Prescribing for the elderly Flashcards
What is bioavailability?
- The fraction of a drug dose reaching the systematic circulation
What is distribution?
- Locations in the body of a drug penetrates expressed as bolume per weight (L/kg)
What is metabolism?
Drug conversion to alternate compounds which may be pharmacologically active or inactive
What is Elimination?
- Drug’s final route of exit from the body expressed in terms of half-life or clearance
What affects does aging have on absorption?
- Reduced gastric acid production
- Raises gastric pH
- May alter solubility of drug
- Longer gastric emptying :
- delay or reduce absorption
- Rate of absorption may be delayed
- Lower peak conc
- Delayed time to peak conc
- Bioavialability unchanged
What is decresased esophogeal motility in ageing?
- Capsules more difficult to swallow
What is the loss of subcutaneous fat in ageing?
– Increased rate of absorption of topical medication
What does an increased fragility of veins lead to in ageing?
- Iv administration = more difficuly
What affects does ageing have on the total body water?
- Decreased vol fo distribution for H20 sol drug
- Increased plasma conc of water soluble drugs
- Lower doses are equired : Lithium, digoxin, ethanol etc
What effects does ageing have on lean body mass and body fat?
- Increased volukme of distribution
- Longer half life of water soluble drugs
- Accumulation into fat of lipid soluble drugs : Benzos , etc
- Prolong medication’s action
- Increase sensitivity
- Increase toxic effects
What are the effects of ageing on seum albumin?
- Increased unbound fraction of highly protein bound drugs
- Decreased SA
- Binds acidic drugs : warfarin, phenytoin, digitalis etc
What are the effects of ageing on decreased alpha 1 acid glycoprotein?
- Increased ubound fraction of highly protein bound drigs
- Binds basic drugs : lidocaine and propranol
What are ageing effects determined by?
- Hepatic function and blood flow
- Capacity of the liver to metabolise drugs does not appear to decline consistently with age for all drugs
- dependent on:
- health and nutritional status
- Use of alcohol, medications
- Long term exposure to environmental toxins/pollutants
What are the effects of ageing on metabolism?
-decreased liver mass/ hepatic blood flow
- Lower serum protein levels
- Loss of protein binding
- metabolic clearamce of drugs by the liver may be reduced
What is the effect of age on renal function?
- Decreased kidney size
- Decreased renal blood flow
- Decreased number of functional nephrons
- Decreased tubular secretion
- Decreased GFR
- Decreased drug clearnace
