The pharmacokinetics of a new benzamide drug clebopride, in the rat and the dog

After intravenous, intramuscular and oral administration of clebopride in the rat and the dog its apparent volume of distribution is high (1.6-3.2 1 kg-1) and it has a longer biological half-life than metoclopramide in both species. High clearance values and concentrations of metabolites in plasma after oral administration indicate that the drug is subjected to an extensive first pass metabolism in the rat. Thus, clebopride administered orally gives relatively low concentrations in the systemic circulation in rats even though it is rapidly absorbed. The metabolic processes appear to become saturated at high doses which is reflected in dose-dependent kinetics. Linear kinetics were observed in the dog, although enterohepatic recycling could occur.     

Pharmacokinetics of barnidipine hydrochloride,a new dihydropyridine calcium channel blocker,in the rat,dog and human

1. The pharmacokinetics of a new calcium antagonist barnidipine hydrochloride, a stereochemically pure enantiomer, was studied after intravenous and oral dosing to the rat and dog, and oral to man.

2. After intravenous dosing, plasma concentrations of barnidipine hydrochloride declined bi-exponentially with the terminal half-lives of 0·6?h in the rat and 4·1?h in the dog. The blood clearance was 5·21/h/kg in the rat and 3·31/h/kg in the dog, and was comparable with hepatic blood flow in both species.

3. After oral dosing, plasma concentrations of barnidipine hydrochloride peaked rapidly (0·3-0·4?h in the rat and dog, 1·0–1·6?h in man). C_max and AUC rose non-linearly with increasing doses in all three species.

4. The absolute bioavailability was low (11–18% in the rat and 6–9% in the dog), suggesting a marked first-pass metabolism.     

PHARMACOKINETICS AND TOXICOKINETICS OF AN ORALLY ACTIVE TRIPEPTIDE,IRI-695, IN ANIMALS

Pharmacokinetics and toxicokinetics of IRI-695, a tripeptide, were investigated in the rat, rabbit, dog, and monkey. Tissue distribution and excretion of [¹⁴C]IRI-695 were determined in the rat. Following a single intravenous (IV) injection, the elimination half-life (t_1/2) of IRI-695 in the rabbit, dog, and monkey was similar (about 65 min) and approximately four times that in the rat (15 min). This difference in t_1/2 can be attributed to about four times higher clearance of the drug in rats (11·2 mL min⁻¹ kg ⁻¹). The volume of distribution (V_ss) in these four species, 132–234 mL kg⁻¹, suggested negligible preferential distribution of IRI-695 to body tissue. After a 5 mg kg⁻¹ oral dose, the absolute bioavailability of IRI-695 was 2·0% in rats and 3·1% in dogs. However, systemic drug exposure in the dog was about five to 10 times that in the rat, which is related to the slower clearance of the peptide in the dog. Toxicokinetic studies in the rat and dog indicated linear kinetics and systemic exposure of IRI-695 up to 300 mg kg⁻¹ d⁻¹ oral doses throughout the 28 d toxicity study. Accumulation of the drug after the repeated oral dosing was negligible. After a single 0·10 mg kg⁻¹ ]¹⁴C[IRI-695 IV injection in rats, almost all of the radioactivity administered was excreted in urine within 24 h postdose.     

Metabolism and disposition of 14C-granisetron in rat,dog and man after intravenous and oral dosing

1. The disposition and metabolic fate of ¹⁴C-granisetron, a novel 5-HT₃ antagonist, was studied in rat, dog, and male human volunteers after intravenous and oral administration.

2. Complete absorption occurred from the gastrointestinal tract following oral dosing, but bioavailability was reduced by first-pass metabolism in all three species.

3. There were no sex-specific differences observed in radiometabolite patterns in rat or dog and there was no appreciable change in disposition with dose between 0·25 and 5 mg/kg in rat and 0·25 and 10mg/kg in dog. Additionally, there were no large differences in disposition associated with route of administration in rat, dog and man.

4. In rat and dog, 35–41% of the dose was excreted in urine and 52–62% in faeces, via the bile. Metabolites were largely present as glucuronide and sulphate conjugates, together with numerous minor polar metabolites. In man, about 60% of dosed radioactivity was excreted in urine and 36% in faeces after both intravenous and oral dosing. Unchanged granisetron was only excreted in urine (5–25% of dose).

5. The major metabolites were isolated and identified by MS spectroscopy and nmr. In rat, the dominant routes of biotransformation after both intravenous and oral dosing were 5-hydroxylation and N1-demethylation, followed by the formation of conjugates which were the major metabolites in urine, bile and plasma. In dog and man the major metabolite was 7-hydroxy-granisetron, with lesser quantities of the 6,7-dihydrodiol and/or their conjugates.     

The Metabolism of Terbutaline in Dog and Rat

Abstract

1. The metabolic fate of [³H]terbutaline has been studied in dog after oral, intravenous and subcutaneous administration and in rat after oral and intravenous administration. In 3–4 days the dog excreted 75% of the dose in the urine after oral administration and more than 90% after intravenous or subcutaneous administration; the remainder was in the faeces. The rat in 24 h excreted about 13% in the urine and 61% in the faeces after oral administration and 48% in the urine and 35% in the faeces after intravenous administration.

2. After oral administration of [³H]terbutaline, the time course of radioactivity concentration was the same in lung, heart and serum; low levels of unchanged drug were found in all tissues. After intravenous administration, the concentration of unchanged drug was higher in lung and heart than in serum.

3. In dog, 1·7% of an intravenous dose was excreted into bile in 6 h. In rat, about 37% of the dose was recovered in the bile during 12 h.

4. Enzymic hydrolysis of urine showed that terbutaline is metabolized by conjugation, forming a glucuronide in rat but probably a sulphate in dog.     

TOXICOKINETIC EVALUATION OF A SELEGILINE TRANSDERMAL SYSTEM IN THE DOG

The toxicology and toxicokinetics of a selegiline transdermal system (STS) were evaluated in a 3 month dog study of daily 24 h applications of placebo 4, 8, or 12 STSs in 32 male and 32 female beagle dogs. Each STS delivered approximately 5 mg selegiline over 24 h. No drug-related signs of toxicity were noted in any group with respect to clinical observations, dermal effects, body weight, food consumption, hematology, urinalysis data, or ophthalmoscopic or electrocardiographic examinations. Clinical chemistry data revealed no consistent adverse effects except for an increase in alanine aminotransferase in dogs receiving 8 and 12 STSs. Histological evaluation of tissues revealed the presence of pigment in the Kupffer cells of dogs treated with 8 and 12 STSs. There were no pathology findings suggestive of hemolysis or cholestasis. The no-effect level (NOEL) was 4 STSs (2·9 mg kg⁻¹ d⁻¹). There were no degenerative or life-threatening toxic effects up to 12 STSs (8·5 mg kg⁻¹ d⁻¹). Gender-related differences in steady-state plasma levels were not observed. Steady-state plasma concentrations were similar to maximum plasma concentrations obtained in single-dose studies, suggesting that drug accumulation was not evident. Simulation of systemic exposure following oral administration of 16·8 mg kg⁻¹ d⁻¹ from previous toxicology studies indicated that selegiline exposure following 12 STSs is sixfold greater while N-desmethylselegiline, L-amphetamine, and L-methamphetamine exposure is 0·5, 0·15, and 0·14 times the exposure in the oral study. The threefold difference in NOEL between oral and transdermal studies in the dog (0·8 versus 2·9 mg kg⁻¹ d⁻¹) is probably related to greater L-amphetamine and L-methamphetamine exposure following oral administration. The reduction in metabolite formation, relative exposure of selegiline in the dog at the NOEL compared to oral toxicology studies, and margin of safety provided, given that the expected clinical dose is less than the dosage of oral Eldepryl^™ (0·15 mg kg⁻¹ d⁻¹), documents the safety of the selegiline drug substance and indicates that additional toxicologic findings with the STS may not be expected. © 1997 by John Wiley & Sons, Ltd.     

Excretion and Biotransformation of Carboxymethyl-cysteine in Rat,Dog, Monkey and Man

1. Following an oral dose of S-carboxymethyl[³⁵S]cysteine, monkey (rhesus and African green), rat, dog, and man excreted 77, 88, 95, and 100% respectively of the ³⁵S radioactivity in urine and 7·0, 2·5, 0·7, and 0·3% in faeces during a 3 to 4 day period.

2. The principal drug-related components excreted were unchanged carboxymethylcysteine, dicarboxymethyl sulphide and inorganic sulphate.

3. Rat, dog, and man excreted primarily dicarboxymethyl sulphide and unchanged carboxymethylcysteine and no inorganic sulphate (rat, 7%).

4. Monkey excreted largely inorganic sulphate, moderate amounts of dicarboxymethyl sulphide and a trace of unchanged drug.     

PHARMACOKINETICS OF THE ENANTIOMERS OF VERAPAMIL AFTER INTRAVENOUS AND ORAL ADMINISTRATION OF RACEMIC VERAPAMIL IN A RAT MODEL

Verapamil is a chiral calcium channel blocking drug which is useful clinically as the racemate in treating hypertension and arrhythmia. The published pharmacokinetic data for verapamil enantiomers in the rat model are limited. Utilizing a stereospecific high-performance liquid chromatographic (HPLC) assay, the enantiomeric disposition of verapamil is reported after intravenous (1·0 mg kg⁻¹) and oral (10 mg kg⁻¹) administration of racemic verapamil to the rat model. After intravenous administration the systemic clearance of R-verapamil was significantly greater than that of S-verapamil; 34·9 ± 7 against 2·7 ± 3·7 mL min⁻¹ kg⁻¹ (mean ± SD), respectively. After oral administration, the clearance of R-verapamil was significantly greater than that of S-verapamil, 889 ± 294 against 351 ± 109 mL min⁻¹ kg⁻¹, respectively. The apparent oral bioavailability of S-verapamil was greater than that of R-verapamil, 0·074 ± 0·031 against 0·041 ± 0·011, respectively. These data suggest that the disposition of verapamil in the rat is stereoselective; verapamil undergoes extensive stereoselective first-pass clearance after oral administration and the direction of stereoselectivity in plasma is opposite to that observed in the human. © 1997 John Wiley & Sons, Ltd.     

Absorption and disposition of ranitidine hydrochloride in rat and dog

1. The pharmacokinetics of ranitidine were studied in the male beagle dog at a dose level of 50 mg (intravenous) or 5 mg/kg (oral).

2. After intravenous administration, Cl_p was moderate (10·4 ml/min/kg) with Cl_r accounting for approximately 30% of total clearance. Vd_area was 3·51/kg, resulting in a t_1/2 of approximately 4 h.

3. After oral administration, F was good (73%) with peak plasma concentrations of ranitidine (2 μg/ml) achieved within 0·5–1 h after dosing. t_1/2 (4·1 h) was similar to that observed after intravenous administration.

4. The absorption, metabolism and excretion of [¹⁴C]-ranitidine were studied in rat and dog after oral administration at a dose level of 50 mg/kg.

5. Urinary excretion was the major elimination pathway for radioactive drug-related material in both species (62–75% of the dose). Unchanged ranitidine was the major radioactive component in both rat and dog urine (0–24 h), accounting for approximately 40% of the dose in each case.

6. In dog, ranitidine undergoes N-oxidation (～ 30% of dose) whereas in rat, N-oxidation, S-oxidation, N-demethylation and oxidative deamination are all evident, with each metabolite accounting for <6% of the dose.

7. Two previously unreported metabolites of ranitidine were identified in rat urine using newly developed hplc and lc/ms methods. These metabolites result from single and di-N-demethylation of ranitidine and accounted for 4 and 1% of the dose respectively.     

THE PHARMACOKINETICS OF 1954U89, 1, 3-DIAMINO-7-(1-ETHYLPROPYL)-8-METHYL-7H-PYRROLO-(3, 2-f )QUINAZOLINE,IN DOGS AND RATS AFTER INTRAVENOUS AND ORAL ADMINISTRATION

1954U89, 1, 3-diamino-7-(1-ethylpropyl)-8-methyl-7H-pyrrolo-(3, 2-f )quinazoline, is a potent, lipid-soluble inhibitor of dihydrofolate reductase. The pharmacokinetics and bioavailability of 1954U89 were examined in male beagle dogs and male CD rats. Dogs received single intravenous (2·5 mg kg⁻¹) and oral (5·0 mg kg⁻¹) doses of 1954U89 with and without successive administration of calcium leucovorin. Single intravenous (5·0 mg kg⁻¹) and oral (10 mg kg⁻¹) doses of [1,3-¹⁴C₂]1954U89 were administered to rats. Plasma concentrations of total radiocarbon were determined by scintillation counting, and intact 1954U89 was measured by HPLC. The mean plasma half-life was 3·2 ± 0·62 and 4·2 ± 0·68 h after intravenous and oral administration, respectively, to dogs. The pooled plasma half-life after intravenous administration to rats averaged 1·2 h; a reliable plasma half-life value after oral administration could not be determined. Mean total-body clearance was 2·4 ± 0·39 and 4·5 ± 1·1 L h⁻¹ kg⁻¹ after intravenous and oral administration, respectively, to dogs, and averaged 12 and 77 L h⁻¹ kg⁻¹ after intravenous and oral administration, respectively, to rats. Neither clearance nor bioavailability of 1954U89 in dogs was affected significantly by administration of calcium leucovorin. Absolute bioavailability was 54 ± 12% in dogs and 16% in rats. © 1997 John Wiley & Sons, Ltd.     

Metabolism of BW 1370U87 in rat,dog, and man

BW 1370U87 is a potent, selective inhibitor of rat and human brain MAO-A. The plasma concentrations of BW 1370U87 and its metabolites were determined in rat, dog, and man. After an oral dose, BW 1370U87 undergoes extensive first-pass metabolism in all species studied. The 1-(1,2, dihydroxyethyl) metabolite, BW 1003U88, was a major metabolite in rat, dog, and human plasma. The 1-(1-hydroxyethyl) metabolite, BW 183U88, was a major metabolite in dog plasma, whereas it was present in much lower concentrations in the rat and man. Both BW 1003U88 and BW 183U88 are active MAO-A inhibitors although not as active as the parent compound. The inactive 1-(2-acetic acid) metabolite, BW 1552U88, was a major metabolite in rat plasma but a minor metabolite in the dog. Plasma concentration versus time profiles in both rat and man suggest that the metabolites undergo enterohepatic recycling. Although plasma concentrations of BW 1370U87 were relatively low compared to the metabolites, the concentrations detected in rat and man after a 50 mg/kg or 400 mg oral dose, respectively, exceeded the IC₅₀ value measured in rat and human brain. Furthermore, the time course of MAO-A inhibition appears to follow the plasma concentration versus time profile of BW 1370U87 in the rat. Preliminary experiments in rats indicate that BW 1370U87 and its metabolites distribute into brain and inhibit MAO-A.     

In vitro and in vivo α-blocking activity of thymoxamine and its two metabolites

The α-adrenoceptor potency of thymoxamine and its two metabolites deacetylthymoxamine and demethyldeacetylthymoxamine were determined on the contraction of rat vas deferens induced by noradrenaline, the blood pressure increase induced by noradrenaline given i.v. to dogs and the contraction of the nictitating membrane induced by electrical stimulation in cats. In vivo the three drugs were administered at 6·35 times 10^?6 mol kg^?1 intravenously. Deacetylthymoxamine presented nearly the same α-blocking activity as the parent drug. This was ascribed in vivo to the rapid deacetylation of thymoxamine. Demethyldeacetylthymoxamine was less active. In vitro its pA₂ was 6·20 ± 0·09 compared with 6·75 ± 0·20 for thymoxamine and 6·57 ±0·13 for deacetylthymoxamine. In vivo, it was inactive in dog and less active than the other two drugs soon after its administration in the cat. The oral LD 50 values in the mouse for the three drugs were respectively 0·81, 0·71 and 1·14 mmol kg^?1 for thymoxamine, deacetylthymoxamine and demethyldeacetylthymoxamine.     

The pharmacokinetics and metabolism of DuP 532, a non-peptide angiotensin II receptor antagonist,in rats and dogs

DuP 532, 2-propyl-4-pentafluoroethyl-1-{[2′-(1H-tetrazol-5-yl)biphenyl-4-yl] methyl} imidazole-5-carboxylic acid, is an orally active, non-peptide angiotensin II (AII) receptor antagonist. DuP 532 is more potent and longer acting than losartan, another AII receptor antagonist currently undergoing phase III clinical trials. The pharmacokinetics and the effect of the salt form on the bioavailability of DuP 532 were determined in rats and dogs. In rats, the absolute oral bioavailability and half-life averaged 8·0% and 3·5 h, respectively, after the sodium bicarbonate solution and 7·6% and 3·6 h, respectively, after the methyl cellulose suspension. In dogs, the absolute oral bioavailability averaged 13.4% after the sodium bicarbonate solution and 11·9% after hard gelatin capsules containing the neat powder. The data demonstrated that there were no differences in bioavailability between the free acid and the sodium salt of DuP 532 after oral administration to rats and dogs. The in vitro metabolism of ¹⁴C-DuP 532 was evaluated with rat, dog, and human liver microsomes. HPLC analyses with UV and radiochemical flow detection showed that recovery of DuP 532 was greater than 99%, suggesting that there was little if any metabolism by liver microsomal enzymes. Therefore, the low oral bioavailability in rats was probably due to poor absorption of DuP 532 from the GI tract rather than extensive metabolism.     

DISCONTINUOUS ORAL ABSORPTION PHARMACOKINETIC MODEL AND BIOAVAILABILITY OF 1-(2-FLUORO-5-METHYL-β-L-ARABINOFURANOSYL)URACIL (L-FMAU) IN RATS

1-(2-fluoro-5-methyl-β-L-arabinofuranosyl)uracil (L-FMAU), the L isomer of FMAU, has shown potent activity against hepatitis B virus and Epstein--Barr virus. L-FMAU showed double peaks in the plasma concentration versus time profiles following oral administration to rats, indicating discontinuous oral absorption. The objective of this study was to characterize the bioavailability and pattern of L-FMAU absorption using a pharmacokinetic model which incorporated two separate absorption processes following oral administration of the nucleoside in an animal model, the rat. Simultaneous fitting of differential equations to L-FMAU plasma concentrations following oral and intravenous administration was performed using PCNONLIN. Total clearance of L-FMAU was moderate, averaging 0·47±0·16 L h⁻¹ (mean±SD). Distributional clearance averaged 0·18±0·14 L h⁻¹. The volume of the central compartment averaged 0·30±0·09 L, and the volume of the peripheral compartment averaged 0·15±0·08 L. The first-order absorption rate constants describing the first and second absorption phases averaged 1·22±1·56 and 4·14±5·42 h⁻¹, respectively. Oral bioavailability was calculated by three methods: AUC, urinary excretion data, and a discontinuous oral absorption pharmacokinetic model. Bioavailability averaged 0·59±0·16, 0·64±0·23, and 0·63±0·13, respectively, for the three methods. The discontinuous oral absorption pharmacokinetic model is a promising new method for estimating absorption from two phases and for calculating oral bioavailability.     

The Metabolism of Talampicillin in Rat,Dog and Man

1. After administration of [phthalidyl-¹⁴]talampicillin (Talpen® to rat. dog and man, radioactivity was excreted mainly in the urine (90%, 86% and 98% in rat, dog and man respectively).

2. After administration of [ampicillin-¹⁴C]talampicillin, radioactivity was excreted in the urine of rats and dogs to a lesser extent (35% in both species) and only a small proportion of the dose was excreted in the bile (6% in rats, less than 0·1% in dogs).

3. The pattern of radiometaboletes was very similar in extracts of the urines of rat, dog and man dosed orally with [phthalidyl-14C]talampicillin. The major metabolite was 2-hydroxymethylbenzoic acid.

4. Unchanged talampicillin was present in the hepatic portal vein blood of dog and thus reached the liver, whereas in rat, no parent compound could be detected in portal vein blood. This result may help to explain differences in toxicity of the compound in rat and dog.

5. Studies in vitro showed that the intestinal wall is an important site of hydrolysis of talampicillin in rat and dog.     

The pharmacokinetics and absolute bioavailability of selegiline in the dog

Selegiline is beneficial to Parkinsonian patients as an adjunct to levodopa therapy. Currently no pharmacokinetic data are available for selegiline in the literature, mainly due to lack of analytical methods that can measure concentrations below 10 ng mL^?1 in plasma. A sensitive fluorimetric assay based on inhibition of rat brain monoamine oxidase-B (MAO-B) in vitro has been developed to measure selegiline in plasma as low as 0.25 ng mL^?1. The pharmacokinetics of selegiline were investigated following intravenous and oral administration to four female mongrel dogs. Each dog received 1 mg kg^?1 selegiline in solution via gavage or by an intravenous route separated by one week. The mean terminal half-life, volume of distribution of the central compartment, and systemic clearance of selegiline were 60.24 ± 9.56 min, 6.56 ± 0.56 L kg^?1, and 159.91 ± 19.28 mL min^?1 kg^?1, respectively. After oral administration selegiline appeared to be absorbed rapidly with a t_max and C_max of 25 ± 5.8 min and 5.2 ± 1.36 ng mL^?1, respectively. The absolute bioavailability of selegiline in the dog was 8.51 ± 3.31%.     

Age related changes in the clearance and oral absorption of sodium cromoglycate in the developing albino rat

A dual radioisotope method was used to investigate the clearance and oral abso***rption of sodium cromoglycate. Radiolabelled sodium cromoglycate was administered orally at a dose of 100 mg kg ¹ (¹⁴ C-labelled) and simultaneously subcutaneously at a dose of 2 mg kg^?1 (³ H-labelled) to rat pups 5, 9, 14, 20, 29 and 75 days old. Blood concentrations of ¹⁴ C and ³ H were measured at intervals for 24 h after dosing. Since the compound is not metabolized the blood concentrations of ¹⁴ C were taken as a measure of the sodium cromoglycate absorbed orally and the blood concentrations of ³ H as a measure of the subcutaneously administered material. Using the area under the oral ¹⁴ C blood curve (AUC) as an index of bioavailability, the calculated bioavailability of sodium cromoglycate (692·9?945·9 min μg ml^?1) in 5, 9 and 14 day old pups was 4–8 times greater than that observed (61·0-118·8 min μg ml^?1) in 20, 29 and 75 day old pups. The blood clearance of sodium cromoglycate was increased four-fold in 75 day old animals (43·9 ml min^?1 kg^?1) and three-fold in 20 and 29 day old pups when compared to the clearance in 5, 9 and 14 day old pups. The clearance in 5, 9 and 14 day old pups was relatively constant (10·8 ? 9·9 ml min^?1 kg^?1). In rats less than 14 days old the systemic absorption of sodium cromoglycate after oral administration was 2–3 times greater (6·8-9·2%) than in rats aged 20, 29 or 75 days old (2·7-3·3%). The reduction in oral bioavailability of sodium cromoglycate as the pups grew older was, therefore, due to both an increased blood clearance and a decreased absorption of the compound.     

Animal pharmacokinetics of inogatran,a low-molecular-weight thrombin inhibitor with potential use as an antithrombotic drug

Pharmacokinetics, excretion, and metabolism of inogatran, a low-molecular-weight thrombin inhibitor, were studied in the rat, dog, and cynomolgus monkey. After intravenous administration the half-life was short in all three animal species, due to a small volume of distribution and a relatively high clearance. At doses of 0.1–5 μmol kg⁻¹, the mean residence time was about 10 min in the rat, 35 min in the dog, and 20 min in the cynomolgus monkey. The oral bioavailability of inogatran was incomplete, presumably due to a low membrane permeability, and dose dependent. The bioavailability was 4.8% at 20 μmol kg⁻¹ and 32–51% at 500 μmol kg⁻¹ in rats, 14% at 10 μmol kg⁻¹ and 34–44% at 150 μmol kg⁻¹ in dogs, and 2.1% at 1 μmol kg⁻¹ in cynomolgus monkeys. The radioactivity excreted in urine and faeces was predominantly unchanged inogatran. After intravenous administration the percentage of the radioactivity recovered in faeces was about equal to or higher than the urinary recovery, which indicates biliary excretion of inogatran. After oral dosing, most of the dose was excreted in faeces, as expected from the estimates of oral bioavailability. The plasma protein binding of inogatran in rat, dog, and human plasma, was 20–28%. The blood–plasma concentration ratio was 0.39–0.56, indicating limited distribution into red blood cells. © 1998 John Wiley & Sons, Ltd.     

Pharmacokinetics of remikiren,a potent orally active inhibitor of human renin,in rat,dog and primates

1. An hplc method with fluorescence derivatization was developed for the quantification of remikiren in plasma (limit of quantification 2 ng/ml). This was used to determine the pharmacokinetics in various species of primate, in which the compound is a potent inhibitor of renin, as well as in the rat and dog in which it is less active.

2. After intravenous administration the mean residence time was ≤ 1.5?h in all species, and the plasma clearance approached the corresponding hepatic blood flows.

3. Studies in the bile-duct cannulated rat and dog demonstrated that the high clearance was due to a combination of rapid metabolism, plus biliary and renal excretion of intact drug.

4. Consistent with the high hepatic clearance, oral bioavailability was low (≤ 6%) in each species. However, all of the species tested absorbed a small proportion of an oral dose extremely rapidly, to give peak concentrations generally within 5?min of administration.

5. ‘Simultaneous’ collection of blood samples from the hepatic portal vein and aorta of rat confirmed that shortly after oral dosing the intact drug did cross the liver; however, the later collections contained predominantly more polar metabolites.

6. The rapid absorption of intact remikiren is consistent with the transient blockade of plasma renin activity, previously observed in primates after oral administration. However, the high clearance appears inconsistent with the subsequent prolonged decrease in blood pressure, suggesting that the latter effect is mediated through a ‘tissue’ compartment.     

生技霉素药代动力学性能研究

目的　研究生技霉素药代动力学过程。方法　测定狗口服生技霉素 10mg·kg-1,2 0mg·kg-1,30mg·kg-1血药浓度并与乙酰螺旋霉素比较 ;测定大鼠灌胃生技霉素 40mg·kg-1,80mg·kg-1,12 0mg·kg-1血药浓度及大鼠灌胃生技霉素 40mg·kg-1后尿、胆汁活性产物回收率。血药浓度及尿、胆汁药物浓度以微生物法测定。 3P87程序拟合计算药物动力学参数。结果　狗口服 3组剂量生技霉素 ,结果表明药物吸收较快 ,lag time为 10～ 30min ;Tmax1 43～ 2 44h ;Cmax1 0 2～ 2 94g·L-1;T1/ 2α0 48～ 1 81h ;T1/ 2 β8 40～10 5 2h ;3组剂量AUC值分别为 15 2 5 ,2 3 70 ,31 40mg·L-1·h-1,表明药物在此剂量范围内呈线形药代动力学特征 ;MRT值分别为 8 11,8 38,8 71h ,不随剂量增减而改变。大鼠口服 3组剂量生技霉素 ,Tmax1 5 7～ 2 45h ;Cmax0 39～ 3 14mg·L-1;T1/ 2α 1 36～ 1 77h ;T1/ 2 β15 6 3～2 0 6 4h ;MRT值约为 13 0h。AUC值分别为 8 44、16 5 4、37 5 8mg·L-1·h-1,同样呈线形药代动力学特征。在相同的实验条件下 ,进行狗口服 3组剂量乙酰螺旋霉素药物动力学对比实验 ,测得ASPM药物动力学参数为 :lag time为0 37～ 0 44h ;Tmax1 49～ 2 2 6h ;Cmax 0 87～ 3 34mg2 0 0 0 0 3 0 5收稿 ,2 0 0