Barbiturates, in general, may appear in milk and readily cross the placental barrier. They are bound to plasma and tissue proteins to a varying degree and binding increases directly as a function of lipid solubility. The plasma half-life is about 35 hours. The bioavailability of the butalbital component of Butalbital compound with Codeine capsules is equivalent to that of a solution except for a decrease in the rate of absorption. Caffeine Like most xanthines, caffeine is rapidly absorbed and distributed in all body tissues and fluids, including the CNS, fetal tissues, and breast milk.
Caffeine is cleared rapidly through metabolism and excretion in the urine.
The plasma half-life is about 3 hours. The bioavailability of the caffeine component for Butalbital compound with Codeine capsules is equivalent to that of a solution except for a slightly longer time to peak.