Fluoride bioavailability from immediate-release sodium fluoride with calcium carbonate compared with slow-release sodium fluoride with calcium citrate.

The circadian variation in serum fluoride was compared between treatment with immediate-release sodium fluoride (IR-NaF) (30 mg) and calcium carbonate (500 mg calcium) and slow-release sodium fluoride (SR-NaF) (25 mg) and calcium citrate (400 mg calcium) in seven patients with postmenopausal osteoporosis maintained on long-term fluoride treatment. During 12 h following a dose of SR-NaF, serum fluoride levels could be largely kept within the therapeutic window (believed to be 95-190 ng/ml or 5-10 mumol/l). In contrast, IR-NaF produced a wide circadian fluctuation with peak-to-trough change of about 200 ng/ml. Compared to SR-NaF, IR-NaF caused a significantly higher peak fluoride concentration in serum (322 vs. 158 ng/ml), and greater area under the curve (2269 vs. 1321 ng.h/ml) and urinary fluoride (6.72 vs. 3.80 mg/12 h). Thus, fluoride absorption from IR-NaF was twice as high as that from SR-NaF.