The Inclusion of Tolfenamic Acid into Cyclodextrins Stimulated by Microenvironmental pH Modification as a Way to Increase the Anti-Migraine Effect

PURPOSE: The poorly soluble nonsteroidal anti-inflammatory drug (NSAID), tolfenamic acid (TA), was studied to maximize its solubility, permeability through biological membranes, and pharmacological activity. METHODS: A mixture with magnesium stearate (MS) – microenvironment pH-modifier was prepared, as well as systems additionally containing incorporating substances methyl-β-cyclodextrin (M-β-CD) and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD). The identification of TA-MS-CD systems was confirmed using experimental methods: X-ray powder diffraction (XRPD) and Fourier transform infrared spectroscopy (FT-IR) with the theoretical support. Apparent solubility study was performed using the paddle apparatus, while in vitro gastrointestinal tract (GIT) and blood-brain barrier (BBB) permeability were conducted by using PAMPA (Parallel Artificial Membrane Permeability Assay). The in vivo part of the study used the mouse nitroglycerin (NTG)-induced migraine pain model. RESULTS: From practically insoluble substance, TA in TA-MS-M-β-CD system dissolved up to 80.13% ± 2.77%, and in TA-MS-HP-β-CD up to 92.39% ± 3.25% in 180 minutes. An increase in TA permeability was also obtained in the TA-MS-M-β-CD and TA-MS-HP-β-CD systems through GIT membranes (P(app) values 2.057 x 10(−5) cm s(−1) and 2.091 x 10(−5) cm s(−1), respectively) and through BBB (P(app) values 3.658 x 10(−5) cm s(−1) and 3.629 x 10(−5) cm s(−1), respectively). The enlargement of the solubility and permeability impacted analgesia. The dose 25 mg/kg of both TA-MS-HP-β-CD and TA-MS-M-β-CD was almost equally effective and only slightly less effective than the dose 50 mg/kg of pure TA. Both TA-MS-HP-β-CD and TA-MS-M-β-CD used at 50 mg/kg more effectively attenuated tactile allodynia in NTG-treated mice than the same dose of pure TA. None of TA forms influenced heat hyperalgesia. CONCLUSION: Increasing solubility of TA caused an increase of its analgesic effect in an animal model of migraine pain.