Prescribing Flashcards
(30 cards)
absorption principles
acidic drugs need acidic (ph<7.35) environment for absorption, e.g. phenytoin, aspirin, penicillin
basic drugs require a basic (ph>7.35). environment for absorption e.g. diazepam, morphine, pethidine
absorption changes with. increased biological age (3)
increased gastric pH (less acid),
decrease small bowel surface area,
more likely to have had previous GI surgery or NG tube etc.
In line with absorption which drugs are absorbed better in older people? acidic or basic
basic drugs increased absorption
distribution principles
protein binding for must drugs - albumin basic so binds to acidic and alpha-1 acid glucoportein acidic binds to basic,
lipid binding
distribution changes in old patients
elderly often low albumin but higher A-1 AG so bind more to basic drugs,
increased fat proportional to muscle mass so increases volume of lipophilic drugs e.g. diazepam, anaesthetics,
decreased body water by about 10-15% so hydrophilic drugs lower Vd so lithium, digoxin
Volume of distribution
theoretical volume into which all of drug is fully dissolved in plasma
volume of distribution indicates what?
indicates lipophylicity of drugs
biological halflife
time for drug concentration to fall to half of its maximum concentration directly proportional to Vd
drugs that are lyphophylic and have high Vd
long half-life
lypophylic drugs clear faster/sloer than one that cleared by kidney/liver
slower
How can sometimes old patients distribution be fine
lower Vd AND clearance both low so balance each other out so half life unaffected
metabolism
hepatic metabolism,
renal metabolism
metabolism old people changes
reduced liver function due to decreased size, blood glue, ,
lower CP yfoj ????,
lower GFR, but serum creatinine not reliable so use egfr
reduced liver function in old people reduces what type of metabolism and give example of drug
first pass metabolism reduced e.g. propranolol
general principle of older people
lower doses achieve same effect in older people but some effects are decreased e.g. beta blockers
therapeutic index
drug with narrow therapeutic index be careful and it narrows as you grow older
Drugs most often associated with adverse reactions
warfarin, digoxin, insulin, Benzos, diuretics, NSAIDs, steroids, anti-hypertensive agents, opioids, theophylline
side effects old people with opioids, Benzes, steroids and levothyroxine
opioids -> laxatives prophylactically, psychomotor function, falls and confusion,
benzos -> psychomotor function, falls and confusion so low dose short time
steroids -> osteoporosis prevention, steroid induced diabetes,
levothyroxine -> calcium interferes with absorption of drug and lots of old people on calcium tabs
problems with NSAIDs in oldies
decreased effectiveness of diuretics, anti-hypertensives,
decline in GFR,
GI haemorrhage
antibiotics in oldies
resistance and c.diff diarrhoea use only when objective evidence of infection e.g. +ve blood culture, urine culture, pyrexia or consolidation on CXR
average use of person >65 yrs is
4 prescription,
2.5 over-the-counter medicines
poylpharmacy prevention
review meds regularly & discontinue unnecessary e.g. NSAIDs,
avoid treating s/e with more drugs e.g. amlodipine causing oedema,
attempt to get one drug to treat two things e.g. CCB/BB for HTx and angina
diarrhoea
loperamide or codeine phosphate
start-GI
PPI,
fibre supplements
