Pharmacology Flashcards
Define pharmacokinetics
Science of the rate of movement of drugs within biological systems, affected by the absorption, distribution, metabolism and elimination of medications
Define pharmacodynamics
the study of the biochemical and physiologic process underlying drug action including mechanism of drug action, drug receptor interaction, efficacy and safety profile
What is bioavailability?
the fraction of the administered dose of the drug which reaches the systemic circulation
What factors affect bioavailability?
Molecular weight / ionisation
absorption
absorption (gastric pH, health of GI tract)
first pass metabolism
What is the apparent volume of distribution?
Total amount of drug in the body divided by the drug blood plasma concentration
What is clearance?
The volume of plasma cleared of drug per unit time
What is half-life?
Time required for serum plasma concentration to decrease by half
How many half lives does it take for a drug to reach a steady state or to be completely cleared?
4-5 times
In non-linear pharmacokinetics dosage increases can saturate binding sites and result in non-proportional increases in drug levels. T/F?
True
Loading doses are used for drugs with a short half-life. T/F?
False - used for drugs with a long half-life
How is morphine prescribing altered when changing from an oral to sub cut dose?
Prescribe 1/3 of the oral dose
At what dose is phenytoin prescribed?
15mg/kg
Renal function affects the loading dose. T/F?
False
Renal function affects maintenance dose. T/F?
True - it depends on drug clearance
Name the different types of drug receptors.
Regulatory proteins
enzymes
transport molecules
structural proteins
What is affinity?
A measure of the propensity of a drug to bind to a receptor
What is efficacy?
The ability of a bound drug to change the receptor in a way which produces an effect
Potency is clinically relevant. T/F?
False
Agonists have affinity and efficacy. What about antagonists?
Antagonists have affinity but not efficacy
How can the actions of competitive antagonists be reversed?
By increasing agonist concentration
How is therapeutic index calculated?
TI = TD50 or LD50 / ED50
Drugs acting on the same receptor or enzyme system often have the same TI. T/F?
True
GFR declines with age. T/F?
True
Give examples of drugs which have increased effects in older people.
Fentanyl, diazepam, alcohol, morphine, theophylline
Give examples of drugs which have a diminished effect in older people.
Isoproterenol
beta blockers
Polypharmacy is a risk for drug-drug interactions and adverse drug reactions. T/F?
True
Give common examples of drug-drug reactions.
Statins and erythromycin/other antibiotics
verapamil and beta blockers
warfarin and aspirin
ACE inhibitors and sulphonylureas
What is the side effect of using decongestants or anticholinergics in benign prostatic hyperplasia?
Urinary retention
What drugs can worsen constipation?
Calcium
Anticholinergics
Calcium channel blockers
Give examples of drugs which lower seizure thresholds.
neuroleptics
quinolone
Give an example of a drug which can exacerbate chronic heart disease.
NSAIDs
How does renal disease affect pharmacokinetics and pharmacodynamics?
Decreased elimination, protein binding and hepatic metabolism
alters sensitivity to drug effects
increased adverse events
Give examples of drugs which should be avoided in renal disease.
Metformin
NSAIDs
Give examples of drugs whose dose should be reduced in renal disease
Antibiotics
digoxin
phenytoin
How does hepatic impairment affect pharmacokinetics and pharmacodynamics
First pass metabolism
activation of prodrugs
decreased protein binding
decreased elimination
Give examples of drugs which increase bioavailability
chlormethiazole
verapamil
paracetamol
Give examples of drugs which decrease bioavailability
enalapril
perindopril
How is dosing interval affected by renal disease?
Require increased dosing interval
How is dosing interval affected by hepatic disease?
Require increased dosing interval
How is dosing interval affected by cystic fibrosis?
Decreased dosing interval
