Pharmacokinetics/ Pharmacodynamics Flashcards
What is pharmacokinetics
The study of what happens to the drug in the animal’s body after it is administered
What is absorption?
The process by which a drug crosses various barriers to reach the bloodstream
The only route where absorption is not a factor to be considered is what route?
IV
What is bioavailability?
The degree to which a drug is absorbed and becomes available via general circulation
What are the two main methods of crossing the cellular membrane?
Active & passive processes
What is passive process?
No energy expended by the cell - Most drugs cross membranes this way
Give 2 examples of passive processes
- Simple diffusion - from an area of high concentration to low concentration
- Facilitated diffusion - water-soluble drugs cross membranes through pores or channels
What is active process?
Requires energy to move substance against a concentration gradient - low to high
What are 2 examples of active processes?
- Active transport - if close in structure to endogenous substrate
- Pinocytosis, phagocytosis
What are 4 factors that affect the absorption of oral drugs?
- Gut fill & rate of pyloric emptying - delay
- Binding to gut contents
- Low gastric pH - destroy / inactivate
- Presence of GI disease - loss of intestinal villi/ increased rate of emptying
What problems do ruminants present when it comes to oral absorption?
Large capacity of rumen dilutes drugs
pH levels cause ion trapping of basic drugs
Microbial activity affects stability of drugs
Rate of passage/ digestibility of feed
Multiple IM/ SQ injection sites increase absorption
True
SQ injections are absorbed faster than IM
False - IM are absorbed faster due to increased blood flow to muscles
What are 4 things to consider when it comes to the formulation of parenteral drugs?
- Pyrogen free
- Sterile
- Adjusted to body pH
- Adjusted to body osmolality
Drugs are generally absorbed _______________ through the skin
Slowly
Topical medications are usually formulated in ____________
Fats - or fat solvents
Increased ____________ allows for increased absorption of topical drugs
Circulation
This type of drug absorbed rapidly due to large surface area with excellent blood supply
Inhaled drugs
________ soluble drugs have enhanced absorption
Lipid
What are some water-soluble antibiotics?
Penicillin, aminoglycosides, sulfonamides, B-lactams
What are some intermediate fat-soluble antibiotics?
Tetracyclines
What are some fat-soluble antibiotics?
Macrolides, fluroquinolones
The ____________ the drug molecule, the easier it can be absorbed
Smaller
Non-ionized drugs diffused through cell membranes easier
True
What types of drugs are absorbed better in acidic and basic environments?
Acid drugs - acidic environment
Basic drugs - basic environment
The stomach has an ____________ pH, whereas the small intestines have a ______________ pH
Acidic, basic
Many drugs have ___________ _____________ that control the rate at which they dissolve prior to being available for absorption
Protective coatings
Skeletal muscle, liver and kidney are well perfused therefore receive significant concentrations of drugs
True
A drug moves from the absorption site into the ____________ then into the ______________ and finally into the cells
Plasma, extracellular fluid
What factors affect the distribution rate of drugs?
Concentration gradient
Protein binding
Storage in various tissues
Dilution in luminal fluids
Specialized barriers
Disease processes
Drugs tent to move from an area of _____________ concentration to an area of _____________ concentration
High, low
Some drugs may temporarily bind to these and become unable to leave the plasma while bound
Plasma proteins (albumin, globulin, glycoproteins)
Plasma proteins can be lower in disease states or in young animals, this is called what?
Hypoproteinemia - lower plasma proteins means decreased plasma binding and more drug entering ECF; therefore a decrease in dose is required
Drugs can be stored in what tissues/ organs?
Fat, liver, kidney, bone
What is the blood-brain barrier?
Exists between plasma and extracellular fluid and has tight junctions - When inflamed it may become more permeable allowing some antibiotics to enter
What type of drugs diffuse across the placenta easily?
Lipid-soluble
Tight capillary and endothelium junctions limit absorption and distribution of drugs in these areas
BBB, eye, joint synovia
Purulent and necrotic debris may bind and inactivate some antibiotics
True
Antibiotics enter exudates, abscesses or necrotic tissue very well
False - They do not enter very well due to the fibrous capsules the body makes around the infected area and the poor blood perfusion that results
Drug metabolism is also known as what?
Biotransformation
What is metabolism/ biotransformation?
The 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
All drugs require metabolism before achieving active form
False - primidone converted to phenobarbital
Metabolism mainly occurs where?
Liver
The amount of enzymes available that help with metabolism depend on what?
Species, age, sex, stress, nutritional status, disease, enzyme induction
The first pass effect is only important to remember when administering what kind of drugs?
Oral
What is the first pass effect?
Orally administered drugs are absorbed in the gut before entering the portal circulation - the blood in portal veins is then filtered by the liver before entering systemic circulation - therefore drugs are exposed to metabolic enzymes before entering systemic circulation (are metabolized before having any effect rendering them ineffective)
What is the major route for drug excretion?
Renal - kidneys
In order for a drug to be eliminated by the kidneys it must be ____________ soluble
Water
Where does biliary excretion happen?
Liver - excretes drugs into bile, bile secreted into GIT, eliminated in feces
Drugs that are ____________ soluble are generally eliminated through biliary excretion
Highly lipid
How does intestinal excretion work?
Drug is secreted across GIT mucosa by active transport or excreted in gut secretions (ruminant saliva) - are then eliminated in feces
Glandular secretions can happen where?
Salivary, mammary, sweat glands, male genitalia
What is something to be aware of when a drug is secreted through glands?
Residues - Some drugs are secreted unchanged which can effect milk when nursing offspring
Gas anesthetics are eliminated through the lungs by ____________ _____________
Expired air
What is the half-life of a drug?
The time required for the amount of a drug in the blood to be reduced by one half
What does the half-life of a drug dictate?
How frequently the drug must be given
Shock results in _____________ distribution due to _____________ blood flow to tissues.
Decreased, decreased
How many half lives are required to remove 99.9% of a drug from the plasma?
10
