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30 Cards in this Set
- Front
- Back
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Describe, in general, pharmacodynamic mechanisms of drug-drug intrxns.
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includes examples of interaction at receptor level and interactions due to independent effect of 2 drugs
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Describe, in general, pharmacokinetic mechanisms of drug-drug interactions.
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involves a change in the availability of drug at the site of action; involves drugs that induce alterations in absorption, distribution, metabolism or excretion of another compound
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Pharmacokinetic drug interactions alter drug delivery to site of action. What are the general mechanisms by which this occurs?
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alterations in absorption, distribution, metabolism or excretion
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3 parameters can be altered in order to decrease GI absorption. What are they?
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(1) binding
(2) gut motility (3) GI fluid pH |
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2 compounds can decrease tetracycline absorption in the gut. What are they?
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antacids and ferrous sulfate
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What bile acid sequestrant can decrease thyroxine absorption?
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cholestyramine
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What drug can decrease ketoconazole absorption and how does it do it?
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Cimetidine raises the stomach pH which decreases ketoconazole absorption.
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Consider a patient who is on the anti-hypertensive drug, guanethidine. What 4 drugs, if also given to this patient, could decrease guanethidine's effects and how?
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(1) tricyclic antidepressants
(2) ephedrine (3) amphetamines (4) phenothiazines They decrease guanethidine uptake by sympathetic nerve endings |
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What are 3 general mechanims that can enhance elimination in order to decrease drug delivery to site of action?
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(1) induce CYP enzymes
(2) induce P-glycoprotein transporter (3) increase renal elimination |
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Name 5 examples of CYP inducers.
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(1) phenobarbital
(2) carbamazepine (3) phenytoin (4) rifampin (5) St. John's Wort |
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St. John's Wort can enhance the elimination of drugs by inducing (blank) and (blank).
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St. John's Wort can enhance the elimination of drugs by inducing CYP enzymes and P-glycoprotein transporter.
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Name the 3 drugs with which St. John's Wort interacts to decrease their delivery to their sites of action.
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(1) indinavir
(2) cyclosporine (3) digoxin |
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Phenobarbital is a weak acid. How would changing the urine pH increase excretion of the drug?
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Alkalinization of urine would increase excretion of phenobarbital.
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Amphetamines are weak bases. How would changing the urine pH increase excretion of the drug?
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Acidification of urine would increase excretion of amphetamines.
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What are 5 mechanims that can decrease elimination in order to increase drug delivery to site of action?
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(1) inhibit xanthine oxidase
(2) inhibit CYP enzymes (3) inhibit MAO (4) decrease renal excretion (5) inhibit P-glycoprotein transporter |
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Allopurinol inhibits inactivation of (blank) and blocks formation of (blank)...see Fig. 1 on page 81
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Allopurinol inhibits inactivation of 6-mercaptopurine and blocks uric acid formation.
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What enzyme does allopurinol inhibit? What is the function of this enzyme?
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Allopurinol inhibits xanthine oxidase, which is responsible for production of uric acid.
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Azathioprine and 6-MP are metabolized by xanthine oxidase. What would happen if allopurinol were given to a patient taking these immunosuppressive drugs?
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Allopurinol would inhibit xanthine oxidase, which then could not metabolize the drugs. The result would be increased drug toxicity.
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Name 4 inhibitors of CYPs.
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(1) amiodarone
(2) erythromycin (3) ketoconazole (4) grapefruit juice |
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Which CYP inhibitor discussed in the notes would decrease warfarin elimination?
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Amiodarone
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Which CYP inhibitor discussed in the notes would decrease terfenadine elimination? What is the EKG finding related to the drug-drug interaction?
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Ketoconazole decreases terfenadine elimination and causes prolonged QT interval & ventricular arrhythmia.
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Terfenadine is an anti-histamine and responsible for cardiac toxicity. It has been replaced with its active metabolite. Name it.
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Fexofenadine or Allegra
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If you had a patient on the calcium-channel blocker, felodipine, what liquid would you tell him/her NOT to drink and why?
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Grapefruit juice b/c it inhibits CYPs and increases the plasma concentration of felodipine
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Tyramine occurs widely in foods that we eat and acts as catecholamine releasing agent. Which class of drugs would inhibit the enzyme that metabolizes tyramine? What would be the side effect?
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MAO inhibitors (anti-depressants) would inhibit metabolism of tyramine. The build up of tyramine is converted to norepinephrine, and this leads to hypertension.
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Which 2 classes of anti-depressants, if taken together, could result in serotonin syndrome?
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MAO inhibitors and selective serotonin reuptake inhibitor
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What drug could be given to a patient taking penicillin so as to increase the levels of the antibiotic? How does the drug work?
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Probenecid decreases renal excretion of penicillin
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What drug could be given to a patient taking lithium so as to increase the levels of the drug? How does the drug work?
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Thiazide diuretic decreases renal excretion of lithium
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What anti-arrhythmic agent would increase plasma concentrations of digoxin and how?
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Quinidine increases plasma concentrations of digoxin by inhibition of P-glycoprotein mediated transport
And possibly involves increased GI absorption, decreased biliary excretion and decreased renal excretion |
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Probenecid decreases renal excretion of penicillin. Would renal clearance of penicillin, then, be increased or decreased? What about plasma half-life?
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Renal clearance: decreased
Plasma half-life: increased |
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These 2 drugs have opposite effects in respect to changing drug concentrations of digoxin. Name them and how do they change the concentrations?
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1. St. John's Wort - induce P-glycoprotein transporter to decrese digoxin levels
2. Quinidine- inhibit P-glycoprotein transporter to increase digoxin levels |
