7.Research and Development Accruals

We have various contracts with third parties related to our research and development activities. Costs that are incurred but not billed to us as of the end of the period are accrued. We make estimates of the amounts incurred in each period based on the information available to us and our knowledge of the nature of the contractual activities generating such costs. Clinical trial contract expenses are accrued based on units of activity. Expenses related to other research and development contracts, such as research contracts, toxicology study contracts and manufacturing contracts are estimated to be incurred generally on a straight-line basis over the duration of the contracts. Raw materials and study materials purchased for us by third parties are expensed at the time of purchase.

In the first quarter of 2017, we entered into a consulting agreement with a third party, pursuant to which we may be required to pay amounts ranging from $1.5 million to $4.0 million if certain future regulatory milestone events occur.  As of September 30, 2017, we do not consider any of the future regulatory milestone events as probable of occurring. As such, no expense was recognized for the three and nine months ended September 30, 2017.