Drug Interactions

Question 1

How many Americans take at least one prescription drug?

Answer 1

70%

Question 2

How many Americans take at least two prescription drugs?

Answer 2

> 50%

Question 3

How many Americans take at least 5 prescription drugs?

Answer 3

20%

Question 4

What is a drug interaction?

Answer 4

A situaiton in which a substance (usually another drug) affects the activity of a drug when both are administered together
This can be synergistic, or antagonistic, or a new effect can be produced that neither produces on its own

Question 5

Antagonism

Answer 5

Biologic or clinical response to a drug is reduced by administration of a second drug

Question 6

What is an example of antagonism?

Answer 6

Penicillin inhibits bacterial wall synthesis
Tetracycline inhibits bacterial protein synthesis
P + T produces less antimicrobial activity that can be achieved with either alone

Question 7

What are the different ways antagonism can occur?

Answer 7

Opposing mechanisms of action
Chemical Antagonism
Altering drug metabolism
Drugs compete at the same receptor
Drugs create opposing actions through signaling at different receptors

Question 8

What is an example of chemical antagonism?

Answer 8

Taking antacid will diminish the effectiveness of tetracycline

Question 9

Potentiation

Answer 9

A second drug with a different activity enhances the activity of the first drug

Question 10

How can potentiation happen?

Answer 10

Example: Drug B enhances absorption, which could alter distribution or inhibit elimination of drug A

Question 11

What is an example of potentiation?

Answer 11

Neostigmine potentiates the activity of succinycholine

Question 12

How does neostigmine potentiate the effect of succinylcholine?

Answer 12

Succinylcholine acts at nicotinic ACh receptors to produce neuromuscular block
Succinylcholine is hydrolyzed by pseudocholinesterase
Pseudocholinesterase is inhibited by neostigmine

Question 13

Whats an example of an unexpected drug effect?

Answer 13

Disuldiram was develop to treat parasitic infections, but found to be an inhibitor of alcohol dehydrogenase, thus producign undesirable side effects if taken with alcohol

Question 14

Summation

Answer 14

The combined activity of two drugs acting at the same or similar sites

Question 15

What are the types of summation?

Answer 15

Additive
Infra-additive
Supra-additive

Question 16

Additive

Answer 16

Drug action is interchangeable when dosed at fractions of their EC50s

Question 17

Infra-additive

Answer 17

Yield less than additive response when dosed at fractions of their EC50s

Question 18

Supra-additive

Answer 18

Yield more than additive response when dosed at fractions of their EC50s

Question 19

Synergism

Answer 19

The combined activity of two drugs produces greater than the maximal effect produced by either drug alone

Question 20

Pharmaceutical Interactions

Answer 20

Drug incompatability of a physical or chemical nature

Basically, drugs should not be mixed within the same syringe

Question 21

How can drug interactions affect drug absorption?

Answer 21

An interaction can affect the rate or extent of effective absorption of the drug into the circulation, causing an increase or decrease in the drug’s effect

Question 22

What factors can effect drug absorption?

Answer 22

pH of lumen fluids
Enzyme activity
Intestinal motility

Question 23

How can drug interactions affect distribution?

Answer 23

After a drug is absorbed, an interaction may alter it’s distribution or it’s rate of transfer from one site to another
IE: Avaliability of ‘free’ drug A for distribution, metabolism, or excretion affected by the presence of drug B

Question 24

What can affect blood concentrations of a drug?

Answer 24

Plasma proteins can bind free drugs

Question 25

Distribution across plasma membrane can be affected by drugs that do what?

Answer 25

Alter p-glycoprotein activity or levels
Alter pH gradients
Disrupt membrane barriers

Question 26

What enzyme metabolizes most drugs?

Answer 26

P450 in the liver

Question 27

Inhibition of what is responsible for many drug interactions?

Answer 27

CYP enzymes

Question 28

What types of drugs can effect the metabolism of other drugs?

Answer 28

Drugs that effect hepatic blood flow

Question 29

What factors affect drug excretion?

Answer 29

Urinary pH

Renal transport inhibition

Question 30

Weak acids are more readily excreted in what type of urine?

Answer 30

alkaline

Question 31

Weak bases are more rapidly in what type of urine?

Answer 31

acidic

Question 32

Probenacid competes with penicilin for transport into renal tubules, which has what effect?

Answer 32

Probenacid increases the duration of the action of penicillin

Question 33

By administering NaHCO3, it will do what to aspirin clearance?

Answer 33

Increase aspirin clearance

Question 34

By administering NH4Cl, it will have what affect on amphetamine clearance?

Answer 34

Increase amphetamine clearance

Question 35

If drug A blocks transmitter reuptake, but drug B stimulates transmitter release, what will happen?

Answer 35

Drug B will be less effective after administration of drug A, because transmitter stores will be depleted

Question 36

What are 3 examples of Pharmacodynamic interactions

Answer 36

1) Drug A blocks transmitter reuptake, whie drug B stimulates transmitter release
2) CNS stimulants and depressants acting at the same time
3) Competition at a receptor site