Prescribing in special groups 2 Flashcards
Why have life expectancies at birth and retirement improved?
reduced impact of risk factors e.g. smoking
advances in healthcare
What are the consequences of the ageing population?
focus shifts to chronic diseases
shit from one time interventions correcting a single problem to… ongoing management of multiple diseases and disabilities
increasing disability => increasing need for long-term care services
need to integrate medical and long term care services
What’s made drug treatment complicated?
co-morbidities - risk of drug interactions => causes polypharmacy
also increases risk of adverse drug reactions
What are the definitions of physiological ageing and frailty?
physiological ageing=> time related loss of functional units within an organ system e.g. nephrons, neurones
Frailty => progressive physiological decline in multiple organ systems => loss of function, loss of physiological reserve and increased vulnerability to disease and death
What is appropriate polypharmacy?
polypharmacy traditionally defined at 4 or more drugs
prescribing for complex conditions or multiple conditions where medicines use is optimised and prescribed according to best evidence - for many this will extend life expectancy and improve QoL
What is problematic polypharmacy?
prescribing of multiple medications inappropriately or where intended benefit of medication is not realised
increase risk of drug interactions and adverse reactions, impair adherence to medication and reduce quality of life
What are the pharmacokinetic changes in absorption in the elderly?
reduced saliva (solid oral formulations) increased gastric pH decreased GI motility Decreased GI and regional blood supply however little evidence that dosage needs to be altered due to this
What happens in terms of 1st pass metabolism in the elderly?
normally 1st pass metabolism can result in extensive metabolism of lipid soluble drugs (90-95%)
but in elderly reduced hepatic blood flow means reduced 1st pass metabolism and greater drug effect
even a minor reduction in 1st pass metabolism can result in significant increase in drug bioavailability
How does the pharmacokinetics of distribution change in the elderly?
distribution of body fat and water is altered in the older adults
- increased proportion of fat => increasing Vd of lipid soluble drugs = therefore lipid soluble drugs accumulate
- decrease in total body water =>decrease Vd for water soluble drugs therefore lower doses of water soluble drugs
reduced plasma protein conc - increase in free drug =>increased risk of toxicity
In terms of metabolism how does it change in the elderly?
hepatic metabolism of many drugs thought CYP50s decreases with age
- reduced metabolic clearance resulting in increased levels or duration of action of drugs extensively metabolised
pro drugs may be less effective
In terms of elimination how does it change in the elderly?
one of the most important pharmacokinetic changes is decreased renal elimination of drugs
GFR falls with age (60-70ml/min by 80)
renal tubular function also falls
therefore renally excreted drugs need dose adjustments - digoxin, gentamicin, lithium salts, opiates
What are the body systems affected during ageing?
heart
- changes in cardiac architecture, less compliance
- loss of pacemaker cells
- calcification of conduction system
- less response to catecholamines
endocrine changes
- reduction in hormone production, target sensitivity - oestrogen, testosterone, GH, IGF-1
skeletal muscle - atrophy
bones and joints- osteoporosis and osteoarthritis
CNS - vision and hearing
What pharmacodynamic changes occur with ageing?
changes in receptor sensitivity
reduction in receptor numbers
=> increases sensitivity to several drugs
What are the categories of impairment that appear in the elderly = geriatric giants?
immobility, instability, incontinence, and impaired intellect/memory
What are the frailty syndromes?
new definitions of geriatric giants
- falls => collapse, legs gave way
- immobility => sudden change in mobility
- delirium => acute confusion, muddledness
- incontinence=> change in continence
- susceptibility to SE of medication=> confusion with codeine, hypotension with antidepressants
What is the leading cause of mortality in older people >75?
falls are a major cause of disability - can lead to osteoporotic fractures
How can fall risk be minimised?
identify drugs causing falls
review of medication to reduce polypharmacy
adequate nutrition, especially with calcium and vit D to reduce risk of osteoporosis
multidisciplinary falls service
What drugs tend to cause falls?
anything acting on brain or circulation - usually mechanism leading to falls is:
1) sedation, with slowing of reaction times and impaired balance
2) hypotension or arrhythmias
Strong associations
- psychotropic medications (benzos, anxiolytics, hypnotics, sedatives, antidepressants, and anti-psychotic drugs)
- cardio medications
What drugs can cause impaired intellect/memory?
ageing associated with marked structural and neurochemical changes in CNS
dementia characterised by gradual deterioration of higher mental functions / intellectual capacity
anticholinergics, hypnotics and antidepressants can all cause intellectual impairment, confusion
cognitive impairment can lead to poor compliance
How can dosage forms affect compliance in the elderly?
simplify regimens (OD or BD) blister packs and bottle tops liquids and measuring sublingual tablets and dry mouths functional capacity
What tools are available to identify if elderly are taking appropriate medications?
beer’s criteria, medication appropriateness index, gerontoNet ADR risk score, STOPP/START
What is the STOPP/START criteria?
screening tool of older people’s prescriptions (STOPP) and screening tool to alert right treatment (START)
START = unless status is en of life these criteria are drug therapies to be considered where omitted for no valid clinical reasons
STOPP - prescriptions which are potentially inappropriate to use in patients >65
What needs to be done for older people with social care needs in terms of their medications?
need to plan collaboratively
- discuss managing medicines with each person and their carer
- note any requirements about managing medicines into the care plan
What drugs shouldn’t be given to patients with renal impairment and why?
nephrotoxicity= NSAIDs cause interstitial nephritis
Some drugs are renally eliminated and shouldnt be given or given with caution - vancomycin
some drugs are BOTH nephrotoxic and eliminated by kidneys
some are just ineffective - bendroflumethiazide, nitrofurantoin
How is renal function determined?
creatinine is a crude marker
can lead to incorrect categorization of patients with both “normal” and decreased GFR
MDRD formula can determine dosage adjustments in place of creatinine or creatinine clearance = mathematically modified serum creatinine with additional info from patients age, sex and ethnicity
What are the different stages of renal impairment in terms of eGFR?
Stage 1 = normal - >90 Stage 2 = mild - 60-89 Stage 3 =moderate - 30-59 Stage 4 = severe - 15-29 Established renal failure - <15
What drugs should be avoided in renal impairment?
aminoglycosides = nephrotoxic
metformin - increased risk of lactic acidosis
nitrofurantoin - not effective if eGFR <45
K supplements - risk of hyperkalaemia (ACEI and K sparing diuretics can potentiate this risk)
lithium - narrow therapeutic index
NSAIDs - avoid chronic kidney disease (exacerbate fluid overload and oedema)
What should you do if a patient develops an AKI?
aim is to prevent further injury and facilitate recovery of renal function
- assess circulating vol ad fluid admin
- prevent and/or treat hyperkalaemia and metabolic acidosis
- discontinue all potentially nephrotoxic drugs
- dose adapt drugs excreted by the kidneys to the patients renal function
- other supportive manage measures (may inc diuretics for fluid management)
What does prothrombin time reflect?
synthesis of clotting factors and is a useful measure of hepatic synthetic capacity, but does not reflect metabolic capacity
What can reduced hepatic function lead to with drug metabolism?
hypoproteinuria = affect protein binding
reduced clotting = increased sensitivity to warfarin, NSAIDs
What other mechanisms does hepatic insufficiency affect the actions of drugs?
biliary obstruction - prevents excretion of some drugs and prevent the actions of others
hypoalbuminaemia = complicate the interpretation of plasma phenytoin concentrations
reduced hepatic synthetic function will increase a patients sensitivity to drugs such as warfarin
What does hepatic insufficiency lead to?
fluid overload => avoid the use of drugs that could exacerbate this = NSAIDs, corticosteroids
What drugs can precipitate hepatic encephalopathy?
avoid :
- sedative drugs
- diuretics = can cause hypokalaemia
- drugs that can cause constipation
What factors need to be considered when prescribing in hepatic impairment?
whether the drug is highly protein bound (phenytoin) - decreased serum albumin can increase free drug
how the drug is metabolised ?
how the drug is excreted?
whether the drug is hepatotoxic
