Example: After an iv administration of 500 mg ampicillin to a patient, the AUC was 16 mg-hr/L. What is the bioavailability of ampicillin capsules and ampicillin suspension in the same patient if the AUC after 500 mg ampicillin capsule was 10 mg-hr/L, and the AUC after 250 mg ampicillin suspension was 4 mg-hr/L?
The bioavailability can be determined from the AUC(oral)/AUC(iv) ratio after administration of similar doses. When the iv and oral doses are different, the AUCs have to be adjusted to represent equal doses before calculating the ratio.
Fcapsule =
AUC capsule
AUC iv
=
10 mg-hr/L
16 mg-hr/L
= 0.625
The AUC after 250 mg susp. is 4 mg-hr/L, so the AUC after 500 mg susp. should be 8 mg-hr/L
Fsuspension =
8 mg-hr/L
16 mg-hr/L
= 0.5
