| When a study subject developed an adverse event, the investigator took appropriate and necessary measures |
|
The quoted material above is ambiguous, but the context in which it occurs might well resolve the ambiguity.
It could mean either of the two paraphrases shown below.
1. (a = a particular known subject = a certain person who was a study subject, say "George")
A (certain) study subject (George) developed an adverse event. When this happened, the investigator took appropriate and necessary measures.
(Something happened. When it happened, the necessary countermeasures were taken.)
2. (when = whenever; if. a = any (not any particular person; some hypothetical person; it could have been George or Henry or Louis or ...) ) Whenever (if) any study subject (might have) developed an adverse event, the investigator [took/ would take] appropriate and necessary measures.
(In any case of a certain kind of event happening, the necessary countermeasures were taken.)
From the point of view of Italian, (and I'm not completely sure of this), 1. is indicative, 2. is subjunctive.
Even if this does not answer your question completely, it may help. I hope so!
CJ