Drug release from non-aqueous suspensions. I. Release of phenobarbital and phenobarbital sodium from paraffin suspensions.

The rate at which phenobarbital and phenobarbital sodium, suspended in liquid paraffin, are released to buffers pH = 3.0, 7.4 and 10.0 has been studied. The release rate of phenobarbital depends on its solubility and hence on the pH, whereas the initial release rate of phenobarbital sodium is governed by sedimentation and hence is independent of the pH. However, when phenobarbital sodium is released to buffer pH = 3.0, it crystallizes in the interfacial layer after an initial release time. The release process in the release apparatus used cannot be described by a theory based on forced convection [i.e. the (E)SCRD-theory], but has to be regarded as a natural convection process.