Example: Ganciclovir is an antiviral drug used in the treatment of cytomegalovirus infections. After an iv dose of 350 mg the plasma conc-time profile can be described by:

Cp = 15 e -0.95 t + 1.5 e -0.2 t

If 95 % of the administered dose is recovered unchanged in urine, calculate the renal clearance of ganciclovir. What is the amount of the drug excreted in urine after 8 hours of drug administration ?

Cp = 15 e-0.95 t + 1.5 e-0.2 t
CLR = 0.95 CLT

Answer

AUC =

15mg/L

0.95 hr -1 +

1.5mg/L

0.2 hr -1 = 23.3 mg-hr/L
CLT =

350 mg

23.3 hr -hr/L = 15 L/hr
CLR = 0.95 x 15 L/hr = 14.25 L/hr
Cp8 hr = 15 e-0.95hr-18hr + 1.5 e-0.2 hr-18hr = 0.3 mg/L
Vdβ=

CLT

β =

15 L/hr

0.2 hr -1 = 75 L
Total amount Eliminated = 350 mg-(0.3 mg/L x 75 L) = 327.5 mg
Amount Excreted in urine = 0.95 x 327.5 mg = 311 mg
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