74, 75 Drug Interactions

Question 1

What is the difference of object drug and the precipitant drug?

Answer 1

Object drug is the drug being affected by the precipitant drug

Question 2

Which of the following are examples of drugs with narrow therapeutic window? > steep dose response curve, increase risk of DDI

A. Digoxins (for heart failure)
B. Warfarin (anticoagulants)
C. Lithium
D. Cytotoxic drugs for chemotherapy 
E. CNS drugs

Answer 2

All of the above

Question 3

What is the difference between pharmacodynamic and pharmacokinetic interactions?

Answer 3

Pharmacodynamics = 1 drug potentiates/ reduces the therapeutic outcome of the other drug;

Pharmacokinetics = absorption, distribution, excretion, metabolism

Question 4

Possible pharmaceutical interactions of diazepam? (anxiolytic)

Answer 4

With infusion fluid > precipitation to inactivate drug

phenytoin too

Question 5

Possible pharmacokinetic interactions of diazepam? (metabolism)

Answer 5

with P450 inhibitor isoniazid 愛Sonia子 (antibiotic)

will cause increase in diazepam concentration, thus increase risk of overdose

Question 6

Possible pharmaceutical interactions of thiopental (IV GA)?

Answer 6

Thiopental + Suxamethonium (NMBA) > precipitation

Question 7

Possible pharmacodynamic interactions of naloxone?

Answer 7

Naloxone + opioids > reduce effectiveness of opioids (as an opioid mu receptor antagonist)

Question 8

Possible pharmacodynamic + metabolic interactions of propranolol?

Answer 8

beta blocker propranolol + bronchodilators (b2 agonists) will reduce effectiveness of the bronchodilators

(metabolism: increase risk of overdose with cimetidine , P450 inhibitor)

Question 9

Give examples of distribution wise drug interactions.
Precipitant drugs?
Object drugs? + consequence

Answer 9

Precipitant drugs:

1. Salicylate (aspirin)
2. valproate (anticonvulsant)

Object drugs

1. Phenytoin (anticonvulsant) > headache, ataxia, confusion
2. Warfarin (anticoagulant) > high risk of bleeding

e.g. aspirin displace warfarin

Question 10

What type of drugs will have high chance of distribution drug interactions?

Answer 10

1. Highly protein bound

2. Low volume of distribution (drugs stay in plasma, increase risk of reaching toxic concentration)

Question 11

Interactions between aspirin and probenecid?

Answer 11

Probenecid increases plasma level of aspirin (+ indomethacin) by reducing its excretion. (competition for same transporter?)
- also increases plasma level of penicillin

Question 12

Methotrexate drug interactions?

immunosuppression for arthritis patients

Answer 12

Methotrexate is partially bound to serum albumin, and toxicity may be increased because of displacement by other highly bound drugs, such as salicylates (aspirin) , phenytoin

> methotrexate toxicity

Question 13

Drug interactions encountered by warfarin in albumin/P450?

Answer 13

Albumin: being displaced by aspirin, valproate >high risk of bleeding;

P450

1. P450 inducers like phenobarbital, rifampicin, alcohol > reduce effectiveness of warfarin
2. P450 inhibitors like cimetidine (H2 antagonist) increase risk of. overdose due to reduced metabolism

Question 14

Cimetidine is a ? DDI?

Answer 14

P450 inhibitor, prolong other drug effects.

Question 15

Phenobarbitone is a ? DDI?

Answer 15

P450 inducer, reduce effectiveness of other drugs.

Question 16

Grapefruit juice drug interactions?

Answer 16

Grapefruit juice: CYP34A inhibitor

+ Terfenidine (antihistamine) > increase risk of arrhythmia

Question 17

Phenytoin and rifampicin are both?

Answer 17

P450 inducers

Question 18

What are the acute and chronic phases of drug interactions of phenytoin?

Answer 18

Acute phase is caused by distribution interaction effect

Chronic phase is caused by P450 induction (takes time to change gene expression)

Question 19

Drugs with additive side effects? 
A. Warfarin
B. Promethazine
C. Alcohol
D. Indomethacin

Answer 19

All of the above

Question 20

DDI of Aprepitant (APR)?

Is it similar to cimetidine?

Answer 20

NK1 antagonist
- CYP34A inhibitor, reduce metabolism of object drugs (after a few days!)

Cimetidine: P450 inhibitor as well

Question 21

Which of the following is false?
A. Danshen / Dong quai + warfarin > increase risk of bleeding
B. Digoxin + St, John’s wort (antidepressant) > reduce bioavailability of object drug
C. Xiao chai hu tang + prednisolone > increase plasmas level of prednisolone

Answer 21

C
should be decrease

A: Danshen CYP inhibitor