Penicillin

Question 1

4 Mechanism of drug resistance in Penicillin

Answer 1

1. Prodn of beta-lactamase
2. Modification of PBP
3. Decreased penetration
4. Prodn of efflux pumps

Question 2

Explain the mechanism of pcn resistance thru prodn of beta lactamase

Answer 2

enzyme produced by organisms called beta lactamase with 2 forms: penicillinase & cephalosporinase. these will destroy the beta lactam ring, particularly ring A, in the nucleus of beta lactam antibiotics. 6aminopenicillanic acid (active form) ➡️ penicillonic acid (inactive form)

Question 3

Pen G is given

a. Parenterally
b. orally
c. transdermally

Answer 3

Pen G is acid labile that is given PARENTERALLY

Question 4

Pen V is given:

a. parenterally
b. orally

Answer 4

Pen V is acid stable and is given ORALLY because it cannot be destroyed by HCl in stomach, hence good oral absorption.

Question 5

what is the significance of plasma protein-binding?

Answer 5

the drug is made unavailable. while the drug is being attached to plasma proteins, the drug cannot be absorbed, distributed, metabolized and excreted.

Question 6

t/f: absorption of penicillin would be impaired by food.

Answer 6

True. So you must have to take it 1-2 hrs either before or after meals. EXCEPT FOR AMOXICILLIN WHICH IS NOT IMPAIRED BY FOOD.

Question 7

Give certain organs and tissues that penicillin has limited distribution

Answer 7

1. eyes
2. prostate
3. brain tissue: generally poor distribution in the CNS (not able to penetrate BBB)
   EXCEPTION: conditions where the meninges are yacutely inflamed

Question 8

t/f: in cases of meningitis, penicillins can be only given during the active stage of infection

Answer 8

true

Question 9

excretion primarily occurs in renal. 90% would be on _______ and 10% would be on ________.

Answer 9

a. proximal tubular secretion

b. glomerular filtration

Question 10

t/f: only give penicillin if you’re sure that the patient has normal renal function. in the presence of renal impairment, the best marker would be creatinine clearance with a level at 10ml/min or less than that then you don’t give penicillin.

Answer 10

true

Question 11

t/f: avoid giving penicillin to newborn due yo inadequate renal function. if really needed, you have to reduce the dose.

Answer 11

true

Question 12

a uricosuric agent; prevents the excretion of penicillin by proximal tubular secretion.

Answer 12

Probenecid. probenecid will compete with Pen G for proximal tubular secretion, that results in excretion of probenecid and pen G will stay in the circulation, prolonging half life, prolonging action.

Question 13

Penicillin is the drug of choice for:

Answer 13

N. meningitidis, treponema and other spirochetes

Question 14

most common adverse reaction of penicillin

Answer 14

hypersensitivity

Question 15

most notorious penicillin that induces seizures

Answer 15

Pen G

Question 16

neutropenia is associated with

Answer 16

Nafcillin.

NN

Question 17

hepatitis is associated with

Answer 17

oxacillin

OH

Question 18

interstitial nephritis is associated with

Answer 18

methicillin

Question 19

associated mostly with clindamycin and ampicillin is

Answer 19

pseudomembranous colitis which is caused by C. difficile

Question 20

DOC for C. difficile infection and its alternative drug

Answer 20

metronidazole

vancomycin

Question 21

associated with aminopenicillins (amox< ampi)

Answer 21

skin rashes not necessarily due to hypersensitivity reaction, but present generalized skin rash

Question 22

antigenic determinants of penicillin

Answer 22

degradation products

products of alkaline hydrolysis

Question 23

management of penicillin hypersensitivity

Answer 23

epinephrine

erythromycin: most common alternative drug to penicillin

Question 24

principle of desensitization

Answer 24

during desensitization, you administer the antigen of the drug initially in serial suboptimal doses. you start with the lowest amount, you give it serially until you reach the full therapeutic dose, and patient might be able to tolerate the penicillin. the goal here is tolerization.

Question 25

drugs that enhances the activity of penicillin (synergism)

Answer 25

beta-lactamase inhibitor

aminoglycosides: increases uptake

Question 26

drugs that antagonizes penicillin

Answer 26

bacteriostatic drugs: tetracycline and chloramphenicol (penicillin inh cell wall synthesis only among organisms that are actively growing and multiplying)

potent inducers of beta-lactamase: imipinem