in the six months ended June 30, 2019 versus the prior year period. Sales and marketing expenses from iContact were $2.6 million for the six months ended June 30, 2018, and $0.4 million for the six months ended June 30, 2019.
Research and Development
Research and development expenses increased $0.9 million, or 5.9%, from $15.0 million for the six months ended June 30, 2018 to $15.9 million for the six months ended June 30, 2019. The change in the U.S. dollar versus other foreign currencies in 2019 compared to 2018 decreased our research and development expenses by approximately $0.4 million for the six months ended June 30, 2019. After adjusting for the change in the U.S. dollar versus other foreign currencies, the increase in research and development expenses was primarily driven by our acquisitions of Prime, Falcon and TrendKite, offset by lower compensation and related costs, lower professional fees, lower depreciation expense, and the divestiture of iContact. Research and development expenses from Prime, Falcon and TrendKite were $5.4 million for the six months ended June 30, 2019 versus $1.3 million for the six months ended June 30, 2018. Excluding our acquisitions of Prime, Falcon and TrendKite and the divestiture of iContact, compensation and related costs, professional fees, and depreciation expense decreased $1.6 million, $0.5 million and $0.8 million, respectively, in the six months ended June 30, 2019 versus the prior year period. Research and development expenses from iContact were $0.4 million for the six months ended June 30, 2018, and $0.1 million for the six months ended June 30, 2019.
General and Administrative
General and administrative expenses increased $9.7 million, or 11.1%, from $87.8 million for the six months ended June 30, 2018 to $97.5 million for the six months ended June 30, 2019. The change in the U.S. dollar versus other foreign currencies, principally the Euro, the British Pound, and the Canadian Dollar, in 2019 compared to 2018 decreased our general and administrative expenses by approximately $2.5 million for the six months ended June 30, 2019. After adjusting for the change in the U.S. dollar versus other foreign currencies, the increase in general and administrative expenses was primarily driven by our acquisitions of Prime, Falcon and TrendKite, offset by a decrease in compensation related costs, a decrease in professional fees, a decrease in rent and related costs, reduced depreciation expense, reduced bad debt expense and the divestiture of iContact. General and administrative expenses from Prime, Falcon and TrendKite were $16.2 million for the six months ended June 30, 2019 versus $2.9 million for the six months ended June 30, 2018. Excluding our acquisitions of Prime, Falcon and TrendKite and the divestiture of iContact, compensation related costs, professional fees, rent and related costs, depreciation expense, and bad debt expenses decreased $2.5 million, $0.9 million, $1.4 million, $0.6 million, and $0.9 million, respectively, in the six months ended June 30, 2019 versus the prior year period. General and administrative expenses from iContact were $1.5 million for the six months ended June 30, 2018, and $0.3 million for the six months ended June 30, 2019.
Foreign Exchange Gains (Losses)
We recognized a $2.1 million foreign exchange loss and an $8.1 million foreign exchange gain for the six months ended June 30, 2019 and June 30, 2018, respectively, due to fluctuations in foreign exchange rates that impacted the carrying value of certain intercompany notes and our 2017 First Lien Euro Term Credit Facility.
Gain on Sale of Business
We recognized a gain on the disposal of our iContact business of $28.1 million during the six months ended June 30, 2019.
Interest Expense
Interest expense decreased $2.0 million, or 4.9%, from $40.2 million for the six months ended June 30, 2018 to $38.2 million for the six months ended June 30, 2019. This decrease was primarily due to lower interest rates on our debt resulting from the debt repricing transactions of our 2017 First Lien Credit Facility on February 8, 2018 and October 22, 2018 that lowered interest rates, that were partially offset by an increase in LIBOR rates, and the write-off of approximately $0.4 million of deferred financing costs that was the result of our entering into an incremental facility amendment (the "January 2019 Incremental Amendment") to the credit agreement on January 11, 2019. The January 2019 Incremental Amendment provided for an incremental $75.0 million dollar-denominated term loan facility (the "Incremental Facility"). The terms of