[In the vivo release of drugs from hydrogels]

The in vivo release of chlorpromazine and dioxopromethazine from equiviscous methyl cellulose and polyvinylpyrrolidone hydrogels has been determined in 8 volunteers and brought in relation to results obtained from in vitro studies. For all the individual variations observed, the availability of the drugs was, as a rule, greater from the hydrogels based on the loosely-binding methyl cellulose (e.g., more than doubled) than from the hydrogels based on polyvinylpyrrolidone. Whereas the in vivo and in vitro liberation rates of chlorpromazine (which has a relatively great association power) were of comparable magnitude, the in vivo release of dioxopromethazine was considerably lower as was to be expected considering the results from in vitro studies. Obviously, physico-chemical factors (in the present case, the coefficient of distribution) super-impose the effect of the binding on the bioavailability. Already 10 min after application of the hydrogels, the liberation rate amounted up to 73%.