Veterinary pharmacology studies drugs: their action on the organism (pharmacodynamics), their behavior within it (pharmacokinetics), and their therapeutic and preventive applications across different animal species. It is the science that allows translating a molecule into a safe and effective treatment, taking into account species differences, age, physiological state and the production or companion-animal context. (Riviere & Papich, 2018)
Importance in veterinary medicine
Proper pharmacological management reduces morbidity and mortality, optimizes recovery, and minimizes adverse effects and residues in food-producing animals. The combination of pharmacological knowledge, clinical evidence and pharmacovigilance is essential for responsible therapeutic decisions and public health. (Plumb, 2023)
Moreover, pharmacology informs dosing, route of administration, interactions and monitoring of response — pillars for clinical practice in small animals, large animals and exotic species.
1. Fundamentals of veterinary pharmacology
Pharmacokinetics (PK): what the body does to the drug — absorption, distribution, metabolism and excretion (ADME).
Pharmacodynamics (PD): what the drug does to the body — mechanism of action, molecular target, dose–response relationship and adverse effects. (Riviere & Papich, 2018)
- Achieve a predictable and safe therapeutic effect.
- Minimize toxicity and residues in animal-derived products.
- Optimize dosing regimens according to species and condition.
2. Brief history and current focus
Veterinary pharmacology was born as a branch of human pharmacology and agricultural toxicology. With advances in the 20th century, drugs specific to animals were developed and dosing and safety studies by species were formalized. (Boothe, 2011)
In recent decades the discipline has integrated population pharmacokinetics, pharmacogenetics, pharmacovigilance and computational models to optimize dosing and predict adverse reactions. The emergence of up-to-date databases and monographs (e.g., Plumb) has facilitated everyday clinical practice. (Plumb, 2023)
Today, regulation, residue control and the need for responsible antimicrobial use shape the field; evidence and clinical trials remain the basis for safe therapeutic recommendations. (Riviere & Papich, 2018)
3. General principles and drug classification
- By therapeutic target: antibacterials, anti-inflammatories, analgesics, antiparasitics, cardiovascular drugs, endocrine drugs, anesthetics, among others.
- By mechanism of action: enzyme inhibitors, receptor agonists/antagonists, ion channel modulators, antigenic drugs or immunomodulators.
- By route of administration: oral, parenteral (IV, IM, SC), topical, intrauterine, inhalational, etc.
4. Pharmacokinetics: ADME and clinical considerations
Absorption depends on route, formulation and physiological state (gastric pH, motility, perfusion). Some drugs are poorly absorbed orally in ruminants or birds; others require parenteral administration to reach therapeutic concentrations. (Riviere & Papich, 2018)
Plasma protein binding and barrier permeability (blood–brain, placental) determine distribution. Species with low albumin or changes in volume of distribution show differences in the free active fraction of the drug.
Hepatic metabolism transforms drugs into active or inactive metabolites; routes such as glucuronidation, oxidation and conjugation vary between species (e.g., cats have limited glucuronidation), which conditions toxicity and drug choice. (Boothe, 2011)
Renal and biliary excretion determine half-life; renal or hepatic insufficiency alters clearance and requires dose adjustment to avoid accumulation. Also, in food-producing animals elimination affects withdrawal periods for products. (Plumb, 2023)
5. Pharmacodynamics: dose, effect and safety
It includes maximal efficacy (Emax), potency (EC50) and therapeutic margin. Understanding these parameters allows selecting effective doses with low risk of adverse effects. Toxicity can be dose-dependent or idiosyncratic and sometimes species-specific.
Pharmacokinetic interactions (e.g., enzyme induction/inhibition) or pharmacodynamic interactions (potentiation or antagonism) can change efficacy or toxicity. Reporting adverse reactions and recording cases improves clinical safety. (Riviere & Papich, 2018)
6. Therapeutic use and safety
Rational use of antibacterials is based on three pillars: etiological diagnosis (when possible), drug selection according to spectrum and pharmacokinetics, and treatment duration supported by evidence. Empirical prescribing should be founded on local protocols and knowledge about concentrations achievable in the target tissue (PK/PD). For example, time-dependent drugs (e.g., β-lactams) require maintaining concentrations above the Minimum Inhibitory Concentration for as long as possible; concentration-dependent drugs (e.g., aminoglycosides) benefit from high, less frequent doses to maximize bactericidal effect and limit toxicity. These differences guide clinical dosing and help reduce selection for resistance. (Giguère et al., 2018)
In food-producing animals, maximum residue limits (MRLs) and withdrawal periods must also be considered; noncompliance has health and legal implications. Resistance surveillance and producer education are essential components of responsible control.
Pain management in veterinary medicine relies on the multimodal principle: combining NSAIDs, opioid analgesics and adjuvants (alpha-2 agonists, gabapentin, regional blocks) reduces doses and adverse effects. For example, in orthopedic surgery combining an NSAID with an opioid analgesic and a regional block improves postoperative analgesia and reduces systemic inflammation, facilitating recovery and shortening hospitalization. Precise choice depends on species, hepatic/renal function and bleeding risk. (Meyer & Harvey, 2020)
Monitoring analgesic response (validated pain scales, physiological parameters) and adjusting therapy according to evolution is recommended practice to avoid under- or over-treatment.
Some drugs have particular uses and limitations: systemic antiparasitics in ruminants must consider parasite life cycles and ruminal dosing; in felines, drugs requiring glucuronidation (e.g., acetaminophen) are contraindicated; in equids, NSAID-associated colitis is a real risk that conditions drug choice and monitoring. Knowing these specifics reduces iatrogenesis and improves therapeutic efficacy. (Boothe, 2011)
7. Pharmacovigilance and usage policies
Pharmacovigilance collects and analyzes adverse events and therapeutic failures to update recommendations and detect early risk signals. Systematic reporting (clinical and regulatory) enables guideline adjustments, dose recommendation changes and product withdrawals if necessary. In the context of antimicrobial resistance, responsible use policies (stewardship programs, restricted lists and prescription audits) are effective tools to preserve antimicrobial efficacy. (WHO & OIE guidelines; Giguère et al., 2018)
Clinically, documenting use (dose, duration, response, reactions) and participating in pharmacovigilance networks provides local data that enrich practice and population safety.
8. Clinical toxicology and advanced poisoning management
Management of poisoning must prioritize ABCs (airway, breathing, circulation), decontamination and metabolic support. History (substance, route, time since exposure) guides strategy: activated charcoal for absorbable toxins, gastric lavage in selected cases and control of seizures or arrhythmias as needed. Identifying specific signs (collapse, arrhythmias, hyperthermia) guides targeted therapy. (Eddleston et al., 2019)
When indicated, dialysis, perfusion or the use of specific antidotes (e.g., naloxone for opioids, N-acetylcysteine for acetaminophen poisoning) can be lifesaving. The decision depends on the toxin's pharmacokinetics, antidote availability and patient condition.
Clinical example: In xylitol poisoning in dogs, early administration of activated charcoal (if applicable), glucose support and hepatic monitoring reduce mortality; knowing the timeline and biochemical parameters is essential for prognosis. (Eddleston et al., 2019)
9. Clinical integration: from theory to practice
Effective therapeutic decision-making combines pharmacological knowledge, patient condition and epidemiological context. A practical example: in a complicated respiratory infection in a geriatric dog, renal/hepatic function, possible drug interactions, the PK/PD profile of the chosen antibiotic and the need for medical support (oxygen, fluid therapy) are evaluated. Documenting response and adapting therapy according to evolution (and cultures when available) optimizes clinical outcome and reduces adverse effects.
Educating the owner about compliance, warning signs and withdrawal periods (if applicable) decisively contributes to therapeutic success and public safety.
10. Conclusion
Veterinary pharmacology is the bridge between the molecule and clinical recovery. Its correct application requires understanding PK/PD, recognizing interspecies differences, anticipating interactions and adverse effects, and actively participating in pharmacovigilance systems. Only through informed, evidence-based prescribing accompanied by clinical follow-up can a balance be achieved between therapeutic effectiveness, animal safety and public health.
In daily practice, integrating local protocols, consulting up-to-date sources and reporting clinical experiences are actions that raise the quality of veterinary care and preserve the effectiveness of medicines for future generations of patients.
References
• Riviere, J. E., & Papich, M. G. (2018). Veterinary Pharmacology and Therapeutics (10th ed.). John Wiley & Sons.
• Plumb, D. C. (2023). Plumb's Veterinary Drug Handbook (10th ed.). Wiley.
• Boothe, D. M. (2011). Small Animal Clinical Pharmacology and Therapeutics (2nd ed.). Elsevier.
• Giguère, S., Prescott, J. F., & Dowling, P. M. (2018). Antimicrobial Therapy in Veterinary Medicine (5th ed.). Wiley-Blackwell.
• Meyer, D. J., & Harvey, J. W. (2020). Veterinary Laboratory Medicine: Clinical Pathology (2nd ed.). Wiley-Blackwell.
• Eddleston, M., et al. (2019). Toxicology of Common Veterinary Poisons. (Review / clinical toxicology reference).
• WHO / OIE. (2017-2021). Guidelines and guidance on responsible use of antimicrobials (reference documents).