68: Geriatric Pharmacology Flashcards
polypharmacy
greater than 5 drugs per week
leading causes of death
heart disease
cancer
“prescribing cascade”
drug –> side effect –> drug for the side effects –> side effect
avoid prescribing until test results confirm suspected diagnosis
start with low dose and titrate slowly
avoid starting multiple medications simultaneously
changes in body composition with aging
decreased total body water
decreased lean body mass
increased body fat
cardiovascular changes with aging
decreased myocardial sensitivity to b-adrenergic stimulation
decreased baroreceptor activity
decreased cardiac output
increased total peripheral resistance
liver changes with aging
decreased liver size
decreased hepatic blood flow
pulmonary changes with aging
decreased respiratory m. strength decreased chest wall compliance decreased total alveolar surface decreased vital capacity decreased max breathing capacity
renal changes with aging
decreased GFR decreased renal blood flow decreased filtration fraction decreased tubular secretory function decreased renal mass
skeletal changes with aging
decreased skeletal bone mass (ostopenia)
what the body does to a drug =
pharmacokinetics
- absorption, distribution, metabolism, clearance/elimination
parameter least affected by aging
absorption
first pass metabolism is _______ with aging
reduced
lower dose requirement in elderly with drugs inactivated by first pass; higher dose requirement with prodrugs requiring activation by first pass liver metabolism (codeine, propranolol, enalapril, perindopril, simvastatin)
metabolism/clearance is ______ with aging
reduced
reduced liver function and blood flow; reduced kidney function
volume of distribution =
how does it change in elderly?
amount of drug in body/ plasma drug concentration
large Vd - drug distributing to extravascular compartments, low Vd - drug staying in blood
more fat - higher volume of distribution for lipophilic drugs
less muscle - drugs like digoxin that bind to muscle will have decreased volume of distibution
less water in elderly - hydrophilic (gentamicin) drugs have decreased volume of distribution
half life =
equation
0.693 x vd / CL
would a highly lipid soluble drug have an increased or decreased half life in an elderly pt when compared to younger pt?
increased half life
water soluble - there will be less of an increase in half life than lipid soluble drugs because decrease in water balanced by reduction in clearance
would the loading dose of a highly water soluble drug be larger or smaller in an elderly pt when compared to a young pt?
loading dose = (Vd x target concentration) / bioavailability
smaller *
CL clearance =
Q x E
Q - flow rate to organ
E - extraction ratio
with aging in liver; ______ activity of phase I enzymes (p450) and ________ activity of Phase III ensymes
reduced;
normal
no change in elderly pts hepatic clearance of a capacity limited drug if it metabolized by phase II enzymes; decreased if phase I
flow rate limited drugs have reduced hepatic clearance in elderly pts
therefore … No change in maintenance dose for capacity limited drugs metabolized by phase II enzymes; decrease in maintenance dose in capacity limited drugs that are phase I and in flow rate limited drugs
how does tubular secretion change in elderly?
polypharmacy increases risk of drugs competing for active transporters (less secretion -more drug stays in body)
index of glomerular filtration rate
creatinine
increases in plasma creatinine levels indicate a decrease in GFR
accounts for decreased m. mass in elderly pts
cockcroft and gault equation
even with decreased GFR, elderly can have same plasma creatinine concentration due to decreased m. mass
most significant parameters that increase half life of drugs in elderly
decreases in hepatic and renal clearance
lipophilic drugs have an even further increase in half life because Vd is increased in elderly
reminder: takes 4-5 half lives to reach steady state plasma concentration OR for a drug to be eliminated
what the drug does to the body =
pharmacodynamics
in general, homeostatic control mechanisms are decreased in elderly
____ responsiveness of elderly individual to hypotensive effect of beta blockers
decreased
acute blood pressure response to calcium channel blockers is ______ in elderly
exaggerated
reduced baroreflex activation with aging
aging ______ sensitivity to anesthetic agents
increases
thought to be due to altered expression of opiate receptors
NSAIDs are dangerous in elderly…
aspirin, ibuprofen, etc.
cleared primarily by kidney
Cause renal damage because NSAIDs block increase in prostaglandins that normally would help to increase the blood flow and GFR in elderly kidney
also cause GI bleeding and irritation
adverse effects of anticholinergic drugs in elderly
dry mouth decreased gut motility bladder hypotonia decreased cognition sedation orthostatic hypotension blurry vision
increases overall risk form falls, impaired cognition = functional decline!
anticholinergic drug classes to watch out for
anticonvulsant antidepressant (TCAs) antihistamine antipsychotic cardiovascular GI antispasmodics H2 antagonists muscle relaxants PD Urinary antispasmodics vetigo
should you use first or second gen antihistamines with elderly?
second gen
first gen have anticholinergic properties that cause adverse side effects
