Pharmacology - Antibiotics

Question 1

Trimethoprim

Answer 1

Inhibits dihydrofolate reductase (prevents reduction of folic acid to tetrahydrofolate)

Question 2

Sulfamethoxazole

Answer 2

Structural analog of para-aminobenoic acid (PABA). Competes with PABA to inhibit dihydrofolic acid synthesis, an intermediate step in formation of tetrahydrofolate.

Question 3

Imipenem

Answer 3

Binds a PBP (penicillin binding protein) and inhibits final step of peptidoglycan synthesis in bacterial cell walls.

Question 4

Cilastatin

Answer 4

Use in conjunction with imipenem - prevents renal metabolism of imipenem by competitively inhibiting dehydropeptidase in renal tubule brush border.

Remember: Imipenem is LASTING with CiLASTatin.

Question 5

Bacitracin

Answer 5

Prevents mucopeptide transfer into growing cell wall, inhibiting cell wall synthesis.

Question 6

Metronidazole

Answer 6

Binds DNA in susceptible cells, unraveling DNA’s helical structure and breaking its strands.

Question 7

Pyrimethamine

Answer 7

Acts the same way as trimethoprim and methotrexate; treats toxoplasmosis because it inhibits parasitic dihydrofolate reductase.

Question 8

Penicillins and cephalosporins

Answer 8

Irreversibly bind penicillin binding proteins, AKA transpeptidases, which cross-link peptidoglycan in the bacterial cell wall.

NOTE: They do NOT bind to the cell wall glycoproteins! They bind to the transpeptidases!

Question 9

Another word for penicillin binding proteins?

Answer 9

Transpeptidases!

Question 10

What do transpeptidases do?

Answer 10

They cross-link peptidoglycan in the bacterial cell wall.

Question 11

Vancomycin

Answer 11

Binds to terminal D-alanine residues of cell wall glycoproteins and prevents transpeptidases from forming cross-links.

Note: Vancomycin actually binds to the glycoproteins of the cell wall.

Side effects: Red man syndrome (histamine mediated), nephrotoxicity

Question 12

Which binds to cell wall glycoproteins, vanc or penicillins?

Answer 12

Vancomycin

Question 13

Fluoroquinolones

Answer 13

Interfere with DNA replication by binding to DNA gyrase

Question 14

Beta lactamase

Answer 14

Degrades penicillin and cephalosporin.

Question 15

Which antibiotics would require entry into the cell to function?

Answer 15

Tetracycline and macrolides for example - probably things that inhibit ribosomal assembly.

Question 16

What are the commonly used drugs for invasive MRSA?

Answer 16

1. Vancomycin
2. Daptomycin
3. Linezolid

Remember: My Dapper Van is Lined with MRSA.

Question 17

Daptomycin

Answer 17

Disrupts bacterial membrane through creation of transmembrane channels which cause leakage of intracellular ions, leading to depolarization of the cellular membrane and inhibition of DNA / RNA / protein synthesis.

Cannot permeate outer membrane of Gram Negative bacteria.

Is inactivated by pulmonary surfactant - do not use for pneumonieas.

Side effects: increased CPK and increased myopathy, especially in patients taking statins.

Question 18

Linezolid

Answer 18

Inhibits bacterial protein synthesis by binding to the 50S subunit.

Basically like clinda.

Side effects: Thrombocytopenia, optic neuritis, high risk for serotonin syndrome.

Question 19

Tetracyclines

Answer 19

Inhibit 30S subunit.

Bacteriostatic, bind to 30S and prevent attachment of amino-acyl tRNA; limited CNS penetration. Do not take with milk.

Remember: Buy AT 30, CCEL at 50.

Question 20

Aminoglycosides

Answer 20

Bactericidal - inhibit formation of initiation complex and cause misreading of mRNA; also block translocation. Require O2 for uptake; therefore ineffective against anaerobes.

Mean GNATS caNNOT kill annaerobes.

Gentamicin
Neomycin
Amikacin
Tobramycin
Streptomycin

Nephrotoxic
Neuromuscular blockade
Ototoxic
Teratogenic

Question 21

Macrolides

Answer 21

Azithromycin, clarithromycin, erythromycin. Inhibit protein synthesis by blocking translocation. bind to 23S rRNA of the 50S ribosomal subunit. bacteriostatic.

Question 22

Chloramphenicol

Answer 22

Binds peptidyltransferase at 50S ribosomal subunit. bacteriostatic. Aplastic anemia and gray baby syndorme.

MOR: Plasmid-encoded acetyltransferase inactivates drug.

Question 23

Clindamycin

Answer 23

Blocks peptide transfer at the 50s ribosomal subunit.

Question 24

Carbapenems

Answer 24

Imipenem, meropenem, ertapenem, doripenem

beta lactam / broad spectrum / beta-lactamase resistant

Question 25

Isoniazid

Answer 25

Decreased synthesis of mycolic acids. Need bacterial catalase peroxidase encoded by KatG to convert INH to active metabolite.

Think Wall of Ice + Acid

Question 26

Rifamycin

Answer 26

Rifampin, rifabutin

Inhibits DNA dependent RNA polymerase.

Question 27

Dapsone

Answer 27

PABA antagonist that acts to inhibit folic acid synthesis, behaves similarly to sulfonamides

Question 28

Pyrazinamide

Answer 28

Thought to acidify intracellular environment by conversion to pyrazinoic acid, TB

Question 29

Ethambutol

Answer 29

TB, decreases carbohydrate polymerization of mycobacterium cell wall by blocking arabinosyltransferase.