Drug: Cladribine
Company: Merck KGaA
PDUFA date: On or about Dec. 5
Market potential: $1.5 billion

At this time last year Merck KGaA was widely billed as a strong contender in the race with Novartis to gain marketing approval for an oral MS drug. But what a difference a few months can make. First the FDA refused to accept the cladribine NDA, saying it still needed work. And then weeks ago European regulators rejected the therapy. That leaves the German company facing a fourth-quarter decision on the would-be blockbuster as Novartis busily rolls out Gilenya at an annual cost of $48,000.

Novartis may have benefited enormously by confronting safety issues raised by Gilenya early on in the trial process. Now that drug is headed to blockbuster status with $1.5 billion-plus in projected sales as it takes on injectables like Rebif and Betaseron. Analysts at Bernstein, meanwhile, are flagging regulatory concerns about Cladribine's long-term immunosuppression with worries about cancer.

The German company has bet a lot on cladribine, which has emerged as its most significant near-term prospect. But a rejection or delay will get Novartis plenty of time to capitalize on a major market shift that will be worth billions of dollars.

Here more on cladribine from the Financial Times, Wall Street Journal and Bloomberg.