Download PENICILLINS

-Commonly used, especially penicillin G (natural penicillin)
-Suffix –cillin
-Effective against most gram-positive bacteria
-Bactericidal
-Interfere with cell wall development (blocks enzymes that build the cell wall), making the
bacterium susceptible to lysing
◦ Various enzymes are used in the construction and the different types of penicillins work against the different
enzymes (explains how efficacy can vary within the class of Penicilllns)
◦ Because the cell wall is developed during cell division, penicillins are only effective against actively dividing
bacteria. Therefore a penicillin (and other antimicrobials that affect cell division) should not be given at the
same time as a Bacteriostatic drug!
PENICILLINS
-Penicillin is absorbed well from injection sites and the GI tract.
◦ Exception is Penicillin G. It is inactivated by stomach acid. Only administer via injection.
-Well distributed to most tissues except eye, brain, or prostate
-Excreted by kidney – reach higher amounts in urine than blood
PENICILLIN PHARMACOKINETICS
-Not effective against Pseudomonas
-Staphylococcus bacteria produce enzymes (beta lactamases) that break down the beta lactam
ring found within the structure of penicillin.
◦ Beta lactamase resistant Penicillins: oxacillin, cloxacillin, dicloxacillin
◦ Narrow spectrum of activity
-Potentiated Penicillins are chemically combined with another compound that inactivates beta
lactamases. They protect the beta lactam ring, keeping the penicillin intact.
◦ Clavulanic acid (Augmentin, Clavamox) and sublactam are examples of substances added to penicillin
◦ Potentiated penicillin tablets are individually wrapped because exposure to moisture in the air decomposes
them.
PENICILLIN'S
SPECTRUM OF
ACTIVITY
-Because penicillins affect cell wall formation, mammalian cells will not be acted upon by
Penicillin since they lack cell walls.
-ALLERGIC REACTIONS are common, ranging from rashes to anaphylactic shock. The more severe
reactions are usually after an Injectable penicillin has been administered.
◦ Avoid all penicillins if animal reacts to one of them. Mark clearly in chart!
-RABBITS, GUINEA PIGS, FERRETS, HAMSTERS
◦ Beneficial bacteria may be destroyed by penicillin, allowing pathogenic bacteria to flourish. Severe diarrhea may
cause death in the animal.
◦ Also use caution in snakes, birds, turtles, and chinchillas
-Dairy cattle are often administered Penicillin to treat mastitis. Milk must be tested for residues
and withdrawal times (milk-out times) must be followed to avoid contaminated milk.
PENICILLIN PRECAUTIONS
Penicillin G: natural penicillin given via injection b/c it is inactivated by stomach acid. Available in
three forms:
◦
◦
◦
◦
◦
◦
Aqueous solution with potassium or sodium added. Can be given IV
Suspension with procaine added. Can be given SQ or IM
Suspension with benzathine added. Can be given SQ or IM.
SQ administration may cause tissue damage
Adding anesthetics delays absorption, extending the duration, but may lower plasma concentration
DON’T GIVE CLOUDY PENICILLIN (Suspensions) IV!!!
Ampicillin and amoxicillin: effective against gram negative bacteria as they can bind to the
bacteria’s cell wall
◦ Food in the GI tract can cause these meds to be less effective
◦ Amoxicillin is often combined with clavulanic acid to add protection against beta lactamases
Cloxacillin, dicloxacillin, and oxacillin are naturally resistant to beta lactamases. They have a
narrow spectrum of activity and are used to treat staphylococcal osteomyelitis, pyoderma, and
mastitis
SPECIFIC PENICILLINS
Very similar to Penicillin in structure and mechanism of action
◦ Beta lactam ring, Interfere with cell wall formation
-Ceph (pre 1975)- or cef- prefixes
-More resistant to bacterial lactamases than penicillin
-More effective against Staphylococcus than penicillin
-Cephalosporins are classified by four generations. Each generation has gained some advantage over the previous
generation but has also lost some advantage.
◦ 1st: primarily effective against gram positive bacteria (staph and strep)
◦ 2nd: more effective against gram negative bacteria than 1st generations (Salmonella, E. coli, Enterobacter) but a little less
effective against gram positive than 1st generation
◦ 3rd: limited gram + activity, high activity against Pseudomonas and other gram negative bacteria
◦ 4th: broadest spectrum of activity. Similar to 1st gens in efficacy against gram + and more effective against beta lactamases and
gram negative bacteria than 3rd gens
CEPHALOSPORINS
1st gen: Cefadroxil (Cefa-Tabs, oral), Cephaphirin (Cefa-Dri, injection), Cefazolin (Ancef, injection), Cephalexin
(Keflex, oral)
2nd gen: Cefoxitin (Mefoxin, Injectable)
3rd gen: Cefpodoxime (Simplicef, oral), Ceftiofur (Naxcel, injection), Cefovecin (Convenia, injection)
4th gen: Cefepime (Maxipime, injection)
SPECIFIC CEPHALOSPORINS
-Bactericidal
-Bind and inhibit enzymes needed for cell wall formation (like penicillins)
◦ Cell will easily burst as water enters
◦ The various cephalosporins inhibit different enzymes that are involved in cell wall formation
-Bacteria must be dividing for cephalosporins to work
-Less effected by beta lactamase producing bacteria than penicillins are
-Do not usually pass through blood brain barrier- not good for CNS infections
-Can affect fetuses and nursing animals
-Removed from body via urine (glomerular filtration)
-Relatively safe for mammals due to lack of cell walls, however if patient is allergic to
penicillin, cephalosporin are usually avoided (and vice versa)
CEPHALOSPORIN MECHANISM OF ACTION