Drug Interactions Flashcards
Amiodarone is both a substrate and an inhibitor of CYP 450 2C9, 2D6, and 3A4. The pharmacist is aware that these medications must have their doses reduced when dispensing amiodarone: (Select ALL that apply.)
Answer
A Clarithromycin B Warfarin C Lithium D Pravastatin E Digoxin
B: Warfarin
E: Digoxin
Although digoxin is largely renally excreted, a percentage of the drug is metabolized hepatically. All these agents must have the doses decreased 30-50% when beginning amiodarone.
VN uses Imitrex for migraines 2-4 times each month. Recently she began to use Sarafem 10 mg daily for premenstrual dysphoric disorder. In addition, she uses Ultram once or twice daily for headache relief. She is at risk for the following symptoms: (Select ALL that apply.)
Answer
A Agitation B Tachycardia, sweating C Diarrhea D Muscle twitching or rigidity, shivering E Acute bradycardia
A Agitation B Tachycardia, sweating C Diarrhea D Muscle twitching or rigidity, shivering
Combining serotonergic agents increases the risk of serotonin syndrome. Patients should be carefully monitored when adding medications or increasing doses of serotonergic medications. The additive effects of fluoxetine (an SSRI) plus sumatriptan and Ultram puts this patient at risk of serotonin syndrome and they should be counseled to monitor for the symptoms.
Which of the following are inducers of CYP 450 3A4? (Select ALL that apply.)
Answer
A Trileptal B Dilantin C Tegretol D St John's wort E Neoral
A Trileptal B Dilantin C Tegretol D St John's wort
A patient with atrial fibrillation has been using warfarin for nine months. The INR is stable between 2.3 - 2.7. Select the correct interactions that can occur with the addition of other drugs: (Select ALL that apply.)
Answer
A
If nutritional drinks rich in vitamin K are added, the INR would decrease, bleeding risk would be lowered, but clot risk would be increased.
B
If ginkgo is added, the INR would stay at about the same level, but bleeding risk would be elevated.
C
If ginkgo is added, the INR would increase and bleeding risk would be elevated.
D
If high doses of fish oils are added, the bleeding risk may become elevated.
E
If nutritional drinks rich in vitamin K are added, the INR would increase and bleeding risk would be elevated.
A
If nutritional drinks rich in vitamin K are added, the INR would decrease, bleeding risk would be lowered, but clot risk would be increased.
B
If ginkgo is added, the INR would stay at about the same level, but bleeding risk would be elevated.
D
If high doses of fish oils are added, the bleeding risk may become elevated.
Ginkgo biloba, a natural (herbal) product used for memory improvement increases bleeding risk with no effect on the INR. Other natural products can also increase bleeding risk and should be evaluated. Nutritional products, including drinks and supplements, can include vitamin K. Any additions of vitamin K will decrease the INR. Check the product for vitamin K content.
Select the correct statements concerning the drug interaction between valproic acid and lamotrigine. (Select ALL that apply.)
Answer
A
Valproic acid inhibits lamotrigine metabolism.
B
This interaction increases the risk for a severe lamotrigine-induced rash.
C
This interaction increases the risk for severe valproate-induced pancreatitis.
D
When using these two medications at the same time, the appropriate Lamictal Starter Kit should be used.
E
This interaction increases the risk for severe valproate-induced hepatotoxicity.
A
Valproic acid inhibits lamotrigine metabolism.
B
This interaction increases the risk for a severe lamotrigine-induced rash.
D
When using these two medications at the same time, the appropriate Lamictal Starter Kit should be used.
Lamotrigine (Lamictal) has a risk of severe rash and requires a slow dose titration to reduce the risk. Inhibitors, such as valproate, will increase the risk of rash.
A patient with atrial fibrillation has been using warfarin for nine months. The INR is stable around 2.3. The patient is having a return of major depressive disorder, which she has had in the past and treated (unsuccessfully) with over-the-counter St. John’s wort. She has asked for a prescription agent that will not interact with her other daily medications. Which of the following agents would not increase bleeding risk in this patient and could be used for a suitable trial? (Select ALL that apply.)
Answer
A Bupropion B Effexor C Pristiq D Lexapro E Cymbalta
A
Bupropion
Incorrect
SSRIs and SNRIs increase bleeding risk. They are sometimes used together, but there is increasing awareness that this is dangerous. The INR does not increase, but the bleeding risk increases. Bupropion is primarily dopaminergic.
Which of the following statements concerning drug interactions are correct? (Select ALL that apply.)
Answer
A prodrug is a compound that is inactive until it is converted into an active form.
B
Induction has a “lag” effect which means that the full effect of adding an inducer is not seen right away, and it takes time for the induction to dissipate once the inducer has been discontinued.
C
Inhibition has a “lag” effect which means that the full effect of adding an inhibitor is not seen right away, and it takes time for the inhibition to dissipate once the inhibitor has been discontinued.
D
Many of the same inhibitors of cytochrome P 450 enzymes also inhibit the P-gp efflux pump.
E
The P-gp efflux pump moves drug from inside the body to outside by “pumping” the drug into the gut, where it can be eliminated.
A prodrug is a compound that is inactive until it is converted into an active form.
B
Induction has a “lag” effect which means that the full effect of adding an inducer is not seen right away, and it takes time for the induction to dissipate once the inducer has been discontinued.
D
Many of the same inhibitors of cytochrome P 450 enzymes also inhibit the P-gp efflux pump.
E
The P-gp efflux pump moves drug from inside the body to outside by “pumping” the drug into the gut, where it can be eliminated.
Incorrect
P-gp inducers and inhibitors have the same net effect on drug concentrations as CYP inducers and inhibitors. This is magnified in agents that affect both CYP and P-gp.
A patient has an estimated creatinine clearance of 25 mL/min. Her potassium level is 4.8 mEq/L. Which of the following drugs will increase her risk of hyperkalemia and should be used with caution:
Answer
A Mycamine B Enalapril C Kayexalate D Microzide E Zaroxolyn
B
Enalapril
ACEIs, such as enalapril, can cause additive potassium accumulation. Potassium is renally cleared and poor renal functioning can contribute to hyperkalemia. Addition of agents that can increase potassium levels should be carefully monitored.
A patient with COPD and seizures has been using theophylline and valproate for many years. Recently, the neurologist took the patient off valproate and started phenytoin due to an increase in seizure activity. The patient has been under a lot of stress lately and took up smoking again. She uses about 15 or 20 cigarettes daily. Which of the following statements are correct? (Select ALL that apply.)
Answer
A
The phenytoin will decrease the theophylline level and the patient may have impaired asthma control.
B
The smoking will decrease the theophylline level and the patient may have impaired asthma control.
C
The smoking will increase the theophylline level and the patient may experience toxicity.
D
Smoking is a potent enzyme inhibitor.
E
Smoking has little effect on theophylline levels but has a significant effect on clozapine levels.
A
The phenytoin will decrease the theophylline level and the patient may have impaired asthma control.
B
The smoking will decrease the theophylline level and the patient may have impaired asthma control.
Incorrect
Many inhibitors increase the theophylline level and many inducers decrease the theophylline level. Do not over-ride theophylline drug interactions without checking because this drug has a narrow therapeutic index-this means that it does not take much to drive the level down below efficacy, or up into the toxic range. Smoking (tobacco or marijuana) causes induction and can lower the efficacy of some substrates, including theophylline and clozapine.
Which of the following are inhibitors of CYP 450 3A4? (Select ALL that apply.)
Answer
A VFEND B Biaxin C Diovan D Cardizem E Grapefruit
A
VFEND
B
Biaxin
D
Cardizem
E
Grapefruit
Which of the following drugs can cause hearing damage? (Select ALL that apply.)
Answer
A Demadex B Amikacin C Tobramycin D Lasix E Adalimumab
A Demadex B Amikacin C Tobramycin D Lasix
CL is about to get on the waiting list for a kidney transplant. She has a creatinine clearance of 22 mL/min and experiences frequent bouts of hyperkalemia. She cannot use any medicines that elevate potassium because even small increases in potassium may trigger an arrhythmia. Which medications elevate potassium and would put her at risk for arrhythmia? (Select ALL that apply.)
Answer
A Altoprev B Demadex C Inspra D Aldactone E Yasmin
C Inspra D Aldactone E Yasmin
Incorrect
Potassium is renally cleared; severe renal disease causes hyperkalemia by itself, and potassium is cleared by dialysis. Additive potassium accumulation can be due to potassium-retaining agents.
A patient is using codeine for pain. She is a CYP 450 2D6 rapid metabolizer. What would be the effect on the conversion of codeine to morphine by the 2D6 enzyme?
Answer
A
The morphine concentration would decrease.
B
The morphine concentration would stay the same.
C
The morphine concentration would increase.
D
The morphine would become subtherapeutic.
E
Codeine is not metabolized by the 2D6 enzyme.
C
The morphine concentration would increase.
Incorrect
The use of codeine in breast-feeding women is to be avoided because if the woman is a rapid metabolizer of 2D6, the codeine to morphine conversion would increase. Morphine crosses readily into breast milk and the infant could suffer fatal respiratory depression. In 2017, the FDA changed the labeling of codeine to include a contraindication for children under 12 years of age.
The antifungal agents itraconazole, ketoconazole and voriconazole have safety issues that the pharmacist must address. These include the following: (Select ALL that apply.)
Answer
A
All are CYP 450 3A4 inhibitors; the dose of 3A4 substrates given simultaneously may need to be lowered.
B
Itraconazole and ketoconazole have pH-dependent absorption; avoid use with drugs that raise pH, such as antacids.
C
Voriconazole is an enzyme substrate and is subject to many drug interactions.
D
Voriconazole metabolism is initially first-order, but can become zero-order with higher doses, and toxicity can result.
E
With severe renal impairment it is safer to use IV voriconazole only, rather than the oral formulation, due to the excipients in the tablets and oral suspension.
A
All are CYP 450 3A4 inhibitors; the dose of 3A4 substrates given simultaneously may need to be lowered.
B
Itraconazole and ketoconazole have pH-dependent absorption; avoid use with drugs that raise pH, such as antacids.
C
Voriconazole is an enzyme substrate and is subject to many drug interactions.
D
Voriconazole metabolism is initially first-order, but can become zero-order with higher doses, and toxicity can result.
With a CrCl < 50 mL/min only one dose of voriconazole should be given IV; use oral voriconazole for subsequent dosing due to accumulation of the IV vehicle SBECD.
Which of the following drugs can cause hearing damage? (Select ALL that apply.)
Answer
A Doans Extra Strength B Vancomycin C Gentamicin D Edecrin E Hydrochlorothiazide
A Doans Extra Strength B Vancomycin C Gentamicin D Edecrin
Incorrect
Doans is an OTC salicylate.
