In vitro and in vivo assessment of the bioavailability of potassium from a potassium tartrate tablet

The bioavailability of potassium from orally administered potassium tartrate was evaluated in 20 normal subjects under metabolic balance conditions. Subjects were given 34 mmol potassium (5 tablets of Cal‐K®) as a divided dose on each of 2 consecutive days. Urinary excretion of potassium, as determined from 24‐h urinary collections on the 3 days preceding dosage totalled 192·6 ± 50·9 mmol (mean ± S.D., n = 20). It increased significantly ( p < 0·05) to 258·7 ± 54·2 mmol for the 2 days of dosage and the following day. The difference of 66.1 mmol representing absorbed potassium was close to the 68 mmol potassium given and indicated a bioavailability of potassium in excess of 97 per cent; after correction for creatinine excretion, potassium recovery rose to 99·9 per cent. The dissolution characteristics of the Cal‐K® tablets were also determined. After dissolution in simulated gastric juice (pH 1·2), 84·4 ± 10·6 per cent (mean ± S.D., 6 experiments) was dissolved; after adjustment to pH 7·3, dissolved potassium increased to 91·3·8·5 per cent. No precipitation or residue formed as a result of the pH change. Both sets of results indicate that potassium from these potassium tartrate tablets is in a highly bioavailable form.