Rational Antimicrobial Therapy: Host factors

A comprehensive set of Q&A flashcards covering host factors, prophylaxis, prudent use, ELDU, tissue residues, withdrawal times, and regulatory aspects from the lecture notes.

What host factors are overviewed in Rational Antimicrobial Therapy-4?

Age factors, disease factors, target site factors (penetration to infection site), hostile infection site effects on drug efficacy, renal disease, cardiovascular disease, and hepatic disease.

Do age and disease mainly affect PK or PD?

They produce changes to pharmacokinetics (PK) rather than pharmacodynamics (PD).

What pharmacokinetic changes are associated with geriatric animals?

Changes in bioavailability, volume of distribution, and slower elimination; often more disease and need for multiple drugs.

What does the immature nature of neonatal body systems imply for PK/PD?

Primarily affects PK due to immature organ systems.

Which organs are listed under disease factors in Host Factors?

Kidney disease, hepatic disease, and heart disease/failure.

Name the target-site factors that reduce drug efficacy at the infection site.

Purulent debris, inoculum size, low oxygen tension, reduced pH, and other hostile site conditions that hinder drug penetration.

What should be assessed when monitoring therapy and within what time frame should improvement be seen?

Response should be observed within 24–48 hours; continue assessment during treatment; use nonspecific and specific methods; consider drug level measurements if available to optimize therapy and minimize toxicity and resistance.

What is the recommended approach to prophylaxis relative to surgical technique?

Prophylaxis is not a substitute for good technique; decisions are guided by wound classification (clean, clean-contaminated, contaminated) with corresponding prophylaxis.

List the typical antimicrobial choices for prophylaxis in dogs/cats, horses, and ruminants.

Dogs/Cats: cefazolin

Equine: cefazolin ± gentamicin

Ruminants: ceftiofur or penicillin

When should prophylactic antimicrobials be given relative to incision?

At least 30 minutes before incision and within 24 hours after surgery.

What is metaphylaxis and when is it used?

Administration of antimicrobials to at-risk herds during transport or high-risk conditions to prevent disease outbreaks; goal is to prevent outbreaks, not treat infection.

What are the goals of prudent antimicrobial use?

Optimal drug, dose, and duration; reduce excessive/inappropriate use to slow resistance; maximize efficacy and ensure infection likelihood before use.

How should dosing regimens be chosen to maximize efficacy and minimize resistance?

Use regimens that achieve concentrations at the infection site above the MIC; avoid concentrations below MIC; avoid too short a treatment duration.

How should a clinician approach using antibacterials in uncertain cases?

Establish a strong likelihood of bacterial infection before using antibacterials; avoid using antibacterials just in case or to cover for uncertainty.

What are the 1st-line antimicrobials listed?

Penicillin, amoxicillin, most cephalosporins, tetracyclines, and trimethoprim-sulfamethoxazole (TMS) → initial treatment

What drugs are categorized as 2nd-line and 3rd-line antimicrobials?

2nd-line: fluoroquinolones (FQ), 3rd-generation cephalosporins, ticarcillin, piperacillin, aminoglycosides → with C/S testing

3rd-line: carbapenems (imipenem-cilastatin), vancomycin, linezolid → serious life-threatening infection

Which drugs are banned from extra-label use (ELDU) in Canada?

Chloramphenicol, clenbuterol, diethylstilbestrol (DES), nitroimidazoles (e.g., metronidazole), nitrofurazone (5-nitrofurans), estrogens or estrogenic drugs in poultry.

What is tissue residue withdrawal and why is it important?

Withdrawal times are the interval between last treatment and marketing to prevent violative residues in edible products; failure to observe WDT can adulterate the food supply.

What are violative residues and common culprits?

Residues in edible products above the maximum residue limit (MRL); common culprits include sulfonamides (e.g., sulfamethazine), penicillin, and oxytetracyclines, especially in long-acting formulations.

What is the primary parameter used to prevent violative tissue residues?

Withdrawal time.

Where can practitioners obtain extended withdrawal time guidance for ELDU in Canada?

Canadian Global Food Animal Residue Avoidance Databank (CgFARAD); Ron Johnson and Trisha Dowling; national non-profit service.

What regulatory bodies govern veterinary drug use and residue monitoring in Canada?

Health Canada (Veterinary Drugs Directorate) and the Canadian Food Inspection Agency (CFIA).

What is ELDU in veterinary medicine?

Extra-label drug use: any use of a drug not specifically listed on the label.

What is a violative tissue residue consequence?

Market rejection or condemnation of edible animal products due to drug residues above MRL; potential health risks.