Bioequivalence and Bioavailability Forum

Hi again, Mauricio,

❝ Therefore, if there are levels measurable in human plasm a pharmacokinetic approach could be applied. I could be wrong, but I do not understand the reason for option clinical. If you or anybody else can explain, I really appreciate!

I share your views to a large extent.
If two products give rise to the same concentrations in the eye,
and
if the effect (safety) is directly a function of the eye concentration
and
if the drug is absorbed from the eye to the blood stream with quantifiable levels

then a comparative PK study would likely be ok scientifically speaking.

We have the same situation for inhaled asthma drugs (substitute eye for lung and the rest is the same). It took FDA more than 15 years to give green light for PK as a safety tool but for effect a PD-trial is still needed. It is extremely controversial, and there have been a million conferences about the topic. It all goes pear-shaped when the originator (who is afraid of generic competition and willing to do everything to stop it) starts arguing that blood levels are not indicative of effect and despite much effort to find consensus this is just an uphill struggle. Internally at agencies it is a very big hurdle for medical doctors, specialists in their field, to start thinking about PK in stead of PD. They just don't like it. Communication does not seem to be the solution.