The effect of polysialylation on the immunogenicity and antigenicity of asparaginase: implication in its pharmacokinetics

Erwinia carotovora L-asparaginase was conjugated via the epsilon-amino groups of its lysine residues with colominic acid (CA) (polysialic acid) of average molecular mass of 10 kDa by reductive amination in the presence of NaCNBH3. Polysialylation using 50-, 100- and 250-fold molar excess CA relative to the enzyme led to an increasing proportion of the enzyme's in-amino groups (5.8, 7.6 and 11.3%, respectively) being conjugated to CA. Polysialylated and native (intact) asparaginase were used to immunize mice intravenously. Results (total IgG immune responses) indicate that all preparations elicited antibody production against the enzyme moiety but not against the CA of the conjugates. Moreover, antibody titres appeared highest for the native enzyme and were generally reduced as the degree of polysialylation increased. In other experiments mice pre-immunized with native or polysialylated asparaginase, with anti-asparaginase antibodies in their blood, were injected intravenously with the corresponding enzyme preparations. Results revealed that polysialylation reduces the antigenicity of asparaginase thus leading to circulatory half-lives (t 1/2 beta) that were 3-4-fold greater than that of the native enzyme, and similar to those observed in naive, non-immunized mice. Our data suggest that polysialylation of therapeutic enzymes and other proteins may be useful in maintaining their pharmacokinetics in individuals with antibodies to the therapeutic proteins as a result of chronic treatment.     

Serious neutropenia in ALL patients treated with L-asparaginase may be avoided by therapeutic monitoring of the enzyme activity in the circulation

The antineoplastic enzyme L-asparaginase is commonly used for the induction of remission in acute lymphoblastic leukemia (ALL). L-Asparagine is an essential amino acid for many lymphoid tumor cells and L-asparaginase catalyzes its conversion to L-aspartic acid and ammonia. The dosage of this highly toxic drug is individualized based on the body surface area of the patient, but monitoring of L-asparaginase activity during the L-asparaginase therapy is not commonly used. We measured L-asparaginase activity in the serum of ten children (aged 3-13 y) with ALL (ALL NOPHO-92 standard or intermediate risk groups) during their L-asparaginase therapy. L-asparaginase was given 30,000 IU/m2 IM during days 37-46 of the induction therapy and no other chemotherapeutic drug except for prednisone was given at the same time. We observed that this dosage schedule resulted in almost 6-fold differences in the serum activity of L-asparaginase between the patients. There was also a relationship between the area under the L-asparaginase activity-time curve (AUC) and even peak L-asparaginase activity in serum during the enzyme therapy and neutropenia after the therapy in the patients: the higher the AUC or peak value was, the more severe was the neutropenia in the patients after treatment. Monitoring L-asparaginase in serum could be useful in optimization of the therapy with this toxic drug.     

Pharmacokinetic/pharmacodynamic relationships of asparaginase formulations: the past, the present and recommendations for the future

The discovery of the tumour-inhibitory properties of asparaginase began 50 years ago with the observation that guinea-pig serum-treated lymphoma-bearing mice underwent rapid and often complete regression. Soon afterwards, the asparaginase of bacterial origin was isolated. The asparaginases of bacterial origin induce anti-asparaginase neutralising antibodies in a large proportion of patients (44-60%), thus negating the specific enzymatic activity and resulting in failure of the target amino acid deamination in serum. There is immunological cross-reaction between the antibodies against various formulations of native Escherichia coli-asparaginase and polyethylene glycol (PEG)-asparaginases, but not to Erwinia asparaginase, as suggested by laboratory preclinical findings. This evidence was strongly inferred from the interim analyses in the Children's Cancer Group (CCG)-1961 study. Thus, anti-E. coli or PEG-asparaginase antibodies seropositive patients may benefit from the Erwinia asparaginase.The inter-relationships between asparaginase activity, asparagine (ASN) and glutamine deamination remain largely unexplored in patients. Studies have shown that ASN depletion is insufficient to induce apoptosis in T lymphoblasts in vitro and that the inhibitory concentration of CEM T-cell line is correlated with the asparaginase concentration responsible for 50% glutamine deamination. The optimal catalysis of ASN and glutamine deamination in serum by asparaginase induces apoptosis of leukaemic lymphoblasts. The percentage of ASN and glutamine deamination was predicted by asparaginase activity. Asparaginase activity of 0.1 IU/mL provided insufficient depletion of both amino acids in high-risk acute lymphoblastic leukaemia (ALL) patients. With increasing glutamine deamination, mean asparaginase activities and percentages of post-treatment samples with effective ASN depletion (<3 micromol/L) increase. Both glutamine and ASN deamination are predicted by asparaginase activity. Further population analyses resulted in identification of sigmoid relationships between asparaginase levels and post-treatment glutamine and ASN deamination.Furthermore, pharmacodynamic analyses strongly suggested that >/=90% deamination of glutamine must occur before optimal ASN deamination takes place, due to the de novo ASN biosynthesis by the liver. These pharmacodynamic results from the best-fit population pharmacokinetic/pharmacodynamic model obtained from nonlinear mixed effects model pharmacodynamic analyses for standard-risk ALL patients are similar. These analyses produced the following results: (i) asparaginase activity 0.4-0.7 IU/mL was required for optimal (90%) ASN and glutamine deamination; and (ii) deamination of glutamine is dependent on asparaginase activity and it correlates with enhanced serum ASN deamination. Thus, glutamine deamination enhances asparaginase efficacy in ALL patients. Deamination of ASN >/=90% of control or ASN concentration <3 micromol/L may be associated with improved survival in this subset of patients. Our findings support the pharmacodynamic mechanism of PEG-asparaginase for disease control in ALL patients. These results taken together strongly support new experimental approaches for application of population pharmacokinetic/pharmacodynamic analyses to further enhance survival of leukaemia patients.     

Kinetic properties and inhibition of Acinetobacter glutaminase-asparaginase

Kinetic parameters, substrate specificity and exclusivity of ligands at binding sites of L-glutaminase-L-asparaginase purified from Acinetobacter glutaminasificans were studied in order to gain knowledge about the dual activities of this enzyme and its inhibition by structural analogs. Both L-glutamine and L-asparagine, which showed similar Km (4 approximately 7 X 10(-5) M) and Vmax (molecular activity 1.0 min-1) values, were competitive with each other for the substrate binding site. The products, L-glutamic acid and L-aspartic acid, showed competitive inhibition with respect to either L-glutamine or L-asparagine as substrates. Multiple inhibition of the glutaminase activity by L-glutamic acid and L-aspartic acid indicated that these ligands are mutually exclusive at the product-releasing site. The initial rates of both of the enzyme's activities were competitively inhibited by the following inhibitors (in rates of both of the enzyme's activities were competitively inhibited by the following inhibitors (in decreasing order of activity): 6-diazo-5-oxo-L-norleucine (DON), L-methionine sulfoximine, azaserine, and Acivicin. DON and azaserine inhibited both the asparaginase and glutaminase activities in a time-dependent and irreversible manner. The kinetic data suggest an ordered mechanism with glutamine or asparagine as the first substrate and glutamic acid or aspartic acid, respectively, as the last product. These results also suggest that a single mechanism and a single set of binding sites are responsible for catalyzing both of the enzyme's activities. The data also showed that succinylated enzyme, which has a 10-fold increase of plasma half-life in animals and humans and, thus, has benefit as a cancer chemotherapeutic agent, retained its catalytic activity and maintained Km and Vmax values similar to the native enzyme.     

Serum aminotransferase activity as a predictor of clearance of drugs metabolized by CYP isoforms in rats with acute hepatic failure induced by carbon tetrachloride

The values of serum aminotransferase activity (AST) in untreated rats and rats with acute hepatic failure at 24h after an oral administration of CCl(4) (0.5 ml/kg) were 85+/-9 IU/l and 4260+/-620 IU/l (mean+/-S.D., n=6), respectively. The values of total clearance (CL(tot)) after intravenous administration of caffeine, tolbutamide, chlorzoxazone or lidocaine (as probe drugs for various CYP isoforms) to CCl(4)-treated rats were decreased to about 1/8, 1/3, 1/3 or 1/2 compared with those in untreated rats. Good correlations were observed between mRNA expression and enzyme activity of CYP2C11, CYP2E1, CYP3A2 and CYP1A2 in livers of rats given various doses of CCl(4). There was also a good negative correlation between serum AST activity and hepatic enzyme activity of each CYP. The serum AST activities corresponding to a 50% decrease of CYP2C 11, CYP2E1, CYP3A2 and CYP1A2 activities were about 710, 780, 1030 and 1300 IU/l, respectively. In conclusion, when the serum AST value in CCl(4)-treated rats reached about 4000 IU/l, the hepatic CYP activities were one-tenth or less of the control, although the degree of decrease of the CL(tot) values varied markedly. Nevertheless, the AST value appears to be a promising candidate for an indicator to predict appropriate dose modification of drugs for patients with acute hepatic failure.     

The pharmacokinetic properties of intramuscular artesunate and rectal dihydroartemisinin in uncomplicated falciparum malaria

AIMS: To obtain pharmacokinetic data for artesunate (ARTS) and its active metabolite dihydroartemisinin (DHA) following i.m. ARTS and rectal DHA administration. METHODS: Twelve Vietnamese patients with uncomplicated falciparum malaria were randomized to receive either i.v. or i.m. ARTS (120 mg), with the alternative preparation given 8 h later in an open crossover design. A further 12 patients were given i.v. ARTS (120 mg) at 0 h and rectal DHA (160 mg) 8 h later. RESULTS: Following i.v. bolus, ARTS had a peak concentration of 42 microm (16 mg l(-1), elimination t1/2 = 3.2 min, CL = 2.8 l h(-1) kg(-1) and V = 0.22 l kg(-1) . The Cmax for DHA was 9.7 microm (2.7 mg l(-1) ), t1/2 = 59 min, CL = 0.64 l h(-1) kg(-1) and V = 0.8 l kg(-1) . Following i.m. ARTS, Cmax was 2.3 microm (3.7 mg l(-1)), the apparent t1/2 = 41 min, CL = 2.9 l h(-1) kg(-1) and V = 2.6 l kg(-1). The relative bioavailability of DHA was 88%, Cmax was 4.1 microm (1.16 mg l(-1)) and t1/2 = 64 min. In the rectal DHA study, relative bioavailability of DHA was 16%. CONCLUSIONS: For patients with uncomplicated falciparum malaria i.m. ARTS is a suitable alternative to i.v. ARTS, at equal doses. To achieve plasma DHA concentrations equivalent to parenteral administration of ARTS, rectal DHA should be given at approximately four-fold higher milligram doses. Further studies are needed to determine whether these recommendations can be applied to patients with severe malaria.     

Effect of thyroid hormones on liver microsomal enzyme induction in rats exposed to 2,3,7,8,-tetrachlorodibenzo-p-dioxin

The effect of thyroidectomy and thyroid hormone replacement therapy on liver microsomal enzyme induction was studied in 2,3,7,8,-tetrachlorodibenzo-p-dioxin (TCDD)-treated rats (100 micrograms/kg). Treatment of non-thyroidectomized rats with TCDD had no effect on the concentration of liver microsomal cytochrome b5. In contrast, cytochrome b5 content was increased by TCDD treatment of thyroidectomized rats, regardless of replacement therapy with either T3 or T4. TCDD treatment increased the concentration of cytochrome P-450 (2-3-fold) and the activities of benzo[a]pyrene hydroxylase (4-7-fold), ethoxyresorufin O-de-ethylase (50-70-fold) and UDP-glucuronosyltransferase (5-7-fold) in non-thyroidectomized and thyroidectomized as well as thyroidectomized thyroid hormone treated rats; indicating the induction of these liver microsomal enzyme activities is independent of thyroid status. Because thyroid status alters the toxicity of TCDD but does not alter the ability of TCDD to induce microsomal enzymes, it appears that TCDD toxicity may not be directly related to microsomal enzyme induction.     

Anti-factor Xa kinetics after intravenous enoxaparin in patients undergoing percutaneous coronary intervention: a population model analysis

AIM: Recent studies have suggested that intravenous (i.v.) enoxaparin could be used as antithrombotic therapy in patients ongoing percutaneous coronary intervention (PCI). However, anti-Xa pharmacokinetics following different i.v. dosing regimens is not clearly established. METHODS: A population pharmacokinetic analysis was developed using anti-Xa activities measured in 546 patients who received a single 0.5 mg kg(-1) i.v. dose of enoxaparin immediately before PCI. Effects of higher doses (0.75 mg kg(-1) and 1 mg kg(-1)) and/or additional bolus after the initial administration were similarly simulated. RESULTS: Enoxaparin anti-Xa time profiles were best described by a one-compartment model with zero-order kinetics. Mean population parameters (intersubject variability, %) were CL 1.2 l h(-1) (33), V 2.9 l (30) and zero-order input 0.25 h (24). With a single bolus of 0.5 mg kg(-1), the totality of the patients reached an effective anticoagulation level (anti-Xa >0.5 IU ml(-1)) and only 2.5% reached levels above 1.5 IU ml(-1). Simulations showed that greater doses (0.75 mg kg(-1) and 1 mg kg(-1)) prolonged the duration of anticoagulation (3.4 and 4.1 h, respectively) compared with the 0.5 mg kg(-1) bolus (2.7 h) and markedly increased the proportion (48% and 79%, respectively) of patients with anti-Xa levels >1.5 IU ml(-1). For delayed and/or prolonged procedures, patients could be administered a second bolus of half the initial dose in a time interval between 90 min to 2 h after in order to maintain similar anticoagulation profile levels. CONCLUSIONS: A single 0.5 mg kg(-1) i.v. dose of enoxaparin reached anticoagulation levels adequately and should be safer compared with greater doses for anticoagulation in patients undergoing an elective PCI. An additional second bolus could be proposed in patients with delayed or prolonged procedures.     

Induction of bradykinin B1 receptors in vivo in a model of ultra-violet irradiation-induced thermal hyperalgesia in the rat.

1. The role of bradykinin B1 receptors in the thermal hyperalgesia following unilateral ultra-violet (u.v.) irradiation of the hindpaw of rats has been investigated. 2. In non-irradiated (naive) animals the B1 receptor agonist des-Arg9-bradykinin and bradykinin (BK) (up to 1 mumol kg-1 i.v.) had no effect on withdrawal latency to a noxious heat stimulus when administered 60 min before testing. 3. Following exposure of one hindpaw to strong u.v. irradiation the withdrawal latency of the u.v.-treated paw to radiant noxious heat fell by a maximum of 50% after 48 h. There was no reduction in latency in the contralateral paw. 4. des-Arg9-BK (1-100 nmol kg-1 i.v.) administered 24 h after u.v. exposure caused a further dose-dependent fall (50 +/- 4% reduction from saline injected animals at 100 nmol kg-1 i.v.) in withdrawal latency in the u.v.-treated paw when measured 60 min after injection. The withdrawal latency of the contralateral paw was also reduced but to a lesser extent following des-Arg9-BK (100 nmol kg-1 i.v.) with a maximum reduction of 19 +/- 3%. 5. Bradykinin also induced a further reduction in withdrawal latency (33 +/- 5% reduction at 1 mumol kg-1) although it was not as effective as des-Arg9-BK. Bradykinin did not reduce the withdrawal latency in the contralateral paw.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinetics of ergotamine after intravenous and intramuscular administration to migraine sufferers

Summary The kinetics of ergotamine has been investigated in migrainous patients using a new, specific, sensitive HPLC assay (detection limit 100 pg/ml plasma). 10 patients were given ergotamine tartrate 0.5 mg i.v. and 5 of them received the same dose i.m. 2–3 weeks later. Blood samples were collected for up to 54 h following administration and the plasma concentration were analysed. After intravenous administration the plasma ergotamine declined rapidly, with an initial distribution half-life of 3 min followed by a mean terminal half-life of 1.86 h (range 90–155 min). The mean total plasma clearance was 11.0 ml kg^–1 min^–1, and the volume of distribution (V_d ) was 1847.6 ml kg^–1. Individual t_1/2 showed a positive linear correlation with the individual V_d . The intramuscular absorption of ergotamine was rapid and maximum plasma levels were usually obtained 10 min following administration. The biological availability was incomplete and variable at 46.6% (range 28.3–60.8%).     

Pharmacokinetics and bioavailability of intravenous and oral chlordesmethyldiazepam in humans

Summary Six healthy, fasting volunteers were given single doses of chlordesmethyldiazepam by 1 mg i. v., or as drops or tablets. Chlordesmethyldiazepam and its metabolite, lorazepam, in multiple plasma samples and in urine collected for 120 h after each dose were determined by electron-capture GLC.Mean kinetic variables for intravenous chlordesmethyldiazepam were: volume of distribution, 1.71 l · kg^–1; elimination half-life, 113 h; total clearance, 0.21 ml · min^–1 · kg^–1; cumulative excretion of lorazepam glucuronide 24.2% of the dose.Following a lag time of 15.5 min (tablets) and 4.2 min (drops), which were significantly different, the absorption of oral chlordesmethyldiazepam was a first order process, with apparent absorption half-life values averaging 1.5 h (tablets) and 1.1 h (drops). Bioavailability was 77% for tablets and 79% for drops.     

Femoxetine and cimetidine: Interaction in healthy volunteers

Summary The kinetics of moxalactam has been investigated in 10 subjects undergoing continuous ambulatory peritoneal dialysis (CAPD). A single 1 g dose was injected i.v. and a 1 g dose was given intraperitoneally in the CAPD fluid during a 4 h dwell-time. Moxalactam was assayed by HPLC. After i.v. injection, the serum kinetics of moxalactam were: plasma t 1/2=17.9 h; volume of distribution at steady-state, 0.27 l/kg; total plasma clearance, 12.8 ml/min; peritoneal clearance, 2.1 ml/min. Dialysate moxalactam concentrations rose rapidly but only 20% of the dose was eliminated by the peritoneal route. After intraperitoneal instillation, moxalactam appeared in the serum rapidly and the peak serum concentration ranged from 21 to 49 µg/ml after between 4 and 5 h. The absorption of moxalactam from the peritoneal space was 57±16%. The data suggest that moxalactam has bidirectional exchange characteristics through the peritoneal membrane. Instillation of moxalactam in CAPD fluid may permit rapid absorption and the appearance of a therapeutic serum concentration.     

Alfentanil kinetics in renal insufficiency

Summary Alfentanil 100 µg/kg was administered as an i.v. bolus to 9 patients with severe chronic renal dysfunction (creatinine clearance 1.0±1.2 ml/min) requiring regular haemodialysis. Plasma alfentanil concentrations were measured by a specific radioimmunoassay. Individual plasma concentration-time curves were fitted to a two-compartment open model. Mean distribution and elimination half-lives were 3.7 min and 58 min, respectively. The apparent volumes of distribution of the central compartment and the total volume of distribution at steady-state were 91 ml/kg and 304 ml/kg, respectively. Alfentanil plasma clearance was 5.3±2.5 ml/min/kg. All the patients tolerated alfentanil well and no side-effects nor delayed recovery were observed.     

抗体夹心酶联免疫吸附法测定重组E.coli L-天冬酰胺酶及药代动力学研究

目的建立大鼠血浆中重组E.coli L-天冬酰胺酶的抗体夹心酶联免疫吸附测定法,并进行药代动力学研究。方法应用重组E.coli L-天冬酰胺酶免疫家兔,分离IgG,用DEAE-纤维素柱色谱纯化,辣根过氧化物酶标记抗体,建立抗体夹心酶联免疫吸附法,测定大鼠血浆中重组E.coli L-天冬酰胺酶浓度。结果方法的线性范围为1～64 U·L^-1,血药浓度与时间的关系符合二房室模型,初期和末端的T_1/2分别为0.50～0.57 h和2.45～3.02 h,AUC与剂量成正比。结论建立的抗体夹心酶联免疫吸附法在灵敏度、特异性、线性范围、精密度和回收率等方面,满足药代动力学研究要求。实验方法和重组E.coli L-天冬酰胺酶在大鼠中的药代动力学参数为临床研究提供了手段和依据。     

A red wine vinegar beverage can inhibit the renin-angiotensin system: experimental evidence in vivo

A new beverage made of red wine vinegar and grape juice (Budo-no-megumi) was developed for people who wish to take effective amount of both polyphenols and vinegar. Since the beverage was recently demonstrated to exert hypotensive effect in rats, we analyzed its underlying mechanisms in this study. Sprague-Dawley rats were anesthetized with pentobarbital, and the blood pressure and lead II ECG were continuously monitored (n=6). The effects of recommended volume of the beverage (3 ml/kg, p.o.) on the renin-angiotensin system were assessed in vivo. At the basal control state, the increase in the mean blood pressure induced by the angiotensin I (1 microg/kg, i.v.) and norepinephrine (0.3-3 microg/kg, i.v.) were +57+/-2 and +36+/-8 mmHg, respectively. Sixty minutes after the administration of the beverage, the angiotensin I-induced pressor response decreased to +45+/-7 mmHg at 60 min (p<0.05), whereas no significant change was detected in the norepinephrine-induced pressor response. In another parallel series of the experiment using Sprague-Dawley rats (n=6), the serum angiotensin-converting enzyme activity was 39.4+/-1.2 IU/l at basal control state, which was slightly but significantly decreased to 37.0+/-1.4 IU/l at 60 min after the administration of the beverage (p<0.01). These results suggest that previously described hypotensive action of the beverage may be partly induced by the inhibition of angiotensin-converting enzyme.     

Pharmacokinetics of furosemide in man after intravenous and oral administration. Application of moment analysis

Summary Furosemide 40 mg was administered to 8 healthy subjects as an i.v. bolus dose, as 1 tablet in the fasting state, and as 1 tablet and a solution after food intake. The i.v. data gave a total body clearance of 162±10.8 ml/min and a renal clearance of 117±11.3 ml/min; the volume of distribution at steady state was 8.3±0.61. Oral administration gave a bioavailability of the tablet (fasting) of 51%. Food intake slightly reduced the bioavailability, but not to a significant extent. There was no significant difference in availability between the tablet and the solution. Moment analysis gave a mean residence time after the i.v. dose, MRT_i.v., of 51±1.5 min. The mean absorption times (MAT) for all oral doses were significantly longer than the MRT_i.v., indicating absorption rate-limited kinetics of furosemide. On average, food delayed the absorption by 60 min. The MAT for the tablet in the postprandial state was significantly longer than for the solution, indicating dissolution rate-limited absorption of the tablet.     

Lack of a centrally-mediated antihypertensive effect following acute or chronic central treatment with AT1-receptor antagonists in spontaneously hypertensive rats.

1. The role of the central renin-angiotensin system in the pathogenesis of hypertension in spontaneously hypertensive rats (SHR) was examined following acute and chronic intracerebroventricular (i.c.v.) infusions of angiotensin1 (AT1) receptor antagonists. 2. Groups of SHR were chronically instrumented for acute i.c.v. administration of the AT1 receptor antagonists, losartan and CV-11974, on mean arterial blood pressure (MAP) and heart rate (HR). Other groups of SHR also had mini-osmotic pumps implanted for chronic i.c.v. infusion of CV-11974. 3. Initially both young (15-18 weeks, n = 8) and old (25-29 weeks, n = 9) SHR received acute i.c.v. injections of losartan (10 micrograms) while a third group of young SHR received CV-11974 (1 microgram, n = 6). In all three groups of SHR, MAP and HR did not change up to 24 h after antagonist injection. However, changes in MAP and HR in response to i.c.v. angiotensin II (AII, 100 ng) were abolished 15 min after administration of the AT1 receptor antagonists. These responses had returned to control levels after 3 h in both groups given losartan but were still significantly depressed at 24 h in the CV-11974-treated group. By contrast, responses to i.v. AII (25 ng) before and 1 h after administration of AT1 receptor antagonists were not significantly different. 4. For chronic studies, four groups of SHR received chronic i.c.v. infusion of either vehicle (n = 9) or CV-11974 (1, 5 and 100 micrograms kg-1 day-1) (n = 4, 7 and 8 respectively) for 4 days. Baseline cardiovascular parameters were monitored daily together with changes in MAP and HR in response to both i.c.v. and i.v. AII (100 ng and 50 ng respectively) and i.v. phenylephrine (3 micrograms). Responses to i.c.v. carbachol (5 micrograms) were also recorded on day 4 while baroreflex function was assessed between days 1-3. In SHR treated chronically with i.c.v. vehicle or CV-11974, at 1 or 5 micrograms kg-1 day-1, resting MAP and HR did not vary over the four day infusion period. However, SHR treated with 100 micrograms kg-1 day-1 CV-11974 had significantly lower MAP compared to vehicle-treated SHR. While there was some variation in resting HR, there were no differences between the drug-treated and vehicle-treated groups. Pressor responses following i.c.v. AII administration were slightly, but significantly, inhibited on days 3 and 4 in the low dose CV-11974-treated (1 microgram kg-1 day-1) SHR. However, these responses were abolished on all 4 days in the 5 and 100 micrograms kg-1 day-1 CV-11974-treated groups. By contrast, changes in MAP and HR following i.v. AII injection did not vary over the 4 day infusion between SHR treated with the 2 lowest doses of CV-11974 and the vehicle-treated group. However, in the high dose CV-11974-treated SHR (100 micrograms kg-1 day-1), the cardiovascular effects of AII were abolished. In addition, phenylephrine (i.v.) and carbachol (i.c.v.) induced changes in MAP and HR were not significantly different in all four treatment groups. Similarly, baroreflex function was unaffected by i.c.v. infusion of 100 micrograms kg-1 day-1 CV-11974, except for a significant fall in BP50 which paralleled the fall in resting MAP. 5. Collectively, these results indicate that acute and chronic central AT1 receptor antagonism does not lower MAP in conscious SHR in doses which only block central AII-induced pressor activity. Chronic central infusion of CV-11974 at sufficiently high doses will lower MAP, as has been reported by others, but not without the abolition of the peripheral effects of AII. Therefore it is most likely that peripheral AT1 receptor blockade contributes to the hypotensive action of CV-11974 under these conditions.     

Population pharmacokinetic approach to compare oral and i.v. administration of etoposide

The antitumor effect of etoposide (ETO) may be related to duration of exposure to a relatively low serum level while myelosuppression may be dependent on peak ETO serum levels. With regard to such therapeutic ranges, duration of exposure to predefined plasma ETO concentration ranges and the related AUC (expressed as percent of total AUC, pAUC) were used to compare pharmacokinetic profiles after oral and short time i.v. (1 h infusion) administration of identical ETO doses (100 mg/m2). Patients included in this study received i.v. (18 patients, short-term infusions) or oral (16 patients) ETO on different treatment schedules. Plasma ETO concentrations were determined by HPLC and population pharmacokinetic parameters were calculated (P-Pharm 1.4). Despite an 'apparent bioavailability' of 59%, oral administration of ETO was associated with the same time of exposure to a predefined 'therapeutic range' of 0.5-3 mg/l and a significantly higher pAUC compared to i.v. administration. By contrast, time of exposure to the probably more myelotoxic concentration range above 3 mg/l was significantly shorter and the related pAUC was highly significantly lower after oral than after i.v. administration. These findings demonstrate that oral ETO therapy is at least equivalent to short time i.v. therapy in terms of achieving specific target concentration ranges and avoiding peak concentrations.     

Pharmacokinetics of tiropramide after single doses in man

The plasma levels and urinary excretions of (+/-) alpha-(benzoylamino)-4-[2-(diethylamino)ethoxy]-N, N-dipropyl-benzenepropanamide (tiropramide) and of some of its metabolites were studied in healthy volunteers after the following single-dose administrations of tiropramide hydrochloride: a) i.v. 50 mg, oral 100 mg or rectal 200 mg; b) i.v. 50 mg or i.m. 50 mg; c) oral 100, 200 or 400 mg. After i.v. bolus the plasma levels of tiropramide are consistent with a three-compartment open pharmacokinetic model. The steady-state volume of distribution is 221 l. The terminal elimination constant is 0.279 h-1 (t1/2 = 2.5 h). After i.m. injection the plasma levels increase rapidly (invasion t1/2 = 2 min) and then are similar to those found after i.v. bolus. After oral administration appreciable plasma levels are found after lag times of 18-27 min. They increase with an invasion t1/2 of 14-22 min. The peak is reached 1-1.7 h after administration and the elimination occurs with a constant of 0.20-0.23 h-1. After rectal administration appreciable plasma levels are found after a lag time of 11 min and increase with an invasion t1/2 of 6 min. The peak is reached at 2.2 h. The elimination constant is 0.21 h-1. Tiropramide and some of its metabolites can be determined in the urine by gas-liquid chromatography. The following percentages of the administered dose of tiropramide and tiropramide-related substances can be found in the 24-h urines. After i.v. bolus: 16.2; after i.m. injection: 17.0; after oral administration: 19.6; after rectal administration 13.1.(ABSTRACT TRUNCATED AT 250 WORDS)     

HPLC-MS法测定大鼠血浆中双-O-甲基四氢呋喃愈创木素B的浓度及药代动力学参数

目的建立测定大鼠血浆中双-O-甲基四氢呋喃愈创木素B(DiB)含量的高效液相色谱-电喷雾离子化-质谱(HPLC-ESI-MS)联用的分析方法,并用于其在大鼠体内的药代动力学研究。方法 SD大鼠6只,单剂量静脉注射(10mg.kg-1)DiB,以三白草酮为内标,用HPLC-MS法测定给药后血浆中的药物浓度,并用DAS 2.0软件计算药动学参数。结果 DiB的血药浓度在0.025～5.0 mg.L-1范围内线性关系良好,最低定量限为0.025 mg.L-1,提取回收率≥91.1%,日间、日内RSD≤10.0%。大鼠单剂量尾静脉注射DiB 10 mg.kg-1后,主要动力学参数AUC(0-t)、T12β、CL、V1分别为:(11.44±2.44)mg.h.L-1、(3.73±1.30)h、(0.65±0.14)L.h-1.kg-1、(3.36±3.19)L.kg-1。结论该方法操作简便、灵敏、快速、专属性强,可用于DiB的血药浓度检测及药代动力学研究。