5. Polypharmacy and drug-drug interactions Flashcards
Why is polypharmacy and drug interactions important?
-causes distress to patient/ families
-may disrupt stable conditions
-potentially fatal
Define polypharmacy
Prescribing of multiple items to one individual
What is health inequality?
individuals living in the most deprived communities more likely to experience polypharmacy
Why are older people likely to experience polypharmacy?
-treated for multiple conditions
-altered pharmacokinetics and pharmacodynamics
-use of OTC and herbals
Why are patients with long term conditions/ co-morbidities?
-multiple disease states and multiple drugs combine to cause interactions and ADRs
-Altered pharmacokinetics
People with learning disabilities?
-potentially treated for multiple conditions
-inappropriate use for antipsychotic medications
What are examples of appropriate polypharmacy?
-manage conditions effectively
-primary or secondary prevention
-avoid tablet burden
-improves concordance
What are examples of problematic polypharmacy?
-tablet burden
-drug-drug interactions
-adverse drug reactions
-poor concordance
What are behavioural drug-drug interactions?
occur when one drug alters the patient’s behaviour to modify compliance with another drug
What are pharmaceutic drug-drug interactions?
occur when the formulation of one drug is altered by another before it is administrated
What are pharmacokinetic drug-drug interactions?
when one drug changes the systemic concentration of another drug, altering ‘how much’ and for ‘how long’ it is present at the site of action
What are pharmacodynamic drug-drug interactions?
when interacting drugs have either additive effects, in which case the overall effect is increased or opposing effects in which case the overall effect is decreased or ‘cancelled out’
Explain how polypharmacy patients more susceptible to drug interactions?
-multiple disease states and multiple drugs combine to cause interactions and ADRs
Explain how elderly patients more susceptible to drug interactions?
-usually have polypharmacy, also altered pharmacokinetics and pharmacodynamics
Explain how gender may increase susceptiblity to drug interactions?
-women are at greater risk of ADRs then men due to altered pharmacokinetics and pharmacodynamics
Explain how concomitant disease patients more susceptible to drug interactions?
-multiple disease states and multiple drugs combine to cause interactions and ADRs, also altered pharmacokinetics
Explain how ethnicity and genetics may increase susceptiblity to drug interactions?
-altered pharmacokinetics and pharmacodynamics
-lack of pharmaceutical company testing
Give examples of how absorption is altered in pharmacokinetic interactions
-pH changes in GI tract will impact on rate and amount of drug absorption
-chemical antagonism
-gastric motility
Give an example of how distribution is altered in pharmacokinetic interactions
-often occurs when two or more drugs compete for the same plasma protein, for example aspirin and warfarin
What are the two ways in which one drug can affect the metabolism of another drug?
-some drugs act as inducers= speed up the activity of specific CYP450 enzymes
-some drugs act as inhibitors= slow down the activity of specific CYP450 enzymes
What foods/ herbals are cytochrome P450 inducers?
-leafy green vegetables
-ethanol
-St Johns Wort
-Valerian
What foods/ herbals are cytochrome P450 inhibitors?
-grapefruit juice
-cranberry juice
-watercress
-gingko biloba
Give an example of how excretion is altered in pharmacokinetic interactions
-pH changes in the urine can act to speed up or slow down excretion
-competition for carriers in the renal tubule can slow excretion
What are the 3 main pharmacodynamic interactions? and why does this happen
- physiological antagonism e.g salbutamol and non-selective beta-blocker
- synergism e.g warfarin and clopidogrel
- interactions with food e.g MAOIs and marmite
This usually occurs when two or more drugs have the same or opposite effect
