Pharmacokinetics

Question 1

What is first pass metabolism?

Answer 1

The process of metabolizing an extravascularly-administered drug prior to it getting into the circulation.

Question 2

What is bioavailability?

Answer 2

The fraction of a drug absorbed systematically after extravascular administration.

Question 3

Which organs contain cells with high amounts of cytochrome enzymes located and what is their significance with regards to drug metabolism?

Answer 3

They are found in the GI mucosal cells and in the liver (mostly). They can metabolize drugs into byproducts before the drugs enter systemic circulation.

Question 4

What is the equation for volume of distribution?

Answer 4

Vd = dose/plasma concentration

Question 5

When should dose weight be calculated for an obese individual? What is the formula?

Answer 5

When total body weight exceeds 120% of the ideal body weight.

DW = IBW + 0.4(TBW-IBW)

Question 6

What does grapefruit juice do?

Answer 6

Inhibits CYP3A enzymes in the gut mucosa

Question 7

How do multivitamins alter absorption of antibiotics like cipro?

Answer 7

The charged mineral ions chelate with the drug to inhibit absorption.

Question 8

How do rifamycins affect anti-retroviral drugs? How is this relevant?

Answer 8

Rifamycins induce CYP450 enzymes and reduce the bioavailability of ARV drugs. This is relevant because TB and HIV co-infection is becoming more common.

Question 9

Name five drug classes in which drug monitoring is commonly performed.

Answer 9

1. Antiarrhythmics
2. Antibiotics
3. Anticonvulsants
4. Antidepressants
5. Antithrombotics

Question 10

How are antithrombotics monitored clinically?

Answer 10

Thrombin or INR

Question 11

Which class of drugs commonly call for use of dosing weight for patients who are obese?

Answer 11

Aminoglycoside antibiotics.

Question 12

Name an aminoglycoside antibiotic. Is it toxic?

Answer 12

Tobramycin. Highly nephrotoxic.

Question 13

When are peak and trough levels measured, respectively, when monitoring multiple daily dosing of aminoglycosides?

Answer 13

Peak: 30 min after end of the infusion
Trough: 30 minutes before administration of the next dose

Question 14

What happens faster: Induction of enzymes or inhibition? Why?

Answer 14

Inhibition happens faster because induction requires upregulation of transcription factors, increased protein synthesis, etc. which takes a few days.

Question 15

By which kinetic order are phenytoin and alcohol eliminated?

Answer 15

Zero order