Correlating in Vitro Solubilization and Supersaturation Profiles with in Vivo Exposure for Lipid Based Formulations of the CETP Inhibitor CP-532,623.

Lipid based formulations (LBFs) are a promising formulation strategy for many poorly water-soluble drugs and have been shown previously to enhance the oral exposure of CP-532,623, an oral cholesteryl ester transfer protein inhibitor. In the current study, an in vitro lipid digestion model was used to probe the relationship between drug solubilization and supersaturation on in vitro dispersion and digestion of LBF containing long chain (LC) lipids and drug absorption in vivo. After in vitro digestion of LBF based on LC lipids, the proportion of CP-532,623 maintained in the solubilized state in the aqueous phase of the digest was highest in formulations containing Kolliphor RH 40, and in most cases outperformed equivalent formulations based on MC lipids. Subsequent administration of the LC-LBFs to beagle dogs resulted in reasonable correlation between concentrations of CP-532,623 measured in the aqueous phase of the in vitro digest after 30 min digestion and in vivo exposure (AUC); however, the LC-LBFs required greater in vitro drug solubilization to elicit similar in vivo exposure when compared to previous studies with MC-LBF. Although post digestion solubilization was enhanced in LC-LBF compared to MC-LBF, equilibrium solubility studies of CP-532,623 in the aqueous phase isolated from blank lipid digestion experiments revealed that equilibrium solubility was also higher, and therefore supersaturation lower. A revised correlation based on supersaturation in the digest aqueous phase and drug absorption was therefore generated. A single, linear correlation was evident for both LC- and MC-LBF containing Kolliphor RH 40, but this did not extend to formulations based on other surfactants. The data suggest that solubilization and supersaturation are significant drivers of drug absorption in vivo, and that across formulations with similar formulation composition good correlation is evident between in vitro and in vivo measures. However, across dissimilar formulations, solubilization and supersaturation alone are not sufficient to explain drug exposure and other factors also likely play a role.

Lymphatic Transport and Lymphocyte Targeting of a Triglyceride Mimetic Prodrug Is Enhanced in a Large Animal Model: Studies in Greyhound Dogs.

In previous studies, a triglyceride (TG) mimetic prodrug of the model immunomodulator mycophenolic acid (MPA) was shown to significantly enhance lymphatic transport of MPA-related species in the rat. The rat gastrointestinal tract, however, is somewhat different from that in higher order species such as dogs and humans and may underestimate lymphatic transport. Here the effectiveness of the prodrug strategy has been examined in conscious greyhound dogs, the GI physiology of which is more representative of that in humans. The bioavailability and lymphatic transport of free MPA and total MPA related materials were examined following oral administration of the parent drug (MPA) and the prodrug (2-MPA-TG) to both thoracic lymph duct cannulated and intact (noncannulated) greyhound dogs. The enrichment of free MPA in lymph nodes and lymph-derived lymphocytes was also determined to examine the efficiency of drug targeting to potential sites of action within the lymph. Via biochemical integration into a series of site-specific metabolic processes, the prodrug markedly increased (288-fold) lymphatic transport of total MPA related material (present as re-esterified 2-MPA-TG) when compared to the parent MPA and the extent of lymphatic transport was significantly greater in the dog (36.4% of the dose recovered in lymph) when compared to the previous data in the rat (13.4% of the dose). Conversion from 2-MPA-TG derivatives to parent MPA occurred in vivo, resulting in a marked increase in MPA concentrations in lymph nodes (5-6-fold) and lymph lymphocytes (21-fold), when compared to animals administered the parent drug. In conclusion, the data demonstrate that the TG prodrug of MPA facilitates efficient delivery of MPA to the lymphatic system in dogs and suggest that the TG prodrug strategy may more effectively facilitate targeted delivery in large animals than in rats.

Plasma Ion Activated Expanded Polytetrafluoroethylene Vascular Grafts with a Covalently Immobilized Recombinant Human Tropoelastin Coating Reducing Neointimal Hyperplasia.

Expanded polytetrafluoroethylene (ePTFE) vascular conduits with less than or equal to 6 mm internal diameter typically occlude due to a combination of thrombus formation and neointimal hyperplasia. We hypothesized that by layering the polymerized elastin precursor, human tropoelastin, in the synthetic vessel lumen we could mimic the internal elastic lamina and so maintain low thrombogenicity while significantly reducing smooth muscle cell proliferation. The luminal surfaces of ePTFE conduits were activated with plasma immersion ion implantation (PIII) treatment to facilitate covalent attachment of tropoelastin. Multilayered tropoelastin vessels (2TE) enhanced endothelial cell attachment and proliferation in vitro and were superior to materials lacking the protein. In an ovine carotid interposition model of graft compatibility, partially tropoelastin coated vessels (1TE) thrombosed at a greater rate than control ePTFE, but 2TE maintained the same patency as controls. 2TE showed a significant reduction in neointimal area down to 9.7 ± 5.2% (p < 0.05) in contrast to 32.3 ± 3.9% for ePTFE alone. This reduction was due to a halving of the number of smooth muscle cells present and a corresponding reduction in their proliferation. 2TE, but not 1TE, enhanced the vascular compatibility of these materials: while both tropoelastin presentations increased in vitro endothelialization, only 2TE displayed the dual benefits of maintained hemocompatibility and simultaneously suppressed neointimal hyperplasia in vivo. We conclude that 2TE surface modification provides a significant improvement over ePTFE vascular conduits in a pilot large animal model study and presents an attractive path toward clinical applications for reduced diameter vessels.

In vitro-in vivo evaluation of lipid based formulations of the CETP inhibitors CP-529,414 (torcetrapib) and CP-532,623.

The present study investigated the use of lipid based drug delivery systems to enhance the oral bioavailability of the CETP inhibitors CP-532,623 and torcetrapib. A series of self-emulsifying lipid based drug delivery systems (SEDDS) were assembled and examined using an in vitro lipid digestion model to evaluate patterns of drug precipitation under simulated intestinal conditions. Drug exposure after oral administration of the same formulations was subsequently assessed in beagle dogs. CP-532,623 was maintained in a solubilised state during dispersion of most formulations in simulated intestinal fluid, however, solubilisation capacity was reduced to various degrees upon in vitro digestion. Administration of SEDDS formulations to beagle dogs resulted in moderate differences in plasma AUC when compared to the differences in solubilisation observed in vitro. Similar trends were observed for torcetrapib. In all cases, however, in vivo exposure of CP-532,623 was greatly enhanced by administration in lipid based drug delivery systems when compared to a powder formulation. Some correlation between in vitro solubilisation and in vivo drug exposure (AUC) was evident; however, this was not linear. The data suggest that for highly lipophilic drugs such as CP-532,623 in vitro digestion data may be a conservative in vitro indicator of utility and that good exposure may be evident even for formulations that result in significant drug precipitation during in vitro digestion.

Non-linear increases in danazol exposure with dose in older vs. younger beagle dogs: the potential role of differences in bile salt concentration, thermodynamic activity, and formulation digestion.

PURPOSE: To explore the possibility that age-related changes in physiology may result in differences in drug bioavailability after oral administration of lipid based formulations of danazol. METHODS: Danazol absorption from lipid formulations with increasing drug load was examined in younger (9 months) and older (8 years) beagles. Age related changes to hepatic function were assessed via changes to systemic clearance and serum bile acid concentrations. Changes to lipolytic enzyme activity and intestinal bile salt concentration were evaluated using in vitro lipolysis. RESULTS: Drug exposure increased linearly with dose in younger animals. In older animals, bioavailability increased with increasing dose to a tipping point, beyond which bioavailability reduced (consistent with initiation of precipitation). No differences in hepatic function were apparent across cohorts. Changes to enzyme concentrations in lipolysis studies had little impact on drug precipitation/solubilisation. In contrast, higher bile salt concentrations better supported supersaturation at higher drug loads. CONCLUSIONS: Differences in animal cohort can have a significant impact on drug absorption from lipid based formulation. For danazol, bioavailability was enhanced under some circumstances in older animals. In vitro experiments suggest that this was unlikely to reflect changes to metabolism or lipolysis, but might be explained by increases in luminal bile salt/phospholipid concentrations in older animals.

Silica-lipid hybrid (SLH) formulations enhance the oral bioavailability and efficacy of celecoxib: An in vivo evaluation.

This study is the first to demonstrate in canines the ability of silica-lipid hybrid (SLH) microparticles to enhance the bioavailability and efficacy of a poorly water-soluble drug after oral administration. Spray-dried SLH microparticles comprising Capmul MCM (mono-diglycerides of C8/C12 fatty acids) and silica nanoparticles (Aerosil® 380) were shown to significantly enhance the fasted state oral bioavailability of celecoxib (CEL) (6.5 fold, relative to an aqueous suspension and more than 2-fold higher relative to the fed state) after oral administration to beagle dogs. Comparable bioavailability was observed between the SLH microparticle formulation and a conventional Capmul lipid solution, however, plasma concentrations were observed to be higher (Cmax, 1.1±0.06 vs. 0.8±0.03µg/mL) (p≤0.05) with the SLH microparticle system. The enhanced bioavailability of CEL observed with the SLH microparticles was reflected in a subsequent efficacy study conducted in an adjuvant-induced arthritis model in the rat. Reduced clinical and histological severity was observed at a dose of 3mg/kg/day, with the progression of arthritic symptoms and tissue damage reduced to a similar degree to that of a higher dose administered at 5mg/kg/day and prepared in an aqueous suspension., The enhanced bioavailability and improved efficacy observed with the SLH microparticles were attributed to the maintenance of CEL in a solubilised form during digestion of the lipid vehicle. We hypothesise that the presence of silica in the formulation may have contributed to the prevention of drug precipitation in the intestinal lumen by providing an alternative binding site for CEL to adsorb to prior to re-solubilisation and absorption. The study highlights the potential utility of novel SLH microparticle formulations as stable dry powders that possess the properties of a lipid-based formulation for the enhanced delivery and efficacy of poorly water-soluble drugs.

Lipid digestion as a trigger for supersaturation: evaluation of the impact of supersaturation stabilization on the in vitro and in vivo performance of self-emulsifying drug delivery systems.

The generation of supersaturation in the gastrointestinal (GI) tract is an increasingly popular means of promoting oral absorption for poorly water-soluble drugs. The current study examined the impact of changes to the quantities of medium-chain (MC) lipid (Captex 300:Capmul MCM), surfactant (Cremophor EL) and cosolvent (EtOH), and the addition of polymeric precipitation inhibitors (PPI), on supersaturation during the dispersion and digestion of MC self-emulsifying drug delivery systems (SEDDS) containing danazol. The data suggest that digestion acts as a "trigger" for enhanced supersaturation and that solubilization/precipitation behavior is correlated with the degree of supersaturation on dispersion (S(M)DISP) or digestion (S(M)DIGEST). The ability of the formulation to maintain solubilization in vitro decreased as the S(M) of the formulation increased. PPI significantly increased supersaturation stabilization and precipitation was inhibited where S(M)DISP < 3.5 and S(M)DIGEST < 4. In the presence of polymer, some degree of supersaturation was maintained up to S(M)DIGEST ∼ 8. Differentiation in the ability of SEDDS to maintain drug solubilization stems from the ability to stabilize supersaturation and for MC SEDDS, utilization of lower drug loads, higher surfactant levels (balanced against increases in S(M)DISP), lower cosolvent and the addition of PPI enhanced formulation performance. In vivo studies confirmed the ability of PPI to promote drug exposure at moderate drug loads (40% of saturated solubility in the formulation). At higher drug loads (80% saturation) and in lipid-free SEDDS, this effect was lost, suggesting that the ability of PPIs to stabilize supersaturation in vitro may, under some circumstances, overestimate utility in vivo.

A highly elastic and adhesive gelatin tissue sealant for gastrointestinal surgery and colon anastomosis.

BACKGROUND: We describe the development of a highly elastic and adhesive surgical tissue sealant, based on photochemically crosslinked gelatin, for sealing sutured incisions in the gastrointestinal (GI) tract in a rabbit surgical model and in a canine colon anastomosis study. METHODS: The study included in vitro assessment of mechanical parameters of the tissue sealant and in vivo analysis of burst strength and histology at 24 h, 3 days and 7 days post surgery, in a rabbit model, to assess progress of wound healing at the suture sites. Utility of this sealant to repair and seal a lower colonic resection and anastomosis procedure in a canine model was also investigated. RESULTS: We show that a photopolymerised gelatin tissue sealant provides effective sealing of GI incisions and facilitates wound healing with no evidence of inflammation up to 28 days post-surgery. Blending of derivatised gelatin with underivatised gelatin allowed tuning of elasticity and elastic modulus of the photopolymerised sealant to suit surgical applications. High tissue adhesive strength was maintained at all blend ratios and exceeded 100 kPa. CONCLUSIONS: This highly elastic and adhesive photopolymerised gelatin tissue sealant offers a number of advantages over currently available sealants suitable for GI surgical procedures.

A highly elastic tissue sealant based on photopolymerised gelatin.

Gelatin is widely used as a medical biomaterial because it is readily available, cheap, biodegradable and demonstrates favourable biocompatibility. Many applications require stabilisation of the biomaterial by chemical crosslinking, and this often involves derivatisation of the protein or treatment with cytotoxic crosslinking agents. We have previously shown that a facile photochemical method, using blue light, a ruthenium catalyst and a persulphate oxidant, produces covalent di-tyrosine crosslinks in resilin and fibrinogen to form stable hydrogel biomaterials. Here we show that various gelatins can also be rapidly crosslinked to form highly elastic (extension to break >650%) and adhesive (stress at break >100 kPa) biomaterials. Although the method does not require derivatisation of the protein, we show that when the phenolic (tyrosine-like) content of gelatin is increased, the crosslinked material becomes resistant to swelling, yet retains considerable elasticity and high adhesive strength. The reagents are not cytotoxic at the concentration used in the photopolymerisation reaction. When tested in vivo in sheep lung, the photopolymerised gelatin effectively sealed a wound in lung tissue from blood and air leakage, was not cytotoxic and did not produce an inflammatory response. The elastic properties, thermal stability, speed of curing and high tissue adhesive strength of this photopolymerised gelatin, offer considerable improvement over current surgical tissue sealants.

Atrial electrophysiology is altered by acute hypercapnia but not hypoxemia: implications for promotion of atrial fibrillation in pulmonary disease and sleep apnea.

BACKGROUND: Chronic pulmonary disease and sleep apnea have been associated with the development of atrial fibrillation (AF). OBJECTIVE: The purpose of this study was to characterize the atrial electrical changes that occur with hypercapnia and hypoxemia and to determine their role in AF development. METHODS: Seventeen sheep (6 control, 5 hypercapnia, 6 hypoxemia) underwent open chest electrophysiologic evaluation under autonomic blockade. A 64-electrode endocardial basket catheter was positioned in the right atrium, and 2 x 128 electrode epicardial plaques were sutured to the right atrial and left atrial appendages to determine atrial refractoriness (effective refractory period [ERP]) at 9 sites and 5 cycle lengths, conduction time to fixed points on each plaque, and AF vulnerability. RESULTS: Hypercapnia was associated with a 152% lengthening of ERP from baseline and increased conduction time. ERPs rapidly returned to baseline, but recovery of conduction was delayed at least 117 +/- 24 minutes following resolution of hypercapnia. AF vulnerability was reduced during hypercapnia (with increased ERP) but increased significantly with subsequent return to eucapnia (when ERP normalized but conduction time remained prolonged). No significant changes in ERP, atrial conduction time, or AF vulnerability occurred in hypoxemic or control groups. CONCLUSION: Differential recovery of ERP and conduction that occurs following hypercapnia might account for the increased vulnerability to AF observed in the phase after return to eucapnia. This may explain in part the increased prevalence of AF in pulmonary disease and sleep apnea.

The role of the intestinal lymphatics in the absorption of two highly lipophilic cholesterol ester transfer protein inhibitors (CP524,515 and CP532,623).

PURPOSE: To evaluate the potential role of intestinal lymphatic transport in the absorption and oral bioavailability of members of an emerging class of anti-atherosclerosis drugs (CETP inhibitors). CP524,515 and CP532,623 are structurally related with eLogD(7.4) >5; however, only CP524,515 (and not CP532,623) had sufficient solubility (>50 mg/g) in long-chain triglyceride (LCT) to be considered likely to be lymphatically transported. METHODS: CP524,515 and CP532,623 were administered intravenously and orally to fasted or fed lymph-cannulated or non-cannulated dogs. Oral bioavailability and lymphatic transport of drug (and triglyceride) was subsequently quantified. RESULTS: Both CETP inhibitors were substantially transported into the lymphatic system (>25% dose) in fed and fasted dogs. Food enhanced oral bioavailability (from 45 to 83% and 44 to 58% for CP524,515 and CP532,623, respectively) and the proportion of the absorbed dose transported via the lymph (from 61 to 86% and from 68 to 83%, respectively). Lymphatic triglyceride transport was significantly lower in fed dogs administered CP532,623. CONCLUSION: Intestinal lymphatic transport is the major absorption pathway for CP524,515 and CP532,623, suggesting that a LCT solubility >50 mg/g is not an absolute requirement for lymphatic transport. The effect of CP532,623 on intestinal lipid transport may suggest a role in the activity/toxicity profiles of CETP inhibitors.

Human cord blood stem cells enhance neonatal right ventricular function in an ovine model of right ventricular training.

BACKGROUND: Nonischemic right ventricular dysfunction and cardiac failure is a source of considerable morbidity in children with congenital heart disease. Cell transplantation has not previously been studied in the pediatric setting in which enhancing ventricular function in response to supraphysiologic workloads might be beneficial. METHODS: Engraftment and differentiation of human cord blood stem cells were studied in an immunosuppressed neonatal ovine model of right ventricular training. Week-old sheep underwent pulmonary artery banding and epicardial injection of cord blood stem cells (n=8) or pulmonary artery banding and placebo injection (n=8). Control groups received cord blood stem cells (n=6) or placebo (n=6) injection without pulmonary artery banding. Right ventricular function was measured at baseline and 1 month later using conductance catheter. RESULTS: Cord blood stem cells were detected in the myocardium, spleen, kidney, and bone marrow up to 6 weeks after transplantation and expressed the hematopoietic markers CD45 and CD23. We identified neither differentiation nor fusion of transplanted human cells. In the groups undergoing pulmonary artery banding, cord blood stem cell transplantation was accompanied by functional benefits compared with placebo injection: end-systolic elastance increased by a mean of 1.4 +/- 0.2 mm Hg/mL compared with 0.9 +/- 0.1 mm Hg/mL, and the slope of preload recruitable stroke work increased by 21.1 +/- 2.9 mm Hg compared with 15.8 +/- 2.5 mm Hg. Cord blood stem cell transplantation had no significant effect on right ventricular function in the absence of pulmonary artery banding. CONCLUSIONS: Our data demonstrate that in the presence of increased workload, cord blood stem cells engraft and augment right ventricular function. Transplanted cells adopt hematopoietic fates in the myocardium, bone marrow, and spleen.

Lymphatic transport of Methylnortestosterone undecanoate (MU) and the bioavailability of methylnortestosterone are highly sensitive to the mass of coadministered lipid after oral administration of MU.

The contribution of lymphatic transport to the oral bioavailability of methylnortestosterone (M) after oral administration of the lipophilic prodrug methylnortestosterone undecanoate (MU) has been evaluated, and the sensitivity of lymphatic MU transport to lymphatic lipid transport has been investigated. M and MU were administered intravenously and orally to greyhound dogs to determine absolute bioavailability after oral dosing of MU. MU was also administered orally with differing quantities of food (lipid) to lymph duct-cannulated greyhound dogs to investigate the relative roles of lymph versus blood transport on M bioavailability and the effect of lipid load on systemic exposure. The relationship between lymphatic lipid and MU transport was further investigated in anesthetized rats. The oral bioavailability of M after administration of MU was found to be highly dependent on coadministration of food, and the bioavailability of M increased approximately 700% in fed versus fasted animals. In both cases, lymph diversion resulted in negligible systemic exposure of M, indicating almost complete dependence on lymphatic transport of MU for systemic exposure of M. Lymphatic transport of MU was even more highly dependent on the quantity of coadministered lipid and increased more than 50-fold with increasing lipid load. Therefore, increasing the quantity of food or lipid coadministered with MU stimulated a significant increase in the lymphatic transport of MU and systemic exposure of M. The lipid sensitivity of lymphatic transport of MU is significantly higher than previously observed for more metabolically stable compounds, suggesting a role for coadministered lipid in promoting avoidance of enterocyte-based cleavage of MU.

Intestinal lymphatic transport enhances the post-prandial oral bioavailability of a novel cannabinoid receptor agonist via avoidance of first-pass metabolism.

PURPOSE: To examine the effect of food on the oral bioavailability of a highly lipophilic, cannabinoid receptor agonist (CRA13) and to explore the basis for the food effect in lymph-cannulated and non-cannulated dogs. METHODS: Oral bioavailability was assessed in fasted and fed human volunteers and in lymph-cannulated dogs. In fasted dogs, the extent of absorption and oral bioavailability was also examined following administration of radiolabelled CRA13. RESULTS: Food had a substantial positive effect on the oral bioavailability of CRA13 in human volunteers (4.3-4.9 fold increase in AUC(0 - infinity)) and in dogs. The absolute bioavailability of parent drug was low in fasted dogs (8-20%), in spite of good absorption (72-75% of radiolabelled CRA13 recovered in the systemic circulation). In post-prandial lymph-cannulated dogs, bioavailability increased to 47.5% and the majority (43.7%) of the dose was absorbed via the intestinal lymphatic system. CONCLUSIONS: The positive food effect for CRA13 does not appear to result from increased post-prandial absorption. Rather these data provide one of the first examples of a significant increase in bioavailability for a highly lipophilic drug, which is stimulated via almost complete post-prandial transport into the lymph, in turn resulting in a reduction in first-pass metabolism.

Expert systems for clinical pathology reporting.

* Conventional automated interpretative reporting systems use standard or "canned" comments for patient reports. These are result-specific and do not generally refer to the patient context. * Laboratory information systems (LIS) are limited in their application of patient-specific content of reporting. * Patient-specific interpretation requires extensive cross-referencing to other information contained in the LIS such as previous test results, other related tests, and clinical notes, both current and previous. * Expert systems have the potential to improve reporting quality by enabling patient-specific reporting in clinical laboratories.

Evaluation of the impact of surfactant digestion on the bioavailability of danazol after oral administration of lipidic self-emulsifying formulations to dogs.

Lipid-based formulations of danazol with varying quantities of included surfactant have been examined in vitro and in vivo. Formulations comprising fatty acid ester surfactants were readily hydrolysed during in vitro digestion, although Cremophor RH40 (CrRH) was less effectively hydrolysed than Cremophor EL (CrEL). Formulations comprising high quantities of digestible surfactant also appeared to less effectively prevent danazol precipitation during in vitro evaluation. These trends were replicated in vivo where danazol bioavailability in beagle dogs was higher after oral administration of self-emulsifying formulations employing 55% (w/w) CrRH when compared with CrEL. The oral bioavailability of danazol after administration of drug formulated in surfactant alone, however, was poor. Studies using predispersed and encapsulated formulations of CrRH subsequently suggested that the low bioavailability of the single surfactant formulations reflected poor dispersion. Mixtures of surfactants, improved dispersion and good oral bioavailability of danazol was evident after administration of formulations comprising CrRH and either Pluronic L121 or Gelucire 44-14, in spite of evidence of danazol precipitation during in vitro digestion of the Gelucire formulation. These data suggest that effective dispersion and resistance to precipitation during both dispersion and digestion are key design parameters for lipid-based formulations comprising high proportions of surfactant.

Lymphatic absorption of subcutaneously administered proteins: influence of different injection sites on the absorption of darbepoetin alfa using a sheep model.

The relative contribution of the lymph and blood in the absorption of darbepoetin alfa (DA) from different s.c. injection sites was determined using a central lymph-cannulated sheep model. DA was administered to parallel groups either as a bolus i.v. injection (0.5 mug/kg) into the jugular vein or as a bolus s.c. injection (2 mug/kg) into the interdigital space, the abdomen, or the shoulder. In the lymph-cannulated groups, the thoracic lymph duct was cannulated for continuous collection of central lymph, and blood samples were periodically collected via the jugular vein in all the groups. The concentration of DA in serum and lymph was determined by enzyme-linked immunosorbent assay. The total fraction of the dose reaching the systemic circulation and the fractions absorbed via the lymph and the blood were determined. A pharmacokinetic model was constructed to simultaneously fit the data from all the treatment groups. Absorption was essentially complete for all three injection sites in non-lymph-cannulated s.c. groups, but the rates of absorption differed significantly. Based on the modeling results for the lymph-cannulated groups, the lymphatics represented the predominant absorption route for both the interdigital (90 +/- 1%) and the abdomen (67 +/- 9%) injection sites. Fluorescein isothiocyanate dextran visualization studies revealed that the lymph draining the shoulder injection site entered the thoracic lymph duct distal to the point of cannulation, effectively precluding collection of thoracic lymph from this site. For that reason, the contribution of the lymphatics following injection in the shoulder could not be determined using these cannulation procedures.

Increasing the proportional content of surfactant (Cremophor EL) relative to lipid in self-emulsifying lipid-based formulations of danazol reduces oral bioavailability in beagle dogs.

PURPOSE: To investigate the impact of a change in the proportions of lipid, surfactant and co-solvent on the solubilisation capacity of self-emulsifying formulations of danazol during in vitro dispersion and digestion studies and correlation with in vivo bioavailability in beagle dogs. METHODS: Formulations from within the phase diagram of the pseudo-ternary system composed of soybean oil:maisine 35-1 (1:1 w/w), Cremophor EL and ethanol were assessed in vitro on dispersion and digestion. The relative bioavailability of danazol after administration of a series of these formulations was also determined. RESULTS: All formulations formed microemulsions in the presence of water and no drug precipitation was observed on dispersion. In contrast, drug solubilisation was markedly affected by lipase-mediated digestion and a reduction in lipid (and increase in surfactant) content resulted in increased drug precipitation. Consistent with these data, the bioavailability of danazol decreased significantly when the lipid content in the formulations was reduced. CONCLUSION: A rank-order correlation was observed between the patterns of solubilisation obtained during in vitro digestion and the in vivo performance of self-emulsifying formulations of danazol. In general a decrease in the lipid content and an increase in the proportions of surfactant and co-solvent resulted in reduced danazol bioavailability.

Atrial electrical and structural abnormalities in an ovine model of chronic blood pressure elevation after prenatal corticosteroid exposure: implications for development of atrial fibrillation.

AIMS: Elevated blood pressure (EBP) is the most prevalent and potentially modifiable risk factor for AF, yet little is known of its atrial effects. We aimed to characterize the atrial electrical and structural changes in a chronic ovine model of EBP after prenatal corticosteroid exposure. METHODS AND RESULTS: Twelve sheep with chronically EBP (mean arterial pressure 94+/-3 mmHg) and six controls (71+/-4 mmHg, P<0.01) underwent acute open chest electrophysiologic and pathologic studies. We measured refractoriness at the atrial appendages at 3 cycle lengths (CL); conduction velocities at Bachmann's bundle, both atrial appendages and free walls at 4 CLs; conduction heterogeneity; atrial wavelength and AF duration. We performed light microscopy (LM) and electron microscopy (EM) and collagen and apoptosis studies. EBP was associated with widespread conduction abnormalities, shortening of atrial wavelength, and increased AF. There was no significant change in refractoriness. LM demonstrated atrial myocyte hypertrophy and myolysis in all EBP sheep and focal scarring in six. EM demonstrated mitochondrial and nuclear enlargement and increased collagen fibrils in EBP sheep, findings not present in any controls. Atrial collagen and apoptosis were increased in EBP animals. CONCLUSION: This study demonstrates that chronically, EBP is associated with significant atrial electrical and structural remodelling. These changes may explain the increased propensity to atrial arrhythmias observed with long-standing EBP.

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 microg/kg) or by subcutaneous (SC) administration (2 microg/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.