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

TEGSEDI inventory related costs incurred subsequent to July 1, 2018 are reflected as inventory on our condensed consolidated balance sheet at the lower of cost or net realizable value under the first-in, first-out, or FIFO, basis. We did not have capitalized costs related to WAYLIVRA on our condensed consolidated balance sheet as of September 30, 2019. 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 statements of operations. We did not record any material inventory write-offs for the nine months ended September 30, 2019 or 2018.

	September 30,		December 31,
	2019		2018
Raw materials	$	6,520	$	—
Work in process		1,802		—
Finished goods		319		85
Total inventories	$	8,641	$	85