Fluoride bioavailability from slow‐release sodium fluoride given with calcium citrate

Clinical pharmacology of slow‐release sodium fluoride given with calcium citrate was examined in acute and long‐term studies. Following a single oral administration of 50 mg slow‐release sodium fluoride, a peak serum fluoride concentration (C_max) of 184 ng/ml was reached in 2 h; thereafter, serum fluoride concentration declined with a T_1/2 of 5.9 h. The concurrent administration of calcium citrate (400 mg calcium) gave an equivalent T_max (time required to attain C_max) and T_1/2, but a lower C_max of 135 ng/ml. The coadministration of a meal with fluoride also reduced C_max but increased T_max. The area under the serum concentration curve of slow‐release sodium fluoride was reduced 17‐27% by a meal or calcium citrate. Thus, calcium citrate reduced fluoride absorption and peak fluoride concentration in serum of slow‐release sodium fluoride but did not affect the time required to reach peak concentration or the rate of subsequent decline. The effect of a meal was similar, except for a longer period required to reach peak serum concentration. During long‐term administration of 25 mg slow‐release sodium fluoride coadministered with 400 mg calcium as calcium citrate on a twice daily schedule, the trough level of serum fluoride could be kept between 95 and 190 ng/ml, believed to be the therapeutic window.