# Isoniazid in Nigeria

Isoniazid has 8 active NAFDAC registrations in our October 2026 copy of the register, from 6 registration holders; 4 further listings have lapsed.

- Source: https://ogbogwu.com/drugs/isoniazid/
- Drug class: Isonicotinic acid hydrazide (Anti-Tuberculosis)
- Also known as: INH, Isonicotinylhydrazide
- Prescription required: yes
- On the WHO Model List of Essential Medicines
- Last updated: February 2026

## Price in Nigeria

Isoniazid is supplied free of charge through Nigeria's National TB programme: TB treatment, including isoniazid-containing regimens, costs the patient nothing at DOTS centres and public facilities nationwide. That is why private listings are scarce and why we quote no price — if you are being charged for TB treatment, ask for the nearest DOTS centre. Private wholesale supply for institutions is quoted by registered distributors.

## What is Isoniazid?

Isoniazid, commonly abbreviated as INH, is one of the most important and widely used anti-tuberculosis medicines in the world. Discovered in the 1950s, it remains a cornerstone of TB treatment and prevention more than seven decades later. Isoniazid works by inhibiting the synthesis of mycolic acid, a critical component of the cell wall of Mycobacterium tuberculosis. Without an intact cell wall, the TB bacterium cannot survive. Isoniazid is bactericidal against actively growing TB bacteria (meaning it kills them) and bacteriostatic against dormant bacteria (meaning it prevents them from multiplying). This dual action makes it essential for both the treatment of active TB disease and the prevention of TB in people who carry latent TB infection. In Nigeria, where tuberculosis remains a leading cause of death — particularly among people living with HIV — isoniazid is a life-saving medicine that is freely available through the National Tuberculosis and Leprosy Control Programme (NTBLCP) at DOTS centres across all 36 states and the Federal Capital Territory.

In the treatment of active TB, isoniazid is never used alone — it is always part of a multi-drug combination to prevent the development of drug resistance. The standard first-line regimen for drug-susceptible TB in Nigeria consists of two months of intensive treatment with four drugs — Rifampicin, Isoniazid, Pyrazinamide, and Ethambutol (known as the RHZE combination) — followed by four months of continuation phase treatment with Rifampicin and Isoniazid (RH). Fixed-dose combination tablets containing isoniazid with other anti-TB drugs are commonly used in Nigeria to simplify dosing and improve adherence. Beyond treating active TB, isoniazid has a uniquely important role in TB prevention through Isoniazid Preventive Therapy (IPT). In Nigeria, IPT is a critical intervention for people living with HIV, as TB is the leading cause of death among HIV-positive individuals. The Nigerian national guidelines recommend that all HIV-positive patients who have been screened and found not to have active TB should receive IPT — typically isoniazid 300mg daily for 6 months — to prevent the development of active TB disease.

A key consideration with isoniazid use is its potential to cause peripheral neuropathy — a painful condition characterised by numbness, tingling, and burning sensations in the hands and feet. This side effect occurs because isoniazid interferes with the metabolism of Vitamin B6 (pyridoxine), which is essential for nerve function. To prevent this complication, isoniazid is always co-prescribed with pyridoxine (Vitamin B6) supplements, typically 25mg to 50mg daily for adults. This is standard practice at DOTS centres and ART clinics throughout Nigeria, from teaching hospitals in Ibadan, Jos, and Maiduguri to community health centres in rural Benue, Taraba, and Cross River states. Patients must be counselled to take their pyridoxine supplement consistently alongside their isoniazid. Another important concern is isoniazid-related hepatotoxicity (liver damage), which can range from a mild, self-limiting elevation of liver enzymes to fulminant hepatic failure. Liver function monitoring is recommended, particularly during the first three months of treatment, in patients over 35 years of age, those with pre-existing liver disease, heavy alcohol users, and patients co-infected with HIV and Hepatitis B or C.

## What is Isoniazid used for?

- Treatment of active pulmonary tuberculosis as part of the standard RHZE/RH combination regimen
- Treatment of extrapulmonary tuberculosis including TB meningitis, TB lymphadenitis, spinal TB, and disseminated TB
- Isoniazid Preventive Therapy (IPT) for HIV-positive patients to prevent the development of active TB — a critical intervention in Nigeria's HIV programme
- TB prophylaxis for children under 5 years who are close contacts of confirmed TB patients
- TB prophylaxis for other high-risk groups including immunosuppressed patients and those on biologic therapies
- Part of shorter preventive regimens such as 3HP (isoniazid plus rifapentine weekly for 3 months) now being introduced in some Nigerian states

## Dosage

Always follow a doctor's or pharmacist's instructions; this is general reference information.

- Adults: For active TB treatment: 5mg per kg of body weight daily (usual dose is 300mg daily), taken as part of the RHZE combination during the 2-month intensive phase, and then as part of the RH combination during the 4-month continuation phase. For Isoniazid Preventive Therapy (IPT): 300mg once daily for 6 months (or up to 12 months in some guidelines). Isoniazid should be taken on an empty stomach, ideally 30 minutes to 1 hour before food, for best absorption. Always take with pyridoxine (Vitamin B6) 25-50mg daily to prevent peripheral neuropathy.
- Children: For active TB treatment in children: 10mg per kg of body weight daily (range 7-15mg/kg), up to a maximum of 300mg daily, as part of age-appropriate fixed-dose combination tablets. For TB preventive therapy in children under 5 years who are contacts of TB patients: 10mg/kg daily for 6 months. Paediatric dispersible tablets are available through the NTBLCP. Children should also receive pyridoxine supplementation, particularly those who are malnourished or HIV-positive.
- Elderly: The standard adult dose of 300mg daily is generally used for elderly patients. However, elderly patients are at significantly higher risk of isoniazid-related hepatotoxicity and peripheral neuropathy. Liver function tests should be monitored closely, particularly during the first 2-3 months of treatment. Pyridoxine supplementation is especially important in elderly patients. Dose reduction may be necessary in patients with severe liver impairment.

Always take isoniazid with pyridoxine (Vitamin B6) to prevent peripheral neuropathy — this is not optional, it is an essential part of the treatment. Take the medication at the same time each day for consistent blood levels. Complete the full course of treatment as prescribed — for active TB this is a minimum of 6 months, and for IPT it is typically 6 months. Do not stop treatment early even if you feel well. Avoid alcohol during treatment as it increases the risk of liver damage. If you develop symptoms of liver problems (nausea, vomiting, abdominal pain, dark urine, jaundice), stop taking isoniazid and seek immediate medical attention.

## Side effects

Common: Peripheral neuropathy — numbness, tingling, and burning in the hands and feet; preventable with pyridoxine (Vitamin B6) supplementation; Mild elevation of liver enzymes — often asymptomatic and detected on blood tests; usually self-limiting; Nausea and loss of appetite — particularly at the start of treatment; Headache and dizziness; Fatigue and general malaise; Gastrointestinal discomfort including abdominal pain.

Serious (seek medical help immediately): Hepatotoxicity (drug-induced liver injury) — can range from mild enzyme elevations to fatal fulminant hepatic failure. Risk factors include age over 35, alcohol use, pre-existing liver disease, and HIV/Hepatitis co-infection. Symptoms include jaundice, dark urine, pale stools, severe nausea, and right upper abdominal pain.; Severe peripheral neuropathy — if pyridoxine is not co-administered, chronic isoniazid use can cause debilitating nerve damage with severe pain, numbness, and muscle weakness in the extremities; Drug-induced lupus-like syndrome — joint pain, fever, and skin rash; more common with prolonged use; Seizures — particularly in overdose situations; isoniazid overdose is a medical emergency; Optic neuritis — inflammation of the optic nerve causing visual disturbances; rare but potentially serious; Sideroblastic anaemia — a rare form of anaemia caused by interference with Vitamin B6 metabolism.

When to see a doctor: Stop taking isoniazid and seek immediate medical attention if you develop yellowing of the eyes or skin, dark-coloured urine, persistent nausea or vomiting, severe abdominal pain, unusual tiredness, loss of appetite lasting more than a few days, or severe numbness and tingling in the hands or feet despite taking pyridoxine. In Nigeria, go to your DOTS centre, ART clinic, or the nearest hospital emergency department. Hepatotoxicity from isoniazid can progress rapidly to liver failure if not detected and managed promptly. Do not restart isoniazid on your own after a serious liver reaction — this must be done under close medical supervision with liver function monitoring.

## Warnings

Do not take if: Known hypersensitivity to isoniazid; Active severe liver disease or acute hepatitis — isoniazid is hepatotoxic and can cause fatal liver failure in patients with pre-existing severe liver damage; Previous isoniazid-associated hepatotoxicity or severe adverse reaction to isoniazid; Acute porphyria — isoniazid may trigger porphyric crises.

Interactions: Alcohol — significantly increases the risk of isoniazid-related hepatotoxicity. Patients should avoid alcohol completely during treatment.; Paracetamol (acetaminophen) — increased risk of hepatotoxicity when used together; use paracetamol cautiously and at the lowest effective dose; Phenytoin and carbamazepine — isoniazid inhibits their metabolism, increasing blood levels and risk of toxicity; dose reduction and monitoring may be needed; Rifampicin — both drugs are hepatotoxic and the combination (necessary for TB treatment) carries an increased risk of liver damage; liver function monitoring is essential; Ketoconazole and fluconazole — increased risk of hepatotoxicity when combined with isoniazid; Tyramine-containing foods (aged cheese, fermented foods, smoked fish) — isoniazid inhibits monoamine oxidase, and consumption of tyramine-rich foods can cause hypertensive reactions (headache, palpitations, flushing).

Pregnancy & breastfeeding: Isoniazid is considered safe and is recommended for the treatment of active TB during pregnancy, as the risk of untreated TB to both mother and baby far outweighs the risk of the medication. It is also recommended for IPT during pregnancy in HIV-positive women, though some clinicians in Nigeria may choose to defer IPT to the second trimester. Pyridoxine supplementation is particularly important during pregnancy to protect both the mother and the developing baby from neurological complications. Isoniazid is excreted in small amounts in breast milk, but the concentrations are too low to be harmful to the nursing infant or to provide effective TB treatment or prevention for the baby. Breastfeeding can be continued safely during isoniazid therapy. However, breastfed infants of mothers on isoniazid should also receive pyridoxine supplementation.

## Brands in Nigeria

Full searchable brand list: https://ogbogwu.com/drugs/isoniazid/brands/

## How to verify it is genuine

1. Check for a valid NAFDAC registration number on the product packaging. All genuine medicines in Nigeria must be NAFDAC-registered.
2. Use the NAFDAC Mobile Authentication Service (MAS): scratch the panel on the packaging and send the code via SMS to 38353 to verify the product is genuine.
3. Obtain isoniazid only through the DOTS programme at designated TB treatment centres, government hospitals, ART clinics, or NAFDAC-registered pharmacies.
4. Check the expiry date, batch number, and ensure the packaging is sealed and untampered with. Discoloured or crumbling tablets may indicate degradation.
5. If you receive isoniazid as part of a fixed-dose combination (FDC) tablet, verify that the combination and strengths match what was prescribed by your healthcare provider.
6. Report any suspected counterfeit or substandard TB medicines to NAFDAC through their reporting hotline or at the nearest NAFDAC office. Substandard TB drugs contribute to treatment failure and the emergence of drug-resistant TB.

Verify any NAFDAC number free (no login): https://ogbogwu.com/nafdac-checker/

## FAQs

### What is Isoniazid Preventive Therapy (IPT), and why is it important for HIV-positive patients in Nigeria?

Isoniazid Preventive Therapy (IPT) is the use of isoniazid 300mg daily for 6 months to prevent the development of active tuberculosis in people who are at high risk, particularly those living with HIV. TB is the leading cause of death among HIV-positive individuals worldwide, and in Nigeria, approximately 14% of TB patients are co-infected with HIV. People living with HIV are up to 20 times more likely to develop active TB compared to HIV-negative individuals. IPT has been shown to reduce the risk of developing active TB by 33-62% in HIV-positive people. Nigerian national guidelines recommend that all HIV-positive patients enrolled in care should be screened for active TB, and those found not to have active TB should be started on IPT. IPT is provided free of charge at ART treatment centres across Nigeria alongside antiretroviral therapy. If you are HIV-positive and have not been offered IPT, ask your healthcare provider at your next clinic visit.

### Why do I need to take Vitamin B6 (pyridoxine) with isoniazid?

Isoniazid interferes with the body's metabolism of Vitamin B6 (pyridoxine), which is essential for the proper functioning of nerves. Without adequate pyridoxine, patients taking isoniazid can develop peripheral neuropathy — a painful condition causing numbness, tingling, burning sensations, and weakness in the hands and feet. This side effect can become permanent if severe and untreated. Taking pyridoxine 25-50mg daily alongside isoniazid effectively prevents this complication. Certain groups are at particularly high risk of isoniazid-related neuropathy: people living with HIV, malnourished individuals (common in some parts of Nigeria), pregnant women, diabetics, alcoholics, and elderly patients. In Nigeria, pyridoxine is routinely co-prescribed with isoniazid at DOTS centres and ART clinics. If you have been given isoniazid without pyridoxine, please ask your healthcare provider for it — it is an essential part of your treatment, not an optional supplement.

### Does isoniazid affect the liver, and do I need liver monitoring?

Yes, isoniazid can cause liver damage (hepatotoxicity), which is the most serious potential side effect of the drug. In most cases, this is a mild, self-limiting elevation of liver enzymes that resolves on its own without stopping treatment. However, in rare cases (estimated at 0.1-0.15% of patients), isoniazid can cause severe hepatitis that can progress to liver failure and death if not detected early. Risk factors for isoniazid hepatotoxicity include age over 35 years, pre-existing liver disease, chronic alcohol use, HIV infection, Hepatitis B or C co-infection, and concurrent use of other hepatotoxic drugs (including rifampicin and paracetamol). Liver function tests (LFTs) should ideally be checked before starting treatment and periodically during the first 2-3 months, especially in high-risk patients. In practice, routine LFT monitoring may not always be available at all DOTS centres in Nigeria. Therefore, clinical monitoring for symptoms of hepatitis (jaundice, nausea, vomiting, abdominal pain, dark urine, fatigue) is critically important. If you develop any of these symptoms, stop isoniazid immediately and seek medical attention.

### How long do I need to take isoniazid, and what happens if I stop early?

The duration of isoniazid therapy depends on whether you are taking it for TB treatment or TB prevention. For active TB treatment, isoniazid is taken for a full 6 months as part of the standard RHZE/RH regimen — 2 months in the intensive phase with four drugs, followed by 4 months in the continuation phase with rifampicin and isoniazid. For Isoniazid Preventive Therapy (IPT) in HIV-positive patients, the standard course is 6 months of daily isoniazid. Stopping treatment early is extremely dangerous for several reasons. For active TB, incomplete treatment allows surviving TB bacteria to develop drug resistance, potentially creating multidrug-resistant TB (MDR-TB) which requires 9-20 months of treatment with more toxic and expensive second-line drugs. MDR-TB treatment is available at only a limited number of centres in Nigeria and has much lower cure rates. For IPT, stopping early means you may not achieve the full protective benefit against future TB disease. Always complete the full prescribed course, attend your scheduled clinic appointments, and discuss any difficulties with your healthcare provider.

## Sources

- NAFDAC Greenbook (official register of approved products in Nigeria)
- WHO Model List of Essential Medicines
- British National Formulary (BNF)
- Nigerian Standard Treatment Guidelines (Federal Ministry of Health)