  Hypothesis. Isoniazid is one of the primary drugs used in tuberculosis
treatment. Isoniazid encapsulation in liposomal vesicles can improve drug
therapeutic index and minimize toxic and side effects. In this work, we
consider mixtures of hydrogenated soy phosphatidylcholine/phosphatidylglycerol
(HSPC/DPPG) to get novel biocompatible liposomes for isoniazid pulmonary
delivery. Our goal is to understand if the entrapped drug affects bilayer
structure.
  Experiments. HSPC-DPPG unilamellar liposomes are prepared and characterized
by dynamic light scattering, $\zeta$-potential, fluorescence anisotropy and
Transmission Electron Microscopy. Isoniazid encapsulation is determined by UV
and Laser Transmission Spectroscopy. Calorimetry, light scattering and Surface
Pressure measurements are used to get insight on adsorption and thermodynamic
properties of lipid bilayers in the presence of the drug.
  Findings. We find that INH-lipid interaction can increase the entrapment
capability of the carrier due to isoniazid adsorption. The preferential
INH-HSPC dipole-dipole interaction promotes modification of lipid packing and
ordering and favors the condensation of a HSPC-richer phase in molar excess of
DPPG. Our findings highlight the importance of fundamental investigations of
drug-lipid interactions for the optimal design of liposomal nanocarriers.
