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Drug Interactions CH.6
Terms in this set (49)
Drug-drug interactions can occur whenever a patient takes....
two or more drugs
When two drugs interact, what are the three possible outcomes?
1) one drug my intensify the effects of the other
2) one drug my reduce the effects of the other
3) the combination may produce a new response not seen with either drug alone
What ia a potentiative interaction?
When a patient is taking two medications, one drug may intensify the effects of the other
When combined with ampicillin, sulbactam...
inhibits the bacterial enzymes which inactivate ampicillin and prolongs and intensifies ampicillin's therapeutic effects
When aspirin and warfarin are combined...
The risk of bleeding is significantly increased
Interactions that result in reduced drug effects are termed...
If propranolol and albuterol are taken together...
propranolol can reduces albuterol's therapeutic effects of bronchi dilation and can result in detrimental therapeutic failure.
Naloxone is a drug that...
blocks morphine's actions and can reverse all symptoms of toxicity.
Drugs interact through four basic mechanisms:
1) direct chemical or physical interaction
2) pharmacokinetic interaction
3) pharmacodynamic interaction
4) combined toxicity
Drugs combined in IV solutions frequently produces...
Never combine two or more drugs in the same container unless...
it has been established that a direct interaction will not occur.
Since dilution decreases chemical interactions, significant interactions within the patient are...
much less likely than in IV solutions.
Mechanism by which one drug can alter the absorption of another:
- elevating gastric pH can increase or decrease the ability of drugs to cross membranes (antacids)
- accelerating their passage through the intestine (laxatives)
- depress peristalsis and increase transit time and absorption (opioids)
- Induce vomiting
- One drug can absorb other drugs onto themselves
- One drugs reduction of regional blood flow can reduce absorption of others in that region.
Two mechanisms by which one drug can alter the distribution of another
1) competition for protein binding
2) alteration of extracellular pH
When two drugs bind to the same site on plasma albumin, binding of one or both agents is _____, causing....
Reduced - causing plasma levels of free drug to rise which can increase therapeutic effects of the free drug. This is usually not an issue due to rapid elimination, unless the patient has liver problems or renal problems
A drug with the ability to change extracellular pH can alter...
the distribution of other drugs
Drugs that alter pH and thereby the distribution of other drugs are often used in the management of...
Drugs that increase the metabolism of other drugs do so by...
inducing synthesis of hepatic drug-metabolizing enzymes
Drugs that decrease the metabolism of other drugs do so by...
inhibiting the synthesis of hepatic drug-metabolizing enzymes
The majority of drug metabolism is catalyzed by...
cytochrome P450 (CYP) group of enzymes. Mostly CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP3A4
Drugs that stimulate the synthesis of CYP isoenzymes are referred to as...
Inducing agents can increase the rate of drug metabolism by as much as...
two to threefold which develops over 7 to 10 days.
A classic example of a drug inducing agent is...
When an inducing agent is taken with another medicine the dosage of the other medicine may...
need to be adjusted - or increased
When a patient discontinues an inducing agents, dosages of other drugs may need...
to be lowered
If drug A inhibits the metabolism of drug B, then levels of drub B will...
rise. The result may be beneficial or harmful
Drugs can alter _______ of renal excretion
all three phases: filtration, reabsorption and active secretion
Glomerular filtration can be decreased by drugs that reduce....
cardiac output - a reducation in cardiac output decreases renal blood flow, which decreases drug filtration at the glomerulus, which in turn decreases the rate of drug excretion
By altering urinary pH, on drug can alter...
the ionization of another which will increase or decrease the extent to which that drug undergoes passive tubular reabsorption.
Competition between two drugs for active tubular secretion can...
decrease the renal excretion of both agents
P-glycoprotein is a transmembrane protein that transports a wide variety of drugs out of...
cells - including cells of the intestinal epithelium, placenta, blood-brain barrier, liver, and kidney tubules
Most drugs that induce or inhibit P450 also have the same impact on...
PGP - P-glycoprotein
Drugs that induce PGP can have these impacts on other drugs:
- reduced absorption - by increasing drug export from cells of intestinal epithelium
- Reduced fetal drug exposure - increasing drug export from placental cells into maternal blood
- Reduced brain drug exposure - increasing drug export from cells of brain capillaries
- Increased drug export from liver into the bile and from renal tubular cells into urine
Pharmacodynamic interactions are of two types:
1) interaction in which the interacting drugs act the at the same site
2) interaction in which the interacting drugs act at separate sites
- may be potentiative or inhibitory
Interactions that occur at the same receptor are almost always...
If two drugs have different mechanism of action and act at separate sites, if both drug influence the same physiologic process then...
one drug can alter responses produced by the other - this can be potentiative or inhibitory.
If drug A and drug B are both toxic to the same organ, than taking them together...
will cause more injury than if they were not combined.
Ways to minimize adverse drug reactions:
- minimize the number of drugs the patient receives
- take a thorough drug history
- monitor for reactions and adjust the regimen accordingly
Food frequently _______ the rate of drug absorption, and occasionally ____ the extent of absorption.
Reducing the rate of absorption...
delays the onset of effects
Reduce the extent of absorption...
reduces the intensity of peak responses
A classic example of food reducing drug absorption is...
calcium containing foods and tetracycline antibiotics
High-fiber foods can...
reduce absorption of some drugs such as digoxin
When food increases the extent of absorption...
peak effects are heightened
Grapefruit juice can inhibit...
the metabolism of certain drugs and thus raise their blood levels
What isoenzyme of cytochrome P450 does grapefruit juice inhibit?
Foods rich in vitamin K can reduce the effects of...
warfarin - which acts by inhibiting vitamin K-dependent clotting factor
To administer a drug on an empty stomach means...
to administer at least 1 hour before a meal or 2 hours after
The combination of an MAO inhibitor with tyramine-rich food...
increases drug toxicity
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