eScript Flashcards
what side effects can oxybutynin cause?
Oxybutynin is an antimuscarinic drug, the adverse effects of which include dry mouth, constipation, blurred vision and occasionally cognitive impairment
Older adults may be more susceptible to these adverse effects
Cognitive impairment can increase the risk of non-adherence
what is adherence?
“The extent to which the patient’s behaviour matches agreed recommendations from the prescriber”
what is compliance?
the extent to which the patient’s medicines-taking behaviour matches the prescriber’s recommendations
OLD TERM
why do thiazide diuretics cause gout?
increase uricaemia, which may precipitate gout in susceptible patients
what drug commonly causes myalgia?
statins
The risk is increased if the statin is prescribed at a high dose or if it is prescribed in combination with a fibrate, macrolide antibaterial or certain calcium-channel blockers.
Treatment should be discontinued if creatine kinase is 5 times the upper limit of normal or if symptoms are severe.
what common drug may cause mood changes?
systemic corticosteroids
what is bioavailability?
the extent to which a drug reaches the systemic circulation where it is available to act at the ‘effector site’ (e.g. the brain for a sedative effect
what is bioavailability of IV drugs?
100%
what is the pathway of oral drugs into systemic circulation?
mouth-> stomach (disintegration of the formulation)-> small intestine (absorption) -> liver (metabolised)-> absorbed into systemic circulation-> effector site -> kidneys (elimination)
are lipid-soluble drugs absorbed better or worse?
better
are protein-bound drugs absorbed better or worse?
worse
what drug metabolism can erythromycin inhibit?
warfarin
what drug metabolism can phenytoin induce?
antiepileptics
what drug metabolism can rifampicin induce?
oestrogen in COCP
what drugs should not be crushed and why?
MR drugs e.g. nifedipine
Enteric-coated e.g. aspirin
they can alter pharmacokinetic profile of a drug by breaking down coating of a drug which are designed to prevent breakdown, so it is absorbed quicker
other side effects of crushing drugs
bad taste e.g ibuprofen
damage skin of handlers
what is a pro-drug and examples?
when a drug is metabolised in the liver to an active form e.g. codeine to morphine, azathioprine to mercaptopurine
why are drugs metabolised in the liver?
Once absorbed, the body treats all drugs as foreign molecules. It will attempt to metabolise them in the liver to water soluble compounds and excrete them via the urine.
Pre-systemic metabolism of oral drugs (termed the ‘first-pass effect’) can significantly reduce drug bioavailability (propranolol, morphine).
what is Volume of Distribution (Vd)
the theoretical volume of fluid that would be needed to achieve the actual plasma drug concentration
Vd is typically reported in (ml or litre)/kg body-weight
If a 1 gram (1000 mg) dose of drug X, given intravenously gives a plasma-drug concentration (Cp) of 50 milligrams/litre, then
Vd = 1000/50 Vd = 20 litres
will drugs with a high Vd have a high or low plasma concentration
low
what type of drugs have a low Vd?
highly water soluble (e.g. gentamicin, atenolol, and insulin) or extensively protein-bound (e.g. warfarin) as they stay in the plasma (blood)
what type of drugs have a high Vd?
highly lipid soluble (e.g. digoxin, morphine, and diazepam) as they go out of plasma into tissues and organs
when is protein binding important in warfarin?
In general, drugs are not metabolised when they are protein-bound. However, protein-bound drugs can act as a ‘reservoir’ of the active drug. For example, warfarin is 97% protein bound. The remaining 3% - the fraction unbound (fu) is active. If another drug (e.g. sulphonamide component of co-trimoxazole) were to displace warfarin from its plasma-protein, the risk of adverse effects and toxicity will transiently increase
what can affect plasma protein concentration?
disease states
pregnancy
malnutrition