Drug to drug interactions Flashcards
what is the definition of a drug to drug interaction?
A drug interaction has occurred when the pharmacological effect of two or more drugs given together is not just a direct function of their individual effects ie the outcome of being on multiple drugs
what types of drug- drug interactions are there?
drug- drug herbal-drug food- drug drink-drug pharmacogenetic interactions (caused by genetic differences)
what is the ‘object drug’
the drug whose activity is effected by such an interaction
what is the precipitant?
the agent which causes a drug- drug interaction. ie the drug that once administered results in reaction with object drug
what are some non-detrimental drug interaction outcomes?
treating hypertension (high BP) treating Parkinsonism
define polypharmacy
loose definition but usually means being on 4 or more drugs
what type of drug is warfarin?
an anticoagulant
name some drugs involved with serious interactions
lithium digoxin warfarin theophylline (asthma) OCP- oral contraceptives gentamicin- anti bacterial erythromicin- pnuemonia, acne neuroleptics- anti psychotics
what would Digoxin do if you took it
may slow your heart rate down
what is so dangerous about drugs that cause serious drug to drug interactions
they are potent drugs with a narrow therapeutic index ie doesn’t take much to become toxic or ineffective- small change in blood levels can induce profound toxicity
therapeutic drug monitoring?
checking for plasma levels of a drug to make sure the levels are within the correct range
who are susceptible to serious drug interactions?
those who are already on a number of medications are at a high risk
also the elderly, young, critically ill and patients undergoing complicated surgical procedures, those with chronic conditions
which chronic conditions can put patients at higher risk of serious drug interactions
liver disease
renal impairment
epilepsy
asthma
why are adolescents less likely to have serious drug to drug interaction?
more likely to have a good physiology
which things can one drug alter in another drug
Absorption
distribution
metabolism
elimination of another drug
changes in GI bacterial flora?
bacterial flora usually found in the large bowel and a broad spectrum of antibiotics destroy the normal gut flora.
This may lead to failur of oral contraceptive or digoxin toxicity
which drugs does Cholestyramine resin bind to in the GI tract?
warfarin and digoxin
which 3 things reduce H+ and so increase pH of blood?
H2 antagonists, proton pump blockers and anti acids
protein-binding displacement?
occurs when there is a reduction in the extent of plasma protein binding of a drug caused by the presence of another drug- results in increased bio-availability of the displaced drug (only unbound drugs are pharmacologically active)
what are the two most important proteins involved in drug binding?
albumin
alpha1-glycoprotein
Drugs that are very highly protein bound
diazepam
ibuprofen
Valproic acid- not to be used in females of child bearing age
warfarin
drug interactions involving metabolism occur when?
when one drug induces or inhibits the metabolism of another
metabolism
where does metabolism usually occur and via which system?
in the liver
via the cytochrome P450 system (a group of enzymes involved in metabolism of drugs)
which drugs inhibit the cytochrome P450 system?
erythromicin clarithromycin omeprazole CCBs cimetidine ie they inhibit a small group of drugs that are metabolised by cytochrome p450 system
which drugs induce the cytochrome P450 system?
phenytoin, tobacco smoke, carbamazepine
enzyme induction causes loss of effect of the drug because you get through the drug more rapidly
what do the effects of enzyme induction depend on?
age
disease
genetics
concurrent drug therapy
what does Rifampicin do and what does it treat?
increases metabolism of ciclosporin by inducing CYP 3A4
bacterial infections including tb
what is st john’s wort
a herbal remedy that can cause rejection of drug ie reduced effect
where are digoxin and lithium excreted?
kidney
which 2 changes can alter elimination/excretion of a drug
changes in how well the kidney filters waste from the blood (GFR) or tubular secretion
pharmacodynamics interactions
occur when what the drug does to the body is changed due to the presence of another drug either acting directly on the same receptor or indirectly on different receptors
like beta blockers or ace inhibitor
what are ACE inhibitors?
heart medications that widen, or dilate, your blood vessel- increases the amount of blood your heart pumps and lowers blood pressure.
what is a beta blocker?
medications that reduce your blood pressure. Beta blockers work by blocking the effects of the hormone adrenaline. When you take beta blockers, your heart beats more slowly and with less force, thereby reducing blood pressure.
what 4 typed of pharmacodynamic interactions are there?
indirect
direct
antagonistic
synergistic/agonistic
direct antagonism
beta blockers such as atenolol will block actions of agonists
what are synergistic interactions
when two drugs with the same pharmacological effect acting on the same receptor are given concurrently- the effect may be additive or multiplicative (even bigger than the 2 added together)
indirect agonism
3 examples and resultant effect
benzodiazepines and tricyclics or alcohol, atenolol
warfarin and NSAIDs
atenolol and verapamil (this could lower heart rate way too much)
all act in different ways but togther have a massive affect on CNS depression
2 examples of indirect antagonism
NSAIDs and antihypertensive medication
NSAIDs and treatment for heart failure
NSAIDs lower BP and antihypertensive increases it
