Equine Med 12 - Antibiotic Tutorial

Antimicrobial vs antibiotics

Antimicrobial:

- Refers to all agents that kills or inhibits the growth of microorganisms, but causes little or no damage to the host

- Bacteria = antibacterial Viruses = antiviral Fungi = antifungal Protozoa = antiprotozoal

Antibiotics:

Refers to a low molecular substance produced by a microorganism, that at a low concentration inhibits or kills other microorganisms

- do not not synthetic or semisynthetic antimicrobials ie TMS/quinolones

Hence all antibiotics are antimicrobials, but not all antimicrobials are antibiotics

What to take away from this tut:

Routes of admin

Duration of action

Spectrum of activity

List very broad and intermediately broad spectrum ABs

*all the non mentioned = narrow*

Very broad spectrum = All bacteria

- Carbapenems

- Chloramphenicol

- 3rd gens flouroquinolones

Intermediately broad

- 2nd and 3rd gen cephalosporins

- Tetracyclines

- Ampicillins and 1st gen cephalosporins

Time vs Concentration dependent

Timing

- need correct dose frequency achieve MIC

Concentration

- need specific doses to get MIC

- timing less important becasue they have prolonged post-antibiotc effects

- can be every 24 hours compared to q8 as some time dependent may be

Example of time dependent vs conc dependent abs

time dependent

- beta lactams

- pencillincs

- macrolides

conc dependent

- aminoglyhcoses

- tms

an example of an antibiotic that undergoing ion-trapping and what is it?

macrlodies (erythromycin) - reach high intracellular concentrations ('trapped') due to pH changes across the cell membrane

Getting the bug to the drug is refered to as?

Getting the drug to kill the bug

Getting the bug to the drug --> pharmacokinetics

Getting the drug to kill the bug --> pharmacodynamics

Considerations when prescribing anitbiotics re PK and PD

Confirmed bacterial infection?

Confirmed species? or will you use wide spectrum?

Location of infection

- behind lipid barriers?

- in non perfused fluids? (joint, cornea)

Local env factors

- anaerobic

- pH

Dosing regimen

- frequency

- route

Patient considerations

- age

- colitis?

Black listed, human importance

Flouroquinolones

3rd and 4th gen cephalosporins

Chloramphemicol

Imipenem

Vancomycin

can be used but must be based off culture with limited systemic exposure ie try regional

Prohibited fo food chainr?

Gentamycin

Metronidazole

Abs commonly used in equine med

Penicillins

- ampicilin

Tetracyclins

- doxy

- oxytet

Aminoglycisdes

- neomycin

- gentamicin

TMS

Corneal Stromal Abscess (likely mixed infections)

• Neomycin, Polymyxin B, Bacitracin (Tricin) or Chloramphenicol

Chloramphenicol because its lipid soluble

12h old septic foal (likely e coli)

- • Procaine penicillin + gentamicin or • Ceftiofur sodium

PenGen because ceftiofur is tier 3

Arytenoid Chondritis (likely strep)

• Trimethoprim Sulfamethoxazole or • Doxycycline + Rifampin

Considerations --> cartialge have poor blood supply so need long duration abs

TMS - due to doxy having potential to cause colitis dt oral administration.

Case 4 - 6m old foal with pneumonia • Clarithromycin + Rifampin or • Oxytetracycline

Clarithromycin and rifampin because their ion trapped

Case 5 -

- Wound Cellulitis

• Penicillin + Gentamicin + Metronidazole

OR Enrofloxacin + Rifampin

Mixed bacterial infection inc streps. Enro is tier 3 and not effective against streps.

PEN GEN TMS

redo me

Penicillins

- drug class

- MoA

- lipid or water soluble

- cidal or static

- time or concentration

- spectrum

- side effects

- duration of action

Beta lactams

Punch hole in cell walls

Water

Cidal

Time

Gram positive aerobes

Newer generations ie ampicillins and cephalosporins also have gram negative aerobic activity

Side effects

- anaphylaxis

- hiarrhoea

- cardiac arrthmias

DoA

- 6-12 hours

Gentamycin

- drug class

- MoA

- lipid or water soluble

- cidal or static

- time or concentration

- spectrum

- side effects

- duration of action

Aminoglycoside

Protein synthesis inhibition

Water

Cidal

Concentration dependent

Gram negative aerobes

NM blockage

Acute tubular necrosis

DoA: 24 hours

TMS

- drug class

- MoA

- lipid or water soluble

- cidal or static

- time or concentration

- spectrum

- side effects

- duration of action

Sulfonamide

Inhibits folic acid synthesis

Lipid

Cidal

Conc

Broad spectrum

Diarrhoea, fatal cardiac arrythmias if concurrent use, chronic anaemia

DoA: 12 hours