Pharmacotherapy in Older adults Flashcards
In pharcokinetics, what DOES not change with older adults? When would this not be the case?
Bioavailability!!
If you have extensive first-pass effect normally, bioavailability may increase b/c less drug is extracted by liver (smaller with reduced blood flow, and decreased size and mass)
Factors affecting drug absorption?
- Divalent cations that can affect absorption of e.g. many fluoroquinolones;
- Enteral feedings interfere with absorption of some drugs (phenytoin)
- Increased gastric pH could increase or decrease absorption of some drugs (however you could have increased risk of osteoporosis and C diff)
- Drugs that affect (slow down) GI motility can affect absorption
As we get older, what happens with body water, lean body mass, fat stores, and plasma protein?
Lower BW means lower VD for hydrophilic drugs; lower LBM means lower VD for drugs binding to muscle; increased fat means higher VD for lipophilic drugs; lower plasma protein means higher percent of unbound drug
Which drugs (phase I or II) are preferred for older patients?
Those metabolized by phase II pathways
Which drugs are very protein bound, primarily use phase 1 pathway metabolism, water-soluble, lipid-soluble?
- Warfarin, phenytoin
- Long-acting benzos like diazepam
- digoxin, lithium
- Diazepam
Some meds requiring dose reduction with decreased creatinine clearance:
Digoxin, meformin, thiazides, ACEi, fluroquinolones, penicillins, lithium
Other factors affecting drug metabolism:
- Gender
- hepatic congestion from heart failure: reduced metabolism of warfarin
- Smoking: increases clearance of theophylline
Effects of aging on the kidney:
- decreased kidney size
- decreased RBF
- decreased number of functioning nephrons
- decreased renal tubular secretion:
LOWER GFR
What can decreased LBM lead to?
lower creatinine production and decreased GFR (serum creatinine stays in normal range)
How can we measure creatinine clearance?
- Do 24-hr urine collection (time-consuming)
2. Estimate with Cockroft-Gault eqn
Most common meds involved in ADEs
Think CV, CNS, MSK meds; also meds with narrow margin of safety like digoxin, warfarin, NSAIDs
Some drugs that can cause ADE’s:
Amitriptyline (TCA), digoxin (>.125 mg/day); maybe antihistamines, diphenhydramine, indomethacine, muscle relaxants
Risk factors for ADE’s:
- 6 or more concurrent chronic conditions
- 12 or more doses of drugs/day
- 9 or more meds
- Prior adverse drug rxn
- LBW or BMI
- Age 85 or older
- Estimated CrCl is less than 50 ml/min
Key facts on drug-drug interactions and most common ADE’s:
- Absorption can be increased or decreased
- You could have exaggerated or diminished effects
- Drug metabolism may be inhibited or induced
- Herbal preps may also interact;
big thing is CONFUSION and cognitive impairment, along with arterial hypotension, ARF
Some common drug-drug interactions:
- ACEi and diuretic leading to hypotensino and hyperkalemia
- ACEi and K leading to hyperkalemia
- Benzo and antidepressant, antipsychotic, benzo means confusion, sedation, falls
- CCB with diuretic or nitrate means hypotension
- Digitalis and antiarrhythmic means brady or arrhythmia
