Isoniazid (Intramuscular, Oral)

Sold under brand name Nydrazid, Isoniazid works by stopping the growth of TB causing bacteria.


Isoniazid is an antibacterial medication that has been used to treat tuberculosis (TB) since 1952. Tuberculosis is an infection caused by Mycobacterium tuberculosis bacterium. Once the bacterium enters into the human system, it usually remains dormant within the lungs for several years before becoming active and spreading to other parts of the body.

Isoniazid is approved for treating both latent and active tuberculosis infections. For active tuberculosis, isoniazid must be administered in combination with other tuberculosis medications to prevent the patient from developing resistance to the drug. The drug has been approved as prophylactic treatment for the following groups of patients:

  • Patients with HIV/AIDS infection and a purified protein derivative (PPD) reaction of at least 5 mm induration.
  • Contacts of tuberculosis patients who have a PPD reaction of at least 5 mm induration
  • Patients whose PPD reactions convert from negative to positive in a 2-year period' at least 10 mm induration for patients under 35 years of age, and at least 15 mm induration for patients over 35 years of age.
  • Patients with pulmonary damage on their chest X-ray that is linked to a healed tuberculosis and also have a PPD reaction at least 5 mm induration
  • Patients or injection drug users whose HIV status is negative or who have a PPD reaction at least 10 mm induration
  • Patients with a PPD of greater than or equal to 10 mm induration who live in high prevalent geographical regions, patients in low-income areas, as well as those living in long-term facilities.

Conditions Treated

  • Active TB treatment
  • TB prevention

Type Of Medicine


Side Effects

Along with the desired effects, this medication may also come with some harmful effects. Some side effects are mild and often go away over time as the body adjusts to medication. However, certain isoniazid side effects can be severe to the extent of requiring medical attention.

Check with your healthcare provider immediately if you experience any of the following isoniazid side effects:

  • Sluggishness and general unsteadiness
  • Loss of appetite
  • Dark urine
  • Nausea and/or vomiting
  • Yellowing of skin and eyes
  • Unusual fatigue and general tiredness
  • Tingling, numbness, pain, or burning sensation in the feet and hands
  • Blurred or lost vision that is accompanied with painful eyes
  • Fever and sore throat,
  • Convulsions
  • Joint pains
  • Mood swings
  • Depression
  • Skin rashes
  • Unusual bruising or bleeding
  • Diarrhea
  • Stomach or abdominal pains
  • Hematologic reactions
  • Hypersensitivity reactions
  • Metabolic and endocrine reactions

Severe isoniazid side effects

  •  Nervous system reactions

Peripheral neuropathy is one of the most common side effects of isoniazid. This side effect is dose related and commonly occurs in patients suffering from malnourishment or are predisposed to neuritis such as diabetic and alcoholic patients. Peripheral neuropathy is preceded by parethesias on the hands and feet. Other nervous system reactions include convulsions, memory impairment, optic neuritis and atrophy, toxic encephalopathy, and toxic psychosis.

Hepatic reactions

Prolonged use of isoniazid can cause hepatitis. This is symptomized by nausea, anorexia, vomiting, malaise, fatigue, yellowing of the eyes and skin, and general body weakness.

Gastrointestinal reactions

This is characterized by epigastric distress, vomiting, pancreatitis, and nausea.

Call your healthcare provider for medical advice about these isoniazid side effects. You may also report the side effects to the FDA at 1-800-FDA-1088.

Isoniazid dosage

Before taking this medicine, be sure to let your healthcare provider know if you are on any special diet, including low-sugar as well as low-sodium diets. Most drugs contain more than just the active ingredient, and most liquid based medications contain alcohol.

Take isoniazid with food to minimize stomach problems. You may also take the medicine with antacids. However, avoid aluminium-containing antacids within 1-2 hours after taking isoniazid as they may prevent the drug from working properly.

Patients taking the oral liquid form of this medication should use a specially marked measuring spoon to get accurate dosage measurement. Do not use the regular teaspoon as it may not hold the right amount of medication.

For complete TB treatment, be sure to complete your prescribed isoniazid dosage even if you begin to feel better after a few weeks of treatment. Your healthcare provider may recommend that you take this medicine every day for as long as 6 months to 2 years. Do not miss any dose.


Isoniazid dosage varies from patient to patient. It is important that you follow the prescription outlined by your healthcare provider. The following dosing is only the average dosing for isoniazid. If your dosing is different, do not change it unless with the approval of your healthcare provider.

The amount of isoniazid that you will take depends on the drug's strength, the number of prescribed daily doses, time recommended in between the doses, length of treatment time, and the medical problem for which you are taking the medicine.

  • Oral dosage forms (syrup and tablets)

Preventing reactivation/return of tuberculosis

Teenagers and adults ' 300 mg once per day

Children 'dosage is based on the patient's body weight with the recommended dose at 10 mg/kg of body weight up to 300 mg once per day.

  • Treating tuberculosis

Teenagers and adults ' 300 mg once per day or 15 mg/kg of body weight up to 900 mg taken twice or three times per week on alternating days.

Children'89 isoniazid dosage in children is based on body weight. The recommended dosage is 10 to 20 mg/kg of body weight up to 300 mg taken once per day; or 20 to 40 mg/kg of body weight up to 900 mg taken two or three times per week depending on the doctor's recommendation.

  • Injection dosage form

Preventing reactivation/return of tuberculosis

Teenagers and adults - 300 mg once per day

Children'dosage is based on body weight with a recommended dosage of 10 mg/kg of body weight up to 300 mg/kg of body weight taken once per day.

Treating tuberculosis

Teenagers and adults ' 300 mg taken once per day; or 15 mg/kg of body weight up to 900 mg taken twice or thrice per week depending on the doctor's recommendation.

Children - the dosage is based on the patient's body weight. The recommended dosage is 10 to 20 mg/kg of body weight, up to 300 mg taken once per day; or 20 to 40 mg/kg of body weight up to 900 mg taken twice or thrice per week depending on the doctor's prescription.

Missed dose

If you miss a dose, be sure to take it as soon as you remember. However, ensure that it is well spaced from the next dose. Be careful not to double dose as this can trigger unwanted side effects. Seek your healthcare provider's advice on missed dosage.

Isoniazid overdose

Contact your healthcare provider or the emergency room immediately in case of isoniazid overdose. You may also report overdose to the Poison Control Center at 1-800-222-1222. Some of the symptoms of isoniazid overdose include dizziness, blurred vision, hallucinations, nausea, loss of consciousness, slurred speech, seizures, vomiting, slow breathing, and symptoms of high blood sugar.

Isoniazid interactions

Although certain medications should not be co-administered together for fear of interactions, there are cases where two drugs may be prescribed together even if their combined use can cause an interaction. In such cases, your healthcare provider may recommend change in dosage, times of use, or recommend other precautionary measures. Before starting isoniazid therapy, inform your healthcare provider of any other medication you are taking including over the counter drugs, vitamins, supplements, as well as herbal medications.

That said, taking isoniazid together with any of the following medications is not recommended, but may be necessary. If both drugs are prescribed together, your doctor may change the dosage or frequency with which you take one or both drugs.

  • Acetaminophen
  • Amiodarone
  • Bupropion
  • Carbamazepine
  • Domperidone
  • Donepezil
  • Eliglustat
  • Glimepiride
  • Ketoconazole
  • Levodopa
  • Piperaquine
  • Rifampin
  • Tegafur

Combining isoniazid with any of the following medications may increase the risk of certain side effects even though the combination may offer the best treatment for your condition. If both drugs are recommended by your healthcare provider, be sure to ask how often you are to take both medications.

  • Aminosalicylic Acid
  • Diazepam
  • Disulfiram
  • Enflurane
  • Fosphenytoin
  • Meperidine
  • Phenytoin
  • Warfarin

Interactions With Food/Tobacco/Alcohol

Certain foods should not be taken while on some medications. Additionally, using alcohol and tobacco products while on some medications may cause an interaction. Specifically, you need to avoid tyramine containing foods as well as alcohol and tobacco products while on isoniazid treatment.

Other Medical Problems

Certain pre-existing medical conditions may affect the efficiency of isoniazid. Be sure to inform your healthcare provider if you have any of the following medical conditions before starting isoniazid therapy.

  • A history of alcohol and substance abuse
  • A history of liver disease ' there may be increased risk of hepatitis on patients who take alcohol while on this medication
  • A history of kidney disease ' patients with a history of kidney failure are at a greater risk of developing kidney failure when put on this medication for a long time
  • A history of seizure disorders such as epilepsy chances of convulsions and seizures are high in patients who use this medication for a long time.

Isoniazid warnings

It is important that you undergo regular organ check ups while on this isoniazid treatment. Also, call your doctor immediately if you experience blurred vision, with or without pain in the eyes while on this medication. Your doctor may recommend that you visit an ophthalmologist for a comprehensive checkup.

Certain foods, especially cheese and some fish products (skipjack, tuna, or Sardinella) may cause reactions in some patients on isoniazid. Check with your healthcare provider if you spot symptoms of reactions such as redness or itching of the skin, fast and pounding heartbeat, hot feeling, profuse sweating, headache, chills and clammy feeling, and lightheadedness.

Patients who consume alcohol while on this medication may suffer from liver problems. In addition, regular consumption of alcoholic beverages may prevent isoniazid from working properly. As such, you should limit the amount or give up alcohol altogether while on isoniazid therapy.

Check with your doctor immediately if this medication causes you to feel sluggish and very weak, or causes unsteadiness, nausea, loss of appetite, numbness, burning, tingling, pain in the feet and hands, and vomiting. These could be early signs of nerve or liver problems.

Isoniazid may affect the urine's sugar test in diabetic patients, causing false test results. Consult your doctor before changing diet or dosage of your diabetes treatment.

Do not take isoniazid if you are allergic to it or any of its ingredients.

Hematologic complications such as anemia have been reported in patients who use this medication for a long time. You can reverse anemia by discontinuing this medication.

Isoniazid should be used during pregnancy only when it is clearly necessary. Discuss the risks and benefits of using this drug while pregnant with your healthcare provider. Finally, this medication can be passed on via breastmilk to breastfeeding babies. Consult with your doctor before taking this medication while breastfeeding.

If you have a history of alcohol and hard drug abuse, diabetes, or poor nutrition, your healthcare provider may recommend that you take vitamin B supplements alongside isoniazid medication. This will help you reduce the risk of developing nerve problems.

Patients who are over 35 years should use isoniazid with great caution as they are at a greater risk of developing severe liver problems.

Hispanic and black women should exercise great caution while taking on isoniazid therapy as they have a greater risk of developing severe liver problems.


Isoniazid should be at room temperature (20 to 25 degrees C) and kept away from excessive humidity, heat and direct light. Do not freeze the medication. Do not keep this medication inside your car where it could be exposed to extreme cold or heat. Do not keep any outdated medicine longer than necessary. Do not flush unused medication in the toilet or kitchen sink. Ask your pharmacist or healthcare professional how to dispose of any unused medicine. Keep all medicine out of reach of pets and children.


Isoniazid is an antibiotic medication that is used in combination with other medications to prevent or treat tuberculosis. It is also administered together with other medications to treat patients with latent/resting TB including people who get into contact with patients with active TB, HIV, as well as those with pulmonary fibrosis. Isoniazid belongs to a class of drugs called antituberculosis agents. It works by stopping the growth of, and subsequently killing, tuberculosis causing bacterium.

Isoniazid works by inhibiting the synthesis of mycoloic acids in TB causing bacteria, resulting in loss of acid-fatness thus stopping the growth of the bacterium. The drug comes in tablet or solution forms to be taken orally with food. Isoniazid is take once per day, and may be administered once, twice, or thrice per week depending on the patient's condition. To help remember your medication, it is recommended that you take this drug at around the same time every scheduled day. Carefully follow your doctor's prescription and ask your healthcare provider or pharmacist to explain anything you do not understand. Take the medication exactly as directed. Do not take more or less of what has been prescribed by your doctor.

Your healthcare provider may recommend that you take this medication for six months or longer. Continue taking your medicine even if you feel well. Do not skip your dosage or stop the medication without your doctor's approval. Failing to complete your medication may cause the bacterium to develop resistance to the antibiotic.

Isoniazid, like other medications, does come with its share of side effects. Some of this drug's side effects such as liver and kidney complications can be very serious (possibly fatal). The risk of hepatitis is higher in patients who are 35 years and older, who are taking alcohol and other hard drugs while on this medication, or those who have a history of liver problems. Inform your healthcare provider right away if you develop symptoms of liver complications such as persistent vomiting and nausea, severe abdominal or stomach pains, general body fatigue and tiredness, yellowing or eyes and skin, and passing of dark urine.

You will be required to avoid taking foods that contain histamine or tyramine while on isoniazid treatment. Such foods include red wine, certain cheese, as well as certain fish products such as tuna and other tropical fish products. In addition, you will need to avoid alcohol and hard drugs when on isoniazid therapy.

Keep a clear list of all the medications you are using before and after starting isoniazid therapy. These include prescription as well as non-prescription medications, minerals, vitamins, and herbal supplements. Carry this list with you every time you visit your doctor for a checkup as well as when visiting the emergency room.