Design And Evaluation Of Lappaconitine Drug-in-Adhesive Transdermal Patch

Objective:The objective of this work was to develop a long-acting pressure-sensitive adhesive patch（PSA）of lappaconitine（LA）with simple process and good permeability in vivo and in vitro by ion-pair technology.Method:The PSA patch of LA was prepared by organic solvent volatilization method.Firstly,the isolated abdominal skin of male Wistar rats was used as the permeability barrier,and the effect of formulation factors including PSAs and drug loading were investigated through the in vitro skin penetration experiment by using the horizontal single-chamber diffusion cell.Ion-pair technology was used to further increase the percutaneous permeability of lappaconitine.Six kinds of organic acids:cinnamic acid（CA）,p-aminobenzoic acid（PABA）,lauric acid（C12）,capric acid（C10）,benzoic acid（BA）,benzenesulfonic acid（BSA）were selected to form ion-pairs with LA.The formation of ion-pairs was characterized by FT-IR.Each ion-pair was used as the main drug to prepare the patch,and the type and molar ratio of ion-pairs were investigated by in vitro skin experiment to screen the optimized formulation.The molecular mechanism of ion-pair technology promoting the percutaneous penetration of lappaconitine was investigated by in vitro drug release experiment,the determination of apparent partition coefficient,ATR-FTIR,MDSC,molecular docking,FT-IR and XPS.The preliminary quality evaluation of the optimized patch was carried out according to the relevant regulations of the Chinese Pharmacopoeia,mainly focusing on its adhesion,content uniformity and drug release.The pharmacokinetics study of the optimized patch and the commercial patch was evaluated using rabbits.The plasma concentration of the patch was determined by LC-MS/MS.KM mice were used as experimental animals and the analgesic effect of the optimized patch was preliminarily evaluated by acetic acid-induced writhing test.Result:The formulation of optimized lappaconitine patch:the PSA matrix was self-made hydroxyl polyacrylate pressure-sensitive adhesive（AAOH）,the drug loading was 7%,the counter-ion was cinnamic acid（CA）,and the molar ratio of drug to counter-ion was 1:1.5.The results of in vitro release experiments showed that the transdermal process was the main rate-limiting step of drug transdermal absorption.The results of apparent partition coefficient showed that the log D_o/w of LA-CA ion-pairs was higher than that of LA,but there was no significant difference between LA-CA ion-pairs with different molar ratios（p>0.05）.The results of ATR-FTIR,MDSC and molecular docking showed that the interaction between counter-ions and skin keratin changed conformation of keratin,which increased the transdermal penetration of drugs.The results of FT-IR and XPS showed that the action intensity of counter-ions on skin was related to the binding level of LA and CA,counter-ions would preferentially combine with drugs to form ion-pairs,and excess counter-ions would interact with skin.The optimized lappaconitine patch had good adhesion and the content uniformity met the relevant requirements.The results of pharmacokinetics in rabbits showed that AUC_0-tof the optimal patch was 2450.40±848.52 h ng/m L,2.93 times higher than the commercial patch,and C_max of the optimal patch was 50.06±13.04 ng/m L,1.97 times higher than the commercial patch.AUC_0-t and C_max of the optimal patch were better than those of the commercial patch,and the relative bioavailability was 292.86%,which was more conducive to long-acting analgesia.The results of writhing test in mice showed that the pain inhibition rate of the optimized patch could reach 81.18%,which was significantly better than the commercial patch and had good analgesic effect.Conclusion:In the present study,a long-acting lappaconitine PSA patch with simple process and good permeability in vivo and in vitro was successfully prepared by ion-pair technology.This work mainly discussed the binding level between counter-ions and drugs and the interaction mechanism between counter-ions and skin keratin:after the CA and LA combine into an ion-pair,the excess counter-ion acted on skin keratin,changed the conformation of keratin,reduced the barrier of stratum corneum,and increased the transdermal delivery of drug.The study mentioned above could provide more references for the application of counter-ions in transdermal drug delivery system.