Final answer:
Amoxicillin and clarithromycin would have been ruled out for the treatment of Michael's pneumonia, as the causative agent is resistant to amoxicillin and Legionella pneumophila is resistant to clarithromycin.
Step-by-step explanation:
Based on the presumed causative agent of Michael's pneumonia, the drugs that would have been immediately ruled out of the empirical therapy are amoxicillin and clarithromycin.
Amoxicillin would have been ineffective because the causative agent, Mycoplasma pneumoniae, does not have a cell wall and is not inhibited by amoxicillin. Clarithromycin would have been ruled out because Legionella pneumophila, the causative agent of pneumonia in another patient, is resistant to clarithromycin.
Therefore, in Michael's case, the appropriate antibiotics were ampicillin and gentamicin, which are effective against the presumed bacterial infection.