Drug Interactions

Question 1

Definition of a drug interaction

Answer 1

The administration of one agent that modifies the effect of a drug
Agent can be a pharmaceutical or recreational drug, a toxin, food, herbals, etc

Question 2

Pharmaceutical drug interactions

Answer 2

Interactions that occur prior to administration

Ex: incompatibility between 2 drugs mixed in an IV solution

Question 3

Pharmacokinetic drug interactions

Answer 3

Drug response is changed due to a change in tissue levels

How drugs effect ADME

Question 4

Pharmacodynamic drug interactions

Answer 4

Alterations in how tissues respond to drugs in the presence of an agent

Question 5

4 outcomes of drug interactions

Answer 5

Decrease in pharmacological activity
Increase in pharmacological activity
Increase in toxicity
Reduction in toxicity

Question 6

3 ways to prevent drug interactions

Answer 6

Understand drug mechanism (pharmacodynamics and pharmacokinetics)
Monitor blood levels of drugs with narrow TWs
Monitor parameters that may help characterize the early events of an interaction or toxicity

Question 7

3 ways pharmacodynamic interactions can cause the same effects as the intended drug

Answer 7

1. Same target
2. Same pathway
3. Complement pathway

Question 8

Chelation

Answer 8

The binding of drugs to metal ions (zinc, Mg, Ca, Fe, etc)

Question 9

Which two antibiotics chelate metals?

Answer 9

Tetracyclines and quinolones

Question 10

Tetracyclines and bone development

Answer 10

Tetracycline-calcium chelates get deposited in developing teeth and bone
Results in suppressed bone growth and permanent staining of teeth
Distributed across placental barrier and during lactation
Prohibited during pregnancy and in young children

Question 11

Effect of milk or antacid on tetracycline absorption

Answer 11

Decreased with milk or antacid

Question 12

How does GI motility affect absorption?

Answer 12

Absorption depends on food transit time with GI
Long transit time = more time for absorption (large meals and some drugs like morphine)
Short transit time = less time for absorption (fasting and laxatives)

Question 13

How do antacids affect:

1. Gastric pH
2. Absorption of weak bases
3. Absorption of weak acids

Answer 13

1. Increase
2. Increase
3. Decrease

Question 14

What is the effect of grapefruit juice on drug metabolism?

Answer 14

The naringin in citrus juices can inhibit CYP3A4 and PGP

This leads to an increase bioavaliability of drugs

Question 15

Grapefruit juice primarily inhibits CYP3A4 in the ____

Answer 15

Enterocytes

Not so much in the hepatocytes

Question 16

2 ways interactions at distribution can occur

Answer 16

Compete for plasma protein binding or tissue binding

Alter barrier function

Question 17

3 drugs that are highly bound to plasma proteins

Answer 17

Phenytoin
Tolbutamide
Warfarin

Question 18

2 drugs that can displace other drugs bound to proteins

Answer 18

Aspirin

Sulfonamides

Question 19

Reversible inhibitor

Answer 19

Two agents compete for the active site of enzyme

Question 20

Irreversible inhibitor

Answer 20

Bind with another agent rendering enzyme permanently inactive
Effect goes away once drug is cleared and new enzyme is produced

Question 21

St. John’s Wort

Answer 21

Hyperforin is active ingredient

Increases the expression of CYP3A4 through PXR activation

Question 22

Probenecid

Answer 22

Inhibits renal penicillin transport
Used in WW2 to reduce the amount of penicillin soldiers needed
It slows down transporters, and increases concentrations

Question 23

Where are drugs concentrated in the nephron?

Answer 23

In the distal nephron due to water reabsorption