With the SPDR S&P Biotech Index up 29% over the trailing 12-month period, it's evident that investment dollars are willingly flowing into the biotech sector. Keeping that in mind, let's have a look at some of the rulings, studies, and companies that made waves in the sector last week.

As you might imagine, most investors are focused on earnings season, so plenty of important biotech news wound up being swept under the rug this week. For the most part, this was a week that went to the small-cap and micro-cap biotechs.

To begin, we had two headline approvals by the Food and Drug Administration this week: Uceris from Santarus (NASDAQ: SNTS) for active, mild-to-moderate ulcerative colitis, and Zecuity from NuPathe (NASDAQ: PATH) for acute migraines.

Let me start off by saying I was dead wrong in my prognostication that Uceris wouldn't get approved by the FDA -- it did, and as I've said, I like my crow with ketchup. Perhaps the even bigger news wasn't the approval itself, but Santarus' fiscal 2013 outlook, which pegs revenue in the $320 million to $325 million range (more than 50% higher than 2012) and EPS at $0.79-$0.85. Santarus has a lot more going on in its product line than just Uceris, so these figures could be reasonably reached, but I'm simply waiting on the sidelines to see how it handles the Uceris launch. 

NuPathe, on the other hand, is in partner-hunting mode after receiving approval for its transdermal migraine patch, which delivers sumatriptan subcutaneously via electronic pulses. It'll definitely be an uphill battle for NuPathe with Zecuity, because cheaper injectable forms of sumatriptan do exist, and, as I highlighted yesterday, even needle-free systems exist from Zogenix. However, assuming it gets a top-tier launch partner and it prices the once-daily patch reasonably, it could end up being quite a bargain here.  

FDA action was also the inspiration behind wild moves in Hyperion Therapeutics (NASDAQ: HPTX) and Neuralstem (NASDAQ:CUR).

Hyperion Therapeutics pulled its best NASA impression this week and soared following an announcement from the FDA that it'll be postponing its PDUFA decision on Ravicti, which was due by Jan. 23 by an additional three months. Normally, that would raise safety or efficacy concerns with investors, but the wording Hyperion used -- "The agency is working on labeling and post-marketing requirements," as pointed out by Foolish health-care analyst David Williamson -- leads investors to believe the drug is as good as approved. Hyperion had planned to bring Ravicti, which manages urea cycle disorders, to market in early 2013, but that's looking more like a midsummer launch as of now. 

Neuralstem shareholders can sleep easier at night knowing that the FDA has given the stem cell therapy company the OK to test NSI-566, its spinal stem cell transplantation therapy, in patients with spinal cord injuries. As the Fool's Brian Orelli reports, the trial is specifically designed to determine safety but will have secondary endpoints such as analyzing graft survival and determining if any motor or sensory functions improve. Although NSI-566 has orphan drug status with the FDA and this is clearly a step in the right direction, I remain skeptical of its long-term potential. 

Finally, Elan (NYSE:ELN) and Biogen Idec announced on Wednesday that they've filed for expanded use of their multiple sclerosis drug, Tysabri, with both the FDA and the European Medicines Agency. Currently, Tysabri is approved to treat MS patients who've tried other medications, but this expanded use would push for Tysabri as a first-line treatment in MS and potentially exposure Elan and Biogen Idec to early-stage revenue, as well as give early onset MS patients a new drug choice.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.