Net revenue for the nine months ended September 30, 2020 was $231.5 million, compared to $186.3 million for the first nine months of 2019, an increase of $45.2 million, or 24%. The increase in net revenue was driven by a $43.6 million increase, or 28%, in net revenue of Advanced Wound Care products and a $1.5 million increase, or 5%, in net revenue of Surgical & Sports Medicine products compared to the prior year. Net revenue of PuraPly products for the nine months ended September 30, 2020 were $102.0 million, compared to $86.9 million for the first nine months of 2019, an increase of $15.1 million, or 17%. Net revenue of PuraPly products represented approximately 44% of net revenue for the nine months ended September 30, 2020, compared to 47% for the first nine months of 2019.
Gross profit for the nine months ended September 30, 2020 was $169.7 million or 73% of net revenue, compared to $130.8 million, or 70% of net revenue, for the first nine months of 2019, an increase of $38.9 million, or 30%. The increase in gross profit resulted primarily from increased sales volume due to the strength in our Advanced Wound Care and Surgical & Sports Medicine products as well as a shift in product mix to our higher gross margin products.
Operating expenses for the nine months ended September 30, 2020 were $164.0 million, compared to $158.5 million for the first nine months of 2019, an increase of $5.6 million, or 4%. The increase in operating expenses in 2020 was driven primarily by higher selling, general and administrative expenses which increased to $150.3 million, compared to $147.3 million for the first nine months of 2019, an increase of $2.9 million, or 2% and, to a lesser extent, higher R&D expense which was $13.8 million, compared to $11.2 million for the first nine months of 2019, an increase of $2.6 million, or 24%. The increase in selling, general and administrative expenses was primarily due to a $10.5 million increase related to additional headcount, primarily in our direct sales force and increased sales commissions due to increased sales, a $2.0 million cancellation fee for certain product development and consulting agreements, and a $0.9 million increase in credit card processing fees due to increased collection. These increases were partially offset by a $6.4 million decrease related to reduced travel and marketing programs amid travel restrictions in place due to the COVID-19, a $1.4 million decrease in legal, consulting fees and other costs associated with the ongoing operations of our business, a $2.0 decrease in amortization associated with the intangible assets amortized using an accelerated method and a $0.8 million decrease in bad debt primarily due to the collection of the previously reserved related party receivables. The increase in research and development expenses was primarily due to an increase in process development costs associated with a new contract manufacturer, increased headcount associated with our existing Advanced Wound Care and Surgical & Sports Medicine products, an increase in product costs associated with our pipeline products not yet commercialized and an increase in costs to move products through the regulatory pathway (e.g., seek BLA approval). The increase was partially offset by a decrease due to delayed enrollment in trials and limited clinical spending due to the COVID-19.
Operating income for the nine months ended September 30, 2020 was $5.6 million, compared to an operating loss of $27.7 million for the first nine months of 2019, an increase of $33.3 million.
Total other expenses for the nine months ended September 30, 2020 were $6.1 million, compared to $8.2 million for the first nine months of 2019, a decrease of $2.2 million, or 27%. The decrease in total other expenses for the nine months ended September 30, 2020 was driven primarily by a gain of $2.2 million on the settlement of deferred acquisition consideration for the nine months ended September 30, 2020, and a $1.9 million non-cash loss on the extinguishment of debt related to the write-off of unamortized debt discount upon repayment of the master lease agreement as well as early payment penalties for the nine months ended September 2019, which did not impact results in the current period. The decrease in total other expenses for the nine months ended September 30, 2020 was partially offset by an increase in interest expense of $2.0 million related to increased borrowings compared to the prior year period.