The Absorption of Darbepoetin Alfa Occurs Predominantly via the Lymphatics Following Subcutaneous Administration to Sheep

Purpose To determine the contribution of the lymphatics to the systemic availability of darbepoetin alfa (DA) using an established sheep model.Materials and Methods DA was administered either by intravenous (IV) injection (0.2, 0.5 or 2 μg/kg) or by subcutaneous (SC) administration (2 μg/kg) into the interdigital space of the hind leg. A SC control group was used to determine the absolute bioavailability (F _sys). Cannulation of the peripheral lymphatics in a parallel SC group allowed the continuous collection of lymph draining the injection site and determination of the cumulative amount of DA absorbed via the lymphatics. Serum and lymph concentrations of DA were determined by ELISA. The fraction of the dose absorbed into the lymphatics (F _lymph) relative to the fraction absorbed directly into the blood (F _blood) was determined using a compartmental approach.Results Dose-linear pharmacokinetics was observed within the dose range investigated. The bioavailability was virtually complete following SC injection into the interdigital space (88.4 ± 15.7%). A high proportion of the administered dose was recovered in peripheral lymph (90.2 ± 4.4%) resulting in a substantial reduction in the systemic availability in lymph cannulated animals (3.7%).Conclusion The high recovery of DA in the peripheral lymph demonstrated near complete absorption of this recombinant protein via the lymphatics in a lymph cannulated sheep model.     

Lymphatic Absorption Is a Significant Contributor to the Subcutaneous Bioavailability of Insulin in a Sheep Model

Purpose: This study was conducted to explore the role of the peripheral lymphatics in insulin absorption following subcutaneous (SC) administration using a sheep model that allows continuous collection of peripheral lymph and simultaneous assessment of systemic bioavailability. Methods: In a parallel group design, soluble human insulin (0.5 IU/kg) was administered by bolus SC injection into the interdigital space of the hind leg of non-cannulated control sheep, and sheep in which the efferent popliteal lymph duct was cannulated. A separate group received a bolus IV injection (0.15 IU/kg). Blood was sampled from all animals, and lymph was collected continuously over 12 h post-dosing. Samples were assayed for insulin by ELISA. Results: The SC bioavailability of insulin in control sheep was 31.5 ± 3.2%, which was significantly higher than when the peripheral lymph was continuously collected (18.4 ± 1.7%). In the lymph-cannulated animals, 17.3 ± 1.0% of the dose was collected in peripheral lymph. Conclusions: Based on the direct measurement of insulin in regional lymph and on the decrease in the systemic bioavailability when regional lymph was continuously collected, the results demonstrate that lymphatic absorption contributed significantly to the overall insulin bioavailability following SC administration to sheep.     

A Heterogeneous Tube Model of Intestinal Drug Absorption Based on Probabilistic Concepts

Purpose. To develop an approach based on computer simulations for the study of intestinal drug absorption. Methods. The drug flow in the gastrointestinal tract was simulated with a biased random walk model in the heterogeneous tube model Pharm. Res. 16, 87-91, 1999), while probability concepts were used to describe the dissolution and absorption processes. An amount of drug was placed into the input end of the tube and allowed to flow, dissolve and absorb along the tube. Various drugs with a diversity in dissolution and permeability characteristics were considered. The fraction of dose absorbed (F _abs ) was monitored as a function of time measured in Monte Carlo steps (MCS). The absorption number An was calculated from the mean intestinal transit time and the absorption rate constant adhering to each of the drugs examined. Results. A correspondence between the probability factor used to simulate drug absorption and the conventional absorption rate constant derived from the analysis of data was established. For freely soluble drugs, the estimates for F _abs derived from simulations using as an intestinal transit time 24500 MCS (equivalent to 4.5 h) were in accord with the corresponding data obtained from literature. For sparingly soluble drugs, a comparison of the normalized concentration profiles in the tube derived from the heterogeneous tube model and the classical macroscopic mass balance approach enabled the estimation of the dissolution probability factor for five drugs examined. The prediction of F _abs can be accomplished using estimates for the absorption and the dissolution probability factors. Conclusions. A fully computerized approach which describes the flow, dissolution and absorption of drug in the gastrointestinal tract in terms of probability concepts was developed. This approach can be used to predict F _abs for drugs with various solubility and permeability characteristics provided that probability factors for dissolution and absorption are available.     

Physiological Modeling to Understand the Impact of Enzymes and Transporters on Drug and Metabolite Data and Bioavailability Estimates

Purpose

To obtain mathematical solutions that correlate drug and metabolite exposure and systemic bioavailability (F _sys) with physiological determinants, transporters and enzymes.

Methods

A series of physiologically-based pharmacokinetic (PBPK) models that included renal excretion and sequential metabolism within the intestine and/or liver as metabolite formation organs were developed. The area under the curve for drug (AUC) and formed metabolite (AUC{mi,P}) were solved by matrix inversion.

Results

The PBPK models revealed that AUC{mi,P} was dependent on dispositional parameters (transport and elimination) for the drug and metabolite. The solution was unique for each metabolite formation organ and was dependent on the type of drug and metabolite elimination organs. The AUC ratio of the formed metabolite after oral and intravenous drug dosing was useful for determination of the fraction absorbed (F _abs) and not the systemic bioavailability (F _sys) when either intestine or liver was the only drug elimination organ.

Conclusions

The AUC ratio of the formed metabolite after oral and intravenous drug dosing differed from that for drug and would not provide F _sys. However, the AUC ratio of the formed metabolite for oral and intravenous drug dosing furnished the estimate of F _abs when intestine or liver was the only drug metabolic organ.     

Pharmacokinetics of carbamazepine polymorphs and dihydrate in rats,related to dogs and humans

Species differences in the oral pharmacokinetics and absolute bioavailability (F _abs ) of carbamazepine polymorphs (form I and form III) and dihydrate were studied. The pharmacokinetics of each form was investigated in rats following a single oral/intravenous administration of 10 mg/kg and an oral dose of 80 mg/kg, which were compared with the published data obtained from dogs and humans. No significant differences were found in their C _max, T _max, AUC_0−∞ and F _abs among the forms at the low dose. However, significant differences were observed at the high dose. The Fabs of each form was markedly reduced with increasing of doses in species (e.g. F _abs in rats ranged from > 82% to 38.4%–56.0%). At a comparable dose, the C _max, and AUC_0−∞ of rats and humans were about 3–10 times higher than in dogs. The absorption rate of form III in rats exhibited a similar trend to that in humans, and was far higher in dogs. A multi-peak phenomenon in plasma curves was observed in rats and humans, but not in dogs. In conclusion, rats appear to be a better predictor of carbamazepine polymorphs absorbed in humans, and form III may be more suitable as a pharmaceutical crystal.     

Studies on the Mechanism of Absorption of Depot Neuroleptics: Fluphenazine Decanoate in Sesame oil

Purpose. The purpose of the present study was to investigate the pharmacokinetic characteristics of fluphenazine (FLU) and its decanoate (FLU-D) after intravenous and intramuscular administration to dogs. Methods. A group of four beagle dogs was used in all intravenous and intramuscular experiments, with washout periods of no less than three months between doses. Results. After intravenous FLU-D, the pharmacokinetics of the prodrug (mean ± SD) were as follows: Clearance (CL) 42.9 ± 6.3 L/h; terminal half-life (t_1/2) 3.5 ± 0.8 h; volume of distribution (Vd) 216 ± 61 L. The fractional availability of FLU was 1.0 ± 0.2. After intravenous FLU, the volume of distribution of FLU (51 ± 17.8 L) was some 4 fold less than that of the prodrug. Simulations (Stella II) suggested that the rate limiting step was slow formation of FLU from the prodrug in the tissue compartment. After intramuscular FLU-D in sesame oil, the apparent t_1/2 of FLU was 9.7 ± 2.0 days whereas after intramuscular FLU base in sesame oil, the apparent t_1/2 was only 7.7 ± 3.4 h showing that the absorption of FLU itself from the intramuscular site and proximal lymph nodes is relatively rapid. Conclusions. The rate limiting step after intramuscular FLU-D appeared to be the slow partitioning of the prodrug out of the sesame oil at the injection site and in proximal lymph nodes.     

A Saturable Transport Mechanism in the Intestinal Absorption of Gabapentin Is the Underlying Cause of the Lack of Proportionality Between Increasing Dose and Drug Levels in Plasma

Gabapentin (l-(aminomethyl)cyclohexaneacetic acid) is a neuroprotective agent with antiepileptic properties. The structure is small (molecular weight less than 200), is zwitterionic, and resembles an amino acid with the exception that it does not contain a chiral carbon and the amino group is not alpha to the carboxylate functionality. Gabapentin is not metabolized by humans, and thus, the amount of gabapentin excreted by the renal route represents the fraction of dose absorbed. Clinical trials have reported dose-dependent bioavailabilities ranging from 73.8 ± 18.3 to 35.7 ± 18.3% when the dose was increased from 100 to 1600 mg. The permeability of gabapentin in the rat intestinal perfusion system was consistent with carrier-mediated absorption, i.e., a 75 to 80% decrease in permeability when the drug concentration was increased from 0.01 to 50 mM (0.46 ± 0.05 to 0.12 ± 0.04). Excellent agreement was obtained between the actual clinical values and the predicted values from in situ results for the fraction of dose absorbed calculated using the theoretically derived correlation, F _abs = 1 - exp(–2P _eff) by Ami-don et al. (Pharm. Res. 5:651–654, 1988). The permeability values obtained for gabapentin correspond to 67.4 and 30.2% of the dose absorbed at the low and high concentrations, respectively. In the everted rat intestinal ring system, gabapentin shared an inhibition profile similar to that of L-phenylalanine. Characteristics of gabapentin uptake included cross-inhibition with L-Phe, sensitivity to inhibition by L-Leu, stereoselectivity as evidenced by incomplete inhibition by D-Phe, and lack of effect by Gly. Our findings support absorption of gabapentin by a saturable pathway, system L, shared by the large hydrophobic amino acids, L-Phe and L-Leu. The saturable absorption pathway makes a major contribution to the lack of proportionality in plasma levels of drug with increasing dose ob-served in the clinic.     

Facilitation of Pulmonary Insulin Absorption by H-MAP: Pharmacokinetics and Pharmacodynamics in Rats

Purpose. Several low molecular weight amino acids have previously been reported to enable the oral delivery of proteins. In the present studies, the effect of H-MAP (hydroxy methyl amino propionic acid) on the pharmacokinetics (PK) and pharmacodynamics (PD) of porcine insulin delivered to the lungs of rats by spray-instillation (SI) has been determined. Methods. Aliquots (100 l) of increasing doses of porcine insulin alone (0.26, 1.3, 2.6, 13, and 26 U/kg) or combined with increasing doses of H-MAP (5, 10, 16, and 25 mg/kg), at pH 7.2-7.6 were administered intratracheally to fasted anesthetized rats using a micro spray-instillator. Blood samples were collected from the jugular vein at specified intervals and the plasma concentrations of insulin and glucose were determined. The PK and PD of porcine insulin alone following subcutaneous (SC) administration of increasing doses were also determined. Results. The PK of insulin administered either by SI to the lungs or SC injection were absorption rate dependent, resulting in post-peak half-lives 10 to 25-fold greater than the reported intravenous elimination half-life (3 min). The relative bioavailability (F') of insulin administered alone by SI varied from 23.8 to 80% for the lowest and highest insulin dose, respectively. Co-administration of H-MAP and insulin to the lungs significantly changed the PK and PD of insulin in a dose dependent fashion. Maximum PK and PD responses were obtained at an H-MAP dose of 16 mg/kg and an insulin dose of 1.3 U/kg. At this combination, the relative bioavailability of insulin was increased more than 2.5 fold, maximum concentration (C_max) increased 2-fold and the minimum plasma glucose concentration (%MPGC) was reduced more than 2-fold with respect to same dose of insulin alone. A greater total reduction in plasma glucose (%TRPG_0t) was achieved for H-MAP/insulin combination (66 ± 5 %) compared to insulin alone (47 ± 10 %). Conclusion. H-MAP has potential for increasing the pulmonary bioavailability of insulin administered through the lungs.     

Effect of Coadministered Uridine on Intestinal First-Pass Metabolism of 5′-Deoxy-5-Fluorouridine in Conscious Rats—An Evaluation by Method of Portal-Systemic Concentration Difference

Purpose. The effect of uridine (UR) coadministration on the intestinal metabolism from 5-deoxy-5-fluorouridine (5-DFUR) to 5-fluorouracil (5-FU) was evaluated by a method of concentration difference between portal and systemic bloods in conscious rats (PS method). Methods. 5-DFUR (100 mg/kg) alone (Group A), or 5-DFUR + UR (100 mg/kg each) (Group B) was orally administered to conscious rats. The portal and arterial bloods were simultaneously withdrawn from two canulas at appropriate time intervals, and blood concentrations of 5-DFUR, 5-FU, UR and uracil (U) were assayed by HPLC. The concentration-time profiles of these drugs and its metabolites were analyzed by local moment analysis. Results. UR coadministration made the local absorption ratio (F_a) of 5-DFUR decrease significantly from 60.1 ± 10.5% to 38.0 ± 18.6% of dose. Though the local absorption ratios (F_a ^m) of the metabolite (5-FU) were the same between Group A and Group B (8.3 ± 1.9 and 8.7 ± 4.0% of 5-DFUR, respectively), AUC of arterial 5-FU in Group B was 5 times greater than that in Group A. UR was not detected in the portal blood, and F_a ^m of U was estimated to be 41.9 ± 26.8% of UR in Group B. Conclusions. It is predicted that a large portion of 5-FU generated from 5-DFUR is further degraded in the intestine in Group A, and U generated from UR blocks 5-FU degradation in the intestine and the systemic circulation in Group B.     

Modeling of the Saturable Time-Constrained Amoxicillin Absorption in Humans

Amoxicillin pharmacokinetics was modeled using a two-compartment disposition model and a saturable time-constrained absorption model with a storage compartment. The absorption model parameters estimated by the nonlinear regression are: a rate constant of the systemic input, k_sys, (median: 1.31 h^–1, range: 0.79–7.01 h^–1), a maximal absorption rate, V_ma, (median: 1407 mg/h, range: 703–4181 mg/h), an account corresponding to the half-maximal rate, K_ma, (median: 1077 mg, range: 235–4376 mg), time of the absorption cessation, T_abs, (median: 1.72 h, range: 0.82–4.53 h) and absorption lag time, T_lag, (median: 0.085 h, range: 0–0.123 h). It was shown, that the first-order absorption parallel to the saturable process is negligible in the dose range studied. The model described well the dependence of areas under concentration-time curves on the dose determined in several earlier studies. It was used also to predict the fraction of the amoxicillin dose absorbed for different doses. Simulations performed over a wide dose range (50–10000 mg) demonstrated that the fraction absorbed decreases nonlinearly from 90% at 50 mg to 22% at 10000 mg and strongly depends on the duration of the absorption period.     

Pharmacokinetics of a Single Intravenous and Oral Dose of Pafenolol—a Beta1Adrenoceptor Antagonist with Atypical Absorption and Disposition Properties—in Man

The pharmacokinetics of pafenolol were studied in eight young healthy individuals. The doses were 10 mg iv and 40 mg orally. Each dose was labeled with 100 µCi [³H]pafenolol. The plasma concentration–time curve of the oral dose exhibited dual maxima. The second peak was about four times higher than the first one. Maximum concentrations were attained after 0.9 ± 0.2 and 3.7 ± 0.6 hr. The mean bioavailability (F) of the oral dose was 27.5 ± 15.5%. The reduction in F was due mainly to incomplete gastrointestinal absorption. The drug was rapidly distributed to extravascular sites; t _1/2l was 6.6 ± 1.8 min. The volumes of distribution were V _c = 0.22 ± 0.08 liter/kg, V _ss = 0.94 ± 0.17 liter/kg, and V _z = 1.1 ± 0.16 liters/kg. The iv dose of pafenolol was excreted in unchanged form in the urine to 55.6 ± 5.1% of the given dose and in the feces to 23.8 ± 5.7% within 72 hr. The corresponding recoveries of the oral dose were 15.8 ± 5.9 and 67.0 ± 10.2%, respectively. About 10% of both doses was recovered as metabolites in the excreta. Approximately 6% of the oral dose was metabolized to nonabsorbable compounds in the intestine. The mean total plasma clearance was 294 ± 57 ml/min, of which renal clearance, metabolic clearance, and gastrointestinal and/or biliary clearance were responsible for 165 ± 31, 31 ± 15, and 95 ± 32 ml/min, respectively. The half-life of the terminal phase determined from plasma levels up to 24 hr after dosing was 3.1 ± 0.3 hr for the iv dose and 6.7 ± 0.7 hr for the oral dose.     

Method to Estimate the Rate and Extent of Intestinal Absorption in Conscious Rats Using an Absorption Probe and Portal Blood Sampling

Purpose. A variety of methods exist which determine the rate and extent of intestinal absorption. The method described here employs an internal absorption reference probe and portal blood sampling in unanesthetized rat. Methods. Theophylline and tritiated water were selected as absorption reference probes since they are quantitatively absorbed in conscious rat. The fraction of an intestinal dose which reaches portal blood was determined from the resulting portal-systemic blood concentration gradients of the drug relative to the absorption probe. The absorption probes provide a means to calculate the drug mass reaching portal blood without the need of measuring the portal blood flow rate. The technique was evaluated with verapamil and a well-absorbed 5-lipoxygenase inhibitor, A-79035. Results. The fraction of an intrajejunal dose of A-79035 reaching the portal vein (F_G) was 0.86 using theophylline as the absorption probe. Verapamil, which is susceptible to extensive hepatic first-pass elimination, was completely absorbed (F_G = 0.98) within 1 hour, but was only 21.4% bioavailable. Absorption rate constants, estimated from initial appearance rates in portal blood, were used to monitor factors that affect drug absorption. For example, with a dose solution containing 30% PEG-400, the absorption rate constants of theophylline and A-79035 were significantly reduced. Anesthesia reduced the absorption rate constant for theophylline in rats by 40% compared to conscious animals. Conclusions. The technique detailed here allows reliable, direct measurement of intestinal absorption which may assist in characterizing oral dosing for novel therapeutic agents.     

Pulmonary Delivery of Powders and Solutions Containing Recombinant Human Granulocyte Colony-Stimulating Factor (rhG-CSF) to the Rabbit

Two powder formulations (MMAD <4 µm) containing rhG-CSF were insufflated (IF) via an endotracheal tube at doses of 5, 75 or 500 µg/kg to New Zealand white rabbits. Doses of 5 and 500 µg/kg of solutions were administered by intratracheal instillation (IT), subcutaneous (SC) injection in the thigh and intravenous injection (IV) via the marginal ear vein. Blood samples were removed at regular intervals from an indwelling jugular catheter. Blood was analyzed directly for total white blood cell counts (WBC). Plasma was assayed for rhG-CSF by a specific ELISA. The distribution of radioactive dose in lung tissue was found after administering Tc99m HSA in solution or when incorporated into powders. The pharmacokinetics and pharmacodynamics were determined for all routes of administration. High dose IV concentration vs. time profiles declined biexponentially (t_1/2 = 0.6 ± 0.2 hrs, t_1/2 = 4.6 ± 0.2 hrs, n = 8). Clearance was dose dependent (11.6 ± 2.6 [500 µg/kg, n = 8] vs. 21.8 ± 3.3 ml/hr/kg [5 µg/kg, n = 5]). A normal systemic response was obtained after IF, indicating that rhG-CSF retains activity in the solid state. Dissolution and absorption of rhG-CSF from the powders were not rate limiting. The plasma concentration vs. time profiles peaked at similar times to those after IT (T_max 1 -2 hrs) but were earlier than obtained after SC (T_max 6-10 hrs). Powders were less efficiently dosed to the lung lobes after insufflation compared with instillates (14.7 ± 10.5 vs. 60.1 ± 10.6%), resulting in bioavailabilities ranging from 5 to 33%. Bioavailability after SC was 11.0 ± 7.0% and 95.3 ± 7.9% (n = 6) for the low and high doses, respectively.     

Rolipram forms a potent discriminative stimulus in drug discrimination experiments in rats

Long Evans rats were trained to discriminate 0.2 mg/kg IP (±)-rolipram from vehicle injection in a food-motivated two-lever operant task. Eight out of nine rats acquired the discrimination after an average of 91 sessions (min 65, max 137). The ED₅₀ of (±)-rolipram was 0.06 mg/kg IP. Generalization tests with (–)- and (+)-rolipram showed that the (–)-isomer was 8 times more active than (+)-rolipram with an ED₅₀ of 0.06 and 0.4 mg/kg IP respectively. The phosphodiesterase inhibitor RO 20-1724 partially (83%) generalized to (±)-rolipram in doses of 0.6 and 1.0 mg/kg IP. IBMX 5 mg/kg IP showed 63% generalization. Tests with imipramine and the (+)- and (–)-isomer of the noradrenaline uptake inhibitor oxaprotiline suggest that NA-uptake inhibiting drugs do not form an interoceptive cue which is (±)-rolipram-like. dbcAMP 12.5 mg/kg SC and 100 mg/kg SC dbcGMP did not generalize to the training drug. The nature of the discriminative stimulus produced by this dose of (±)-rolipram in rats remains to be elucidated. Offprint requests to: R. Ortman     

Sex Specificity in Methadone Analgesia in the Rat: A Population Pharmacokinetic and Pharmacodynamic Approach

Purpose. To quantify the extent to which a sex-specific dichotomy in the temporal evolution of the analgesic effect, after intravenous (i.v.) methadone injection in the rat, relates to the pharmacokinetics (PK) and pharmacodynamics (PD) that mediate the dose-to-effect pathway. Methods. Tail-flick analgesia was measured after i.v. methadone injection (0.35 mg/kg) in female (n = 16) and male (n = 16) Sprague-Dawley rats. The PK were evaluated in separate female (n = 56) and male (n = 56) rats after they had received the same dose of methadone i.v. (0.35 mg/kg). A bicompartmental model described the kinetics and a sigmoid E_max model-related drug effect vs. simulated concentrations (pharmacodynamics) at the times of effect measurement. All model parameters as well as interanimal and assay variabilities were estimated with a mixed-effects population method using the program NONMEM. Results. The area under the effect-time curve (AUCE_0-120) was (mean ± interanimal SD) 1859 ± 346 min in the females, which was significantly lower than the 4871 ± 393 min in the males (P < 0.0001). On the contrary, the profiles of concentration vs. time were higher in females and, therefore, corresponded inversely to the effect vs. time-relative magnitudes. The central volume of distribution, V1, was 1.94 ± 0.37 l/kg for female rats and 3.01 ± 0.33 l/kg for male rats. Also, the central clearance was 0.077 ± 0.006 l/min/kg and 0.102 ± 0.005 l/min/kg, respectively, for female and male rats. Both parameters differed significantly between sexes (P < 0.0001). The pharmacodynamic maximum observed effect parameter (E_max) was 37% ± 29% in female rats and 85% ± 16% in male rats, and these values were significantly different (P < 0.0001). The parameter for the concentration eliciting half of E_max (EC₅₀) was 24.1 ± 7.5 g/l in female rats and 20.3 ± 2.9 g/l in male rats, and the Hill-related exponent, , was 6.3 ± 3.9 in female rats and 5.5 ± 4.1 in male rats. These parameters did not differ significantly (at the P < 0.05 level). Conclusions. A sex-specific dichotomy in the methadone antinociceptive effect, in the rat, was not proportionally related to plasma concentrations. Each sex corresponded to a distinct subpopulation of the PK parameters and one of the pharmacodynamic parameters (E_max). When the course of a drug involves PK or PD subpopulations, PK/PD modeling can afford the safest prediction of the effect-time evolution for a particular dose.     

Evaluation of Capacity-Limited First-Pass Effect through Liver by Three-Points Sampling in Portal and Hepatic Veins and Systemic Artery

Purpose. The three-points method was newly developed by sampling the portal and hepatic veins and systemic artery. A model of hepatic local disposition with the Michaelis-Menten elimination was proposed to explain the concentration dependency of the hepatic recovery ratio (F _H). Methods. 5-fluorouracil (5-FU) was selected as a model drug. 5-FU was administered orally 90 min after its intraarterial dose. Blood specimens in both femoral artery and hepatic vein were sampled after intraarterial dose, and blood specimens in both femoral artery and portal vein were taken after oral administration. Results. It was shown that F _H increased with an increase in the input drug concentration into the liver. The mean absorption time (MAT) estimated by nonlinear analysis agreed with the mean local absorption time (t _a) whereas MAT by linear analysis was significantly smaller than t _a. Conclusions. The three-points method was newly developed, and the proposed nonlinear model explained well the capacity-limited elimination of 5-FU through the liver. MAT by the nonlinear analysis was in good agreement with t _a.     

Lymphatic transport of puerarin occurs after oral administration of different lipid-based formulations to unconscious lymph duct-cannulated rats

Abstract

This study investigated the potential of targeted intestinal lymphatic transport of puerarin via a lipid formulation approach. Three formulations of PEG nanoemulsion, nanosuspension and an oil suspension containing puerarin were examined with the lymph-cannulated anaesthetized rat model. Plasma and lymph samples were analyzed by HPLC. Lymph triglyceride was measured using an enzymatic colorimetric technique. After 8?h, the total administered dose accumulated in the thoracic lymph duct was analyze. Nanoemulsion, nanosuspension and oil suspension was 0.065?±?0.006%, 0.137?±?0.018%, 0.021?±?0.002% of the administered dose, respectively. In nanoemulsion, nanosuspension and oil suspension group, the systemic bioavailability of oral puerarin was 11%, 16% and 11% for lymph-cannulated rats, 41%, 67% and 18% for control rats. Absorption into the intestinal lymph should thus contribute to ～30%, 51% and 7% of the systemic bioavailable puerarin. This data indicated that lipid-based nano drug formulation produced higher lymph concentrations of puerarin than oil suspension. The nanosuspension formulation may be considerable in terms of increased local concentrations in lymphoid tissue.     

鸡尾酒法评价石蒜对大鼠细胞色素P450酶活性的影响

目的 运用鸡尾酒法评价石蒜对细胞色素P450酶活性的影响。方法 将大鼠随机分为对照组和石蒜低、高剂量组。对照组给予生理盐水，石蒜低、高剂量组大鼠灌胃给药0.5，1.0 g·kg^-1石蒜，连续给药15 d。然后第16天给予探针药物，UPLC-MS/MS检测探针药浓度。结果 与对照组对比，石蒜低剂量组和高剂量组的安非他酮AUC_（0-t）、C_max都显著升高（P<0.05），CL_z/F显著降低（P<0.05）。与对照组对比，石蒜高剂量组的美托洛尔、咪达唑仑和非那西丁AUC_（0-t）显著降低（P<0.05）、CL_z/F显著升高（P<0.05），而低剂量组与对照组比较差异无统计学意义。与对照组对比，石蒜组的甲苯磺丁脲AUC_（0-t）、CL_z/F差异无统计学意义，C_max显著降低（P<0.05）。结论 石蒜能抑制大鼠CYP2B1酶活性，诱导大鼠CYP2D1、CYP3A2和CYP1A2酶活性，稍有诱导大鼠CYP2C11酶活性的作用。     

The Roles of Depot Injection Sites and Proximal Lymph Nodes in the Presystemic Absorption of Fluphenazine Decanoate and Fluphenazine: Ex Vivo Experiments in Rats

Purpose. The release and presystemic absorption of fluphenazine and its decanoate ester from intramuscular depots were investigated. Methods. Rats were sacrificed in groups of three at various times after injection of drug or prodrug in sesame oil. Muscle tissues at the injection sites and various lymph nodes were excised. Blood (plasma) was harvested by cardiac puncture. Results. Following administration of fluphenazine decanoate, the amount of prodrug at the sites of injection declined exponentially (half-life 3.4 days). Highest concentrations of drug and prodrug were found in iliac and hypogastric lymph nodes nearest to injection sites in which both analytes were detectable 28 days post dose. The half-life for the decline of fluphenazine from lymph nodes (4.6 days) was similar to that from plasma (4.3 days). Following administration of fluphenazine base, only 2.8% of the dose remained at the sites of injection after 2 days. Concentrations of drug in iliac and hypogastric lymph nodes were comparable to those in distal lymph nodes. Fuphenazine concentrations in the lymphatic tissues decreased at about the same rate as plasma concentrations. Conclusions. The rate limiting step appeared to be slow partitioning of the decanoate from oily deposits at the injection site and proximal lymph nodes with subsequent hydrolysis of the ester group.     

In Vivo Assessment of Intestinal,Hepatic, and Pulmonary First Pass Metabolism of Propofol in the Rat

Purpose. The relative contribution of the intestinal mucosa, liver and lung to the in vivo disposition of propofol in the rat was investigated. Methods. Propofol (4.9–5.1 mg · kg^–l) was administered to groups of rats (n = 4) via the intra-arterial, intravenous, hepatic portal venous and oral routes. The AUC's of propofol were estimated and the fractions of the administered dose escaping first pass metabolism by the gut wall (f_G), liver (f_H) and lung (f_L) were calculated. In addition, transport experiments were carried out using Caco-2 cell monolayers to rule out the possibility that intestinal permeability is limiting the oral absorption of propofol. Results. Values for f_G, f_H and f_L were the following: 0.21 ± 0.07, 0.61 ± 0.13, and 0.82 ± 0.09, respectively. The apparent permeability coefficient of propofol across Caco-2 cell monolayers was 24.2 ± 0.3 × 10^–6 cm · sec^–1, which is similar to the apparent permeability coefficient obtained for propranolol (30.7 ± 1.7 × 10^–6 cm · sec^–1), a compound known to easily cross the intestinal epithelial membranes. The formation of propofol glucuronide, a major metabolite of propofol, could not be demonstrated during the flux experiments across the Caco-2 cell monolayers. Conclusions. The intestinal mucosa is the main site of first pass metabolism following oral administration of propofol in the rat. Intestinal metabolism could therefore also contribute to the systemic clearance of propofol.