Prior to the regulatory approval of our medicines, we incur expenses for the manufacturing of drug product that could potentially be available to support the commercial launch of our products. We record all such costs as research and development expenses until the first reporting period when regulatory approval has been received or is otherwise considered probable.

WAYLIVRA inventory-related costs incurred subsequent to April 1, 2019 and TEGSEDI inventory-related costs incurred subsequent to July 1, 2018 are reflected as inventories on our condensed consolidated balance sheet at the lower of cost or net realizable value under the first-in, first-out, or FIFO, basis. At March 31, 2020, a majority of our physical inventory for WAYLIVRA and a portion of our physical inventory for TEGSEDI included API that we produced prior to regulatory approval. As such, there is no cost basis for this API as we previously expensed the related costs as research and development expenses.

We periodically analyze our inventory levels and write down inventory that has become obsolete, inventory that has a cost basis in excess of its estimated realizable value and inventory in excess of expected sales requirements as cost of product sales. The determination of whether inventory costs will be realizable requires estimates by our management and if actual market conditions are less favorable than projected by our management, additional write-downs of inventory may be required which would be recorded as a cost of product sales in the condensed consolidated statement of operations.

	March 31,		December 31,
	2020		2019
Raw materials	$	10,476	$	6,520
Work in process		2,646		2,039
Finished goods		601		258
Total inventories	$	13,723	$	8,817