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Pharmacology (Topic C) > C2. Antimycobacterial drugs > Flashcards

C2. Antimycobacterial drugs Flashcards

1
Q

What are Mycobacteria?

A
  1. Mycobacteria are slow-growing aerobic, non-motile rods with a resistant lipid-rich wall.
  2. They are facultative intracellular pathogens and can remain dormant.
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2
Q

List the 1st line anti-TB medications.

A

“RIPE” Drugs:

  1. Rifampin (RA)
  2. Isoniazide (INH)
  3. Pyrazinamide (PZA)
  4. Ethambutol (ETB)
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3
Q

List the 2nd line anti-TBC meds.

A
  1. Ethionamide
  2. Cycloserine
  3. PAS (para-aminosalicylic acid)
  4. Kanamycin/Amikacin
  5. Capreomycin
  6. Fluoroquinolones
  7. Rifabutin
  8. Linzolid
  9. Bedaquiline
  10. Delamanid
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4
Q

List the anti-leprosy meds.

A
  1. Dapsone
  2. Rifampin
  3. Clofazemine
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5
Q

List the agents used to treat Mycobacterium Avium Complex (MAC) infection.

A

Mneumonic: “AIDS”

  1. Azithromycin
  2. Claritromycine
  3. Ethambutol
  4. (+/-) Rifabutin
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6
Q

How long do you give First-Line Agents?

A

You give all 4 for first 2 months then just Rifampin (RA) and Isoniazide (INH) for 4 more months after that.

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7
Q

What considerations should you make regarding the Drug Distribution of the anti-TB medications?**

A
  1. In younger, well-vascularized, cellular granulomas → anti-TBC drugs must enter interstitium and penetrate immune cells to enter phagolysosomes where bacteria are In necrotic granulomas / cavities → drugs must diffuse through the caseated material to reach extracellular pathogens
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8
Q

What is the MOA of Nitrofurantoin?

A

Nitrofurantoin concentrates in urine and is reduced inside bacteria by flavoproteins → highly reactive intermediates → cause damage to ribosomes, DNA and metabolic processes.

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9
Q

What is the MOA of Bacitracin?

A

Bactracin is used topically and it inhibits a carrier for transfer of peptidoglycan subunits → disrupts cell wall synth of the bacteria.

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10
Q

What is the MOA of Phosphomycin?

A

Phosphomycin is administered as prodrug called trometamol. It inhibits the formation of N-acetyl muramic acid → cell wall synth disruption.

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11
Q

What is the MOA of Colistin?

A

Colistin also known as polymyxin E is a cationic detergent → membrane disruption.

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12
Q

What is Mycobacterium Avium Complex (MAC)?**

A
  1. Common in systemic disease in AIDs patients with CD count <50 can use azithromycin/clarithromycin with ethambutol +/- rifabutin
  2. Mycobacterium avium complex is a group of mycobacteria comprising Mycobacterium intracellulare and Mycobacterium avium (No mention of M. chimera in ref) that are commonly grouped together because they infect humans together; this group, in turn, is part of the group of nontuberculous mycobacteria. These bacteria cause disease in humans called Mycobacterium avium-intracellulare infection or Mycobacterium avium complex infection.[2]
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13
Q

What is the MOA of Dapsone?

A

Dapsone inhibits folate synthesis used in combo with rifampin.

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14
Q

What is Clofazimine used for?

A

It is used for lepromatous form of leprosy with ‘leonine facies’, from Sketchy.

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15
Q

What is the MOA of Rifampin?

A

Rifampin inhibits RNA polymerase → bactericidal effect, especially dormant microbes with a long post-antibiotic effect (PAE).

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16
Q

What is the MOA of Linezolid?

A

Linzolid inhibits protein synthesis.

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17
Q

When is Rifabutin used?

A
  1. Rifabutin is similar to rifampin, but less enzyme induction.
  2. Its used to replace rifampin when treating TBC in HIV patients, due to less interaction with antiretroviral protease inhibitors.
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18
Q

List the Fluoroquinolones.

A
  1. ciprofloxacin
  2. levofloxacin
  3. gatifloxacin
  4. moxifloxacin
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19
Q

What is the MOA of Capreomycin and what is it used for?

A

Capreomycin acts by protein synthesis inhibition and its used for multiresistant M. tuberculosis.

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20
Q

What are the indications for Kanamycin / Amikacin?

A

They are used in case of streptomycin resistance / multiresistance.

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21
Q

What is the MOA of Para-aminosalicylic Acid (PAS)?

A

It inhibits folate synthesis as an analog of PABA → bacteriostatic.

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22
Q

What is the MOA of Cycloserine?

A

Cycloserine is a D-Ala analog → inhibits Ala racemase + thus cell wall synthesis.

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23
Q

What is the MOA of Ethionamide?

A

It is related to isoniazid and also inhibits mycolic acid synth.

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24
Q

What are the indications of Second-Line TB Agents?

A

Indicated in resistance to first-line agents or to limit adverse reactions.

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25
Q

What is the MOA of Isoniazid?

A
  1. The active metabolites block of isoniazid mycolic acid synth via enzyme/carrier protein inhibition.
  2. bactericidal in actively growing microbes,
  3. -static in dormant Mycobacterium
  4. specific catalase G enzymes create active metabolites within the microbes.
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26
Q

What is the MOA of Pyrazinamide?

A

Pyrazinamide is a prodrug is converted to activated pyrazinoic acid by mycobacterial pyrazinamidase. The mechanism itself is unknown. It does however seem to cause membrane/metabolism disruption and therefore results in a bactericidal effect, esp. in dormant Mycobacteria. Resistance does develop fast by pyrazinamidase mutations. This drug is not given by itself but in combo with the other “RIPE” drugs.

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27
Q

What is the MOA of Streptomycin?

A
  1. Also a “first-line” anti-TB drug, but not part of the classic combination
  2. Active against M. tuberculosis (no Kansasii or Avium) in open caverns / bronchi only since aminoglycosides require O2 to enter cells
28
Q

What is the MOA of Ethambutol?

A
  1. It inhibits arabinogalactan formation by blocking arabinosyl transferases.
  2. Has a bacteriostatic effect.
29
Q

What spectrum does Nitrofurantoin cover?

A

It has good activity against:

  1. Staph
  2. Strep
  3. Enterococcus
  4. E. coli.
30
Q

What are the side effects of Nitrofurantoin?

A
  1. Nausea
  2. Headache
  3. Flatulence more rarely
  4. Pulmonary hypersensitivity reactions
  5. Skin reactions (itching, urticaria, hair loss)
31
Q

What are the indications of Nitrofurantoin?

32
Q

What spectrum does Bacitracin cover?

A

Mainly covers Gram+.

33
Q

What are the side effects of Bacitracin?

A
  1. High nephrotoxicity → local topical use only
34
Q

What are the indications for Bacitracin?

A

Mixed skin infections.

35
Q

What spectrum does Phosphomycin cover?

A

Gram + (Staph) and Gram - (E. coli, Klebs, Enterobacter, Proteus) bacteria.

36
Q

What are the kinetics like for phosphomycin? **

A
  1. Only therapeutic in urine
  2. Safe in pregnancy!
  3. Well absorbed from the GI and widely distributed, including tuberculous meningitis.
37
Q

What spectrum does Colistin cover?

A
  1. Colistin covers a narrow spectrum
  2. Only Gram - aerobe (GI rods), but Proteus, Serratia are resistant. Pseudomonas + Acinetobacter are highly susceptible.
38
Q

What are the side effects of Colistin?

A

Highly toxic → nephro- and peripheral neurotoxic (no CNS entry)

39
Q

What are the indications for Colistin?

A
  1. Severe multi-resistant infections (eg, multi-resistant Acinetobacter)
  2. UTI
  3. cystitis (as local wash)
40
Q

What are the side effects of Dapsone?

A

It is generally well-tolerated, but can cause hemolysis in G6PD deficiency (showing “bite cells” with Heinz bodies) (also may cause agranulocytosis)

41
Q

What spectrum does Rifampin cover?

A
  1. Most Mycobacteria (incl. leprae) plus N. meningitidis and H. flu (as prophylactic monotherapy), and Pox viruses.
  2. Good for highly resistant Staph endocarditis/osteomyelitis with ciprofloxacin.
42
Q

What are the pharmacokinetics like for Rifampin?

A
  1. good oral absorption + distribution (phagocytes, abscess/cavity, CSF)
  2. accelerates its own hepatic metabolism (CYP inducer, incl. 3A4)
  3. hepatic and renal elimination.
43
Q

What are the side effects of Rifampin?

A
  1. Hepatotoxicity - ↑ enzymes, rarely hepatitis
  2. Orange Discoloration - urine, sweat, tears (rare neuro issues)
44
Q

What spectrum does Linzolid cover?

A

Linzolids are used for multiresistant / atypical Mycobacteria.

45
Q

What are the Pharmacokinetics like for Linzolid?

A

Given orally long-term therapy

46
Q

What are the possible side effects of Linzolid therapy?

A
  1. Bone marrow suppression
  2. Neuropathy.
47
Q

What are the side effects of Kanamycin/Amikacin?

A

It is nephro-/ototoxic.

48
Q

What is the route of administration for Kanamycin/Amikacin?

A

They are given parenterally.

49
Q

What are the indications for PAS?

A

PAS is good for M. tuberculosis, with little resistance.

50
Q

What are the pharmacokinetics like for PAS?

A
  1. Oral absorption
  2. Good distribution
  3. Metabolized by acetylation
51
Q

What are the side effects of PAS?

A
  1. GI effects (ulcer, nausea, D)
  2. CNS effects
  3. Hypersensitivity
52
Q

How is the pharmacokinetics like for Cycloserine?

A
  1. Oral absorption
  2. CNS penetration
  3. Partial metabolism
53
Q

What are the indications for Cycloserine?

A

Cycloserine is good for INH / streptomycin-resistant M. tuberculosis (plus many G+/- but only used for TBC).

54
Q

What spectrum does Ethionamide cover?

A

Ethionamide is good for M. tuberculosis, kansasii and avium.

55
Q

How is the pharmacokinetics like for Isoniazide?

A
  1. Isoniazide is a pro-drug given orally
  2. Distributes well, even in CSF and granulomas metabolized in liver by acetylation + eliminated in urine.
56
Q

What spectrum does Pyrazinamide cover?

A

Only for M. tuberculosis good substitute for INH in case of resistance.

57
Q

How does the pharmacokinetic of Streptomycin look like?

A
  1. Only parenteral via IM 2-3x/wk.
  2. It does not enter the CNS.
58
Q

What spectrum does Ethambutol cover?

A

M. tuberculosis, kansasii and some avium.

59
Q

What are the side effects of Cycloserine administration?

A
  1. Severe CNS effects: tremor, acute psychosis, seizure
  2. Peripheral neuropathy
60
Q

What are the side effects of Ethionamide?

A
  1. can be hepatotoxic
  2. GI side effects
  3. allergy
61
Q

How are the pharmacokinetics like for Ethionamide?

A
  1. absorbed orally
  2. enters CNS
  3. metabolized by liver + excreted in urine.
62
Q

What are the side effects of Isoniazide?

A
  1. Hepatotoxic: worse w/ alcohol or rapid acetylators
  2. Peripheral Neuropathy: paresthesias (sometimes CNS effects: headache, memory loss, seizure) via B6 deficiency caused by INH-pyridoxine binding worse in slow acetylators + reversible with B6 supplementation.
  3. Muscle cramps, fever, rash (Drug-Induced Lupus, anion-gap acidosis and CYP450 inhibition)
63
Q

How are the Pharmocokinetics like for Pyrazinamide?

A
  1. Good oral absorption and good distribution (penetrates BBB).
  2. Liver metabolism and urine excretion.
64
Q

What are the side effects of Streptomycin?

A
  1. Nephrotoxic
  2. Ototoxic
65
Q

What are the side effects of Ethambutol?

A
  1. Retrobulbar Neuritis: ↓ visual acuity, red-green color blindness and scotomas (check vision monthly)
  2. Rarely nausea, joint pain, headache and allergy
66
Q

How do the pharmacokinetics of Ethambutol look like?

A
  1. Good oral absorption (but ↓ by alcohol) and macrophage penetration / CNS
  2. Excreted unchanged in urine
67
Q

What are the side effects of Pyrazinamide?

A
  1. Hepatotoxicity: as severe as liver necrosis
  2. Hyperuricemia: can precipitate gout attacks; but rifampin ↓ uric acid!

Pharmacology (Topic C) (20 decks)

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