Absorption kinetics of cyclosporin in the rat

Enhanced oral bioavailability of valsartan in rats using a supersaturable self-microemulsifying drug delivery system with P-glycoprotein inhibitors

Valsartan (VST) is a poorly water-soluble drug and a P-glycoprotein (P-gp) substrate. To enhance the dissolution and oral absorption of VST, a novel supersaturable self-microemulsifying drug delivery system (Su-SMEDDS) was formulated. Based on the previously reported Su-SMEDDS composed of Capmul^® MCM (oil), Tween^® 20 (T20; surfactant), Transcutol^® P (cosurfactant), and Poloxamer 407 (supersaturating agent), P-gp inhibitory surfactants including Tween^® 80 (T80) and Cremophor^® EL (CR) were newly introduced to replace T20. All Su-SMEDDS formulations had a droplet size of <200 nm and showed rapid (>90% within 5 min) and pH-independent dissolution characteristics. The effective permeability coefficient (P_eff) in rat jejunum was obtained using an in situ single-pass intestinal perfusion study: P_eff values of Su-SMEDDS-T20, Su-SMEDDS-T80, and Su-SMEDDS-CR were 2.3, 4.1, and 3.4 times greater, respectively, than that of the VST solution. After oral administration of various formulations to rats (equivalent dose of VST 10 mg/kg), plasma drug levels were measured by liquid chromatography-tandem mass spectrometry. The relative bioavailabilities of Su-SMEDDS-T20, Su-SMEDDS-T80, and Su-SMEDDS-CR were 262%, 470%, and 458%, respectively, compared with the VST suspension. Thus, we propose that the Su-SMEDDS-T80 formulation is a good candidate for improving the oral absorption of poorly water-soluble and P-gp substrate drugs such as VST.

Cyclic Penta- and Hexaleucine Peptides without N-Methylation Are Orally Absorbed

Development of peptide-based drugs has been severely limited by lack of oral bioavailability with less than a handful of peptides being truly orally bioavailable, mainly cyclic peptides with N-methyl amino acids and few hydrogen bond donors. Here we report that cyclic penta- and hexa-leucine peptides, with no N-methylation and five or six amide NH protons, exhibit some degree of oral bioavailability (4-17%) approaching that of the heavily N-methylated drug cyclosporine (22%) under the same conditions. These simple cyclic peptides demonstrate that oral bioavailability is achievable for peptides that fall outside of rule-of-five guidelines without the need for N-methylation or modified amino acids.

Effects of Nigella sativa and Lepidium sativum on cyclosporine pharmacokinetics

The present study was conducted to investigate the effects of Nigella sativa and Lepidium sativum on the pharmacokinetics of cyclosporine in rabbits. Two groups of animals were treated separately with Nigella sativa (200 mg/kg p.o.) or Lepidium sativum (150 mg/kg p.o.) for eight consecutive days. On the 8th day, cyclosporine (30 mg/kg p.o.) was administered to each group one hour after herbal treatment. Blood samples were withdrawn at different time intervals (0.0, 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 6.0, 8.0, 12, and 24 hrs) from marginal ear vein. Cyclosporine was analyzed using UPLC/MS method. The coadministration of Nigella sativa significantly decreased the C_max and AUC_0−∞ of cyclosporine; the change was observed by 35.5% and 55.9%, respectively (P ≤ 0.05). Lepidium sativum did not produce any significant change in C_max of cyclosporine, although its absorption was significantly delayed compared with control group. A remarkable change was observed in T_max and AUC_0−t of Lepidium sativum treated group. Our findings suggest that concurrent consumption of Nigella sativa and Lepidium sativum could alter the pharmacokinetics of cyclosporine at various levels.

Pharmacokinetic changes of cyclosporine after intravenous and oral administration to rats with uranyl nitrate-induced acute renal failure

The effects of renal failure on the pharmacokinetics of cyclosporine were investigated after intravenous, 30 mg/kg, and oral, 100 mg/kg, administration of the drug using a rat model of uranyl nitrate-induced acute renal failure (U-ARF). After intravenous administration to rats with U-ARF, the volume of distribution at steady state (1.97 vs. 2.56 l/kg) was significantly smaller, and the area under the blood concentration-time curve (348 vs. 296 microg h/ml) tended to be greater and total body clearance (0.0851 vs. 0. 102 l/h per kg) tended to be slower than those in control rats. After oral administration, the pharmacokinetic parameters were not significantly different between the control rats and rats with U-ARF, suggesting that U-ARF did not considerably affect the pharmacokinetics of cyclosporine after oral administration.

Depressed renal and vascular nitric oxide synthase expression in cyclosporine-induced hypertension

BACKGROUND

Introduction of cyclosporine (CsA) for clinical use has greatly enhanced the outcome of organ transplantation. However, CsA can cause nephrotoxicity and hypertension (HTN). This study was designed to test the hypothesis that CsA-induced HTN is related to depressed nitric oxide (NO) production.

METHODS

Urinary excretion of NO metabolites (NOx) and endothelial and inducible NO synthase (eNOS and iNOS) proteins were determined in thoracic aortas and kidneys of CsA-treated (given CsA 18 mg/kg/day for 3 weeks) and placebo-treated rats. In addition, renal tissue eNOS and iNOS mRNA and aorta iNOS activity were measured.

RESULTS

CsA administration resulted ina significant rise in arterial blood pressure (BP) coupled with a steady decline in urinary NOx excretion, suggesting depressed NO production. This was accompanied by a significant reduction in iNOS protein abundance in the kidney and thoracic aorta but no change in eNOS protein abundance. The fall in renal iNOS protein in CsA-treated rats was accompanied by a parallel decline in iNOS mRNA abundance and enzymatic activity.

CONCLUSION

Administration of CsA for three weeks resulted in a significant rise in BP together with marked reductions in urinary NOx excretion, and renal and vascular iNOS expression. These observations suggest that CsA-induced HTN may be, in part, related to impaired NO production. If true, strategies designed to restore NO availability may mitigate HTN and other vascular complications of CsA therapy.

Bioavailability of cyclosporine in rats after intragastric administration: a comparative study of the L2-phase and two other lipid-based vehicles

The purpose of this study was to evaluate formulations based on surface active dietary lipids only as oral vehicles for cyclosporine. The absolute bioavailability of cyclosporine from two new lipid vehicles was determined in rats after intragastric administration and compared to that of Sandimmun oral solution, which contains non-ionic surface active substances in addition to dietary lipids. In the new vehicles, cyclosporine was dissolved in two different mixtures of glycerides from long-chained fatty acids. One mixture forms an L2-phase, an oil with very low interfacial tension towards water, and was administered both as the oily L2-phase and as a predispersed emulsion formulation. The other mixture forms a liquid crystalline phase and was administered only as an aqueous dispersion. The mean bioavailability of cyclosporine from Sandimmun was 8% while it was 34% from the L2-phase, 38% from the predispersed L2-phase and 27% from the dispersed liquid crystalline phase. The coefficients of variation in area under the blood concentration curve after administration of the two formulations based on the L2-phase were quite low (31% for the L2-phase and 24% for the predispersed L2-phase) and comparable to that after intravenous administration (24%), while the dispersed liquid crystalline phase gave a higher variability (91%), comparable to that of Sandimmun oral solution (101%). The low variabilities found with the two L2-phase vehicles suggest that this formulation is "self-emulsifying' in the gastrointestinal tract. Since the L2-phase is based on dietary lipids only, it is expected to be well tolerated and could prove to be a good vehicle for long-term clinical use of oral cyclosporine.

Liposomal formulations of cyclosporin A: influence of lipid type and dose on pharmacokinetics

PURPOSE

Liposomal formulations of Cyclosporin A (CyA)3 have been described in more than 30 publications to substitute Cremophor EL (CrEL), a triricinoleate ester of ethoxylated glycerol, as drug carrier. However, conflicting reports did not allow to draw consistent conclusions about the influence of liposomes on CyA pharmacokinetics (PK) and pharmacodynamics.

METHODS

A series of liposomal CyA-formulations with varying liposome composition and lipid dose but constant CyA dose was compared in rats. Data were analysed with a PK-model taking into account the varying volume of distribution with the varying lipid concentration in blood.

RESULTS

Surface properties and lipid type of liposomes are not important PK predictors of liposomal CyA, at least for small dosages of liposomes. Rather, the absolute lipid amount and the lipophilicity of cyclosporins are critical factors influencing the PK of liposomal CyA. The higher the concentration of lipid in blood and the greater the lipophilicity of cyclosporin is, the higher are the concentrations of CyA in blood.

CONCLUSIONS

These relations may explain the inconsistent literature results. Together with earlier observations from our group the above findings indicate, that CyA is not caged in the liposomal membranes. Reports in literature, which claim lower clearance and a lower volume of distribution of CyA in obese rats compared to lean rats, support our assumption about the involved mechanisms. A semi-quantitative model of CyA distribution is presented, which points to the variable free fraction of CyA in plasma as the crucial factor for all previously reported phenomena in liposomal CyA formulations.

Pharmacokinetics and absolute bioavailability of cyclosporin following intravenous and abomasal administration to sheep

Cyclosporin A pharmacokinetics were studied following intravenous and abomasal dosing in an open, crossover study in healthy, merino ewes. Five different doses of cyclosporin A were dispersed in milk and administered into the abomasum through a surgically inserted fistula which simulates oral administration. Cyclosporin A was well tolerated. Whole blood concentrations of cyclosporin A were measured by HPLC and mean clearance (0.45 +/- 0.05 L h-1 kg-1), distribution volume (4.4 +/- 2.0 L kg-1), mean residence time (9.6 +/- 4.1 h) and half-life (12.1 +/- 3.1 h) were calculated cyclosporin A was excreted in urine or bile. Area under the curve increased proportionally with doses up to 26.3 mg kg-1, but was curvilinear above this dose. Abomasal bioavailability at 6.4 mg kg-1 was 0.26 +/- 0.09, and mean absorption time was 4.7 +/- 11.1 h. Considerable pharmacokinetic variability was observed, particularly after abomasal administration. Cyclosporin A pharmacokinetics in sheep lie within the values reported in man after renal, bone marrow and cardiac transplantation.