Pharmacokinetics And Pharmacodynamics Of Poly(Lactide-co-glycolide) Microspheres Containing Ropivacaine After Subcutaneous Administration In Rabbits

Background & objectivePain is a major problem of human health problems. The prevalence rate of pain is about 21.5% around the world. The harmful and negative effects of pain are incalculable, such as it can cause different degrees of fear, panic, anxiety, grief and other undesirable emotions, system dysfunction, lower immunity, leading to various complications, and even cause disability or death.Local anesthetics as an effective pain treatment have been widely used in clinical medicine, but their action time can only maintain for 6-12hours.They can not meet the need of intractable pain control and treatment, such as advanced cancer pain and trigeminal neuralgia. These years,domestic and foreign scholarshave explored a variety of methods to extend local anesthetics analgesia,such as repeated injection of analgesic drugs,the application of micro-pump. But the results are not satisfactory, there are still large dosage and patient compliance. Extend-release and sustained-release preparation are very important directions for domestic and foreign pharmaceutical industry. Micro-encapsulation and Microspheres technology have been used in the field of pharmaceutical preparations in the last 40 years, which is characterized by natural or synthetic polymers as controlled release drug carrier for the purpose of extending the efficacy time of drug. The preparation is simple and it can be used to many drugs. Microsphere can suspend in the aqueous medium and can be injected through small needle. Therefore microsphere has been paid enough attention in the pharmaceutical research and application. At present, the microspheres have been used to clinical treatments, which obtained approval of the United States Food and Drug Administration (FDA). With the development of microsphere technique, the study of long-acting local anesthetic agents has shifted to manufacture various forms of local anesthetic microspheres. Single dose of local anesthetic microspheres appears prolonged analgesic effect and reduces velocity of drug delivery, the plasma concentration and toxicity. Biodegradable release system has advantages,in which carrier material can absorbed in the body. So surgery doesn't need in the end of the practice to control pain.Both PLA and PLGA are completely biodegradable plastics. PLGA is a typicalα-hydroxy acid polymer, which has good biocompatibility and human adaptability. In organisms, the ultimate degradation products of PLGA are lactic acid,which ultimately completely degrade to carbon dioxide and water, and then all of these degradation products are discharged out of organisms. So PLGA is a kind of safe biodegradable material,which can delete obvious inflammatory response, immune response and cell toxicity response. It has its own characteristic that completely biological degraded in vivo and discharged out of organisms to avoid secondary victimization for patients. PLA and PLGA microspheres have been used in anticancer drugs, antibiotics, eye diseases, gene therapy, and many other studies.PLA and PLGA microspheres have been used in local anesthetics research for 30 years. As early as 1981, Wakiyama N has prepared several kinds of local anesthetics PLA-MS. In 1994, Le Corre studied preparations and characteristics of BUP-PLA/PLGA-MS, both of them proved that it is feasible to take biodegradable materials to prepare local anesthetics sustained-release microspheres. In 1990s, Jean, MM, Fletcher D, Passcal LC, Jean PE, et. took different animals as test targets to study the pharmaco kinetics and pharmacodynamics of local anesthetics release microspheres,the results showed that local anestheticss release microspheres can significantly extend the action-time local anesthetics for one-time delivery and reduce the fluctuations of plasma concentrations. 1996 Joanne C, 1998 Christiane D proved that addition of small amounts of dexamethasone to bupivacaine incorporated in microcapsules prolonged local analgesia compared with microcapsules with plain bupivacaine after subcutaneous aministration in humans.Ropivacaine is a new kind of amide local anesthetics agent. At present, There are few reports about microsphere which take ropivacaine as the parcel drug have been carried out in the international communities. Ropivacaine and bupivacaine have similar local properties. But ropivacaine owns a reduced potential for both neurotoxicity and cardiotoxicity. More important is that ropivacaine has a high degree of feeling - motor nerve block separation characteristics, low concentration, just cause sensory nerve block but not motor nerve block; increasing the possibility of early recovery movement for patients. So ropivacaine is more suitable for intractable pain treatment.As mentioned above, we took biodegradable polymer materials lactate acid copolymer as carrier materials and ropivacaine as parceled drug to fabricate poly (lactide-co-glycolide) microspheres containing ropivacaine (RoP-PLGA-MS), by a water-in-oil-in-water (W/O/W) emulsion - solvent evaporation method. Through our previous work, studying the preparation of sustained-release poly (lactide-co-glycolide) microspheres of ropivacaine, observeing the vitro-released characteristics of RoP-PLGA-MS, we had found that it had an sustained release effect and microsphere production method was feasible. In this study, we want to investigate the stability of drug loading of ropivacaine in RoP-PLGA-MS and how about the Pharmacokinetics and pharmacodynamics of RoP-PLGA-MS after subcutaneous administration in rabbits.MethodsWe took PLGA as a carrier material to manufacture RoP-PLGA-MS, by W/O /W emulsion - solvent evaporation method. Twenty-four rabbits were randomly divided into three groups, namely group A,group B and group C. Ropivacaineinjiection (RoP) 4mg.kg^-1 RoP-PLGA-MS200mg.kg^-1 (equal to RoP12mg.kg^-1) and poly (lactide-co-glycolide) microspheres (PLGA-MS) 200mg.kg^-1 were administered subcutaneous to rabbits respectively. Nonresponse Diameter to Pinprick (PND) and Electrical Stimulation Threshold of Escape Movement (EMT) were used to evaluate the anaglestic effect. The ropivacaine concentrations in plasma were determinated by HPLC method.Statistics and analysisOne-Sample T test was used to evaluate stability of drug loading of ropivacaine in RoP-PLGA-MS. We took one-way ANOVA to compare the average weight and basic PND and basic EMT of rabbits in each group. The PND and EMT at different time points after administration compared with that of 20min before the experiment in each group, by single factor repeated measure ANOVA. Plasma concentration datas are analysised by the software DAS2.1.1. We took statistical moment parameters as pharmacokinetic parameters statistical moment parameters as pharmacokinetic parameters. Independent-Samples T test was used to compare pharmacokinetic parameters of group A and that of group B. The relative standard deviation (RSD) of intra-day and inter-day were reported as the mean±standard deviation (x|-±s ). The SPSS (version 13.0) software packages were used for the statistical analyses. P values of <0.05 was accepted as significant.RESULTS1. Drug loading of ropivacaine in RoP-PLGA-MS was (6.06±0.17) %.2. The average weight and basic PND and basic EMT of rabbits in each group were no statistically significant difference (P>0.05).3. PND_max was (5.28±0.08)cm and (2.81±0.08)cm for group A and group B, respectively. The PND and EMT at different time points after administration 5min to 5h had statistical significance (P <0.05) than that of 20min before the experiment in group A. Anaglestic time of group A was about five hours. The PND and EMT at different time points after administration 2h to 36h had statistical significance (P <0.05) than that of 20min before the experiment in group B. Anaglestic time of group B was about thirty-four hours. The PND and EMT at different time points after administration had no statistical significance (P>0.05) than that of 20min before the experiment in group C. There was no anaglestic effect for groupC.4. C_max was 2.238 and 1.306μg·mL^-1, t_1/2 was 2.848 and 17.606h, MRTwas 4.175 and 24.823h in group A and B, respectively. In group A, plasma concentration of ropivacaine reach C_max at one hour after administration, it descended rapidly and less than 0.5μg·mL^-1 until fifth hour. In group A, plasma concentration of ropivacaine reached C_max at fifth hour after administration, and then it kept in a low level last a long time. It was 0.066μg·mL^-1 at fifth hour after administration. CONCLUSION1. We took PLGA as a carrier material to manufacture RoP-PLGA-MS, by W / O / W emulsion - solvent evaporation method. The reproducibility was good and drug loading was stable.2. Local analgesic effect of RoP-PLGA-MS emerged latter and lasted for a longer time than that of ropivacaine injection.3. Diffusion area of RoP-PLGA-MS in local tissue was smaller than that of ropivacaine injection.4. RoP-PLGA-MS, compared with ropivacaine injection, owned obvious sustained-release properities and kept a lower concentration level of stability in plasma for a long time, after subcutaneous administration in rabbits.5. PLGA as carrier material didn't own analgesic effect.