A5312: High-Dose Isoniazid

A5312: The Early Bactericidal Activity of High Dose or Standard Dose Isoniazid among Adult Participants with Isoniazid-Resistant or Drug Sensitive Tuberculosis

Study Description

This study is for participants who have pulmonary tuberculosis (TB), a bacterial infection in their lungs. Isoniazid (INH) is a drug commonly used to treat TB. Sometimes, the bacteria that cause TB can become resistant to INH, and then INH does not work as well at fighting the bacteria. This study will treat people with INH-resistant TB with different doses of INH to see whether INH can still fight the bacteria if we just increase the dose.

Treatment Category


Study Status


Why is this study being done?

This study will compare how well INH works at higher doses for participants who have resistant TB to how well the drug works at regular doses for participants who have TB that is sensitive to the drug. The study will also evaluate the safety and tolerability of the different doses of INH.

Who can join?

  • New or recurrent pulmonary TB
  • TB strain that is INH resistant
  • Adults over 18 years old.
  • No known exposure to extensively resistant TB (XDR-TB)

What do I need to do in the study?

Participants who meet the eligibility requirements for the study will have a test to see if they have INH-resistant TB, and if it is low-level or high-level resistance. (With low-level resistance, the bacteria are not as resistant to INH as with high-level resistance.) Participants may also be asked to provide sputum for other types of resistance tests.

Depending on the INH resistance test result, participants will be assigned to one of three groups:

Low-level INH resistance:

  • Referred to receive standard TB treatment outside of the study OR
  • Randomized (like a flip of a coin) to receive 5, 10, or 15 mg/kg INH once a day for 7 days.

No INH resistance:

  • Referred to receive standard TB treatment outside the study OR
  • Receive 5 mg/kg INH once a day for 7 days.

High-level resistance:

  • Will not receive INH treatment, but will be referred to receive standard TB treatment outside the study.

In addition, participants must also take vitamin B6 once a day while taking INH, to help prevent possible side effects of INH.

Participants will need to be admitted to the hospital for at least 9 days. While in the hospital, sputum (phlegm) will be collected to assess how well the medicine is working. About 14 days after discharge from the hospital, participants will come to the clinic for a final visit.

What treatments or drugs are involved with this study?

INH will be provided for participants who are in one of the groups that will receive INH. Vitamin B6 will also be provided. When finished taking 7 days of study drug, participants will be referred for full TB treatment outside the study.

Study Status: 

Participating ACTG Sites