Subcutaneous infiltration of doxylamine on cutaneous analgesia in rats

Novel insights on the encapsulation mechanism of PLGA terminal groups on ropivacaine

Currently, the influences of free terminal groups (hydroxyl, carboxyl and ester) of PLGA on encapsulating active pharmaceutical ingredient are relatively ambiguous even though PLGA types were defined as critical quality attributes in vast majority of design of experiment process. In this study, emulsion method combined with premix membrane emulsification technique has been used to encapsulate ropivacaine (RVC), a small molecule local anesthetic in clinical. Based on the narrow particle size distribution, the influences and mechanisms of the terminal groups on properties of ropivacaine loaded microspheres have been investigated in detail. It was found that microspheres prepared by PLGA with hydroxyl or ester groups exhibited lower encapsulation efficiency but faster in vitro release rate than that of carboxyl groups. In the meanwhile, on microcosmic level analysis by quartz crystal microbalance with dissipation, atomic force microscope and confocal laser scanning microscopy, we attributed this distinction to the specific interaction between ropivacaine and different terminal groups. Subsequently, the reaction activation centers were verified by density functional simulation calculation and frontier molecular orbital theory at molecular level. Additionally, pharmacokinetics and pharmacodynamic research of infiltration anesthesia model were performed to compare sustained release ability, duration and intensity of the anesthetic effect in vivo. Finally, potential safety and toxicity were evaluated by the biochemical analysis. This study not only provides a novel mechanism of drug encapsulation process but also potential flexible selections in terms of various anesthesia indications in clinical.

Spinal sensory and motor blockade by intrathecal doxylamine and triprolidine in rats

OBJECTIVES

The aim of this experiment was mainly to examine the effects of intrathecally injected doxylamine and triprolidine, two antihistamine drugs spinal motor and sensory functions.

METHODS

After intrathecally injecting the rats with five different doses, the dose-response curves of spinal sensory and motor block with doxylamine and triprolidine were constructed. In comparison with the local anaesthetic mepivacaine, the quality and duration of spinal anaesthesia with doxylamine or triprolidine were conducted.

KEY FINDINGS

Doxylamine, mepivacaine and triprolidine elicited spinal motor and sensory (nociception and proprioception) blockades in a dose-dependent fashion. On the ED₅₀ (50% effective dose) basis, the rank order of drug potency was triprolidine > mepivacaine > doxylamine (P < 0.05) at provoking spinal motor, proprioceptive and nociceptive blockades. On the equianaesthetic doses (ED₂₅ , ED₅₀ and ED₇₅ ), the duration of spinal anaesthesia with doxylamine was longer (P < 0.01) than that with mepivacaine or triprolidine. Moreover, doxylamine or triprolidine displayed greater potency (ED₅₀ ) (P < 0.05) and duration (P < 0.05) of sensory block over motor block.

CONCLUSIONS

Doxylamine or triprolidine produces a dose-dependent effect of spinal motor and sensory block. Triprolidine with a better nociception-selective action over motor block has a better potency than mepivacaine or doxylamine. Doxylamine and triprolidine produce longer durations than mepivacaine.