FA Drug Use & Antibiotic Therapy

Two components needed to establish WDT

o Tolerance: target tissue concentration established as safe by the appropriate regulatory authority

o The time it takes for the drug in a specific tissue to deplete to TOL

What are the factors that alter withdrawl time?

• Inappropriate handling of a medication/product (ex don't shake penicillin procaine G well enough)

• Disease states that alter metabolism (ex mastitis is labeled for milk withdrawal of 36hr, but the study found that it should be 72hr)

• Age, changing the route, dose, frequency, etc

Identify locations of resources for labeled indications for drugs in FA medicine

• Product label

• Plumb's (not as up to date)

• CSU formulary (not as up to date)

• FARAD —BEST!!!

• Bayer's CVP

When is extra drug use allowed?

AMDUCA says that extra-label drug use IS allowed when health of animal is threatened or when suffering or death may result from failure to treat animals — NOT PROPHYLACTIC USE

What are drugs with NO ALLOWABLE ELDU in ANY food producing species?

-Clenbuterol

-Chloramphenicol

-Fluoroquinolones

-Vancomycin

-DES

-Nitroimidazoles

-Nitrofurans

NOTE that all of these drugs are NOT labeled for use in food animals and are illegal EXCEPT for fluoroquinolones

Drugs with restricted ELDU in food producing species

-Phenylbutazone in female dairy cattle 20 months pf age or older

-Sulfonamides in lactating dairy cattle > 20 months of age

-Gentian violet is prohibited in feed

-Neuraminidase inhibitors

-Cephalosporins

What drugs are not to be stored on farm or used in lactating dairy cattle?

-non-medical grade DMSO

-colloidal silver

-dipyrone

-topical systemically-acting drugs

What's the deal with cephalosporins?

o In major food animals, cephalosporins can only be used according to the label for species, class, dose, route, and duration, with the only wiggle room being that you can use them for a different disease than listed (as long as it's treatment, not prevention).

o This does not apply to minor species

What's the deal with aminoglycosides?

o Streptomycin and neomycin are oral formulations that are approved for use in swine for ETEC

o Profoundly sequesters in the kidneys

o Voluntary ban for use in food animals

List your responsibilities (requirements) as a veterinarian when prescribing medication

Metaphylaxis

getting infection under control when it is likely to be brewing. Example is label for Draxxin and Micotil that uses wording "for the control of respiratory disease in cattle at high risk of developing BRD associated with M heamolytica, P multocida, H somni, and M bovis"

PO antibiotic administration

Rumen microflora will breakdown most abx except for sulfas, tetracyclines, macrolides, and rifampin. Rifampin rarely used in food animal medicine.

IM antibiotic administration

o Injection in the neck only because there is no high quality cut coming from the neck region

o Can cause granuloma is suspension causes irritation

o Risk for neuropathy if injections given in rump/leg

SQ antibiotic administration

Need to be careful because you need to check the label for recommended mLs per injection site

If the drug can be given IM or SQ, give it

SQ

Do not exceed more than xmL of any product in any location

10

What do we NEVER give IV?

PPG, Tilmicosin, Procaine or benzathine penicillin

Topical antibiotic not sufficient for anything deeper than

The dermis

Static drugs

Macrolides, tetracyclines, chloramphenicol(illegal)/florfenicol(legal), liconsamides, sulfonamides

Cidal drugs conditions for use

weak immune system, life-threatening such as peritonitis or septicemia, meningitis

Cidal drugs

Penicillins & cephalosporins, potentiated sulfas, fluoroquinolone, aminoglycosides

Lipid soluble drugs

Florfenicol, macrolides, fluoroquinolones (special = lipid and water soluble), tetracyclines, lincosamides, trimethoprim

Which one is good for abscesses

Weakly basic antimicrobials, such as macrolides, accumulates the drug at site (good for abscesses)

Which one is excellent for UTI, bacteremia, bone infection

Beta lactams, sulfonamides, fluoroquinolones, aminoglycosides

Tetracycline side effects

nephrotoxicosis if dehydration and repeat treatments, cardiotoxic if administered rapidly IV (Ca binder), enamel staining in young animals

Fluoroquinolones side effects

Toxic to growing cartilage

Tilmicosin side effects

cardiotoxic to horses, goats, camelids, humans

Aminoglycoside side effects

nephrotoxicosis if dehydration and repeat treamtnets

The only concentration dependent drugs are

aminoglycosides and quinolones

Common names of beta lactams

polyflex (ampicillin), durvet (penicillin), excenel (ceftiofur hydrochloride), naxcel (ceftiofur sodium), excede (ceftiofur), ceftiofur is cephalosporin!

MOA beta lactams

penetrates cell wall and bind to penicillin binding proteins in peptidoglycan layer that

Beta lactams resistance

o Beta lactamase is produced by some bacteria and destroys drug before it reaches the cell wall

o Can use clavulanic acid and suibactam that mimic the beta lactam rings and occupies the beta lactamase

Beta lactams atypical bacteria

NOT susceptible to beta lactams because they do not have a cell wall (mycoplasma, chlamydia, chlamydophila, ehrlichia)

Penicillins

o Gram + anaerobes except resistant bacteroides, few gram -

o Bactericidal, time-dependent

o Water-soluble

o Inhibits bacterial cell wall construction

o Poor penetration of lipid membranes, can reach high concentrations in urinary tract and other aqueous fluid compartments

Penicillin labeled dose

LABELED DOSE ON THESE BOTTLES IS ONE THIRD OF THE EFFICACIOUS DOSE!

Common names cephalosporins

excede, naxcel (ceftiofur sodium)

What are the ONLY cephalosporins with labeled claims for food animals

3rd gen

Cephalosporins MOA

inhibits bacterial cell wall construction

Aminoglycosides common names

gentamycin, amikacin, neomycin

What is important to note about aminoglycosides?

Rarely use these in cattle cause 18+ month witholding time! Can use them in camelids, but make sure you write in the record that the animal cannot enter the food chain

Aminoglycosides MOA

disrupt protein synthesis (bacteriacidal), gram negative spectrum

Monitoring for nephrotoxicity from aminoglycosides

o Most sensitive: elevated serum trough concentrations of the drug

o Abnormal urinalysis

o Least sensitive: azotemia, increases in creatinine

Uptake of aminoglycosides is

Energy and oxygen dependent

Do we use the sulfonamide that is combined with trimethorpim

Don't really use the version that is combined with trimethoprim cause the rumen will just break it downfrom

Sulfonamides

• One of very few PO antimicrobials that we have

• Be mindful of the restrictions in dairy cattle

• MOA = prevent bacterial nucleic acid synthesis

Tetracyclines

• Bind to 30S ribosome, bacteriostatic, broad spectrum

• Do got give in milk, with antacids, in hard water, or LRS

• Most common toxic side effect is nephrotoxicosis especially in volume depleted neonates (use doxy instead)

• Dilute in large volumes cause can cause CV collapse or death

Macrolides

• Bind to 50S ribosome

• Gram + except for pateurella and haemophilus, mycoplasma

• Lipid soluble

• Extensive cross resistance among macrolides

Florfenicol

• Thick and really hard to use during cold weather

• Gram pos, neg, anaerobes, mycoplasma, brucella, salmonella

Fluoroquinolones

• Not good for anaerobes

• Bactericidal, concentration-dependent

• Lipid soluble

• Inhibits bacterial DNA gyrase

• ELDU is ILLEGAL!

• Juvenile articular cartilage damage