The quaternary lidocaine derivative, QX-314, produces long-lasting local anesthesia in animal models in vivo.
BACKGROUND
QX-314 is a quaternary lidocaine derivative considered to be devoid of clinically useful local anesthetic activity. However, several reports document that extracellular QX-314 application affects action potentials. Hence, the authors tested the hypothesis that QX-314 could produce local anesthesia in animal models in vivo.


METHODS
The authors tested QX-314 (10, 30, and 70 mM) in three standard in vivo local anesthetic animal models, using a randomized, blinded experimental design with negative (placebo) and positive (70 mM lidocaine) controls. The guinea pig intradermal wheal assay (n = 29) was used to test for peripheral inhibition of the cutaneous trunci muscle reflex, the mouse tail-flick test (n = 30) was used to test for sensory blockade, and the mouse sciatic nerve blockade model (n = 45) was used to test for motor blockade.


RESULTS
In all three animal models, QX-314 concentration-dependently and reversibly produced local anesthesia of long duration, at concentrations equivalent to those clinically relevant for lidocaine. In the guinea pig intradermal wheal assay, QX-314 produced peripheral nociceptive blockade up to 6 times longer than lidocaine (650 +/- 171 vs. 100 +/- 24 min [mean +/- SD]; n = 6 per group; P < 0.0001). In the mouse tail-flick test, QX-314 produced sensory blockade up to 10 times longer than lidocaine (540 +/- 134 vs. 50 +/- 11 min; n = 6 per group; P < 0.0001). Finally, in the mouse sciatic nerve model, QX-314 produced motor blockade up to 12 times longer compared with lidocaine (282 +/- 113 vs. 23 +/- 10 min; n = 9 or 10 per group; P < 0.0001). The onset of QX-314-mediated blockade was consistently slower compared with lidocaine. Animals injected with saline exhibited no local anesthetic effects in any of the three models.


CONCLUSIONS
In a randomized, controlled laboratory study, the quaternary lidocaine derivative, QX-314, concentration-dependently and reversibly produced long-lasting local anesthesia with a slow onset in animal models in vivo. The authors' results raise the possibility that quaternary ammonium compounds may produce clinically useful local anesthesia of long duration in humans and challenge the conventional notion that these agents are ineffective when applied extracellularly.
Vancouver General Hospital, British Columbia, Canada.
Tony K Y
TK
Lim
Bernard A
BA
Macleod
Craig R
CR
Ries
Stephan K W
SK
Schwarz
D000200:Action Potentials / Q000187:drug effects; D000772:Anesthesia, Local / Q000379:methods*; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D007428:Intradermal Tests / Q000379:methods; D008012:Lidocaine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D051379:Mice; D009407:Nerve Block / Q000379:methods; D010146:Pain / Q000188:drug therapy*; D010147:Pain Measurement / Q000187:drug effects; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D011897:Random Allocation; D012584:Sciatic Nerve / Q000187:drug effects; D020426:Sciatic Neuropathy / Q000188:drug therapy*; D012965:Sodium Chloride / Q000008:administration & dosage; D016019:Survival Analysis; D013997:Time Factors
D000779:Anesthetics, Local; D000644:Quaternary Ammonium Compounds; C012647:QX-314; D012965:Sodium Chloride; D008012:Lidocaine