Elderly - Drugs and Polypharmacy Flashcards
Explain the impact ageing has on organ systems, and the resultant effect this has on homeostasis?
- Ageing cause an impairment of organ function, which disrupts the complex interplay that occurs between organs, resulting in dyshomeostasis.
- This dyshomeostasis affects both the pharmacokinetics and pharmacodynamics of drugs.
Are ADRs preventable?
- Nearly one third of adverse drug events in ambulatory settings are preventable
What is Pharmacokinetics?
What an organism does to the drug.
- Absorption
- Distribution
- Metabolism
- Excretion
How does the physiological changes of old age impact the absorption of drugs?
- Changes affect the rate, rather than the extent of absorption from the GI tract.
- This may lead to a delay in onset of the drugs action.
For example:
- Reduction in saliva production - may result in a reduced rate of absorption of buccally administered drugs (e.g. GTN)
What drug used in the elderly actually shows an increased absorption in the elderly and why?
Levodopa - used in Parkinson’s treatment.
Because substantial mucosal metabolism of the drug occurs by the enzyme dopa-decarboxylase, this is at a reduced level in the elderly - leading to a substantial increase in absorption of Levodopa.
How do body changes as a result of ageing impact the distribution of drugs in the body?
-
Body composition changes
- Reduced muscle mass
- Increased adipose tissue
- Fat soluble drugs - increased duration of action (e.g. diazepam)
- Reduced body water
- Water soluble drugs - increased serum levels. (propranolol, atenolol)
-
Protein binding changes
- Decreased albumin
- Reduced binding, leading to increased levels of acidic drugs (increased risk of ADR)
- Decreased albumin
- Increased permeability across the Blood-brain barrier
What ageing changes is there on metabolism?
- Hepatic metabolism is affected by:
- Decreased liver mass
- Decreased liver blood flow
- Consequences
- Toxicity due to reduced metabolism/excretion
-
Reduced first pass metabolism
- Increase in bioavailability with some drugs e.g. propanolol
- Can cause a decrease in bioavailability of pro-drugs e.g. enalapril
What impact on drug excretion does ageing have?
- Renal function decreases with age.
- Reduces clearance and increases half-life of many drugs leading to toxicity.
What is Pharmacodynamics?
What the drug does to the organism.
What is the impact of ageing on Pharmacodynamics?
- Increased sensitivity to particular medicines.
- Due to:
- changes in receptor binding
- A decrease in receptor number
- ALtered translation of a receptor-initiated cellular response.
Examples:
- Diazepam - Increased sedation
- Warfarin - Increased anti-coagulation
Why is there interpersonal variability of pharmacodynamics?
- Wide variation between individuals in pharmacokinetic and pharmacokinetic response.
- Due to the extent each individual is affected by dyshomeostasis.
Why are drug-disease interactions so relevant in the aged population?
These people have more chronic diseases.
Diseases can affect pharmacokinetics.
Some drugs can even make diseases worse.
Why are drug-drug interactions so relevant in older people?
- Older people have more chronic diseases.
- More likely to be on multiple drugs.
- These drugs can interact, with impacts on pharmacodynamics and pharmacokinetics.
What are the prinicples when prescribing a drug for older people?
Why do you want to prescribe a drug?
- Symptom control
- To prevent future problems
Could the symptoms be a side effect of another drug?
Is there evidence for prescribing this drug to this person?
With the patient benefit?
What are the side effect risks?
Administration or compliance issues?
When starting a drug:
- Start low
- Go slow
- Be clear about review.
What is polypharmacy?
Why does this affect older people more?
Taking many drugs.
Older adults get more prescriptions.
Even older adults take on average 9 prescriptions and 2 OTCs.
Why?
- More disease
- More Dr visits
- Drugs are given to counteract SE of another drug.
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