One interesting thing about earnings updates for biotechs is that their stocks can jump even when there aren't any positive earnings in the update. That's what happened for three biotechs this week.

Strongbridge Biopharma (NASDAQ:SBBP), Endo International plc (NASDAQ:ENDP), and Ziopharm Oncology (NASDAQ:ZIOP) saw their share prices soar by 27% or more over the last several days after the companies provided second-quarter updates. Here's what was in those updates that caused the stocks to move -- and whether or not any of these biotechs are buys now. 

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1. Strongbridge Biopharma: Pushing forward with its Cushing's drug

Shares of Strongbridge Biopharma skyrocketed 32% higher this week. The big catalyst for the biotech was its announcement on Wednesday of positive clinical results for endogenous Cushing's syndrome drug Recorlev. Strongbridge's management also highlighted those results in its Q2 update on the same day.

The company reported that Recorlev met the primary endpoint of the phase 3 clinical study evaluating the drug in treating endogenous Cushing's syndrome, a rare disease caused by chronic elevated cortisol exposure. Thirty percent of patients receiving Recorlev achieved normalization of mean urinary free cortisol (UFC) after six months of treatment without a dose increase of the drug. In addition, statistically significant improvement in patients taking Recorlev was seen in several cardiovascular risk measures.

Strongbridge's results were impressive enough that the company thinks that it might be able to win accelerated approval from the U.S. Food and Drug Administration (FDA). The biotech also plans to seek regulatory approvals for Recorlev in other countries.

2. Endo International: Adding more oomph to a great year

Endo International was another big winner this week. The biotech's share price increased 28%, thanks primarily to Endo's announcement of its second-quarter results on Wednesday. Endo was already having a great year in 2018, with the stock gaining 57% prior to this week. That's a marked improvement from the huge drops in its share price in the previous two years.

It's not that Endo's Q2 results were all that spectacular, however. Endo reported that its revenue fell 18% year over year, to $715 million. The company also posted a net loss of $52 million, or $0.23 per share. Investors were encouraged, though, that Endo's adjusted earnings per share (EPS) of $0.76 handily beat analysts' expectations of $0.54 per share.

The best news for Endo was that the company raised its full-year 2018 guidance. Endo now expects 2018 revenue of between $2.75 billion and $2.85 billion, up from its previous projection of revenue between $2.6 billion and $2.8 billion. The company is looking for full-year adjusted EPS between $2.50 and $2.60 compared to its previous outlook of $2.15 to $2.55.

3. Ziopharm Oncology: Musical chairs and a pipeline update 

Ziopharm Oncology stock jumped 27% this week. The biotech's shares began to move on Tuesday after Ziopharm announced upcoming changes to its board of directors. Momentum continued on the next day following the company's Q2 results update.

Investors seemed to like Ziopharm's game of musical chairs with its board. Two long-term board members, Sir Murray Brennan and Sen. Wyche Fowler, are stepping down when their terms expire on Sept. 18, 2018. Doug Pagan and Elan Ezickson are being nominated to take their places. Pagan and Ezickson have solid experience in leading biotech companies.

Ziopharm's Q2 update didn't contain any real surprises. The company's net loss of $0.12 per share was in line with Wall Street estimates. Ziopharm's management said, though, that they hope to resume trials of its CD19-targeted chimeric antigen receptor T cell (CAR-T) therapy by the end of 2018, pending resolution of questions that led the FDA to place a clinical hold on the program.

Are they buys?

Stonebridge could have a winner with Recorlev. However, assuming the drug wins approval, I think the jury is still out on how well it will compete against Corcept Therapeutics' Korlym. Corcept also has another promising Cushing's syndrome candidate, relacorilant, which should enter phase 3 clinical testing later this year.

My concern with Endo is that it's in debt -- heavily. The company has a net debt of $7.2 billion. It expects to spend close to $540 million this year just on interest, more than double what the biotech will invest in research and development. My preference is to wait for Endo to deliver consistent growth and pay down its huge debt for a while before considering buying this stock. 

The main problem for Ziopharm is cash. Although the biotech has enough money to fund operations into Q2 of next year, I expect that Ziopharm isn't too far away from from another stock offering that would likely hammer its stock price.

The bottom line, in my view, is that none of these three high-flying biotech stocks are great picks at this point. There are plenty of other stocks with stronger growth prospects and less murky outlooks that investors can buy.

Keith Speights has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.