Pitfalls in Prescribing for older people - PowerPoint PPT Presentation

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Pitfalls in Prescribing for older people

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Title: Pitfalls in Prescribing for older people


1
Pitfalls in Prescribing for older people
  • Christopher Patterson
  • McMaster University,
  • Hamilton, Ontario
  • Canada

2
Objectives
  • Pharmacokinetic changes with age
  • Pharmacodynamic changes
  • Polypharmacy and interactions
  • Underprescribing
  • Medication errors

3
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4
Pharmacokinetics and aging
  • Absorption
  • Distribution
  • Metabolism
  • Excretion
  • Andtherapeutic effect at receptor level

5
Absorption
  • Changes in gastric pH (higher with aging)
  • Changes in GI transit time (increased with aging)
  • Changes in intestinal absorptive area (reduced)
  • BUT
  • Very little change in absorption of drugs

6
Absorption
  • Type of preparation often more important e.g.
    absorption of phenytoin
  • liquidgttabletgtcapsule
  • Interactions important e.g. calcium and
    levothyroxine

7
Distribution
  • Chronic illness associated with lower levels of
    serum albumin
  • Highly protein bound drugs may be affected by
    acute displacement eg. Warfarin and sulphonyureas
  • Acid 1 alpha glycoprotein elevated in acute
    illness may affect binding e.g.amitriptyline

8
Changes in body composition with aging
9
Water soluble vs. fat soluble drugs
  • H2O soluble-hydrophilic
  • Atenolol
  • Hydrochlorthiazide
  • Sotalol
  • Theophylline
  • Triazolam
  • Aminoglycosides
  • Fat soluble-lipophylic
  • Amiodarone
  • Diazepam
  • Haloperidol

10
Phenytoin zero order kinetics saturation of
protein binding sites
11
Metabolism
  • Mostly in liver
  • Phase 1
  • Oxidation, reduction, hydrolysis
  • Most affected by aging
  • Phase 2
  • Acetylation, glucuronidation, sulfation,
    glycine
  • Mostly unaffected by aging

12
Metabolism
  • Changes in hepatic metabolism with age

13
Serum t ½ (hours) and agePhase 1 metabolism
Young Old
Amitriptyline 14.7 27.2
Diltiazem 3.8 4.2
Diazepam 20 75
Warfarin 3.7 4.4
14
Serum t ½ unchangedphase 2 metabolism
  • Glucuronidation
  • Oxazepam
  • Temazepam
  • Lorazepam
  • Oxidation
  • Metoprolol
  • Acetylation
  • Hydralazine

15
Elimination
  • Elimination represents clearance of drug from the
    body
  • May be predominantly renal (water soluble drugs
    and metabolytes)
  • Biliary (e.g. some metabolytes of digoxin)
  • Other

16
Renal function and aging
17
Drugs predominantly eliminated via renal route
  • Digoxin
  • Aminoglycoside antibiotics
  • Lithium
  • Spironolactone
  • Vancomycin

18
Calculation of creatinine clearanceCockcroft-Galt
equation
19
Pharmacodynamic changes with aging
  • Increased receptor sensitivity
  • Opioids
  • Some benzodiazepines (e.g. nitrazepam)
  • Reduced response to ß adrenergic receptors
  • Isuproteronol
  • Impaired homeostasis
  • Antihypertensives (e.g. prazosin)

20
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21
Adverse Drug Reaction
  • Idiosyncratic
  • Unpredictable
  • Exaggeration of pharmacological effects
  • Predictable
  • Start low, go slow!

22
Incidence of Preventable AEs(Thomas Brennan
BMJ 2000320741)
Event type Incidence ages 16-64 Incidence age gt65
Diagnostic 0.22 0.27
Operative 0.76 0.99
Procedure 0.13 0.69
Drug 0.17 0.63
Fall 0.01 0.10
23
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24
Drug interactions
  • Absorption
  • Calcium and iron salts
  • Metabolism
  • Warfarin plus metronidazole
  • Pharmacodynamic
  • E.g. Glyceryl trinitrate and sildanefil

25
Conditions that affect drug metabolism or action
  • Malnutrition
  • Heart failure
  • Hepatic dysfunction (especially parenchymal
    disease cirrhosis)
  • Renal impairment or failure
  • And many others

26
Some drugs to be used with extreme caution in
older people
  • Anticholinergic drugs (antihistamine H1,
    tricyclic antidepressants etc.)
  • Long acting benzodiazepines (diazepam,
    chlordiazepoxide )
  • Theopylline
  • NSAIDs (indomethacin, )
  • Some opiates (pethidine, meperidine)
  • Antipsychotics

27
Antipsychotics and sudden death
Ray W et al N Engl J Med 2009 360 225
28
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29
SUMMARY
  • Changes in pharmacokinetics important
  • Especially renal changes (do calculate Cr/cl)
  • Pharmacodynamic changes not always pedictable
  • Watch for drug interactions and side effects
  • Do not overlook effects of illness plus aging

30
Serum t ½ (hours) and age
Young Old
Amitriptyline 14.7 27.2
Diltiazem 3.8 4.2
Sotalol 7.1 11.4
Warfarin 3.7 4.4
31
Undertreatment (Grymonpre Patterson CPS 2006)
Medication class Percent of optimal
ASA in ischemic heart disease 50
Beta blockers after MI 50
Hypertension 50
Warfarin for atrial fibrillation 15-44
Antidepressants 10-30
Osteoporosis after hip 10
32
Adverse Event
  • An unintended injury or complication which
    results in disability, death or prolonged
    hospital stay and is caused by health care
    management
  • Wilson R et al Med J Aus 1995163458

33
Adverse Events
  • Incidence in hospital 2.9-16.6
  • Meta analysis of incidence 6.7
  • Adverse drug events 50
  • Operative complications 30
  • Nosocomial infections 20
  • Preventable 30-60

34
Medication Errors
  • Sins of commission wrong drug, wrong dose, wrong
    patient, wrong time, or wrong route
  • Sins of omission not providing appropriate
    medication
  • Many errors do not cause adverse events (we are a
    very resilient species)

35
Detection of Adverse Events
  • Voluntary reporting 0.7
  • Computer monitoring 9.6
  • Chart review 13.3
  • Direct observation Higher
  • Jha K et al J Am Med Informatics Assoc
    5305

36
Why wont people report errors or near misses?
  • Not aware of error
  • Not aware of need to report
  • Patient apparently unharmed
  • Fear of disciplinary action or litigation
  • Unfamiliar with reporting mechanisms
  • Loss of self esteem
  • Too busy
  • Lack of feed back when errors are reported

37
Near Misses unique opportunities
  • Occur 3-300 times more often than errors
  • Fewer barriers to data collection
  • Higher incidence allows quantitative analysis
  • Proactive intervention
  • Reduces blame
  • Hindsight bias reduced
  • Barach P Small S BMJ 2000320759

38
Prescribing Problems
  • Illegible handwriting
  • Wrong drug
  • Wrong dose
  • Wrong frequency
  • Wrong route
  • Wrong patient
  • Name confusion

39
Name Confusion
  • Losec
  • amiloride
  • Fluoxetine
  • hydralazine
  • carbamazepine
  • chlorpropamide
  • thyroxine
  • Lasix
  • amlodipine
  • Paroxetine
  • hydroxyzine
  • carbimazole
  • chlorpromazine
  • thioridazine

40
Inappropriate Abbreviations
  • AZT
  • CPZ
  • HCl
  • HCT
  • MSO4
  • MTX
  • PIT
  • D/C
  • SC
  • gt,lt
  • _at_
  • ug
  • AU
  • HS
  • IU
  • OS
  • OD
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