CH 12 DOSE CALCULATION

Question 1

Standard Doses

Answer 1

-With standard doses there are no drug calculations, so it is less likely that a major overdose or underdose will occur

• without any individualization of dosage, the target concentration will not be met eg. a standard dose will yield higher serum concentrations in smaller people than in large people

Question 2

Steady-State Concentration (Css)

Answer 2

• when the amount of drug coming in (the dose) balances the drug leaving (elimination) will a steady state be achieved
• 4 - 5 1/2 lives

Question 3

clearance rate

Answer 3

• the plasma volume cleared per unit time (usually milliliters per minute)
• stays constant over a wide range of drug concentrations and is an intrinsic function of the organs involved in the elimination of the drug
• Clearance is a measure of the body’s efficiency at removing a drug from the systemic circulation

Question 4

drug elimination

Answer 4

• varies with drug concentration whereas drug clearance does not
• Elimination is a measure of the time taken for clearance to occur

Question 5

Clearance Equation

Answer 5

Elimination Rate (mg/hr) / Concentration (mg/L)

Question 6

Half Life

Answer 6

• The time it takes for a drug concentration to decrease by 1/2

Question 7

First Order Kinetics

Answer 7

• a drug has a 1/2 life
• increased infusion increases elimination
• the clearance rate stays constant over a wide range of drug concentrations

Question 8

zero-order kinetics

Answer 8

• the drug concentration will never reach a steady state
• the apple picking analogy - you can only pick so many apples when the trees are full

Question 9

Maintenance dose

Answer 9

Ro (mg/h) = Css (mg/L) . Clp (L/h)

Maintenance dose (.25) = .5 x .5

Question 10

Calculating Steady-State Drug Concentration

Answer 10

Css (mg/L) = Ro (mg/h) / Clp (L/h)

Plasma clearance of 4 L/h and infusion rate is 100 mg/h
Calculate the Css
100 mg/h / 4 L/h = 25 mg /L

Question 11

Drugs with high volume of distribution

Answer 11

• Large concentration of drug in tissues (versus in blood)
  -plasma can be cleared of the drug, but it doesn’t mean the 1/2 life is short

Question 12

Nomograms

Answer 12

use a combination of height, surface area and weight to determine drug dosing

more nuanced than weight alone

surface area is correlated to cardiac output, GFR, rate of biotransformation