Prescribing in the Elderly Flashcards
(40 cards)
What is meant by pharmacokinetics and pharmacodynamics?
Kinetics = how drug works on the body Dynamics = how the body works on the drug
What are the 4 parts of Pharmacokinetics?
A - Absorption
D - Distribution
M - Metabolism
E - Excretion
What difference occurs in the elderly when patients are prescribed BOTH atorvastatin and dabigatran (DOAC)?
This combination in the elderly increases the activity of dabigatran(DOAC) by 18%
Give examples of patient groups in which doses/strengths must be altered
Decreased renal function
Overweight/obese
What are the 2 main principles of drug absorption?
Acidic drugs require an acidic environment for absorption
Basic drugs require a basic environment for absorption
Give examples of acidic drugs which require an acidic envrionment for absorption?
Phenytoin
Aspirin
Penicillins
Give examples of basic drugs which require a basic environment for absorption?
Diazepam
Morphine
Elderly patients tend to have a higher gastric pH than younger patients. TRUE/FALSE?
TRUE
therefore their stomach is more basic and basic drugs get absorbed better
What condition may affect the absorption of drugs via a transdermal patch?
Oedema
What is the best way to deliver drugs in patients with dysphagia?
Liquid formulations (syrups etc)
What is the best way to deliver drugs to patients with an NG or PEG feeding tube?
Consult BNF to check if any tablets can be crushed for use in these devices
If patients are confused and refusing tablets, in what ways can these medications be delivered?
Patches
Intravenous infusions
Intramuscular injections?
If patients are null by mouth in preparation for surgery, which of their medications can and cant they omit?
- Antiplatelets should be taken
- Statins can be missed
- BP should be checked and judgement made on the reading (if they become hypertensive this can be sorted in surgery)
How are drugs distributed throughout the body?
- Bound to proteins
- Bound to lipids/dissolved in lipid
- Dissolved in water
What protein molecules are responsible for binding acidic and basic drugs?
ACIDIC = albumin (=> albumin itself is BASIC)
BASIC = Alpha-1 Acid Glycoprotein (=> it is ACIDIC)
Explain the ratio of albumin to alpha-1 acid glycoprotein in the elderly and how this contributes to pharmacodynamics?
Elderly have LOWER albumin than alpha-1 acid glycoprotein
=> they absorb more BASIC drugs
A loss in muscle mass contributes to increased fat in the elderly. How does this affect drugs which are lipid soluble?
Gives lipophilic drugs a bigger volume to distribute themselves across
=> drug has a longer half life
What can decrease the volume of distribution of certain drugs in the elderly?
Less body water in older people
=> less Vd for water soluble drugs (Lithium and Digoxin)
What factors can affect hepatic metabolism in the elderly?
Reduced liver function due to:
- decreased size
- decreased blood flow
- disease
- bio-transforming enzymes are reduced in the elderly
Why is it a problem if elderly patients cannot complete first pass metabolism?
Some drugs require this process to be broken down into their active parts
=> patient wont receive any benefit from drug if their liver cannot break it down
A small concentration of drug in the blood means what in regards to the volume of distribution?
Means the drug is very lipid soluble and dissolved in a large Vd and not much has dissolved in blood
What happens to lipid soluble drugs when patients become cahectic?
- Cahectic patients break down fat stores for energy/metabolism
- the drugs which have been stored in the adipose tissue are then released and drug concentrations increase if these are measured
Generally lower doses achieve same effect in the elderly. TRUE/FALSE?
TRUE
e.g. think alcohol
Why should drugs with a narrow therapeutic index be avoided?
there is not much between their effective concentration and their toxic concentration
=> dangerous for elderly patients with differences in pharmacodynamics
