Antimycobacterial Drugs

Question 1

What is the classification of Ethambutol (EMB), Isoniazid (INH), Pyrazinamide (PZA), and Rifampicin (RIF)?

Answer 1

Antimycobacterial drugs

Question 2

What is the mechanism of action of Isoniazid (INH)?

Answer 2

• inhibits the synthesis of mycolic acids

- inhibits enzymes in sensitive Mycobacterium tuberculosis isolates

Question 3

What are the therapeutic indications of Isoniazid (INH)? (3)

Answer 3

• Tuberculosis
• Extracellular and intracellular organisms
• Bacteriostatic and bactericidal

Question 4

Describe the distribution of Isoniazid (INH)

Answer 4

readily absorbed from GIT

Question 5

Describe the distribution of Isoniazid (INH)

Answer 5

Widely distributed throughout the tissues and body fluids. The concentration in the cerebrospinal fluid is similar to that in the serum.

Question 6

Describe the metabolism of Isoniazid (INH)

Answer 6

Acertylation in the liver

Question 7

How is the metabolism of Isoniazid (INH) determined?

Answer 7

Genetically

Question 8

What is the half-life of Isoniazid (INH)? (2)

Answer 8

slow acetylators - 3 hours

fast acetylators - 1 hour

Question 9

What are the adverse effects of Isoniazid (INH)? (6)

Answer 9

• peripheral neuropathy
• optic neuritis
• psychosis and seizures
• skin eruptions
• hepatitis and idiosyncratic hepatotoxicity
• inhibits metabolism of phenytoin, worsens its adverse effects

Question 10

What is the mechanism of action of Rifampicin (RIF)?

Answer 10

Inhibits DNA-dependent RNA-polymerase in the process where DNA is used as template for RNA transcription. This leads to cessation of protein synthesis

Question 11

What are the therapeutic indications of Rifampicin (RIF)? (3)

Answer 11

• Bactericidal against G+ and G- cocci, some enteric organisms, mycobacteria and chlamydia
• antituberculosis agent
• used in combination with other drugs

Question 12

How is Rifampicin (RIF) administered?

Answer 12

orally

Question 13

Describe the distribution of Rifampicin (RIF)?

Answer 13

widely distributed in the tissue and body fluids (including the cerebrospinal fluid)

Question 14

What effect does Rifampicin have on tears, sweat and urine?

Answer 14

causes orange-red coloration

Question 15

Describe the metabolism of Rifampicin (RIF)?

Answer 15

Excreted partly in urine and bile, some undergo

enterohepatic cycling

Question 16

What is the half-life of Rifampicin (RIF)? (and what changes this)

Answer 16

1-5 hours, becomes shorter during treatment

Question 17

What are common adverse effects of Rifampicin (RIF)? (4)

Answer 17

• skin eruptions
• fever
• GIT disturbances
• Hepatitis

Question 18

What are the less common adverse effects of Rifampicin (RIF)?

Answer 18

• “flu-like syndrome”
• CNS system effects
• Allergic manifestations
• Induction of hepatic metabolising enzymes resulting in an increase in the degradation of warfarin, glucocorticoids and oral antidiabetic agents (causes a need for a higher dose of these drugs)