Introduction
Veterinary pharmacology studies the drugs used in animals, including their origin, properties, mechanisms of action, therapeutic effects, adverse reactions, and fate within the organism. Mastery of its fundamental concepts is essential for the rational and safe use of medications in veterinary medicine (Cunningham & Klein; Papich).
Pharmacological knowledge makes it possible to optimize treatments, minimize risks, and consider physiological differences among species, ages, and productive stages. This is essential in both companion animals and food-producing animals (Papich; Riviere & Papich).
Drug, medication, and active ingredient
A drug is a substance capable of producing a biological effect by interacting with the animal organism. The active ingredient is the component responsible for this effect and acts on specific targets such as receptors, enzymes, or ion channels (Papich).
A medication is the final pharmaceutical form that contains the active ingredient together with excipients that facilitate its stability, administration, and absorption. The formulation directly influences therapeutic efficacy and treatment safety (Riviere & Papich).
Pharmacokinetics: what the body does to the drug
Absorption is the process by which a drug moves from the site of administration into the systemic circulation. Bioavailability represents the fraction of the drug that reaches the bloodstream in an active form and depends on the route of administration, formulation, and animal species (Papich; Cunningham & Klein).
Distribution describes the transport of the drug to body tissues. Factors such as plasma protein binding, lipid solubility, and the blood–brain barrier influence the concentration reached in target organs (Riviere & Papich).
Metabolism occurs mainly in the liver and transforms the drug into more water-soluble compounds. Metabolic differences among species explain variations in toxicity and duration of pharmacological effects (Papich).
Excretion eliminates the drug and its metabolites, primarily via renal or biliary routes. Half-life is the time required for the plasma concentration of a drug to decrease by half and determines dosing intervals (Riviere & Papich).
Pharmacodynamics: what the drug does to the body
Pharmacodynamics studies how a drug produces its biological effect. Most drugs act by binding to specific receptors, triggering cellular responses that explain their therapeutic action (Papich).
Agonists activate receptors, whereas antagonists block their action. The ceiling effect represents the dose beyond which no further therapeutic benefit is achieved, although the risk of toxicity increases (Cunningham & Klein).
Dose and safety parameters
The therapeutic dose is the amount required to produce the desired effect without causing harm. In veterinary medicine, it is adjusted according to species, body weight, age, and physiological status of the animal (Papich).
The median lethal dose (LD50) is the amount of a drug capable of causing death in 50% of an experimental population. This parameter is used to evaluate toxicity and establish safety margins (Riviere & Papich).
The therapeutic index compares the toxic or lethal dose with the therapeutic dose. A wide margin of safety indicates a safer drug, whereas a narrow margin requires strict clinical monitoring (Papich; Cunningham & Klein).
Adverse effects, toxicity, and tolerance
Adverse reactions are unwanted effects that may occur at normal therapeutic doses. Early identification is essential to prevent clinical complications (Papich).
Toxicity occurs when the organism’s adaptive capacity is exceeded. Tolerance develops when higher doses are required to achieve the same effect, and dependence may occur after prolonged use of certain drugs (Cunningham & Klein).
Withdrawal period and pharmacology in food-producing animals
The withdrawal period is the time required between the last drug administration and the collection of animal-derived products. Compliance is essential to prevent drug residues and protect public health (Riviere & Papich).
Conclusion
The fundamental concepts of veterinary pharmacology allow for rational drug use, optimization of therapeutic efficacy, and reduction of toxicity-related risks. Mastery of these principles is essential for safe, ethical, and scientifically sound veterinary practice (Papich; Cunningham & Klein).
References
Papich, M. G. Saunders Handbook of Veterinary Drugs. Elsevier.
Riviere, J. E., & Papich, M. G. Veterinary Pharmacology and Therapeutics. Wiley-Blackwell.
Cunningham, J. G., & Klein, B. G. Textbook of Veterinary Physiology. Elsevier.