This article describes isoniazid oral tablet’s dosages and strengths and gives details on how to take it. You’ll also find information on cost savings and coupon options for isoniazid. If you want to know more about isoniazid oral tablet, see this overview article. It covers details about the drug’s uses and side effects, ways to save on cost, and more.
Isoniazid oral tablet is a generic medication. It’s not available in a brand-name version. Isoniazid also comes in an injectable form and an oral syrup, but those forms aren’t described in this article. To learn more about those forms, talk with your doctor.
Boxed warning: Risk of hepatitis
Isoniazid has a boxed warning for the risk of hepatitis (liver inflammation). A boxed warning is the most serious warning from the Food and Drug Administration (FDA).
See the end of this article for more information about this warning.
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Form and strengths of isoniazid
Isoniazid oral tablet comes as follows:
- Form: oral tablet, which you’ll take by swallowing
- Strengths: 100 milligrams (mg) and 300 mg
Dosage of isoniazid
This article describes the recommended dosages for isoniazid oral tablet. The drugmaker provides these dosages.
If your doctor prescribes this medication, you should follow the dosage they prescribe. Your doctor will determine the dosage that best meets your needs. Do not change your dosage of isoniazid oral tablet without your doctor’s recommendation.
Usual recommended dosages of isoniazid in adults
The recommended dosage of isoniazid oral tablet in adults varies based on a few factors:
- whether you’re taking it to treat an active TB infection or to help prevent active TB infection (that is, to treat latent TB)
- the specific regimen you’re prescribed and how long treatment will last
- whether you’re pregnant or have other conditions, such as HIV
The dosages of isoniazid oral tablet are described in mg. The dosages are based on body weight in kilograms (kg). One kg is about 2.2 pounds (lb).
Dosage for treating active tuberculosis
To treat active TB, the prescribing information for isoniazid oral tablet provides the usual oral dosages for adults shown below (depending on the regimen used):
- 5 mg/kg up to 300 mg taken once per day by mouth
- 15 mg/kg up to 900 mg taken by mouth once in a day, two or three times per week
Isoniazid oral tablet must be taken with other antibiotics to treat active TB. The Centers for Disease Control and Prevention (CDC) provides the most current recommendations and dosages for how to treat active TB in the United States. For regimens that include isoniazid, treatment lasts for 6 or 9 months.
Dosage for preventing active tuberculosis
To help prevent active TB, which means to treat latent TB (TB that is not yet an active infection), the prescribing information for isoniazid oral tablet provides the following recommended dosage for adults who weigh more than 30 kg (about 66 lb):
- 300 mg taken once per day by mouth
Isoniazid oral tablet may be used alone or in combination with other antibiotics to treat latent TB. The CDC provides the most current recommendations and dosages for how to treat latent TB in the United States. Treatment lasts for 3 months when isoniazid is taken with another antibiotic. When isoniazid is taken by itself, treatment lasts for 6 or 9 months.
Talk with your doctor if you have questions about your dosage of isoniazid oral tablet.
Usual recommended dosages of isoniazid in children
The recommended dosage of isoniazid oral tablet in children varies based on a few factors:
- whether the child is taking it to treat an active TB infection or to help prevent active TB infection (that is, to treat latent TB)
- the specific regimen prescribed and how long treatment will last
- whether the child has other conditions, such as HIV
Dosage for treating active tuberculosis
To treat active TB, the prescribing information for isoniazid oral tablet provides the usual oral dosages for children below (depending on the regimen used):
- 10–15 mg/kg up to 300 mg taken once per day by mouth
- 20–40 mg/kg up to 900 mg taken by mouth once in a day, two or three times per week
Isoniazid oral tablet must be taken with other antibiotics to treat active TB. The CDC provides the most current recommendations and dosages for how to treat active TB in the United States. For regimens that include isoniazid, treatment lasts for 6 or 9 months.
Dosage for preventing active tuberculosis
To help prevent active TB, which means to treat latent TB (TB that is not yet an active infection), the prescribing information for isoniazid oral tablet provides the following recommended dosage for infants and children:
- 10 mg/kg (up to 300 mg) taken once per day by mouth
- 20–30 mg/kg (not to exceed 900 mg) taken two times per week in the company of a healthcare professional, if there are concerns about taking isoniazid oral tablet on a daily basis
Isoniazid oral tablet may be used alone or in combination with other antibiotics to treat latent TB. The CDC provides the most current recommendations and dosages for how to treat latent TB in the United States. Treatment lasts for 3 months when isoniazid is taken with another antibiotic. When isoniazid is taken by itself, treatment lasts for 6 or 9 months.
Talk with your child’s doctor if you have questions about their dosage of isoniazid oral tablet.
Dosage adjustments for isoniazid
Your doctor will prescribe a dosage of isoniazid oral tablet based on several factors. These include:
- the specific condition being treated and how severe it is
- your age
- how well your liver works
- other health conditions you may have
- other medications you take
Missed dose of isoniazid
Talk with your doctor or pharmacist right away if you realize you forgot to take a dose of isoniazid oral tablet. They may advise you to take the missed dose. Or they may advise you to skip it and take your next dose as scheduled.
It is very important for you to take isoniazid exactly as your doctor prescribes and to avoid missing doses. You should take the entire treatment course, even if you feel better. If you miss doses or don’t complete your treatment, your TB may come back, or it may become resistant to treatment. This means that treatments you might need in the future would not work as well.
For tips on how to plan your doses of isoniazid oral tablet and avoid missing a dose, read this article. You could also try:
- downloading a reminder app on your phone
- setting an alarm
- putting a note where you’ll see it, such as on your calendar, bathroom mirror, or bedside table
If you have any concerns about the cost of isoniazid oral tablet, see this article about cost-saving options.
Frequently asked questions
Below are answers to some commonly asked questions about isoniazid oral tablet and its dosage.
How does the dosage of isoniazid compare with the dosage of rifampin?
It depends. Rifampin is another drug that’s used to treat an active TB infection or to help prevent an active TB infection (that is, to treat latent TB). Like isoniazid, rifampin must be used with other antibiotics to treat an active TB infection.
And like isoniazid, the dosage of rifampin varies based on a few factors:
- whether you’re taking it to treat an active TB infection or to help prevent active TB infection (that is, to treat latent TB)
- the specific regimen you’re prescribed and how long treatment will last
- whether you’re pregnant or have other conditions, such as HIV
- your age and body weight
Because the dosages of rifampin and isoniazid vary, talk with your doctor or pharmacist if you have questions about how the dosages compare. Your doctor or pharmacist can give you dosage information specific to you and your condition.
Is isoniazid taken long term?
Yes, doctors typically prescribe isoniazid oral tablet as a long-term treatment. If you and your doctor find that it’s safe and effective for your condition, you’ll likely take it long term. It’s typically taken for at least 3 months, depending on why it’s prescribed.
If you have questions about how long you should take isoniazid oral tablet, talk with your doctor.
How isoniazid is taken
You’ll swallow isoniazid oral tablet once per day or a certain number of times per week as prescribed by your doctor. The prescribing information does not state that isoniazid oral tablet may be split or crushed.
If you take isoniazid oral tablet once per day, your doctor may advise you to take it around the same time each day. This helps keep a consistent amount of the drug in your body. And that can help the drug work more effectively. Always follow your doctor’s instructions and take isoniazid oral tablet exactly as your doctor prescribes.
The prescribing information for isoniazid oral tablet states that it should not be taken with food. Taking it with food can reduce blood levels of the drug.
You should also avoid taking isoniazid oral tablet with foods containing tyramine or histamine, such as strong or aged cheeses, red wine, and certain fish, such as tuna. Taking isoniazid oral tablet with these foods may increase the risk of side effects, such as headache, flushing, or changes in blood pressure.
Your doctor or pharmacist may also tell you to take vitamin B6 (pyridoxine) with isoniazid oral tablet. This is because taking isoniazid can sometimes lead to a vitamin B6 deficiency. Ask your doctor or pharmacist if you have questions about taking vitamin B6 with isoniazid oral tablet.
If it’s hard for you to swallow tablets, view this article. It provides suggestions on how to swallow medications that come in pill form.
Also, be sure to talk with your doctor or pharmacist if you’re having difficulty taking your medication. They can offer recommendations about taking it.
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