The absorption of estramustine is reduced by milk,foods, anddrugs containing calcium.
A randomised three-way crossover study in 6 patients with prostate cancer showed that absorption of single-doses of estramustine disodium (equivalent to 140mg of estramustine) was reduced by 59 % when taken with 200 mL of milk, and by 33 % when taken with a standardised breakfast (2 pieces of white bread with margarine, ham, tomato, marmalade and water). Peak serum estramustine levels were reduced by 68 % and 43%,respectively (See reference number 1).
In vitro studies suggest that estramustine combines with calcium ions in milk and food to form a poorly-soluble complex that is not as well absorbed as parent compound (See reference number 1)
An established interaction although information is limited. The manufacturers recommend that estramustine should be taken not less than 1 hour before or 2 hrs after meals,and that it should not be taken with milk, milk products, calcium-rich foods,(See reference number 2,3) or drugs (such as calcium-containing antacids) (See reference number 3).
Gunnarsson P O,Davidsson T, Andersson S-B, Backman C, Johansson S-Å. Impairment of estramustine phosphate absorption by concurrent intake of milk and food. Eur J Clin Pharmacol (1990) 38, 189–93.
Estracyt (Estramustine sodium phosphate). Pharmacia Ltd. UK Summary of product characteristics,July 2007.
Emcyt (Estramustine phosphate sodium). Pharmacia & Upjohn Co. US Prescribing information,February 2006.