Pharm Topic 13: Penicillins And Beta Lactams

Front 1

2 rings of a penecillin

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Beta lactam ring and a thiazolidine ring

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Penicillin pharmacokinetics (admin, distrib, elimination)

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Admin - Give oral on empty stomach
Distrib - Well, crosses placenta and milk, enters CNS when meninges inflamed.
Elim - All excreted renally without metabolism except beta lactamase resistant which are hepatically.

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Penicillin Mech

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Cidal:
Act as pseudosubstrates and bind to PBP proteins preventing cross linking of cell wall. Bacteria die from lysis of fragile cell wall (via osmotic stress). Bacteria must be actively multiplying for penicillin to work.

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G+ Lactamase

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Excreted in large amount into external environment, plasmid mediated, obtained via transduction, act primarily against penicillins. Staph is penecillin resistant.

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Penicillin Resistance mechs

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1) Lactamase production - Most important. Hydrolyzes B lactam ring.
2) Pumps and Pores - G- bacteria have pores where penicillin enters, these can be downregulated. Also there can be increased efflux via pumps.
3) Mutations of PBPs leading to decreased affinity

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G- Lactamase

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Secreted between cell wall and membrane (periplasmic space) in lower amounts, generally heterohenous (wide range), work agianst cephalosporins, and can initiate self transmission via conjugation. Ecoli is often penicillin resistant.

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Penicillin Side effects and contraindications

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SE - Allergic Rxs, two types:
1) Immediate - anaphylaxis, urticaria, and edema
2) Delayed - serum sickness, rashes.
Also can get non allergic probs such as CNS tox at high doses and nephritis.
Contraindicated if one has had a previous hypersensitivity Rx.

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Penicillin G and V (uses and not uses)

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-Used for:
All G+
G- cocci
Sprochettes (syphilis)
Anaerobes
-NOT:
G- bacilli (pseudomonas)
Staph (now resistant)

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Beta lac Resistant penicillins (examples, Uses and not uses)

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Methicillin, Cloaxacillin, Dicloxacillin, Oxacillin
-Used for:
Staph infections only
-Not for:
Any G-
MRSA = methicillin resistant staph

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Aminopenicillins (examples, uses, not uses)

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Broad spectrum (+ and -), often used for ear/resp infections in kids.
Ampicillin - Used for meningitis due to lysteria ,used with sulbactam.
Amoxicillin - Used as combo with Clavulcanic acid.

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Extended spectrum penicillins (examples, uses, not uses)

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AKA antipsuedomonal penicillins. Piperacillin, Ticaracillin, carbenicillin.
-Used for:
Broad spectrum, used to treat pseudomonas as well as complicated G- resp infections
-Not used for:
G+ bacteria

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Penicillins + Aminoglycosides

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Common drug combo, Increases strength and shortens length of treatment. Penicillin increases cell wall permeability, increasing entrance of other ABs like aminoglycosides. Used to treat endocarditis caused by pen-suseptible strep (Pen G and Gentamicin).

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Cephalosporins pharmacokinetics (admin, distrib, elimination)

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Distrib - Widely distributed, only ceftriaxone and cefotaxime enter CNS
Elim - Excreted in kidneys. All unmetabolized except Cefotaxime which is biotransformed.

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Cephalosporins mech

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Bactericital. Same as penicillin

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Cephalosporin Resistance

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Same as penicillin, some cross resistance to both.

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Cephalosporin Side effects and counterindications

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SE - Hypersensitivity, nephrotoxicity, and all untoward effects of penicillin.
Counterindicated if had allergic Rx to itself or penicillin.

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5 generalizations of cephalosporins

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1) G+ coverage decreases and G- increases with increasing gen.
2) Total daily dosage of drugs is similar in each gen.
3) Frequency of dosing decreases with increasing gen.
4) Palatability increases with increasing gen.
5) 2nd and 3rd gen cephalosporins arent approved for kids less than 6 mo age.

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First Gen Cephalosporins (ex, uses, not uses)

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Cephalexin and Cephazolin
-Uses
G+ cocci
Often used on skin and pre-op
-Not used
Meningitis (does not enter CNS)
Enterococci
Listeria

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Second Gen Cephalosporins (ex, uses, not uses)

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Broad G-, not as good as 1st for +.
Cefoxitin - Good for anaerobic bacteria.
Cefaclor - Better for staph than other 2nd gens, good for G-, used in pneumonia and throat infections.

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Third Gen Cephalosporins (ex, uses, not uses)

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Ceftriaxone and Cefotamine - Broad spectrum, good for G+ cocci, enterobacteria, works on pseudomonas, can cross into CSF and treat meningitis.
Ceftazidime - Effective against pseudomonas

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Fourth Gen Cephalosporins (ex, uses, not uses)

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Cefeprime - Similar to 3rd gen but more B lac resistant. Good for G+ cocci, enterobacteria, and pseudomonas, meningitis, and is stable against B Lac.

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B Lac Inhibitors and examples

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Clavulanic acid, Sulbactam, and Tazobactam.
While no antibiotic properties on their own, are given with penicillins and cephalosporins to improve effect.

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Carbepenems

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Names all end in -penem. Broad spectrum Abs, Highly resistant to B lac, are effective against pseudomonas

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Monobactrams

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Ex, Aztreoman. Narrow range of coverage, only G- aerobic. Effective agasint pseudomonas.