Effect of promethazine on lumbar vertebral bone mass in postmenopausal women

Work in mice suggests that the age-related loss of bone mineral noted in that species is caused by an intrinsic defect in a haematopoietic cell population which results directly or indirectly in increased bone resorption. This age-related loss of bone mineral is prevented or reversed by well-tolerated doses of promethazine HCL. The present study was undertaken to determine if promethazine would retard or reverse bone loss in postmenopausal women.

Postmenopausal women whose spine (L2 to L4) bone mineral content (BMC) was two standard deviations below young normal values were assigned randomly to receive calcium or promethazine and calcium daily. Subjects who had been taking oral oestrogen for more than 4 years also were assigned randomly but independently to the calcium or promethazine groups.

All subjects were seen in the out-patient clinic of the Department of Medicine, School of Medicine, University of California, Los Angeles.

Healthy, ambulatory postmenopausal females were recruited by word of mouth and by advertisement from the local community. Fifty-four subjects completed the first 6 months of the study and 43 completed 30 months.

The subjects were assigned randomly to receive 1000 mg calcium daily or promethazine 50 mg and calcium 1000 mg daily throughout the period of the study.

Bone mineral content of the lumbar vertebrae (L2 to L4) was determined by dual photon densitometry every 6 months. Dorsolumbar spine X-rays were obtained yearly and at the completion of the study to detect new compression fractures.

In the groups not taking oestrogen, BMC decreased at the rate of 1.53% year-1 in the group given only calcium; in contrast, BMC increased at 3.22% year-1 in the group given promethazine and calcium (P < 0.001). Among the women taking oestrogen, increases in mean BMC were noted in both groups, but those taking promethazine and calcium had a greater rate of increase than observed in the group taking only calcium (5.62% vs. 1.97% per year-1, P < 0.001).

These results suggest that promethazine can induce a modest increase in vertebral BMC in postmenopausal women who are not taking oestrogen and greater increases in those who are.