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U Christians

Publications and source records attributed to U Christians.

At least 55 records · Page 3Linked to original sources
PubMed1999

Grapefruit juice activates P-glycoprotein-mediated drug transport.

PURPOSE: Grapefruit juice (GJ) is known to increase the oral bioavailability of many CYP3A-substrates by inhibiting intestinal phase-I metabolism. However, the magnitude of AUC increase is often insignificant and highly variable. Since we earlier suggested that CYP3A and P-glycoprotein (P-gp) form a concerted barrier to drug absorption, we investigated the role of P-gp in GJ-drug interactions. METHODS: The transcellular bidirectional flux of drugs that are (i) CYP3A-and/or P-gp substrates (Vinblastine, Cyclosporine, Digoxin, Fexofenadine, Losartan) or that are (ii) primary CYP3A-substrates (Felodipine, Nifedipine) was evaluated across MDCK-MDR1 cell monolayers with or without GJ, verifying monolayer integrity at all times. RESULTS: While both apical-to-basal (A-B) and basal-to-apical (B-A) fluxes of all CYP3A/P-gp substrates tested were increased in the presence of GJ, the resulting net efflux (B-A/A-B) was in all cases significantly greater with GJ than control (Vin, 28.0 vs. 5.1; CsA, 9.9 vs. 2.8; Dig, 22. 9 vs. 14.7, Fex, 22.3 vs. 11.1, Los, 39.6 vs. 26). In contrast, no such GJ flux effect was observed with Fel and Nif, substrates of CYP3A only (2 vs. 1.7 and 1.2 vs. 1.3). CONCLUSIONS: GJ significantly activates P-gp-mediated efflux of drugs that are substrates of P-gp, potentially partially counteracting the CYP3A-inhibitory effects of GJ.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

An individual bioequivalence approach to compare the intrasubject variability of two ciclosporin formulations, SangCya and Neoral.

A novel bioequivalence testing approach was used to determine intrasubject variability and switchability of two ciclosporin formulations, SangCya (test) and Neoral (reference). Twenty healthy volunteers were enrolled into a single-dose, randomized, open-label, 4-period, 2-sequence study with a crossover replicate design. Subject-by-formulation interaction variances were compared using a mixed effects linear model. Intrasubject variability for ln AUC(0-infinity) and ln C(max) of SangCya and Neoral were not significantly different. The 95% confidence intervals of the intrasubject variability of AUC(0-infinity) (0.94) and C(max) (1.28) as determined using the bootstrap nonparametric percentile method (n = 2,000) were below the individual bioequivalence limit estimated at 2.25. We concluded equivalent intrasubject variability of ciclosporin pharmacokinetics and switchability between SangCya and Neoral.

Adult↗
PubMed1999

Evaluation of individual and combined neurotoxicity of the immunosuppressants cyclosporine and sirolimus by in vitro multinuclear NMR spectroscopy.

Neurotoxicity, a crucial side effect of immunosuppressive therapy with cyclosporine, also has been demonstrated in vitro for sirolimus, a novel macrolide immunosuppressant, which is under clinical investigation in combination with cyclosporine. NMR spectroscopy was used to study the separate and combined effects of cyclosporine and sirolimus on cerebral metabolism, both in brain cells and in perfused rat brain slices. The high-energy phosphate metabolism was already affected significantly at cyclosporine concentrations as low as 100 micrograms/liter: phosphocreatine was reduced by 10 +/- 2% [half-maximal inhibition concentration (IC50) = 1850 +/- 600 micrograms/liter], and nucleoside triphosphate was reduced by 11 +/- 5% (IC50 = 1110 +/- 420 micrograms/liter; n = 4, P <.05). At 500 micrograms/liter cyclosporine, N-acetylaspartate and glutamate were decreased by 13 +/- 7% (IC50 = 1100 +/- 330 micrograms/liter) and 22 +/- 9% (IC50 = 360 +/- 220 micrograms/liter; n = 4, P <.05), respectively. As evaluated using an algorithm based on Loewe isobolograms, combination of cyclosporine and sirolimus resulted in a synergetic reduction of high-energy phosphate metabolites. Addition of sirolimus to the perfusion medium increased brain slice concentrations of cyclosporine. It is concluded that cyclosporine significantly reduced high-energy phosphate metabolism in brain tissue at in vivo relevant concentrations. Combination with sirolimus resulted in synergism, which, in part, is explained by a greater distribution of cyclosporine into the brain tissue in the presence of sirolimus.

Animals↗
PubMed1999

Small intestinal metabolism of the 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor lovastatin and comparison with pravastatin.

We compared the intestinal metabolism of the structurally related 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors lovastatin and pravastatin in vitro. Human small intestinal microsomes metabolized lovastatin to its major metabolites 6'beta-hydroxy (apparent K(m) = 11.2 +/- 3.3 microM) and 6'-exomethylene (apparent K(m) = 22.7 +/- 9.0 microM) lovastatin. The apparent K(m) values were similar for lovastatin metabolism by human liver microsomes. 6'beta-Hydroxylovastatin formation by pig small intestinal microsomes was inhibited with the following inhibition K(i) values: cyclosporine, 3.3 +/- 1.2 microM; ketoconazole, 0.4 +/- 0.1 microM; and troleandomycin, 0.8 +/- 0.9 microM. K(i) values for 6'-exomethylene lovastatin were similar. Incubation of pravastatin with human small intestinal microsomes resulted in the generation of 3'alpha,5'beta, 6'beta-trihydroxypravastatin (apparent K(m) = 4560 +/- 1410 microM) and hydroxypravastatin (apparent K(m) = 5290 +/- 1740 microM). In addition, as in the liver, pravastatin was metabolized in the small intestine by sulfation and subsequent degradation to its main metabolite 3'alpha-iso-pravastatin. It was concluded that lovastatin is metabolized by cytochrome P-450 3A enzymes in the small intestine. Compared with lovastatin, the cytochrome P-450-dependent intestinal intrinsic clearance of pravastatin was >5000-fold lower and cannot be expected to significantly affect its oral bioavailability or to be a significant site of drug interactions.

Animals↗
PubMed1999

Comparison of cytochrome P-450-dependent metabolism and drug interactions of the 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors lovastatin and pravastatin in the liver.

In an in vitro study, the cytochrome P-450 3A (CYP3A)-dependent metabolism and drug interactions of the 3-hydroxy-3-methylglutaryl-Co A reductase inhibitors lovastatin and pravastatin were compared. Lovastatin was metabolized by human liver microsomes to two major metabolites: 6'beta-hydroxy [Michaelis-Menten constant (Km): 7.8 +/- 2.7 microM] and 6'-exomethylene lovastatin (Km,10.3 +/- 2.6 microM). 6'beta-Hydroxylovastatin formation in the liver was inhibited by the specific CYP3A inhibitors cyclosporine (Ki, 7.6 +/- 2.3 microM), ketoconazole (Ki, 0.25 +/- 0.2 microM), and troleandomycin (Ki, 26.6 +/- 18.5 microM). Incubation of pravastatin with human liver microsomes resulted in the generation of 3'alpha,5'beta, 6'beta-trihydroxy pravastatin (Km, 4,887 +/- 2,185 microM) and hydroxy pravastatin (Km, 20,987 +/- 9,389 microM). The formation rates of 3'alpha,5'beta,6'beta-trihydroxy pravastatin by reconstituted CYP3A enzymes were (1,000 microM pravastatin) 1.9 +/- 0.6 pmol.min-1.pmol CYP3A4 and 0.06 +/- 0.04 pmol.min-1.pmol CYP3A5, and the formation rates of hydroxy pravastatin were 0.12 +/- 0.02 pmol.min-1.pmol CYP3A4 and 0.02 +/- 0.004 pmol.min-1.pmol CYP3A5. The specific CYP3A inhibitors cyclosporine, ketoconazole, and troleandomycin significantly inhibited hydroxy pravastatin formation by human liver microsomes, but only ketoconazole inhibited 3'alpha, 5'beta,6'beta-trihydroxy pravastatin formation, suggesting that other CYP enzymes are involved in its formation. It is concluded that, compared with lovastatin [CLint formation 6'beta-hydroxylovastatin (microl.min-1.mg-1): 199 +/- 248, 6'-exomethylene lovastatin: 138 +/- 104)], CYP3A-dependent metabolism of pravastatin [CLint formation 3'alpha,5'beta, 6'beta-trihydroxy pravastatin (microl.min-1.mg-1): 0.03 +/- 0.03 and hydroxy pravastatin: 0.02 +/- 0.02] is a minor elimination pathway. In contrast to lovastatin, drug interactions with pravastatin CYP3A-catalyzed metabolism cannot be expected to have a clinically significant effect on its pharmacokinetics.

Biotransformation↗
PubMed1998

Development of a high-performance liquid chromatographic-electrospray mass spectrometric assay for the specific and sensitive quantification of the novel immunosuppressive macrolide 40-O-(2-hydroxyethyl)rapamycin.

It was our objective to develop a rapid, sensitive and specific assay to quantify the immunosuppressive macrolide 40-O-(2-hydroxyethyl)rapamycin (SDZ-RAD) in blood of transplant patients. SDZ-RAD was extracted from blood by solid-liquid extraction. SDZ-RAD and its internal standard 28,40-diacetyl rapamycin were quantified using HPLC-electrospray MS. The assay was linear from 0.1 to 100 microg/l (r2 = 0.99). The mean recovery was 83% for SDZ-RAD and 80.5% for the internal standard. The mean day-to-day precision was 8.0%. Extracted samples were stable at 20 degrees C for at least 48 h and SDZ-RAD blood samples at -80 degrees C for at least six months.

Chromatography, High Pressure Liquid↗
PubMed1998

Metabolism and drug interactions of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors in transplant patients: are the statins mechanistically similar?

3-Hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.88) inhibitors are the most effective drugs to lower cholesterol in transplant patients. However, immunosuppressants and several other drugs used after organ transplantation are cytochrome P4503A (CYP3A, EC 1.14.14.1) substrates. Pharmacokinetic interaction with some of the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, specifically lovastatin and simvastatin, leads to an increased incidence of muscle skeletal toxicity in transplant patients. It is our objective to review the role of drug metabolism and drug interactions of lovastatin, simvastatin, pravastatin, fluvastatin, atorvastatin, and cerivastatin. In the treatment of transplant patients, from a drug interaction perspective, pravastatin, which is not significantly metabolized by CYP enzymes, and fluvastatin, presumably a CYP2C9 substrate, compare favorably with the other statins for which the major metabolic pathways are catalyzed by CYP3A.

Drug Interactions↗
PubMed1998

Metabolism and transport of the macrolide immunosuppressant sirolimus in the small intestine.

Small intestinal metabolism and transport of sirolimus, a macrolide immunosuppressant with a low and highly variable oral bioavailability, were investigated using small intestinal microsomes and intestinal mucosa in the Ussing chamber. After incubation of sirolimus with human and pig small intestinal microsomes, five metabolites were detected using high performance liquid chromatography/electrospray-mass spectrometry: hydroxy, dihydroxy, trihydroxy, desmethyl and didesmethyl sirolimus. The same metabolites were generated by human liver microsomes and pig small intestinal mucosa in the Ussing chamber. Anti-CYP3A antibodies, as well as the specific CYP3A inhibitors troleandomycin and erythromycin, inhibited small intestinal metabolism of sirolimus, confirming that, as in the liver, CYP3A enzymes are responsible for sirolimus metabolism in the small intestine. Of 32 drugs tested, only known CYP3A substrates inhibited sirolimus intestinal metabolism with inhibitor constants (Ki) equal to those in human liver microsomes. The formation of hydroxy sirolimus by small intestinal microsomes isolated from 14 different patients ranged from 28 to 220 pmol.min-1.mg-1 microsomal protein. In the Ussing chamber, >99% of the sirolimus metabolites reentered the mucosa chamber against a sirolimus gradient, indicating active countertransport. Intestinal drug metabolism and countertransport into the gut lumen, drug interactions with CYP3A substrates and inhibitors in the small intestine and an 8-fold interindividual variability of the intestinal metabolite formation rate significantly contribute to the low and highly variable bioavailability of sirolimus.

Animals↗
PubMed1997

[Effect of diltiazem on concentration of cyclosporin metabolites in Sandimmune and Neoral treated kidney transplant patients].

BACKGROUND: Diltiazem reduces the cyclosporine dose required for blood levels in the therapeutic target range by 30 to 40%. The effect of diltiazem on the pharmacokinetic disposition of cyclosporine after oral Neoral application is unknown and it is unclear whether or not the diltiazem-cyclosporine interaction is affected by the galenic cyclosporine formulation. PATIENTS AND METHODS: Fifty-one stable renal allograft patients (19 females, 32 males) were enrolled in this prospective, randomized and double-blind study. The patients were assigned to 3 treatment groups: with diltiazem (I, n = 17), with nifedipine (II, n = 17) and without calcium channel blockers (III, n = 17). Nine patients in each group received Sandimmun and 8 patients Neoral. Blood concentrations of cyclosporine and its metabolites AM1 and AM9 were measured using HPLC for 12 weeks. The 3 treatment groups were not different in respect to age, gender distribution and serum creatinine concentration. Cyclosporine doses were adjusted on basis of the blood levels. RESULTS: The cyclosporine doses required to achieve target blood levels were significantly lower in group I compared with group II (-43%) and group III (-33%; p < 0.0001). Although the cyclosporine blood concentrations in all groups were in the therapeutic range, the blood levels in group I showed a much lower variability. The blood concentrations of the metabolite AM1 in group I were significantly higher than those in groups II and III after dose correction (p < 0.0001), those of AM9 were significantly lower in group I than in groups II and III (p < 0.0001). The average dose, and the blood concentration of cyclosporine was not different when patients receiving Neoral were compared with those receiving Sandimmun within the groups. In the patients in group I, the blood concentration of metabolite AM1 was significantly higher after Sandimmun application than after Neoral. No other differences in the metabolite concentrations were detected within the groups comparing patients taking Sandimmun or Neoral. The incidences of acute rejection were lower in group I (17.6%) than in the other groups (II: 52.9%; III: 41%). CONCLUSION: Diltiazem significantly reduced the necessary dose of cyclosporine. Compared with groups II and III, the blood concentrations were more stable in patients in group I. Diltiazem increased the blood concentration of AM1 in patients treated with Sandimmun to a larger extent than in patients taking Neoral. No additional pharmacokinetic differences of the 2 cyclosporine applications different with Sandimmun or Neoral were found.

Adult↗
PubMed1997

Accumulation of lovastatin, but not pravastatin, in the blood of cyclosporine-treated kidney graft patients after multiple doses.

OBJECTIVES: To study pravastatin and lovastatin pharmacokinetic and pharmacodynamic effects and their interactions with cydosporine (INN, ciclosporin) in kidney transplant patients after single and multiple doses. SUBJECTS AND METHODS: The pharmacokinetic and pharmacodynamic effects of administration of 20 mg/day oral pravastatin and lovastatin for 28 days and their interactions with cyclosporine (2 to 6 mg/kg/day) were studied in a double-blind, double-dummy, randomized, parallel-group multicenter trial in 44 stable kidney graft recipients. RESULTS: The median area under the curve [AUC(0-24)] of pravastatin was 249 microg x hr/L (range, 104 to 1026 microg x hr/L) after a single dose (day 1) and 241 microg x hr/L (114 to 969 microg x hr/L) after multiple doses (day 28) and was fivefold higher than values reported in the absence of cyclosporine. The median AUC(0-24) of lovastatin was 243 microg x hr/L (105 to 858 microg x hr/L) on day 1 and 459 microg x hr/L (140 to 1508 microg x hr/L) on day 28. Besides a significant accumulation during the study period (p < 0.001), the lovastatin AUC(0-24) values were twentyfold higher than values reported without cyclosporine. Coadministration of pravastatin or lovastatin did not alter cyclosporine pharmacokinetics. In this study, 20 mg/day doses of both drugs resulted in a significant improvement of the lipid profile and were well tolerated. CONCLUSIONS: In contrast to lovastatin, pravastatin did not accumulate over the study period, which is probably one of the reasons rhabdomyolysis has been reported in lovastatin-treated but not pravastatin-treated transplant patients receiving cyclosporine immunosuppression.

Adult↗
PubMed1997

Assessment of the mechanism of astrocyte swelling induced by the macrolide immunosuppressant sirolimus using multinuclear nuclear magnetic resonance spectroscopy.

The toxic effect of the macrolide immunosuppressant sirolimus on cell metabolism of primary astrocytes was studied by multinuclear NMR spectroscopy of viable cells and perchloric acid (PCA) extracts and compared to the effects of the immunosuppressant cyclosporine. The addition of 5 mg/L sirolimus (5.5 mumol/L) induced swelling of primary astrocytes to 110% of the original volume. Alteration in astrocyte volume in the presence of sirolimus was accompanied by reduction of the following important cell osmolytes and amino acid metabolites: myo-inositol, -58 +/- 12% (mean +/- standard deviation, n = 5); taurine, -44 +/- 5%; glutamine, -13 +/- 2%; compared with control. Sirolimus altered glucose metabolism and partially inhibited the tricarboxylic acid (TCA) cycle: sigma TCA/sigma glycolyse = 1.36 +/- 0.09 (control, n = 3), 0.96 +/- 0.08 (with sirolimus). The increased concentration of phosphodiesters by sirolimus addition (glycerophosphoethanolamine, 52 +/- 18%; glycerophosphocholine, 61 +/- 14%; compared with control, n = 5) indicated disorders in phospholipid metabolism of cellular membranes. Addition of sirolimus led to a decline of the energy state in astrocytes: the concentration of phosphocreatine (PCr) decreased to 75% of control value within 60 min of perfusion with sirolimus and the nucleotide triphosphate (NTP) concentration to 85% within 90 min (n = 3). The effect of sirolimus on the cell metabolism of astrocytes equals that of the immunosuppressants cyclosporine and tacrolimus, the neurotoxicity of which is well-established in clinical studies. The results of this in vitro study indicate that sirolimus possesses neurotoxic potential as well.

Animals↗
PubMed1997

Pitfalls in monitoring tacrolimus (FK 506).

Tacrolimus (FK 506) is a new, potent immunosuppressive drug for primary and rescue therapy in liver and kidney transplantation. Therapeutic drug monitoring is essential for this drug because of its narrow therapeutic window. Blood levels are monitored routinely by enzyme linked immunoassay (ELISA) or by microparticle enzyme immunoassay (MEIA). In a 13-year-old recipient of a liver transplant who had poor hepatic function during the first postoperative week, the authors observed unusually high tacrolimus blood concentrations using either the ELISA (26.6 to 49.0 microg/l) or MEIA (58.5 to 64.5 microg/l). Parent drug levels measured in the same blood samples by high-performance liquid chromatography/mass spectrometry (HPLC/MS) were up to 10-fold lower (5.1 to 9.0 microg/l). The discrepancies between the immunoassay and HPLC/MS results could not be attributed to any of the known metabolites of tacrolimus.

Adolescent↗
PubMed1996

Evaluation of the effects of immunosuppressants on neuronal and glial cells in vitro by multinuclear magnetic resonance spectroscopy.

The use of the undecapeptide cyclosporine and the macrolide tacrolimus as immunosuppressants in transplantation medicine and for the therapy of immune diseases often provokes side effects, among the most important one is neurotoxicity. Changes in the cellular metabolism of glial cells (C6 rat glioma), neuronal cells (N1E-115 mouse neuroblastoma) and primary glia cells (isolated from rats) after addition of cyclosporine and tacrolimus were investigated using 1H-, 13C- and 31P-NMR spectroscopy in vitro. Cells were exposed to various concentrations of the drugs from 3 h to 42 days. The immunosuppressants (cyclosporine IC50 : 55 mumol/l; tacrolimus IC50 : 47 mumol/l) inhibited cell proliferation in a concentration- and time-dependent fashion. Multinuclear NMR studies of PCA extracts of drug-treated cells showed a significant deterioration in the energy status (a decreasing level of PCr : -46 +/- 11%; an increasing NDP/NTP ratio: +136 +/- 4% and an increasing level of Pi : +248 +/- 15%; mean +/- standard deviation). It also showed decreasing concentrations of major cell metabolites like NAA (-59 +/- 12%) in neuroblastoma cells and myo-inositol (-47 +/- 6%) in glia cells compared with untreated controls. Immunosuppressive treatment caused a large reduction of taurine (-36 +/- 12%) and glutamate (-68 +/- 10%) in all cell cultures, whereas intermediates of phospholipid biosynthesis (PE: +59 +/- 13%; PC: +127 +/- 27%;) and breakdown (GPE: +215 +/- 24%; GPC: +245 +/- 17%) increased. No significant differences were observed between the two immunosuppressants. The toxic effects of immunosuppressants on cell cultures are in line with MRI studies of brain oedema observed in patients under immunosuppressive treatment.

Animals↗
PubMed1996

A new oral formulation of cyclosporine for early oral immunosuppressive therapy in liver transplant recipients.

CsA-ME is a new oral microemulsion formulation of CsA. Studies in stable liver grafted patients with cholestasis and subsequent poor absorption of the conventional cyclosporine formulation showed a substantial increase in CsA absorption after conversion to CsA-ME. To investigate its use in patients during the early course after liver transplantation we recruited 50 liver transplant recipients in two centers. During the first study phase A CsA-ME was administered to 20 patients in incremental doses after a short initial course of intravenous cyclosporine. During the second study phase B (30 patients) CsA-ME was administered from the time of transplantation. One year actual patient and graft survival of patients included in phase A and B of the trial was between 90% and 93.3%; 50% and 60% of the patients enrolled in phase A and phase B of the trial were free from rejection at month 3, respectively. Chronic rejection was diagnosed in one patient. No increase in the incidence of CsA related side effects was observed. The optimum CsA-ME starting dose was found to be 10 mg/kgbw/day for patients without external biliary diversion and 15 mg/kgbw/day for patients with a T tube in situ. Using these starting doses, 26 consecutive patients with external bile diversion via T tube were treated with CsA-ME from the day of transplantation. Intravenous CsA was necessary only in three patients. When CsA-ME absorption in patients with stable liver function was compared with that in patients with early liver dysfunction, no difference in the pharmacokinetic profiles was observed between the groups. Our results indicate that CsA-ME therapy is effective and well tolerated in liver graft recipients, even in patients with external biliary diversion during the early posttransplant phase. Thus, CsA-ME is a useful alternative to intravenous CsA treatment in these patients.

Administration, Oral↗
PubMed1996

Tacrolimus (FK 506) biotransformation in primary rat hepatocytes depends on extracellular matrix geometry.

Established in vitro models for studies of hepatic drug biotransformation include the use of primary hepatocytes. In normal liver the space of Disse provides the possibility of bilateral attachment to extracellular matrix for each hepatocyte. This configuration is disrupted by the cell isolation procedure of normal liver tissue, which delivers suspensions of round shaped cells. In standard culture configurations this unphysiologic cell shape terminates in a morphological dedifferentiation and inability to biotransform drugs. This study analyses the relevance of extracellular matrix geometry in hepatocyte monolayer configurations for expression and activity of cytochrome P450 3A. This enzyme is involved in the biotransformation of a large number of pharmaceuticals including the immunosuppressants tacrolimus and sirolimus. Morphological analysis of primary rat hepatocytes cultured with and without overlay of collagen type I was performed by transmission and scanning electron microscopy. Expression and activity of cytochrome P450 3A was studied by Western blot and the use of two model drugs specific for this enzyme. To this purpose the immunosuppressive drugs tacrolimus and sirolimus were used. Metabolites were analyzed by HPLC and HPLC/MS. Two sided attachment to extracellular matrix induces profound changes of the hepatocellular morphology in vitro resulting in the reconstitution of a polyhedric cell shape. This phenomenon is paralleled by an enhanced expression of cytochrome P450 3A and corresponding metabolic activity. As shown for tacrolimus biotransformation, the model may be useful to study complex metabolic patterns. In addition this model may facilitate studies of the kinetics of hepatocellular drug biotransformation in a setting with prolonged stability.

Albumins↗
PubMed1996

Diltiazem increases blood concentrations of cyclized cyclosporine metabolites resulting in different cyclosporine metabolite patterns in stable male and female renal allograft recipients.

1. Six male and six female stable renal allograft recipients under cyclosporine immunosuppression and without concomitant therapy with drugs known either to induce or inhibit CYP3A enzymes were included in the study and received 180 mg day-1 diltiazem for 1 week in a two-period cross-over fashion. Cyclosporine (352 +/- 56 mg day-1) was given in two daily oral doses. The daily doses were not changed during the study. Blood samples were collected for 12 h after receiving cyclosporine alone and after receiving diltiazem in addition for 1 week. Cyclosporine and nine of its metabolites were quantified using h.p.l.c. 2. Co-administration of diltiazem caused a 1.6 fold increase of the AUC (0, 12 h) of cyclosporine and a 1.7 fold increase of the AUC(0, 12 h) of its metabolites. Analysis of the metabolite patterns showed an over-proportional increase of the AUC(0, 12 h) of the cyclized metabolites AM1c (2.6 fold) and AM1c9 (2.2 fold). The AUC(0, 12 h) values of cyclosporine and the hydroxylated metabolites increased less than two fold. 3. Differences of the AUC(0, 12 h) values of cyclosporine with and without diltiazem were significantly higher in female than in male patients (P < 0.02). The differences in the AUC(0, 12 h) values of the metabolites, especially AM1c, tended to be higher in female patients as well. 4. It is concluded that coadministration of diltiazem not only increases the blood concentration of cyclosporine but also those of its metabolites, leads to a shift of the metabolite pattern towards cyclized metabolites, and that the pharmacokinetic changes under diltiazem administration are more prominent in female than in male patients.

Adult↗
PubMed1996

Evaluation of the Pro-Trac tacrolimus monoclonal whole-blood enzyme-linked immunosorbent assay for monitoring of tacrolimus levels in patients after kidney, heart, and liver transplantation.

In a prospective study, we evaluated a novel enzyme-linked immunosorbent assay (ELISA) (Pro-Trac) for determining tacrolimus (FK 506) concentrations in whole blood. Results obtained by the ELISA were compared with those obtained either by microparticle enzyme immunoassay (MEIA) or by high-performance liquid chromatography/mass spectrometry (HPLC-MS). The lower limit of quantitation of the ELISA was 0.5 microgram/L. The within-series coefficient of variation (CV) was < 11%. For spiked blood samples containing different concentrations of tacrolimus, interassay CV was 23.6% at 2.5 micrograms/L; however, at 15 and 60 micrograms/L, interassay CV was 44.9 and 50.8%, respectively. In crossover studies including blood samples from patients after liver, heart, or kidney transplantation, ELISA results correlated with those of the HPLC-MS (r = 0.73) as well as with those generated by MEIA (r = 0.82). The ELISA and MEIA showed 52.3 and 56.2% cross-reactivity with 15-O-demethyltacrolimus, respectively, but only 5.0 and 5.4% cross-reactivity with 13-O-demethyltacrolimus. We conclude that if assay precision in the upper range is improved, the Pro-Trac ELISA might be a valuable alternative to the MEIA for therapeutic drug monitoring of tacrolimus.

Chromatography, High Pressure Liquid↗