Alendronate, an oral bisphosphonate (e.g., Fosamax ), is eŠective in the treatment of osteoporosis, and the Fosamaxpackage insert advises that the bioavailability is reduced when taken with mineral water containing high levels of metal cations (Ca 2＋ , Mg 2＋ , etc.). However, standards regarding the water used when taking alendronate are unclear. In this study, the in‰uence of mineral water on the absorption of oral alendronate was investigated based on urinary excretion of its unchanged form in rats. Alendronate was diluted in each water sample and administered orally (0.7 mg/kg) to male Wistar rats after 24-hour fast. Urine samples were collected until 24 h after dosing. Urine samples were alkalinized, and alendronate in urine was precipitated as a calcium salt, followed by loading on an anion exchange cartridge. Eluted alendronate was derivatized with 9-‰uorenylmethoxycarbonyl (Fmoc) chloride and determined by HPLC with ‰uorescent detection. Cumulative urinary excretion recoveries of alendronate were calculated from the amounts of urinary excretion. Alendronate was rapidly excreted in theˆrst 6 h, and similar elimination rate constants were seen (from 0.28 to 0.45 h -1/2 ) among the water samples. Cumulative urinary excretion recoveries with tap water, evian  and 100％ deep ocean water were 0.98±0.17％, 0.80±0.18％ and 1.01±0.16％ (mean±S.E., n＝4). Those with Contrex (0.33±0.07％) were signiˆcantly lower when compared with ultrapure water (1.56±0.35％, p＜0.01). Theseˆndings suggest that the absorption of alendronate decreases based on the calcium concentration of mineral water. In conclusion, mineral water containing high levels of calcium is not recommended when alendronate is taken.

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