DDIs

Question 1

Alcohol

Answer 1

CNS depressants Acetaminophen

Additive CNS depression, sedation, ataxia, increased risk of accidents
Increased formation of hepatotoxic metabolites of acetaminophen

Question 2

Antacids

Answer 2

Digoxin, iron supplements, fluoroquinolones, ketoconazole, tetracyclines, thyroxine

Decreased gut absorption due either to reaction with the affected drug or due to reduced acidity

Question 3

Antihistamines (H1 blockers)

Answer 3

Antimuscarinics, sedatives

Additive effects with the drugs affected

Question 4

Barbiturates, especially phenobarbital

Answer 4

Azoles, calcium channel blockers, cyclosporine, propranolol, protease inhibitors, quinidine, steroids, warfarin, and many other drugs metabolized in the liver

Increased clearance of the affected drugs due to enzyme induction, possibly leading to decreases in drug effectiveness

Question 5

Beta blockers

Answer 5

Insulin, Prazosin

Masking of symptoms of hypoglycemia Increased first-dose syncope

Question 6

Bile acid-binding resins

Answer 6

Acetaminophen, digitalis, thiazides, thyroxine

Reduced absorption of the affected drug

Question 7

Carbamazepine

Answer 7

Cyclosporine, doxycycline, estrogen, haloperidol, theophylline, warfarin

Reduced effect of other drugs because of induction of metabolism

Question 8

Cimetidine

Answer 8

Benzodiazepines, lidocaine, phenytoin, propranolol, quinidine, theophylline, warfarin

Risk of toxicity due to inhibition of metabolism

Question 9

Disulfiram, metronidazole, certain cephalosporins

Answer 9

Ethanol

Increased hangover effect due to inhibition of aldehyde dehydrogenase

Question 10

Erythromycin

Answer 10

Carbamazepine, cisapride, quinidine, sildenafil, SSRIs

Risk of toxicity due to inhibition of metabolism

Question 11

Furanocoumarins (grapefruit juice)

Answer 11

Alprazolam, atorvastatin, cyclosporine, midazolam

Risk of toxicity due to inhibition of metabolism

Question 12

Ketoconazole and other azoles

Answer 12

Benzodiazepines, cisapride cyclosporine, fluoxetine, lovastatin, omeprazole, quinidine, tolbutamide, warfarin

Risk of toxicity due to inhibition of metabolism

Question 13

MAO inhibitors

Answer 13

Catecholamine releasers (amphetamine, ephedrine), Tyramine-containing foods and beverages

Increased norepinephrine in sympathetic nerve endings released by the interacting drugs Hypertensive crisis

Question 14

NSAIDs

Answer 14

Anticoagulants
Angiotensin-converting enzyme (ACE) inhibitors Loop diuretics, thiazides

ncreased bleeding tendency because of reduced platelet aggregation
Decreased antihypertensive efficacy of ACE inhibitor
Reduced diuretic efficacy

Question 15

Phenytoin

Answer 15

Doxycycline, methadone, quinidine, steroids, verapamil

Reduced effect of other drugs because of induction of metabolism

Question 16

Rifampin

Answer 16

Azole antifungal drugs, corticosteroids, methadone, sulfonylureas

Reduced effect of other drugs because of induction of metabolism

Question 17

Ritonavir

Answer 17

Benzodiazepines, cyclosporine, diltiazem, HMG-CoA reductase inhibitors, lidocaine, metoprolol, other HIV protease inhibitors, SSRIs

Risk of toxicity due to inhibition of metabolism

Question 18

Salicylates

Answer 18

Corticosteroids Heparin, warfarin Methotrexate
Sulfinpyrazone, probenecid

Additive toxicity to gastric mucosa
Increased bleeding tendency
Decreased clearance, causing greater methotrexate toxicity
Decreased uricosuric effect

Question 19

Selective serotonin reuptake inhibitors (SSRIs)

Answer 19

Monoamine oxidase (MAO) inhibitors, meperidine, tricyclic antidepressants, St. John’s wort

Serotonin syndrome (hypertension, tachycardia, muscle rigidity, hyperthermia, seizures)

Question 20

Thiazides

Answer 20

Digitalis, Lithium

Increased risk of digitalis toxicity because thiazides diminish potassium stores
Increased plasma levels of lithium due to decreased total body water

Question 21

Warfarin

Answer 21

Amiodarone, cimetidine, erythromycin, fluconazole, lovastatin, metronidazole
Aspirin, NSAIDs, quinidine, thyroxine
Barbiturates, carbamazepine, phenytoin, rifabutin, rifampin, St. John’s wort

Increased anticoagulant effect via inhibition of warfarin metabolism
Increased anticoagulant effects via pharmacodynamic mechanisms
Decreased anticoagulant effect due to increased metabolism