Adverse effects of lidocaine and methylparaben on tracheal ciliary activity

The effect of standard concentrations of lidocaine HCl and methylparaben (preservative) on the ciliary activity of ferret tracheal rings in organ culture was assessed. Pure lidocaine concentrations as low as 0.5% caused complete ciliostasis which was reversible after removal of the drug. One percent and two percent effects were not completely reversible. Pure methylparaben concentrations as low as 0.06 mg/ml paralyzed cilia; and, at concentrations of 0.5 mg/ml or higher, adverse effects were not completely reversible. When lidocaine and methylparaben were combined at the same ratio used in commercial preparations, their ciliotoxic effects were additive. These data suggest that topical respiratory anesthesia may result in prolonged ciliary paralysis.