Herb–drug pharmacokinetic interaction of artiﬁcial calculus

Herbdrug pharmacokinetic interaction of artificial calculusbovis with diclofenac sodium and chlorpheniraminemaleate in ratsCan Penga,b, Mengying Lva,b, Jixin Tiana,b, Yin Huanga,b, Yuan Tiana,b,c and Zunjian Zhanga,b,c

aKey Laboratory of Drug Quality Control and Pharmacovigilance, bDepartment of Pharmaceutical Analysis, cState Key Laboratory of NaturalMedicines, China Pharmaceutical University, Nanjing, China

Keywordsartificial calculus bovis; chlorpheniraminemaleate; diclofenac sodium; herbdrugpharmacokinetic interaction; HPLC-MS/MS

CorrespondenceZunjian Zhang, Department of PharmaceuticalAnalysis, China Pharmaceutical University,Tongjia Xiang 24, Nanjing 210009, China.E-mail: [email protected]

Received December 15, 2012Accepted March 18, 2013

doi: 10.1111/jphp.12069

Abstract

Objectives To investigate the herbdrug pharmacokinetic interaction of artificialcalculus bovis (ACB) with diclofenac sodium (DS) and chlorpheniramine maleate(CPM) in rats.Methods A sensitive high-performance liquid chromatography coupled withtandem mass spectrometry method was developed and validated for the simulta-neous determination of DS and CPM in rat plasma. The proposed method wassuccessfully applied to compare the herbdrug pharmacokinetic interaction ofACB with DS and CPM in rats following intragastric administration.Key findings The proposed method had good linearity and no endogenous mate-rial interfered with the analytes and internal standard peaks. The lower limit ofquantification of DS and CPM was 1 and 0.1 ng/ml, respectively. There was noapparent pharmacokinetic interaction between DS and CPM. Co-administrationof ACB with DS noticeably increased the area under the concentrationtime curve(AUC0-) and peak plasma concentration (Cmax) of DS, while the parameters timeof peak concentration (Tmax), clearance (ClZ/F) and apparent volume of distribu-tion (VZ/F) of DS significantly decreased. Meanwhile, co-administration of ACBwith CPM noticeably increased the Tmax, ClZ/F and VZ/F of CPM. A marked declinein AUC0- and Cmax of CPM occurred in the presence of ACB.Conclusions This study indicated that co-administration of ACB with DS andCPM can result in an apparent herbdrug pharmacokinetic interaction in rats.

Introduction

As a representative natural medicine, Traditional ChineseMedicine (TCM) is becoming more widely used in manycountries.[1,2] According to a World Health Organizationreport, nearly 80% of the global population relies on TCMas a part of disease treatment.[3] Even in the USA, whereherbal remedies are only considered as dietary supple-ments, approximately one-fifth of the population regularlyconsume TCM products.[4,5] The combination of TCM andconventional therapies necessitates a sufficient understand-ing of the use of different forms of treatment concurrentlyand especially herbdrug interactions.

The common cold is a respiratory disease caused by avariety of viruses. Combination of TCM and Western medi-cine can improve clinical efficacy,[68] and this treatment

model is accepted in many countries, such as China, Japan,India and South Korea.[911] Compound diclofenac sodiumchlorphenamine maleate tablets, composed of artificial cal-culus bovis (ACB), diclofenac sodium (DS) and chlorphen-amine maleate (CPM), is an herbdrug preparationgenerally used to relieve the symptoms of headache, febric-ity, nasal obstruction and pharyngodynia.[12] DS, 2-((2,6-dichlorophenyl) amino) benzene acetic acid, mainlyused in the treatment of joint inflammation, is a classicnon-steroid anti-inflammatory drug and a potent prostag-landin synthesis inhibitor.[1315] CPM, 1-p-chlorophenyl-1-(2-pyridyl)-3-dimethylaminopropane maleate, is analkylamine antihistaminic drug (H1RAS) commonly used inthe prevention of symptoms of allergic conditions such as

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And PharmacologyJournal of Pharmacy

Research Paper

2013 Royal Pharmaceutical Society, Journal of Pharmacy and Pharmacology, 65, pp. 106410721064

rhinitis and urticaria.[16,17] Although numerous studies onthe pharmacokinetics of DS and CPM individually havebeen carried out,[1822] the pharmacokinetic interaction ofthese two drugs has not yet been reported.

As the primary substitute for calculus bovis (commonlyknown as Niuhuang in China), ACB is clinically useful forits various pharmacological actions such as sedation, immu-noregulation, antihyperspasmia, fever-relieving and anti-inflammatory effects.[2325] Bile acids, bilirubin and taurineare viewed as the main effective components in ACB andthere is a great variation in its internal quality because ofdiverse sources and species.[26,27] Several methods have beenused to assay the effective components in calculus bovis andits substitutes. Kong et al. presented an ultra-performanceliquid chromatography-evaporative light scattering detec-tion method for the simultaneous determination of six bileacids and commented on the various inherent qualityamong different origins.[28] In our previous work, bilirubin,taurine and 11 bile acids were simultaneously quantified byhigh-performance liquid chromatography coupled withtandem mass spectrometry (HPLC-MS/MS) to control thequality of ACB.[29] In this prescribed preparation, ACB actsas the antipyretic analgesic. However, the effects of ACB onthe pharmacokinetics and pharmacodynamics of DS andCPM are still elusive.

HPLC-MS/MS has become increasingly common in thequantitative analysis of drugs owing to its high selectivityand sensitivity, particularly the selected reaction monitoringmode. Many methods have been developed to determine DSand CPM in plasma, among which HPLC-MS/MS is exten-sively adopted.[3033] However, to our knowledge, no studyhas reported the simultaneous determination of these twodrugs in biological samples by HPLC-MS/MS. In this study,a simple HPLC-MS/MS method was successfully developedfor the simultaneous determination of DS and CPM inplasma, and the herbdrug pharmacokinetic interaction ofACB with DS and CPM was investigated in rats to provideinformation on the combined use of ACB, DS and CPM inthe clinical setting.

Materials and Methods

Chemicals and reagents

DS, CPM, ACB, midazolam, bilirubin, taurine, cholic acid(CA), deoxycholic acid (DCA), chenodeoxycholic acid(CDCA), ursodeoxycholic acid (UDCA) and hyodeoxy-cholic acid (HDCA) were purchased from National Insti-tutes for Food and Drug Control (Beijing, China).Lithocholic acid (LCA), taurocholic acid (TCA), taurode-oxycholic acid (TDCA), taurolithocholic acid (TLCA),glycocholic acid (GCA), glycochenodeoxycholic acid(GCDCA) and dehydrocholic acid (dhCA) were purchasedfrom Sigma-Aldrich (St Louis, MO, USA). Methanol (HPLC

grade) was obtained from Merck (Darmstadt, Germany).Deionized water was prepared by a Milli-Q system (Milli-pore, MA, USA). All other chemicals were of analyticalgrade.

HPLC-MS/MS analysis of ACB

The HPLC-MS/MS system comprised a Finnigan SurveyorLC pump, a Finnigan Surveyor auto-sampler and a triplequadrupole TSQ quantum mass spectrometer via electro-spray ionization (ESI) interface (Thermo Fisher, Palo Alto,CA, USA) for the identification and quantification of ACB.The column, ZORBAX SB-C18 (150 2.1 mm, i.d. 5 mm),was maintained at 30C. The mobile phase consisted of(A) methanol and (B) 10 mmol/l ammonium acetate inaqueous solution (adjusted to pH 3.0 with formic acid).Gradient elution program: 03 min, 1 : 99; 720 min,70 : 30; 40 min, 80 : 20; 5070 min, 98 : 2 (A : B, v/v). Theflow rate was 0.3 ml/min.

Animal studies

The study was approved by the Animal Ethics Committee ofChina Pharmaceutical University. A total of 36 SPF gradeWistar male rats (200 20 g) were provided by ChinaPharmaceutical University Laboratory Animal Center(Nanjing, China; certificate no. SCXK2009-0001). All ratswere fed with standard rodent chow and water ad libitum,and then fasted for 12 h before the pharmacokinetic experi-ment. The rats were divided into six groups followed by oraladministration. The dosage schedules were converted bymeans of body surface area to conform to the human clini-cal schedule as described in the commercial product.[34] Thetreatment groups were designated as: group 1 (DS, 10 mg/kg), group 2 (CPM, 2 mg/kg), group 3 (DS, 10 mg/kg +CPM 2 mg/kg), group 4 (DS, 10 mg/kg + ACB 10 mg/kg),group 5 (CPM, 2 mg/kg + ACB 10 mg/kg) and group 6 (DS,10 mg/kg + CPM 2 mg/kg + ACB 10 mg/kg). Blood samples(0.5 ml) were collected from each rat at predetermined timepoints: 0 (pre-dose), 2, 5, 10, 15, 30, 45, 60, 90, 120, 180,240, 300, 360 and 480 min after administration. Plasmasamples were obtained after centrifugation (12 000 rev/min,14 000g) for 10 min and were frozen at -20C until analysis.

Preparation of samples

Stock solutions of 1 mg/ml DS and CPM were preparedseparately in methanol and stored at 5C. Working standardsolutions were prepared by serially diluting the stock solu-tion using methanol. The internal standard stock solution(midazolam, 50 mg/ml) was prepared in methanol. Calibra-tion samples were prepared by mixing solutions of thestandard mixture with blank rat plasma to form a concen-tration series of 50, 25, 12.5, 5, 0.5, 0.25 and 0.05 mg/ml for

Can Peng et al. Herbdrug pharmacokinetic interaction

2013 Royal Pharmaceutical Society, Journal of Pharmacy and Pharmacology, 65, pp. 10641072 1065

DS, and 5, 2.5, 1.25, 0.5, 0.05, 0.025 and 0.005 mg/ml forCPM. Quality control samples of DS and CPM in differentconcentrations were also prepared in a similar manner. Allsolutions were stored at -20C before use.

All frozen standards and samples were allowed to thaw atroom temperature and were then homogenized by vortex. A100-ml plasma sample was transferred to a 1.5-ml centrifugetube together with 10 ml of the internal standard. Thesample mixture was mixed with 400 ml of methanol andvortexed for approximate 5 min, then allowed to stand for5 min to deproteinize and the precipitate was removed bycentrifugation at 16 000 rev/min (25 000g) for 10 min. Thesupernatant was then pipetted into an injected vial and a10-ml aliquot was injected into the HPLC-ESI-MS/MSsystem for analysis.

HPLC-MS/MS assay

Liquid chromatographic separation and mass spectrometricdetection were performed using the Finnigan TSQQuantum Discovery MAXTM LC-MS/MS system compris-ing a Finnigan Surveyor LC pump, a Finnigan Surveyorauto-sampler and a triple quadrupole TSQ Quantum massspectrometer via ESI interface (Thermo Fisher). The chro-matographic separation was on a ZORBAX SB-C18(150 2.1 mm, i.d. 5 mm) analytical column. An isocraticelution lasting for 3.5 min was obtained with a mobilephase consisting of methanol and 10 mmol/l ammoniumacetate in aqueous solution (adjusted to pH 3.0 with formicacid) (85 : 15, v/v) at a flow rate of 0.25 ml/min. The HPLCeffluent was introduced into the mass spectrometer withoutsplitting. The column temperature was set at 30C and thesample tray temperature was maintained at 16C.

The mass spectrometer was operated in the positivemode and ran with Xcalibur 2.0 software (Thermo Fisher).The capillary voltage was 3900 V and the temperature of thecapillary was set at 300C. Nitrogen was used as the sheath(49 arb) and auxiliary gas (20 arb). Argon was used as thecollision gas at a pressure of 0.2 Pa. The mass spectrometerwas operated in the multiple reaction monitoring (MRM)mode. The precursor product ion pairs used for MRM ofDS, CPM and internal standard were m/z 296.0213.8(collision energy: 33 V), m/z 275.0229.8 (18 V) and m/z326.0291.0 (24 V), respectively, with a scan time of 0.5 sper ion pair. The scan width for MRM was 0.1 m/z and bothQ1 and Q3 were set at 0.7 unit mass resolution.

Method validation

The method was validated in terms of selectivity, linearity,accuracy, precision, stability, extraction recovery and matrixeffect according to FDA guidelines for the bioanalyticalmethod validation.[35]

Statistical analysis

Statistical analysis was performed using Microsoft Excel2010 and BAPP software. The pharmacokinetic softwareDAS 2.0 package based on the non-compartment modelwas used to calculate the pharmacokinetic parameters(Mathematical Pharmacology Professional Committeeof China, Shanghai, China). Statistical significance wasassessed by one-way analysis of variance followed by theTukey post-hoc test (SPSS version 20.0, SPSS Inc., Chicago,IL, USA). P < 0.05 was considered to be statistically signifi-cant. All results were expressed as mean SD.

Results

Identification and quantitativedetermination of ACB

The contents of the effective components in ACB werequantified by a HPLC-MS/MS method described in ourprevious work.[29] The ACB used in this study contained4.387 mg/mg LCA, 1.274 mg/mg UDCA, 27.931 mg/mgHDCA, 8.975 mg/mg CDCA, 24.173 mg/mg DCA,75.923 mg/mg CA, 12.037 mg/mg GCDCA, 68.277 mg/mgGCA, 8.214 mg/mg TLCA, 4.597 mg/mg TDCA,29.229 mg/mg TCA, 36.747 mg/mg taurine and 9.470 mg/mgbilirubin (Figure 1).

Quantitative basis and method validation

The HPLC-MS/MS method described was selective andspecific. Analysis of the plasma samples confirmed that noendogenous material or drug metabolite peaks interferedwith the analytes and the internal standard at the retentiontimes. The retention times of DS, CPM and internal stand-ard were 2.35, 1.58 and 2.01 min, respectively. As shown inFigure 2, the proposed HPLC-MS/MS method showed sat-isfactory results for the simultaneous determination of DSand CPM in rat plasma and was successfully used for theinvestigation of the herbdrug pharmacokinetic interac-tion of ACB with DS and CPM in rats after intragastricadministration.

The method exhibited an excellent linear response overthe range of the selected concentration by weighted (1/c2)least-squared linear regression analysis. The standard cali-bration for DS and CPM was linear over the range 0.0550and 0.0055 mg/ml, respectively. The mean values of theregression equation of the analytes in rat plasma were:y = 0.3435x + 0.0138 (r = 0.9981, DS) and y = 0.0444x 0.0003 (r = 0.9991, CPM), where y corresponds to the peak

area ratios of the analytes to the internal standard and xrefers to the concentrations of DS and CPM added toplasma. The lower limit of quantification proved to be1 ng/ml for DS and 0.1 ng/ml for CPM.

Can Peng et al.Herbdrug pharmacokinetic interaction


The precision and accuracy of the proposed method weredetermined in rat plasma by conducting replicate analysesof spiked samples based on the calibration standards. Theprocedure was repeated on the same day and on 7 differentdays by the same spiked standard series. The precision(RSD%) was less than 9.8%, which confirmed that the pre-cision and accuracy of the method were acceptable accord-ing to FDA guidelines.

The recovery was determined for six replicates of ratplasma with low, medium and high concentrations of thetwo analytes (0.10, 2.00, 40.00 mg/ml for DS, and 0.01,0.20, 4.00 mg/ml for CPM). The mean absolute extractionrecovery of DS was 85.1 4.3%, 89.7 3.5% and90.7 4.9%, and the mean recovery of CPM was97.6 6.2%, 101.3 4.5% and 96.8 3.8%. The RSD%of DS was 0.874.65% and of CPM was 2.685.02%.The data indicated that the recovery of the analytes wasacceptable.

All the ratios of the peak area of analytes resolved in theblank sample (the final solution of blank plasma afterextraction) to that of standard solutions at the same con-centration were between 90 and 107%, which means thatthere were no significant matrix effects in the proposedmethod.

Pharmacokinetic interaction study

The plasma concentrationtime profiles for DS alone andDS co-administrated with ACB and CPM are shown inFigure 3. The plasma concentrationtime profiles for CPMalone and CPM co-administrated with ACB and DS areshown in Figure 4. The main pharmacokinetic parametersof DS and CPM in different groups are presented andfurther statistically analysed in Tables 1 and 2, respectively.

From the comparison of the main pharmacokineticparameters among groups 1, 2 and 3, there was no signifi-cant difference in each parameter (P > 0.05), which indi-cated no drug pharmacokinetic interaction between DSand CPM. Compared with group 1, the pharmacokineticparameters of area under the concentrationtime curve(AUC0-) and peak plasma concentration (Cmax) in groups 4and 6 were much greater (P < 0.01), and the time of peakconcentration (Tmax), clearance (ClZ/F) and volume of distri-bution (VZ/F) of DS were lower than that of group 1(P < 0.05). There were statistically significant differences inthese parameters. There was no statistically significant dif-ference in the t12 among these groups. Additionally, com-pared with group 2, the pharmacokinetic parameters ofAUC0- and Cmax in groups 5 and 6 showed a greater degree

67

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0 10 20 30Time (min)

1. UDCA 2. HDCA 3. CDCA 4. DCA 5. LCA 6. CA 7. TLCA 8. TCA 9. Bilirubin 10. TDCA 11. GCDCA 12. GCA 13. Taurine

40 50 60 70

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Figure 1 Selected reaction monitoring chromatogram of a representative artificial calculus bovis sample.



CPMRT=1.58

DSRT=2.35

ISRT=2.01

m/z 275.0229.8 (18V)100

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ativ

e ab

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Figure 2 Typical multiple reaction monitoring chromatograms of diclofenac sodium (DS), chlorpheniramine maleate (CPM) and the internal stand-ard (IS) in a rat plasma sample.

group 1 (DS alone)

group 3 (DS+CPM)

group 4 (DS+ACB)

group 6 (DS+ACB+CPM)

0

Co

nce

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Figure 3 Plasma concentrationtime profiles of diclofenac sodium(DS). ACB, artificial calculus bovis; CPM, chlorpheniramine maleate.Values are the mean SD, n = 6.

group 2 (CPM alone)

group 3 (DS+CPM)

group 5 (CPM+ACB)

group 6 (DS+ACB+CPM)

0

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Figure 4 Plasma concentrationtime profiles of chlorpheniraminemaleate (CPM). ACB, artificial calculus bovis; DS diclofenac sodium.Values are the mean SD, n = 6.



of decline, the Tmax, ClZ/F and VZ/F of CPM were markedlyhigher than that of group 2, and there were statisticallysignificant differences in these parameters (P < 0.05).Although the t12 of CPM was found to be slightly differentamong these groups, there was no significant differencebecause of large variations in the data. From the resultsabove, we concluded that no apparent herbdrug pharma-cokinetic interaction existed between DS and CPM, and thecombination of ACB, DS and CPM noticeably altered theabsorption, distribution and disposition of the drug.

Discussion

The pharmaceutical action and therapeutic value of tradi-tional Chinese medicines are expressed by multiple chemi-cal components. In our previous work, we quantitativelydetermined the content of bile acids, bilirubin and taurinein ACB.[29] The batch of herb with higher levels of theseeffective components was used in this study to ensure thereliability of results.

TCM is considered as an alternative and complementarymedicine system in many Asian and Western countries. Anintegration of TCM and Western medicine has begun inseveral international medical centers. The combination ofTCM and Western medicine necessitates a comprehensive

understanding of the interaction between drugs, particu-larly herbdrug interactions.[2,5,36,37] As a treatment for thecommon cold, compound diclofenac sodium chlorphen-amine maleate tablets are a herbdrug preparation com-posed of ACB, DS and CPM. Although the concomitantadministration of these three drugs is often used in clinicaltreatment, there have been no studies systematically andcomprehensively determining their pharmacokinetic inter-actions. The aim of this study was to elucidate the herbdrug pharmacokinetic interaction of ACB with DS andCPM in rats.

Previous investigations revealed that DS had rapidabsorption, high plasma protein binding (>99.7%) andminimal tissue binding, which is consistent with the presentresults.[38,39] Compared with the DS alone group, there weresignificant differences in the AUC0-, Cmax, Tmax, ClZ/F andVZ/F for DS after co-administration of ACB with DS. The DSconcentration increased to 33.769 6.548 mg/ml (Cmax)and 31.311 3.197 mg/ml (Cmax), with a Tmax range of1015 min in groups 4 and 6, respectively, which increased3.1-fold and 2.9-fold compared with the DS alone group.There was a significant difference in the AUC0- amongthe three groups (P < 0.01). The DS from groups 4 and 6presented a relative bioavailability 2.9-fold and 2.7-foldgreater than that of the DS alone group. The increase in

Table 1 Pharmacokinetic parameters of diclofenac sodium in plasma

Parameter

Group 1 Group 3 Group 4 Group 6

DS alone DS + CPM DS + ACB DS + ACB + CPM

AUC0-(mg/ml) 23.047 3.35 23.313 2.337 65.824 7.926** 61.958 8.764**

Tmax (h) 0.750 0.224 0.750 0.224 0.236 0.034* 0.236 0.034**

Cmax (mg/ml) 10.742 1.184 10.874 0.958 33.769 6.548** 31.311 3.197**

t12 (h) 1.933 0.595 2.150 0.452 2.088 0.715 1.975 0.393ClZ/F (l/h/kg) 0.442 0.069 0.433 0.046 0.154 0.018* 0.164 0.025*

VZ/F (l/kg) 1.222 0.345 1.342 0.301 0.467 0.174* 0.461 0.074**

AUC0-, area under the concentrationtime curve to infinity; Tmax, time of peak concentration; Cmax, peak plasma concentration; t12, biological half-life; ClZ/F, clearance; VZ/F, apparent volume of distribution. ACB, artificial calculus bovis; CPM, chlorpheniramine maleate; DS, diclofenac sodium.Values are mean SD, n = 6. *P < 0.05, significantly different compared with the DS alone group. ** P < 0.01, significantly different comparedwith the DS alone group.

Table 2 Pharmacokinetic parameters of chlorpheniramine maleate in plasma

Parameter

Group 2 Group 3 Group 5 Group 6

CPM alone CPM + DS CPM + ACB DS + ACB + CPM

AUC0- (mg/ml) 5.775 0.472 5.651 0.123 2.483 0.071** 2.575 0.102**

Tmax (h) 0.667 0.129 0.667 0.129 0.917 0.129* 0.958 0.102**

Cmax (mg/ml) 2.475 0.095 2.499 0.105 0.932 0.014** 0.932 0.013**

t12 (h) 1.800 0.344 1.367 0.167* 1.972 0.571 2.313 0.413ClZ/F (l/h/kg) 0.348 0.029 0.354 0.008 0.810 0.020** 0.778 0.030**

Vz/F (l/kg) 0.915 0.242 0.698 0.081 2.296 0.669* 2.598 0.501**

AUC0-, area under the concentrationtime curve to infinity; Tmax, time of peak concentration; Cmax, peak plasma concentration; t12, biological half-life; ClZ/F, clearance; VZ/F, apparent volume of distribution. ACB, artificial calculus bovis; CPM, chlorpheniramine maleate; DS, diclofenac sodium.Values are mean SD, n = 6. *P < 0.05, significantly different compared with the CPM alone group. **P < 0.01, significantly different comparedwith the CPM alone group.



Cmax and AUC0- indicated that ACB was effective in pro-moting the drug absorption of DS. Meanwhile, the clear-ance of DS from groups 4 and 6 was 2.7-fold lower thanthat of the DS alone group, and the apparent volume of dis-tribution for DS was decreased by 2.6-fold owing to theco-administration of ACB. These results suggest that ACBsignificantly inhibited the rate of elimination of DS.

Interestingly, the effects of ACB on the pharmacokineticbehaviour of CPM were virtually the opposite of its effectson DS. ACB apparently decreased the relative bioavailabilityand promoted the rate of elimination for CPM (as shown inTable 2). In contrast with DS, CPM distributed rapidly andextensively in body tissues such as kidney, brain and lung,and the concentration in these tissues was more than31-fold higher than the plasma level.[40] Although themechanism of the herbdrug pharmacokinetic interactionis still unclear, the different pharmacokinetic and distribu-tion behaviours between DS and CPM may contribute tothe observed opposite effects, and further investigations arerequired to clarify this.

Cytochromes P450 (CYP) are the primary enzymesrelated to drug metabolism. Therefore, slight changes inCYP activity may alter the pharmacokinetic profile of atherapeutic agent and lead to many important drugdruginteractions. Previous findings indicated that the metabo-lism of DS mainly involved CYP2C9 and CYP3A4, andCPM was a substrate of CYP2D6.[41,42] Since CYP partici-pates in the metabolic process, substrates that can alter CYPactivity may account for the variability in the pharmacoki-netic behaviour of DS and CPM. In the present study, thepharmacokinetic profile of DS and CPM were both alteredin the presence of ACB, which indicated that ACB was apossible effective inducer and/or inhibitor of CYP and hadthe potential to alter CYP activity. The exact mechanismwould require further investigation.

The stereoselective pharmacokinetics of CPM meritattention. Although CPM is administered as a racemate inthe products market, its pharmacological activity primarilyresides in the (S)-(+)-enantiomer.[43] Koch et al. investigatedthe potential effect of ranitidine on the stereoselective phar-macokinetics of CPM and the results demonstrated thatranitidine had no effect on the pharmacokinetics of eitherthe (S)-(+)- or (R)-()-enantiomer, indicating no pharma-cokinetic drugdrug interaction.[44] The present study hasconfirmed that ACB had an influence on the pharmacoki-netic profile of CPM. Whether such stereoselective pharma-cokinetics exist between ACB and CPM would need to beassessed in a future study.

Concurrent use of TCM and Western medicine canimprove the clinical efficacy, expand the scope of treatmentand have positive effects on some diseases.[1,45] However, tra-ditional Chinese medicines comprise multiple chemicalcomponents and so the interaction mechanisms that causethe therapeutic effects are complicated, and this may inturn cause more difficulty in investigating the interactionbetween TCM and Western medicine. The combination ofTCM and Western medicine has an impact on drug absorp-tion, distribution, metabolism, excretion and other relatedbody process, but may sometimes have a negative impact onthe pharmacodynamics, decreasing the effects of the medi-cine or even producing adverse reactions. The apparentimpact of ACB on the pharmacokinetic behaviour of DSand CPM has been confirmed in this study, and futureresearch will focus on the effects of ACB on the drugmetabolism of both, as well as the adverse reactions arisingfrom concomitant administration of TCM and Westernmedicine.

Conclusions

A sensitive HPLC-MS/MS method was successfully appliedto characterize the herbdrug pharmacokinetic interactionof ACB with DS and CPM in rats. Co-administration ofACB with DS noticeably increased the AUC0- and Cmax ofDS, and the parameters of Tmax, ClZ/F and VZ/F of DS weresignificantly decreased. Co-administration of ACB withCPM increased the Tmax, ClZ/F and VZ/F of CPM. A markeddecline in AUC0- and Cmax of CPM occurred in the pres-ence of ACB. However, there was no apparent pharmacoki-netic interaction between DS and CPM. This studyindicates that co-administration of ACB with DS and CPMcan result in an apparent herbdrug pharmacokinetic inter-action in rats.

Declarations

Conflict of interest

The Author(s) declare(s) that they have no conflicts ofinterest to disclose.

Funding

This work was supported by the Xiansheng InnovationFund (CX11B-003XS) and the Fundamental ResearchFunds for the Central Universities (JKY2011037).

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Herb–drug pharmacokinetic interaction of artiﬁcial calculus