Pharmacy Foundations: Drug interactions

Question 1

Pharmacodynamics

Answer 1

effect or change that a drug has on the body or some other type of organism

Question 2

pharmacodynamic drug interaction

Answer 2

When two or more drugs are given together, and their effects impact each other

Question 3

Additive effects can be caused when….

Answer 3

1. multiple drugs that are agonists at the same receptor are given together
   ie. 2 opioids given together, side effects (respiratory depression, sedation) can be increased
2. multiple drugs have similar end effects through different mechanisms
   ie. Benzo = sedating w/ Opioids = sedating too

Question 4

Synergism is when….

Answer 4

two drugs taken in combo have a greater effect than that obtained by simply adding the 2 individual effects

ie. taking Tylenol w/ opioid provides more effect than you’d expect if adding effect of opioid + Tylenol

A + B > A & B

Question 5

Pharmacokinetics

Answer 5

effect or change that body has on a drug

ADME

Question 6

ADME:

Answer 6

Absorption
Distribution
Metabolism
Excretion

Question 7

Chelation is when….

Answer 7

drug binds to polyvalent cations in another compound, and cant be dissolved in gut fluid so will pass in stool

Question 8

Drugs with polyvalent cations or other binding properties, should be separated from….

Answer 8

quinolones
tetracyclines
levothyroxine
oral bisphosphonates

Question 9

Majority of Pharmacokinetic interactions occur during….

Answer 9

metabolism in the liver

Question 10

CYP450 enzymes primarily expressed in the…

Answer 10

Liver

Question 11

Prodrugs

Answer 11

Taken in inactive form, and converted by CYP450 enzymes into active from

can be used to extend dosing interval or prevent abuse

Question 12

CYP enzyme inhibitors wil…

Answer 12

decrease enzyme function and ability to metabolize compounds

Question 13

If drug is substrate for same CYP enzyme that is affected by an inhibitor then….

Answer 13

decreased rate of drug metabolism, leading to increased serum drug level

Question 14

Common CYP inhibitors: GPACMAN

Answer 14

G = Grapefruit
P = protease inhibitors ie ritonavir
A = azole antifungals (fluc,itra,keto,posaco,voriconazole and isavuconazonium)
C = cyclosporine, cobicistate
M = macrolides (no azithromycin, just clarity/eryth)
A = amiodarone ( & dronedarone)
N = Non- DHP CCB (Dilt n Verapamil)

Question 15

CYP enzyme inducers will…

Answer 15

increase enzyme production or activity

Question 16

If drug is substrate for the same CYP enzyme that is affected by an inducer then….

Answer 16

increased rate of drug metabolism, leading to decreased serum drug level

Question 17

Common CYP inducers: PS PORCS

Answer 17

P = Phenytoin
S = smoking
P = Phenobarbital
O = Oxcarbazepine
R = Rifampin ( & rifabutin, rifapentine)
C = Carbamazepine (also auto-inducer)
S = St. Johns Wort

Question 18

“Lag” time for Enzyme Inducation

Answer 18

Induction often requires additional enzyme production, taking time. Full effect on drug levels not seen for up to 4 weeks, and when inducer stopped then can take 2-4 weeks for inducer effects to disappear

Question 19

P-gp inhibition will cause…..

Answer 19

drugs that are substrate of P-gp to have increased absorption and higher drug levelsC

Question 20

Common P-gp substrates

Answer 20

Anticoag = apixaban, edoxaban,rivarogaban and dabigatran
Cardiovascular = digoxin, diltiazem, carvedilol, ranolazine, verapamil
Immunosupressants = cyclosporine, sirolimus tacrolimus
HCV drugs = sofosbuvir

Others: colchicine, atazanavir, dolutegravir, posaconazole, raltegravir, saxagliptin

Question 21

Common P-gp inducers

Answer 21

Carbamazepine
Dexamethasone
Phenobarb
Phenytoin
rifampin
St. Johns Wort
Tipranavir

Question 22

Common P-gp inhibitors

Answer 22

anti-infectives = clarithromycin, itraconazole, posaconazole
Cardiovascular = amiodarone, carvedilol, conivaptan, diltiazem, dronedarone, quinidine, verapamil
HIV = cobicistat, ritonavbir
HCV = ledipasvir

Others = cyclosporine, fibanserin, ticagrelor

Question 23

Where are most drugs absorbed?

Answer 23

small intestine, entering portal vein and back to liver

Question 24

Enterohepatic Recycling

Answer 24

recycling of an already metabolized drug, which increases the duration of action of many drugs