Thinking about starting INH (isoniazid) for TB? The biggest question is usually the dose. Getting it right matters for cure rates and for keeping your liver happy. Below you’ll find the most common dosing rules, what to do if you’re lighter or have liver issues, and easy tricks to stay on track.
For most adults, doctors prescribe 5 mg per kilogram of body weight, up to a maximum of 300 mg once a day. That means a 70‑kg person usually gets 300 mg, while someone who weighs 50 kg would take 250 mg. Children get the same 5 mg/kg rule but never exceed the adult maximum.
If you’re on a fixed‑dose combination (FDC) pill that contains INH with other TB drugs, the INH portion is still calculated the same way. Your pharmacist will break the tablet or give you a liquid form to hit the exact number.
Take the pill on an empty stomach – at least one hour before or two hours after a meal. Food can slow absorption and make the medicine less effective. A glass of water is enough; no need for anything fancy.
INH can hit the liver, especially if you drink alcohol or have existing liver disease. Your doctor will check liver enzymes before you start and may repeat the test after a few weeks. If the numbers rise, the dose might be cut to 2.5 mg/kg or stopped entirely.
Vitamin B6 (pyridoxine) is often prescribed alongside INH to prevent nerve problems. The usual dose is 25 mg daily. It’s cheap, easy to find, and can save you from tingling or numbness in the hands and feet.
Missing a dose? Take it as soon as you remember, unless it’s almost time for the next one. Then just skip the missed pill – don’t double up. Double‑dosing can cause nausea, vomiting, or worse liver irritation.
Stay hydrated and avoid alcohol while you’re on INH. Even occasional drinks can increase liver stress. If you feel sore muscles, persistent headache, or dark urine, call your doctor right away – those could be warning signs.
Remember, completing the full course (usually six months) is crucial. Stopping early can let TB bacteria survive and become resistant, turning a treatable infection into a tough one.
Got questions about your specific dose? Grab a pen, write down your weight, and use the 5 mg/kg rule. Then ask your pharmacist or doctor to confirm. A quick check now prevents confusion later.
In short, the right INH dose is simple math, taken on an empty stomach, paired with B6, and monitored for liver health. Follow these steps, stick to the schedule, and you’ll give TB the best shot at being wiped out.
Sep, 21 2025
A thorough, up‑to‑date look at Isoniazid-what it treats, how it works, proper dosing, common side effects, and practical tips for patients and clinicians.
