Pharmaceutical Research And In-Vitro And In-Vivo Evaluation Of Lidocaine-Prilocaine Patch

1 Research background and purposeLidocaine and prilocaine are both of amides sodium channel blockers,which can reduce the generation of nerve impulses from the source to relieve pain,and are often used clinically for topical anesthesia.The effect of the two is similar,and the commonly used concentration is5%.Lidocaine can be degraded in the body to produce genotoxic impurities,and the combination with prilocaine can reduce its dosage and have higher safety.Lidocaine and prilocaine can also form a eutectic mixture which is liqid at room temperature and can significantly improve the transdermal penetration rate.The marketed lidocaine-prilocaine cream is widely used for local and superficial anesthesia,and the curative effect is positive.However,the cream is inconvenient to administer,easy to erase and has a short duration of action,so it is not suitable for use in chronic pain.Research and development of lidocaine-prilocaine patch for chronic pain relief（post-herpetic neuragia）can significantly reduce the frequency of administration and has important clinical value.This study took lidocaine-prilocaine patch as the research goal,mainly explored the relationship between the formulation with key quality attributes such as formability,adhesion,rheological properties,in vitro penetration and in vivo absorption by establishing a scientific quality evaluation method,screening and optimizing the prescription of the patch.The patch was prepared at the laboratory level,and its quality standards were preliminarily formulated and its stability was studied.This study provides the basis for the scale-up production,clinical research and drug registration of lidocaine-prilocaine patch.2 Methods and results2.1 Formulation study and optimizationThe matrix layer of the patch is usually cross-linked by skeleton materials,cross-linked agents,cross-linked regulators,p H regulators,fillers,preservatives,moisturizing agents,and water.In this study,the tack,cross-linked time,and key rheological parameters were used as indicators.Through single-factor exploration,it was found that when the proportion of sodium polyacrylate（one of the skeleton materials）gradually increased in the range of 3%-7%,the formability and the storage modulus reflecting the hardness and stability of the matrix of the patch was gradually increased,the cross-linked time was shortened from more than 13 days to 5 days,the adhesive force of the patch gradually decreased that the tack decreased from 28 balls to 18 and the loss tangent decreased from 0.2337 to 0.0658.When the dosage of the cross-linked agent dihydroxyaluminium aminoacetate（0.05%-0.60%）and the p H adjusting agent tartaric acid（0.7%-2.2%）increased,the change law of the formability and adhesion of the patch is consistent with the above.But when the dosage is too high（dihydroxyaluminium aminoacetate≥0.40%or tartaric acid≥1.70%）,the adhesion of the patch is almost unchanged.When the dosage of Ethylene-diamine-tetraacetic acid disodium salt（EDTA-2Na）was increased from 0%to 0.40%,the formability of the patch gradually deteriorated.However,the dosage changes of sodium carboxymethylcellulose（1.0%-5.0%）and kaolin（0%-4.0%）had no significant effect on the formability and adhesion of the patchOn this basis,taking the tack and loss tangent as the indicators,and sodium polyacrylate,EDTA-2Na and tartaric acid as the factors,Box-behnken design method in response surface optimization with three factors and three levels was carried out to optimize the formulation of lidocaine-prilocaine patch.In the optimization experiment,the interaction between sodium polyacrylate and EDTA-2Na was weak,and the interaction between tartaric acid and sodium polyacrylate and EDTA-2Na was strong.A fitting model between the inspection indicators and the inspection factors is established and it is verified that the model can be used to predict the optimal prescription of lidocaine-prilocaine patch.To maximize tack on the basis of patch molding,the preferred formulation composition is as follows:sodium polyacrylate is 4.76%,EDTA-2Na is 0.00%,tartaric acid is 0.70%.In this study,using an improved Franz diffusion cell as the experimental device,the in vitro permeation test method of lidocaine-prilocaine patch was established based on high performance liquid chromatography-tandem mass spectrometry;and the detection method was verified to meet the analysis requirements.Based the optimal formulation,in vitro permeation behavior of lidocaine-prilocaine patch added different penetration enhancers[blank,5%propylene glycol,5%propylene glycol-5%isopropyl myristate（IPM）,5%propylene glycol-0.5%l-menthol]was investigated.Among them,the in vitro permeation behavior of the blank group,the experimental group with 5%propylene glycol and 5%propylene glycol-0.5%l-menthol was similar.The cumulative penetration and intradermal retention of lidocaine and prilocaine in the experimental group with 5%propylene glycol-5%IPM were the highest,and the in vitro penetration behavior of lidocaine were close to those of the commercially lidocaine patch(Lidoderm^?,5%).2.2 Quality EvaluationExcepted adhesion,the key quality of patch include content,related substances,content uniformity,in vitro release,in vitro penetration and stability,etc.The above key attributes will significantly affect the efficacy and safety of the patch.Based on the above experiment,the quality standards are formulated as follows:（1）The tack of lidocaine-prilocaine patch should be between 25-32 balls.（2）The theoretical content of lidocaine and prilocaine is 2.5%respectively,the relative content should be in the range of 90%-110%,and the content uniformity results should meet the requirements of Chinese Pharmacopoeia（2020）（A+2.2S≤L,L=25）.（3）The content of N-dichloroacetyl-2,6-xylidine,lidocaine impurities A,H and I should not exceed 0.1%,prilocaine impurity B and other impurities should not exceed 2.0%and 0.2%respectively,The total content of impurities other than prilocaine impurity B should not exceed1.0%.（4）The cumulative release rate of lidocaine and prilocaine within 6hours should not be less than 70%.In this study,high performance liquid chromatography was used to establish the content and related substances determination methods of lidocaine-prilocaine patch respectively.After preliminary verification,the above two methods both met the detection requirements.The tack,content,content uniformity,related substances and in vitro release of lidocaine-prilocaine patch prepared at laboratory level all meet the requirements.Preliminary stability studies show that the samples are stable under high temperature（40°C）for 30 days.However,after being placed for 3 months under accelerated experimental conditions（30°C±2°C,relative humidity 75%±5%）,the content of related substances exceeded the limit requirements,and the formulation needed to be optimized.2.3 Pharmacokinetic studies of humanA method for the detection of lidocaine and prilocaine in human plasma by high performance liquid chromatography-tandem mass spectrometry was established in this study.The selectivity,sample stability,precision and accuracy were suggested the determination methods meet the analytical requirements.Based on the above,with the approval of the Ethics Committee of Xiangya School of Pharmacutical sicience,Central South University,12 healthy subjects were selected to conduct a randomized open,two-sequence,two-cycle crossover,single-dose dosing study to research the in vivo pharmacokinetic behavior of lidocaine-prilocaine patch and lidoderm^?.In lidocaine-prilocaine patch,T_maxof lidocaine and prilocaine were both16 h,C_maxand AUC of lidocaine and prilocaine were 11.371 ng·m L^-1and165.305 ng·m L^-1and 2.750 ng·m L^-1,31.886 ng·m L^-1respectively.T_max,C_maxand AUC of lidoderm^?were 14 h,31.969 ng·m L^-1and 495.587ng·m L^-1respectively.After correction,C_maxand AUC of lidocaine in lidocaine-prilocaine patch were 71.70%and 64.94%of lidoderm^?.There is no obvious correlation between in vitro permeation and in vivo absorption,which may be caused by insufficient experimental operation,experimental design or formulation.The reliability of the experiment can be improved by formulating standard operating procedures for in vitro permeation test and increasing the number of experimental cases.Pharmacokinetic behavior can be improved by adjusting the type or proportion of penetration enhancer and the cross-linkied degree of matrix.3 ConclusionIn this study,through single factor exploration and Box-behnken response surface optimization,the influence of the key formulation factors of the patch on its formability and adhesion was obtained,which scientifically and reasonably guided the formulation develpoment of the patch.5%propylene glycol-5%IPM as penetration enhancer,the in vitro permeability of lidocaine-prilocaine patch was about twice of lidoderm^?.But the Cmax and AUC of lidocaine in the former were about 70%of that in the latter,there was no significant correlation between in vitro permeability and in vivo absorption.This study has basically achieved the expected goal,and laid a foundation for the scale-up production,clinical research and drug registration of lidocaine-procaine gel patch.