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CHAPTER 1: GENERAL PHARMACOLOGY Introduction What is a drug? Any substance used to diagnose, prevent or treat disease The veterinary technician’s role: Administration of drugs Filling patient prescriptions Client education (indications, contraindications, possible adverse effects) ...
CHAPTER 1: GENERAL PHARMACOLOGY Introduction What is a drug? Any substance used to diagnose, prevent or treat disease The veterinary technician’s role: Administration of drugs Filling patient prescriptions Client education (indications, contraindications, possible adverse effects) Drug Sources Plants alkaloids – end in –ine glycosides – end in –in gums, resins, oils Bacteria & Molds Animals hormones & anticoagulants Minerals electrolytes, iron, selenium Laboratories Pharmacotherapeutics Drug selection Diagnostic: follows assessment of patient & identification of the causative microorganism or altered physiological state Empirical: uses of practical experience & common sense Symptomatic: treats symptoms of disease $$$ Pharmacotherapeutics Regimen: plan for administering the drug route of administration dose frequency duration Prescription drug: drug limited to use under the supervision of a veterinarian because of potential danger, difficulty of administration, or other considerations “Caution: Federal law restricts this drug to use by or on the order of a licensed veterinarian.” Pharmacotherapeutics Veterinarian-client-patient relationship: set of circumstances that must exist between veterinarian, client & patient before the dispensing of prescription drugs is appropriate Conditions required for a valid veterinary-clientpatient relationship: assumed responsibility sufficient knowledge follow-up Pharmacotherapeutics Responsibilities of the technician Correct drug Correct route & time Observe response of the animal Question unclear orders Create & affix labels accurately Explain administration instructions to clients Record appropriate information in medical record Pharmacokinetics What happens to drugs once they enter the body Absorbed into bloodstream & distributed to various fluids & tissues Must reach target site & accumulate at required concentration to be effective Body immediately starts to break down & excrete Loading dose: initial high dose used to reach appropriate blood level Steady state: point at which drug accumulation equals drug elimination Therapeutic drug monitoring: used to measure drug levels in blood, urine, CSF fluid or other appropriate fluid Pharmacokinetics Factors that influence blood concentration levels & patient response Rate and amount of drug Absorption Distribution throughout the body Metabolism/biotransformation Rate & route of Excretion “ADME” Pharmacokinetics Selection of route of administration Available form of drug Physical or chemical properties Onset of action Use of restraint or behavioral characteristics Nature of condition Drug Absorption Bioavailability: degree to which a drug is absorbed & reaches the general circulation Factors that affect absorption Mechanism of absorption pH & ionization status of drug Absorptive surface area & blood supply to the area Solubility of the drug Dosage form Status of GI tract Interaction w/ other medications Drug Absorption Passive absorption/transport – no energy required simple diffusion facilitated diffusion Pinocytosis – energy required Active transport – energy required Passive transport Pinocytosis Active transport Drug Distribution Absorption→plasma→interstitial fluid→cell→receptors Rate of movement is based on concentration gradient (difference b/w amounts of drug in 2 compartments) Protein bound drugs are inactive & unavailable; storage sites Tissues w/ natural barriers – brain, eye, placenta Disease processes that can interfere w/ – abscesses, heart failure & shock & kidney, renal or liver failure Biotransformation/Metabolism Body’s ability to change a drug chemically from the form in which it was administered into a form that can be eliminated from the body Biotransformation Biotransformation/Metabolism Chemical reactions that occur in the liver Oxidation: loss of electrons Reduction: gain of electrons Hydrolysis: splitting of drug molecule w/ addition of water molecule Conjugation: addition of glucuronic acid resulting in more water soluble molecule Biotransformation/Metabolism Factors that can alter Species Age Nutritional status Tissue storage (fat and plasma proteins) Health status Drug Excretion Kidneys glomerular filtration & tubular secretion urine Liver bile → sm. intestine → feces or reabsorbed into blood Mammary glands, lungs, intestinal tract, sweat glands, salivary glands & skin Drug Excretion Residues: drug that remains in animal products when they are consumed Half-life: time required for the amount of drug present in the body to be reduced by half Pharmacodynamics Study of mechanisms by which drugs produce physiologic changes in the body Affinity: tendency of a drug to combine w/ a receptor Efficacy: degree to which a drug produces its desired response Potency: amount of drug needed to produce a desired effect Drug Pharmacodynamics Agonist: drug w/ a high level of affinity & efficacy which causes a specific action Antagonist: drug that blocks another drug from combining w/a receptor * *A partial agonist will have similar action as the agonist + antagonist. Pharmacodynamics Therapeutic index: relationship b/w a drug’s ability to achieve the desired effect its tendency to produce toxic effects LD50/ED50 Quantitates drug’s safety margin Adverse drug reaction: undesirable response to a drug Allergic, photosensitivity, abortion, L/K damage, infertility, V/D & cancer Idiosyncratic drug rxn: unusual or unexpected rxn peculiar to an individual Drug Interactions Altered pharmacologic response to a drug caused by the presence of a 2nd drug Normal response can be increased or decreased Beneficial or harmful Classifications Pharmacokinetic Plasma or tissue levels of a drug are altered by the presence of another Pharmacodynamic Action or effect of 1 drug is altered by another Pharmaceutic Occurs when physical or chemical rxns take place as a result of mixing drugs Drug Names Chemical – describes the molecular structure of a drug Code or laboratory – name given to a drug by R&D Compendial – name listed in the US Pharmacopoeia Official – usually same as above or generic name Proprietary or trade – name chosen by the manufacturing company; ®; begins w/ capital letter Generic – common name chosen by company (patents expired or patent never issued); begins w/ lowercase letter Drug Name Example Chemical – 6-chloro-α-methyl-9H-carbazole-2-acetic acid Code or laboratory – ??? Compendial – carprofen Official – carprofen Proprietary or trade – Rimadyl, Novox, Norocarp, Vetprofen Generic – carprofen Drug Labels Must contain Drug names (generic & trade) Concentration & quantity Name & address of manufacturer Controlled substance status Control or lot # Expiration date Instructions for use & warnings or possible adverse effects (insert) Withdrawal time (if applicable) Drug Labels Development & Approval of New Drugs Regulatory agencies FDA – development and approval of drugs and feed additives through its Center for Veterinary Medicine EPA – development and approval of animal topical pesticides USDA – development and approval of biologics (vaccines, serums, antitoxins) The Food Animal Residue Avoidance Databank (FARAD) – database of residue avoidance info. (withdrawal/withholding times) and educational materials Development & Approval of New Drugs Steps in the development of a new drug Preliminary trials – product tested on bact., yeast or molds, computer models used to simulate animal models Preclinical (animal safety) trials – lab animals used to determine appropriate doses; few target animals may be used Clinical trials – product tested on target animal Submission of a new animal drug application Final review by the FDA (EPA or USDA) Product monitoring Federal Law Related to Drug Development & Use The Animal Medicinal Drug Use Clarification Act (AMDUCA) Made extralabel use of approved veterinary drugs legal under specific well-defined conditions FDA may prohibit extralabel use if it finds that such use presents a risk to public health Some drugs are prohibited for extralabel use in food animals See handout Compounding of Veterinary Drugs Conditions approved by FDA Identification of a legitimate veterinary need Need for an appropriate regimen for a particular species, size, gender or medical condition Lack of an approved animal or human drug that when used as labeled will treat the condition Too long a time interval for securing the drug to treat the condition Federal Law Related to Drug Development & Use The Veterinary Feed Directive (VFD) Established a new category of drugs as “an alternative to prescription status” for certain antimicrobial animal feed additives The Minor Use & Minor Species Animal Health Act (MUMS) Intended as a mechanism to provide FDA-authorized drugs for less common species & indications Marketing of Drugs Vet-VIPPS – voluntary certification program created by the National Assoc. of Boards of Pharmacy & advocated by the AVMA to validate the legitimacy of online pharmacies Ethical products – products for which the manufacturer has voluntarily limited their sale to veterinarians as a marketing decision