Example: In the previous example, the plasma conc-time profile after a single iv bolus dose of 100 mg lidocaine can be describe by the following expression:
Cp (mg/L) = 2.6 e-5.0 t + 0.52 e-0.4 t
where t is in hours. Calculate the amount of lidocaine remaining in the body after 4 hours. Also, what will be the plasma lidocaine concentration when 90% of the dose is eliminated.
The conc after 4 hours can be calculated
Since lidocaine is in the elimination phase after 4 hours, the amount can be determined using Vdβ
When 90% of lidocaine dose is eliminated there is 10 mg remaining. The conc can be determined using Vdβ
From the previous example: Vdβ = 137 L
Cp4 hr = 0.105 mg/L
Amount 4 hr = 0.105 mg/L x 137L
= 14.4 mg
When 90% of dose excreted, the drug is in the elimination phase:
Cp10% remaining =
10 mg
137 L
= 0.073 mg/L
