A 25% drop in the stock price of Rule Breakers pick Panacos Pharmaceuticals (NASDAQ:PANC) because its chief financial officer resigned seems a little harsh punishment, but there may have been more to the announcement: The company also slipped in word of yet another delay in clinical trials for its lead drug, bevirimat.

Bevirimat is in phase 2b testing to treat HIV. It's the first of a new class of HIV antiviral treatments called maturation inhibitors. Since last December, bevirimat's development has been beset with problems, after a tablet formulation of the drug failed in testing due to pharmacokinetic absorption issues, and Panacos had to revert back to using a liquid formulation.

Panacos has continued testing the liquid formulation while it tries to find a new tablet formulation that works. Initially, progress with this liquid formulation appeared to be on track, with data from another group of the phase 2b study reported in June.

Data from the next group of patients in this study was expected in the third quarter, but with the quarter almost at a close, Panacos has pushed that back to "early in the fourth quarter." This may represent a small delay in the program, but it really shouldn't take four months to enroll 10 subjects and complete 15 days of treatment for an ongoing study.

Last December, when Panacos first announced its formulation problems with the tablet form of bevirimat, I called the fall in the share price a buying opportunity. But with all the delays and new formulation problems cropping up at Panacos, it's no wonder investor confidence is slipping.

Setbacks are to be expected with development-stage drugmakers, because it can be tough to predict what will happen in clinical trials. But Panacos is starting to push things too far. If the next 300-milligram group in the phase 2b trial does not improve on the effectiveness of the past 250-mg group, the future will get much tougher for Panacos. 

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Fool contributor Brian Lawler owns shares of Panacos, but holds no position in any other company mentioned in this article. The Fool's disclosure policy is enrolled in clinical testing.