Prescribing in the older patient Flashcards
What type of environment do acidic drugs require for absorption?
Acidic environment
What are some examples of acidic drugs?
Phenytoin
Aspirin
Penicillins
What are some drugs that increase pH and therefore reduce absorption of acidic drugs?
PPIs
What type of environment is required for absorption of basic drugs?
Basic environment
What are some examples of basic drugs?
Diazepam
Morphine
Pethidine
Why do older patients absorb basic drugs more?
They have an increased gastric pH and decreased small bowel surface area
What are some factors that increase levels of basic drug absorption (E.g. diazepam, morphine)
- Ageing
- Previous gastric surgery
- NJ or PEG feeding
- Transdermal patches and oedema
What protein binds acidic drugs in the blood?
Albumin (Basic)
What protein binds basic drugs in the blood?
Alpha-1 acid glycoprotein (Acidic)
How do binding proteins differ in older patients and how does this affect drug distribution?
They have higher levels of A1AG and lower levels of albumin so bind basic drugs more (E.g. diazepam, morphine)
What is meant by large Vd?
Lower concentration in sample (Swimming pool rather than bucket), so volume of water is higher
This means there must be more sequestered in fatty tissue, so the drug must be lipophilic
What is meant by low Vd?
Larger concentration in sample (Bucket rather than swimming pool), so volume of water is lower
This means there is more drug in the blood, and so must be hydrophilic
How does ageing affect Vd and half-life?
Older people have a lower body water, so hydrophilic drugs will have an even lower Vd
Half-life usually unaffected due to also reduced kidney function, unless there is pathological reduction in kidney function (E.g. AKI, CKD)
How does ageing affect hepatic metabolism?
Reduced liver function due to reduced liver size, reduced blood flow and higher incidence of liver disease
This reduces first-pass metabolism
Why is serum creatinine not a good measure of kidney function in older patients?
They have a lower muscle mass and so will produce less creatinine
What are some drugs that have a decreased effect in older age (Usually drugs have increased effect)
ß-blockers
What is the calculation for therapeutic index?
50% lethal dose ÷ 50% effective dose
What are some drugs with a narrow TI?
- Theophylline
- Warfarin
- Lithium
- Digoxin
- Gentamicin
- Vancomycin
- Phenytoin
- Cyclosporin
- Carbamazepine
- Levothyroxine
How does ageing affect therapeutic window?
It narrows therapeutic window making monitoring much more important
What are some drugs with common side effects?
- Warfarin
- Digoxin
- Insulin
- Benzodiazepines
- Diuretics
- NSAIDs
- Corticosteroids
- Anti-hypertensives
What should be given with opioids in the elderly?
Prophylactic laxatives (Cause constipation)
What should be given with steroids in the elderly?
Bone protection (Vitamin D + Bisphosphonates)
Blood glucose monitoring
Why are calcium and levothyroxine taken at different times of the day?
Calcium reduces levothyroxine absorption
How do NSAIDs effect diuretics and anti-hypertensives?
Decreases their effectiveness
What screening tool is used for prescribing the right drugs and stopping the wrong drugs in the elderly?
STOPP-START
