Bioequivalence and Bioavailability Forum

Dear Mahesh!

❝ Please guide me how to back calculate the concentrations from the plasma

❝ concentration time curves in bioequivalence data.

I'm afraid that I don't understand you question.
Back calculate concentrations to what? The response of the analytical instrument? Or do you mean calculate concentrations from the response instead? For a linear function like Y=a+bx (regardless any weighting you might have used) solve the equation for x, i.e., x=(Y-a)/b, where Y is the response, x the concentration, a the intercept, and b the slope of the calibration curve.
For calculation of the quadratic function Y=a+bx+cx² see this post.

Back calculation of concentrations generally is only performed for calibrators and QCs (and other known concentrations in validation like freeze-thaw, stability, ...): You measure the response of spiked samples and (back-) calculate the concentration. The comparison of back calculated concentrations to known ones gives accuracy.