isoniazid (Discontinued brands: Nydrazid, Laniazid, INH, Rimifon, Stanozide, Hyzyd, Dow-Isoniazid)

  • Pharmacy Author:
    Omudhome Ogbru, PharmD

    Dr. Ogbru received his Doctorate in Pharmacy from the University of the Pacific School of Pharmacy in 1995. He completed a Pharmacy Practice Residency at the University of Arizona/University Medical Center in 1996. He was a Professor of Pharmacy Practice and a Regional Clerkship Coordinator for the University of the Pacific School of Pharmacy from 1996-99.

  • Medical and Pharmacy Editor: Jay W. Marks, MD
    Jay W. Marks, MD

    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

PREPARATIONS: Tablets: 100 or 300 mg. Syrup: 50 mg per teaspoonful. Injection: 100 mg/ml.


  • Antacids containing aluminum (for example, Mylanta; Maalox, Gelusil; Amphojel; Alternagel) reduce the amount of isoniazid that is absorbed from the intestine, and this can result in reduced blood levels and effect of isoniazid. If aluminum-containing antacids must be taken, they should be taken at least one hour after the isoniazid to prevent binding.
  • Isoniazid can increase the effectiveness of the blood thinner, warfarin (Coumadin) by interfering with the enzyme in the liver that eliminates warfarin.
  • Isoniazid can increase the effect of certain benzodiazepines, such as diazepam (Valium), triazolam (Halcion), and others, by interfering with the enzymes in the liver that eliminate benzodiazepines. This may result in excessive sedation.
  • Carbamazepine (Tegretol) taken at the same time as isoniazid, can result in an increased risk of side effects from both carbamazepine and isoniazid. Isoniazid can decrease the rate at which the liver eliminates phenytoin (Dilantin), which can raise the blood levels and result in side effects of phenytoin. Because rifampin can be toxic to the liver, the use of rifampin and isoniazid together increases the risk of liver toxicity to a level that is greater than with either drug alone.


  • Isoniazid has not been shown to cause birth defects in humans or animals; however, studies in rats and rabbits have shown that it may increase the risk of fetal death. Nevertheless, tuberculosis is a very serious infection, and many women have been treated with isoniazid during pregnancy with no problems in their infants. Ultimately, the physician and the pregnant female must evaluate the risks and benefits of isoniazid.
  • Isoniazid is secreted into breast milk, however, it has not been reported to cause problems in nursing babies. Ultimately, the physician and the nursing mother must evaluate the risks and benefits of isoniazid.
Medically Reviewed by a Doctor on 6/27/2016

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