Bioequivalence and Bioavailability Forum

Dear Rameswari jena
In general the Principal Investigator judges whether or not, in his/her opinion, the adverse drug reaction was related with the drug. In your case the adverse event is to be recorded as follows:
Unlikely: if the clinical event has a temporal relationship to drug administration which makes a causal relationship improbable and in which other drugs, chemicals or underlying disease provide plausible explanation.
Unrelated: if the clinical event can be explained by any reason excluding the administered drug. (So if your PI does not provide a reasonable explanation he/she can not categorize the event as unrelated.)
Not assessable/unclassified: if the report suggesting an adverse event cannot be judged because information is insufficient or contradictory and which cannot be supplemented or verified.
I hope this helps
Kind regards
Dan