ABSOLUTE BIOAVAILABILITY OF FOLIC-ACID FOLLOWING ORAL-ADMINISTRATION OF A FOLIC-ACID TABLET FORMULATION IN HEALTHY-VOLUNTEERS

5 mg folic acid were administered in two sessions to 9 female and 8 ma le healthy subjects within a balanced 2-way crossover trial either as one Folsan(Ra) tablet (CAS 59-30-3, test preparation A) or as 2.5 ml o f an injection solution (Folsan(R) 2, reference preparation B). Folic acid was determined in serum and urine collected in fractions over 12 h after administration by means of a radioassay. Before each session a saturation period of 9 days duration was performed by administering 1 tablet per day containing 5 mg folic acid followed by a 4-day wash-ou t period. The mean predose serum level of folic acid amounted to 17.9 +/- 5.62 mg/ml before the oral and 18.2 +/- 5.73 ng/ml before the intr avenous administration. The post dose serum levels were corrected with the individual predose levels. After oral administration of test prep aration A a mean peak serum concentration of 243 +/- 33.0 ng/ml (C-max ) was obtained after 2.24 +/- 0.85 h (t(max)). The mean area under the corrected serum level time curve was determined with 1160 +/- 177 ng x h/ml (AUC ((0-12)). 6 min after intravenous administration serum lev els ranged from 559 to 1490 mg/ml. Following correction with the indiv idual predose levels the mean area under the curve amounted to 1550 +/ - 249 ng x h/ml. The individual bioavailability ratios of AUC (0-12) ( A versus B) varied between 49.3% and 96.7%. The mean absolute bioavail ability of folic acid was 76.2% +/- 13.8% (p < 0.001). Following oral administration of 5 mg folic acid 3180 +/- 1050 mu g (range: 1760-5640 mu g) folic acid was renally excreted in mean during the 0-12 h inter val. The respective mean excretion following 5 mg folic acid i.v. amou nted to 3830 +/- 1090 mu g (range: 1520-5860 mu g). Based upon urine e xcretion the mean absolute bioavailability of folic acid from the tabl et was 93.0% +/- 47.2% (ns).