drug-drug interactions Flashcards
define the term drug interaction
modification of a drugs effect by prior or concomitant administration of another Drug, Herb, Foodstuff, Drink
when has a drug interaction occured
pharmacological effect of two or more drugs given together is not just a direct function of their individual effects
what are the types of drugs
drug, herbal, food, drink, pharmacogenetics
whats an object drug
The Drug whose Activity is effected by such an Interaction
what is the precipitant
The agent which precipitates such an interaction
what are the factors that modify its action
food, smoking, alcohol, herbs
are the interactions of drugs always detrimental? if not give examples
no and treatment of hypertension and parkinsons
what does a small therapeutic index mean
small change in blood levels can induce profound toxicity
what are the mechanisms of drug interactions
Absorption
Distribution
Metabolism
Elimination
what is pharmacodynamic interactions
Antagonistic Interactions
Additive or synergistic interactions
Interactions due to changes in drug transport
Interactions due to fluid and electrolyte disturbances
Indirect pharmacodynamic interactions
what are pharmacokinetic interactions
Absorption
Distribution
Metabolism
Elimination of another drug
what are absorption interaction mechanisms
Formation of insoluble complexes
Altered PH.
Altered bacterial flora..
Altered GIT motility.
why is the GI tract complex
Most of this type of interactions result in changes in absorption rate rather than the extent of absorption
when is delayed absorption important
when a drug has a short half life or when we want high plasma levels rapidly
what happens to drugs in the GI tract
drugs bind to eachother
what is absorption affected by
ionisation which is dependent on pH
where is bacterial flora usually found?
large bowel
what does broad spectrum antibiotics destroy?
normal gut flora
where are most oral medicines absorbed?
small intestines
where are the sites of action for distrubution of drugs
protein-protein displacement
when does Protein-binding displacement occur?
when there is a reduction in the extent of plasma protein binding of a drug caused by the presence of another drug
what does The displacement of a drug from plasma protein results in
increased bioavailability of the displaced drug
what are the two most important proteins?
albumin and alpha glycoprotein
when does drug interactions involving metabolism happen
when one drug induces or inhibits the metabolism of another
where does metabolism of drugs occur and via what system
liver, via the cytochrome P450
what drugs inhibit the cytochrome system
clarithromycin and erythromycin
which drugs are potent inducers of cytochrome P450
barbiturates, carbamazepine, phenytoin, rifampacin and tobacco smoke
what 2 drugs increase metabolism of ciclosporin by inducing CYP 3A4
Rifampicin
St john’s wort
where are most drugs excreted
urine or bile
what kind of secretion are changes in GFR
tubular
when do Pharmacodynamics interactions occur
when the pharmacodynamic actions of a drug are changed due to presence of another drug either acting directly on the same receptor) or indirectly on different receptors.
what are pharmacodynamic interactions
direct, indirect, antagonistic and synergistic/ agonist
what is direct antagonism
beta-blockers such as atenolol will block the actions of agonists e.g. bronchodilators such as salbutamol
what are synergistic interactions
When two drugs with the same pharma-cological effect acting on the same receptor are give concurrently
