This is a pivotal week for Amgen (NASDAQ:AMGN), as it awaits Wednesday's Food and Drug Administration ruling on the approval of its lead pipeline drug candidate, Nplate, as a treatment for the blood disorder immune thrombocytopenic purpura (ITP).

In March, an advisory panel voted unanimously in favor of FDA approval for Nplate to treat patients with chronic ITP. But the agency hit Amgen with a three-month approval decision delay in April, after the drugmaker submitted a new risk-management plan for Nplate. Now Amgen's July 23 PDUFA date for the compound is finally approaching.

Besides its osteoporosis drug denosumab, Amgen's pipeline isn't exactly brimming with late-stage compounds. Since Amgen's revenue got creamed by the safety issues surrounding it and partner Johnson & Johnson's (NYSE:JNJ) anemia-drug franchise, Nplate represents Amgen's best chance to get itself back into positive revenue growth territory, provided it can eventually hit a couple hundred million dollars in annualized sales.

Nothing is ever certain in FDA approval decisions, and many seemingly positive advisory panel hearings have failed to translate into drug approval. The FDA's reaction to Nplate should also signal the agency's opinion of other ITP compounds up for review and in the pipeline, like Ligand Pharmaceuticals (NASDAQ:LGND) and GlaxoSmithKline's (NYSE:GSK) Promacta.

I'm not the only observer who thinks the agency's been unduly harsh with some of its approval decisions lately. Still, Nplate has a good chance of getting approved, thanks to its relatively positive advisory panel hearing and past FDA comments on the drug. Expect an interesting week for Amgen shares, as investors anxiously await the ruling.