Drug Drug Interactions

Question 1

what is the interaction between Warfarin and NSAIDs

Answer 1

Effect: Increased risk of bleeding.
Mechanism: Both drugs inhibit platelet function, and NSAIDs can cause GI bleeding, which is exacerbated by warfarin’s anticoagulant effect.

Question 2

what is the interaction between Digoxin and Amiodarone

Answer 2

Effect: Increased risk of digoxin toxicity.
Mechanism: Amiodarone inhibits the metabolism of digoxin, leading to increased plasma levels.

Question 3

what is the interaction between ACE Inhibitors and Potassium Supplements/Diuretics

Answer 3

Effect: Hyperkalemia (elevated potassium levels).
Mechanism: ACE inhibitors decrease the excretion of potassium, and potassium-sparing diuretics or supplements increase potassium levels.

Question 4

what is the interaction between Statins and CYP3A4 Inhibitors (e.g., Clarithromycin, Azole Antifungals)

Answer 4

Effect: Increased risk of myopathy and rhabdomyolysis.
Mechanism: CYP3A4 inhibitors reduce the metabolism of statins, increasing their plasma concentration.

Question 5

what is the interaction between SSRIs and MAOIs

Answer 5

Effect: Serotonin syndrome.
Mechanism: Excessive serotonin due to inhibition of serotonin metabolism by MAOIs and increased serotonin levels by SSRIs.

Question 6

what is the interaction between Warfarin and Antibiotics (e.g., Ciprofloxacin, Clarithromycin)

Answer 6

Effect: Increased risk of bleeding.
Mechanism: Antibiotics inhibit warfarin metabolism or reduce vitamin K-producing gut flora, enhancing warfarin’s anticoagulant effect.

Question 7

what is the interaction between Verapamil and Beta-blockers

Answer 7

Effect: Severe bradycardia or heart block.
Mechanism: Both drugs decrease heart rate and contractility through different mechanisms.

Question 8

what is the interaction between Phenytoin and Oral Contraceptives

Answer 8

Effect: Reduced contraceptive efficacy.
Mechanism: Phenytoin induces hepatic enzymes, increasing the metabolism of estrogen/progesterone.

Question 9

what is the interaction between Aspirin and Methotrexate

Answer 9

Effect: Increased methotrexate toxicity.
Mechanism: Aspirin decreases renal clearance of methotrexate, increasing its levels.

Question 10

what is the interaction between Ciprofloxacin and Theophylline

Answer 10

Effect: Increased theophylline toxicity.
Mechanism: Ciprofloxacin inhibits the metabolism of theophylline via CYP1A2 inhibition.

Question 11

what is the interaction between Lithium and Diuretics (e.g., Thiazides)

Answer 11

Effect: Lithium toxicity.
Mechanism: Diuretics reduce lithium clearance by decreasing sodium reabsorption in the kidneys, leading to increased lithium levels.

Question 12

what is the interaction between Clopidogrel and Omeprazole

Answer 12

Effect: Reduced efficacy of clopidogrel.
Mechanism: Omeprazole inhibits CYP2C19, the enzyme responsible for converting clopidogrel into its active form.

Question 13

what is the interaction between Sildenafil (Viagra) and Nitrates

Answer 13

Effect: Severe hypotension.
Mechanism: Both drugs cause vasodilation, leading to a dangerous drop in blood pressure when combined.

Question 14

what is the interaction between Tamoxifen and Paroxetine

Answer 14

Effect: Reduced efficacy of tamoxifen.
Mechanism: Paroxetine inhibits CYP2D6, an enzyme required to activate tamoxifen.

Question 15

what is the interaction between Rifampin and Oral Contraceptives

Answer 15

Effect: Reduced contraceptive efficacy.
Mechanism: Rifampin induces hepatic enzymes, leading to increased metabolism of oral contraceptives.

Question 16

what is the interaction between Cyclosporine and Grapefruit Juice

Answer 16

Effect: Increased risk of cyclosporine toxicity.
Mechanism: Grapefruit juice inhibits CYP3A4, reducing cyclosporine metabolism and increasing its levels.

Question 17

what is the interaction between Metronidazole and Alcohol

Answer 17

Effect: Disulfiram-like reaction (nausea, vomiting, flushing).
Mechanism: Metronidazole inhibits aldehyde dehydrogenase, leading to the accumulation of acetaldehyde when alcohol is consumed.

Question 18

what is the interaction between Oral Hypoglycemics (Sulfonylureas) and Fluoroquinolones

Answer 18

Effect: Hypoglycemia or hyperglycemia.
Mechanism: Fluoroquinolones can interfere with glucose metabolism and insulin secretion.

Question 19

what is the interaction between Macrolides (e.g., Erythromycin) and Calcium Channel Blockers

Answer 19

Effect: Hypotension or bradycardia.
Mechanism: Macrolides inhibit the metabolism of calcium channel blockers, increasing their plasma levels.

Question 20

what is the interaction between Anticholinergics and Cholinesterase Inhibitors (e.g., Donepezil)

Answer 20

Effect: Reduced efficacy of cholinesterase inhibitors.
Mechanism: Anticholinergics counteract the cholinergic effects of cholinesterase inhibitors used in Alzheimer’s disease.

Question 21

what is the interaction between Benzodiazepines and Opioids

Answer 21

Effect: Increased risk of respiratory depression and sedation.
Mechanism: Both drugs have CNS depressant effects, which can combine to cause severe sedation or respiratory failure.

Question 22

what is the interaction between Methotrexate and Trimethoprim-Sulfamethoxazole (Bactrim)

Answer 22

Effect: Increased risk of bone marrow suppression and nephrotoxicity.
Mechanism: Bactrim can increase methotrexate levels and enhance its toxic effects.

Question 23

what is the interaction between Valproic Acid and Carbapenems (e.g., Meropenem)

Answer 23

Effect: Reduced valproic acid levels, leading to loss of seizure control.
Mechanism: Carbapenems reduce the serum concentration of valproic acid by inhibiting its enterohepatic recirculation.

Question 24

what is the interaction between Monoamine Oxidase Inhibitors (MAOIs) and Tyramine-Containing Foods

Answer 24

Effect: Hypertensive crisis.
Mechanism: MAOIs inhibit the breakdown of tyramine, which can lead to excessive catecholamine release and severe hypertension.

Question 25

what is the interaction between Fluoroquinolones and Corticosteroids

Answer 25

Effect: Increased risk of tendon rupture.
Mechanism: Fluoroquinolones may weaken connective tissue, and corticosteroids can exacerbate this effect, increasing the risk of tendon damage.

Question 26

what is the interaction between Levothyroxine and Calcium Supplements

Answer 26

Effect: Reduced absorption of levothyroxine, leading to hypothyroidism.
Mechanism: Calcium binds to levothyroxine in the GI tract, reducing its absorption.

Question 27

what is the interaction between Metformin and Iodinated Contrast Media

Answer 27

Effect: Lactic acidosis.
Mechanism: Iodinated contrast can impair renal function, leading to accumulation of metformin and increased risk of lactic acidosis.

Question 28

what is the interaction between Linezolid and Serotonergic Drugs (e.g., SSRIs, SNRIs)

Answer 28

Effect: Serotonin syndrome.
Mechanism: Linezolid has MAOI-like properties and can increase serotonin levels, leading to serotonin syndrome when combined with other serotonergic agents.

Linezolid is a synthetic oxazolidinone antimicrobial drug. Linezolid is indicated for gram-positive infections

Question 29

what is the interaction between Phenytoin and DoxycyclineEffect:

Answer 29

Effect: Reduced efficacy of doxycycline.
Mechanism: Phenytoin induces hepatic enzymes, increasing the metabolism of doxycycline and reducing its effectiveness.

Question 30

what is the interaction between Cimetidine and Theophylline

Answer 30

Cimetidine is a gastric acid reducer used in the short-term treatment of duodenal and gastric ulcers

Effect: Increased theophylline toxicity.
Mechanism: Cimetidine inhibits CYP1A2 and CYP3A4 enzymes, decreasing the clearance of theophylline and increasing its levels.

Question 31

what is the interaction between Oral Anticoagulants (e.g., Apixaban, Rivaroxaban) and NSAIDs

Answer 31

Effect: Increased risk of bleeding.
Mechanism: Both classes affect platelet function and increase the risk of gastrointestinal and systemic bleeding.

Question 32

what is the interaction between Methotrexate and Proton Pump Inhibitors (PPIs)

Answer 32

Effect: Increased methotrexate toxicity.
Mechanism: PPIs can inhibit the renal clearance of methotrexate, leading to elevated levels and increased toxicity.

Question 33

what is the interaction between Clozapine and Carbamazepine

Answer 33

Effect: Increased risk of agranulocytosis.
Mechanism: Both drugs can cause bone marrow suppression, increasing the risk of severe neutropenia.

Question 34

what is the interaction between Tacrolimus and Azole Antifungals (e.g., Voriconazole)

Answer 34

Effect: Increased risk of tacrolimus toxicity.
Mechanism: Azole antifungals inhibit the CYP3A4 enzyme, decreasing the metabolism of tacrolimus and increasing its levels.

Question 35

what is the interaction between Bupropion and MAOIs

Answer 35

Effect: Hypertensive crisis.
Mechanism: Bupropion increases the release of norepinephrine, which can lead to dangerous hypertension when combined with MAOIs.

Bupropion (brand name Zyban) is a medicine originally used to treat depression, but it has since been found to help people quit smoking.

It’s not clear exactly how it works, but it’s thought to have an effect on the parts of the brain involved in addictive behaviour.

Question 36

what is the interaction between Spironolactone and ACE Inhibitors/ARBs

Answer 36

Effect: Hyperkalemia.
Mechanism: Both spironolactone and ACE inhibitors/ARBs reduce potassium excretion, leading to elevated potassium levels.

Question 37

what is the interaction between Fluoxetine and Tramadol

Answer 37

Effect: Increased risk of serotonin syndrome and seizures.
Mechanism: Fluoxetine increases serotonin levels, and tramadol’s serotonergic and pro-convulsant properties can exacerbate these effects.

Question 38

what is the interaction between Oral Contraceptives and Anticonvulsants (e.g., Carbamazepine, Phenytoin)

Answer 38

Effect: Reduced efficacy of oral contraceptives.
Mechanism: Anticonvulsants induce hepatic enzymes, increasing the metabolism of contraceptive hormones and reducing their efficacy.

Question 39

what is the interaction between Sulfonylureas and Beta-blockers

Answer 39

Effect: Masking of hypoglycemia symptoms.
Mechanism: Beta-blockers can mask the adrenergic symptoms of hypoglycemia (e.g., tachycardia, tremor), making it harder to recognize low blood sugar.

Question 40

what is the interaction between Aliskiren and ACE Inhibitors/ARBs

Answer 40

Effect: Increased risk of renal impairment, hyperkalemia, and hypotension.
Mechanism: Combining these drugs leads to dual blockade of the renin-angiotensin system, increasing the risk of adverse renal and cardiovascular effects.

Aliskiren is the first in a class of drugs called direct renin inhibitors
The National Institute for Health and Care Excellence (NICE) does not recommend
the use of aliskiren due to insufficient evidence of its effectiveness in resistant
hypertension.

Question 41

What medications does erythromycin interact with?

Answer 41

Aminophylline, Theophylline – increases plasma concentration of these (also these may reduce absorption of oral erythromycin)
Amiodarone – increased risk of ventricular arrhythmias when parenteral erythromycin given with amiodarone—avoid
Atomoxetine – increased risk of ventricular arrhythmias when parenteral erythromycin given with atomoxetine
Atorvastatin – increased risk of myopathy
Cimetidine – increases plasma concentration of erythromycin
Citalopram – avoidance of intravenous erythromycin advised by manufacturer of citalopram (risk of ventricular arrhythmias)
Clopidogrel – erythromycin possibly reduces antiplatelet effect of Clopidogrel
Colchicine – possibly increases risk of colchicine toxicity—suspend or reduce dose of colchicine (avoid concomitant use in hepatic or renal impairment)
Domperidone, dronedarone – increases plasma concentration of these = risk of ventricular arrhythmias – avoid
Fluconazole – avoid
Quetiapine – erythromycin increases plasma concentration of quetiapine—manufacturer of quetiapine advises avoid
Sildenafil – erythromycin increases plasma concentration of sildenafil—reduce initial dose of sildenafil for erectile dysfunction or reduce sildenafil dose frequency to twice daily for pulmonary hypertension
Simvastatin – increased risk of myopathy – avoid for duration of erythromycin course
Venlafaxine – avoidance of erythromycin advised by manufacturer of venlafaxine (risk of ventricular arrhythmias)
Digoxin – macrolides increase plasma concentration of digoxin (increased risk of toxicity)