Prescribing in the Elderly Flashcards
What environment is required for an acidic drug to be absorbed?
Acidic environment
pH < 7.35
What are 3 examples of acidic drugs?
Phenytoin
Aspirin
Penicillin
What environment is required for a basic drug to be absorbed?
Basic environment
pH > 7.35
What are 3 examples of basic drugs?
Diazepam
Morphine
Pethidine
How does gastric pH change with age?
Gastric pH rises with ageing.
Why is gastric acidity lost with ageing?
Degeneration occurs of the parietal cells that produce HCl in the stomach.
Small bowel surface area also lost.
In which individuals is the natural loss of gastric acidity an issue?
Those with previous GI surgery
Those with feeding that bypasses the stomach
Those with transdermal patches or with oedema present
Are older patients at greater-risk of drug side-effects?
Yes,if the drug is basic - they absorb this more easily.
Which molecule binds to acidic drugs?
Albumin
It itself is a basic molecule.
Which molecule binds to basic drugs?
Alfa-1-acid glycoprotein
It itself is an acidic molecule.
What are albumin levels usually like in elderly patients?
Usually low.
What are alfa-1-acid glycoprotein levels usually like in elderly patients?
Usually raised.
Is muscle mass greater in the elderly?
No, fat mass is greater.
What does the increased fat mass of elderly people do for lipophilic drugs?
Increases their volume of distribution.
What is volume of distribution?
A theoretical volume into which a drug is fully dissolved in the plasma.
Indicates how long a drug will stay in the body.
What is half-life?
The time-taken for drug concentration to fall to half of its maximal concentration.
Do lipophilic drugs have a long half-life in elderly people?
Yes, as they have more fat, meaning the drug will stay around for longer.
What is first-pass metabolism?
Where a drug is greatly reduced prior to reaching circulation due to processing within the liver.
This is where most drugs are metabolised.
How does ageing affect first-pass metabolism?
Ageing reduces the ability of first-pass metabolism.
How does ageing affect GFR?
GFR drops.
Caused by decreased tubular secretions, size and renal bloodflow.
Is serum creatinine a reliable measure?
No, only indicates muscle mass.
Use creatinine clearance instead.
How is therapeutic index calculated?
50% of lethal dose/50% of effective dose
What should be given alongside opioids prophylactically, in order to prevent constipation?
Laxatives
What should not be given alongside levothyroxine?
Calcium supplementation - will impact absorption.
