Drug interactions

Question 1

Alcohol

Answer 1

• CNS depressans
  
  • additive CNS depression, sedation, ataxia, increased risks of accidents
• Acetaminophen
  
  • Increased formation of hepatotoxic metabolites of acetamonophen

Question 2

Antacid

Answer 2

• Digoxin, iron supplements, fluoroquinolones, ketoconazole, tetracyclines, thyroxine
  
  • Decreased gut absorption due to either to reaction with the affected drug or due to reduced acidity

Question 3

Antihistamines

Answer 3

• Antimuscarinis, sedatives
  
  • Additive effects with the drugs affected

Question 4

Antimuscarnic drugs

Answer 4

• Drugs absorbed from the small intestine
  
  • Slowed onset of effect because stomach emptying is delayed

Question 5

Barbiturates (phenobarbital)

Answer 5

• Azoles, CCB, cyclosporine, propanol,protease inhibitors, quinidine, steroids, warfarin, kinase inhibitors, methadone, ansd many other drugs metabolzied in the liver
  
  • Increased clearance of the affected drugs due to enzyme induction, possibly leading to decreases in drug effectiveness

Question 6

Beta blockers

Answer 6

• Insulin
  
  • masking of symptoms of hypoglycemia
• Prazosin
  
  • increased first dose syncope

Question 7

Bile acid-binding resins

Answer 7

• Acetaminophen, digitalis, thiazides, thyroxine
  
  • Reduced abdorption of the affected drug

Question 8

Carbamazepine

Answer 8

Cyclosporine, lidocaine, phenytoin, propanolol, quinidine, theophylline, warfarin, dofetilide

Reduced effect of other drugs because of induction of metabolism

Question 9

Cimetidine

Answer 9

BZ, lidocaine, phenytoin, propanol, quinidine, theophylline, warfarin, dofetilide

Risk of toxicity due to inhibition of metabolism or reduced renal excretion

Question 10

Disulfiram, metronidazole, certain cephalosporins

Answer 10

Ethanol

Increased hangover effect due to inhibition of aldehyde dehydrogenase

Question 11

Erythromycin

Answer 11

Carbamazepine, cisaparide, quinidine, sildenafil, SSRIs

Risk of toxicity due to to inhibition of metabolism

Question 12

Furanocoumarins (grapefruit)

Answer 12

Alprazolam, atorvastatin, cyclosporine, midazolam, nifedipine

Risk of toxicity due to inhibition of metabolism

Question 13

ketoconazole and other azoles

Answer 13

Benzodiazepines, cisapride, cyclosporine, fluoxetine, lovastatin, omeprazole, quinidine, tolbutamide, oral anticoagulants (warfarin, apixaban, rivaroxaban)

Risk of toxicity due to inhibition of metabolism, Increased bleeding with oral anticoagulants, myopathy with statins

Question 14

MAO inhibitors

Answer 14

• Catecholamine releasers (amphetamine, ephedrine)
  
  • Increased norepinephrine in sympathetic nerve endings released by the interacting
• Tyramine-containing foods and beverages
  
  • hypertensive crisis

Question 15

NSAIDs

Answer 15

• Anticoagulants
  
  • Increased bleeding tendency because of reduced platelt aggregation
• ACE inhibitors
  
  • Decreased hypertensive efficacy of ACE inhibitor
• Loop diuretics
  
  • reduced diuretic efficacy

Question 16

Phenytoin

Answer 16

Doxycycline, methadone, quinidine, steroids, verapamil, anticoagulants

Reduced effect of other drugs because of induction of metabolism

Question 17

Rifampin

Answer 17

Azole antifungal drugs, corticosteroids, methadone, sulfonylureas, oral anticoagulants

Reduced effect of other drugs because of induction of metabolism

Question 18

Ritonavir

Answer 18

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

Risk of toxicity due to inhibition of metabolism

Question 19

Salicylates

Answer 19

• Corticosteroids
  
  • Additive toxicity to gastric mucosa
• Heparin, oral anticoagulants
  
  • increased bleeding tendency
• MEthotrexate
  
  • decreased clearance, causing greater methotrexate toxicity
• Sulfinpyrazone, probenecid
  
  • Decreased uricosuric effect

Question 20

SSRIs

Answer 20

MAO inhibitors, meperidine, TCA, St. John’s wort

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

Question 21

thiazides

Answer 21

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

Question 22

A 55 year old patient currently receiving a drug for a psychiatric condition is to be starred on diuretic therapy for mild heart failure. Consideration should be given to the fact that thiazides are known to reduce the excretion of what drug_______

Answer 22

lithium

Question 23

A hypertensive patient has been using nifedipine for some time without untoward effects. If he experiences a rapidly developing enhancement of the antihypertensive effect of the drug, it is most likely due to

Answer 23

Furacocoumarins in grapefruit juice

Question 24

A patient suffering from a depressive disorder is being treated with imipramine. If he uses diphenhydramine for allergic rhinitis, a drug interaction is likely to occur because

Answer 24

Both drugs block muscarinic receptors

Question 25

If phenelzine is administered to a patient taking fluoxentine, which of the following is most likely to occur?

Answer 25

Agitation. muscle rigidity, hyperthermia, seizures

Question 26

Ajis a 45 year old man participating in a drug rehab program that supplies daily methadone. AJ reports that he needs more methadone to avoid withdrawal, since he started treatmetn for his tuberculosis. What drug might have caused this?

Answer 26

Rifampin

Question 27

The antihypertensive effects of captopril can be antagonized by which of the following?

Answer 27

NSAIDs

Question 28

Which drug has resulted in severe hematoxicity when adminsitered to a aptient being treated with azathioprine?

Answer 28

Allopurinol

Question 29

In patients with HIV infection, the inhibitory action of this agent on drug metabolism has clinical value

Answer 29

Ritonavir

Question 30

The drug enhances the toxicity of methotrexate by decreasing its renal clearance

Answer 30

Ibuprofen

Question 31

Concomitant use of St. John's wort is reported to increase the effectivity of \_\_\_\_\_\_

Answer 31

Ibuprofen