PENICILLINS

-Commonly used, especially penicillin G

-end in –cillin

-Bactericidal against most gram-positive bacteria

-Interfere with cell wall development (blocks enzymes that build the cell wall), making the bacterium susceptible to lysing

◦ Different types of penicillins exist because they work against the different enzymes that are used in the construction of the cell wall (explains how efficacy can vary within the class of Penicilllns)

◦ 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!

PENICILLIN FACTS

-Mammalian cells will not be acted upon by Penicillin, as 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!

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.

PENICILLIN'S SPECTRUM OF ACTIVITY

-Staphylococcus bacteria produce enzymes (beta lactamases) that break down the beta lactam ring found within the structure of penicillin.

◦ Oxacillin, cloxacillin, dicloxacillin are resistant to beta lactamase. Downside is they have a 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.

PENICILLIN PRECAUTIONS

-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.

SPECIFIC PENICILLINS

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. DO NOT GIVE IV.◦ Suspension with benzathine added. DO NOT GIVE IV.

◦ Adding anesthetics delays absorption, extending the duration◦ 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◦ 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.

CEPHALOSPORINS

-Very similar to Penicillin in structure and mechanism of action

-Beta lactam ring, but less effected by beta lactamase producing bacteria than penicillins are

-Bactericidal

-Bind and inhibit enzymes needed for cell wall formation (like penicillins)

◦ The various cephalosporins inhibit different enzymes that are involved in cell wall formation◦ Bacteria must be dividing for cephalosporins to work

-More effective against Staphylococcus than penicillin

-If patient is allergic to penicillin, cephalosporins are usually avoided (and vice versa) -Ceph (pre 1975)- or cef- prefixes

SPECIFIC CEPHALOSPORINS

Cephalosporins are classified by four generations.

◦ 1st: primarily effective against gram positive bacteria (staph and strep)◦ Cefadroxil (Cefa-Tabs, oral), Cephaphirin (Cefa-Dri, injection), Cefazolin (Ancef, injection), Cephalexin

(Keflex, oral)

◦ 2nd: more effective against gram negative bacteria than 1st generations , but a little less effective against gram positive than 1st generation

◦ Cefoxitin (Mefoxin, Injectable)

◦ 3rd: limited gram + activity, high activity against Pseudomonas and other gram negative bacteria◦ Cefpodoxime (Simplicef, oral), Ceftiofur (Naxcel, injection), Cefovecin (Convenia, injection)

◦ ◦ 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 ◦ Cefepime (Maxipime, injection)