Isoniazid (INH)

Please note: these are basic guidelines, refer to your doctor for a professional medical opinion.

Popular brand names:

Be-Tabs Isoniazid, Norstan-Isoniazid

Popular combinations:

Rifafour, Rifinah, Rimactazid, Rimcure

Drug group:

Antituberculous drug

Prescription needed?

Yes

What does it do?

Isoniazid is used in the prevention and treatment of tuberculosis:

• Prevention of TB: used alone
• Treatment of TB: used in combination with other drugs - usually for six months, but courses of nine months or a year may sometimes be prescribed

How should it be used?

Take doses 30 minutes before eating - food decreases the absorption of isoniazid

What is the typical dosage?

Your doctor will recommend a dosage tailored to your need, but typically:

Adults: 300mg taken once daily, Children: dose according to age and weight

How quickly will it start to work?

2–3 days  
                            

How long will the effects last?

Up to 24 hours     

When should I stop using it?

Complete the course as prescribed  
                   

Is it safe for prolonged use?

Long-term use can cause pyridoxine (vitamin B6) deficiency which can lead to nerve damage/peripheral neuropathy – this is more likely with high doses and more common in people with poor nutrition.  B6 supplements are usually prescribed.

There is also a risk of serious liver damage - regular blood tests are done to monitor liver function.

What are the possible side effects?

Isoniazid usually causes few side effects. The following have been reported:

• More common: nausea, vomiting, fatigue, weakness, rash, mood changes
• Less common: numbness/tingling of fingers/toes (peripheral neuropathy)
• Report to your doctor before taking your next dose if you experience: blurred vision, jaundice, twitching, or muscle weakness

What other considerations are important?

Dosage may be adjusted by your doctor under certain conditions.

• Certain health problems: liver/kidney problems, previous liver damage following isoniazid treatment, drug or alcohol abuse, diabetes, porphyria, HIV infection, epilepsy/seizures
• Other medicines: theophylline, anti-epileptics, antacids, ketoconazole,
• Pregnancy and breast-feeding: No evidence of risk in pregnancy, passes into breast milk and may affect the breast-fed baby
• Children: Reduced dose necessary
• Over 60: Caution, increased likelihood of adverse effects
• Driving and hazardous work: No special problems
• Alcohol: Avoid excessive amounts, reduced effectiveness of isoniazid and increased likelihood of liver damage