Dose-dependent pharmacokinetics of KR-31378, a new neuroprotective agent for ischaemia-reperfusion damage in dogs

Dose-dependent pharmacokinetic parameters of KR-31378, a new neuroprotective agent for ischaemia-reperfusion damage, were evaluated after intravenous and oral administration of the drug at doses of 5, 10 and 25 mg/kg to male beagle dogs. After intravenous administration, the dose-normalized (based on 5 mg/kg) areas under the plasma concentration-time curve from time zero to time infinity (AUC values, 725, 1450 and 2300 micro g min/ml for 5, 10 and 25 mg/kg, respectively) were significantly different among the three dose ranges studied; the value increased more proportionally as the dose increased. This could be due to slower total body clearance (Cl) with increasing doses (6.90, 3.46 and 2.17 ml/min/kg). The slower Cl value with increasing doses may be due to saturable metabolism of KR-31378 in dogs. After oral administration, the dose-normalized (based on 5 mg/kg) AUC values (833, 1450 and 1920 micro g min/ml) at 5 mg/kg were significantly smaller than those at 10 and 25 mg/kg. Note that the AUC values were comparable (not significantly different) between intravenous and oral administration at all doses studied, indicating that the absorption of KR-31378 from the gastrointestinal tract was essentially complete and the first-pass (gastric, intestinal and/or hepatic first-pass) effects were almost negligible in dogs.     

Dose-dependent and time-dependent pharmacokinetics in the dog after intravenous administration of dextrorphan.

The disposition of dextrorphan after single ascending iv doses and multiple iv dosing regimens was studied in Marshall beagle dogs. A dose-dependent decrease in plasma clearance was observed after the administration of single iv doses of 0.88 mg/kg, 2.64 mg/kg, and 8.8 mg/kg of dextrorphan (i.e. mean plasma clearance values +/- SD were 100 +/- 25 vs. 68 +/- 28 vs. 48 +/- 20 ml/min.kg, respectively; p less than 0.001). Upon multiple dosing, the plasma clearance of dextrorphan increased in a time-dependent fashion for the two highest doses, approaching values observed for the 0.88 mg/kg/day iv dosing regimen. Female dogs exhibited a greater increase in plasma clearance with time. For all dogs, however, dextrorphan plasma clearance approached or exceeded hepatic plasma flow rate, suggesting the possibility of extrahepatic metabolism or elimination. Modest dose- and time-dependent changes in the steady-state volume of distribution of dextrorphan also were observed. The AUC of the conjugated metabolites of dextrorphan decreased in a time-dependent manner for the 8.8 mg/kg/day dosing regimen. The nonlinear kinetics of dextrorphan after iv administration appeared to occur only after potentially toxic dosing regimens of dextrorphan hydrochloride. We postulate mechanisms to explain the dose- and time-dependent kinetics of dextrorphan observed in the beagle dog.     

Liquid chromatography/tandem mass spectrometry for the determination of magnesium lithospermate B in beagle dog serum

A sensitive and specific isocratic liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed for the quantification of magnesium lithospermate B (MLB) in beagle dog serum with silibinin as internal standard. The serum samples were treated by special liquid-liquid extraction, and the analytes were determined using electrospray negative ionization mass spectrometry in the selective monitoring mode, with sufficient sensitivity to allow analysis of dog serum samples generated following administration of a clinically relevant dose. The calibration curve for MLB was linear over the range 8-2048 ng/ml with coefficients of correlation >0.999. The intra- and inter-day precisions (CV) of analysis were <7%, and accuracy ranged from 90 to 106%. This quantitation method was successfully applied to a pharmacokinetic study of i.h. administration of MLB with dosages of 3, 6, 12 mg/kg in beagle dogs.     

Bioavailability and pharmacokinetics of S-propargyl-L-cysteine, a novel cardioprotective agent, after single and multiple doses in Beagle dogs

As a novel hydrogen sulfide-modulated agent, S-propargyl-L-cysteine (SPRC) is proven to be a potent cardioprotective candidate. Bioavailability and pharmacokinetics of SPRC (20?mg/kg) in beagle dogs after oral and intravenous administrations were investigated in this study. Plasma concentrations of SPRC were measured by a LC-MS/MS method. Intravenous administration of SPRC (single dose) to beagle dogs gave a mean plasma half-life of 14.7?h, mean clearance of 0.4?ml min?1 kg?1 and mean apparent volume of distribution of 0.56?L/kg. Single oral administration was completely, fast absorbed (T(max)= 0.33?±?0.20?h) with a mean absolute availability of 112% and mean plasma half-life of 16.5?h. Multiple oral administration (once daily for 10 consecutive days) of SPRC to dogs resulted in steady state plasma drug concentration being reached after seven doses and didn't cause obvious accumulation. No significant difference was found between the single and multiple pharmacokinetic parameters.     

雷公藤内酯醇在Beagle犬体内的药代动力学

雷公藤内酯醇(triptolide，TP)是雷公藤的主要有效成分之一。研究不同剂量TP在Beagle犬灌胃给药时的绝对生物利用度和药代动力学， 可望为其临床研究提供参考。以泼尼松龙作内标， 用乙酸乙酯液液萃取， 建立LC-APCI/MS选择性离子监测方法测定血浆TP浓度。Beagle犬分别静脉注射TP 0.05 mg·kg^-1、 灌胃TP 0.05，0.08和0.1 mg·kg^-1进行药代动力学和绝对生物利用度研究。结果表明， TP在1～200 ng·mL^-1呈良好线性关系(r=0.999 7)，批内和批间精密度RSD均小于10%，准确度在95.0%～105.0%，提取回收率大于75%。静注0.05 mg·kg^-1 TP后，T_1/2β为(2.5±0.8) h。3个剂量灌胃组，T_max，T_1/2α和T_1/2β，经检验无统计学差异。AUC和C_max与剂量之间线性相关。灌胃0.05 mg·kg^-1后，TP在Beagle犬体内绝对生物利用度为(75±17)%。可见，LC-APCI/MS法灵敏、可靠、专属性强，可用来测定Beagle犬血浆TP的浓度；TP在Beagle犬体内消除较快，灌胃给药生物利用度较高。     

盐酸关附甲素在Beagle犬体内口服药代动力学和绝对生物利用度研究

目的：采用液相色谱-质谱联用分析方法研究盐酸关附甲素在Beagle犬体内的吸收特性。方法：6只Beagle犬采用双交叉实验设计,空腹单次静脉或灌胃给予盐酸关附甲素（4mg/kg）,采集不同时间点的血样,采用LC-MS法进行血浆药物浓度测定,求算相应的药代动力学参数。结果：6只Beagle犬灌胃4mg/kg盐酸关附甲素后体内过程符合二房室模型,实测的血浆药物浓度曲线下面积AUC0-48h为（18429±7281）ng·mL-1·h,最大血浆药物浓度Cmax为（1988±972）ng/mL,达峰时间tmax为（0.8±0.7）h,末端相消除半衰期t1/2为（11.2±1.6）h。与静脉注射给药相比其绝对生物利用度F为（99.0±11.2）%,拟合求得的吸收速率常数（K01）为（7.563±4.612）/h。结论：盐酸关附甲素在Bea-gle犬体内吸收迅速且完全,临床上可考虑采用口服剂型代替注射剂以便于病人用药。     

LC-MS/MS法测定比格犬血浆中芬太尼浓度及药动学研究

目的 建立比格犬血浆中芬太尼的液相色谱-串联质谱（LC-MS/MS）测定方法,并用于药动学研究。方法 采用固相萃取（SPE）法从血浆中提取芬太尼和内标芬太尼-d5,建立比格犬血浆中芬太尼的LC-MS/MS测定方法,进行特异性、准确度、精密度、基质效应、灵敏度、稀释可靠性、稳定性方法学验证;8只比格犬,分别单次iv给予芬太尼的生理盐水溶液400 mg/只,用LC-MS/MS测定给药后血浆中芬太尼浓度,并用WinNonLin软件计算药动学参数。结果 芬太尼的线性范围为2～1 000 pg/mL,精密度、准确度、基质效应、灵敏度、稀释可靠性、稳定性均符合生物样品分析要求。比格犬体内芬太尼药动学参数：t_1/2为（4.53±0.748）h,AUC_0-t为（19 659±3 889）h·ng/mL,CL为（2 259±284）mL/（h·kg）,符合二室开放模型。结论 建立的LC-MS/MS分析方法准确灵敏,适用于芬太尼的药动学研究。     

HPLC analysis and pharmacokinetic characteristics of 11-hydroxyaclacinomycin X (ID-6105), a novel anthracycline, in rats and beagle dogs

We investigated the pharmacokinetic characteristics of 11-hydroxyaclacinomycin X (ID-6105), a novel anthracycline, after intravenous (i.v.) bolus administration in rats and beagle dogs. We developed an HPLC-based method to analyze ID-6105 levels in plasma, bile, urine, feces, and tissue homogenates and validated the method in a pharmacokinetic study. The plasma concentration of ID-6105 decreased to below the quantifiable limit (0.02 microg/ml) at 4 and 8 h after i.v. administration in rats at doses of 2 and 10 mg/kg, respectively (t(1/2,alpha) and t(1/2,beta) of 0.78 and 17.8 min at a dose of 2 mg/kg, 0.91 and 176 min at a dose of 10 mg/kg, respectively). The AUC increased with nonlinear pharmacokinetics following the dosage increase from 2 to 10 mg/kg in rats, while the pharmacokinetics were not significantly altered in beagle dogs following a dosage increase from 0.5 to 2.5 mg/kg. Of the various tissues tested, ID-6105 was mainly distributed in the lung, spleen, kidney, adrenal gland, and liver after i.v. bolus administration. ID-6105 levels in the lung or kidney 2 h after i.v. bolus administration were comparable to the initial plasma concentration. However, the ID-6105 concentrations in various tissues 48 h after i.v. bolus administration became too small to measure. The cumulative amounts of ID-6105 found in the bile 48 h after the administration of 2 and 10 mg/kg were calculated to be 26.7 and 18.5% of the initial dose, respectively. The corresponding values in the urine 72 h after i.v. administration were 4.33 and 3.07% of the initial dose, suggesting that ID-6105 is mostly excreted in the bile. In conclusion, our observations indicate that ID-6105 was rapidly cleared from the blood and transferred to tissues such as the lung, spleen, kidney, and liver 2 h after i.v. bolus administration. Moreover, the majority of ID-6105 appears to be excreted in the bile by 24 h after i.v. bolus administration.     

溴泰君(W198)在大鼠和比格狗体内的药代动力学

目的研究溴泰君(W198)在大鼠和比格狗的药代动力学。方法采用HPLC紫外检测方法测定大鼠及比格狗注射W198后血清药物浓度。结果大鼠iv W198 10,20和40 mg·kg^-1 3个剂量的T_1/2β分别为6.60,7.36和6.77 h,AUC_0-24h分别为3.797,7.371和15.192 mg·h·L^-1,V_d分别为7.14,4.33和4.13 L·kg^-1,CL分别为2.83,2.60和2.71 L·(kg·h)^-1。大鼠im W198 20 mg·kg^-1后T_1/2β为11.61 h,AUC_0-24h为4.191 mg·h·L^-1,im的生物利用度为56.9%。比格狗iv W198 5 mg·kg^-1,T_1/2β为11.72 h,AUC_0-24h为12.646 mg·h·L^-1,V_d为0.70 L·kg^-1,CL为0.46 L·(kg·h)^-1。W198与人血浆蛋白的结合率平均为78.0%。结论W198 im的T_1/2β比iv的略长,其生物利用度为56.9%。在10～40 mg·kg^-1剂量内的吸收呈现一级动力学特征。     

灵仙新苷在Beagle犬体内的药动学及其绝对生物利用度研究

目的：研究灵仙新苷在Beagle犬体内的药动学和绝对生物利用度。方法：采用四周期交叉设计,即Beagle犬8只,雌雄各半,随机等分为4组,分别采取单剂量静脉注射（0．75mg／kg）及灌胃（7．5、15和30mg／kg）两种给药方式,交叉给药,间隔1周。并于给药后不同时间点取血,采用LC—MS／MS测定血浆中灵仙新苷的浓度,利用DAS2．0软件估算灵仙新苷在Beagle犬体内的药动学参数,并计算绝对生物利用度。结果：Beagle犬i．g．7．5、15和30mg／kg灵仙新苷后,估算的tl／2分别为（14．3±2．7）、（13．3±1．3）和（13．7±2．4）h,AUC0—36分别为（1．9±1．2）、（4．5±1．9）和（8．0±3．3）μg·h·mL-1,Cmax分别为（0．14±0．08）、（0．27±0．10）和（0．52±0．28）μg／mL。i．v．0．75mg／kg灵仙新苷后,估算的t1／2为（13．3±3．0）h,AUC0-36为（66．2±12．8）μg·h·mL-1。灌胃灵仙新苷在Beagle犬体内的绝对生物利用度分别为0．32％、0．35％和0．30％。结论：口服灵仙新苷后在Beagle犬体内绝对生物利用度很低,其药动学过程在研究剂量范围内是线性的。     

梓醇在大鼠体内的药代动力学和生物利用度研究

目的:研究梓醇在大鼠体内的药代动力学和生物利用度。方法:建立LC-MS/MS分析方法,应用Xcalibur 1.4数据处理工作站,以待测物(梓醇)与内标物(桃叶珊瑚苷)的色谱峰面积比计算大鼠灌胃50、100和200mg/kg和静脉注射50mg/kg梓醇后,各时间的血浆药物浓度。选用DAS 2.0软件计算药动学参数,t检验法统计实验数据,计算生物利用度。结果:梓醇在大鼠体内的药动学过程符合二室模型,大鼠灌胃50、100和200mg/kg梓醇后,AUC0→∞与剂量呈正比,t1/2与剂量无关;大鼠灌胃与静注50mg/kg梓醇后,AUC0→∞分别为(70±23)、(104±11)μg.h.mL-1,该剂量下梓醇的绝对生物利用度为66.7%。结论:梓醇的吸收和消除呈一级动力学特征,在大鼠体内的绝对生物利用度较高。     

注射用酒石酸长春瑞滨胶束及注射用长春瑞滨在比格犬体内的毒动学比较

目的 测定连续给予注射用酒石酸长春瑞滨胶束的毒动学参数，并与注射用酒石酸长春瑞滨进行比较。方法 选取16只比格犬随机分为4组，雌雄各半，分别连续iv给予注射用酒石酸长春瑞滨胶束低、中、高剂量（0.29、0.58、1.174 mg/kg）与注射用酒石酸长春瑞滨1.174 mg/kg，建立测定比格犬血浆中酒石酸长春瑞滨浓度的液相色谱-串联质谱（LC-MS/MS）法，测定血药浓度，采用DAS3.1.4药动学软件计算动力学参数。结果 比格犬iv给予注射用酒石酸长春瑞滨胶束低、中、高3个剂量，血药浓度、AUC_（0-t）、C_max随给药剂量的增加而增大；连续iv给药，低、中、高剂量组动物血药浓度、AUC_（0-t）、C_max在给药第1、29、71天时均变化不大，无明显蓄积倾向。而注射用长春瑞滨胶连续iv给药后随给药时间延长，动物血药浓度、AUC_（0-t）、C_max有上升趋势，AUC_（0-t）蓄积因子分别为2.08、1.80，C_max蓄积因子分别为2.58、2.32，均有蓄积倾向。结论 注射用酒石酸长春瑞滨胶束与普通注射用酒石酸长春瑞滨毒动学参数比较，无明显的蓄积倾向，可降低长期服药的毒性风险。     

丹七注射液中丹参素钠在Beagle犬体内药代动力学及生物利用度研究

目的研究丹七注射液中丹参素钠在Beagle犬体内的药代动力学。方法液相色谱-紫外光谱法,乙腈-1％的冰醋酸水溶液（8：92）为流动相,测定一次性静脉注射丹七注射液（28．4mg·kg^-1）和一次性口服丹七丸（114．7mg·kg^-1）后Beagle犬血浆中丹参素钠含量。采用BAPP2．3生物利用度数据处理通用程序中的模型拟合与统计矩法计算药物的药代动力学参数。结果静注和口服丹七制剂中的丹参素钠在Beagle犬体内的药代动力学均符合二室模型,T1/2为0．573、2．258h,AUC分别为29．792、77．84h·μg·ml^-1,口服生物利用度为63．8％。结论丹七注射液中丹参素钠在Beagle犬体内呈快吸收慢消除动力学特征。     

四季青中原儿茶酸在beagle犬体内的药动学研究

目的 建立LC-MS/MS法测定血浆中原儿茶酸的浓度,并对beagle犬灌胃四季青水煎液后原儿茶酸的药动学进行研究。方法 Beagle犬血浆样品以酮洛芬为内标,用乙腈沉淀蛋白,采用LC-MS/MS法进行分离和测定。色谱柱为C18(4.6mm×100mm, 2.7μm);流动相为80%乙腈-20%水(含0.1%甲酸),流速为0.2mL/min,柱温为30℃。质谱条件：电喷雾离子源(ESI),负离子模式,多反应离子监测(MRM),检测离子为原儿茶酸m/z 153.0→109.0,内标酮洛芬m/z 253.1→209.1。6只beagle犬单次灌胃四季青水煎液50mL(0.2g/mL)后,于给药前及给药后0.083、0.167、0.333、0.5、0.667、0.833、1、1.5、2、3、4和6h采血,以LC-MS/MS法测定原儿茶酸在beagle犬体内的血浆浓度,并用非房室模型计算药动学参数。结果 原儿茶酸浓度在0.05~2.00μg/mL范围内线性关系良好,定量下限为0.05μg/mL,批内和批间精密度RSD均小于8.6%,准确度为92.3%~102.0%。Beagle犬分别单次灌胃1g/kg(生药量)四季青水煎液后,其主要药动学参数Cmax为(1.53±0.33)μg/mL,Tmax为(0.42±0.09)h,t1/2为(0.80±0.16)h,MRT0~t 为(1.04±0.14)h,MRT0~∞ 为(1.32±0.26)h,AUC0~t为(1.90±0.35)(μg/mL)·h,AUC0-∞为(2.02±0.33)(μg/mL)·h。 结论 本实验中建立的LC-MS/MS法专属性强、快速灵敏,可以用于犬血浆中原儿茶酸的测定。Beagle犬单次灌胃四季青水煎液后,血浆中原儿茶酸能快速吸收,达峰速度较快,在体内能滞留一定时间,有利于四季青药效作用的发挥。     

Extremely low bioavailability of magnesium lithospermate B, an active component from Salvia miltiorrhiza, in rat

We assessed the bioavailability of magnesium lithospermate B (MLB), a main polyphenolic component of Salvia miltiorrhiza and a potent antioxidant having various pharmacological activities, to evaluate its action in vivo. The plasma concentrations of lithospermic acid B (LSB) showed a biexponential decrease after intravenous administration of MLB to rats at doses of 4 and 20 mg/kg. The values of area under the concentration-time curve (AUC; 87.8 +/- 10.9 and 1130 +/- 329 microg.min/mL), total body clearance (CL (tot); 55.52 +/- 7.07 and 23.51 +/- 5.98 mL/min/kg), and distribution volume at steady state (V (ss); 7.60 +/- 1.03 and 3.61 +/- 1.16 L/kg) suggested non-linear pharmacokinetics between the two doses. After oral administration of MLB at a high dose of 100 mg/kg, the mean AUC was barely 1.26 +/- 0.36 microg.min/mL. Absolute bioavailability of MLB was calculated to be 0.0002 from the AUC values after both intravenous dosing at 20 mg/kg and oral dosing at 100 mg/kg. The extremely low bioavailability was caused mainly by poor absorption from the rat gastrointestinal tract; about 65 % of the dose was retained in the tract even 4 h after oral administration, and most of the dose was retained even 20 min after infusion in an in situ jejunal loop experiment. Urinary and biliary excretion of LSB were only 0.70 % +/- 0.26 % and 5.10 % +/- 2.36 %, respectively, over a 30 h time period after intravenous injection despite the large CL (tot) and V (ss) values, and were much less (0.010 % +/- 0.001 % and 0.12 % +/- 0.04 %) after oral dosing. These findings suggest that extensive metabolism, including a first-pass effect, and wide distribution of LSB besides the poor absorption contributed significantly to the extremely low systemic bioavailability.     

Rapid determination of isocorydine in rat plasma and tissues using liquid chromatography--tandem mass spectrometry and its applications to pharmacokinetics and tissue distribution

A rapid and sensitive method for the determination of isocorydine in rat plasma and tissues was developed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The biological samples were processed by extracting with diethyl ether-dichloromethane (3:2, v/v) and tetrahydropulmatine was used as the internal standard (IS). Detection of the analytes was achieved using positive ion mode electrospray ionization in the multiple reaction monitoring mode. The MS/MS ion transitions monitored were m/z 342.0→279.0 and 356.0→191.9 for isocorydine and IS, respectively. The maximum plasma concentration (C(max) 2496.8 ± 374.4 μg/L) was achieved at 0.278 ± 0.113 h (T(max)) and the half-life (t(1/2)) of isocorydine was 0.906 ± 0.222 h after a 20 mg/kg oral administration. As for a 2 mg/kg intravenous (i.v.) administration, the C(max) and clearance (CL) were 1843.3 ± 338.3 μg/L and 2.381 ± 0.356 L/h/kg, respectively. Based on the AUC(0-∞) obtained from oral and i.v. administration, the absolute bioavailability (F) was estimated as 33.4%. Tissue distribution results indicated that isocorydine underwent a rapid and wide distribution into tissues and it could effectively cross the blood-brain barrier.     

Pharmacokinetics of astragaloside iv in beagle dogs.

In this study, the pharmacokinetics of Astragaloside iv (AGS-IV) in Beagle dogs was studied by high performance liquid chromatography (HPLC) coupled with tandem mass spectrometry (MS). The concentrations of the drugs in plasma were determined after i.v. administration of 0.5, 1, 2 mg.kg(-1) AGS-IV and p.o. administration of 10 mg.kg(-1) AGS-IV. The areas under concentration-time curve (AUC) were linearly correlated to the doses administrated. The absolute bioavailability of AGS-IV after p.o. administration was found to be 7.4%. The plasma protein binding rate of AGS-IV was about 90% within a concentration range of 250-1000 ng.ml(-1). There was no significant species difference regarding the pharmacokinetics of AGS-IV between the rat and the Beagle dog.     

异硫氰酸基雷公藤内酯醇活性代谢物雷公藤甲素在大鼠体内的药代动力学

目的观察大鼠单剂量静脉注射异硫氰酸基雷公藤内酯醇后雷公藤甲素的药代动力学。方法将大鼠分为2组(每组5只),分别单次尾静脉注射异硫氰酸基雷公藤内酯醇低、高剂量(4.25,8.50 mg·kg-1)。用LC-MS/MS法,检测大鼠血浆中雷公藤甲素的浓度,用BAPP 3.2软件计算药代动力学参数。结果低、高剂量的主要药代动力学参数如下:Cmax分别为(12.36±1.09),(55.74±21.20)ng·mL-1,Tmax均为(2.0±0.0)min,t1/2分别为(12.82±2.41),(13.73±2.84)h,AUC0-t分别为(245.93±42.50),(1034.45±471.76)ng·min.mL-1。结论在4.25～8.50 mg·kg-1,雷公藤甲素的药代动力学表现出非线性消除特征。     

Bioavailability and pharmacokinetics of S-propargyl-L-cysteine,a novel cardioprotective agent,after single and multiple doses in Beagle dogs

1. As a novel hydrogen sulfide-modulated agent, S-propargyl-L-cysteine (SPRC) is proven to be a potent cardioprotective candidate. Bioavailability and pharmacokinetics of SPRC (20?mg/kg) in beagle dogs after oral and intravenous administrations were investigated in this study. Plasma concentrations of SPRC were measured by a LC-MS/MS method.

2. Intravenous administration of SPRC (single dose) to beagle dogs gave a mean plasma half-life of 14.7?h, mean clearance of 0.4?ml min^?1 kg^?1 and mean apparent volume of distribution of 0.56?L/kg. Single oral administration was completely, fast absorbed (T_max= 0.33?±?0.20?h) with a mean absolute availability of 112% and mean plasma half-life of 16.5?h.

3. Multiple oral administration (once daily for 10 consecutive days) of SPRC to dogs resulted in steady state plasma drug concentration being reached after seven doses and didn’t cause obvious accumulation. No significant difference was found between the single and multiple pharmacokinetic parameters.

     

Effect of vigabatrin and gabapentin on phynytoin pharmacokinetics in the dog.

The study was aimed at investigating whether or not the kinetics of intravenously administered phenytoin (PT) was altered by oral administration of vigabatrin (VGB) or gabapentin (GBP). A group of five beagle dogs were given a daily dose of PT (12 mg/kg, i.v.) for a period of 1 week. On day 8, plasma samples were serially collected over 24 hr. after administration of the PT dose. PT administration was continued with oral supplementary dose of VGB (60 mg/kg) for another week and then plasma samples were collected for analysis of PT levels. The same protocol was followed for the PT (12 mg/kg, i.v.)-GBP (300 mg caps., p.o.) study on a separate group (n = 5) of dogs. Orally administered GBP did not significantly alter the pharmacokinetic parameters of parental PT. VGB, however markedly changed the drug's kinetics as evidenced by a 31% (P = 0.015) reduction in total body clearance (CL) and increase of over 45% in half-life (t1/2), (P = 0.013) and area under the plasma PT concentration-time curve (AUC), (P = 0.044). GBP does not appear to have any pharmacokinetic interaction with PT, while coadministration of VGB and PT results in marked reduction in systemic clearance of the latter in the dog.