Drug Interactions and Therapeutic Drug Monitoring

Question 1

What is the medical importance of drug interactions in terms of morbidity and mortality

Answer 1

Costs to healthcare is high due to increased hospitalisation and administration of drugs to resolve it

Question 2

Factors that may predispose a patient to a drug interactions

Answer 2

The number of medications
Elderly
Young
Critically ill
Patients undergoing complicated surgery
Patients with chronic conditions:
Liver disease
Kidney impairment
Diabetes mellitus
Epilepsy
Asthma

Question 3

Classification of Drug-Drug interactions

Answer 3

Pharmacodynamic: Direct antagonism, synergistic, indirect agonist, indirect antagonism
Pharmacokinetic: Absorption, Distribution, Metabolism and Elimination

Question 4

Importance of Therapeutic drug monitoring

Answer 4

Drugs have small therapeutic index

Question 5

Precipitant

Answer 5

The agent which precipitates out in such an interaction

Question 6

Drugs involved with serious interactions and why?

Answer 6

Warfarin
Gentamicin
Erythromycin
Linezolid
These drugs have a narrow therapeutic index which means that a small change in blood plasma levels can induce prodounf toxicity

Question 7

Food that interact with Warfarin

Answer 7

Vegetables like: Asparagus, Broccoli, Cabbage, Kale, Lettuce, Onions, Spinach, Watercress
Herbals like: Ginseng, Green tea
Miscellaneous: Avocado, Fish oils, Liver, Soya beans

Question 8

Food that interact with Warfarin

Answer 8

Vegetables like: Asparagus, Broccoli, Cabbage, Kale, Lettuce, Onions, Spinach, Watercress
Herbals like: Ginseng, Green tea
Miscellaneous: Avocado, Fish oils, Liver, Soya beans

Question 9

Direct Antagonism

Answer 9

beta-blockers will block actions of agonists

Question 10

Synergistic Interaction

Answer 10

Two drugs with the same pharmacological effect acting on the same receptor given concurrently

Question 11

Indirect Agonism

Answer 11

Warfarin and NSAIDs, Atenolol and Verapamil

Question 12

Indirect Antagonism

Answer 12

NSAIDs and anti-hypertensiive medication and NSAIDs and treatment for heart failure

Question 13

Drug-drug interactions in Absorption

Answer 13

Formation of insoluble complexes
Altered PH
Altered bacterial flora
Altered GI motility

Question 14

Drug-drug interactions in Distribution

Answer 14

Protein binding displacement

Question 15

Drug-drug interactions in Metabolism

Answer 15

Occurs when one drug induces or inhibits the metabolism of another

Question 16

Drug-drug interactions in Elimination

Answer 16

Inhibit secretion

Increase tubular reabsorption

Question 17

Tetracyclin and erythromycin complex with _________ to form insoluble complexes

Answer 17

Magnesium, iron and calcium

Question 18

__________ reduce H+ and increase____

Answer 18

H2 antagonist, proton pump blockers and antacids and PH

Question 19

__________ destroy normal gut flora leading to

Answer 19

Broad spectrum antibiotics and failure of oral contraceptive or digoxin toxicity

Question 20

Oral medicines are mostly absorbed in the ______ and ______ is the limiting step and increase leads to_______

Answer 20

small intestine and gastric emptying and increased absorption

Question 21

Anticholinergics delays_____

Answer 21

Gastric emptying

Question 22

If a drug is 99% bound displacement of 1% leads to______

Answer 22

Doubling of free plasma levels

Question 23

2 most important proteins are_____

Answer 23

Albumin and alpha-1 glycoprotein

Question 24

Drugs with 99% protein binding

Answer 24

Ibruprofen, naproxen, Warfarin, Valproic acid, Phenytoin

Question 25

Drug-Drug interactions that affect metabolism normally occur in the _____

Answer 25

Liver via the cytochrome P450

Question 26

Drugs that inhibit the metabolism of drugs metabolised by the P450 system

Answer 26

Cimetidine (warfarin, diazepam), Metronidazole (Warfarin, alcohol), Omeprazole (phenytoin, warfarin)

Question 27

Drugs that induce cytochrome P450

Answer 27

Barbiturates, Carbamazepine, Phenytoin (warfarin, steroid, OC), Rifampacin (warfarin, OC) and tobacco smoke

Question 28

How long does enzyme induction take

Answer 28

2-3 weeks

Question 29

Rifampicin___

Answer 29

Increases metabolism of ciclosporin by inducing CYP 3A4

Question 30

St John's Wort_____

Answer 30

Increases metabolism of ciclosporin by inducing CYP 3A4

Question 31

Verapamil/diltiazem and digoxin____

Answer 31

Inhibit secretion

Question 32

Loop diuretic and lithium

Answer 32

Increase tubular reabsorption