Cytochrome p450 system

Question 1

Where the cytochrome p450 enzymes are mostly located

Answer 1

Liver and small intestine

Question 2

Importance of the cytochrome p450 SYSTEM

Answer 2

Excretes exogenous toxins

Much of the inactivation of psychotropic drugs is via the hepatic cytochrome system

Question 3

Ethnic group showing the highest frequency of poor metabolisers of CYP2D6

Answer 3

Africans and African-Americans

Question 4

CYP group which shows the largest phenotypic variation

Answer 4

CYP2D6

Question 5

Proportion of Caucasians who are poor metabolisers of CYP2D6

Answer 5

6-10%

Question 6

Most abundant CYP group

Answer 6

CYP3A

Question 7

Psychotropics metabolised by CYP2D6

Answer 7

TCAs, fluoxetine, paroxetine, antipsychotics, trazodone, valproate, amphetamines, venlafaxine

Question 8

Psychotropic inhibitors of CYP2D6

Answer 8

Paroxetine (can inhibit its own clearance), antipsychotics, amitriptyline, clomipramine

Question 9

Psychotropics which induce CYP2D6

Answer 9

Nil

Question 10

Drugs metabolised by CYP3A4

Answer 10

Clomipramine, mirtazapine, carbamazepine, fluvoxamine, nefazodone, aripiprazole, quetiapine, clonazepam, donepezil, most benzodiazepines

Question 11

Psychotropics which induce CYP3A4

Answer 11

Carbamazepine (can cause autoinduction), barbiturates, St John’s Wort

Question 12

Drugs which inhibit CYP3A4

Answer 12

Calcium channel blockers, fluoxetine, paroxetine

Question 13

Psychotropics metabolised by CYP1A2

Answer 13

Clozapine, olanzapine, agomelatine

Question 14

Substances which induce CYP1A2

Answer 14

Smoking, barbiturates

Question 15

Substances which inhibit CYP1A2

Answer 15

Grapefruit juice, caffeine, fluvoxamine

Question 16

Effect of smoking on clozapine levels

Answer 16

Lowers levels

Question 17

Effect of grapefruit juice on clozapine levels

Answer 17

Increases levels

Question 18

Effect of carbamazepine autoinduction

Answer 18

Rate of metabolism gradually increases over the first few weeks of treatment

Question 19

Three ways in which drug interactions can influence the CYP system

Answer 19

Induction
Non-competitive inhibition
Competitive inhibition

Question 20

Part of the body CYP3A4 is most prominent

Answer 20

Gut wall mucosa

Question 21

The gradual speeding up of the rate of metabolism of a newly started drug because it induces the CYP system which metabolises it

Answer 21

Autoinduction

Question 22

Medication which classically undergoes autoinduction

Answer 22

Carbamazepine

Question 23

Type of metaboliser who has more than two copies of fully active CYP450 enzyme alleles

Answer 23

Ultrarapid metaboliser

Question 24

Type of metaboliser who has more two copies of fully active CYP450 enzyme alleles

Answer 24

Extensive metaboliser

Question 25

Type of metaboliser who has more one copy of fully active CYP450 enzyme alleles

Answer 25

Intermediate metaboliser

Question 26

Type of metaboliser who has more no copies of fully active CYP450 enzyme alleles

Answer 26

Poor metaboliser

Question 27

CYP enzyme which primarily metabolises caffeine

Answer 27

CYP1A2

Question 28

Psychiatric drugs where levels are most altered by grapefruit juice

Answer 28

``` Carbamazepine Pimozide Triazolam Midazolam Methylprednisolone Buspirone ```

Question 29

Effect of reboxetine on cytochrome P450 enzymes

Answer 29

No impact