Comparative Analysis of Intrathecal Lidocaine Combined With Guanfacine or Dexmedetomidine on Nociceptive and Motor Blockade in Rats

The aim of this study was to examine the effects of intrathecal lidocaine combined with guanfacine or dexmedetomidine on nociceptive and motor blockade, in comparison to clonidine. Using a rat model of intrathecal injection, we evaluated the effects of lidocaine combined with guanfacine, dexmedetomidine, or clonidine on nociceptive and motor blockade. The dose-dependent effects of guanfacine on spinal nociceptive and motor blockade were compared to those of lidocaine, a well-known local anesthetic. Guanfacine (0.46 μmol/kg, 3 mM), dexmedetomidine (0.02 μmol/kg, 0.1 mM), or clonidine (1.52 μmol/kg, 10 mM) alone produced no spinal nociceptive or motor blockade. Co-administration of guanfacine (0.46 μmol/kg) or dexmedetomidine (0.02 μmol/kg) with lidocaine (3.14 or 8.38 μmol/kg) prolonged the duration of spinal blockade, an effect attenuated by yohimbine (0.76 μmol/kg), which alone produced no spinal nociceptive or motor blockade. In contrast, the addition of clonidine (1.52 μmol/kg) did not enhance the duration of lidocaine-induced spinal blockade. Guanfacine produced a dose-dependent spinal blockade of both nociceptive and motor functions. The potency ranking (ED₅₀, 50% effective dose) of spinal blockade showed that guanfacine and lidocaine were equal. Guanfacine resulted in a markedly longer spinal block duration than lidocaine at equivalent anesthetic doses (ED₂₅, ED₅₀, and ED₇₅). In summary, co-administration of subeffective doses of guanfacine or dexmedetomidine with lidocaine prolonged the duration of spinal blockade, likely involving α2-adrenergic receptors, whereas subeffective doses of clonidine did not. Guanfacine produced dose-dependent spinal blockade and was equipotent to lidocaine. At equianesthetic doses, guanfacine produced a longer duration of blockade than lidocaine.