Example: In animal experiments to study the pharmacokinetics of carbamazepine (CBZ) and its metabolite CBZ-epoxide and procainamide (PA) and its metabolite NAPA, the following results were obtain after iv administration of 5 mg/kg of each drug to a different group of animals. Calculate the half lives for the two metabolites
| Time (hr) |
CBZ (mg/L) |
CBZ-O (mg/L) |
PA (mg/L) |
NAPA (mg/L) |
| 2 |
3.23 |
0.10 |
1.6 |
0.32 |
| 5 |
2.78 |
0.19 |
0.92 |
0.54 |
| 10 |
2.30 |
0.27 |
0.34 |
0.56 |
| 15 |
1.68 |
0.28 |
0.12 |
0.45 |
| 24 |
1.08 |
0.24 |
0.02 |
0.25 |
| 36 |
0.59 |
0.16 |
0.002 |
0.10 |
| 50 |
0.29 |
0.08 |
0.000 |
0.03 |
Drug
The decline in the CBZ-eposide profile is dependent on its formation rate and the metabolite half life cannot be determined directly from the metabolite profile.
Drug
The decline in NAPA profile is dependent on its elimination. NAPA half life can be determined from the terminal phase of NAPA profile.
CBZ-epoxide half life cannot be determined directly from the data.
Graphically NAPA half life is 8.5 hours
