Difficult Pharmacology Quiz

Routes of Drug Administration and Pharmacokinetics

• The first pass effect refers to the metabolism of drugs by the liver after absorption, which can affect drug bioavailability.
• Drugs that do not dissolve in the intestinal contents may not be absorbed effectively.
• Oral drug administration can result in slower drug action compared to injectable routes and may be inconvenient for certain animal species like cattle, pigs, and cats.
• Rectal administration allows for erratic drug absorption, with 50% bypassing the liver, making it useful for certain drug types and conditions.
• Protected oral dosage forms, such as enteric coatings, can target drug release in specific parts of the gastrointestinal tract to improve absorption and reduce side effects.
• Ruminants present unique challenges for oral drug dosing, including drug dilution in rumen fluid and inactivation by rumen microflora.
• Parenteral routes of drug administration include intravenous, intramuscular, subcutaneous, and other methods, each with specific advantages and disadvantages.
• Injectable dosage forms can provide rapid and high blood drug concentrations, protect drugs from intestinal degradation, and avoid first pass metabolism.
• Intravenous administration ensures 100% bioavailability, as all the drug enters the circulation unchanged.
• A farmer treating cows with an oral antibiotic for a kidney infection may face challenges related to drug absorption, metabolism, and effectiveness.
• For a dehydrated dog with gastroenteritis, rectal administration of fluids may be considered, in addition to other non-intravenous methods, depending on the dog's ability to retain the fluid.
• Pharmaceutical technologies can selectively release drugs to specific parts of the gastrointestinal tract, offering potential benefits for drug absorption and side effects.

Pharmacodynamics and Pharmacokinetics: Mechanisms of Drug Action

• Pharmacodynamics refers to the mechanisms by which drugs achieve anesthesia.
• The initial drug-receptor interaction is the action of the drug.
• Drug effects are quantitative and alter pre-existing cell function.
• Anaesthetic drugs work by depressing excitatory neurons, stimulating inhibitory neurons, or depressing all neurons.
• Non-cellular mechanisms of drug action include physical effects, chemical reactions, physicochemical effects, and modification of body fluid composition.
• Cellular mechanisms of drug action involve physicochemical and biophysical processes, modification of cell membrane structure and function, neurohumoral transmission, enzyme inhibitors, and regulatory molecule activation or inhibition through receptor-mediated effects.
• The most numerous drug receptors are the cells' proteins, with properties such as specificity, saturable kinetics, and action vs. effect.
• Results of receptor activation include the induction of synthesis of specific protein, regulation of gated ion channels in the plasma membrane, and regulation of plasma membrane enzymes.
• An agonist stimulates a reaction in the cell, with affinity and potency determining its level of activity.
• An antagonist interferes with a receptor or part of the effector mechanism without eliciting a reaction.
• Drug-receptor bonding is reversible, and increasing concentrations of ligand can displace the antagonist.
• Drug effects on the patient are proportional to the concentration of the drug in the body, correlating with the concentration of the agent in the plasma.