Ch. 1: Issues for Practitioners in Drug Therapy

Question 1

Omeprazole (Prilosec) is a potent inhibitor of three CYP isozymes responsible for the metabolism of this drug, which can thus lead to its increased plasma concentrations and increased risk of bleeding:

Answer 1

Warfarin (Coumadin)

Question 2

This juice (?) is a potent inhibitor of this isozyme (?), which may lead to higher levels and/or greater potential for toxic effects with drugs such as nifedipine, clarithromycin, and simvastatin, that are metabolized by the CYP 450 system.

Answer 2

Grapefruit juice/CYP3A4

Question 3

A drug reaches “steady state” in about ______ half-lives?

Answer 3

4 to 5 half lives

Question 4

T or F:

The rate of approach to steady state is not affected by the rate of drug infusion.

Answer 4

True

Question 5

What is the formula to calculate loading dose?

Answer 5

Loading dose=(Vd) x (desired steady-state plasma concentration)

Question 6

What is the formula for calculating apparent volume of distribution?

Answer 6

Vd=dose/peak plasma concentration (C)

Then divide patient weight in kg/the Vd

I.e.:
Dose of vancomycin: 2000 mg
Peak plasma concentration: 28.5 mg/L
Patient weight: 70 kg

2000mg/28.5mg/L=70.1 L

Apparent Vd is 1L/kg (70.1L/70 kg)

Question 7

Describes the actions of a drug in the body and the influence of drug concentrations on the magnitude of the response.

Answer 7

Pharmacodynamics

Question 8

Most drugs exert their effects, both beneficial and harmful, by interacting with ___________ (specialized target macromolecules) present on the cell surface or within the cell.

Answer 8

Receptors

*The drug-receptor complex then initiates alterations in biochemical and/or molecular activity of a cell by a process called “signal transduction”.

Question 9

________act as signals, and their ________act as signal detectors.

Answer 9

Drugs/receptors

• Cells have many different types of receptors.
• The magnitude of the response is proportional to the number of drug-receptor complexes (concept closely related to formation of complexes between enzyme and substrate or antigen and antibody).

Question 10

Cardiac cells have ________receptors that bind and respond to epinephrine and norepinephrine. They also have _______receptors specific for acetylcholine.

Answer 10

Beta (B)-receptors

Muscarinic receptos

Question 11

Agonists, antagonists, and partial agonists are all examples of _______ (small molecules that bind to the activation site on a receptor and although they are not responsible for the actual action, they help stimulate the cascade of events).

Answer 11

Ligand

Question 12

What are the four families of receptors:

Answer 12

1. Ligand-gated ion channels
   (i. e. cholinergic nicotine comes receptors)
2. G protein-coupled receptors
   (i. e. a and B adrenoceptors)
3. Enzyme-linked receptors
   (i. e. insulin receptors)
4. Intracellular receptors
   (i. e. steroid receptors)

Question 13

When a receptor is exposed to repeated administration of an agonist, the receptor becomes desensitized, resulting in a diminished effect (a mechanism designed to protect the target cells). What is the term for this phenomenon?

Answer 13

Tachyphylaxis

(May occur through phosphorylation of similar chemical event that renders receptors on cell surface unresponsive to the ligand. In addition, cell surface receptors may be “down-regulated” so that they are internalized and sequestered within the cell).

Question 14

A drug approaches 90% of the final steady state in _______(t1/2) hours.

Answer 14

(3.3)(t1/2)

So a drug with a half-life of 12 hours, given by continuous IV infusion, would approach 90% of the final steady state in (3.3)(12)=40 hours.

Question 15

A drug will reach full steady state in how many half-lives?

Answer 15

Four-five half lives.