polypharmacy Flashcards
common side effects of polypharmacy
cognition + consciousness - increased risk of delirium
bowel function - constipation esp
dizziness + balance - postural hypotension + parkinsonism - risk of falls/immobility
anticholinergic side effects
Short term
o Confusion + hallucinations
o Tachycardia
o Blurred vision
o Urinary retention
o Constipation
o Dizziness
Long term
o Increased risk of developing dementia
gabapentin for chronic low back pain?
no!
no evidence for MSK pain (only neuropathic)
clear evidence of dizziness, fatigue, visual disturbances esp in old
risk benefit balnce in prescribing anticholinergics for urinary incontinence
Reduction in symptoms vs severe side effects
- Independent active – might benefit
- Residential home with mild dementia – more likely to harm
pharmacokinetics vs pharmacodynamics
pharmacokinetics = movement of drug through body, ADME (absorption, distribution, metabolism, excretion)
pharmacodynamics = drug action on body, biological response to drug (+ADRs)
2 basic principles of absorption
- acidic drugs require an acidic environment for absorption - phenytoin, aspirin, ppenicillins
- basic drugs require a basic environment for absorption - diazepam, morphine, pethidine
changes in elderly affecting absorption of a drug
increased gastric pH (less acidic), decrease small bowel surface area
usually not a problem except if -
- previous GI surgery
- NJ tube or PEG feed composition
- transdermal patches + oedema
- proportionally more basic drugs absorbed
distribution
largely transported by protein binding - free vs bound proportion of drugs
- albumin (basic) binds to acidic drugs
- alpha-1 acid glycoprotein (acid) binds to basic drugs
–> elderly often low albumin but higher A-1 AG
differences in distribution in elderly
lipid binding
- increased fat - proportional to muscle mass
- increase the Vd of lipophilic drugs (diazepam, anaesthetics), longer half life
decreased body water (10-15%)
- most important change
- lower Vd of hydrophilic drugs - lithium, digoxin
- lower Vd AND CrCl = t1/2 usually unchanged significantly in elderly
volume of distribution
theoretical volume into which all of drug is fully dissolved in plasma
Example –
100mg drug X given to patient
Steady state conc = 0.1mg/L
0.1mg = 1L
100mg = 1000L
-> volume of distribution = 1000L
half life calculation
t1/2 = In2 (0.69) x Vd / CL
(CL= CL(R(kidney)) + CL (H (liver)))
biological half-life = elimination half-life
hepatic metabolism in elderly
reduced liver function due to decreased liver size (30%), blood flow, and disease (CHF)
first pass metabolism reduced (propanolol)
in general, bio transforming enzymes are reduced in elderly
3 phases that facilatate metabolism + excretion
mainly affect phase 1 pathways (oxidation, recution or hydrolysis), functional “polar groups” to facilitate metabolism or excretion
older patients rely on phase II metabolism but slow acetylators at risk of prolonged exposure/toxicity
renal metabolism in elderly
lower GFR - decreased size, tubular secretion, renal blood flow
serum creatinine not a reliable measure
pharmacodynamics in elderly
general principle = lower doses achieve the same effect in elderly (eg alcohol)
BUT some effects are decreased - beta blockers + HR
drugs with narrow therapeutic index
warfarin
lithium
digoxin
gentamicin
theophylline
vancomycin
phenytoin
cyclosporin
carbamazepine
levothyroxine
therapeutic window gets narrower with age, toxic response increases
drugs most frequently assoc with adverse reactions in elderly
warfarin
digoxin
insulin
benzodiazepines
diuretics
NSAIDS
corticosteroids
antihypertensives
opioids
theophylline
polypharmacy management summary
review regularly, discontinue unnecessary mediction
avoid treating adverse reactions/side effect of drugs with more drugs - eg amlodipine for oedema
attempt to prescribe a drug that will treat more than one existing problem - CCB/BB for high BP + angina
STOPP-START tool for prescribing
STOPP - screening tool of older peoples potentially inappropriate prescriptions
- prescriptions that are potentially inappropriate in persons aged >=65yrs of age
START - screening tool to alert doctors to right treatments
- medication that should be considered for people >= 65yrs of age where no contraindications exist
STOPP GI drugs
loperamide or codeine phosphate
- for mx of diarrhoea of unknown cause (delays diagnosis)
- may exacerbate constipation with iverflow diarhoea
- may precipitate toxic megacolon in IBD
- may delay recovery in gastronteritis
prochlorperazine or metoclopramide
- in patients with PARKINSONS - exacerbates parkinsonism
stimulant laxatives
- for patients with intestinal obstruction (risk of bowel perforation)
STOPP cardio drugs
beta blocker
- in combo with verapamil (risk of heart block)
non-cardioselective BB (propanolol, sotalol)
- in patients with COPD (risk of bronchospasm)
calcium channel blockers
- with chronic constipation
- diltiazem or verapamil with class III or IV HF
statins
- atorvastatin 80mg for longer than 6months post MI
START GI drugs
PPI
- for severe acid reflux or peptic stricture
- for patients over 80 on antiplatelets + SSRIs
fibre supplement
- for chronic, symptomatic diverticular disease with constipation
START cardio drugs
antihypertensive
- where systolic consistently >160mmHg
ACEi
- chronic HF or post MI
PPI
- with aspirin + warfarin in combination
warfarin/DOACs
- chronic AF
- following DVT or PE if benefits outweigh risks
