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Arena Pharmaceuticals Inc. (ARNA) and Eisai Co. (ESALY, 4523.TO) said that a study of the diet pill lorcaserin showed that the drug seems to concentrate in the human brain less than it does in rats.
The data is part of the companies' work to respond to Food and Drug Administration concerns that led to the pill being rejected for approval last year. The agency requested multiple sets of new data including studies related to breast cancer and brain cancer occurring in rats, and more information on heart-related risk.
The company said that the effort to address other FDA concerns is ongoing.
Arena conducted the study by measuring lorcaserin concentrations in human cerebrospinal fluid and then seeing how that compared to the amount of the drug in blood plasma.
The company used an "apparent consistent relationship" of the amount of lorcaserin in the brain in relation to the spinal fluid of mice, rats and monkeys. That ratio was used to predict the corresponding amount of the drug in the human brain using the spinal fluid measurements.
Using the new data and previous information, Arena estimates that human brain exposure to the drug is 1.7 times the plasma concentration at normal dose. In rats with a much higher dose, but which didn't have brain cancer, the ratio was 24 times.
Arena noted that its estimates in the study are based on "certain assumptions and extrapolations" and the FDA may have different findings when looking at the raw data. The agency also may not view the company estimates as "reliable or predictive of the safety margin," Arena said in a statement.
-By Thomas Gryta, Dow Jones Newswires; 212-416-2169; firstname.lastname@example.org