Improvement of tetracaine antinociceptive effect by inclusion in cyclodextrins

Abstract

Local anesthetics (LA) are among the most important pharmacological compounds used to attenuate or eliminate pain. However, systemic toxicity is still a limitation for LA application, especially for ester-type drugs, such as tetracaine (TTC) that presents poor chemical stability (due to hydrolysis by plasma esterases). Several approaches have been used to improve LA pharmaceutical properties, including the employment of drug-delivery systems. Here we used beta-cyclodextrin (β-CD) or hydroxypropyl-beta-cyclodextrin (HP-β-CD) to develop two new TTC formulations (TTC:β-CD and TTC:HP-β-CD). The inclusion complexes formation, in a 1:1 stoichiometry, was confirmed by differential scanning calorimetry, X-ray diffraction, UV-VIS absorption and fluorescence. Nuclear magnetic resonance (DOSY experiments) revealed that TTC association with HP-β-CD is stronger (K_a = 1200 mol/L⁻¹) than with β-CD (K_a = 845 mol/L⁻¹). Moreover, nuclear Overhauser effect (NOE) experiments provided information on the topology of the complexes, where TTC aromatic ring is buried inside the CD hydrophobic cavity. In vitro tests with 3T3 fibroblast cells culture revealed that complexation decreased TTC cytotoxicity. In addition, the total analgesic effect of TTC, tested in rats through the infraorbital nerve test, was improved in 36% with TTC:β-CD and TTC:HP-β-CD. In conclusion, these formulations presented potential for future clinical use, by reducing the toxicity and increasing the antinociceptive effect of tetracaine.

Keywords::

• Tetracaine
• cyclodextrin
• inclusion complex
• cytotoxicity
• in vivo

Acknowledgment

The authors would like to thank the Brazilian Synchrotron Light Laboratory (LNLS) for the use of NMR facilities. Roberta Aline Franco de Lima and Marcelo Bispo de Jesus have contributed equally to this research.

Declaration of interest

This research was supported by São Paulo Research Foundation (FAPESP). M.B.J. and E.P. were the recipients of fellowships from FAPESP (Procs. 06/03838-1 and 02/04103-4) and National Council for Scientific and Technological Development (CNPq), respectively.