I use graphpad prism and/or phoenix winnonlin.  I believe there are excel functions to do AUC also.  Hope this helps. 

Dear Sunil,

you need to calculate AUC by the trapezoidal method, the total AUC is the sum of the trapezoids (AUC0-t= (C1+C2/2)*(t2-t1) and so on). You can do this in excel. The next step is to calculate de bioavailability and for this you should use this formula: AUCoral* i.v. Dose/ AUCiv* oral Dose. The value is a fraction, so you multiply by 100 to have % number.

Hope this can help you.

http://www.uiowa.edu/~c046170/PDFs/auc.PDF

thanx to every one to give the nice suggestions 

Morphit http://www.edge-ka.com/downloads/ has the trapezoidal method already programmed in and also offers standard binders for all the common in vivo PK assays including Bioavailability, PK/PD, Single and Multidose studies.

Here's a video of it in action: http://www.edge-ka.com/products/morphit/morphit_biology

There's a free 30 day trial version available on the first link.

I would make a PK population model and calculate AUC from that, or from an individual patient's Bayesian posterior individualized model. Trapezoidal rule, I think, is not nearly as good. Also, what do you want to do with the AUC? If you want to develop a dosage regimen to get another AUC that is  better in your opinion, you need software for good Bayesian adaptive control. You might consider the USC Bestdose software, and the Pmetrics population modeling software. They will permit getting the maximally precise dosage regimen, while software that uses only parametric models (NONMEM, MW/Pharm, Doseme, and Abbottbase, for example) cannot do this, and can never be aware of the issue of max precision. You might look at www.lapk.org. 

U CAN TRY PKSOLVER EXCEL ADDIN

Graph Pad prism  software is another  internationally accepted way to get AUC done.

The easier way is use pksovler addin in excel which is based on the trapezoidal method or just calculate it yourself on excel. We did this previously. But I agree with Roger that using a designed model will give you more accurate estimation. See if you can get that later.