Penicillin Flashcards
4 Mechanism of drug resistance in Penicillin
- Prodn of beta-lactamase
- Modification of PBP
- Decreased penetration
- Prodn of efflux pumps
Explain the mechanism of pcn resistance thru prodn of beta lactamase
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)
Pen G is given
a. Parenterally
b. orally
c. transdermally
Pen G is acid labile that is given PARENTERALLY
Pen V is given:
a. parenterally
b. orally
Pen V is acid stable and is given ORALLY because it cannot be destroyed by HCl in stomach, hence good oral absorption.
what is the significance of plasma protein-binding?
the drug is made unavailable. while the drug is being attached to plasma proteins, the drug cannot be absorbed, distributed, metabolized and excreted.
t/f: absorption of penicillin would be impaired by food.
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.
Give certain organs and tissues that penicillin has limited distribution
- eyes
- prostate
- brain tissue: generally poor distribution in the CNS (not able to penetrate BBB)
EXCEPTION: conditions where the meninges are yacutely inflamed
t/f: in cases of meningitis, penicillins can be only given during the active stage of infection
true
excretion primarily occurs in renal. 90% would be on _______ and 10% would be on ________.
a. proximal tubular secretion
b. glomerular filtration
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.
true
t/f: avoid giving penicillin to newborn due yo inadequate renal function. if really needed, you have to reduce the dose.
true
a uricosuric agent; prevents the excretion of penicillin by proximal tubular secretion.
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.
Penicillin is the drug of choice for:
N. meningitidis, treponema and other spirochetes
most common adverse reaction of penicillin
hypersensitivity
most notorious penicillin that induces seizures
Pen G
neutropenia is associated with
Nafcillin.
NN
hepatitis is associated with
oxacillin
OH
interstitial nephritis is associated with
methicillin
associated mostly with clindamycin and ampicillin is
pseudomembranous colitis which is caused by C. difficile
DOC for C. difficile infection and its alternative drug
metronidazole
vancomycin
associated with aminopenicillins (amox< ampi)
skin rashes not necessarily due to hypersensitivity reaction, but present generalized skin rash
antigenic determinants of penicillin
degradation products
products of alkaline hydrolysis
management of penicillin hypersensitivity
epinephrine
erythromycin: most common alternative drug to penicillin
principle of desensitization
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.
drugs that enhances the activity of penicillin (synergism)
beta-lactamase inhibitor
aminoglycosides: increases uptake
drugs that antagonizes penicillin
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
