Description
Isoniazid is used to treat tuberculosis (TB) or prevent its return (reactivation). It may be given alone, or in combination with other medicines, to treat TB or to prevent its return (reactivation). This medicine may also be used for other problems as determined by your doctor.
This medicine may cause some serious side effects, including damage to the liver. Liver damage is more likely to occur in patients over 50 years of age. You and your doctor should talk about the good this medicine will do, as well as the risks of taking it.
If you are being treated for active tuberculosis (TB): To help clear up your TB infection completely, you must keep taking this medicine for the full time of treatment, even if you begin to feel better. This is very important. It is also important that you do not miss any doses.
Isoniazid is available only with your doctor's prescription.
This product is available in the following dosage forms:
- Tablet
- Solution
Before Using
In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For this medicine, the following should be considered:
Allergies
Tell your doctor if you have ever had any unusual or allergic reaction to this medicine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.
Pediatric
Isoniazid can cause serious side effects in any patient. Therefore, it is especially important that you discuss with the child's doctor the good that this medicine may do as well as the risks of using it.
Geriatric
Hepatitis may be especially likely to occur in patients over 50 years of age, who are usually more sensitive than younger adults to the effects of isoniazid.
Breastfeeding
Studies in women suggest that this medication poses minimal risk to the infant when used during breastfeeding.
Drug Interactions
Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking this medicine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Acetaminophen
- Aluminum Carbonate, Basic
- Aluminum Hydroxide
- Aluminum Phosphate
- Amifampridine
- Bupropion
- Calcium Carbonate
- Calcium Silicate
- Carbamazepine
- Diazepam
- Dihydroxyaluminum Aminoacetate
- Dihydroxyaluminum Sodium Carbonate
- Domperidone
- Donepezil
- Enflurane
- Fosphenytoin
- Glimepiride
- Haloperidol
- Itraconazole
- Ketoconazole
- Levodopa
- Levoketoconazole
- Magaldrate
- Magnesium Carbonate
- Magnesium Hydroxide
- Magnesium Oxide
- Magnesium Peroxide
- Magnesium Trisilicate
- Methotrexate
- Pexidartinib
- Phenobarbital
- Phenytoin
- Piperaquine
- Primidone
- Rifampin
- Sodium Bicarbonate
- Tegafur
- Theophylline
- Valproic Acid
- Warfarin
Using this medicine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Aminosalicylic Acid
- Disulfiram
- Meperidine
Other Interactions
Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using this medicine with any of the following is usually not recommended, but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use this medicine, or give you special instructions about the use of food, alcohol, or tobacco.
- Ethanol
- Histamine Containing Food
- Tyramine Containing Food
Other Medical Problems
The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:
- Alcohol abuse (or history of) or
- Liver disease—There may be an increased chance of hepatitis with daily drinking of alcohol or in patients with liver disease
- Kidney disease (severe)—There may be an increased chance of side effects in patients with severe kidney disease
- Seizure disorders such as epilepsy—There may be an increased chance of seizures (convulsions) in some patients
Proper Use
Make certain your health care professional knows if you are on a low-sodium, low-sugar, or any other special diet. Most medicines contain more than just the active ingredient, and many liquid medicines contain alcohol.
If you are taking isoniazid by mouth and it upsets your stomach, take it with food. Antacids may also help. However, do not take aluminum-containing antacids within 1 hour of taking isoniazid. They may keep this medicine from working properly.
For patients taking the oral liquid form of isoniazid:
- Use a specially marked measuring spoon or other device to measure each dose accurately. The average household teaspoon may not hold the right amount of liquid.
To help clear up your tuberculosis (TB) completely, it is very important that you keep taking this medicine for the full time of treatment, even if you begin to feel better after a few weeks. You may have to take it every day for as long as 6 months to 2 years. It is important that you do not miss any doses.
Your doctor may also want you to take pyridoxine (e.g., Hexa-Betalin, vitamin B 6) every day to help prevent or lessen some of the side effects of isoniazid. This is not usually needed in children, who receive enough pyridoxine in their diet. If it is needed, it is very important to take pyridoxine every day along with this medicine. Do not miss any doses.
Dosing
The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.
The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.
- For oral dosage forms (tablets, syrup):
- For preventing the return (reactivation) of tuberculosis:
- Adults and teenagers—300 milligrams (mg) once a day.
- Children—Dose is based on body weight. The usual dose is 10 mg per kilogram (kg) (4.5 mg per pound) of body weight, up to 300 mg, once a day.
- For treatment of tuberculosis:
- Adults and teenagers—300 mg once a day; or 15 mg per kg (6.8 mg per pound) of body weight, up to 900 mg, two times a week or three times a week, depending on the schedule your doctor chooses for you.
- Children—Dose is based on body weight. The usual dose is 10 to 20 mg per kg (4.5 to 9.1 mg per pound) of body weight, up to 300 mg, once a day; or 20 to 40 mg per kg (9.1 to 18.2 mg per pound) of body weight, up to 900 mg, two times a week or three times a week, depending on the schedule your doctor chooses for you.
- For preventing the return (reactivation) of tuberculosis:
- For injection dosage form:
- For preventing the return (reactivation) of tuberculosis:
- Adults and teenagers—300 mg once a day.
- Children—Dose is based on body weight. The usual dose is 10 mg per kg (4.5 mg per pound) of body weight, up to 300 mg, once a day.
- For treatment of tuberculosis:
- Adults and teenagers—300 mg once a day; or 15 mg per kg (6.8 mg per pound) of body weight, up to 900 mg, two times a week or three times a week, depending on the schedule your doctor chooses for you.
- Children—Dose is based on body weight. The usual dose is 10 to 20 mg per kg (4.5 to 9.1 mg per pound) of body weight, up to 300 mg, once a day; or 20 to 40 mg per kg (9.1 to 18.2 mg per pound) of body weight, up to 900 mg, two times a week or three times a week, depending on the schedule your doctor chooses for you.
- For preventing the return (reactivation) of tuberculosis:
Missed Dose
If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.
Storage
Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.
Keep out of the reach of children.
Do not keep outdated medicine or medicine no longer needed.
Precautions
It is very important that your doctor check your progress at regular visits. Also, check with your doctor immediately if blurred vision or loss of vision, with or without eye pain, occurs during treatment. Your doctor may want you to have your eyes checked by an ophthalmologist (eye doctor).
If your symptoms do not improve within 2 to 3 weeks, or if they become worse, check with your doctor.
Certain foods such as cheese (Swiss or Cheshire) or fish (tuna, skipjack, or Sardinella) may rarely cause reactions in some patients taking isoniazid. Check with your doctor if redness or itching of the skin, hot feeling, fast or pounding heartbeat, sweating, chills or clammy feeling, headache, or lightheadedness occurs while you are taking this medicine.
Liver problems may be more likely to occur if you drink alcoholic beverages regularly while you are taking this medicine. Also, the regular use of alcohol may keep this medicine from working properly. Therefore, you should strictly limit the amount of alcoholic beverages you drink while you are taking this medicine.
If this medicine causes you to feel very tired or very weak; or causes clumsiness; unsteadiness; a loss of appetite; nausea; numbness, tingling, burning, or pain in the hands and feet; or vomiting, check with your doctor immediately. These may be early warning signs of more serious liver or nerve problems that could develop later.
For diabetic patients:
- This medicine may cause false test results with some urine sugar tests. Check with your doctor before changing your diet or the dosage of your diabetes medicine.
Side Effects
Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.
Check with your doctor immediately if any of the following side effects occur:
More common
- Clumsiness or unsteadiness
- dark urine
- loss of appetite
- nausea or vomiting
- numbness, tingling, burning, or pain in hands and feet
- unusual tiredness or weakness
- yellow eyes or skin
Rare
- Blurred vision or loss of vision, with or without eye pain
- convulsions (seizures)
- fever and sore throat
- joint pain
- mental depression
- mood or other mental changes
- skin rash
- unusual bleeding or bruising
Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:
More common
- Diarrhea
- stomach pain
For injection form
- Irritation at the place of injection
Dark urine and yellowing of the eyes or skin (signs of liver problems) are more likely to occur in patients over 50 years of age.
Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.
Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
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