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20
What happens to body composition in the elderly and how can this affect drug handling?
1. body water
2. body fat
3. lean body mass
1. body water
2. body fat
3. lean body mass
1. Body water
- decreases by up to 15%
- Vd of polar (water soluble drugs decreases
- plasma concentratoin goes up (digoxin, cimetidine)
N.B diuretics exacerbate this
2. Body fat
- increases as a proportion of body mass
- Vd of fat soluble drugs increases
- accumulation of drugs ( e.g benzodiazepines)
3. Lean body mass
- decreases
- Vd of highly protein bound drugs decreases
- increased plasma concentration (e.g. digoxin)
- use lean body weight for doese calculations
- decreases by up to 15%
- Vd of polar (water soluble drugs decreases
- plasma concentratoin goes up (digoxin, cimetidine)
N.B diuretics exacerbate this
2. Body fat
- increases as a proportion of body mass
- Vd of fat soluble drugs increases
- accumulation of drugs ( e.g benzodiazepines)
3. Lean body mass
- decreases
- Vd of highly protein bound drugs decreases
- increased plasma concentration (e.g. digoxin)
- use lean body weight for doese calculations
