Endotracheal tube cuffs filled with lidocaine as a drug delivery system: in vitro and in vivo investigations

The purpose of this study was to examine if lidocaine diffusion across an e ndotracheal tube cuff could improve post-operative tolerance, especially so re throat. The in vitro release of lidocaine from tube cuffs filled with di fferent lidocaine formulations (base form, hydrochloride form or alkalinize d lidocaine hydrochloride) was investigated. A preliminary pilot clinical s tudy in anaesthesia for spine surgery in smoker patients was carried out to examine the pharmacokinetic (i.e. systemic uptake) and pharmacodynamic eff ects (i.e. incidence of sore throat) obtained with the endotracheal tube cu ff filled with Lidocaine solution, compared to cuffs inflated only with air . From our in vitro experiment, only the hydrophobic neutral base form of l idocaine was able to diffuse (65.1 +/-1.1% released after 6 h), while for t he charged hydrochloride form, only a permeation phenomenon occurred concer ning only 1% of the total drug. Alkalinization of lidocaine hydrochloride ( the only form available as a drug) allows smaller amounts to be used compar ed to previous published studies (20-40 mg vs. 200-500 mg) and no lag time for diffusion. Such a system could provide a controlled release reservoir f or lidocaine to adjacent tracheal tissue. This was shown in our pilot study with sustained plasmatic profiles and improved tolerance (decreased pain s cores) in the rank order: air group much less than lidocaine hydrochloride group < alkalinized lidocaine group. (C) 2001 Elsevier Science B.V. All rig hts reserved.