Bioequivalence and Bioavailability Forum

Dear Rana!

❝ Why only 90% Confidence Interval is being used in generally to prove bioequivalence.

Let me reformulate ElMaestro’s answer (see also this presentation, slide 53). α (aka error type I or error of the first kind) is the patient’s risk of falsely accepting bioequivalence (hardcore-statistics: rejecting the null hypothesis of bioinequivalence). Therefore the risk for a particular patient to be treated with a non-BE formulation is 5% at the lower end of the acceptance range (<80%) and 5% at the upper end (>125%). In other words we accept that there are two groups of patients: 5% with expected BA of <80% and 5% with expected BA of >125%. If we look at the entire population of patients we get 5% (below) + 5% (above) = 10%. Since in a particular patient BA cannot be <80% and >125% at the same time, his/her risk it still 5% although we deal with a 90% (1–2×α) confidence interval.

❝ why can't 80% or 70% ???

90% CI  ⇒   5% risk
80% CI  ⇒  10% risk
70% CI  ⇒  15% risk

❝ What is rationale behind this?

Convention; seems to work. Note that in Brazil for narrow therapeutic index drugs α has to be kept at 2.5% (i.e., 95% CI). This is unique because in many other regulations for NTIDs α is kept at 5% but the acceptance range is narrowed to 90–111% instead.