Anti TB Therapy

Question 1

• Phases of Drug Treatment in TB

- Overall Objective of anti-TB therapy

Answer 1

2 Phases:

Initial Phase

• Purpose: to decrease bacterial population as rapidly as possible and prevent emergence of drug-resistant bacteria
• Minimum of 2 months duration + until susceptibility results are known
• Isoniazid, Rifampicin, Ethambutol, Pyrazinamide

Continued Phase

• Purpose: prolonged therapy is required to kill dormant organisms in necrotic lesions
• Minimum of 4 months duration but may be longer depending on site of infection and clinical circumstances
• Rifampicin + Isoniazid

Overall Objective of Anti-TB Therapy:
- to achieve a lifetime cure of the disease while preventing drug resistance

Question 2

Rifampicin

• M.O.A
• Toxicity
• Resistance

Answer 2

M.O.A - inhibits DNA dep RNA poly
Toxicity - hepatotoxicity, induces CYP450, red body fluids
Resistance - develops rapidly due to mutations which reduce drug binding to RNA poly

Question 3

Isoniazid

• M.O.A
• Toxicity
• Resistance

Answer 3

M.O.A - inhibits the synthesis of mycolic acids
Toxicity - hepatotoxic, inhibits CYP450, neurotoxic (prevented by taking pyridoxine, B6)
Resistance - due to mutations which cause under expression of KatG, which codes for catalase-peroxidase, which activates isoniazid

Question 4

Pyrazinamide

• M.O.A
• Toxicity

Answer 4

M.O.A - Unknown

Toxicity - hepatotoxic, hyperuricaemia

Question 5

Ethambutol

• M.O.A
• Toxicity

Answer 5

M.O.A - inhibits arabinose polymerisation, which interferes with cell wall function
Toxicity - reduced visual acuity, red/green color vision loss