, maximum 300 mg/day.
• Adults (Intermittent): 15 mg/kg (for twice or thrice weekly regimens), maximum 900 mg/dose.
• Pediatrics (Daily): 10-15 mg/kg, maximum 300 mg/day.
• Pediatrics (Intermittent): 20-30 mg/kg (for twice or thrice weekly regimens), maximum 900 mg/dose.

It is crucial to co-administer Pyridoxine (Vitamin B6) at 25-50 mg/day to all patients receiving Isoniazid to prevent peripheral neuropathy.

Switching Regimens

Any decision to switch a patient's dosing regimen, such as moving from daily to intermittent (twice or thrice weekly) therapy, must be made by a qualified healthcare provider. Intermittent regimens are typically administered as part of a directly observed therapy (DOT) program to ensure adherence and efficacy.

Missed Dose Information

Management of a missed dose depends on the treatment regimen and the time elapsed. Patients should be instructed not to double their next dose. Refer to local guidelines or consult an infectious disease specialist for specific advice. For intermittent regimens, a single missed dose may require adjustment of the administration schedule.

Safety Alerts

Frequently Asked Questions (FAQ)

Why is the 'Recommended Dose' rounded?

The recommended dose is rounded to the nearest 50 mg to facilitate practical dosing using available tablet formulations (e.g., 50 mg, 100 mg, 300 mg), making it easier for patients to adhere to treatment.

Does this calculator account for renal or hepatic impairment?

No. This tool calculates standard doses for patients with normal organ function. Significant dose adjustments may be required in patients with severe renal or hepatic impairment. Always consult specific guidelines and prescribing information for these populations.

What is Directly Observed Therapy (DOT)?

DOT is a strategy where a healthcare worker observes the patient taking their medication. It is the standard of care for intermittent (twice or thrice weekly) TB treatment regimens to ensure adherence and prevent the development of drug resistance.

Why is Vitamin B6 (Pyridoxine) given with Isoniazid?

Isoniazid can interfere with pyridoxine metabolism, leading to a deficiency that causes peripheral neuropathy (numbness, tingling, or pain in the hands and feet). Co-administration of pyridoxine prevents this adverse effect.

What is the maximum dose of Isoniazid?

For daily therapy, the maximum dose is 300 mg. For intermittent therapy (twice or thrice weekly), the maximum dose is 900 mg.

Can this calculator be used for neonates?

While the tool includes a 'Pediatric' category, dosing for neonates and very young infants requires specialized consultation. Always refer to pediatric infectious disease guidelines for this population.

Is the dosing different for active TB versus latent TB infection (LTBI)?

The mg/kg dose of Isoniazid is similar for both indications. However, the overall treatment regimen, including duration and the use of other medications, differs significantly. This tool only calculates the Isoniazid dose, not the full regimen.

Who needs regular liver function monitoring?

Patients with risk factors such as pre-existing liver disease, regular alcohol use, age >35, or those taking other hepatotoxic medications should have their liver enzymes monitored regularly during therapy.

References

1. Nahid, P., et al. (2016). Official American Thoracic Society/Centers for Disease Control and Prevention/Infectious Diseases Society of America Clinical Practice Guidelines: Treatment of Drug-Susceptible Tuberculosis. Clinical Infectious Diseases, 63(7), e147–e195. https://doi.org/10.1093/cid/ciw376
2. Centers for Disease Control and Prevention (CDC). (2016). Core Curriculum on Tuberculosis: What the Clinician Should Know. Treatment of Latent TB Infection and TB Disease. View PDF
3. World Health Organization (WHO). (2017). Guidelines for treatment of drug-susceptible tuberculosis and patient care. https://www.who.int/publications/i/item/9789241550000
4. Isoniazid Tablet - Prescribing Information. U.S. Food and Drug Administration (FDA). View Label