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Isoniazid
Aka: Isoniazid, INH
- See Also
- Isoniazid Overdose
- Indications
- Tuberculosis Prophylaxis
- Multi-drug Tuberculosis Treatment regimen
- Background
- Structurally similar to Pyridoxine
- Interferes with formation of Mycobacteria cell walls
- Contraindications
- G6PD Deficiency
- Severe hepatic insufficiency (reduce INH dose)
- Active hepatitis
- End-stage liver disease
- Dosing
- See Tuberculosis for specific dosing protocols and durations of treatment
- Daily dosing
- Adult: 300 mg PO or IM
- Child: 5 mg/kg (up to 300 mg daily)
- Intermittent dosing
- Adult: 900 mg orally twice weekly (15 mg/kg twice weekly)
- Adverse Effects: Hepatic
- Hepatotoxicity
- Subclinical Hepatitis: 10%
- Clinical Hepatitis: 1%
- Risk increases with age and Alcohol intake
- Progressive liver damage
- Under age 20 years: rare
- Age 30 to 50 years: 1.5%
- Age over 50 years: 2.5%
- Common presenting symptoms of drug-induced hepatotoxicity
- Nausea or Vomiting
- Abdominal Pain (>50% of patients)
- Fever (10%)
- Rash (5%)
- Adverse Effects: Neurologic
- Peripheral Neuropathy
- See prevention below
- Insomnia
- Restlessness
- Muscle twitching
- Urinary Retention
- Seizures
- Psychosis
- Monoamine toxicity (MAO inhibitor-like reaction)
- Presents with Flushing
- Avoid concurrent aged cheese and wine
- Prevention: Peripheral Neuropathy
- Indications for concurrent Vitamin B6 supplementation (Neuropathy risks)
- Pregnancy
- Diabetes Mellitus
- Alcoholism
- Comorbid other Neuropathy
- Uremia
- Malnutrition
- HIV Infection
- Epilepsy
- Vitamin B6 (Pyridoxine)
- Pyridoxine 10 mg/day per 100 mg of INH
- Typical dose is 25-50 mg orally daily
-
Drug Interactions
- Phenytoin (Dilantin)
- INH Increases blood level and toxicity
- Disulfiram (Antabuse)
- Monitoring: Liver Function Tests
- Significant liver function abnormalities exceed 3-5 times normal with Isoniazid
- Baseline Liver Function Tests
- Controversial (some experts do not recommend baseline LFTs)
- Others recommend baseline testing and then monthly if abnormal baseline LFTs or if otherwise indicated (as below)
- Obtain monthly Liver Function Tests if:
- Abnormal baseline Liver Function Test
- History suggestive of Possible liver disorder
- Human Immunodeficiency Virus (HIV)
- Pregnancy
- Postpartum (within 3 months)
- Chronic Liver Disease
- Viral Hepatitis (Hepatitis B or Hepatitis C)
- Alcoholic Hepatitis
- Cirrhosis
- References
- (2000) MMWR Recomm Rep 49(RR-6): 1-51 [PubMed]