Drug interactions

Question 1

What to avoid with tetracycline

Answer 1

Dairy products in the two hour window before and after taking tetracyclines because they inhibit the absorption of calcium or FE2+ salts

Question 2

Effects of antacids

Answer 2

Alter pH of stomach which will affect the absorption of other drugs

Question 3

What does digoxin do

Answer 3

Is a substrate for P-glycoprotein which takes out drugs from the cell

Question 4

How is cytochrome P450 metabolism relevant in drug interactions

Answer 4

If they go down the pathways, the two possible mechanisms for two drugs to show interactions with each other is:

• INhibition
• INduction (increasing the action of it )

Question 5

What does an inhibitor do

Answer 5

Increase the conc past the therapeutic window

Question 6

What does an inducer do

Answer 6

Decrease the conc below the therapeutic window

Question 7

What are some cytochrome P450 inhibitors

Answer 7

Macrolides eg erythromycin and clarithromycin

Question 8

Drug interactions with macrolides (cytochrome P450 inhibitors) and warfarin

Answer 8

Increase in INR so there is a risk of bleeding

Question 9

How to control the interaction of cytochrome P450 inhibitors and warfarin

Answer 9

Measure the INR at regular intervals and keep an eye on it and if it has risen then it is bad because there is a risk of bleeding

-If INR is too high, reverse the the action of warfarin with vitamin K

Question 10

Interactions of warfarin and quinolone antibiotics (ciprofloxacin)

Answer 10

Severe

-Enhance the actions of warfarin (would increase the INR)

Question 11

If someone is taking warfarin and ciprofloxacin, what do you do

Answer 11

Try to see if there is an antibiotic that doesnt interfere

Check the INR and decrease the dose of warfarin

Question 12

What shouldn’t be taken with simvastatin

Answer 12

Macrolides because they prevent the breakdown of simvastatin which increases toxicity

Question 13

What is enzyme induction

Answer 13

Increase activity of metabolising enzymes

Question 14

What do rifampicin and carbamazepine do

Answer 14

Potential to reduce the concentration of warfarin because they increase the quantity of cytochrome P450

Question 15

What to do when rifampicin or carbamazepine are taken with warfarin

Answer 15

Measure the INR

If the INR is dropping, then increase the dosage of warfarin

Question 16

What to avoid to with warfarin

Answer 16

NSAIDs ie aspirin and ibuprofen as they all increase bleeding

Question 17

What are NSAIDs associated with

Answer 17

Gastric bleeding which is enhanced by warfarin

Question 18

What foods to avoid when taking warfarin

Answer 18

Cranberry juice

Question 19

How do clopidogrel and proton pump inhibitors affect each other

Answer 19

Both are biotransformed by the same cytochrome P450, and clopidogrel needs to turn from the inactive form to the active form. However, some proton pump inhibitors prevent this from happening so the clopidogrel becomes ineffective

Question 20

What specific proton pump inhibitor do you avoid the using clopidogrel

-What to use instead

Answer 20

Omeprazole (therefore use another PPI or H2RA)

Question 21

What antibiotics to avoid when taking warfarin

Answer 21

Erythromycin and ciprofloxacin (leads to enhanced bleeding)

Question 22

Effects of taking simvastatin and amlodipine

Answer 22

Amlodipine doubles the effect of simvastatin so you should take the lowest dose of simvastatin