Bioequivalence and Bioavailability Forum

Hi Mithu,

❝ please let me know under what condition, free and total analyte needs to be measured in biological fluids?

Please define your terms.

Are you referring by “free” to the fraction which is not protein-bound? Protein-binding is caused by Van-der-Waals forces which will be broken in any sample preparation (SPE, LLE, protein precipitation). Hence, what we measure is always the total analyte. If you are interested in protein-binding (not relevant in BE) go with equilibrium dialysis, ultrafiltration, ultracentrifugation.

Or are you talking about a liposome-encapsulated drug (unencapsulated and encapsulated fractions)? The EMA and the FDA require both (examples: EMA, FDA*).

---

• At last year’s 3^rd GBHI-conference nitpickers pointed out that the term “free” should not be used when “unencapsulated” is meant.