Simultaneous membrane transport of two active pharmaceutical ingredients by charge assisted hydrogen bond complex formation

Using permeation through a model membrane in a Franz diffusion cell, we have demonstrated that acidic and basic active pharmaceutical ingredients (APIs) in deep eutectic ‘liquid co-crystal’ form can be held tightly together, even in solution, via strong hydrogen bonds or partially ionized interactions, providing simultaneous transport at rates much higher than solutions of their corresponding, commercially available crystalline salts, albeit at rates that are lower than the neutral forms of the individual molecules. It was also shown that the deep eutectic APIs do not have to be premade, but hydrogen-bonded complexes can be formed in situ by mixing the corresponding API–solvent solutions. To understand the behavior, we have extensively studied a range of nonstoichiometric mixtures of lidocaine and ibuprofen spectroscopically and via membrane transport. The data demonstrates the nature of the interactions between the acid and base and provides a route to tune the rate of membrane transport.