Product Sales

Net product sales consist of the following:



	Three Months Ended March 31,
Net Product Sales in the United States	2018		2017
EYLEA^®	$	984,049	$	854,387
ARCALYST^®	3,860		3,858
	$	987,909	$	858,245

The Company had product sales to certain customers that accounted for more than 10% of total gross product revenue for the three months ended March 31, 2018 and 2017. Sales to each of these customers as a percentage of the Company's total gross product revenue are as follows:



	Three Months Ended March 31,
	2018		2017
Besse Medical, a subsidiary of AmerisourceBergen Corporation	55	%	53	%
McKesson Corporation	40	%	27	%
Curascript SD Specialty Distribution, a subsidiary of Express Scripts	**		19	%
** For the three months ended March 31, 2018, sales to Curascript SD Specialty Distribution represented less than 10% of total gross product revenue.

Revenue from product sales is recognized at a point in time when our customer is deemed to have obtained control of the product, which generally occurs upon receipt by our distributors and specialty pharmacies. The Company's written contracts with its customers stipulate product is shipped freight on board destination (FOB destination).

The amount of revenue we recognize varies due to rebates and chargebacks provided under governmental and other programs, distribution-related fees, and other sales-related deductions. We estimate the amount of variable consideration that we will be entitled to, in order to determine the transaction price, based upon contracts with customers and government agencies, statutorily-defined discounts applicable to government-funded programs, historical experience, estimated payer mix, and other relevant factors.

The following table summarizes the provisions, and credits/payments, for these sales-related deductions during the three months ended March 31, 2018 and 2017.



	Rebates & Chargebacks			Distribution- Related Fees			Other Sales- Related Deductions			Total
Balance as of December 31, 2017	$	29,840		$	34,142		$	21,320		$	85,302
Provisions	48,495			51,716			11,170			111,381
Credits/payments	(30,674		)	(42,025		)	(14,665		)	(87,364		)
Balance as of March 31, 2018	$	47,661		$	43,833		$	17,825		$	109,319

Balance as of December 31, 2016	$	12,712		$	29,465		$	3,674		$	45,851
Provisions	38,908			41,175			9,520			89,603
Credits/payments	(28,502		)	(42,287		)	(8,632		)	(79,421		)
Balance as of March 31, 2017	$	23,118		$	28,353		$	4,562		$	56,033

Accruals for chargebacks are recorded as a direct reduction to accounts receivable and accruals for rebates and distribution-related fees are recorded within accrued liabilities.