The effect of grapefruit juice on cyclosporine and prednisone metabolism in transplant patients.

OBJECTIVE: To estimate the effect of grapefruit juice on cyclosporine and prednisone metabolism. METHODS: This was an open, placebo-controlled, two-way crossover study performed in the academic departments of clinical pharmacology and nephrology. On two study occasions, 12 kidney transplant patients with stable cyclosporine trough levels received either grapefruit juice or water every 3 hours for a period of 30 hours. The main outcome measures were peak concentration and time to peak, area under the concentration-time curve, the ratio of the area under the curve of the metabolites/area under the curve of the parent drug, terminal half-life, and 24-hour trough levels of cyclosporine. RESULTS: Grapefruit juice increased the peak concentration of cyclosporine by 185 ng/ml (95% confidence interval, 60 to 310; p = 0.008). The ratio of the area under the curve of the metabolites of cyclosporine to the area under the curve of cyclosporine was reduced by 0.137 on the grapefruit day (95% confidence interval, -0.221 to -0.054; p = 0.004). After grapefruit juice, no significant changes were observed in the area under the curve and the time to peak of cyclosporine, prednisone, and prednisolone. Cyclosporine trough levels were unchanged by grapefruit juice. CONCLUSIONS: Grapefruit juice inhibits the metabolism of cyclosporine for a brief period after administration, which may be explained by the inhibition of cytochrome P450 enzymes in the gut wall and to a lesser extent by inhibition of these enzymes in the liver. Grapefruit juice can be one of the factors leading to intraindividual variability in the pharmacokinetics of cyclosporine. Grapefruit juice had no significant effect on the metabolism of prednisone or prednisolone.

Acute effect of cyclosporin on renal function following the initial changeover to a microemulsion formulation in stable kidney transplant patients.

Potential differences in the acute effect of cyclosporin on renal function when dosed orally as the current market formulation or following a milligram-to-milligram conversion to a new microemulsion formulation were investigated in 14 stable kidney transplant patients. The study consisted of three sequential periods of 2 weeks duration each. Patients entered (period I) and completed (period III) the investigation with the market formulation and received the microemulsion formulation in period II; individualized cyclosporin doses remained unchanged throughout the study. Over one steady-state dosing interval at the end of each study period, whole blood cyclosporin pharmacokinetic profiles were assessed in parallel with endogenous creatinine clearances over sequential 1- to 2-h intervals. The rate and extent of cyclosporin absorption were significantly greater (P < 0.01) from the microemulsion formulation with average increases of 73% in peak concentration and 44% in area under the curve compared to the market formulation. Sequential creatinine clearances exhibited a transient decrease with the nadir occurring on average between 4 and 6 h post dose followed by a rapid return to baseline. Specifically in period I on the market formulation, clearances decreased from a baseline of 71.7 +/- 20.6 to a minimum of 51.1 +/- 17.9 ml/min per 1.73 m2 (similar values in period III) and from 76.8 +/- 24.8 to 53.5 +/- 17.5 ml/min 1.73 m2 in period II on the microemulsion. Neither the baseline nor minimum clearances were significantly different among the study periods.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclosporine pharmacokinetics and variability from a microemulsion formulation--a multicenter investigation in kidney transplant patients.

The steady-state pharmacokinetics and tolerability of a microemulsion formulation of cyclosporine (Sandimmune Neoral) were compared with the commercial formulation (Sandimmune) in 55 clinically stable renal allograft recipients. In study period I (2 weeks' duration), patients entered the study on a stable, individualized twice-daily dosage regimen of the commercial formulation. In period II (2 weeks), they were changed over to the microemulsion formulation at the same dose as at study entry. In period III (2 weeks), dose titration was subsequently allowed if necessary to provide comparable steady-state trough concentrations as at study entry. The commercial formulation was reinstituted during period IV (2 weeks). Safety and tolerability were assessed at weekly clinic visits, and the steady-state pharmacokinetics of cyclosporine in whole blood were characterized at the end of each study period. A milligram-to-milligram dose conversion was adequate when making the initial change between formulations in order to maintain steady-state trough concentrations in the target therapeutic range. Concomitant with this conversion, the steady-state peak concentration and area under the curve increased on average by 59% and 30%, respectively, due to absorption-related differences between the formulations. These increases were not associated with an increase in adverse experiences or changes in blood pressure or clinical laboratory parameters over the first four weeks after the change-over. Trough concentrations were more stable and were more strongly correlated with systemic exposure (area under the curve) during treatment with the microemulsion formulation. Intraindividual coefficients of variation in steady-state peak concentration, time to attain the peak, area under the curve, and percent peak-trough fluctuation ranged from 18% to 74% from the commercial formulation. Variability from the microemulsion formulation was significantly less, ranging from 10% to 22%.

Within-day consistency in cyclosporine pharmacokinetics from a microemulsion formulation in renal transplant patients.

A new microemulsion formulation of cyclosporine (Sandimmune Neoral) was compared to the commercially available formulation (Sandimmune) in 11 stable renal transplant patients with regard to the consistency in cyclosporine pharmacokinetics between a daytime fasting, and a nighttime nonfasting administration. Daily cyclosporine doses were individualized and administered in equal, divided doses every 12 h as soft gelatin capsules; doses were kept constant throughout the study. Serial blood samples were obtained over a 24-h period (two consecutive dosing intervals) at steady-state for each formulation, and cyclosporine concentrations were determined in whole blood by a specific radioimmunoassay method. Within-formulation consistency in pharmacokinetic parameters between the daytime and nighttime administrations was assessed in terms of bioequivalence criteria. Following the mg-to-mg conversion from the commercial to the microemulsion formulation, area under the curve (AUC) was increased on average by 30% due to absorption-related pharmacokinetic differences, while trough concentrations remained in the therapeutic range. Within each formulation, AUC was bioequivalent when comparing the daytime fasting to the nighttime nonfasting administration. For the commercial formulation, however, there was considerable variation in absorption rate, dampening of peak-trough fluctuation, and elevation of trough concentration following the nighttime nonfasting dose. By contrast, the microemulsion exhibited a more stable concentration-time profile over the two dosing intervals, with bioequivalence in peak-trough fluctuation and trough concentrations. Hence, the steady-state pharmacokinetics of cyclosporine from the microemulsion formulation exhibit greater within-day consistency compared to the commercial formulation in stable renal allograft recipients.

Pharmacokinetics and tolerability of a microemulsion formulation of cyclosporine in renal allograft recipients--a concentration-controlled comparison with the commercial formulation.

The steady-state pharmacokinetics and tolerability of a microemulsion formulation of cyclosporine (Sandimmune Neoral) were compared with Sandimmune in 18 clinically stable renal allograft recipients. In study period I (2 weeks duration), patients entered the study on a stable, individualized twice-daily dosage regimen of Sandimmune. Two approaches were assessed for changing patients over from Sandimmune to Sandimmune Neoral. In period II (2 weeks), doses were converted based on the area under the curve ratio derived from a relative bioavailability study comparing the two formulations in healthy volunteers. In period III (2 weeks), doses were titrated to provide comparable steady-state trough concentrations as at study entry. Sandimmune was reinstituted during period IV (2 weeks). Safety and tolerability were assessed at weekly clinic visits and the steady-state pharmacokinetics of cyclosporine in whole blood were characterized at the end of each study period. Dose conversion in period II based on the AUC ratio derived from healthy volunteers was inadequate for achieving comparable cyclosporine exposure as assessed by steady-state AUC and troughs. The concentration-controlled approach (period III) indicated that maintaining the same cyclosporine dose when changing between formulations yields comparable steady-state trough concentrations. Concomitant with this conversion, steady-state peak concentration and AUC increased on average by 39% and 15%, respectively, due to absorption-related differences between the formulations. These increases were not associated with adverse events or changes in blood pressure or clinical laboratory parameters. Furthermore, they were not detrimental to the transplanted kidney as monitored by ultrasound examination. The pharmacokinetic profiles from Sandimmune Neoral exhibited less variability and yielded a stronger correlation between trough concentration and systemic exposure (AUC) compared with Sandimmune.

Reduced inter- and intraindividual variability in cyclosporine pharmacokinetics from a microemulsion formulation.

The inter- and intraindividual variability of cyclosporine pharmacokinetics from a microemulsion formulation were compared with the currently marketed formulation in a sequential bioreplication study. Twenty-four healthy male volunteers were randomized to receive each formulation on two separate occasions; the reference treatment was a single oral dose of 300 mg of Sandimmune and the test treatment was a single oral dose of 180 mg of Sandimmune Neoral, both given as soft gelatin capsules. Serial venous blood samples were obtained over a period of 48 h after each administration, and cyclosporine concentrations were measured in whole blood by a specific monoclonal RIA method. Between- and within-subject variabilities were quantified from the appropriate sums of squares from analysis of variance and statistically compared between formulations. Both inter- and intraindividual variation for the peak concentration, time to reach the peak, area under the curve, and terminal half-life of the test formulation were significantly reduced (p < 0.05) with two exceptions. For area under the curve between subjects (p < 0.2) and peak concentration within subjects (p < 0.1), trends toward reduced variability for the test formulation were evident. These results were further reflected in the inter- and intraindividual coefficients of variation of the pharmacokinetic parameters that ranged from 3 to 22% for the test formulation compared with 19 to 41% for the reference formulation. In comparison with the currently marketed formulation, reduced variability in the pharmacokinetics of cyclosporine following oral administration of Sandimmune Neoral provides a more predictable and consistent concentration-time profile.

Improved dose linearity of cyclosporine pharmacokinetics from a microemulsion formulation.

The pharmacokinetic dose proportionality and relative bioavailability of cyclosporine from a microemulsion formulation (Sandimmune Neoral) were compared to those of the commercial formulation (Sandimmune) over the dosage range 200 to 800 mg. Single oral administrations were given as soft gelatin capsules in an open randomized study with 48 healthy volunteers. Whole-blood cyclosporine concentrations were determined by a specific monoclonal radioimmunoassay. In comparison to Sandimmune, the absorption rate (maximum concentration) and systemic availability (area under the curve) of cyclosporine were greater for Sandimmune Neoral at all dose levels investigated. The area under the curve for Sandimmune increased in a less than proportional manner with respect to dose, whereas that for Sandimmune Neoral was consistent with linear pharmacokinetics. Because of this difference, no global assessment of relative bioavailability could be performed. The relative bioavailability of cyclosporine from Sandimmune Neoral ranged from 174 to 239% compared to Sandimmune, depending on the dose level. The improvements in oral bioavailability and dose linearity of cyclosporine exposure after administration as Sandimmune Neoral should facilitate more accurate dosage titration in the clinical setting.

Safety and steady-state pharmacokinetics of a new oral formulation of cyclosporin A in renal transplant patients.

The steady-state pharmacokinetics of a new oral formulation of cyclosporin A (Sandimmun Neoral, NOF, a microemulsion) was compared with those of the market formulation (Sandimmun, SIM) in stable renal transplant patients. Both formulations were administered as soft gelatin capsules every 12 h with doses adjusted to provide comparable trough concentrations (CminSS). Whole blood samples were obtained over a steady-state dosing interval (tau), and the cyclosporin A level was determined by a specific monoclonal RIA. Both formulations were well tolerated. The mean doses were 139 +/- 27 mg (SIM) vs. 120 +/- 19 mg (NOF), indicating a milligram dose-conversion factor of approximately 1:1 to yield comparable troughs. NOF exhibited a stronger correlation between AUCtauSS and CminSS (r2 = 0.821) compared with SIM (r2 = 0.288), due in part to less variability in the NOF profiles. Average increases of 39% in CmaxSS and 15% in AUCtauSS during treatment with NOF were not associated with any safety concerns over the 4-week exposure to Sandimmun Neoral, as evidenced by the absence of changes in blood pressure, hematologic and biochemical parameters (including serum creatinine and blood urea nitrogen, BUN) and ultrasound of the transplanted kidney.

Influence of a fat-rich meal on the pharmacokinetics of a new oral formulation of cyclosporine in a crossover comparison with the market formulation.

The influence of a fat-rich meal on the pharmacokinetics of cyclosporine from a new oral formulation (Sandimmune Neoral) was compared in a randomized, four-way crossover study to the currently marketed formulation (Sandimmune) in 24 healthy male volunteers. Single oral doses of 300 mg Sandimmune and 180 mg Sandimmune Neoral were each administered once under fasting conditions and once 30 min after starting a high-fat meal. Serial blood samples were obtained over a 48-hr period after each administration, and whole-blood cyclosporine concentrations were determined by a specific monoclonal radioimmunoassay method. Food had a marked effect on cyclosporine absorption from Sandimmune manifested by a nearly doubled time to reach the peak concentration and a 37% increase in the area under the curve. This was associated with significant elevations in subsequent whole-blood cyclosporine concentrations compared to the fasting administration. For Sandimmune Neoral the influence was less pronounced. The maximum concentration was decreased by 26%, without a relevant change in the time to reach the peak; the area under the curve showed a slight reduction of 15%. The relatively minor influence of a fat-rich meal on the absorption of cyclosporine from Sandimmune Neoral is advantageous when individualizing a dosage regimen under clinical and outpatient administration conditions.

Drug transport across the blood-brain barrier. III. Mechanisms and methods to improve drug delivery to the central nervous system.

This is the third part of a review on the transport of drugs across the blood-brain barrier. In the first two parts, the anatomical and physiological aspects and the various techniques that can be used to study blood-brain transport have been discussed and reviewed. This third part focuses specifically on the mechanisms that are involved in drug transport across the blood-brain barrier. In addition, the opportunities to improve drug transport into the brain will be reviewed. Emphasis is on the transport of peptides.

Drug transport across the blood-brain barrier. II. Experimental techniques to study drug transport.

This is part II of a review on the transport of drugs across the blood-brain barrier. In this part, the emphasis is on the various experimental techniques that can be used to characterize the blood-brain barrier transport of drugs. Generally speaking, three approaches can be distinguished: in vitro techniques using isolated brain capillaries, cerebrovascular endothelial cells in primary culture or endothelium-derived cell lines; in vivo techniques (both single-passage and multi-passage techniques) and in situ perfusion techniques. Each of these techniques has specific advantages and disadvantages associated with it. Therefore, in many instances, a combination of different approaches is needed to study the fundamental aspects of drug transport across the blood-brain barrier.

Drug transport across the blood--brain barrier. I. Anatomical and physiological aspects.

This review describes various aspects of the transport of drugs across the blood-brain barrier and comprises three parts. In this first part, the anatomical and physiological aspects of blood-brain transport are discussed. It appears that the blood-brain barrier has an anatomical basis at the endothelium of the capillary wall. This endothelium is characterized by the presence of very tight junctions. As a result, the transport by passive diffusion of drugs with a low lipophilicity, is restricted. For certain classes of closely related relatively hydrophilic compounds, however, the presence of specialized carrier systems has been demonstrated which may facilitate transport. Also evidence is presently available, that the permeability of the blood-brain barrier may be under active regulatory control. It is expected that improved knowledge of the anatomical and physiological aspects of the blood-brain barrier and its regulation will provide a scientific basis for the development of strategies to improve the transport of drugs into the central nervous system.

In vitro penetration of des-tyrosine1-D-phenylalanine3-beta-casomorphin across the blood-brain barrier.

The blood-brain barrier transport and metabolism of the synthetic beta-casomorphin (beta CM) derivative des-tyrosine1-D-phenylalanine3-beta-casomorphin (DT-D-Phe3-beta CM) were investigated using an in vitro model consisting of primary cultures of bovine cerebrovascular endothelial cells. DT-D-Phe3-beta CM was transported across the endothelial monolayer without significant metabolism. The endothelial permeability expressing the transport rate ranged between 1.4 and 2.2 cm x 10(-3)/min and was neither affected by luminal concentration changes (1 nM and 1 microM) nor different after luminal and abluminal administration. The metabolic inhibitor 2-desoxy-D-glucose did not affect the permeability of DT-D-Phe3-beta CM. These results suggest that DT-D-Phe3-beta CM is able to cross the blood-brain barrier by paracellular transport without using a carrier system.

Stereoselective transport of baclofen across the blood-brain barrier in rats as determined by the unit impulse response methodology.

The blood-brain barrier transport characteristics of racemic baclofen and the separate R- and S-enantiomers have been determined in vivo in rats by using the unit impulse response methodology. Transport rate was determined as blood-brain barrier clearance, the volume of plasma per unit time cleared of baclofen by transport across the blood-brain barrier. Plasma elimination kinetics and CSF elimination kinetics did not differ among racemic baclofen and the R- and S-enantiomers. Transport of each compound could be described by a linear V(t) curve, suggesting the absence of saturable transport processes in the concentration range studied. However, for R-baclofen the blood-brain barrier clearance (4.7 +/- 1.0 microliters/min, mean +/- SE; n = 6) and cumulative transported amount (0.085 +/- 0.007%; n = 6) were significantly higher than these values for the S-enantiomer (1.1 +/- 0.3 microliters/min, 0.031 +/- 0.005%; n = 6) and racemic baclofen (1.0 +/- 0.1 microliters/min, 0.036 +/- 0.003%; n = 6). These findings indicate that there is stereoselective transport of baclofen across the blood-brain barrier.

Development of specific antisera against 9-desglycinamide-8-arginine vasopressin by site-specific immunization.

Four specific and sensitive antisera against 9-desglycinamide-8-arginine vasopressin (DGAVP) were obtained by means of site-specific immunization in rabbits, using a Keyhole Limpet haemocyanin-DGAVP conjugate synthesized by a specific reaction of a thiol function with a maleimide group. Compared with conventionally raised antisera, the cross-reactivity with endogenous arginine vasopressin (AVP) and vasopressin-derived fragments was substantially lower. Interassay variability was 18.1% at maximum. Possible applicability of the new antisera in pharmacokinetic studies of DGAVP with respect to blood-brain barrier transport was tested by means of a pilot study in the rat.

Transport of desglycinamide-arginine vasopressin across the blood-brain barrier in rats as evaluated by the unit impulse response methodology.

The pharmacokinetic characteristics of desglycinamide-arginine vasopressin (DGAVP) with respect to its transport across the blood-brain barrier (BBB) were studied with the use of serial CSF sampling in an individual animal and the unit impulse response methodology. Transport rate is determined as BBB clearance, the volume of plasma per unit time cleared of the peptide by BBB transport, and the extent of transport as the percentage of the administered dose transported into the central nervous system. Plasma kinetics of DGAVP were shown to be linear within the dose range studied (50-150 micrograms), plasma mean residence time (MRT) being 18 +/- 4 min (mean +/- SE; n = 9). Elimination of DGAVP from CSF after icv administration was linear, with an MRT of 10 +/- 1 min (n = 9). After iv administration of 100 micrograms DGAVP, CSF concentrations were detectable for 90 min. Transport from plasma to the central nervous system was linear. The BBB transport clearance value was 1.0 +/- 0.3 microliters/min, and 0.026 +/- 0.007% of the administered dose was transported into the central nervous system. Results demonstrate that, within the concentration range studied, DGAVP is transported across the BBB by passive diffusion, although to a very low extent.

Rectal absorption enhancement of cefoxitin and desglycinamide arginine vasopressin by sodium tauro-24,25-dihydrofusidate in conscious rats.

The effects of sodium tauro-24,25-dihydrofusidate (STDHF), an enhancer of nasal insulin absorption, on the rectal absorption of cefoxitin and desglycinamide arginine vasopressin (DGAVP) were evaluated in the rat. Cefoxitin and DGAVP proved to be poorly absorbed rectally without STDHF, but their bioavailability was considerably increased by STDHF in concentrations of 0.15 to 8% w/v. Both rectal infusion and rectal bolus delivery resulted in complete cefoxitin absorption at 4% w/v of STDHF. Delivery rate appeared to be an important factor in the effect of 4% w/v of STDHF on DGAVP bioavailability; on infusion a mean DGAVP bioavailability (+/- S.D.) of 47 +/- 12% was obtained, whereas after bolus delivery it amounted to 27 +/- 6%. For both compounds the effect of STDHF was significant at 0.5% w/v. It is concluded that STDHF is capable of actively enhancing the rectal absorption of poorly absorbed drugs, including small peptides.

The unit impulse response procedure for the pharmacokinetic evaluation of drug entry into the central nervous system.

The unit impulse response theory has been adapted to characterize the transport profile of drugs into the central nervous system (CNS). From the obtained input function, the cumulative plasma volume (V) cleared by transport into the CNS in time can be calculated. Simulation studies demonstrated that transport governed by passive diffusion resulted in a linear relationship between V and time, while the slope of the line, the blood-brain barrier (BBB) clearance, proved to be an adequate and model independent parameter to characterize drug transport into the CNS. The error in the result of the numerical procedure could be limited to less than 10% of the theoretically predicted value. Superposition of 5 or 10% random noise on simulated data did not result in significant differences between the calculated and theoretically predicted clearance values. Simulations of carrier-mediated transport resulted in nonlinear transport curves; the degree of nonlinearity, and thus the detectability, was dependent on the initial degree of saturation of the system, the rate of desaturation, as caused by drug elimination processes and the noise level on the data. In vivo experiments in the rat were performed, using atenolol, acetaminophen, and antipyrine as model drugs. Linear transport relationships were obtained for all drugs, indicating that transport was dependent on passive diffusion or a low affinity carrier system. BBB-clearance values were 7 +/- 1 microliters/min for atenolol, 63 +/- 7 microliters/min for acetaminophen and 316 +/- 25 microliters/min for antipyrine. These experiments validate the applicability of the presented technique in in vivo studies.