I have a deal with my fearless healer by which he gives me his outdated P. D. R. whenever a new version arrives. If you can't wangle a deal with your family physician to get a free copy of the P. D. R., from him, maybe you should consider changing doctors. Virtually all of the major pharmaceutical manufacturers have a pharmacopoeia under their own logo. They scatter copies of these volumes throughout the land, to every drug store, dispensary and street-corner pharmacy that stocks any of their products. Since drugs, and the prescription protocols under which they are legally dispensed, are constantly undergoing changes, so are the books that define and explain those drugs - and their uses.
New editions supplant older editions at relatively short intervals.
A modest amount of sweet-talk should result in your friendly neighborhood pharmacist giving you one of his superfluous copies. And you should be able to get your copy free. Beyond just buying or otherwise acquiring these books, I urge you to familiarize yourself with their contents before you need to use them. Trust me on this one. Yet this is precisely how these midnight dramas play themselves out.