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Questions and Answers
What is the primary site of action of Isoniazid (INH)?
What is the primary site of action of Isoniazid (INH)?
- Mycobacterial cell wall (correct)
- Intracellular bacilli
- Macrophages
- Extracellular bacilli
Which type of bacilli does Rifampin (RIF) primarily work on?
Which type of bacilli does Rifampin (RIF) primarily work on?
- Rapidly growing bacilli (correct)
- Slowly proliferating bacilli
- Extracellular bacilli
- Resting bacilli
What is the clinical use of Rifampin (RIF) in addition to treating TB?
What is the clinical use of Rifampin (RIF) in addition to treating TB?
- Prophylaxis against active TB in individuals at risk
- Treating optic neuritis
- Treating latent TB in patients with positive tuberculin skin test (correct)
- Inhibiting cytochrome P450 2C19 isoform
Which adverse drug reaction (ADR) is associated with Isoniazid (INH) and requires Pyridoxine supplementation?
Which adverse drug reaction (ADR) is associated with Isoniazid (INH) and requires Pyridoxine supplementation?
Why is Vitamin B6 prescribed with Isoniazid (INH)?
Why is Vitamin B6 prescribed with Isoniazid (INH)?
When is hepatitis caused by Isoniazid (INH) more likely to occur?
When is hepatitis caused by Isoniazid (INH) more likely to occur?
What is the main mechanism of action of the drug described in the text?
What is the main mechanism of action of the drug described in the text?
Which side effect is NOT associated with the drug?
Which side effect is NOT associated with the drug?
What is the consequence of being a fast acetylator of the drug?
What is the consequence of being a fast acetylator of the drug?
Which vitamin is affected by the drug's inhibition of pyridoxine?
Which vitamin is affected by the drug's inhibition of pyridoxine?
What enzyme isoforms are strongly induced by the drug?
What enzyme isoforms are strongly induced by the drug?
What type of infection can the drug be used to treat besides TB?
What type of infection can the drug be used to treat besides TB?
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Study Notes
Isoniazid (INH)
- First-line treatment for tuberculosis
- Bacteriostatic, effective against resting bacilli
- Inhibits the synthesis of mycolic acid, a key component of mycobacterial cell wall
- Penetrates into macrophages
- Clinical uses:
- Treatment of TB
- Treatment of Latent TB in patients with positive tuberculin skin test
- Prophylaxis against active TB in high-risk individuals
- Adverse drug reactions (ADRs):
- Peripheral neuritis (pins and needles sensation in the feet)
- Optic neuritis and atrophy
- Hepatitis (toxic metabolites, age-dependent, and increased with alcohol use)
- Interactions:
- Inhibits cytochrome P450 2C19 isoform, leading to accumulation of drugs metabolized by 2C19
- Slow and fast acetylators: genetic variation affects metabolism and toxicity
Rifampin (Rifampicin)
- Bactericidal, effective against rapidly growing bacilli
- Inhibits RNA synthesis by binding to bacterial DNA-dependent RNA polymerase enzyme
- Clinical uses:
- Treatment of TB
- Prophylaxis against meningococcal and staphylococcal infections
- Adverse drug reactions (ADRs):
- Harmless red-orange discoloration of body secretions (saliva, sweat, urine, tears)
- Hepatitis (less common compared to INH)
- Flu-like syndrome
- Hemolytic anemia
- Interactions:
- Strongly induces most cytochrome P450 isoforms (2C19, 2C9, 3A4)
- Clinically significant drug interactions: warfarin, methadone (faster metabolism, reduced activity)
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