Longitudinal pharmacokinetic study of β-carotene as a photoprotective agent was performed in vitro and in vivo.
During long-term administration, changes in the serum β-carotene concentration were investigated in a man and his son who both had erythropoietic protoporphyria. Over a period of 4yr, 150mg of β-carotene were administered per day to the man and 50mg per day to his son.It took one yr for both patients to reach 1μg/ml of β-carotene concentration in serum. The serum concentration of β-carotene remained constant at 1-2 μg/ml in serum after continued administration for 3yr.
In a single-dose study, 50 mg of β-carotene were administered to 3 healthy male volunteers, but the β-carotene was undetectable in serum in all 3 cases.
β-carotene was stable in artificial gastric and enteric juices.
In enterohepatic circulation experiments with rats, the amount of β-carotene absorbed from gastrointestinal tract was low.
Fifteen nanograms of β-carotene were adsorbed to the erythrocyte membrane per 1 hematocrit.
Since β-carotene is hardly absorbed from the gastrointestinal tract, and is rapidly adsorbed on the erythrocyte membrane, we can conclude that it took a very long time to reach the steady state of β-carotene concentration in serum under the longitudinal administration.
