Cases in Geriatric Pharmacology (ARS) Flashcards
What is “always the answer on the boards” and the take home point of this talk?
Discontinue the amitriptyline
Which of the following changes least with age?
- absorption
- distribution
- metabolism
- elimination
- absorption
- amount absorbed (bioavailability) doesn’t change
- peak serum concentrations may be lower and delayed
Exceptions:
drugs with extensive first-pass effect (bioavailability may increase; serum concentrations may be higher because less drug is extracted by a smaller liver with reduced blood flow, e.g., nitrates)
Factors that affect drug absorption
- what is taken with the drug (ie food)
- comorbid illnesses (diabetic gastroparesis)
- enteral feedings interfere with absorption of some drugs (phenytoin)
- drugs that increase gastric pH or affect GI motility affect absorption (eg PPIs, iron)
An older woman is switched from atenolol to propranolol. What happens and why?
- bradycardia, confused, despondent
- Why? propranolol is more lipophilic (enters CNS)
Effects of aging on volume of distribution (VD)
- decreased body water– so lower VD for hydrophilic drugs
- decreased lean body mass– so lower VD for drugs binding muscle
- increased fat stores– so higher VD for lipophilic drugs and lipid soluble more likely to get into brain
- decreased plasma protein (albumin)– so higher percentage of drug that is unbound (active)
Most common site of drug metabolism
Liver
- metabolic clearance of a drug by the liver may be reduced because liver blood flow, size, and mass decreases
- individual hereditary differences in enzyme levels may be more important to explain inter-patient variation
Are drugs that undergo phase I or phase II metabolism preferred for older pts?
Phase II pathways are preferred in older pts.
(Phase I pathways convert drugs to metabolites with less than, equal, or greater pharm effect than parent compound. Hydrolysis, oxidation, reduction)
(Phase II: (e.g., conjugation) pathways convert drugs to inactive metabolites that do not accumulate)
Which factor accounts for most change in drug effects with age?
- absorption
- distribution
- metabolism
- elimination
ELIMINATION
Estimation of creatinine clearance with age
-With advancing age and lower body weight, serum creatine becomes a weaker estimator of creatinine clearance
- decrease in lean body mass leads to lower creatinine production AND less creatinine to clear
- so serum creatinine may stay in normal range despite decline in creatinine clearance
Cockroft-Gault Equation
[(Ideal weight in kg)(140-age)]/(72)(serum creatinine in mg/dL)
x(0.85 if female)
Pharmacokinetics vs pharmacodynamics
Pharmacokinetics - What the body does to the drug: Pharmacodynamics - What the drug does to the body
Why are elderly at greater risk for bleeding at any given INR (with warfarin)?
they are more like to have additional problems that increase that risk (e.g., friable stomach, more likely to fall & suffer head trauma, etc.)
What is the most common cause of adverse drug reactions in the elderly?
number of medications prescribed
Risk factors for ADR: 6 or more concurrent chronic conditions 12 or more doses of drugs/day 9 or more medications (potential drug interactions: 6% on 2 meds, 50% on 5 meds, approx. 100% on 8 meds) Prior adverse drug event Low body weight or low BMI Age 85 or older Estimated CrCl less than 50 mL/min
Beers Criteria
Comprehensive review and grading of drug-related problems and adverse drug events in older adults
-Examples: all “muscle relaxers”, tricyclic antidepressants
Other top drugs to avoid: Diphenhydramine, hydroxyzine, and first-generation antihistamines Clonidine Amiodarone, class 1 antiarrhythmic drugs Digoxin greater than 0.125 mg daily All benzodiazepines Glyburide, chlorprompramide Indomethacin, meperidine
Two types of errors to watch out for
prescription errors monitoring errors (ex: taking ACE-I, must monitor K+, serum creatinine)
Also be aware of OTC medications
