Pharmacology Principles Flashcards
3 phases of pharmacology
Pharmaceutic, Pharmokinetic, Pharmacodynamic
Pharmaceutic phase
Dissolution occurs—drug begins to dissolve in order to be absorbed; tablet—granula—particle—GI solution—absorption
Pharmacokinetic phase
4 stages—absorption into the blood thru the GI tract, distribution at the site of action (effect exerted), metabolism by the liver, excretion by the kidneys (and a small part of the liver)
Cell membrane—phospholipid bilayer
Drug passes thru the cell membrane in the intestinal walls to the blood and travels to the site of action if lipid soluble (needs facilitator if water soluble)
First pass effect
A % of a drug is broken down by the liver in a first pass before systemic circulation; bioavailability of the drug decreases accordingly for drugs that pass thru the GI tract instead of going directly into the blood (IV)
Bioavailability
Amount of drug available in the blood; drugs with lower bioavailability may require higher dose or more frequent dose
Where does the first pass effect NOT occur
IV, highly vascularized tissues like SL, buccal, rectal, parenteral, topical meds
Enteral
By way of the GI tract (PO, oral, rectal, small intestine); first pass occurs
Parenteral meds
SQ, IM, IV, intrathecal (spinal cord), epidural (space around spinal cord); no first pass
Topical meds (transdermal)
Apply to body surfaces; eyes, skin, ears, nose, lungs;no first pass effect occurs
Distribution
Mvt of drug thru body; drug arrives at site of body
What does distribution depend on?
Blood circulation; less blood flow, less circulation; harder to reach tissue (abscesses, tumors, peripheral vascular disease)
Blood brain barrier
Cells in capillary wall in brain have tight junctions that prevent drug passage except for lipid soluble drugs; not fully developed in infants; alcohol and glucose can cross
Protein binding effect
Temporary storage of a drug molecule that lets a drug be available for longer periods of time; unbound drug binds to a protein and becomes bound; binding is reversible and unbound molecules are active and free to exert effect
Goal of dosing
Maintain a steady state of free drug concentrations
Albumin
Primary blood protein that molecules bind to
Hypoalbuminemia
Low protein levels cause by liver disease or malnutrition; more free drug availability and higher chance of overdose and toxicity (drugs that bind highly to proteins will have a stronger effect on people with low protein levels like Coumadin)
Metabolism (biotransformation)
Method by which drugs are inactivated into metabolites; liver converts lipid-soluble drugs into water-soluble metabolites so the kidneys can excrete them
CYP450 family
Group of enzymes that metabolize about 1/2 of all drugs; causes lots of drug-drug interactions
CYP450 substrate
For metabolism; a substrate (drug) can bind to CYP450 and it will activate the drug
CYP450 inducer
Speeds up metabolism of CYP450; causes a decreased amount of a drug in the body and therapeutic effect
CYP450 inhibitor
Slows CYP450 metabolism; increased amount of drug in body and increased toxicity (ex: grapefruit juice)
Excretion
Removal from body via pee
How do the kidneys excrete?
With glomerular filtration, tubular secretion, tubular reabsorption; some drug is excreted and some is reabsorbed in the renal tubules
How does kidney disease affect excretion?
Causes toxicity thru improper excretion
Half life
Time required for serum concentration of drug to drop by 50%; determines dosing; takes 4-5 half lives to achieve a steady state (drug intake equals amount metabolized/excreted)
Around the clock dosing (ATC)
Goal is to maintain 50% concentration in body
Drug onset
Time for drug to reach therapeutic response
Drug peak
Time to reach max therapeutic effect
Drug duration
Time it takes drug concentration to elicit a therapeutic response
Pharmacodynamic phase
Drugs can increase, decrease, replace, inhibit, destroy; exert multiple effects on the body (desired, undesired, adverse)
Receptors
Proteins on cell surfaces that can be hormones or NTs
Agonist
Drug that initiates a therapeutic effect by binding to a receptor
Antagonist
Prevents or inhibits/blocks other substances from binding and causing a response
Receptor-less activation
No receptor involved; act thru simple physical/chemical intake of small molecules
Therapeutic index
Measure of safety; range in which a drug is safe
Narrow therapeutic index
Small range of safety for a drug; often monitored with blood tests
Black box warning
Required by the FDA for especially dangerous drugs; strongest warning; appears prominently on the package or insert
Med errors
Major cause of mortality and morbidity; variables include fatigue and staffing; prevention includes reminders, standardizing, watching for similar drug names
High alert meds (Institute for Safe Medicine Practices)
More likely to cause harm (insulin, heparin, opioids, IV, KCl, chemo)
Drug-drug interactions increase with…
Especially with NTIs; intended or unintended; polypharm— nurse can bring attention to or may be able to consolidate; food, herbs, and disease
Additive effect
2 drugs taken with similar MOA that amounts to a similar effect as that of the drugs separately
Synergism
Difference MOA but make an effect greater than 1 drug alone
Activation of drug metabolizing enzymes in the liver causes…
Decreased metabolism of the drug
Displacement
One drug from a pharma protein-binding site displaced by a second drug and causes an increased effect of the displaced drug
Antidote
Antagonized other drug (naloxone)
Barrier to intestinal absorption
Lack of anatomy to break down meds
