For the nine months ended September 30, 2020, the increase in CPI-006 costs of $1.1 million as compared to the nine months ended September 30, 2019, primarily consisted of an increase of $2.4 million in clinical trial expenses and an increase of $0.3 million in other outside services, partially offset by a decrease of $1.6 million in drug manufacturing costs.
For the three months ended September 30, 2020, the decrease in CPI-818 costs of $1.2 million as compared to the three months ended September 30, 2019, primarily consisted of a decrease of $0.8 million in drug manufacturing costs and a decrease of $0.3 million in other outside services.
For the nine months ended September 30, 2020, the decrease in CPI-818 costs of $2.7 million as compared to the nine months ended September 30, 2019, primarily consisted of a decrease of $2.2 million in drug manufacturing costs and a decrease of $0.6 million in other outside services, partially offset by an increase of $0.1 million in clinical trial expenses.
For the three months ended September 30, 2020, the decrease in other program costs of $0.4 million as compared to the three months ended September 30, 2019, primarily consisted of a decrease of $0.3 million in outside services and a decrease of $0.1 million in drug manufacturing costs.
For the nine months ended September 30, 2020, the decrease in other program costs of $0.2 million as compared to the nine months ended September 30, 2019, primarily consisted of a decrease of $0.7 million in outside services, partially offset by an increase of $0.5 million in drug manufacturing costs.
For the three months ended September 30, 2020, the decrease in unallocated costs of $0.7 million as compared to the three months ended September 30, 2019, primarily consisted of a decrease of $0.5 million in personnel and related costs and a decrease of $0.2 million in other outside services.
For the nine months ended September 30, 2020, the decrease in unallocated costs of $1.5 million as compared to the nine months ended September 30, 2019, primarily consisted of a decrease of $1.1 million in outside services and a decrease of $0.4 million in personnel and related costs.
General and Administrative Expense
For the three months ended September 30, 2020, the increase in general and administrative expenses of $0.7 million as compared to the three months ended September 30, 2019, primarily consisted of an increase of $1.0 million in professional service costs, partially offset by a $0.3 million decrease in stock-based compensation expense.
For the nine months ended September 30, 2020, the increase of $0.9 million in general and administrative expenses as compared to the nine months ended September 30, 2019, primarily consisted of an increase of $1.6 million in professional service costs and an increase of $0.2 million in personnel costs, partially offset by a decrease of $0.9 million in stock-based compensation expense.
Interest Income and Other Expense, net
For the three months ended September 30, 2020, the decrease in interest income and other expense, net of $0.5 million as compared to the three months ended September 30, 2019, primarily consisted of a decrease in interest income earned due to a decrease in cash equivalents and marketable securities and a decrease in interest rates.
For the nine months ended September 30, 2020, the decrease in interest income and other expense, net of $1.3 million as compared to the nine months ended September 30, 2019, primarily consisted of a decrease in interest income earned due to a decrease in cash equivalents and marketable securities and a decrease in interest rates.