Overview of Pharmacology

Pharmacology:

The study of drugs

Therapy:

Treatment of disease

Pharmacotherapy:

Treatment of disease with drugs

Pharmacokinetics:

The physiological movement of drugs through the body into the cells (the stud vcy of drug motion)

What is a VCPR?

-Veterinarian Client Patient Relationship

-Doctor has to see and put his hands on the patient

Extra- label drug use (ELDU):

Drugs used in a manner that is not specifically described on the FDA- approved label

Off- label:

Drugs that are prescribed for a different purpose than what the FDA has approved

Over-the-counter drugs (OTC Drugs):

Drugs that don’t have a significant potential for toxicity or do not require special administration

Controlled substances:

Drugs considered dangerous because of their potential for human abuse or misuse

Who regulates controlled substances?

Drug Enforcement Agency (DEA)

Effective dose:

The amount of the test drug that causes a defined effect in 50% of the animals that received it (ED50)

Lethal dose:

The amount of test drug that kills 50% of the animals (mice, rats) that receive it (LD50)

Therapeutic index or margin of safety:

Drug dosage or dose that produces the desired effect with minimal or no signs of toxicity

How do you determine the therapeutic index?

LD50 divided by ED50

Direct marketing:

Drug is purchased directly from the company that makes it (Zoetis)

Distributors or Wholesalers:

Drug is purchased from the manufacturing company and resold to veterinarians (MWI)

Generic companies:

Sell drugs that are no longer under patent protection (generic)

3 factors that keep drugs in therapeutic range:

-Route of administration

-Drug dose

-Dosage interval

Parenteral drugs:

-Given by a route other than the GI tract (IV, IM, SQ, any injectable route)

-Others- inhalation and topical

Non-parenteral drugs:

Given through the GI tract

Factors that affect the route of drug administration:

-Water soluble drugs can be given IM, but not IV

-Some drugs are destroyed by stomach acid and cannot be given orally

Onset time and duration of drugs given IV:

-Have rapid onset of action

-Higher initial body levels of drug

-Shorter duration of activity

Onset time and duration of drugs given IM:

-Have rapid onset of action

-Longer duration of activity

Solutions:

Clear liquids that contain one or more solvents and one or more solutes (vaccines that have powder and liquid that need to be mixed)

Suspensions:

Liquid preparations that can contain solid drug particles suspended in suitable medium (ampicillan)

Onset time and duration of drugs given SQ:

-Slower onset of action

Longer duration of activity

Inhalation administration:

-Introduces the drug to the animal by having it breathe the drug into lungs

-Particles diffuse across the alveolar membrane

Topical medication:

-Goes on the surface of the skin or mucous membranes

-Mucous membrane application is almost as fast as IV when in the buccal area

Types of non-parenteral administration:

Oral

Oral administration

-Delivers the drug directly into the animals GI tract

-Expecting it to pass through the liver, may need a higher dose than injectable)

Onset time and durations of drugs given orally:

-Slower onset of action

-Longer duration of activity

-Absorption rates may be affected by the type of digestive tract/GI diseaseD

Dose:

Amount of drug administered at one time to achieve the desired eLffect

Loading dose

Initial dose of drug given to get the drug concentration up to the therapeutic range in a very short period of time

Maintenance dose:

Dose of drug that maintains or keeps the drug in the therapeutic range

Total daily dose:

Total amount of drug delivered in 24 hours

Dosage:

The amount of drug per animal species body weight (30mg/kg)

Dosage interval:

How frequently the dosage is given (BID,TID)

Dosage regimen:

Dosage interval and the dosage together (30mg/kg TID)

Examples of drug toxicities:

-Outright overdose

-Relative overdose

-Side effects

-Accidental exposure

-Interaction with other drugs

-Incorrect treatment

Examples of ways to treat toxicities:

-Removal of the offending drug

-Enhancing drug removal by the animal

-Counteracting with an antidote

-Providing symptomatic care (treat the symptoms)

4 steps of pharmacokinetics:

-Absorption

-Distribution

-Biotransformation (metabolism)

-Excretion

Basic mechanisms of moving substances across cell membrane:

-Passive diffusion

-Facilitated diffusion

-Active transport

-Pinocytosis/Phagocytosis

Passive diffusion:

-Movement of particles from an area of high concentration to an area of low concentration

-Good for small, lipophilic, nonionic particles (easily passes through the cell membrane)

Facilitated diffusion:

-Passive diffusion that uses a special carrier molecule (molecule is too big and needs a carrier molecule)

-Good for bigger molecules that are not lipid soluble

Active transport:

-Molecules move against the concentration gradient from areas of low concentration to areas of high concentration (requires ATP and a carrier molecule)

-Good for accumulation of drugs within a part of the body (antibiotics)

Pinocytosis/Phagocytosis:

-Molecules are physically taken of engulfed

-Good for bigger molecules or liquids

Difference between pinocytosis and phagocytosis:

-Pinocytosis: engulfing liquid

-Phagocytosis: engulfing solid particlesD

Drug absorption:

Movement of drug from the site of administration into the fluids of the body that carry it to its site of action (how the drug is getting to the cell when broken down)

Drug absorption drug factors:

-Drug solubility

-Drug pH

-Drug molecular sizeD

Drug absorption patient factors:

-Animal’s age

-Animal’s health statusBi

Bioavailability:

Percent of drug administered that actually enters the systemic circulation (how much drug reaches the desired site)

Ionization:

Property of being charged

Hydrophilic:

Combine/dissolve with water= ionized

Lipophilic:

Combine/dissolve with fats= nonionized

Weak acid will be absorbed:

Primarily in the acidic environment (stomact)

Weak base will be absorbed:

Primarily in the alkaline environment (small intestines)

Drug distribution:

The physiological movement of drugs from the systemic circulation to the tissues

Membrane permeability:

Large molecules cannot pass through fenestrations of blood capillaries

Tissue perfusion:

Relative amount of blood supple to an area or body system

Protein binding:

Drugs bound to proteins cannot leave the capillaries due to the size of the protein

Volume of distribution:

How well a drug is distributed throughout the body based on the concentration of drug in the blood

Biotransformation:

-Chemical alteration of drug molecules by the body cells of patients to metabolite that is in an inactive form

-Metabolism

Primary site of biotransformation:

In the liver

Drug interactions that may affect metabolism:

-Altered absorption

-Competition for plasma proteins

-Altered excretion

-Altered metabolism

Altered absorption:

One drug may alter the absorption of other drugs

Competition for plasma proteins:

-Drug A and drug B may both bind to plasma proteins

-One may have a higher affinity than the other

Altered metabolism:

The same enzymes may be needed for biotransformation of 2 drugs that are prescribed at the same time for the animal

Drug elimlimination:

-Removal of a drug from the body

-Excretion

Primary site for drug elimination:

Kidneys

Renal elimination of drugs involves:

-Glomerular filtration

-Tubular secretion

-Tubular reabsorption

Withdrawal time:

Period of time after drug administration during which the animal cannot be sent to market because of the potential for drug residues

Half-life:

Time required for the amount of drug in the body to be reduced by half of its original level

Steady state:

-Point at which drug accumulation and elimination are balanced

-Therapeutic range

How drugs work:

-Alter existing cellular functions

-Alter the chemical composition of body fluids

-Can form a chemical bond with specific cell components on target cells within the animal’s body

Receptors:

-3 dimensional proteins or glycoproteins

-Located on the surface, in the cytoplasm, or within the nucleus of cells

Affinity:

-The strength of binding between a drug and its receptor

-High affinity drugs bind more tightly to a receptor than low affinity drugs A

Agonist:

Drug that binds to a cell receptor and caused action

Antagonist:

-Drug that inhibits or blocks the response of a cell when the drug is bound to the receptor

-Prevents action to occur