I read that to mean the doctor prescribed antibiotics for something else and the person went on to develop a rash as a result. The prescription of antibiotics precedes the development of the rash with those tenses, doesn't it?
Exactly. That's my point. You can establish a time relationship if one clause is in the past perfect tense. That's (partly) why 2. in the original question is not as good.
I think the problem overall is with the use of "develop".
I don't.
"The doctor prescribed/had prescribed antiobiotics for the man who had a rash" wouldn't be quite as ambiguous, in my view.
You'll note that I was specifically illustrating why Nersi's post was wrong. Sentence 2 does not mean what he claimed, and I gave him one that was more consistent with what he wanted.
2. "
The doctor prescribed antibiotics for the man who developed a rash." establishes no time relationship. Either event could have occurred first.
Using the past perfect tense in either first or the second clause establishes which event happened first.
The usefulness of these sentences depends on the context.
If one were trying to determine the cause of the rash, you want to know whether the antibiotics were prescribed before the development of the rash. Sentence 2. doesn't help you.
One the other hand, if you wanted to determine what treatment the doctor gave for the rash, Sentence 2 still doesn't help you.
The past perfect is better because it's more specific about timing. It contains more information. But the sentences out of context could be said to mean anything. It's only when they're used in context that they become more meaningful.
Doctor1: I wonder what caused his rash.
Doctor2: Well, he
had been prescribed antibiotics.
Doctor1: Ah, that could be it.
Doctor1: I wonder what caused his rash.
Doctor2: Well, he
was prescribed antibiotics.
Doctor1: What, before he developed the rash? (Doctor1 needs to establish a timeframe which doesn't occur in the simple past).
Doctor2: Yes
Doctor 1: Ah, that could be it.
