Differences In Pharmacokinetic Behavior Research Articles

Comparative Pharmacokinetic Study of Rhubarb Anthraquinones in Normal and Nonalcoholic Fatty Liver Disease Rats.

Rhubarb anthraquinones contain five main components, that is, rhein, emodin, aloe-emodin, chrysophanol, and physcion, which demonstrate good therapeutic effects on nonalcoholic fatty liver disease (NAFLD). However, research on its pharmacokinetics in NAFLD remains lacking. This study aimed to investigate the pharmacokinetic differences of rhubarb anthraquinones in normal and NAFLD rats. This study developed an NAFLD rat model by high-fat diet feeding for 6weeks. Normal and NAFLD groups were orally administered different rhubarb anthraquinones doses (37.5, 75, and 150mg/kg). The concentration of the rhein, emodin, aloe-emodin, chrysophanol, and physcion in plasma was determined by high-performance liquid chromatography-ultraviolet. The results revealed significant differences in pharmacokinetic behavior between normal and NAFLD rats. Compared with normal rats, NAFLD rats demonstrated significantly increased maximum plasma concentration (Cmax) and area under the plasma concentration-time curve (AUC0 → ∞) of rhubarb anthraquinones (P<0.05), as well as significantly prolonged time to reach maximum plasma concentration (Tmax), terminal elimination half-life (t1/2), and mean residence time (MRT) of rhubarb anthraquinones (P<0.05). This study indicates significant differences in the pharmacokinetics of rhubarb anthraquinones between the physiological and NAFLD states of rats. Rhubarb anthraquinone demonstrated a longer retention time and slower absorption rate in NAFLD rats and exhibited higher bioavailability and peak concentration. This finding provides important information for guiding the clinical use of rhubarb anthraquinones under pathological conditions.

Biodistribution of nanodiamonds is determined by surface functionalization

Solid-core nanoparticles made of carbon, metals and other inorganic materials are gaining interest as nanocarriers to facilitate nucleic acid therapeutics. Our group designed amino acid-functionalized nanodiamonds (NDs, collectively fNDs) to serve this purpose via covalent conjugation of basic amino acid lysine and di-peptide lysyl-histidine on the ND surface. The purpose of this study is to elucidate the functionalization-dependent biodistribution profiles of fNDs, a key step in the process of developing these novel nano-systems. Here the aim was two-fold i.e., to establish an optimized protocol for radiolabeling of fNDs and to study the functionalization-dependent differences in pharmacokinetic behavior of NDs. Both types of fNDs yielded a surface loading of 1.94 and 14.45 mmol/g of lysine and lysyl-histidine amino acid conjugates respectively. Deferoxamine (DFO) was conjugated directly on the ND surface for the first time to chelate zirconium (89Zr), the radiolabel of interest for in vivo tracking. To achieve an effective balance between radiolabeling efficiency, surface chemistry and colloidal stability of DFO-conjugated fNDs, attachment of DFO was evaluated in the range of 1–8 %. A 3 % loading with DFO was sufficient to chelate 2 MBq 89Zr with good radiochemical yield (≥90 %) while maintaining the physicochemical characteristics of the fNDs, namely particle size ≤300 nm and overall positive zeta potential of higher than 15 mV. Furthermore, 89Zr-labeled fNDs remain stable in phosphate buffered saline and mouse serum for over 96 h maintaining a radiochemical stability of ≥97 %. Following process optimization, we evaluated differential organ distribution and pharmacokinetic profile of 89Zr-labeled fNDs. All NDs showed the highest uptake in the liver, followed by the spleen. However, the degree of uptake and retention time in the liver varied based on the surface functionalization. The lysyl-histidine-NDs showed the highest AUC, followed by the carboxylated NDs and the lysine-NDs. Unlike lysine-NDs, which depleted quickly from the liver (marked decline in ND-associated radioactivity from 5.6 to 2.3 %), the lysyl-histidine-NDs maintained a longer residence for at least 72 h in the liver marked by ND-associated radioactivity of 8.9 % after 6 h that increased further to 11.7 % after 72 hours post injection. Overall, this work presents a proof-of-concept to study the effect of surface characteristics on the in vivo behavior and organ deposition of NDs. Here, we successfully established an optimized protocol to achieve radiolabeling of NDs while maintaining the optimum physicochemical traits of fNDs to act as potential gene carriers. Using these approaches, we elucidated that the biodistribution and the pharmacokinetic behavior of NDs varies based on the functionalization design.

Comparison of in vivo plasma pharmacokinetics and urine excretion of main components in Xihuang Formula in rats with precancerous lesions of breast cancer

The UPLC-MS/MS was established for the determination of acetyl-11-keto-beta-boswellic acid(AKBA) and β-boswellic acid(β-BA), the main active components of Olibanum and Myrrha extracts in Xihuang Formula, in rat plasma and urine. The effects of compatibility on the pharmacokinetic behaviors of AKBA and β-BA in rats were investigated, and the differences in pharmacokinetic behaviors between healthy rats and rats with precancerous lesions of breast cancer were compared. The results showed that compared with RM-NH and RM-SH groups, the AUC_(0-t) and AUC_(0-∞) of β-BA increased(P&lt;0.05 or P&lt;0.01), T_(max) decreased(P&lt;0.05 or P&lt;0.01), and C_(max) increased(P&lt;0.01) after compatibility. The trends of AKBA and β-BA were the same. Compared with RM-SH group, the T_(max) decreased(P&lt;0.05), C_(max) increased(P&lt;0.01), and the absorption rate increased in the normal group of Xihuang Formula. The results of urinary excretion showed that there was a decreasing trend in the urinary excretion rate and total urinary excretion of β-BA and AKBA after compatibility, but there was no statistical difference. Compared with normal group of Xihuang Formula, the AUC_(0-t) and AUC_(0-∞) of β-BA increased(P&lt;0.05), T_(max) increased(P&lt;0.05), and the clearance rate decreased in the breast precancerous lesion group. AUC_(0-t) and AUC_(0-∞) of AKBA showed an increasing trend, the in vivo retention time was prolonged, and the clearance rate was reduced, but there was no significant difference compared with the normal group. The cumulative urinary excretion and urinary excretion rate of β-BA and AKBA decreased under pathological conditions, indicating that pathological conditions could affect the in vivo process of β-BA and AKBA, and reduce their excretion in the form of prototype drugs, showing different pharmacokine-tic characteristics from normal physiological conditions. In this study, UPLC-MS/MS analysis method was established, which was sui-table for in vivo pharmacokinetic analysis of β-BA and AKBA. This study laid a foundation for the development of new dosage forms of Xihuang Formula.

Pharmacokinetics and anti-liver fibrosis characteristics of amygdalin: Key role of the deglycosylated metabolite prunasin

BackgroundAmygdalin (Amy) is a cyanoside and is one of the chief active ingredients in Persicae Semen, Armeniacae Semen Amarum, and Pruni Semen. Amy has extensive and remarkable pharmacological activities, including against anti-hepatic fibrosis. However, the pharmacokinetic and anti-liver fibrosis effects of Amy and its enzyme metabolite prunasin (Pru) in vivo have not been studied and compared, and studies on Pru are limited. PurposeTo investigate the pharmacokinetic characteristics and anti-liver fibrosis effect of Amy and its metabolite Pru in vivo and in vitro, and elucidate whether the metabolism of Amy in vivo for Pru is activated. MethodsPru was prepared from Amy via the enzymatic hydrolysis of β-glucosidase, and isolated by silica gel column chromatography. An efficient and sensitive ultrahigh-performance liquid chromatography-Q exactive hybrid quadrupole orbitrap high-resolution accurate mass spectrometry was developed and validated to determine simultaneously Amy and Pru in rat plasma after dosing intravenously and orally for pharmacokinetic studies. The affinities of Amy and Pru for β-glucosidase were compared by enzyme kinetic experiments to explain the possible reasons for the differences in pharmacokinetic behavior. In vitro, the inhibitory effects of Amy and Pru on hepatic stellate cell activation and macrophage inflammation on JS1 and RAW 264.7 cells were determined. In vivo, the ameliorative effects of Amy and Pru on liver fibrosis effects were comprehensively evaluated by CCl4-induced liver fibrosis model in mice. ResultsThe standard curves of Amy and Pru in rat plasma showed good linearity within the concentration range of 1.31–5000.00 ng/ml, with acceptable selectivity, carry-over, detection limit and quantification limits, intra- and inter-day precision, accuracy, matrix effect, and stability. The Cmax and AUC(0−∞) of Pru (Cmax = 1835.12 ± 268.09 ng/ml, AUC(0−∞) = 103,913.17 ± 14,202.48 ng•min/ml) were nearly 79.51- and 66.22-fold higher than those of Amy (Cmax = 23.08 ± 5.08 ng/ml, AUC(0−∞) = 1569.22 ± 650.62 ng•min/ml) after the oral administration of Amy. The oral bioavailability of Pru (64.91%) was higher than that of Amy (0.19%). The results of enzyme hydrolysis kinetics assay showed that the Vmax and Km of Pru were lower than those of Amy in commercial β-glucosidase and intestinal bacteria. In vitro cellular assays showed that Amy and Pru were comparable in inhibiting the NO production in the RAW264.7 cell supernatant and the mRNA expression of α-SMA and Col1A1 in JS1 cells. Amy and Pru were also showed comparable activity in ameliorating CCl4-induced liver fibrosis in mice. ConclusionThe pharmacokinetic characteristics of Amy and Pru in rat plasma were significantly different. After the separate gavage of Amy and Pru, Amy was absorbed predominantly as it's metabolite Pru, whereas Pru was absorbed predominantly as a prototype. The anti-liver fibrosis effects of Amy and its deglycosylated metabolite Pru were comparable in vivo and in vitro. The deglycosylated activated metabolite Pru of Amy plays an important role in anti-liver fibrosis. These findings will facilitate the further exploitation of Amy and Pru.

Improved Pharmacokinetic Characteristics of Ursolic Acid in Rats Following Intratracheal Instillation and Nose-Only Inhalation Exposure.

Ursolic acid (UA) is a common pentacyclic triterpene phytochemical with various pharmacological activities. However, UA is classified as a class IV drug in BCS system and its development as an oral drug is limited. Pulmonary delivery is an effective way to improve the bioavailability of drugs with low absorption. In this study, the differences in pharmacokinetic behaviors of UA after pulmonary and oral administration was explored in rats. Compared with oral administration, the plasma concentration of UA increased rapidly after pulmonary administration, and the bioavailability increased about 80 times. UA instantly accumulated in the lungs after pulmonary administration, and the pulmonary AUC0-t/dose increased by 114 times compared to oral dosing. Incubation experiments showed that the metabolism of UA in rat lung microsomes was significantly reduced compared with that in liver microsomes, in which the clearance rate of phase I and phase II metabolism was reduced by 14.7 times and 1.4 times respectively. These results indicated that pulmonary administration could improve the bioavailability of UA and reduce its metabolism. This study not only provides a preferable route of administration for the application of UA but also offers new insights for the development of phytochemical drug candidates with poor pharmacokinetic properties.

Differences in pharmacokinetic behaviors of two lipophilic 3-substituted 2,2,5,5-tetramethylpyrrolidine-N-oxyl radicals, in vivo probes to assess the redox status in the brain using magnetic resonance techniques.

The pharmacokinetics of 3-methoxycarbonyl- and 3-hydroxymethyl-2,2,5,5-tetramethylpyrrolidine-N-oxyl radicals (MCP and HMP, respectively), magnetic resonance probes to assess the brain redox status, were examined in healthy mouse brains. The time course of the concentration of the radical form of the probe in the brain was examined by signal enhancements on T1 -weighted MR image after an intravenous injection. The distribution of the total probe (sum of radical and reduced forms) was investigated using brain homogenates. MCP distributed to the brain more than HMP. MCP exhibited biphasic decay with fast and slow components, whereas HMP exhibited monophasic decay with a similar rate constant to the slow component of MCP. Similar profiles were observed in various regions of the brain. The total probe for MCP exhibited monophasic decay at a similar rate constant to the slow component of the radical form; however, the initial content of the total probe was similar to its radical form. For HMP, decay of the total probe coincided with that of the radical form. The decay of MCP needs to consider the reduction of the probe in and its elimination from the brain, while the decay of HMP may mainly result from its elimination from the brain.

Comparative pharmacokinetics of six coumarins in normal and breast cancer bone-metastatic mice after oral administration of Wenshen Zhuanggu Formula

Ethnopharmacological relevanceWenshen Zhuanggu Formula (WSZG) is a traditional Chinese medicine (TCM) prescription used in clinics for adjuvant treatment of breast cancer bone metastases in Longhua Hospital in China. WSZG has been reported to decrease the risk of bone metastases and alleviate the severity of bone lesions in a breast cancer xenograft model. Aim of the studyThe present study aimed at investigating the pharmacokinetic behaviors of six coumarins in normal and breast cancer bone-metastatic mice following oral administration of WSZG extract. Materials and methodsA bone-metastatic mouse model was established by intracardiac injection of MDA-MB-231BO breast cancer cells, and WSZG extract (1.60 g/kg) was given orally to the model and normal mice for 4 weeks. Then, the blood pharmacokinetic parameters of six bioactive components from WSZG (psoralen, isopsoralen, bergapten, xanthotoxin, osthole, and imperatorin) were analyzed by liquid chromatography tandem mass spectrometry. ResultsThere were significant differences in pharmacokinetic behaviors between normal and pathological states. Compared with normal mice, the model mice showed significantly increased AUC0–t and AUC0–∞ of the bioactive compounds (P < 0.05) and significantly decreased total blood clearance (CLZ/F) (P < 0.05). ConclusionsThe different pharmacokinetic behaviors might be partly ascribed to intestinal functional disorders and imbalance of gastrointestinal microbiota under the morbid state. The findings provide some valuable information to evaluate the clinical efficacy and safety of this TCM formula.

Betahistine dihydrochloride or betahistine mesilate: two sides of the same coin or two different coins

The antivertigo drug betahistine exerts a histamine modulatory action in the vestibular system and the brain. It is marketed both as the dihydrochloride and the mesilate salt in India. We conducted a published literature based systematic review to ascertain differences, in any, between the salt and ester forms of the drug. Search of the Medline database was supplemented by searching through references in full text papers and retrieving summary of product characteristic literature. Although the weight of published evidence is greater for betahistine dihydrochloride, in the absence of head-to-head studies comparing the efficacy of the two formulations in Ménière's disease and other vertigo disorders of vestibular origin, it is not possible to conclude that there are definite differences in this regard. However, potentially relevant differences exist to suggest that the two forms are not interchangeable for the treatment of vestibular dysfunction. Molecular weight comparison indicates that the pill burden would be higher for betahistine mesilate for delivering equivalent doses. There could be ethnically influenced differences in pharmacokinetic behavior. There are concerns of potential long-term DNA toxicity due to mesilate ester contaminants during production of betahistine mesilate, which is not there for the hydrochloride form. Detailed post-marketing surveillance data exists only for the dihydrochloride salt. Otorhinolaryngologists and other physicians seeking to optimize treatment with betahistine should be aware of these differences.

Farmacokinetiek van geneesmiddelen bij vogels en de toepassingen en beperkingen van dosisextrapolatie

De farmacokinetische processen van geneesmiddelen, i.e. absorptie, distributie, metabolisatie en excretie, kunnen sterk verschillen tussen vogels en zoogdieren. Zo worden aminoglycosiden bij vogels trager geklaard en hebben een lager distributievolume dan bij zoogdieren. Deze farmacokinetische verschillen zijn hoofdzakelijk het gevolg van anatomische, biochemische en fysiologische verschillen tussen vogels en zoogdieren. Deze diersoortverschillen en verschillen in geobserveerde en voorspelde farmacokinetische parameters van geneesmiddelen bij vogels geëxtrapoleerd vanuit zoogdieren, zoals de klaring voor enrofloxacine, salicylzuur, meloxicam en flunixine, wijzen erop dat farmacokinetische gegevens van een geneesmiddel bij zoogdieren nauwelijks geëxtrapoleerd kunnen worden naar vogels. Ook tussen vogelsoorten onderling kunnen er verschillen aanwezig zijn. Indien mogelijk dient de dosisselectie van een geneesmiddel voor vogels bijgevolg te gebeuren op basis van de farmacokinetische gegevens van de desbetreffende vogelsoort. Indien dergelijke gegevens niet beschikbaar zijn, kan er gebruik gemaakt worden van allometrische schaling, waarbij de dosisselectie gebeurt op basis van de farmacokinetische gegevens van een andere vogelsoort gecorreleerd aan het lichaamsgewicht van deze vogelsoorten. Schaling op basis van zoogdiergegevens wordt slechts aangeraden indien de farmacokinetische gegevens van andere vogelsoorten niet beschikbaar zijn en het betreffende geneesmiddel een lage toxiciteit heeft.

Differences in pharmacokinetic behaviour of branded enoxaparin and a US generic version in a non-human primate model

Differences in pharmacokinetic behaviour of branded enoxaparin and a US generic version in a non-human primate model

Comparison of the Pharmacokinetic and Pharmacodynamic Behavior of Branded and Generic Enoxaparin in Non-Human Primates

Abstract 1254 Introduction:Low molecular weight heparins (LMWHs) have been shown to be safe and effective in the prevention and treatment of venous thrombosis and in the treatment of patients with pulmonary embolism or acute coronary syndrome. Commercially available LMWHs are distinct agents in terms of their molecular weight profile and in vitro potency. Molecular weight influences the pharmacokinetics (PK) and pharmacodynamics (PD) of heparin oligosaccharides. Although there continues to be interest in developing biosimilar versions of LMWHs, defining biosimilarity for LMWHs is challenging because chemical means of measuring plasma heparin levels do not exist, potency measures typically only measure AT-dependent activities, bioequivalence in terms of one activity does not ensure identical pharmacokinetic behavior in terms of other biological activities and identification and quantification of the various oligosaccharide components in a LMWH preparation is difficult. In vitro studies have shown that biosimilar LMWHs can differ considerably from the branded product as well as from each other. In the current study, the PD behavior of branded and biosimilar enoxaparin was compared in a cross-over study following a single subcutaneous dose to non-human primates. Methods:Lovenox (lot #514956, sanofi-aventis, Paris, France) and Fibrinox (lot#0002, Sandoz S.A., Buenos Aires, Argentina) were obtained in pre-filled syringes at a concentration of 100 mg/ml. Upon anesthesia, the non-human primates (Macaca mulatta) were weighed and a baseline blood sample was collected. A site on the abdomen was shaved and cleansed prior to the subcutaneous administration of LMWH. Blood samples were collected at 1, 4, 6 and 28 hours post-administration and were centrifuged to make platelet poor plasma which was stored in aliquots at −70°C until analysis. Primates were randomly dosed with one of the two test agents. After a minimum of one week wash-out, the same primates were dosed with the other test agent. Plasma samples were evaluated using clot-based and amidolytic assays. LMWH concentrations in the blood samples were determined by extrapolation from in vitro concentration-response curves and used to calculate values for PK parameters. p-values < 0.05 determined by two-way repeated measures analysis of variance were considered to be statistically significant. Results:LMWH levels determined by circulating anti-Xa activity following Fibrinox and Lovenox administration were not observed to be significantly different. Circulating anti-IIa levels, however, were significantly higher in Lovenox-treated animals at 1, 4 and 6 hours post-administration. Using the Heptest assay, higher circulating drug levels were measured in Fibrinox-treated animals at 4 and 6 hours. A high degree of variability was observed in the absorption and elimination of the LMWHs. Statistically significant differences in pharmacokinetic behavior was not observed when circulating drug concentrations were determined using anti-Xa activity or Heptest prolongation. Using drug concentrations determined from anti-IIa activity, the AUC following Lovenox treatment was significantly larger than following Fibrinox treatment. Plotting mean drug levels based on anti-IIa activity versus mean drug levels based on anti-Xa activity at the various sample times indicated a hysteretic relationship which was distinct for Fibrinox and Lovenox-treated primates. Clear differentiation of the two LMWHs was also observed when drug levels measured by anti-IIa activity were plotted against those determined using the prolongation of the Heptest. Conclusions:Potency of LMWHs can be expressed in terms of a number of AT-dependent and AT-independent activities, which may not be proportional. The PK/PD behavior of LMWHs is different when drug levels are determined using distinct biologic activities. The measured concentration of a drug and its corresponding effect can be asynchronous, that is, peak drug levels may not occur at the same time as peak effect levels. In this study, plotting drug concentrations determined by one functional parameter against those derived from a different parameter provided clear visual evidence that the two LMWHs tested exhibit distinct pharmacodynamic behavior. In vivo behavior is an important consideration for defining pharmacoequivalence of complex biologic drugs. Disclosures:No relevant conflicts of interest to declare.

New Insights Into the Pharmacokinetics and Pharmacodynamics of the Calcineurin Inhibitors and Mycophenolic Acid: Possible Consequences for Therapeutic Drug Monitoring in Solid Organ Transplantation

Although therapeutic drug monitoring (TDM) of immunosuppressive drugs has been an integral part of routine clinical practice in solid organ transplantation for many years, ongoing research in the field of immunosuppressive drug metabolism, pharmacokinetics, pharmacogenetics, pharmacodynamics, and clinical TDM keeps yielding new insights that might have future clinical implications. In this review, the authors will highlight some of these new insights for the calcineurin inhibitors (CNIs) cyclosporine and tacrolimus and the antimetabolite mycophenolic acid (MPA) and will discuss the possible consequences. For CNIs, important relevant lessons for TDM can be learned from the results of 2 recently published large CNI minimization trials. Furthermore, because acute rejection and drug-related adverse events do occur despite routine application of CNI TDM, alternative approaches to better predict the dose-concentration-response relationship in the individual patient are being explored. Monitoring of CNI concentrations in lymphocytes and other tissues, determination of CNI metabolites, and CNI pharmacogenetics and pharmacodynamics are in their infancy but have the potential to become useful additions to conventional CNI TDM. Although MPA is usually administered at a fixed dose, there is a rationale for MPA TDM, and this is substantiated by the increasing knowledge of the many nongenetic and genetic factors contributing to the interindividual and intraindividual variability in MPA pharmacokinetics. However, recent, large, randomized clinical trials investigating the clinical utility of MPA TDM have reported conflicting data. Therefore, alternative pharmacokinetic (ie, MPA free fraction and metabolites) and pharmacodynamic approaches to better predict drug efficacy and toxicity are being explored. Finally, for MPA and tacrolimus, novel formulations have become available. For MPA, the differences in pharmacokinetic behavior between the old and the novel formulation will have implications for TDM, whereas for tacrolimus, this probably will not to be the case.

Pharmacokinetics and Mammary Elimination of Imidocarb in Sheep and Goats

The pharmacokinetics and mammary excretion of imidocarb dipropionate, a therapeutic/prophylactic agent against a variety of tick-borne hemoparasitic diseases in domestic animals, have been investigated in sheep and goats. A commercial formulation of imidocarb di-propionate was injected i.m. at a single dose of 3mg/kg of body weight in 7 mature lactating ewes and 8 lactating does in good health. Blood samples were collected for 48h after administration and milk samples were collected every 12h for 10 d. A weak cation-exchange solid-phase procedure was used to remove imidocarb from plasma. A hexane/isoamyl alcohol liquid-liquid procedure was adopted to extract the drug from the milk of sheep. The same method was used for goat milk after exposing the matrices to enzymatic digestion. The extracted samples were analyzed by HPLC. The i.m. disposition kinetics of imidocarb in the 2 species showed significant differences in the rate of elimination (0.0075±0.002 and 0.025±0.004 L/h in sheep and goats, respectively), being faster in ewes than in does. Nevertheless, a smaller area under the concentration-time curve (12.21±0.76 and 9.49±0.54μg/mL per h in sheep and goats, respectively), a larger volume of distribution (4.18±0.44 and 7.68±0.57 L/kg in sheep and goats, respectively), and a longer mean residence time (9.07±0.77 and 14.75±2.20h in sheep and goats, respectively) were found in goats, suggesting a more rapid and effective drug storage in tissues during the first 48h after the injection. The concentrations of imidocarb in milk of both species were higher than in plasma. However, a fast passage through the blood-milk barrier and a high storage of imidocarb were observed in the milk of ewes, whereas the drug concentrations were not as high nor was the extent of drug penetration from blood to milk as great in the milk of goats (AUCmilk 0–48/AUCplasma 0–48 = 2.5±0.45 and 1.26±0.27 in sheep and goat, respectively). Despite the differences in pharmacokinetic behavior, and considering the sensitivity of pathogens to imidocarb, the same dosage regimen can be used for clinical efficacy against Babesia spp. infection in both species. In contrast, the differences in depletion of imidocarb residue in milk and the large variability in mammary drug elimination found in goats suggests that great care should be taken in defining the withdrawal time in small ruminant dairy species.

Toxicokinetics

The toxicokinetic determinants of dioxin and related chemicals depend on three major properties: lipophilicity, metabolism, and binding to CYP1A2 in the liver. The induction of CYP1A2 is partially under the control of the aryl hydrocarbon receptor (AhR). Lipophilicity increases with more chlorination and controls absorption and tissue partitioning. Metabolism is the rate limiting step for elimination. Induction of CYP1A2 leads to hepatic sequestration of TCDD. Binding to this inducible hepatic protein results in non-linear dosedependent tissue distribution: with increasing doses, the relative concentration in extra-hepatic tissues decreases while that in liver increases. The induction of this protein occurs in both animals and humans and results in an increase in the liver to fat ratio of these compounds. Humans have similar sensitivities to rodents for dioxin-like compounds when using tissue concentration (from in vitro studies), body burden, average lifetime serum lipid concentration, or lifetime area-under-the-curve concentration based on both low dose (biochemical) and high dose (cancer) driven endpoints. To reach the same tissue concentration in humans as rodents however, humans need a lower daily intake than rodents based on differences in pharmacokinetic behaviour. This clearly indicates that physiologically based pharmacokinetic models should be explored for the estimation of the daily intake of dioxin-like compounds in humans based on tissue dose levels or derivatives of those.

Binding and antiresorptive properties of heterocycle-containing bisphosphonate analogs: structure-activity relationships

To define structure-activity relationships for bisphosphonate activity, we examined the bone binding and antiresorptive properties of heterocycle-containing analogs of risedronate, a pyridylbisphosphonate, in cultures of mouse fetal bone explants. Our studies indicated that hydroxybisphosphonates with the nitrogen molecule in the pyridyl ring were very potent inhibitors of osteoclastic resorption. Changing the place of the nitrogen in the ring structure of risedronate or its methylation did not significantly alter antiresorptive potency in relation to risedronate. Extension of the R 2 chain, however, reduced efficacy. In binding experiments, we found that all heterocyclic bisphosphonates with a hydroxyl group in R 1 had comparable affinity for bone mineral and inhibited calcium incorporation into bone explants to a similar extent. The affinity of a risedronate analog without R 1 was markedly reduced. We also examined the properties of a risedronate analog (NE-10790) belonging to the group of phosphonocarboxylates in which one of the phosphonate groups is substituted by a carboxyl group. NE-10790 had strongly reduced binding affinity, but still retained some antiresorptive activity. Interestingly, the continuous presence of NE-10790 in cultures of fetal mouse metacarpal bones increased its antiresorptive efficacy by about 40-fold compared with 24 h preincubation, whereas, under the same conditions, the potency of high-affinity hydroxybisphosphonates did not change or only slightly increased. This may be explained by the differences in pharmacokinetic behavior between compounds of high and of low affinity for bone mineral. These data show that, as with alkylbisphosphonates, heterocycle-containing bisphosphonates with a nitrogen functionality in the R 2 chain are potent antiresorptive agents and a hydroxyl substitution in the R 1 chain confers high affinity for bone mineral, probably due to tridentate configuration. The group of phosphonocarboxylates, with strongly reduced bone affinity, provides an interesting therapeutic option.

Stereoselective disposition of sulbenicillin in humans.

Stereoselective disposition of sulbenicillin (SBPC) epimers in healthy human volunteers was studied in order to clarify the differences in pharmacokinetic behavior between the epimers. Stereospecific high-performance liquid chromatography was used for the determination of SBPC epimers. Plasma protein binding was measured in vitro with an ultrafiltration method. The binding was stereoselective, with the unbound fraction (fu) of the R-epimer being approximately 1.3-fold greater than that of the S-epimer. SBPC was administered intravenously to human volunteers, and concentrations of SBPC in plasma and urinary excretion rates were measured. Renal clearance (CLR) for the unbound drug (approximately 400 ml/min) was greater than the glomerular filtration rate (GFR) (approximately 109 ml/min) for both epimers, suggesting that both epimers are secreted at the renal tubules. Renal tubular secretion appeared to be greater for the S-epimer. When probenecid was coadministered, the CLR values of both epimers were significantly reduced and were approximately equal to the GFR values. CLR was greater for the S-epimer (37.5 and 49.8 ml/min for R-SBPC and S-SBPC, respectively), which was simply due to the greater fu of the S-epimer in plasma. In contrast, total body clearance was greater for the R-epimer (67.8 and 56.3 ml/min for R-SBPC and S-SBPC, respectively) because of the stereoselective degradation of the R-epimer in plasma. It was revealed that stereoselective degradation in the body had significant influence on the disposition of SBPC epimers.

Significance of water solubility in the gastrointestinal absorption of trans-bis(n-valerato)(1R,2R-cyclohexanediamine)(oxalato)platinum(IV), an orally active antitumor platinum complex, and its analogs.

Trans-bis(n-valerato)(1R,2R-cyclohexanediamine)(oxalato++ +)platinum(IV) (C5-OHP) is an orally active platinum complex we prepared. The gastrointestinal absorption of C5-OHP was examined in rats and compared with those of C5-OHP analogs which have a general formula of trans-bis(n-OCOCnH2n+1)(1R,2R-cyclohexanediamine)(oxalato )platinum(IV) as well as C5-OHP. The complexes did not show significant differences in pharmacokinetic behavior after i.v. injection. Plasma platinum level after a single oral administration at a dose was higher for a complex with higher water solubility. The intestinal absorption rate measured by an in situ recirculating perfusion technique was higher for a complex with higher lipophilicity. These results indicate that the water solubility is a more dominant factor than the lipophilicity in the gastrointestinal absorption of the complexes. Then, the effects of surfactants and alpha-cyclodextrin (alpha-CD) on the solubility of C5-OHP was studied. Among the agents tested, alpha-CD showed the highest effect in increasing the solubility. Administration of C5-OHP together with alpha-CD gave approximately three times higher plasma platinum levels than administration of C5-OHP alone. Water solubility was found to be a dominant factor in the gastrointestinal absorption of C5-OHP and its analogs.

Structure-function relationship of recombinant follicle stimulating hormone (Puregon).

After separation by means of preparative isoelectrofocusing, the isohormones of a Chinese hamster ovary (CHO)-derived recombinant follicle stimulating hormone (rFSH, Puregon) were characterized with respect to structural and functional features. A carbohydrate analysis revealed that rFSH isohormones with a low isoelectric point (pl) have a high sialic acid/galactose ratio and are rich in tri- and tetra-antennary N-linked carbohydrate chains in comparison with the high pl isohormones. The relative basic isohormones exhibit receptor binding activity and intrinsic bioactivity 2-3-fold higher than the relative acidic isohormones. However, due to their lower clearance rate these acidic isohormones displayed a 20-fold higher in-vivo bioactivity in the rat. A comparison of the isohormone profile of rFSH and urinary FSH (Metrodin) revealed that rFSH contains about 2-fold more basic isohormones with pl > or = 4.7 and 2-fold less acidic isohormones with pl < 4.1. In-vitro studies showed that the receptor binding affinity and intrinsic bioactivity of both FSH preparations are similar. Also the in-vivo efficacy and the pharmacokinetic behaviour of rFSH and urinary FSH in the rat were similar, which is not surprising since both preparations were compared in terms of in-vivo bioactivity calibrated in the rat Steelman-Pohley assay. However, in dogs the bioavailability of rFSH was lower than that of urinary FSH, which is in agreement with the higher percentage of relative basic isohormones in rFSH. This suggests that the pharmacokinetic behaviour of FSH in rats and dogs is different, which is supported by the much longer elimination half-life of rFSH and urinary FSH in dogs (27.9 and 30.4 h respectively) compared with rats (11.4 and 10.4 h respectively) for rFSH and urinary FSH respectively. The observed differences in pharmacokinetic behaviour in dogs and rats indicate that the rat Steelman-Pohley assay might not be a valid model for the prediction of the FSH bioactivity in species other than rat.

Pharmacokinetic Evaluation of (Glycolato‐O, O′) diammine Platinum(II) in Lung Lymph in Sheep

The pharmacokinetics of (glycolato‐O, O′)diammine platinum(II) (254‐S), especially the distribution and behavior in the lung lymph in sheep, was investigated and compared with that of cis‐diammine‐dichloroplatinum(II) (CDDP). The blood and lung lymph fluid were collected from the carotid artery and a lung lymph fistula, respectively, in conscious sheep following intravenous infusion of 100 mg/body of 254‐S and CDDP for 30 min. The concentrations of these platinum complexes were measured by using atomic absorption spectrometry. We analyzed the data using an anatomically based model including part of the lymphatic circulation. The ultrafilterable platinum of 254‐S showed much larger area under the curve (AUC) and transfer rate constants than that of CDDP, even though the mean residence times were the same. The total platinum showed the opposite pharmacokinetic behavior. In anesthetized sheep, when lung tissue samples were obtained by biopsy at the same times as those of blood and lung lymph sampling after infusion of these drugs, 254‐S distributed in lung tissue appeared to move more easily into lung lymph than CDDP, which tended to be retained in lung tissue. These differences in pharmacokinetic behavior between 254‐S and CDDP seemed to be caused by differences in their strength of protein binding, the association constants of 254‐S for plasma and lymph protein were much less than those of CDDP. From these results, 254‐S may have favorable therapeutic effects on intrathoracic malignacies such as lung cancer and lymph metastasis

Cyclopentenyl cytosine: Interspecies predictions based on rodent plasma and urine kinetics

A hybrid compartmental-physiological model for cyclopentenyl cytosine (CPE-C) is designed on the basis of early limited rodent pharmacokinetic data. Application of model independent pharmacokinetics and biochemical knowledge was first used to conceptualize such a model. The approach was to scale the physiological parameters of the model (compartmental clearances) and keep constant the anatomic parameters of the model (compartment volumes). Scaling of physiological mechanisms was based on body weight/surface area ratios. Using these principles, simulations with the model can reasonably anticipate the in vivo behavior of (CPE-C) in several species (mouse, rat, dog). The model is useful in understanding species differences in pharmacokinetic behavior of CPE-C.