[Absolute bioavailability of folic acid after 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 male healthy subjects within a balanced 2-way crossover trial either as one Folsan tablet (CAS 59-30-3, test preparation A) or as 2.5 ml of an injection solution (Folsan 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-out period. The mean predose serum level of folic acid amounted to 17.9 +/- 5.62 ng/ml before the oral and 18.2 +/- 5.73 ng/ml before the intravenous administration. The post dose serum levels were corrected with the individual predose levels. After oral administration of test preparation. A a mean peak serum concentration of 243 +/- 33.0 ng/ml (Cmax) was obtained after 2.24 +/- 0.85 h (tmax). 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 levels ranged from 559 to 1490 ng/ml. Following correction with the individual 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 bioavailability of folic acid was 76.2% +/- 13.8% (p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)