Example: Ciprofloxacin is a quinolone antibiotic which is active against enterobacteriaceae. After administration of a single 400 mg iv dose of ciprofloxacin 240 mg excreted unchanged in urine, while after administration of a single 400 capsule only 180 mg excreted in urine. Calculate the bioavailability of this capsule. If the total body clearance of ciprofloxacin is 0.45 L/hr/kg, calculate the renal clearance of this drug.

Absolute Bioavailability

The bioavailability of the capsule is determined from the amount of ciprofloxacin excreted in urine after iv and after oral administration:

F =

A e∞ oral

A e∞ iv

Renal Clearance

The fraction of the iv dose excreted in urine is equal to the ratio of the renal clearance to the total body clearance:

A e∞

Dose
=

Renal clearance

Total body clearance

Answer

F =

A e∞ oral

A e∞ iv
=

180mg

240mg
= 0.75

240 mg

400 mg
=

Renal clearance

0.45 L/hr/kg
Renal clearance = 0.27 L/hr/kg
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