Gabapentin (Neurontin) may provide a safe and effective treatment for hot flashes in men receiving androgen deprivation therapy (ADT) for prostate cancer.
The drug originally was approved as a treatment for epileptic seizures, but it is being tested at much lower dos-ages for ADT-related hot flashes.
“To my knowledge, this is the first non-hormonal treatment of hot flashes in men, where results from a placebo-controlled trial support that a non-hormonal medication can be used to help some of our patients,” said lead investigator Charles Loprinzi, MD, professor of oncology at the Mayo Clinic in Rochester, Minn.
Dr. Loprinzi presented results of a 223-patient phase III trial that showed gabapentin reduced the frequency and intensity of hot flashes by up to 46% in men receiving androgen deprivation therapy. Interestingly, the men who received gabapentin reported fewer side effects than those men receiving a placebo, he said.
Until now, the only therapeutic agents proven to provide relief from hot flashes in this patient population have been hormones, some of which can actually fuel prostate cancer. Consequently, many men with prostate cancer do not use hormonal treatments for fear that their hormone-sensitive cancer will recur or because some therapies, such as estrogen, produce too many unwanted side effects, such as breast growth.
Because gabapentin works on the central nervous system, its function may be similar to that of some antidepressants that are prescribed to reduce hot flashes in women who have hot flashes. “But we don’t understand exactly how any of these drugs work to reduce hot flashes,” Dr. Loprinzi said.
The FDA approved gabapentin as a treatment of epileptic seizures in 1994 and for treating post-herpetic neuralgia pain in 2002. Two clinical trials testing gabapentin in menopausal women have found that dos-ages up to 900 mg a day decreased hot flashes by about 50%, the same dose and a similar degree of effectiveness found in this clinical trial.
The mean age of the men in the study was 70 years and all suffered from hot flashes that occurred at least 14 times a week. The men were randomized into four groups. Forty-four men received placebo and 48 received gabapentin 300 mg a day. A third group consisted of 42 men who received gabapentin as dosages that escalated up to 600 mg per day. The fourth group included 45 men whose gabapentin dosages reached 900 mg a day.
Using a scale of 1 to 4, the men recorded the daily number of mild, moderate, severe, and very severe hot flashes. The investigators found that median hot flash frequency and score decreased between 22% to 27% in the placebo group, 23% to 30% in the 300 mg per day group, 32% to 34% in the men receiving up to 600 mg per day, and 44% to 46% in group receiving up to 900 mg a day.
About 40% of men had hot flashes for longer than nine months and a similar percentage reported having at least 10 hot flashes a day, prior to entering the trial.
As the dosages increased from 300 to 900 mg per day, hot flashes progressively decreased. “There are data in women now that suggest up to 2,400 mg per day may be better than 900 mg per day, but whether that is true or not in men is a hypothesis at this time,” Dr. Loprinzi told Renal & Urology News.
It is common for patients on gabapentin to experience edema and some light-headedness or dizziness during the initial phases of therapy, but these effects were not observed in this study, he said. The likely reason, he explained, is that his group started patients on a very low dose. Even the men who received up to 900 mg a day were started on only 300 mg a day for the first week and then 600 mg a day the second week.