With the SPDR S&P Biotech Index up 75% 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.

If a tree falls in the Forest ...
The age-old riddle has been answered: If a tree falls in the forest, Actavis picks it up!

We began the week with a megabuyout announcement that Actavis would be purchasing global pharmaceutical company Forest Laboratories (NYSE: FRX) for roughly $25 billion (at the time of the announcement). Under the terms of the deal, Forest Labs shareholders will receive $26.04 in cash per share and 0.3306 Actavis shares. Overall, shares of Forest Labs rocketed higher by 36% this week on the news, and they could remain quite volatile as the purchase price is primarily tied to the performance of Actavis' share price.

The deal itself will add to Actavis' bottom line immediately and should provider double-digit EPS accretion in 2015 and 2016. Furthermore, cost synergies from the combination of the two companies could read up to $1 billion with Actavis forecasting free cash flow in excess of $4 billion. While the Street seems to like the buyout, I remain skeptical with Forest's primary drug, Namenda, which accounts for nearly half of its current revenue, losing patent protection next year.

An A-OK from the FDA
It's been a long road coming for Chelsea Therapeutics (NASDAQ: CHTP) and Northera, its low blood pressure medication designed to reduce dizziness in Parkinson's disease patients, but the FDA on Tuesday approved Northera as a treatment of symptomatic neurogenic orthostatic hypotension, or NOH. 

The approval itself was no guarantee, given that Northera had been denied an approval previously and, while demonstrating efficacy over the short term (one to two weeks), had not previously established any statistically significant effectiveness when used for many weeks. With this approval Northera swoops in as the only FDA-approved treatment for symptomatic NOH and is estimated to have peak sales potential of $400 million. In theory, this means shares could have more room left to run, but that's only if Chelsea Therapeutics can successfully launch and market its drug.

Half the battle is over. Now the other half begins!

Isis notches another victory
Chalk up another positive trial outcome for Isis Pharmaceuticals (IONS -3.16%), whose antisense technology platform has afford it one of the largest clinical pipelines for any mid-cap biopharma in the world.

Yesterday, Isis announced positive results from its multiple-dose study of ISIS-SMN Rx, which it's developing in collaboration with Biogen Idec as a treatment for children with spinal muscular atrophy, or SMA. Utilizing the Hammersmith Functional Motor Scale-Expanded point scale, which measures improvements in muscle function for patients with SMA, the 3 mg, 6 mg, and 9 mg doses produced HFMSE scores of 1.5 points, 2.3 points, and 3.7 points, respectively, after initial dosing with ISIS-SMN Rx nine months prior. In addition, an assay test developed to measure SMN protein levels in patients' cerebral spinal fluid more than doubled in the two highest dosing cohorts. In short, ISIS-SMN Rx delivered notable increases in muscle function.

There are few treatment options currently available for SMA patients, so if ISIS-SMN Rx continues to outperform in studies, there's a decent chance it could become a blockbuster drug if approved.

Raptor attacks Huntington's disease
Sharing in Isis' bullishness was Raptor Pharmaceuticals (NASDAQ: RPTP) which, on Thursday, reported positive results from its ongoing phase 2/3 trial involving RP103 as a treatment for Huntington's disease.

At the 18-month mark, Raptor noted there was a "positive trend toward slower progression of Total Motor Score, or TMS, in patients treated with RP103 vs. those patients on placebo, the primary endpoint of the study." Raptor specifically noted that TMS progression was 32% slower in the RP103 intent-to-treat group at 18 months, and that 89 of 96 patients had remained in the study which lends to the drugs' safety and tolerability profile. Raptor will also be running an additional 18-month open-label extension study on RP103 with these patients.  

While I'd personally love to see Huntington's disease patients get pharmacologic assistance where little currently exists, I also understand it's a very difficult disease to treat. It's also no easy task convincing the FDA that a drug can treat a difficult disease, either. With that being said, I'd suggest more of a wait-and-see approach with Raptor at the moment than attempting to buy or sell off of this data.

Finally, this week's disaster du jour moment goes to small-cap biopharmaceutical company Onconova Therapeutics (ONTX -0.08%), which lost 37% on the week after announcing on Thursday that experimental drug rigosertib failed to meet its primary endpoint in its phase 3 ONTIME trial for patients with higher-risk myelodysplastic syndrome (MDS) who had progressed or relapsed while using hypomethylating agents.

Although the median overall survival in Onconova's analysis favored rigosertib at 8.2 months versus 5.8 months for the placebo, a relatively high p-value of 0.27 brought too much of an element of chance to the table in the final results, making them not statistically significant. It may not be a total wash for Onconova and rigosertib, however, as a smaller subset of patients in a post-hoc analysis demonstrated a median overall survival of 8.5 months, compared with 4.7 months in the placebo. This group had a low p-value (implying the differentiation in results was because of rigosertib) and a 33% reduction in death risk relative to the placebo.

Ultimately, Onconova was hoping for a broad-market approval for high-risk MDS but may have to settle for just a sliver, if anything. Let's not forget that rigosertib also failed to deliver in a late-stage study in December for metastatic prostate cancer. The company still has ongoing tests involving rigosertib for low-risk MDS, but beyond that has only an early stage clinical or wholly preclinical platform. Following these results, I'd suggest parking yourself safely on the sidelines unless rigosertib delivers strong results in low-risk MDS.