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.

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.

Area-under-the-curve versus trough level monitoring of cyclosporine concentration: critical assessment of dosage adjustment practices and measurement of clinical outcome

Cyclosporine (CsA) immunosuppressive therapy is confounded by a narrow therapeutic window and large intersubject variability. Trough-level monitoring cannot prevent the frequent occurrence of toxic side effects and graft rejection. Area-under-the-curve (AUC) monitoring affords better control of exposure of an individual patient to CsA, which is compensated for by a moderate increase in the number of blood samples. A linear pharmacokinetic model for CsA dosage adjustment using AUC measurements as feedback information decreased the incidence of delayed graft loss during the first month. This strategy failed, however, to lower the frequency of acute graft rejection despite a significant relationship between the probability of rejection and exposure to CsA (measured as average steady-state concentration). A nonlinear Michaelis-Menten model describes the relationship between oral dose rate and average steady-state concentration better than does a linear clearance model. Clinical utility of the nonlinear model remains to be proven.

Adrenochrome reaction implicates oxygen radicals in metabolism of cyclosporine A and FK-506 in rat and human liver microsomes

The role of oxygen radicals in the metabolism of cyclosporine A (CyA), FR900506 (FK-506) and carbon tetrachloride (CCl4) catalyzed by the cytochrome P450 system was investigated in vitro in rat and human microsomal preparations. Varying concentrations of CyA, FK-506 and CCl4 (100 microM-1.0 mM) were added to microsomal preparations, and lipid peroxidation was measured by malondialdehyde (MDA) formation as detected by the thiobarbituric acid assay. The effects of oxygen radical scavengers [superoxide dismutase (SOD) and catalase (CAT)] and an antioxidant [glutathione (GLUT)] were tested on various incubations of CyA, FK-506 and CCl4 to assess the role of oxygen radicals in lipid peroxidation. CyA-dependent MDA formation was moderately inhibited by SOD in the rat model and increased by SOD in the human model. In both models, CAT slightly inhibited CyA-dependent MDA formation and GLUT significantly inhibited MDA formation. FK-506-dependent MDA formation, studied only in the rat model, paralleled CyA-induced MDA formation but showed greater inhibition with CAT and less inhibition with SOD or GLUT. In both models, CCl4-dependent MDA formation was significantly inhibited by GLUT and showed no sensitivity to SOD or CAT. In addition, the adrenochrome reaction, which measures the oxidation of epinephrine to adrenochrome, was used to measure the increased oxygen radical-flux resulting from the metabolism of CyA, FK-506 and CCl4. CyA with epinephrine showed the highest oxidative activity, followed by FK-506 and then CCl4, which showed the least formation of adrenochrome. These results indicated a role for oxygen radicals in CyA and FK-506 metabolism.

Michaelis-Menten kinetics determine cyclosporine steady-state concentrations: a population analysis in kidney transplant patients

Dosage adjustments of cyclosporine are confounded with an unexpected degree of variability, thus invalidating a direct proportionality between the oral dose rate and the steady-state concentration. In 1033 observations of dose rate and average steady-state concentration collected during therapeutic monitoring (area under the curve method) in 134 adult kidney transplant patients, a population pharmacokinetic analysis showed that a Michaelis-Menten model fitted the data better than a linear clearance model. It was further shown that the Michaelis-Menten constant (Km) parameter of the Michaelis-Menten model (the average steady-state concentration at half-maximal dose rate) increased during the first 4 months after transplantation whereas the maximal dose rate of the Michaelis-Menten model (Vmax) remained constant. The following parameters with interindividual variation in parenthesis were estimated: Vmax = 852 mg/24 hr (43%) and Km at 114 days after transplantation = 349 ng/ml (117%). An algorithm was derived from this population model that guides the clinician during the adjustment of oral cyclosporine dose rates.

Generation of oxygen free radicals during the metabolism of cyclosporine A: a cause-effect relationship with metabolism inhibition

A better understanding of the mechanism of lipid peroxidation during the metabolism of cyclosporine A (CsA) might help explain the toxicities of this immunosuppressive drug on various organs. Our in vitro work used microsomes prepared from livers of phenobarbital-induced male rats. The incubations (total volume 1ml) also contained a NADPH regenerating system and substrate (i.e., CsA, carbon tetrachloride, or aminopyrine) dissolved in ethanol. Lipid peroxidation was inferred from the presence of malondialdehyde (MDA) which was detected by the thiobarbituric acid assay. The formation of CsA hydroxylated metabolites (AM9 and AM1) was monitored by liquid chromatography. The activity of the microsomal incubation was confirmed by measurements of MDA and formaldehyde production caused by increasing concentrations of CsA, carbon tetrachloride, and aminopyrine. The occurrence of hydroxylated metabolites was not coupled to the production of MDA. Aminopyrine could inhibit MDA production by CsA, but CsA could not reduce the formation of formaldehyde by aminopyrine. Erythromycin, a competitor for the binding site of CsA on cytochrome P450, reduced MDA production by CsA, and CsA inhibited formaldehyde production by erythromycin. Interaction studies with SKF 525A, ketoconazole, superoxide dismutase, catalase, alpha-tocopherol, and reduced glutathione confirmed the role of cytochrome P450 and the presence of activated oxygen species as a source of microsomal peroxidation which in return may explain the inhibitory effect of CsA on cytochrome P450 itself.

Optimisation of immunosuppressive therapy using pharmacokinetic principles

Clinical experience with immunosuppressive therapy is more extensive in the area of preventing the rejection of transplanted organs than in the treatment of autoimmune diseases. Among the many pharmacological agents presently in use, only prednisone (or methylprednisolone) and cyclosporin require dosage individualisation. Sources of interindividual variability in the pharmacokinetics of prednisone have been identified and are guiding the selection of individual dosage rates. As an alternative, a single timed concentration can determine an apparent value for prednisone clearance from which an individual dosage can be calculated. In contrast, numerous sources of inter- and intraindividual variability in cyclosporin pharmacokinetics prevent the easy selection of safe and effective starting dose rates. Indeed, test doses of cyclosporin followed by series of blood samples and the calculation of individual pharmacokinetic parameters are needed to assure successful immunosuppression right from the start. Furthermore, only continued monitoring sustains immunotherapy vis-à-vis intraindividual variability and a narrow therapeutic range of cyclosporin concentrations.

Pharmacokinetic strategies for cyclosporin therapy in organ transplantation

Marked interindividual variations in cyclosporin (CsA) produce disparate clinical results in organ transplant recipients. In an attempt to eliminate marked deviations of insufficient or excessive CsA concentrations consequent to the administration of uniform drug doses, test dose pharmacokinetics were performed on each potential organ transplant candidate. An intravenous 3 mg/kg test dose delivered over 3 h proved to be readily performed, namely 53% perfect studies, and relatively reliable, namely 73% of observed concentrations within 10% of the predicted values. Furthermore, the use of CsA doses predicted by pretransplant studies reduces the incidence of delayed graft function, early rejection episodes and transplant loss. The oral test dose study predicted a suitable amount of CsA to achieve sufficient gastrointestinal absorption but was less accurate than the iv prediction method: namely, 40% of observed post-transplant concentrations were within 10% of the predicted target value. Furthermore, patients who received oral doses predicted by the test dose strategy showed no improvement in the incidence of acute rejection episodes between 7 and 60 days, and only modestly improved serum creatinine values. The lower accuracy of predictions from oral test dose studies may reflect the impact of non-linear oral (as opposed to iv) drug pharmacokinetics, of variable diet, and/or of altered postoperative gastrointestinal function.

The ability of pretransplant test-dose pharmacokinetic profiles to reduce early adverse events after renal transplantation

Pretransplant test-dose pharmacokinetic profiles were used to determine individual cyclosporine drug bioavailability and clearance rates in renal transplant patients. Assuming a linear relation between dose and area under the concentration curve (AUC), starting i.v. and p.o. CsA doses were computed from the test-dose results. Target values were 400 ng/ml steady-state concentration (Css) during continuous intravenous infusion, and 500 ng/ml average drug concentration (Cavss = AUC/dosing interval) after oral administration, based upon measurements with the specific monoclonal antibody 3H-tracer radioimmunoassay. The outcomes after dose individualization with a 1-(n = 32), 2-(n = 38), or 3-(n = 41) hr i.v. infusion test dose and a p.o. test dose (n = 111) were compared with 228 historical control patients who received a uniform protocol of CsA i.v. at 2.5 mg/kg/day and p.o. at 14 mg/kg/day. The observed Css after i.v. CsA was within 10% of the target concentration in 73% of recipients tested with the 3-hr protocol, a significantly greater fraction than achieved with either the uniform dose (14%), or the 1-(34%) and 2-(25%) hr protocols. Patients in the 3-hr protocol group showed reduced incidences of delayed graft function, early graft loss, and rejection episodes, and a lower mean serum creatinine value, particularly at 7 but also at 30 days posttransplantation. Administration of the predicted oral dose produced a peak concentration of greater than or equal to 700 ng/ml drug absorption in 60% of recipients at 3 days, 90% at 5 days, and 98% at 7 days. The test-dose method less effectively predicted the appropriate oral CsA dose to produce target Cssav and failed to reduce the 90-day rejection incidence. Despite its limitations with the more-complicated p.o. route, the test-dose method successfully predicts i.v. CsA doses, thereby reducing the incidence of early adverse events.

Abbreviated kinetic profiles in area-under-the-curve monitoring of cyclosporine therapy

Abbreviated kinetic profiles can reduce the number of phlebotomies and drug assays, and thereby the cost of area-under-the-curve (AUC) monitoring. In the present investigation, we used two independent data sets: group 1, 101 AUC profiles from 77 stable renal-transplant patients, which included a 5-h sample in addition to the usual 0-, 2-, 4-, 6-, 10-, 14-, and 24-h samples; and group 2, 100 profiles from 50 stable renal-transplant patients before and after a change in their daily oral dose of cyclosporine. Group I demonstrated a fair correlation between cyclosporine trough concentrations and the AUC calculated from a complete set of seven concentrations (r2 = 0.820 and 0.758 for the 24- and 0-h samples, respectively). Stepwise multiple linear-regression analysis revealed that the abbreviated set of three time points (2, 6, and 14 h) explained 96% of the variance in AUC values calculated from the full set of seven samples; additional time points increased the accuracy only slightly. For group 2, we examined the difference between the observed and the predicted concentrations by linear extrapolation; the error in the observed AUC value, compared with the predicted value calculated from seven time points (-13.2% to -1.2%), was similar to the error from just three time points (-11.5% to 4.5%). Abbreviated AUC profiles involving three time points used with a model equation seem to provide a reliable alternative to full seven-point profiles.

Abbreviated kinetic profiles in area-under-the-curve monitoring of cyclosporine therapy

Abbreviated kinetic profiles can reduce the number of phlebotomies and drug assays, and thereby the cost of area-under-the-curve (AUC) monitoring. In the present investigation, we used two independent data sets: group 1, 101 AUC profiles from 77 stable renal-transplant patients, which included a 5-h sample in addition to the usual 0-, 2-, 4-, 6-, 10-, 14-, and 24-h samples; and group 2, 100 profiles from 50 stable renal-transplant patients before and after a change in their daily oral dose of cyclosporine. Group I demonstrated a fair correlation between cyclosporine trough concentrations and the AUC calculated from a complete set of seven concentrations (r2 = 0.820 and 0.758 for the 24- and 0-h samples, respectively). Stepwise multiple linear-regression analysis revealed that the abbreviated set of three time points (2, 6, and 14 h) explained 96% of the variance in AUC values calculated from the full set of seven samples; additional time points increased the accuracy only slightly. For group 2, we examined the difference between the observed and the predicted concentrations by linear extrapolation; the error in the observed AUC value, compared with the predicted value calculated from seven time points (-13.2% to -1.2%), was similar to the error from just three time points (-11.5% to 4.5%). Abbreviated AUC profiles involving three time points used with a model equation seem to provide a reliable alternative to full seven-point profiles.

Cyclosporine pharmacokinetics in liver transplant recipients: evaluation of results using both polyclonal radioimmunoassay and liquid chromatographic analysis

Pharmacokinetic variables were derived from cyclosporine measurements using liquid chromatography (HPLC) and radioimmunoassay with a non-selective polyclonal antibody (PARIA) in 11 orthotopic liver transplant recipients studied in paired oral and intravenous studies both before and after permanent clamping of the biliary T-tube. After oral drug administration, mean areas under blood cyclosporine concentration versus time curves before clamping were around 5.2-fold greater by PARIA than HPLC but 2.9-fold greater after clamping and closer to comparable values after intravenous cyclosporine (2.5 and 2.3-fold, respectively). Cyclosporine clearance was smaller by PARIA than HPLC (mean 7.3 versus 3.3 ml.min-1.kg-1, respectively, before clamping). Both values decreased by 25% after clamping (to 5.5 and 2.4 ml.min-1.kg-1, respectively), although there was no significant change in distribution or elimination half-lives (around 0.5 and 8 h, respectively). The mean bioavailability of oral cyclosporine increased significantly after clamping in 9 patients (from 10.6% to 28.1% by HPLC and from 14.8 to 35.1% by PARIA) but in two patients who developed the vanishing bile duct syndrome values fell to less than 10% and the proportional overestimation of cyclosporine concentrations by PARIA increased. Clamping had no singificant effect on the mean apparent volumes of distribution but values of Vz were approximately twice those of Vss (around 2.6 and 1.31.kg-1 by PARIA and HPLC respectively). Mean half lives after clamping were shorter following oral than intravenous cyclosporine (t 1/2 lambda 2 around 15 h enterally versus 8 h parenterally).(ABSTRACT TRUNCATED AT 250 WORDS)

Area under the curve monitoring of cyclosporine therapy: the early posttransplant period

The impact of a new monitoring strategy on whole blood concentrations of cyclosporine measured by a specific monoclonal radioimmunoassay was investigated in a group of 37 renal transplant patients. Before transplantation, the patients received a standard intravenous (i.v.) and oral (p.o.) test dose of cyclosporine to calculate their individual i.v. and p.o. starting dose rates to achieve a certain target steady-state cyclosporine concentration. After transplantation, the designated i.v. dose rate was continuously infused for 2 days, at which time the steady-state concentration was measured. Then, the designated oral dose for 24 h was administered while the infusion was continued at an unaltered rate. The oral absorption of cyclosporine was documented by blood samples over the following 8 h. If necessary, this overlap of i.v. and p.o. dosing was repeated until blood concentrations of cyclosporine rose at least 700 ng/ml over the steady-state concentration. By that time, the infusion was stopped and oral dosing continued. Individualized infusions led to steady-state concentrations within a range that did not exceed 1.1 times the median concentration of 472 ng/ml. Standard infusion rates in the past produced a much wider range of steady-state concentrations (9.6 times the median). Individualized infusions reached the target steady-state concentration with a significant positive bias of 17% (SEM = +/- 32%, range of -36 to +105%). Individualized oral doses reached the target average steady-state concentration (calculated by dividing the area under the concentration-time curve by the dosing interval) with an inferior precision (median = 2.6%, range of -54 to +130%) but without a positive or negative bias.(ABSTRACT TRUNCATED AT 250 WORDS)

Preemptive transplantation--an analysis of benefits and hazards in 85 cases

The benefit of transplantation without prior dialysis might be contravened by the failure to develop possible immunologic disabilities associated with chronic uremia and dialysis. This study compares graft and patient outcome, cyclosporine toxicity, pharmacokinetics, rejection episodes, nutritional status, and social and vocational rehabilitation between a preemptive group of 85 patients transplanted without prior dialysis and a cohort of 84 demographically, temporally, and disease-matched recipients of renal transplants after a minimum of 6 months' chronic dialysis therapy. The groups were matched for donor type, gender, and age, as well as immunologic risk factors of HLA-mismatch and percent panel-reactive antibody. All patients received CsA and prednisone immunosuppression. There were only two differences between the cohorts. The preemptive group included more diabetic patients: 32 versus 15 (P less than 0.01). The control cohort included more recipients who had received any pretransplant transfusion: 55 versus 28 (P less than 0.001). Both of these factors (if having any impact) would be expected to reduce graft survival in the preemptive group. All patients in the study had a minimum follow-up of 1 year and over half of the recipients are beyond 40 months. The preemptive patients showed survival rates of 94, 93, and 91 percent at 1, 2, and 5 years. These rates were not significantly different from those of the control group, namely 96, 96, and 93 percent, respectively. The actuarial graft survival rates in the preemptive group of 83, 81, 76, 73, and 73 percent at 1, 2, 3, 4, and 5 years were not statistically different from the control group rates, namely 90, 81, 80, 77, and 76 percent. Preoperative blood transfusion or percent positive panel-reactive antibodies had no effect on postoperative outcome in either group. The incidence of CsA nephrotoxicity was 9.4 percent in the preemptive group, which was not statistically different from the 17.9 percent in the control group. The incidence of rejection episodes in the absence of patient noncompliance was comparable between the groups. Seven of the irreversible rejection episodes in the preemptive group were due to noncompliance, compared with none in the control group (P less than 0.001). Preemptive recipients were also more likely than control group patients to be employed fulltime both before transplantation (36 vs. 22, P less than 0.05) as well as after transplantation (38 vs. 20, P less than 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)

Prediction of acute graft rejection in renal transplantation: the utility of cyclosporine blood concentrations

While cyclosporine is recommended to be used only in conjunction with monitoring of its blood concentrations, the utility of these measurements in preventing treatment failure is not established. In a group of 52 patients trough levels and steady-state concentrations were monitored in serum and whole blood by specific (SP) and nonspecific (NS) assays (polyclonal radioimmunoassay, PR; fluorescence polarization immunoassay, FP; high-pressure liquid chromatography, HP). From as many as 10 determinations of trough level and steady state concentrations during the first 40 days after renal transplantation, the lowest measurement was selected. In the case of an acute rejection episode within that time period, only values until that event were considered. Trough level measurements in serum by PR/NS and by FP/NS and in whole blood by HP/SP were not significantly different between patients with and patients without rejection episodes. However, simultaneously measured steady-state values (serum/PR/NS and serum/FP/NS) were significantly lower in patients suffering from rejection (with rejection SS/serum/PR/NS mean = 127 ng/ml, SD = 41 ng/ml; without rejection mean = 163 ng/ml, SD = 60 ng/ml; P = 0.027, t test). This difference could not be demonstrated for steady state/whole blood/HP/SP measurements. A logistic regression analysis demonstrated that the probability of rejection can be decreased by up to 40% if steady state/serum/PR/NS or steady state/serum/FP/NS values never drop below 250 ng/ml early after renal transplantation.

Consensus document: Hawk's Cay meeting on therapeutic drug monitoring of cyclosporine

The optimal measurement method and clinical application of the therapeutic drug monitoring of cyclosporine remain uncertain. At a workshop held at Hawk's Cay, FL, from January 14 to January 17, 1990, 57 scientists presented their latest research findings, either in formal papers or as discussants. Lively debate and discussion followed presentation of extant and new methodologies for drug measurements as well as multicenter validation studies: applications of trough-concentration monitoring in renal, hepatic, and bone-marrow transplants as well as in autoimmune disease; and alternative pharmacokinetic approaches to guide cyclosporine therapy. The process of inducing and maintaining optimal immunosuppression to facilitate graft success is a complex and often challenging task, requiring the combined expertise of multiple disciplines. Thus, the assembly of four of the groups essential to the transplant process--clinicians, laboratory scientists, the pharmaceutical company, and the manufacturers of cyclosporine measurement kits--provided a unique opportunity to evaluate therapeutic drug monitoring issues facing the transplant field. Here we present the major conclusions reached at the meeting, brief discussions of the study data on which they are based, and a summary of unresolved problems that will require further rigorous investigations. The Consensus Document was reviewed by all the workshop participants before we submitted this final manuscript.

The impact of steady-state cyclosporine concentrations on renal allograft outcome

It has been reported that initial cyclosporine levels over 400 ng/ml posttransplantation result in an increased incidence of delayed graft function (DGF). Several studies have shown early graft function to be a major determinant for long-term graft survival. Continuous intravenous infusion (CIVI) has been employed to induce immunosuppression establishing therapeutic drug levels while minimizing toxicity in renal allograft recipients. This study examines the impact of the achieved serum CsA steady-state concentration (Css) levels upon transplant outcome in 228 patients given CsA by CIVI. In spite of administration of a specific drug dose, interindividual variation in elimination rates yields a broad range of Css levels. Six groups were stratified by CsA Css levels: group A 0-75 ng/ml, group B 76-100 ng/ml, group C 101-150 ng/ml, group D 151-200 ng/ml, group E 201-250 ng/ml, and group F greater than 250 ng/ml. Group A showed a significantly lower age and greater incidence of rejection at 0-10 days. Group F had significantly higher incidences of nephrotoxicity, hepatotoxicity, and delayed graft function. The findings suggest that the antirejection Css threshold for CsA may be at least 75 ng/ml, and the toxicity threshold above 250 ng/ml. Controversy exists about whether CsA influences the incidence of DGF, therefore risk factors for DGF were examined among the groups stratified by CsA Css levels. While cold ischemia time for all 228 patients as a group was highly correlated with DGF (P less than 0.001), neither cold ischemia time nor donor age was significantly different among the groups. There does appear to be a synergistic effect between CsA Css and CIT, since the incidence of DGF was significantly higher when the cold ischemia time was 21-24 hr and CsA Css greater than 200 ng/ml. Long-term graft function did not appear to be affected by early CsA Css levels. The Css of 100-250 ng/ml appears to achieve a satisfactory outcome with a 19.5% incidence of rejection within 10 days, 29.7% DGF, and 5.1% nephrotoxicity. Only 118/228 patients (52%) in this study achieved that range despite a fixed low CIVI of CsA. Thus potential renal allograft recipients may benefit from a pretransplant pharmacokinetic study to predict the proper CIVI dose.

Lipid abnormalities in cyclosporine-prednisone-treated renal transplant recipients

Hyperlipidemia and hypertension, two major risk factors for accelerated atherosclerosis, undoubtedly contribute to the excessive cardiovascular morbidity and mortality experienced by renal transplant recipients. The present survey of posttransplant hyperlipidemia in 500 cyclosporine-treated patients documented a 37.6% incidence of hypercholesterolemia, which occurred within 6 months posttransplant in 82% of patients. An etiologic relation to corticosteroid therapy was suggested by the strong correlation between prednisone doses and cholesterol levels, by the reduced cholesterol levels in patients undergoing steroid withdrawal, and by the reduction in hypercholesterolemia to 13% by 3 years posttransplant when steroid doses were less than 10 mg daily. Hypertriglyceridemia, which was present in 14.7% of the patients, was more severe under CsA-prednisone compared with azathioprine-prednisone therapy. Hypertriglyceridemia, which occurred later in the posttransplant course than hypercholesterolemia, strongly correlated with an excessive percent relative weight and elevated serum creatinine but not with steroid or CsA doses. Increasing age, diabetes mellitus, beta-blockers and nephrotic syndrome contribute to posttransplant hyperlipidemia in the CsA-Pred era as they did in the azathioprine era of immunosuppression.

Population pharmacokinetic analysis of bisoprolol

The technique of population pharmacokinetic analysis was employed to study the variability in the dose concentration relationship of bisoprolol during its clinical development. The influence of demographic factors on the variability of clearance was investigated in 3 different populations: group I, patients (including an elderly group) with essential hypertension receiving multiple oral doses of bisoprolol 10 or 20mg for 3 months; group II, patients with different degrees of renal impairment and healthy controls; and group III, patients with different types of hepatic impairment and healthy controls. Patients and controls in groups II and III received only a single oral dose of bisoprolol 10mg. The 3 data sets were analysed separately, using a non-linear mixed effects model (the NONMEM program). A 2-compartment pharmacokinetic model with first-order absorption described the data adequately. The typical values of volume of central compartment, volume of distribution at steady-state and the absorption rate constant for the 3 populations were: for group I, 68L, 235L, and 0.7h-1; for group II, 28L, 179L, and 0.3h-1; and for group III, 55L, 256L, and 0.4h-1, respectively. Plasma clearance was related to age in group I, to serum creatinine in group II and to aspartate transaminase activity in group III. The 68% confidence limits for clearance and elimination half-life were 8.2 to 21.5 L/h and 7.6 to 19.7h, respectively, for 50-year-old patients in group I. The analysis predicted that progressive increases in serum creatinine or aspartate transaminase activity will result in only a 50% reduction of clearance.

Influence of demographic factors on cyclosporine pharmacokinetics in adult uremic patients

The causes of variability in cyclosporine (CS) clearance (CL) are mostly unknown. The pharmacokinetics of CS were studied in 30 adult uremic patients after single intravenous and oral doses by analyzing serial concentrations in serum by radioimmunoassay (SR) and in whole blood by radioimmunoassay (WR) and high pressure liquid chromatography (WH). Bioavailability (F) and CL were calculated by noncompartmental models and were significantly different depending upon the assay method except for FSR = FWR: FSR = 43.2 +/- 21.7%; FWR = 43.5 +/- 18.5%; FWH = 36.4 +/- 17.3%; CLSR = 849 +/- 363 ml/min; CLWR = 380 +/- 156 ml/min; CLWH = 559 +/- 174 ml/min. The age of the patients and parameters describing body size such as weight, surface area and percent of ideal weight were not correlated with CL. The height of the patients correlated with CLWH but not CLSR or CLWR. Parameters responsible for CS binding in blood such as cholesterol, triglyceride, hemoglobin concentration or hematocrit did not explain variability in CL. Of the factors indicative of liver function alanine transaminase activity but not aspartate transaminase, lactate dehydrogenase, alkaline phosphatase activity nor total bilirubin concentration in serum was correlated with CL. F was not correlated with any of the demographic factors except for alanine transaminase. None of the significant correlations explained enough of the variability to afford a reliable prediction of CL or F.

Cyclosporin A pharmacokinetics in liver transplant recipients in relation to biliary T-tube clamping and liver dysfunction

Cyclosporin A pharmacokinetics were studied after oral (4-14 mg/kg body weight) and intravenous dosing (1.5-3.5 mg/kg) in 13 orthotopic liver transplant recipients before and after permanent clamping of the biliary T-tube. After T-tube clamping, cyclosporin A absorption was faster and more complete with the mean time of peak concentration, tmax, reduced to around three hours from around six hours and mean bioavailability rising from only 16.6% (n = 13) to 30% in the entire group (n = 11 after clamping) or to 35% after excluding two patients who developed severe cholestasis after the preclamping study. Bioavailability in these two patients fell below 8% and to around 1% in a further patient with severe graft dysfunction. Clamping reduced the metabolic clearance of cyclosporin A by only 25% from a mean before clamping of 2.9 ml/min/kg to 2.3 ml/min/kg (n = 11). Oral cyclosporin A becomes a reliable means of maintaining therapeutic drug concentrations only after bioavailability increases in association with T-tube clamping and in the absence of severe liver dysfunction or cholestasis.

Optimization of cyclosporine therapy in renal transplantation by a pharmacokinetic strategy

Although cyclosporine (CsA) displays high immunosuppressive efficacy due to potent selective inhibition of T cell, but not nonspecific, immune functions, the pleiotropic toxicities of the drug result in a low therapeutic index. Thus for a given individual there is at best only a narrow dosage range producing immunosuppression not beclouded by toxicity. Selection of the appropriate CsA dose to achieve this state is complicated by marked inter- and intraindividual variability in drug pharmacokinetics and pharmacodynamics (1). Even considering renal transplant recipients solely, pharmacokinetic variations in drug absorption, volume of distribution, and metabolism as estimated by clearance rates are so great that strategies based on median population values are not useful for a great proportion of patients. Thus it is necessary to devise a CsA strategy that tailors therapy to compensate for interindividual variations. Implementation of such a strategy not only standardizes drug therapy, but also reveals the clinical impact of interindividual differences in the profile of CsA metabolites and in pharmacodynamic effects of a given quantity of CsA, reflecting both the therapeutic actions on the immune system and toxic effects on target organs. Thus a dosing strategy that achieves uniform drug levels by compensating for pharmacokinetic variation is essential for the eventual dissection of a rational CsA regimen.

The absolute systemic availability of a new oral formulation of co-dergocrine in healthy subjects

We have studied the absolute systemic availability (f) of an oral formulation (Hydergin spezial = Hydergine FASR 4 mg per tablet) of co-dergocrine by three different methods. Twelve healthy volunteers received single doses of 0.9 mg co-dergocrine intravenously and 8.0 mg orally in a randomized crossover design. The pharmacological effect of co-dergocrine was monitored as a reduction in plasma prolactin. Maximal plasma concentrations of co-dergocrine after oral dosing ranged between 0.181 and 1.307 ng.ml-1. Maximal urinary excretion ranged between 4.7 and 9.9 micrograms.h-1 and between 0.3 and 2.3 micrograms.h-1 after intravenous and oral doses respectively. Clearance was measured as 90 +/- 22 l.h-1 and the absolute systemic availability (f) as 2.25 +/- 0.65% by using the areas under the plasma concentration-time curves extrapolated to infinity. Calculation of f by comparing areas up to 32 h or the fractions of the dose excreted in urine led to identical results. The intravenous and oral doses produced similar pharmacological effects (reduction of plasma prolactin concentrations) despite the small value of f.

Population analysis of the pharmacokinetic variability of high-dose metoclopramide in cancer patients

Metoclopramide infusions are used to prevent nausea and vomiting in cancer patients during chemotherapy. 47 patients received metoclopramide during 109 chemotherapeutic treatments as a loading (dose range = 0.55 to 4.5 mg/kg over 15 minutes) and maintenance (dose range = 0.57 to 4.8 mg/kg over 8 hours) infusion. During and up to 24 hours after the end of the maintenance infusion between 4 and 10 blood samples were collected per treatment. Metoclopramide was analysed in plasma by liquid chromatography. Pharmacokinetic and demographic data of 83 treatments were analysed by the NONMEM program using a linear 2-compartment model. It was found that bodyweight and serum alkaline phosphatase activity explain some of the interindividual variability in clearance (CL). The typical pharmacokinetic parameters for an average individual (70kg, alkaline phosphatase = 100 IU/L) were: CL = 20 L/h; volume of distribution at steady state (Vdss) = 190L; terminal half-life = 8h. The interindividual variabilities in clearance, volume of central compartment and Vdss were 50%, 35% and 35%, respectively. The residual variability in plasma concentrations was estimated as 13%.

Kinetic-effect models and their applications

This article focuses on mathematical models that analyze the time course of drug effects in humans. Any such model, whether parametric or nonparametric, is termed a kinetic-effect model (KEM). These models serve to describe (interpolation) and to predict (extrapolation) the effect-time profile. KEMs are applicable to many problems in pharmaceutics, pharmacology, and clinical pharmacology.

Absorption of cyclosporine A after oral dosing

Variability in the absorption of CsA seems to contribute to the observed lack of correlation between the size of the oral dose and the trough concentration at steady state. Absorption is probably improved by thorough dispersion of the oral solution of CsA in the drink the patient prefers. Evidence for GI metabolism of CsA has only been gathered in animal experiments. The importance of bile for absorption of CsA into the portal blood is established. The bioavailability of CsA does not seem to be determined by the metabolism during the first passage through the liver. Enterohepatic recycling is likely for CsA metabolites and unlikely for unchanged CsA. A pharmacokinetic model that assumes zero-order absorption of CsA describes human data better than a model with first-order absorption. According to the zero-order model, CsA is absorbed only in the upper part of the small intestine by a mechanism that operates under saturation. Two independent findings in transplantation patients support this model. First, it was shown that small doses of CsA produce disproportionally high blood concentrations, probably due to a better bioavailability. Second, accelerated transit times in the intestine (diarrhea) lead to unexpectedly low blood concentrations, probably due to poor bioavailability. Further factors have been identified that cause low absorption of CsA: liver dysfunction and external bile drainage after liver transplantation. The influence of food on the absorption of CsA is still not determined conclusively, but it seems that giving CsA together with a standard breakfast results in higher blood concentrations. The observed increase in the bioavailability of CsA with time after transplantation could be caused by the attempt to steadily lower the dose.

Pharmacokinetics of high-dose metoclopramide in cancer patients

The introduction of new cytotoxic drug regimens has been associated with an increase in the incidence and severity of adverse effects. This in turn has highlighted the need for more effective adjuvant therapy. The use of metoclopramide for the prophylaxis of nausea and vomiting, in high intravenous doses (50 to 1000 mg), has become established since 1981. As a lipid-soluble drug, metoclopramide has a large volume of distribution. The reported mean values after high doses range between 2.8 and 4.6 L/kg. The mean values for total body clearance and terminal half-life range from 0.31 to 0.69 L/kg/h and from 4.5 to 8.8 hours, respectively. The values of these pharmacokinetic parameters are essentially similar to those obtained after conventional doses (less than 50mg). Pharmacokinetic parameters appear unaffected by age, although no high-dose study has been conducted in children. Bodyweight is apparently correlated with clearance. An influence of renal function indices on terminal half-life and clearance has been shown, which is rather surprising since renal clearance accounts for only 20% of the total clearance. No thorough investigations exist which examine the influence of hepatic disease, cancer type and cytotoxic drug regimen on the disposition of metoclopramide. A relationship between dose (or concentration) and therapeutic or adverse effects of metoclopramide is outlined. The therapeutic benefit of high doses (up to 14 mg/kg) may be dependent on age, and on the combination of cytotoxic drugs. The advantages of high doses of metoclopramide are most apparent when the drug is used as protection against the adverse effects of high doses of cisplatin (greater than 60 mg/m2). Despite considerable pharmacokinetic variability, intravenous administration of high doses of metoclopramide is relatively safe due to its large therapeutic index.

Population pharmacokinetics. Theory and clinical application

Good therapeutic practice should always be based on an understanding of pharmacokinetic variability. This ensures that dosage adjustments can be made to accommodate differences in pharmacokinetics due to genetic, environmental, physiological or pathological factors. The identification of the circumstances in which these factors play a significant role depends on the conduct of pharmacokinetic studies throughout all stages of drug development. Advances in pharmacokinetic data analysis in the last 10 years have opened up a more comprehensive approach to this subject: early traditional small group studies may now be complemented by later population-based studies. This change in emphasis has been largely brought about by the development of appropriate computer software (NONMEM: Nonlinear Mixed Effects Model) and its successful application to the retrospective analysis of clinical data of a number of commonly used drugs, e.g. digoxin, phenytoin, gentamicin, procainamide, mexiletine and lignocaine (lidocaine). Success has been measured in terms of the provision of information which leads to increased efficiency in dosage adjustment, usually based on a subsequent Bayesian feedback procedure. The application of NONMEM to new drugs, however, raises a number of interesting questions, e.g. 'what experimental design strategies should be employed?' and 'can kinetic parameter distributions other than those which are unimodal and normal be identified?' An answer to the later question may be provided by an alternative non-parametric maximum likelihood (NPML) approach. Population kinetic studies generate a considerable amount of demographic and concentration-time data; the effort involved may be wasted unless sufficient attention is paid to the organisation and storage of such information. This is greatly facilitated by the creation of specially designed clinical pharmacokinetic data bases, conveniently stored on microcomputers. A move towards the adoption of population pharmacokinetics as a routine procedure during drug development should now be encouraged. A number of studies have shown that it is possible to organise existing, routine data in such a way that valuable information on pharmacokinetic variability can be obtained. It should be relatively easy to organise similar studies prospectively during drug development and, where appropriate, proceed to the establishment of control systems based on Bayesian feedback.

Description of the time course of the prolactin suppressant effect of the dopamine agonist CQP201-403 by an integrated pharmacokinetic-pharmacodynamic model

Six male volunteers (mean age 24 years) received a single oral dose of 0.025 mg CQP201-403 and placebo in a randomised double-blind crossover design. Fifteen plasma samples were collected over 48 h and were assayed by radioimmunoassay for drug substance and prolactin (PRL). Three of the samples were drawn during sleep on the first study day. The pharmacological effect (E%) of CQP201-403 was expressed as reduction in plasma PRL levels. The pharmacokinetic (PK)-pharmacodynamic (PD) model consisted of two kinetic compartments and an effect compartment linked to the central compartment. A sigmoid Emax model (Hill equation) described the relationship between the drug concentration in the effect compartment and E%. Curve-fitting of PK and PD data provided individual parameter estimates which served to generate computer-simulated PK and PD profiles after single and multiple doses in order to: investigate the in vivo concentration-effect relationship; evaluate the consequence of dosage reduction on the steady-state PD profile; and study the robustness of the response to changes in drug potency and bioavailability.

Pharmacokinetics of oral cyclosporin A (Sandimmun) in healthy subjects

Extensive pharmacokinetic (PK) profiles after oral dosing of 300 mg cyclosporin A (CsA) were determined in whole blood by radioimmunoassay (RIA) in 14 healthy male volunteers, using two-compartment models with either first order (M1) or zero order (M0) absorption. According to zero order absorption the mean of the following PK parameters was determined: terminal half-life = 12.1 +/- 5.0 h, apparent volume of distribution at steady-state = 5.6 +/- 2.11 X kg-1, apparent clearance = 0.51 +/- 0.11 l X h-1 X kg-1. The time lag between drug ingestion and first blood level was short, 0.38 +/- 0.11 h. Drug absorption lasted for 2.8 +/- 1.6 h. The end of absorption was indicated in each individual by a sharp drop in blood levels. The observations support the assumption that CsA is absorbed in the upper part of the small intestine with a clear-cut termination (absorption window). This assumption may explain the high degree of variability in the bioavailability of CsA.