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Isoniazid is a first-line drug for the treatment of tuberculosis in conjunction with other anti-tuberculosis drugs

Last Modified: 13 May 2024

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What is Isoniazid? 

Isoniazid (INH) is an antibiotic that belongs to a class of drugs known as antitubercular agents. It works by inhibiting the growth of bacteria specifically Mycobacterium tuberculosis, the bacteria  that causes tuberculosis (TB). 

The active ingredient in Isoniazid is isonicotinic acid hydrazide, and it typically comes in the form of tablets or an oral suspension. 

The drug is synthesized from isonicotinic acid and hydrazine, resulting in a compound that is highly effective against mycobacterial cells. 

Global Name

Generic name: Isoniazid
Brand name: Nydrazid, Laniazid, Isozid, Isotamine, Nicotibine, Rimifon


What is Isoniazid used for? 

Isoniazid is a first-line drug for the treatment of tuberculosis in conjunction with other anti-tuberculosis drugs. It is effective against active TB infections and is also used in a preventive capacity to treat individuals who have been exposed to TB but do not yet show symptoms (latent TB). A usual course of treatment for susceptible TB mycobacterium is two months of isoniazid, rifampicin, pyrazinamide and ethambutol followed by four months of INH + rifampicin. 

How do you use Isoniazid? 

Isoniazid is available in the form of tablets, capsules, and an oral syrup. It is also available as an injectable solution, but this form is less common. 

Dosage information, across all ages: 

  • Adults: The typical oral dosage for adults is 5 mg/kg up to 300 mg single daily dose. 
  • Children: For children, the daily dose is 10-15 mg/kg up to 300 mg daily. 
  • Elderly: Dosages for the elderly may be adjusted based on liver function and overall health. 

Are the following suitable to take the drug: 

  • Children: Yes, following the correct dosage and duration. 
  • Adults: Yes, following the correct dosage and duration. 
  • Elderlies: Yes, but with caution and potential dosage adjustments with consideration of liver function. 
  • Pregnancy and Lactation: Isoniazid can be used during pregnancy if clearly needed. It is excreted in breast milk but is generally considered safe for use while breastfeeding. Pyridoxine (vitamin B6) supplement is recommended while on INH. 

Is there anyone who can’t take Isoniazid? 

  • Those with a known hypersensitivity to isoniazid should not take this medication. 
  • Patients with severe liver disease 
  • Patients with history of drug-induced hepatitis
Warnings and Precautions: 
  • Isoniazid should be taken on an empty stomach 1 hour before or 2 hours after meals. 
  • Liver function should be monitored regularly due to the risk of hepatotoxicity. 

Interactions and contraindications of the drug: 

  • Isoniazid may interact with foods containing tyramine and histamine (e.g., aged cheeses, cured meats), which can lead to hypertension. 
  • It should not be used with alcohol or other hepatotoxic drugs. 

Side Effects

  • Common side effects include nausea, vomiting, and mild rash. 
  • Severe side effects can include liver toxicity, peripheral neuropathy, and hypersensitivity reactions. 

Pharmacist Tips

  • Understanding Your Medication: Isoniazid is a cornerstone drug for the treatment and prevention of tuberculosis. It's crucial to take it exactly as prescribed by your healthcare provider to ensure the best outcome. 
  • Correct Usage: Take Isoniazid on an empty stomach, either one hour before or two hours after a meal, to maximize absorption. 
    Do not skip doses. Consistency is key in preventing the development of drug-resistant TB. 
  • Combating Side Effects: To reduce the risk of peripheral neuropathy, a side effect of Isoniazid, your doctor may recommend taking vitamin B6 (pyridoxine) supplements. 
    Report any signs of liver issues, such as jaundice (yellowing of the skin or eyes), dark urine, or severe fatigue, to your healthcare provider immediately. 
  • Lifestyle Considerations: Avoid alcohol consumption during treatment with Isoniazid, as it can increase the risk of liver toxicity. 
    Maintain a balanced diet and stay hydrated to support your overall health while on medication. 
  • Monitoring Treatment: Keep regular appointments for liver function tests to catch any potential hepatotoxicity early. 
    Inform your healthcare provider of all medications you're taking, including over-the-counter drugs and supplements, to avoid interactions. 
  • Storage and Handling: Store Isoniazid in a cool, dry place away from light and moisture to ensure it remains effective. 
    Keep all medications out of reach of children and pets. 
  • Preventing Transmission: While on treatment, follow public health guidelines to prevent the spread of TB, such as wearing a mask if advised, until your doctor confirms you're no longer infectious. 
  • Being Informed: Read the patient information leaflet provided with your Isoniazid prescription for additional details on how to take the medication and potential side effects. 
    Don't hesitate to ask your pharmacist any questions about your medication or its side effects. 
  • Traveling with Medication: If you’re traveling, make sure to bring enough Isoniazid to last your entire trip and keep it in its original container, clearly labeled. 
  • Emergency Preparedness: Have a plan in place and know the signs of an allergic reaction, such as rash, itching, swelling, dizziness, or trouble breathing, and seek immediate medical attention if these occur. 


Where is Isoniazid available in Hong Kong?

Isoniazid is a prescription medication that can be prescribed by healthcare providers.


Is Isoniazid for purchase over-the-counter?

No, Isoniazid is only available with a prescription due to the need for medical supervision during treatment.

How long will I need to take Isoniazid?

The duration of treatment depends on whether you are being treated for active or latent TB, ranging from 6 months to 1 year or more.

Can I drink alcohol while taking Isoniazid?

Alcohol should be avoided while taking Isoniazid due to the increased risk of liver damage. 

This website provides content related to drug use and medicine for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Do not use the information on this website to diagnose or treat a health problem or disease without consulting a qualified healthcare provider. The website's owners and contributors are not liable for any repercussions, adverse effects, or consequences resulting from the use of any medication or information provided herein.

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