The company developing Indiplon says federal regulators may require additional clinical tests before approving the experimental insomnia drug. Last month Neurocrine Biosciences and Pfizer received an approvable letter on the 5 mg. and 10-mg. doses of indiplon but a rejection letter on the 15-mg. strength. After reviewing the letters, Neurocrine said the FDA “may require” additional clinical trials on the lower doses and “will likely” require additional clinical data on the higher dose.