Hyperprolactinemic response after bromocriptine withdrawal in women with prolactin-secreting pituitary tumors.

In patients with prolactin (PRL)-secreting tumors, plasma PRL concentrations after discontinuation of bromocriptine therapy have been used clinically as an index of tumor activity. To investigate the pattern of PRL response under these conditions, seven women on chronic bromocriptine therapy for PRL-producing pituitary tumors were followed with serial PRL determinations for 2 months after bromocriptine withdrawal. In these patients, peak PRL concentrations were achieved 28.1 days (mean; range, 14 to 49 days) after bromocriptine discontinuation. However, PRL concentrations did not usually plateau until at least 40 days after cessation of therapy, and the pattern of PRL response was highly variable. Because of the inconsistent pattern of serum PRL response during the first 40 days after discontinuation of bromocriptine, decisions regarding tumor activity based on PRL concentrations should not be made until at least 6 weeks after withdrawal of the drug.