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Isoniazid (INH) is a key antitubercular agent, which exhibits poor chemical stability in the solid state associated with the hydrazide group. Cocrystallization with Gentisic Acid having antioxidant activity, may produce solid forms with improved pharmaceutical properties. The complementary nature of the functional groups of isoniazid and the chosen coformer resulted in success for cocrystal formation. Cocrystal (INH-Gentisic acid) was characterized by solid-state NMR, DSC, PXRD and single crystal-XRD. The synthesized cocrystals were tested for the inhibition of synthetic-free radicals, DPPH. INH-Gentisic acid demonstrated high free radical scavenging activity against DPPH (78.36% for 125µg/ml concentration) which were better than that of ascorbic acid (37.16%) used as standard. Moreover solubility, stability and flowability properties of the synthesized cocrystals are optimized.

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This study reports an organic salt prepared from an antibacterial drug, levofloxacin and antioxidant γ-resorcylic acid. A simple preparation method leads to a crystal with disordered structure. The idea is to prepare an organic salt comprising of pharmaceutically acceptable acidic and basic components. The salt is characterised by IR, solid state NMR, and single crystal XRD. Crystal data for C25H26N3O8F: triclinic, space group P-1 (no. 2), a = 7.0037(8) Å, b = 12.764(3) Å, c = 13.909(3) Å, α = 104.821(4)°, β = 92.039(4)°, γ = 95.334(4)°, V = 1194.6(4) Å3, Z = 2, T = 296(2) K, μ(MoKα) = 0.113 mm-1, Dcalc = 1.433 g/cm3, 16879 reflections measured (5.048° ≤ 2Θ ≤ 54.186°), 5139 unique (Rint = 0.0663, Rsigma = 0.0975) which were used in all calculations. The final R1 was 0.1121 (I>2σ(I)) and wR2 was 0.2505 (all data). SC-XRD analysis shows that the crystal packing is stabilized by strong H-bonding of type N-H···O and comparatively weak interactions of type C-H···O, C-H···π and off-set π···π stacking.

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