NEW YORK (Reuters) - Pfizer Inc.'s experimental drug to raise "good" HDL cholesterol was effective and well tolerated in two small mid-stage trials, but appeared to cause a small increase in blood pressure among some patients, according to industry analysts.

Investors should note that even minor elevations in blood pressure could partially offset the cardiovascular benefits of elevated HDL," Merrill Lynch analyst David Risinger said in a research report about the drug, called torcetrapib.


Complete data on the studies of torcetrapib, the most important medicine in Pfizer's drug pipeline, will be formally presented Monday at the annual scientific meeting of the American College of Cardiology in Orlando, Florida.


But Wall Street analysts, including JP Morgan's Chris Shibutani and Lehman Brothers' Anthony Butler, this week issued research reports that analyze brief descriptions of the studies already provided by the cardiology group.


Pfizer aims to combine torcetrapib in a single tablet with the company's widely marketed Lipitor , which works instead by lowering levels of "bad" LDL cholesterol.


Pfizer has said the combination product, if approved, has the potential to outstrip Lipitor's current $10 billion in annual sales. It could do so, Pfizer believes, by better preventing heart attacks and stroke through its dual method of action.


In a highly publicized different trial described last April in the New England Journal of Medicine , volunteers who took daily 120-milligram doses of torcetrapib had a 46 percent increase in HDL. When Lipitor was added to the mix, the good cholesterol rose 61 percent.


Analysts said the latest mid-stage trials involved 162 subjects who took torcetrapib alone at various doses up to 90 milligrams, or who took placebos. Patients in the other 174-person trial took the same doses of torcetrapib, while also taking Lipitor.


HDL levels rose from 9 percent to 54.5 percent in those taking torcetrapib alone, and rose between 8.3 percent to 40.2 percent in those also taking Lipitor.


Risinger said researchers reported "small increases in systolic and diastolic blood pressure" in some treated patients. The analyst questioned whether the hypertension findings might help explain why Pfizer has decided to keep doses of torcetrapib down to 60-milligrams in far larger late-stage trials now being conducted.


"Is there an adverse hypertension signal?" Risinger asked in his report, adding that U.S. regulators can be expected to focus on the problem, if it is truly worrisome.


Lehman Brothers' Butler said neither study showed an increase in overall side effects with increasing dosages of torcetrapib.


"However, we expect further details on the significance (or insignificance) of the observed hypertension in the treatment groups during the American College of Cardiology" meeting, Butler said.


Butler said Pfizer officials commented that hypertension seems to be observed "mostly with higher dosages of torcetrapib."


But Pfizer spokeswoman Kate Robins told Reuters she could not comment on the studies until they were officially presented in their entirety on Monday.


"We prefer to comment on data that we know is accurate and look forward to discussing the full information," she said.