Metyrapone, an inhibitor of endogenous adrenal corticosteroid synthesis currently used in U.S. practice to test adrenocorticotropic hormone (ACTH) function, was safe and effective for treating endogenous Cushing’s syndrome in a multicenter, open-label, single-arm study of 50 patients, the first prospective test of metyrapone (Metopirone) as a therapeutic agent.
Treatment with metyrapone for 12 weeks normalized mean levels of urinary free cortisol (UFC) in 23 of the 49 patients (47%) in the efficacy analysis, and cut pretreatment mean UFC levels by at least 50% in another 16 patients (33%). Treatment also improved clinical signs of hypercortisolism, associated comorbidities, and quality of life, and was well tolerated, Lynnette K. Nieman, MD, said at the annual meeting of the Endocrine Society.
“This prospective study confirms that metyrapone is effective, has a rapid onset of action, and is a safe medical treatment for endogenous Cushing’s syndrome,” declared Dr. Nieman, chief of the endocrinology consultation service of the National Institutes of Health Clinical Center in Bethesda, Md.
The study included a 24-week extension phase of continued metyrapone treatment in patients whose mean UFC level fell to less than two times the upper limit of normal (ULN), but Dr. Nieman did not report results from this extension.
Confirmation of off-label and European experience
“This was the first prospective study of metyrapone, albeit a small study and with only short-term data presented. It confirms what we have known from its off label use in the U.S. and retrospective studies in the U.K. and Europe: Metyrapone normalizes mean UFC in approximately half of patients. Probably with more aggressive up titration efficacy will have been even higher, but of course with the trade-off of adrenal insufficiency,” said Maria Fleseriu, MD, professor and director of the pituitary center at Oregon Health & Science University in Portland, who was not involved with the study.
Dr. Maria Fleseriu
“Longer-term data from this prospective study is clearly needed to evaluate for possible loss of response, as well as adverse events related to precursors accumulation. We also need data on tumor size with long-term use in patients with Cushing’s disease, “Dr. Fleseriu added in an interview.
“Metyrapone, an 11-hydroxylase inhibitor, is not [Food and Drug Administration–approved for therapy] and thus it will be hard for it to become a first-line medical therapy,” she continued. “Furthermore, multiple times a day administration is not ideal for most patients; however if metyrapone is readily available and cheaper than other drugs, its use might increase over time. Hirsutism in women (though not all women develop this) and hypertension could be issues with long-term use,” she cautioned.
“We have used metyrapone off label for many years. It has a rapid onset of action, and we also have experience using it in combination therapy with ketoconazole, especially in patients with severe Cushing’s, although ketoconazole is not [FDA] approved for Cushing’s syndrome, and all combination therapies are off-label, too,” Dr. Fleseriu noted.
Metyrapone is approved by the European Medicines Agency for treating Cushing’s syndrome based “on observational, retrospective studies published over more than 50 years,” according to Dr. Nieman. The drug has FDA approval only for diagnostic purposes.
The PROMPT (Effects of Metyrapone in Patients With Endogenous Cushing’s Syndrome) study enrolled patients in eight European countries who were newly diagnosed with endogenous Cushing’s syndrome of any etiology. The study excluded patients with an advanced adrenal carcinoma, as well as patients with recurrent or persistent Cushing’s disease following transsphenoidal surgery. Patients also needed three 24-hour measures of UFC that were at least 50% above the ULN (165 nmol/24 hours).
The average age of the patients was 46 years; 69% were women, 90% had Cushing’s disease, and 8% had ectopic ACTH secretion. The average time from initial symptom onset was 4 years. Sixty-one percent had a history of pituitary surgery, 69% were hypertensive, 43% had diabetes or glucose intolerance, and 41% had osteoporosis. The median mean UFC at entry was 570 nmol/24 hours, which is 3.5 times the ULN, and ranged from 291 to 8,476 nmol/24 hours.
Patients began on a metyrapone dosage of 750 mg/day unless their mean UFC exceeded 5 times the ULN, in which case the dosage doubled to 1,500 mg/day. During the 12-week period, clinicians up- or down-titrated the dosage to ideally achieve a UFC less than the ULN while maintaining serum cortisol levels of 7-12 mcg/dL to preclude adrenal insufficiency effects. The median dosage at the end of 12 weeks was 1,500 mg/day, and ranged from 250 to 5,500 mg/day. One of the 50 patients dropped out because of an unrelated acute medical condition, and two patients underwent pituitary surgery despite a response to metyrapone and were included in the efficacy analysis.
After the first week on treatment, patients had a median 49% cut from their baseline UFC level, and after 12 weeks this rose to a median 74% cut from baseline. The study’s primary endpoint was normalization of UFC after 12 weeks, which occurred in 47% of patients, while 22% had a normal level in a late-night salivary cortisol measurement.
Two-thirds of patients had an improvement or resolution of their signs and symptoms, on average quality of life scores improved, median systolic and diastolic blood pressures decreased by 4-5 mm Hg, and average A1c levels were stable, but the mean cholesterol level decreased significantly, and testosterone levels rose significantly in women.