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Module 3 Term 4 > Antimycobacterials > Flashcards

Antimycobacterials Flashcards

1
Q

Mycobacteria

A

Located intracellularly. Resistant to most antibiotics. Quick to develop resistance. Therapy can take months or years. Combination therapy is required.

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2
Q

1st Line drugs for TB

A
  • Isoniazid
  • Rifampin
  • Rifabutin (1st line in HIV +ve patients)
  • Ethambutol
  • Pyrazinamide
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3
Q

2nd Line drugs for TB

A
  • Streptomycin
  • Ethionamide
  • Levofloxacin
  • Amikacin
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4
Q

TB Therapy

A

3-4 drug combination therapy

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5
Q

Latent TB Prophylaxis

A
  1. Persons who have been recently infected with TB bacteria

2. Persons with medical conditions that weaken the immune system

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6
Q

Isoniazid MOA

A

Targets enzymes involved in mycolic acid synthesis:

  1. enoyl acyl carrier protein reductase (InhA)
  2. b-ketoacyl-ACP synthase (KasA)
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7
Q

Isoniazid is activated by

A

KatG- a mycobacterial catalase peroxidase.

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8
Q

Isoniazid is what kind of drug

A

Prodrug

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9
Q

Isoniazid Antibacterial Spectrum

A

Bacteriostatic effects against bacilli in stationary phase. Bactericidal against rapidly dividing bacilli. Specific for M.tuberculosis

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10
Q

Isoniazid Resistance

A

Chromosomal mutations resulting in:
• mutation of deletion of KatG
• mutations of acyl carrier proteins
• overexpression of inhA

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11
Q

Isoniazid AE

A
  • Peripheral neuritis: corrected by pyridoxine supplementation
  • Hepatotoxicity: clinical hepatitis & idiosyncratic
  • CYP P450 inhibitor
  • Lupus-like syndrome: rare
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12
Q

Isoniazid in Pregnancy

A

Safe in pregnancy (however, hepatitis risk is increased, pyridoxine supplementation is recommended)

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13
Q

Rifamycins

A

Rifampin & rifabutin. First-line drugs for treatment of all susceptible forms of
TB. Part of COMBINATION THERAPY for active infections. Sole drug in treatment of latent infection (2nd line).

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14
Q

Rifampin

A

USUALLY GIVEN IN COMBINATION

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15
Q

Rifampin MOA

A

Blocks transcription by binding to beta subunit of bacterial DNA-dependent RNA polymerase leading to inhibition of RNA synthesis.

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16
Q

Rifampin Antimicrobial Spectrum

A

Bactericidal for intracellular AND extracellular mycobacteria: M.tuberculosis and M.kansasii. Active against Gram-positive & Gram-negative organisms. Activity against MRSA.

17
Q

Rifampin Resistance

A

Point mutations in rpoB, the gene for the beta subunit of RNA polymerase: decreased affinity of bacterial DNA-dependent RNA polymerase for drug. Decreased permeability.

18
Q

Rifampin Clinical Applications

A

• Active TB infections
• Latent TB in isoniazid intolerant patients
• Leprosy (delays resistance to dapsone)
• Prophylaxis for individuals exposed to meningitis
• Prophylaxis in contacts of children with H.influenzae type B
• MRSA (with vancomycin)
28

19
Q

Rifampin AE

A
  • Light chain proteinuria
  • GI distress
  • Occasional effects: thrombocytopenia, rashes, nephritis, liver dysfunction
  • Imparts harmless orange/red color to bodily fluids
  • Strongly induces most CYP P450 isoforms
  • SAFE IN PREGNANCY
20
Q

Rifabutin

A

Preferred drug for use in HIV patients (due to less induction of CYP enzymes)

21
Q

Ethambutol

A

First-line agent for treatment of all susceptible forms of TB. Specific for most strains of M.tuberculosis & M.kansasii. Used in combination with pyrazinamide, izoniazid &
rifampin.

22
Q

Ethambutol MOA

A

Inhibits arabinosyltransferase leading to decreased carbohydrate polymerization of cell wall.

23
Q

Ethambutol AE

A
  • Dose-dependent visual disturbances (eg, red/green color blindness) – cannot be used in children too young to receive sight tests
  • Headache, confusion, hyperuricemia, peripheral neuritis (rare)
  • Safe in pregnancy
24
Q

Pyrazinamide

A
  • First-line agent
  • Used in combination with isoniazid, rifampin & ethambutol
  • Must be enzymatically hydrolysed to active pyrazinoic acid.
25
Q

Pyrazinamide AE

A
  • Nongouty polyarthralgia (~ 40%)
  • Acute gouty arthritis (rare unless predisposed)
  • Hyperuricemia
  • Hepatotoxicity, myalgia, GI irritation, porphyria, rash, photosensitivity
  • Recommended for use in pregnancy when benefits outweigh risks
26
Q

Streptomycin

A

Aminoglycoside. Used for drug resistant strains. Used in drug combinations for treatment of life-threatening tuberculous disease:
• meningitis
• miliary dissemination
• severe organ tuberculosis

27
Q

Amikacin

A

Used for streptomycin- or multi-drug-resistant strains. Similar adverse effects to streptomycin. Teratogenic

28
Q

Levofloxacin

A

Recommended for use against first-line drug- resistant strains. Should always be used in combination. Teratogenic

29
Q

Ethionamide

A

Congener of INH (no cross-resistance). Severe GI irritation & adverse neurologic effects. Also hepatotoxicity & endocrine effects. Teratogenic

30
Q

Leprosy alternative name

A

Hansen’s disease

31
Q

Leprosy Caused by

A

Mycobacterium Leprae and Mycobacterium Lepromatis.

32
Q

Leprosy Definition

A

Granulomatous disease of peripheral nerves and mucosa of URT.

33
Q

Drugs for leprosy

A

• Dapsone
• Clofazimine
• Rifampin
(used in combination)

34
Q

Dapsone

A

Structurally related to sulfonamides. Inhibits folate synthesis (via dihydropteroate synthetase inhibition). Also used in treatment of pneumonia (P.jiroveci) in HIV +ve patients.

35
Q

Acedapsone

A

Respiratory form of Dapsone

36
Q

Dapsone AE

A

• Hemolysis (esp. G6PD deficiency)
• Erythema nodosum leprosum (treated with
corticosteroids or thalidomide)
• Other effects – GI irritation, fever, hepatitis, methemoglobinemia
• CYP P450 inhibitor

37
Q

Clofazimine

A
  • Phenazine dye
  • Binds to DNA & inhibits replication
  • Redox properties may generate cytotoxic oxygen radicals
  • Bactericidal to M.leprae (some activity against M. avium- intracellulare complex)
38
Q

Clofazimine AE

A
  • Red-brown discoloration of skin
  • GI irritation
  • Eosinophillic enteritis
  • Erythema nodosum DOES NOT develop (drug has anti- inflammatory action)

Module 3 Term 4 (3 decks)

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