(PHA 5127-1999)
Homework 1
- Give the equation that may be used to calculate the
half-life when (1) two time points and the corresponding
concentrations are known, or (2) clearance and volume of
distribution are known, or (3) the elimination rate
constant is known.
- Define volume of distribution and clearance.
- A drug is given as an i.v. bolus injection. The rate of
change in the plasma concentration is described by -dC/dt
= K * C. Show mathematically that the half-life does not
depend on the concentration.
- An i.v. bolus dose of gentamycin is given to a patient. A
peak concentration of 6.8 mg/ml is determined and the
concentration 7 hours later is 1.7 mg/ml. Assume
first-order kinetics, calculate the elimination rate.
- What factors lead to a small volume of distribution? What
is the smallest possible volume of distribution of a
drug?
- Taking alcohol as an example, explain what zero-order
elimination implies. (Does half-life depend on
concentration? Does the rate of decrease in concentration
depend on concentration? Is a constant amount or a
constant fraction of alcohol eliminated from the body
every hour? And so on.)
- For first-order kinetics, if the initial plasma
concentration is 11.5 mg/L and the half –life is 3.2
hours, what is the plasma concentration going to be two
and half hours after injection?
- What kind of information does AUC reveal?
- A patient was given a bolus i.v. injection of 1000mg of a
drug. The volume of distribution is 30L. When the plasma
concentration (Cp) was assayed, the following data was
obtained:
| Time t[min] |
Cp[mg/L] |
| 5 |
32.7 |
| 10 |
32.0 |
| 15 |
31.3 |
| 25 |
30.0 |
| 50 |
27.1 |
| 100 |
22.0 |
| 150 |
17.8 |
| 200 |
14.5 |
| 250 |
11.8 |
| 300 |
9.55 |
| 355 |
7.95 |
| 400 |
6.30 |
| 500 |
4.15 |
| 600 |
2.74 |
| 800 |
1.19 |
| 10001 |
0.52 |
Calculate AUC by trapezoidal rule and determine Vd.
Schedule