Antiepileptic Drug Interactions

Question 1

When trying to determine pharmacological effect what is it determined by

Answer 1

The free concentration

Question 2

T/F: The total concentration is the free concentration PLUS the bound concentration

Answer 2

True

Question 3

T/F: If the fraction unbound increase total concentration also increases meaning there will automatically be an increase in pharmacological effect

Answer 3

False: Fraction unbound or total concentration will only cause a change in pharmacological effect if the FREE CONCENTRATION is changed

Question 4

What is a key counseling tip for patients with AEDs, why

Answer 4

Take with food to slow the rate of absorption

Question 5

T/F: Antacids reduce phenytoin and gabapentin bioavailability by 20-30% and should be seperated by 2 hours

Answer 5

True

Question 6

If there is hepatic enzyme inhibition what happens to clearance, half-life, free and total concentration

Answer 6

Lowered clearance, increased half life, increased total and free concentration

Question 7

What is the primary enzyme pathway that metabolizes carbamazepine

Answer 7

85% by CYP 3A4

Question 8

What is the primary enzyme pathway that metabolizes phenytoin

Answer 8

CYP 2C19/9

Question 9

What are two major AEDs that are enzyme inducers, what do they induce

Answer 9

carbemazepine,phenytoin/ CYP 1A,2C,3A and glucuronidation

Question 10

What are major AEDs is a hepatic enzyme inhibitor, what does it inhibit

Answer 10

Valporic acid/ glucuronidation, CYP 2C9, epoxide hydrolase

Question 11

What AEDs induce the metabolism and reduce effectiveness of hormonal contraceptives

Answer 11

Carbamazepine, oxcarbazepine, phenobarbital, phenytoin, topiramate

Question 12

Why should epoxide levels not cause immediate concern if a patient is taking carbamezapine

Answer 12

Carbamezapine has an active metabolite that is an epoxide after CYP 3A4 metabolism

Question 13

What happens when phenytoin and warfarin interact

Answer 13

displacement of warfarin from plasma proteins by phenytoin, initial competivie inhibition (CYP2C9), induction of hepatic metabolism

Question 14

What happens to INR and anticoagulation effect after adding phenytoin to warfarin, warfarin to phenytoin

Answer 14

Initially the INR will shoot up but because phenytoin is an inducer there will be less anticoagulation effect because phenytoin will induce enzymes that metabolize warfarin, will need a high dose to combat already induced enzymes

Question 15

What is the main pathway that lamotrigine is metabolized by

Answer 15

Glucuronidation

Question 16

What is a major risk of using Valporic Acid and Lamotrigine

Answer 16

Severe skin rash due to valporic acid inhibiting glucoronidation

Question 17

What happens when valproiic Acid and phenytoin interact

Answer 17

Valporic acid does not allow phenytoin metabolism due to inhibition of CyP 2C9