Drug Interactions and Contraindications

Question 1

how does allopurinol work?

Answer 1

by inhibiting the enzyme xanthine oxidase
the same enzyme that metabolizes immunosuppressant drugs (azathioprine and mercaptopurine)

Question 2

when taking what drugs together increases the risk of QT prolongation?

Answer 2

macrolides
quinine
amiodarone

Question 3

when do contraindications occur?

Answer 3

when two meds interact to a point where it could potentially be fatal for the patient

Question 4

what happens when 2 drugs are contraindicated?

Answer 4

they cannot be dispensed to the patient

Question 5

what is the most common contraindication refer to?

Answer 5

pregnancy

Question 6

when are penicillins contraindicated in patients?

Answer 6

when there is an established allergy

Question 7

drug interaction of N-acetylcysteine?

Answer 7

no clinically significant drug interactions

Question 8

drug interaction of acetaminophen?

Answer 8

they are CYP inducers, just like phenytoin and carbamazepine

they increase rate of NAPQI production/ liver toxicity, after acetaminophen overdose

Question 9

drug interaction of activated charcoal?

Answer 9

prevents absorption of many drugs
For this reason, it is used in cases of toxicity / overdose

Question 10

drug interactions of acyclovir ?

Answer 10

probenecid increases acyclovir concentration.
interferon increases acyclovir concentration

Question 11

drug interaction of adenosine?

Answer 11

Dipyridamole blocks cellular uptake of adenosine.
Theophylline is a competitive antagonist at adenosine receptors.

Question 12

drug interaction of epinephrine

Answer 12

Beta-blockers can induce widespread vasoconstriction.

Question 13

drug interaction of aldosterone antagonists

Answer 13

ACE inhibitors; ARBs and other K-elevating drugs / supplements increase hyperkalemia risk.

Question 14

drug interactions of antacids/ alginates

Answer 14

Divalent ions reduce serum conc. Of drugs such as bisphosphonates, levothyroxine, tetracyclines, digoxin and PPIs. Antacids increase alkalinity of urine and so increase lithium and aspirin excretion.

Question 15

drug interaction of Albendazole

Answer 15

Plasma concentration lowered by phenytoin and carbamazepine. Cimetidine increases albendazole concentration.

Question 16

drug interaction of allopurinol

Answer 16

Toxicity risk of mercaptopurine / azathioprine increases because allopurinol inhibits xanthine oxidase. Amoxicillin increases skin rash risk. ACE inhibitors and thiazide diuretics increase risk of hypersensitivity reactions.

Question 17

drug interactions of alpha blockers

Answer 17

Other blood pressure lowering drugs increase risk of first-dose hypotension and hypotension risk generally thereafter.

Question 18

drug reactions of aminoglycosides?

Answer 18

Loop diuretics / vancomycin increase ototoxicity risk. Cyclosporine, platinum chemotherapy, cephalosporins and vancomycin increase nephrotoxicity risk.

Question 19

drug interactions of aminosalicylates

Answer 19

PPIs increase gastric pH and so may affect gastric coating of aminosalicylates. Lactulose reduces stool pH and so can prevent 5-ASA release into the intestine.

Question 20

drug interaction of amidarone

Answer 20

Amiodarone increases plasma concentration of digoxin, diltiazem and verapamil – increasing risk of AV block, bradycardia and heart failure.

Question 21

drug interaction of ACE inhibitors

Answer 21

Hyperkalemia risk increases when taken with other potassium-elevating drugs / supplements.Renal failure risk increases when taken with NSAIDs.

Question 22

Drug interactions of Amphotericin B

Answer 22

• Increased risk of flucytosine toxicity.
• Increased renal toxicity with cisplatin / diuretics.
• Increased risk of hypokalemia with corticosteroids.
• Renal damage with aminoglycosides / other nephrotoxic drugs.

Question 23

Drug interactions of Angiotensin-receptor blockers?

Answer 23

same as ACE inhibitors

Question 24

Drug interactions of antidepressants (SSRIs)

Answer 24

• Serotonin syndrome when taken with other serotonergic drugs, such as MAO inhibitors.
• Anticoagulants increase bleeding risk of SSRIs.
• Avoid with QT prolonging drugs such as macrolides, quinine and antipsychotics.

Question 25

Drug interactions of antidepressants (tricyclic/ related drugs)

Answer 25

Serotonin syndrome when taken with other serotonergic drugs, such as MAO inhibitors.
- TCAs augment antimuscarinic and sedative effects of other drugs.

Question 26

Drug interactions of antiemetics (H1 antagonists)

Answer 26

• Sedation risk increases when taken with other sedative drugs – benzodiazepines, Z-drugs etc.
• Anticholinergic effects more pronounced when taken with ipratropium / tiotropium etc.

Question 27

Drug interactions of antiemetics (Prochlorperazine and chlorpromazine)

Answer 27

QT prolongation risk increases when taken with antipsychotics, quinine, SSRIs, macrolides, fluoroquinolones and ciprofloxacin.

Question 28

Drug interactions of Antiemetics (5-HT3 antagonists)

Answer 28

Same QT prolongation interactions above.

Question 29

Drug interactions of antifungal drugs (Fluconazole)

Answer 29

• Fluconazole inhibits CYP enzymes – increasing plasma concentration of phenytoin, carbamazepine, warfarin, simvastatin and sulfonylureas. - - Reduces the antiplatelet effect of clopidogrel.
• Risk of arrhythmias increases when taken with QT prolonging drugs

Question 30

Drug interactions of antihistamines (H1 antagonists)

Answer 30

No major drug interactions. [Cetirizine / Loratadine / Fexofenadine etc.]

Question 31

drug interactions of antimotility drugs? (Loperamide)

Answer 31

P-glycoprotein inhibitors – such as quinidine, ritonavir and ketoconazole – increase loperamide levels.

Question 32

drug interactions of antimuscarinics (bronchodilators, ipratropium, tiotropium)

Answer 32

Low systemic absorption reduces risk of any major drug interactions.

Question 33

drug interactions of antimuscarinics (cardiovascular Atropine Hyoscine butylbromide)

Answer 33

Antimuscarinic effects more pronounced when taken with other drugs with the same effects, such as tricyclic antidepressants.

Question 34

drug interactions of antimuscurarinics