Pharma WS and Practical Questions

How can antimicrobial agents contribute to bacterial resistance?

• Resistance to antibiotics

• stimulating horizontal gene transfer

Why are Gram‑negative bacteria more resistant to certain antibiotics compared to Gram‑positive bacteria?

• Possess an outer membrane

• Limits antibiotic entry

Why is it important to distinguish between bactericidal and bacteriostatic antibiotics?

Some patients, such as immunocompromised individuals, may require bactericidal antibiotics for effective treatment.

A veterinarian prescribes an antibiotic for a bacterial infection in a cat. The owner asks whether the antibiotic could harm the cat’s own cells. The veterinarian explains that the drug specifically targets bacteria.

What is the MOST LIKELY reason why the antibiotic kills bacteria but not the cat's own cells?

The antibiotic is designed to attack structures specific to bacteria ex. as the bacterial cell wall or unique enzymes

Case (Dog – Pseudomonas aeruginosa):

A dog has a wound infection not healing despite previous antibiotics. Lab results show Pseudomonas aeruginosa, known for high resistance.

Why is this concerning?

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Pseudomonas aeruginosa is naturally resistant to many antibiotics (multiresistant) making infections harder to treat

Case (Dairy farm – E. coli co‑resistance):

Cows treated with oxytetracycline show increasing treatment failures. Lab tests show E. coli resistant to tetracyclines and aminoglycosides, even though aminoglycosides were never used.

What BEST explains this pattern?

• Cross‑resistance

• Multidrug efflux pump that expels both tetracyclines and aminoglycosides

Case (Poultry – multidrug resistant E. coli):

A farm uses enrofloxacin (a fluoroquinolone) preventively. Over time, E. coli becomes resistant not only to fluoroquinolones but also cephalosporins and aminoglycosides.

What is the MOST LIKELY explanation?

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• Continuous use exerted selective pressure

• Promoting mutations and horizontal gene transfer of resistance genes

Case (Dog A vs Dog B – different infections):

Dog A has Streptococcus canis skin infection → improves.

Dog B has Pseudomonas aeruginosa ear infection → worsens.

Why did the antibiotic work for Dog A but not Dog B?

Some bacteria are naturally more resistant to certain antibiotics due to structural and defense differences

β‑lactams bind to ____, which are enzymes involved in bacterial cell wall construction, leading to ____ of susceptible bacteria.

• penicillin‑binding proteins (PBPs)

• osmotic rupture and lysis

Regarding β‑lactam safety?

Penicillins are considered very safe drugs, with relatively few adverse effects reported.

Regarding gastrointestinal and superinfection risks

• Digestive disorders such as vomiting and diarrhea may occur as non‑allergic adverse reactions

• Superinfections may occur due to disruption of the normal gut flora

Genetic aspects of β‑lactam resistance

• β‑lactamase genes carried on plasmids, transposons or integrons (facilitating horizontal transfer)

Resistance due to reduced drug access?

Gram‑negative bacteria may resist β‑lactams by restricting drug entry through porin modifications

What antibiotic inhibits bacterial folate synthesis? And how?

• Sulfonamides compete with PABA for the enzyme dihydropteroate synthase

• Sulfanomides are competitive antagonists

Describe how fluoroquinolones disrupt bacterial DNA processes?

• They inhibit the unwinding and supercoiling of DNA required for replication and transcription

• They stabilize the DNA‑enzyme complex after strand cleavage, preventing re‑ligation

Why do fluoroquinolones spare mammalian cells?

Mammalian topoisomerase II is not inhibited until drug concentrations reach 100–1000 µg/ml, far higher than therapeutic levels.

Musculoskeletal adverse effects of Fluoroquinolones?

Fluoroquinolones can damage developing cartilage in young animals

Activity of fluoroquinolones against gram‑negative bacteria

• Fluoroquinolones are highly effective against many Enterobacteriaceae, including E. coli, Klebsiella, Proteus, and Salmonella

• Ciprofloxacin is typically one of the most active fluoroquinolones against Pseudomonas aeruginosa

A key mutation leading to fluoroquinolone resistance?

Mutations may occur in the genes encoding DNA gyrase, reducing the drug’s ability to bind

Describe the role of efflux pumps in resistance

• Efflux pumps reduce intracellular concentrations of fluoroquinolones

• Some efflux systems can pump out multiple antibiotic classes, causing multidrug resistance

Why are aminoglycosides ineffective against anaerobes?

Transport of the drug into the bacterial cytoplasm requires oxygen‑dependent energy

Ribosomal effects caused by aminoglycosides

• misread mRNA —> faulty proteins

• inhibit process of translation

• They block formation of the initiation complex required for translation

What is the most important dose‑limiting toxicity of aminoglycosides?

They cause nephrotoxicity due to accumulation in renal proximal tubular cells

Decreased intracellular drug accumulation as a resistance mechanism

• Some bacteria reduce aminoglycoside uptake by altering membrane transport systems

• Efflux pumps can remove aminoglycosides from the bacterial cell.

What describes a major bacterial strategy for aminoglycoside resistance?

Production of aminoglycoside‑modifying enzymes that inactivate the drug

Why should oral tetracyclines be avoided in adult ruminants?

They disrupt the ruminal microbiota (microflora), which can lead to severe digestive upset.

What is the primary mechanism of action for Tetracyclines?

• Bacteriostatic antibiotics

• Inhibit protein synthesis

• reversibly binding to the 30S ribosomal subunit

• preventing the attachment of aminoacyl tRNA.

Name the specific pharmacokinetic interaction involving oral tetracyclines and diet.

• Absorption impaired by divalent or trivalent cations (calcium, magnesium, iron, aluminum).

• Milk, antacids, or iron salts should be avoided 3 hours before and after administration.

What are the characteristic side effects of tetracyclines on developing skeletal systems?

• Chelate calcium in teeth and bones

• yellowish-brown discoloration

• Inhibition of calcification.

Which tetracycline is the exception to the rule regarding contraindication in renal insufficiency?

Doxycycline (it is not contraindicated in renal failure, unlike others in the class).

Why is Chloramphenicol strictly prohibited for use in food-producing animals?

It can cause irreversible aplastic anaemia (bactericidal) in humans who consume residues in animal products.

How does the metabolism of Phenicols differ in cats?

Cats have a genetic deficiency in glucuronidase enzymes, leading to slower metabolism (longer half-life) and requiring dosage adjustments to avoid toxicity.

What is a unique adverse effect of Chloramphenicol regarding the immune system?

• It can suppress anamnestic (secondary) immune responses

• Therefore, animals should not be vaccinated while being treated.

What is the specific mechanism of action for Phenicols?

• Bind to 50S ribosomal subunit

• Inhibit protein synthesis in both prokaryotic and eukaryotic (mitochondrial) ribosomes.

Which macrolide is specifically associated with potentially fatal cardiac toxicity?

Tilmicosin.

What is the mechanism of action for Macrolides?

• Reversibly bind (bacteriostatic) to the 50S subunit of the ribosome

• Prevent the translocation step of protein synthesis.

In which species are Lincosamides (like Clindamycin or Lincomycin) strictly contraindicated and why?

• Horses, rabbits, and rodents.

• Can cause a disruption of GI flora

• Lethal pseudomembranous enterocolitis.

Between which two antibiotic classes is cross-resistance most common?

Lincosamides and Macrolides.

What is the primary clinical indication for Clindamycin in small animal practice?

• Treatment of infected wounds, abscesses, and dental infections (due to efficacy against anaerobes and Gram-positive cocci).

What is the mechanism of action for Polymyxin B and E?

• Detergents; they interact with phospholipids in the bacterial cell membrane

• Disrupting permeability and function.

Why are Polymyxins rarely used systemically and instead found in "Triple Antibiotic" ointments?

They are highly nephrotoxic and neurotoxic when administered systemically.

What is the antimicrobial spectrum of Polymyxins?

• Narrow-spectrum

• Gram-negative bacteria ONLY (notably Pseudomonas aeruginosa).

Tetracyclines

Bind with?

Do not give with?

• 30S

• Do not give with milk/antacids; stains teeth.

Phenicols

Bind with?

Prohibited in?

• 50S

• Prohibited in food animals (Aplastic Anemia).

Macrolides

Bind with?

What kind can have a lethal adverse reaction?

• 50S

• Tilmicosin = Cardiac toxicity.

Lincosamides

Bind with?

Contraindication?

• 50S

• Fatal colitis in horses/rabbits.

What is the primary mechanism of action for β-lactam antibiotics?

Bactericidal or Bacteriostatic?

• Bactericidal (bind irreversibly to ribosomal subunits)

• They inhibit cell wall synthesis.

• Bind to penicillin-binding proteins (PBPs) and inhibiting the transpeptidation of peptidoglycan.

• This leads to cell wall deficiency and eventual lysis due to osmotic pressure.

Why is oral Amoxicillin-Clavulanic acid generally avoided in herbivores?

Oral absorption is poor in herbivores, making the route ineffective for these species

Name the most common and potentially serious adverse effect associated with penicillins.

Allergic reactions, the severity of which is independent of the dose administered

Which specific generations of cephalosporins are generally acid-stable and suitable for oral administration in dogs and cats?

1st-generation drugs like Cephalexin and Cefadroxil

Explain the mechanism of action of Sulfonamides.

Bactericidal or bacteriostatic?

What do they block?

What is typically added with it?

Describe resistance patterns of sulfonamides.

What is a major mechanism for sulphonamide resistance?

Accurately describe blood‑related adverse reactions of sulfonamides?

• Sulfonamides are competitive antagonists of PABA, reversibly blocking folic acid synthesis (bacteriostatic).

• Trimethoprim is often added because it blocks a different step in the same pathway (dihydrofolate reductase), creating a synergistic bactericidal effect and lowering resistance.

• Cross‑resistance is common: resistance to one sulfonamide generally confers resistance to all

• Resistance can be due to overproduction of PABA or target enzyme alteration

• Bacteria may increase PABA production, overcoming competitive inhibition by sulfonamides.

• Some sulfonamides (e.g., sulfaquinoxaline) can cause hypoprothrombinemia by inhibiting vitamin K epoxide reductase

• Sulfonamides may produce anemia or thrombocytopeniadue to effects on folate metabolism or immune‑mediated mechanisms
  

Why are dogs more sensitive to Sulfonamide toxicity than other species?

What conditions can it cause them?

• Dogs lack the ability to acetylate sulfonamides into metabolites.

• This can lead to the persistence of more toxic metabolites, resulting in conditions like keratoconjunctivitis sicca ("dry eye") or hepatic necrosis

What is a major pharmacokinetic risk associated with Sulfonamides in pregnant animals?

• Widely distributed, including to fetal tissue

• May be potentially teratogenic.

What are the two primary bacterial targets of Fluoroquinolones?

• Inhibit DNA gyrase (primarily in Gram-negative bacteria) and topoisomerase IV (primarily in Gram-positive bacteria).

List the two most critical contraindications for Fluoroquinolones based on age and species.

What conditions can it cause?

• Young, growing animals (especially dogs and foals): Due to the risk of erosion of articular cartilage and joint growth disorders.

• Cats: Must be used with caution due to the risk of retinal degeneration

Why are Fluoroquinolones particularly effective in treating deep-seated infections or abscesses?

• They accumulate in inflammatory cells

• high concentrations of the drug directly at the site of cellular inflammation.

How do Aminoglycosides enter the bacterial cell, and what is a major limitation of this process?

• Diffuse through porins

• Use an oxygen-requiring transport process to enter the cell.

• Therefore, anaerobic bacteria are intrinsically resistant.

Why is the systemic use of Aminoglycosides highly restricted in food-production animals?

Where do they accumulate?

They tend to accumulate and persist as prolonged residues in the renal cortex (kidney), which severely limits their use to label instructions only

What are the three hallmark toxicities/adverse reactions of Aminoglycosides?

1. Ototoxicity (ear damage)

2. Nephrotoxicity (kidney damage).

3. Neuromuscular blockade

What is the mechanism of action for Aminoglycosides?

Bacteriostatic or bactericidal?

• Bind irreversibly (bactericidal) to the 30S ribosomal subunit

• Misreading of mRNA and blocking the initiation of protein synthesis

β-Lactams

• Cell wall; Lysis by osmotic pressure

• Bactericidal

• Allergies

Sulfonamides

• Folic acid (PABA)

• Bacteriostatic (when potentiated (e.g., with Trimethoprim))

• Dry eye in dogs; Teratogenic

Quinolones

• DNA Gyrase

• Bactericidal

• Cartilage damage in young; Retinal damage in cats

Aminoglycosides

• 30S Ribosome

• Bactericidal

• Ototoxic/Nephrotoxic; No effect on anaerobes

Define the difference between bactericidal and bacteriostatic antibiotics.

Bactericidal drugs actively kill bacteria, while bacteriostatic drugs inhibit their growth and reproduction

List the five major mechanisms of action for antimicrobial agents and provide one example of an antibiotic class for each.

1. Inhibition of cell wall synthesis: β-lactams (Penicillins, Cephalosporins) or Glycopeptides (Vancomycin).

2. Alteration of cell membranes: Polymyxins (Colistin).

3. Inhibition of protein synthesis: Tetracyclines, Aminoglycosides, or Macrolides.

4. Inhibition of nucleic acid synthesis (DNA related): Quinolones (Fluoroquinolones) or Rifamycins.

5. Inhibition of metabolic processes (folic acid synthesis): Sulfonamides or Trimethoprim

What are the two main ways bacteria withstand the effects of an antibiotic?

1. Stopping the antibiotic from reaching its target at a high enough concentration.

2. Modifying or bypassing the specific target the antibiotic acts upon

Name and describe three specific strategies bacteria use to resist antibiotics.

• Efflux Pumps: Bacteria create pumps that actively move the antibiotic out of the bacterial cell.

• Inactivating Enzymes: Bacteria produce enzymes that destroy the antibiotic, such as β-lactamase destroying penicillins.

• Target Alteration: Bacteria change the structure of the target or add chemical groups to "shield" it, preventing the drug from binding.

• (Alternative) Decreased Permeability: Developing a thicker external membrane to prevent the drug from entering the cell

According to the WHO, what are the primary causes of the rise in antibiotic resistance?

• Over-prescribing

• Patients not finishing treatments

• Over-use in livestock/fish farming

• Poor infection control in clinics

• Lack of hygiene/sanitation

• Lack of new antibiotics being developed

Define "Metaphylaxis" in a veterinary context.

It is the administration of an antimicrobial to a group of clinically healthy (but presumably infected) in-contact animals to prevent them from developing clinical signs and to stop the spread of disease. Note: the presence of the disease in the group must be established before use

Rank routes of administration from lowest to highest estimated impact on antibiotic resistance.

1. Lowest: Local individual treatment (e.g., eye/ear drops) *because it is personalised dosage

2. Parenteral individual treatment (e.g., IM, SC, IV).

3. Oral individual treatment (e.g., tablets).

4. Injectable group medication (Metaphylaxis).

5. Oral group medication via water/milk.

6. Highest: Oral group medication via feed or premixes. *because it is general dosage

What are the three key principles of selecting and applying antimicrobials appropriately?

1. Use the narrowest spectrum possible. (more specific)

2. Use the appropriate dose for the shortest duration possible.

3. Base treatment on pathogen identification and susceptibility testing whenever

Compare Ointments, Creams, and Gels in terms of drug absorption.

Ointment > Cream > Gel. (Note: Ointments have the highest absorption and greasiest consistency, while Gels have the highest water content )

What is an OROS® system and how does it function?

• Oral Release Osmotic System.

• It consists of an osmotic core covered by a semi-permeable membrane with a calibrated orifice.

• Water enters the tablet, creating osmotic pressure that forces the drug solution out through the orifice at a constant speed

Identify three specialized delivery systems used specifically for large or wild animals.

• Darts: Used via blowpipes for zoo animals.

• Biobullets: Solid, controlled-release implants for large animals like bison or elephants.

• Modified release boluses: Such as the OROS® Push-Pull system used for poorly water-soluble drugs

What is the difference between a Hard Capsule and a Soft Capsule?

• Hard capsules: Have a two-part gelatin container and solid contents

• Soft capsules: have a one-part container and usually contain liquid

Classify the following routes as "Systemic" or "Local":

Intravenous

Ophthalmic

Transdermal Patch

Otic

Intravenous: Systemic.

Ophthalmic: Local.

Transdermal Patch: Systemic.

Otic: Local

Which parenteral route involves "non-absorption" because the drug is placed directly into the blood?

Intravenous (IV).

Match the following symbols/legends found on veterinary packaging to their meaning:

• A circle (○)

• An asterisk (*)

• Snowflake/Ice crystal

• TLD

A circle (○): Prescription-only products.

An asterisk (*): Psychotropic substances (Annex II).

Snowflake/Ice crystal: Products to be stored between 2–8°C.

TLD: Tratamiento de Larga Duración (Long-lasting treatment)

Granule

• A mixture of powders subjected to a process where the particles adhere to each other, producing larger particles

Multilayer tablet

Typically designed to keep incompatible active ingredients separate or to allow for different release rates within a single dose.

Capsules

Gelatine containers holding the drug.

Hard capsules

Consist of two parts with solid content.

Soft capsules

A single-part container usually containing liquid.

Tablets

Mixtures of powders or granules subjected to compression.

Types include coated, uncoated, sugar-coated (gragea), enteric-coated, and multilayer.

Suppositories

Solid, bullet-shaped forms for rectal administration that melt at body temperature.

Vaginal Suppositories (Pessaries/Ovules)

Solid ovoid forms for vaginal insertion.

Solutions

One or more drugs completely dissolved in a solvent; usually clear

Suspensions

Solid particles dispersed in a liquid phase in which they are not soluble (must be shaken before use).

Emulsions

Stabilized oil-in-water dispersions (must be shaken before use).

Syrups

Aqueous solutions with a high sugar concentration close to saturation.

Injectables

Sterile solutions, emulsions, or suspensions for parenteral administration.

Ointments

• Greasy, anhydrous preparations for skin or mucous membranes

• highest drug absorption among semi-solids.

Pastes

Ointments with a high percentage of powder, making them thick and stiff.

Creams

Viscous emulsions of oil and water that are miscible with skin secretions.

Gels

• Semi-solid systems where a liquid phase is constrained within a 3-D polymeric matrix

• Highest water content.

Transdermal Patches

Adhesive patches that provide controlled, constant drug release through the skin for systemic action

OROS® (Oral Release Osmotic System)

Coated tablets with an osmotic core and a calibrated orifice that releases the drug at a constant speed.

Modified Release Boluses

Used for poorly water-soluble drugs in livestock

Darts and Biobullets

Specialized forms for remote or controlled-release administration in large or wild animals.