The antiepileptic primidone impairs male rat sexual behavior

Many antiepileptic drugs (AEDs) produce sexual impairments. Of commonly prescribed AEDs, primidone produces the greatest impairments. Here we examined the effects of primidone on male rat sexual behavior. Sexually-experienced male rats received administration of either vehicle or primidone. After baseline measures were obtained, the effects of daily primidone treatment on home cage sexual performance were assessed three times over the course of 14 days. Motor activity and sucrose preference were also assessed during this time period. Results indicate that primidone impaired copulation but not sexual motivation. Specifically, animals receiving primidone displayed fewer ejaculations, required more time to achieve an intromission, and displayed fewer intromissions per attempted mount as evidenced by a lower intromission ratio. However, animals treated with primidone also chose a goal box containing a sexually-receptive female in an x-maze as often as animals receiving vehicle. The lower intromission ratio suggests an inability to achieve intromissions perhaps as a result of impaired erectile function. Primidone did not affect motor activity or sucrose consumption, an additional measure of natural reward. Together, these data indicate that primidone impairs male sexual activity and suggest that these impairments result primarily from changes in erectile function and not changes to mechanisms mediating motivation.