Chapter 6: Drug Interactions

Question 1

Drug Interactions- when do they occur?

Answer 1

A drug interaction occurs when another substance alters a drug’s efficacy, effects, or safety.

Question 2

Drug-Drug interactions

Answer 2

Drug-drug interactions can occur whenever a patient takes two or more drugs.

Question 3

Consequences of Drug-Drug Interactions: When two drugs interact, there are three possible outcomes:

Answer 3

1. One drug may intensify the effects of the other,
2. One drug may reduce the effects of the other, or
3. The combination may produce a new response not seen with either drug alone.

Question 4

Drugs can interact through four basic mechanisms:

Answer 4

1. direct chemical or physical interaction,
2. pharmacokinetic interaction
3. pharmacodynamic interaction
4. combined toxicity

Question 5

When do direct interactions occur with drugs?

Answer 5

Direct interactions occur most commonly when drugs are combined in IV solutions.

Question 6

How do two drugs taken together alter pharmacokinetic interactions?

Answer 6

When two drugs are taken together, one may alter the absorption, distribution, metabolism, or excretion of the other

Question 7

How does drug interactions affect absorption?

Answer 7

Drug absorption may be enhanced or reduced by drug interactions.

Question 8

There are two principal mechanisms by which one drug can alter the distribution of another:

Answer 8

1. competition for protein binding
2. alteration of extracellular pH.

Question 9

Altered metabolism

Answer 9

Some drugs increase the metabolism of other drugs, and some drugs decrease the metabolism of other drugs.

Question 10

Drugs that increase the metabolism of other drugs do so by

Answer 10

Drugs that increase the metabolism of other drugs do so by inducing synthesis of hepatic drug-metabolizing enzymes.

Question 11

Drugs that decrease the metabolism of other drugs do so by

Answer 11

Drugs that decrease the metabolism of other drugs do so by inhibiting those enzymes.

Question 12

The majority of drug metabolism is catalyzed by

Answer 12

cytochrome (CY) P450 enzymes, which are composed of isoenzyme families

Question 13

Inducing agents

Answer 13

Drugs that stimulate the synthesis of CYP isoenzymes are referred to as inducing agents.

Question 14

What do inducing agents do?

Answer 14

Inducing agents can increase the rate of drug metabolism by as much as twofold to threefold.

Question 15

Drugs can alter all three phases of renal excretion:

Answer 15

1. filtration,
2. reabsorption, and
3. active secretion.

Question 16

Pharmacodynamic interactions are of two basic types:

Answer 16

1. Interactions in which the interacting drugs act at the same site and
2. Interactions in which the interacting drugs act at separate sites.

Question 17

Drug Interactions at the Same Receptor:

Answer 17

Interactions that occur at the same receptor are almost always inhibitory.

Question 18

Drug Interactions Resulting From Actions at Separate Sites:

Answer 18

Interactions resulting from effects produced at different sites may be potentiative or inhibitory

Question 19

Combined Toxicity when drugs interact

Answer 19

If drug A and drug B are both toxic to the same organ, then taking them together will cause more injury than if they were not combined.

As a rule, drugs with overlapping toxicity are not used together.

Question 20

Drug-Food Interactions:

Answer 20

Coadministration with food can significantly alter the efficacy and safety of
some drugs.

The primary mechanisms are by decreased or increased absorption and altered metabolism.

Question 21

Coadministration with food can significantly alter the efficacy and safety of
some drugs. How?

Answer 21

The primary mechanisms are by decreased or increased absorption and altered metabolism.

Question 22

Effect of Food on Drug Absorption:
Decreased absorption:

Answer 22

Food frequently decreases the rate of drug absorption and occasionally decreases the extent of absorption.

Question 23

What does reducing the rate of absorption mean?

Answer 23

Reducing the rate of absorption merely delays the onset of effects; peak effects are not lowered.

Question 24

What does reducing the extent of absorption mean?

Answer 24

In contrast, reducing the extent of absorption reduces the intensity of peak responses.

Question 25

Example of food reducing the extent of absorption

Answer 25

The interaction between calcium-containing foods and tetracycline antibiotics is a classic example of food reducing drug absorption.

Hence, if tetracyclines are administered with milk products or calcium supplements, absorption is reduced and antibacterial effects may be lost.

Question 26

What happens when food increases the extent of absorption of drugs?

Answer 26

When this occurs, peak effects are heightened.

Question 27

Example of when when food increases the extent of absorption of drugs

Answer 27

a high-calorie meal more than doubles the absorption of saquinavir [Invirase], a drug for HIV infection.

Question 28

Impact of Grapefruit on Drug Metabolism

Answer 28

Grapefruit juice can inhibit the metabolism of certain drugs, thereby raising their blood levels.

Question 29

Why should certain drugs be administered on an empty stomach?

Answer 29

the absorption of some drugs can be significantly decreased by food, and hence these drugs should be administered on an empty stomach.

Question 30

Why should some drugs be administered with meals

Answer 30

the absorption of other drugs can be increased by food, and hence these drugs should be administered with meals.

Question 31

To administer a drug with food means

Answer 31

To administer a drug with food means to administer it with or shortly after a meal.

Question 32

To administer a drug on an empty stomach means

Answer 32

To administer a drug on an empty stomach means to administer it at least 1 hour before a meal or 2 hours after.