What kind of a medical representative are you? Don't know what you mean by lectures. Ask your employer. The PDR is the best reference as mentioned above. But you really need training about conflicts between major groups of medications which can cause medical disasters.
In the United States and many other countries information regarding current medical treatments and differential diagnosis is in the "Merck Manual", which is updated every six years. Information regarding ethical medications is in the PDR (Physician's Desk Reference), which is updated yearly.