manufacturing costs for IV meloxicam, an increase in salaries and benefits expense, an increase in Phase IIIb clinical trials and a modest increase in development costs for other pipeline products. These increases were partially offset by a decrease in Phase III clinical trial costs.
General and administrative expenses were $13.0 million and $6.3 million for the three months ended June 30, 2018 and 2017, respectively. The increase of $6.7 million was primarily due to increased commercial costs as well as increased legal and consulting fees associated with addressing the CRL issued by the FDA regarding the NDA for IV meloxicam. General and administrative expenses were $22.5 million and $10.4 million for the six months ended June 30, 2018 and 2017, respectively. The increase of $12.1 million was primarily due to increased commercial costs as well as increased legal and consulting fees associated with addressing the CRL.
Amortization expense was $0.6 million for each of the three months ended June 30, 2018 and 2017, and $1.3 million for each of the six months ended June 30, 2018 and 2017. This expense was solely related to the amortization of Recro’s royalties and contract manufacturing relationships intangible asset over its estimated useful life.
Interest expense, net, was $2.1 million and $1.1 million for the three months ended June 30, 2018 and 2017, and, $4.0 million and $2.2 million during the six months ended June 30, 2018 and 2017, respectively. The increase in both periods was primarily due to the higher principal balance on the Athyrium senior secured term loan and amortization of the related financing costs, which was partially offset by a lower interest rate on the Athyrium senior secured term loan versus Recro’s previous loan with OrbiMed.
Income tax benefit was $2.7 million and $1.7 million for the three months ended June 30, 2018 and 2017, and, $5.1 million and $2.0 million during the six months ended June 30, 2018 and 2017, respectively, related exclusively to our U.S. operations. The increase in tax benefit for both periods was primarily due to increased losses in the United States.
For the three months ended June 30, 2018, Recro reported a net loss of $12.7 million, or $0.62 diluted loss per share, compared to net loss of $8.9 million, or $0.48 diluted loss per share, for the comparable period in 2017. For the six months ended June 30, 2018, Recro reported a net loss of $25.2 million, or $1.27 diluted loss per share, compared to net loss of $16.9 million, or $0.89 diluted loss per share, for the comparable period in 2017.
Financial Guidance
The Company reaffirms its 2018 CDMO guidance and believes it will generate approximately $70 million in revenue despite the anticipated unfavorable impact of the adoption of the new revenue recognition standard, and taking into consideration existing contracts and timing of customer order patterns, as well as our experience with customer’s product market estimations.