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pharmacokinetics in the elderly
Pharmacology:
- increased 1/2life of lipid-soluble drugs
- increased peak concentration of hydrophilic drugs
- increased time for drug clearance
- increased sensitivity to:
- benzodiazepines
- anticoagulants
- thrombolytics
- narcotics
- calcium channel blockers
- diminished sensitivity to:
- beta-adrenergic receptor agonists
- beta-adrenergic receptor antagonists
- factors that alter drug levels in the elderly:
a) absorption
1] decreased gastric acidity ?
2] decreased gastric emptying
3] decreased absorptive surface
4] decreased GI blood flow
5] increased intestinal transit time
6] decreased GI active transport
7] decreased liver blood flow
8] decreased liver size
9] generally considered NOT greatly affected by age
b) distribution
1] decreased cardiac output
2] decreased total body water
3] decreased lean body mass
4] increased body fat
5] decreased total body size
6] decreased serum albumin
a] greater free drug for a given serum drug level
b] potential complications with: phenytoin, benzodiazepines, warfarin, etc.
7] increased alpha-1 acid glycoprotein (orosomucoid)
a] major serum protein binding basic drugs
b] diminished free drug for a given serum drug level
c] reduced effectiveness of: quinidine, lidocaine, tricyclic antidepressants
c) metabolism
1] decreased hepatic blood flow (10-15% by age 80)
2] decreased liver mass & volume (20-50% by age 80)
3] decreased enzyme activity ?
4] poor nutritional status
5] concurrent drug use (interactions)
d) renal excretions
1] decreased filtration rate
2] decreased tubular secretion
3] decreased tubular reabsorption
4] renal disease
General
pharmacokinetics
References
- Ambrose P. In: Intensive Course in Geriatric Medicine &
Board Review, Marina Del Ray, CA, Sept 12-15, 2001
- Ambrose P. In: Intensive Course in Geriatric Medicine &
Board Review, Marina Del Ray, CA, Sept 25-28, 2002
- Taffet GE, Physiology of Aging,
In: Geriatric Medicine: An Evidence-Based Approach, 4th ed,
Cassel CK et al (eds), Springer-Verlag, New York, 2003