The most appropriate treatment is a dopamine agonist such as cabergoline. Hyperprolactinemia as a result of a prolactinoma is a possible cause of erectile dysfunction and decreased libido and may be successfully treated with a dopamine agonist. In addition to the sexual dysfunction associated with hyperprolactinemia, semen parameters are often abnormal; patients commonly demonstrate oligoasthenospermia (reduced sperm motility) and at times complete azoospermia. Three months of treatment are typically needed prior to return of improved semen parameters. Prolactin is secreted by the pituitary lactotroph cells under tonic inhibition by dopamine. Dopamine agonist therapy can normalize prolactin levels, reverse hypogonadism, and shrink tumors by at least 50% in almost 90% of patients. Evaluation of the infertile male with abnormal findings on semen analysis should always include investigation of the hypothalamic-pituitary-testicular (HPT) axis. Disturbances in this axis may result in failure of gonadotropin release from the anterior pituitary and insufficient testosterone production as well as absent or diminished spermatogenesis.

Clomiphene citrate is effective only when the HPT axis is intact, which does not apply for this patient. Although the indication for clomiphene citrate in the infertile male population remains controversial, some clinicians use it to increase endogenous follicle-stimulating hormone and luteinizing hormone output from the anterior pituitary to support testosterone production by Leydig cells.

Sildenafil may improve erectile dysfunction in this patient, but it will not increase endogenous testosterone levels and will not improve his hyperprolactinemic state.

Testosterone replacement therapy would be helpful to alleviate the sexual side effects of this patient's hyperprolactinemic state; however, no restoration of spermatogenesis would occur, and therefore infertility would persist. Neither testosterone replacement nor sildenafil therapy will reduce the size of the patient's prolactinoma.