奥比沙星在兔体内的药物动力学研究

应用反相高效液相色谱法（RP—HPLC）研究奥比沙星在健康家兔体内的药物动力学规律。家兔以10mg/kg的单剂量肌肉注射奥比沙星,取给药后不同时间的血浆,用高效液相色谱仪测定血浆中奥比沙星的质量浓度,MCPKP药物动力学软件程序处理血浆药物浓度与时间数据。房室模型分析表明,免肌注给药的药时数据适合吸收二室开放模型：吸收和消除半衰期（T1／2Ka,T1/2β）分别为0．2669h和7．1546h;达峰时间（Tmax）为0．563h;峰浓度（Cmax）为4．8717μg／mL;药时曲线下面积（AUC）为18．4535mg／L·h。奥比沙星在家免体内的主要药动学特征为：吸收迅速,分布快,消除较缓慢,达峰时间短,峰浓度高,药时曲线下面积大。     

EGF和IGF-I对绵羊卵母细胞体外成熟和卵裂的影响

本文研究了EGF、IGF-I以及EGF和IGF-I联合对绵羊卵母细胞体外成熟和卵裂的影响,以确立绵羊卵母细胞体外成熟的最佳条件。结果表明：50ng／mL的EGF的成熟率和卵裂率分别为71．2％和45．5％,显著高于对照组和10、20、30、40ng／mL组（P〈0．05）,当EGF浓度达到100ng／mL时,成熟率和卵裂率最高,分别为72．9％和45．7％;40ng／mL IGF-1的成熟率和卵裂率分别为70．7％和58．5％,显著高于对照组和10、20、60、80、100ng／mL组（P〈0．05）,当IGF-I的浓度为100ng／mL时,成熟率和卵裂率最低,分别为38．8％和20．0％,与对照组和其它各试验组差异显著（P〈0．05）;50ng／mLEGF和40ng／mLIGF-I联合使用,成熟率和卵裂率分别为85．6％和61．0％,同对照组和50ng／mLEGF组、40ng／mLIGF-I组之间差异显著（P〈0．05）。     

喹胺醇与鸡血浆蛋白结合的初步研究

采用平衡透析法结合反相高效液相色谱法（RP—HPLC）测定鸡血浆中喹胺醇的蛋白结合率。色谱条件为ZORBAX Eclipse XDB C18色谱柱（250mm×4．6mm,5μm）,流动相为乙腈：水（40：60,v／v）,流速1．0mL／min,检测波长352nm。结果显示,喹胺醇浓度为1．1、5．5、22．0μg／mL缓冲液中鸡血浆的蛋白结合率分别为84．41％、75．30％、66．96％;透析平衡时间约为30h。表明喹胺醇的鸡血浆蛋白结合率较高,药物浓度与血浆蛋白结合率之间呈反比关系。     

兽用伊曲康唑凝胶剂的皮肤毒理试验

为了研究犬用抗真菌药伊曲康唑凝胶剂对皮肤的毒理学作用,探讨其使用安全性,试验采用一次给药的方法,将低、中、高3种浓度的伊曲康唑凝胶剂涂抹于大鼠完整皮肤及破损皮肤处,观察大鼠皮肤急性毒性反应:通过一次给药及多次给药方法将伊曲康唑凝胶剂涂抹于家兔完整皮肤及破损皮肤处,观察家兔皮肤刺激性反应;用伊曲康唑凝胶剂、空白凝胶及阳性...     

猪肉和牛奶中10种磺胺类药物残留检测超高效液相色谱法研究

建立了猪肉和牛奶中磺胺嘧啶（SD）、磺胺噻唑（ST）、磺胺二甲嘧啶（SM2）、磺胺甲氧嗪（SMP）、磺胺氯哒嗪（SPD）、磺胺间甲氧嘧啶（SMM）、磺胺甲基异嗯唑（SM2）、磺胺氯吡嗪（Esb3）、磺胺地索辛（SDM）和磺胺喹嗯啉（SQ）共10种磺胺类药物残留检测的超高效液相色谱（UPLC）法。色谱条件：色谱柱为Acquity UPLC BEH C18柱（2．1mm×50mm,1．7μm）;流动相为50％甲醇乙腈溶液-2％乙酸水溶液,梯度洗脱;紫外检测波长270nm;柱温30℃;进样量4μL;外标法定量。结果表明：10种组分在20～1000ng／mL浓度范围内,呈良好线性关系,相关系数R^2均大于0．998;方法检出限为20ng／g,定量限为50ng／g;在猪肉和牛奶中添加浓度分别为50、100、200ng／g时,平均回收率为75．1％～99．8％,批内、批间平均RSD均小于13．2％。     

鸡肉和鸡蛋中金刚烷胺与金刚乙胺残留检测UPLC-MS/MS法研究

建立了鸡肉和鸡蛋中金刚烷胺与金刚乙胺残留检测的超高效液相色谱-串联质谱方法（UPLC-MS／MS）。样品在酸性条件下乙腈提取后,用正己烷去除脂肪,高速离心去除蛋白质等杂质,上机测试。液相色谱条件：色谱柱为BEHC18（50×2．1mm,1．7μm）,流动相为0．1％甲酸乙腈溶液＋0．1％甲酸水溶液,流速0．3mL／min,柱温30cI二,进样量10μL。质谱条件：电喷雾离子源（ESI^＋）,多反应监测（MRM）方式进行采集。结果表明：金刚烷胺与金刚乙胺在2～100ng／mL浓度范围内均呈现良好的线性关系,相关系数（R。）分别为=0．9977和0．9988;鸡蛋和鸡肉中金刚烷胺与金刚乙胺残留检测方法检测限均为1ng／g,定量限均为2ng／g。从鸡肉组织在2、5和10ng／g三个添加浓度检测结果可以看出,金刚烷胺与金刚乙胺的平均回收率分别为79．6％～107．5％和78．4％～101．2％,批内和批间RSD均小于15％。从鸡蛋在2、5和10ng／g三个添加浓度检测结果可以看出,金刚烷胺与金刚乙胺的平均回收率分别为90．8％～111．1％和75．4％～87．4％,批内和批间RSD均小于15％。该方法具有简便快捷、灵敏度高、定性准确等特点。     

地克珠利在雏鸡体内的药动学研究

目的应用高效液相色谱测定单次给药后雏鸡体内地克珠利的血药浓度,研究其药动学规律。方法44羽雏鸡按10mg／kg．BW经口单次灌服地克珠利预混剂,采用高效液相色谱系统的流动相为乙腈：0．1％三氟乙酸：水,流速1．0mL／min,分流比57：20：23,固定相为TC-C18柱,检测波长280nm,测定地克珠利血浆浓度,计算其药动学参数。结果在0．3125～20μg／mL范围内,地克珠利血药浓度呈线性关系,最低检测浓度为0．16μg／mL,回收率在79．75％以上,日内RSD小于5．68％。单剂量给药后地克珠利的主要药动学参数为：血药浓度峰值（Cmax）32．97μg／mL,达峰时间（Tpeak）1．64h,消除半衰期（T1／2β）24．29h,药时曲线下面积（AUC）349．47（mg／L）·h,血浆清除率（CL）0．03mg／kg·h。结论地克珠利在雏鸡体内代谢符合一级吸收的二室模型,药物吸收比较快和消除缓慢。     

高效液相色谱法同时测定猪血浆中的SMM、SMZ和TMP

建立了同时测定SMM、SMZ和TMP血药浓度的HPLC方法。采用Waters HPLC系统，Waters ODS2柱，以乙腈：0．017mol／L磷酸液(20：80)为流动相，检测波长230nm。SMM、SMZ在0．05～10．0μg／mL范围内线性良好(r=0．99998)，TMP在0．01～2．0μg／mL范围内线性良好(r=0．99999)。平均方法回收率分别为94．5％、98．6％和86．8％。最低血浆检测浓度分别为SMM0．15μg／mL、SMZ0．15μg／mL，TMP0．03μg／mL。该法采血量少，样品预处理简单，检测快速、灵敏。     

牛奶巾6种磺胺类药物残留的HPLC分析方法研究

本文对反相高效液相色讲仪（HPLC）分析牛奶中6种磺胺类药物（SAs）残留的样品前处理方法和色谱条件进行优化。结果表明：采用乙腈提取SAs残留，用正己烷液-液分配（除去脂溶性物质）和碱性氧化铝SPE柱净化，UV270nm检测，在0．01-8．0μg／mL浓度范围内，各药物峰面积与药物浓度之间呈良好的线性关系假（R^2=0．999）；平均添加回收率均在80％以上，变异系数在6％以下。SD、SM2、SMD、SMZ、SDM和SQX的检测限分别为2．30、3．16、3．60、5．42、11．76ng／mL和15．66ng／mL。     

猪尿中6种β-受体激动剂残留的超高效液相色谱-串联质谱法同时测定

建立了猪尿中苯乙醇胺A、莱克多巴胺、克仑特罗、西马特罗、特布他林、沙丁胺醇等6种β-受体激动剂在多反应监测模式下超高效液相色谱．串联质谱同时检测的方法。尿样经酶解,调至酸性,经固相萃取技术（SPE）净化富集。6种受体激动剂在0．2-5ng／mL的浓度范围内线性关系良好。方法的检出限和定量限分别为0．2ng／mL和0．5ng／mL。考察了0．5ng／mL、1ng／mL和2ng／mL三个添加浓度的回收率。6种化合物的加标回收率为87．2％-106．6％：RSD为1．2％-13．8％。该方法精密度好,灵敏度高,重现性好,能简便、快速、准确地测定猪尿中六种β-受体激动剂。     

Treatment of Blastomycosis With Itraconazole in 112 Dogs

One hundred twelve client-owned dogs with blastomycosis were treated with itraconazole, 5 or 10 mg/kg/d. The first group of 70 dogs treated in 1987 and 1988 received 10 mg/kg/d (group 1), and the second group of 42 dogs treated after October 1988 received 5 mg/kg/d (group 2). Even though the groups were treated at different times, the dogs were similar in age and gender distribution, number of sites involved, and percent and severity of pulmonary involvement. The proportion of dogs cured with a 60–day course of itraconazole was similar for both groups (53.6% versus 54.3%) and for a second historical control group treated with amphotericin B (57%); the recurrence rate was also similar, 20%, 21.4%, and 20%, respectively. Dogs treated with itraconazole had similar mortality rates (25.7% at 5 mg/kg/d; 25% at 10 mg/kg/day) to those treated with amphotericin B (23%). Seventeen of the 23 dogs that died (74%), did so during the first week of treatment; these early deaths were usually attributed to respiratory failure. The only site of infection that was significantly associated with failure (death or recurrence) was the brain. There was a marked difference in survival times between dogs without lung disease or with mild lung disease compared with dogs with moderate or severe lung disease. Serum itraconazole concentrations reached steady state by 14 days of treatment. Dogs receiving 5 mg/kg/d of itraconazole (group 2) had mean serum concentrations of 3.55 ± 2.81 mg/mL (range, 0.67 to 10.8 μg/mL), whereas dogs receiving 10 μg/kg/d (group 1) had mean concentrations of 13.46 ± 8.49 μg/mL (range, 1.8 to 28 μg/mL) (P ≤ .001). There was no association between cure and serum itraconazole concentrations. Dogs in group 1 had significantly more adverse effects than dogs in group 2 (P= .046). Anorexia was the most common adverse effect, occurring in 14.9% of dogs in group 1. Only 8% of dogs in group 2 had adverse effects. Serum concentrations of itraconazole were positively correlated with serum alkaline phosphatase and alanine aminotransferase activities. Our findings indicate that itraconazole administered at a dose of 5 mg/kg/d is the drug of choice for blastomycosis in dogs.     

Pharmacokinetics of subcutaneous fentanyl in Greyhounds

The purpose of the study was to describe the pharmacokinetics of subcutaneous fentanyl (15μg/kg) in six healthy Greyhound dogs. Fentanyl plasma concentrations were determined by a liquid chromatography with mass spectrometry method. Non-compartmental pharmacokinetic analysis was used. Fentanyl was rapidly absorbed with a mean peak concentration (C(MAX)) of 3.56ng/mL at 0.24h. The mean terminal half-life, volume of distribution per bioavailability, and clearance per bioavailability were 2.97h, 7.09L/kg, 27.60mL/min/kg, respectively. Pain occurred on injection in all six dogs, but addition of 8.4% sodium bicarbonate (1mL per 20mL fentanyl) resulted in no pain on injection in 3/3 dogs but similar C(MAX) values. The subcutaneous route may be an alternative route of fentanyl administration if intravenous administration is not practical.     

Assessment of a point‐of‐care cardiac troponin I test to differentiate cardiac from noncardiac causes of respiratory distress in dogs

Objectives – To (1) determine a reference interval for cardiac troponin I (cTnI) using a point‐of‐care device in normal dogs and compare the results with those published by the manufacturer and (2) determine if cTnI differs among dogs with cardiogenic and noncardiogenic respiratory distress. Design – Prospective observational study. Setting – Emergency and referral veterinary hospital. Animals – Twenty‐six clinically normal dogs and 67 dogs in respiratory distress. Interventions – All dogs underwent whole blood sampling for cTnI concentrations. Measurements and Results – Normal dogs had a median cTnI concentration of 0.03 ng/mL (range 0–0.11 ng/mL). Thirty‐six dogs were diagnosed with noncardiogenic respiratory distress with a median cTnI concentration of 0.14 ng/mL (range 0.01–4.31 ng/mL). Thirty‐one dogs were diagnosed with cardiogenic respiratory distress with a median cTnI concentration of 1.74 ng/mL (range 0.05–17.1 ng/mL). A significant difference between cTnI concentrations in normal dogs and dogs with noncardiogenic respiratory distress was not detected. Significant differences in cTnI concentrations were found between normals versus cardiogenic and cardiogenic versus noncardiogenic respiratory distress groups. Significant differences in cTnI concentrations were identified in >10 when compared with the <5 and the 5–10 years of age groups. Receiver operating curve analysis identified cTnI concentrations >1.5 ng/mL as the optimal “cut‐off point” having a sensitivity of 78% and specificity of 51.5%. The area under the receiver operating curve was 0.72. Overall test accuracy was 65%. Conclusions – cTnI concentrations were significantly increased in dogs with cardiogenic respiratory distress versus dogs with noncardiogenic respiratory distress and normal dogs. A significant difference between normal dogs and dogs with noncardiogenic causes of respiratory distress was detected. Although highly sensitive when cTnI concentrations exceed 1.5 ng/mL, the test has low specificity. Assessment of cTnI by the methodology used cannot be recommended as the sole diagnostic modality for evaluating the cause of respiratory distress in dogs.     

Comparison of plasma histamine levels after intravenous administration of hydromorphone and morphine in dogs

This study compared plasma histamine concentrations, behavioral and cardiovascular parameters following intravenous administration of hydromorphone and morphine in conscious dogs. Five adult female dogs received a 15-sec bolus injection of saline, hydromorphone (0.1 and 0.2 mg/kg) or morphine (0.5 and 1.0 mg/kg) randomly at weekly intervals. Blood samples were collected from the jugular vein before and at 1, 2, 5, 15, 30, 60 and 120 min after drug administration. Plasma histamine concentration, noninvasive oscillometric blood pressure, heart rate and rhythm were evaluated. Data were analyzed with repeated measures anova and Tukey-Kramer post hoc test with a 5% significance level. Median plasma histamine increased significantly only after the higher dose of morphine. Maximum plasma histamine measured was 0.8 ng/mL after saline and, after the lower and higher doses, respectively, 10.2 and 9.7 ng/mL for hydromorphone, and 440 and 589 ng/mL for morphine. One dog became hypotensive immediately after receiving the highest dose of morphine. Occasional ventricular premature contractions occurred in one dog after both opioids and dosages. No dogs vomited or defecated, but all salivated profusely with both opioids. Neuroexcitation occurred in four dogs following each opioid. In conclusion, intravenous hydromorphone induced minimal histamine release and was well tolerated by these conscious healthy dogs.     

Pharmacokinetics of epidural butorphanol in isoflurane-anaesthetized dogs

Sixteen healthy male dogs were used at random in this protocol. The dogs were anaesthetized with isoflurane in oxygen. Eight of the dogs received 0.25 mg/kg of butorphanol (group B) and the others an equal volume of isotonic saline (group S) administered by a catheter inserted in the lumbosacral epidural space. Butorphanol concentrations in plasma and cerebrospinal fluid (CSF) were measured using high-performance liquid chromatography with electrochemical detection. Maximum concentration of butorphanol and time to obtain this concentration were 42.28 ng/mL at 13.88 min in blood, and 18.03 ng/mL at 30 min in CSF. Volume of distribution, clearance, mean distribution and elimination half-lives were respectively 4.39 L/kg, 2.02 L/h.kg, 16.5 min and 189.1 min. Mean isoflurane minimal alveolar concentration values for group B obtained following hind- or forelimb stimulation decreased by 31% after epidural butorphanol. Cutaneous analgesia (to pin-prick test) persisted for 3 h after the end of isoflurane anaesthesia in group B and was in correlation with the plasmatic analgesic dose of butorphanol (9 ng/mL). These results suggested that analgesia was predominantly obtained by action of butorphanol on the supraspinal structures following its vascular systemic absorption.     

Cerebrospinal Fluid Myelin Basic Protein as a Prognostic Biomarker in Dogs with Thoracolumbar Intervertebral Disk Herniation

Background: Release of myelin basic protein (MBP) into the cerebrospinal fluid (CSF) is associated with active demyelination and correlates with outcome in various neurological diseases. Hypothesis/Objectives: To describe associations among CSF MBP concentration, initial neurological dysfunction, and long‐term ambulatory outcome in dogs with acute thoracolumbar intervertebral disk herniation (IVDH). Animals: Five hundred and seventy‐four dogs with acute thoracolumbar IVDH and 16 clinically normal dogs. Methods: Prospective case series clinical study. Signalment, initial neurological dysfunction as determined by a modified Frankel score (MFS), and ambulatory outcome at >3‐month follow‐up were recorded. Cisternal CSF MBP concentration was determined by an ELISA. Associations were estimated between CSF MBP concentration and various clinical parameters. Results: Dogs with thoracolumbar IVDH that did not ambulate at follow‐up had a higher CSF MBP concentration (median, 3.56 ng/mL; range, 0.59–51.2 ng/mL) compared with control dogs (median, 2.22 ng/mL; range, 0–3.82 ng/mL) (P= .032). A CSF MBP concentration of ≥3 ng/mL had a sensitivity of 78% and specificity of 76% to predict an unsuccessful outcome based on receiver‐operating characteristics curve analysis (area under the curve =0.688, P= .079). Affected dogs with a CSF MBP concentration ≥3 ng/mL had 0.09 times the odds of ambulation at follow‐up compared with affected dogs with CSF MBP concentration <3 ng/mL when adjusted for initial MFS (95% confidence interval 0.01–0.66, P= .018). Conclusions and Clinical Importance: These results would suggest that CSF MBP concentration may be useful as an independent prognostic indicator in dogs with thoracolumbar IVDH.     

The utility of plasma D-dimer to identify thromboembolic disease in dogs

This prospective study was designed to investigate D-dimer concentrations in clinically healthy dogs, clinically ill dogs without thromboembolic disease (TE), and dogs with TE. The goals of this study were to determine whether the coagulation cascade is activated in nonembolic metabolic and inflammatory conditions and whether differentiation from TE is possible. Group 1 consisted of 30 clinically healthy dogs presented for routine care. Group 2 consisted of 67 clinically ill dogs without TE. This group was subdivided into the following categories: postoperative surgical procedures, congestive heart failure, renal failure, hepatic disease, and neoplastic disease. Group 3 consisted of 20 dogs diagnosed with TE. A CBC and a measurement of prothrombin time (PT), activated partial thromboplastin time (PTT), fibrinogen degradation product (FDP) concentration, and plasma D-dimer concentration was performed on dogs in all groups. D-dimer concentrations were highest in dogs with TE; next highest was the hepatic disease group. Only these 2 groups had median D-dimer concentrations markedly different from clinically healthy dogs. The frequency of platelet abnormalities was markedly greater for the TE and neoplastic disease groups. The sensitivity of D-dimer concentrations >500 ng/mL for predicting TE was 100%; however, the specificity of D-dimer for TE at that concentration was 70%. The specificity of D-dimer concentrations >1,000 ng/mL to predict TE was 94% (sensitivity, 80%), and the specificity of D-dimer concentrations >2,000 ng/mL was 98.5% (sensitivity, 36%). FDPs were not high in any TE patient; thus, they may be an insensitive indicator of thromboembolism, with or without overt disseminated intravascular coagulation (DIC).     

Relationship of disease progression and plasma histamine concentrations in 11 dogs with mast cell tumors

Plasma histamine concentrations (PHCs) were measured serially over 9 months or until death in 11 dogs with mast cell tumors (MCTs). Eight dogs had grossly visible disease and the other 3 dogs had microscopic disease. Initial PHCs in the dogs with gross disease were significantly higher than PHCs in healthy dogs (median, 0.73 ng/mL and 0.19 ng/mL respectively; P < .009), whereas initial PHCs in dogs with microscopic disease showed no difference from controls. Seven dogs subsequently had progressive increases in PHC, and developed hyperhistaminemia (median, 14.0 ng/mL; range, 5.11-30.1 ng/nL). These 7 dogs died from MCTs, and 1 had general weakness with rapid lysis of a large tumor burden after radiation therapy. PHCs of the other 4 dogs were less than 1 ng/mL during the study. These 4 dogs were still alive with adequate control of the tumor at the conclusion of the study. Four of the 11 dogs initially had gastrointestinal (G1) signs, which abated soon after administration of histamine-2 (H-2) blockers. No significant difference was found between PHCs in dogs with GI signs and those without GI signs (median, 0.86 ng/mL and 0.35 ng/mL. respectively). Thereafter, 7 dogs had serious GI complications for which H-2 blocker therapy was ineffective. PHCs in these 7 dogs were extremely high (median, 12.2 ng/mL; range, 3.42-30.1 ng/nL). Results of this study demonsrated that PHC was one factor related to disease progression, and indicated that marked hyperhistaminemia was associated with the GI signs refractory to H-2 blocker therapy in dogs with MCTs.     

牦牛皮蝇蛆病低残留防治技术研究

应用埃普利诺菌素注射剂采用常规与微量给药技术,进行对牦牛皮蝇蛆病的防治试验,10月下旬给药,翌年3、5月份两次触摸检查牛背部皮下瘤疱和皮肤虫孔,并设阳性对照组,评价两种给药技术对牦牛皮蝇蛆病的防治效果。结果:两次检查阳性对照组平均感染率为39.15%,平均感染强度6.75(1~17)个;埃普利诺菌素注射剂常规剂量100、200、300μg/kg试验组牦牛两次检查平均治愈率和驱虫率均达100.0%;埃普利诺菌素注射剂微量10、20、30μg/kg防治组平均治愈率分别为86.3%、94.2%和100.0%,驱虫率分别为79.7%、93.2和100.0%。使用安全。给泌乳牦牛皮下注射埃普利诺菌素注射液0.2mg/kg后54.00h,牛奶中的埃普利诺菌素浓度达到峰值7.38±2.61ng/m L,低于美国(12 ng/m L)和欧盟(20ng/m L)规定的埃普利诺菌素在牛奶中的最高残留限量标准,不需休药期;皮下注射0.4mg/kg后56.00±26.31h,牛奶中的皮下注射浓度达到峰值6.98±2.98ng/m L,低于欧盟规定(20ng/m L),不需休药期,高于美国规定(12ng/m L),需休药期。适合当前家畜健康养殖中对牦牛寄生虫病防治的需要。     

Use of a von Frey device for evaluation of pharmacokinetics and pharmacodynamics of morphine after intravenous administration as an infusion or multiple doses in dogs

OBJECTIVE: To evaluate the pharmacokinetics and pharmacodynamics of morphine after IV administration as an infusion or multiple doses in dogs by use of a von Frey (vF) device. ANIMALS: 6 dogs. PROCEDURE: In the first 2 crossover experiments of a 3-way crossover study, morphine or saline (0.9%) solution was administered via IV infusion. Loading doses and infusion rates were administered to attain targeted plasma concentrations of 10, 20, 30, and 40 ng/mL. In the third experiment, morphine (0.5 mg/kg) was administered IV every 2 hours for 3 doses. The vF thresholds were measured hourly for 8 hours. Plasma concentrations of morphine were measured by high-pressure liquid chromatography. RESULTS: No significant changes in vF thresholds were observed during infusion of saline solution. The vF thresholds were significantly increased from 5 to 8 hours during the infusion phase, corresponding to targeted morphine plasma concentrations > 30 ng/mL and infusion rates > or = 0.15 +/- 0.02 mg/kg/h.The maximal effect (EMAX) was 78 +/- 11% (percentage change from baseline), and the effective concentration to attain a 50% maximal response (EC50) was 29.5 +/- 5.4 ng/mL. The vF thresholds were significantly increased from 1 to 7 hours during the multiple-dose phase; the EC50 and EMAX were 23.9 +/- 4.7 ng/mL and 173 +/- 58%, respectively. No significant differences in half-life, volume of distribution, or clearance between the first and last dose of morphine were detected. CONCLUSIONS AND CLINICAL RELEVANCE: Morphine administered via IV infusion (0.15 +/- 0.02 mg/kg/h) and multiple doses (0.5 mg/kg, IV, every 2 hours for 3 doses) maintained significant antinociception in dogs.