Unusual hypersensitivity to warfarin in a critically ill patient

A patient was admitted to the intensive care unit because of respiratory failure, and warfarin therapy was started at 2 mg/day for the treatment of pulmonary embolism, together with other medications. Despite the low dosage of warfarin, international normalized ratio (INR) was markedly elevated from 1.15 to 11.28 for only 4 days, and bleeding symptoms concurrently developed. Vitamin K2 was infused along with discontinuation of warfarin. One day later, the INR was found to have decreased, and bleeding was also improved. An objective causality assessment indicated a probable relationship between clotting abnormality and warfarin administration, although the degree of elevation of the INR was unusual in the light of the daily warfarin dose and duration of its exposure. Based on the clinical status of the patient, it was suspected that several conditions contributed to the abnormal hypersensitivity to warfarin. Contributory factors probably included pharmacokinetic interactions with co-administrated drugs, vitamin K deficiency caused by decreased dietary intake, reduced gut bacterial production, impaired intestinal absorption and hepatic synthetic capacity, and increased consumption of clotting factors. In view of our experience in the present case, it should be stressed that close monitoring of coagulation capacity is necessary in critically ill patients in order to avoid fatal haemorrhage after initiating warfarin therapy regardless of the dosage.

Serum carvedilol concentration and its relation to change in plasma brain natriuretic peptide level in the treatment of heart failure: a preliminary study

OBJECTIVE

To examine the influence of carvedilol dose and concentration in serum on plasma brain natriuretic peptide (BNP), a measure of heart failure progression.

METHODS

12 patients with New York Heart Association (NYHA) functional class II-III chronic heart failure were enrolled in the study. They received carvedilol at daily doses of 1-20 mg with a 1-2 weekly adjustment. Serum carvedilol trough concentrations were measured in steady-state using a specific fluorescence HPLC method. The degree of improvement in heart failure was assessed from the ratio of change in the plasma BNP concentration, 2 weeks, 1 month and 3 months after the commencement of carvedilol administration.

RESULTS

From the pharmacokinetic aspect, there was no valid correlation between the trough serum carvedilol concentration (Cmin) and daily dose per body weight (Dd/BW), indicating that there was a wide difference in the carvedilol elimination capacity among individuals. A significant decrease in the BNP was observed at the 3rd month in patients treated with the high dose (> 750 mg/3 months). On the other hand, in patients with a mean serum carvedilol level (Cmin) of less than 2.5 nmol/l up to 2 weeks after the start ofcarvedilol therapy, the degree of reduction in the BNP value after the 3rd month was significantly larger, relative to the patient group with Cmin over 2.5 nmol/l.

CONCLUSIONS

The total carvedilol dose was confirmed to be one of the determinants for improvement in heart failure, and it was suggested that the initial serum level also plays an important role in therapeutic outcome. Therefore, it may be important to monitor the serum carvedilol level at the introductory period to determine the daily dose requirements because of the wide inter-individual variability in its metabolic clearance.

Predictive performance of serum digoxin concentration in patients with congestive heart failure by a hyperbolic model based on creatinine clearance

OBJECTIVES

To formulate a simple equation for determining the daily dose requirements of digoxin by inclusion of creatinine clearance (Ccr) values as an explanatory variable.

METHODS

We included 235 routine monitoring and clinical laboratory test data (steady-state serum digoxin concentration and Ccr values), obtained from hospitalized patients receiving digoxin for treatment of congestive heart failure. The 107 data sets were fitted to a hyperbolic model to account for the relation between the ratio of serum digoxin level to the daily dose (L/D) and the Ccr values determined by six methods. Their correlation coefficients (r) were computed by non-linear regression analysis. To evaluate the validity of the best-fitting model, the predictive performance of the L/D ratios was compared with those given by seven reference models previously published, using another 128 data sets.

RESULTS

The hyperbolic model involving the Ccr values estimated by Cockcroft and Gault's equation showed the closest correlation (r = 0.81) between the actual and estimated Ccr values. Mean prediction error (ME), a measure of bias, of the L/D ratio (0.018 ng/mL) was almost negligible when other data were fitted to the proposed model, and this ME value proved to be much smaller than those calculated from the previously published prediction models. Mean absolute prediction error, a measure of precision, by the proposed model was also satisfactory for prediction.

CONCLUSION

The newly developed model provided good predictive performance of serum digoxin level. Taking simplicity in practical use into account, the clinical application of the proposed model will allow for accurate and rapid determination of the initial maintenance dosing regimen of digoxin based on the individual Ccr value, without actual measurement of its serum concentration.

Factors that affect absorption behavior of cyclosporin a in gentamicin-induced acute renal failure in rats

Factors that affect the absorption of cyclosporin A (CsA) were examined in gentamicin-induced acute renal failure (ARF) rats. In ARF rats, the area under the blood CsA concentration-time curve after oral administration was significantly decreased in comparison with that of control rats; 5.81 +/- 0.55 vs 11.30 +/- 1.59 mg h mL(-1)(mean+/-s.e.m.), respectively, and the relative bioavailabilities in ARF and control rats after oral administration were 15.2% and 43.4%, respectively. The flow rate of bile and the amount of bile acids in ARF rats were markedly decreased to about 61% of control, and 41% of control, respectively. The amount of CsA uptaken into the evened sac of jejunum, transferred to serosal side, and metabolized in tissues was significantly decreased in ARF rats without verapamil, while with 0.3 mM verapamil, the amount in ARF rats recovered to the levels of control rats. The absorption clearance of CsA in ARF rats was significantly decreased, however it was significantly improved by adding bile or bile acid. Adenosine triphosphate released from enterocytes in ARF rats was significantly decreased in the presence of 2.0 microM CsA, 0.3 mM verapamil, or both, in comparison with control rats. From these findings, we concluded that a reduction of CsA bioavailability during ARF is caused by depression in bile excretion and renal function-dependent depression of uptake from intestinal tract via maybe P-gLycoprotein in enterocytes. They are main two factors that reduce the absorbed fraction of CsA in ARF rats.

Adsorption and pharmacokinetics of cyclosporin A in relation to mode of infusion in bone marrow transplant patients

Two main factors that affect the pharmacokinetics of cyclosporin A (CsA) during 24-h durable intravenous (DIV) administration have been reported, namely physiological changes after bone marrow transplantation, and blood sampling through indwelling lines. In addition, it has been found that infusion sets made of polyvinyl chloride (PVC) markedly adsorb CsA. We conducted in vitro adsorption studies of CsA on infusion sets, and the administration routes that are used in the treatment of patients with bone marrow transplantation. We also examined the effects of administration route on CsA pharmacokinetics in clinical practice. The in vitro adsorption study using 30-mm segments of lumen from commercially available infusion sets showed that the degree of CsA adsorption per area of lumen made of PVC was significantly higher than that in those made of polyethylene (PE) or polybutadiene (PB), which showed no adsorption of CsA. Due to its adsorption, use of infusion sets made of PVC resulted in about a 40-50% loss of CsA dose, which affected the pharmacokinetic parameters during 24-h DIV, while those made of PE and PB did not. The use of non-PVC infusion sets should allow for accurate monitoring of CsA results, and provide cost benefit in the treatment of bone marrow transplantation.

Influence of glycerol-induced acute renal failure on the pharmacokinetics of cyclosporin in rats

Although it is widely believed that renal dysfunction has no effect on the pharmacokinetics of cyclosporin, many clinical reports suggest that renal dysfunction after renal transplantation is closely related to the pharmacokinetics of cyclosporin. To clarify the relationship between renal dysfunction and the pharmacokinetics of cyclosporin, we examined the influence of acute renal failure (ARF) on its pharmacokinetics in glycerol-induced ARF rats. The values of indicators of renal function (serum creatinine, blood urea nitrogen), but not those of indicators of hepatic function, were significantly increased in ARF rats that received glycerol compared with values for control rats. The area under the blood cyclosporin concentration-time curve after oral administration (AUCpo) were 4.976+/-0.847 mghL(-1) for ARF rats and 9.684+/-1.100 mghL(-1) for control rats; AUCpo in ARF was significantly reduced in a manner dependent on renal function. The oral clearance of cyclosporin in ARF and control rats was 1.172+/-0.207 and 0.544+/-0.062Lh(-1) kg(-1), respectively, whereas total body clearance in ARF and control rats was 0.151+/-0.008 and 0.183+/-0.010Lh(-1)kg(-1), respectively. The relative bioavailability of cyclosporin in ARF and control rats was 0.118 and 0.336, respectively. In an in-vitro study using everted sac and liver-slice methods, the apparent first-order rate constants for cyclosporin uptake (k(uptake)) and metabolism (k(metab)) in gut tissues were reduced, whereas k(uptake) and k(metab) in liver were increased. Gastric emptying, measured by use of paracetamol, was significantly reduced in ARF rats. These results suggest that glycerol-induced ARF results in several changes in the pharmacokinetics of cyclosporin in rats. From these results, we conclude that reduction of the absorbed fraction of cyclosporin strongly contributes to the decrease in AUCpo in the presence of ARF.

Preferential inhibition of CYP1A enzymes in hepatic microsomes by mexiletine

We examined the inhibitory behavior of theophylline oxidations and a variety of cytochrome P450 (P450)-dependent metabolism in the presence of mexiletine (MEX), using hepatic microsomes from both control mice and mice exposed to beta-naphthoflavone (beta-NF). Theophylline metabolism, which is mainly catalyzed by CYP1A2, was susceptible to competitive inhibition by MEX. The calculated inhibition constants (Ki) for theophylline 3-demethylation and its 8-hydroxylation were 4.3 microM and 8.3 microM, respectively, which are comparable to the recommended therapeutic serum range for MEX. The inhibitory potency of MEX on cytochrome P450-dependent enzyme activities diverged among the several metabolic reactions, which were probes for CYP1A, 2A, 2C, 2D, 2E and 3A subfamilies. The Ki value (6.7 microM) for methoxyresorufin O-demethylation mediated by CYP1A2 agreed with those from theophylline oxidations. These metabolic reactions exhibited the smallest Ki values, 1-3 orders of magnitude lower than activities of other constitutive cytochrome P450 species. Similar degrees of inhibition were observed in CYP1A1, a beta-NF-inducible isoform with a relatively high conformity to CYP1A2. These results indicate that MEX acts as a selective and potent inhibitor of the CYP1A enzymes responsible for oxidative biotransformation of chemicals such as theophylline. This evidence provides a fundamental explanation for the pharmacokinetic interactions experienced in clinical practice.

Relationship between area under the concentration versus time curve of cyclosporin A, creatinine clearance, hematocrit value, and other clinical factors in Japanese renal transplant patients

We evaluated the relationship between the area under the concentration versus time curve (AUC) of cyclosporin A (CsA) and several other clinical factors, because the clinical utility of AUC monitoring has been ambiguous. Fifty-four clinical time courses from 14 Japanese renal transplant patients during hospitalization, in the period from April 1990 to March 1997, were examined. In a bivariate regression analysis there was no correlation between the AUC and the daily dose of CsA (mg/kg/day) when the individual data or total series data were analyzed. In a chi-square test, the donor type of kidney (chi(2) = 25.254, df = 1, p = 0.0000) and renal function-related episodes, i.e. acute tubular necrosis, hemodialysis, hypertension, nephrotoxicity, or rejection (chi(2) = 13.982, df = 1, p = 0.0002) directly affected posttransplant renal function assessed by creatinine clearance, while episodes of hepatic function as assessed by the glutamate-pyruvate transaminase (GPT) activity level had no correlation with the posttransplant renal function evaluated according to creatinine clearance. In contrast, the renal function-related episodes significantly affected the AUC after renal transplantation (chi(2) = 4.934, df = 1, p = 0.0263), while hepatic function assessed by GPT did not. In a multivariate analysis, the creatinine clearance and obesity had significant positive correlations with the AUC, whereas the hematocrit had a significant negative correlation with the AUC. From these observations, we concluded that the dosage adjustment of CsA cannot be performed using the linear relationship between the daily oral dose and the AUC, and that renal function, obesity, and the CsA blood distribution properties affect the CsA pharmacokinetics after renal transplantation. Posttransplant renal function as well as obesity and CsA blood distribution properties are important factors to be considered when therapeutic monitoring is performed.

Simultaneous determination of glucocorticoids in plasma or urine by high-performance liquid chromatography with precolumn fluorimetric derivatization by 9-anthroyl nitrile

A new method for simultaneous determination of glucocorticoids (GCs) in plasma or urine by high-performance liquid chromatography (HPLC) with fluorimetric detection has been developed. Following extraction with ethyl acetate using a reversed-phase disposable cartridge, the six GCs [cortisol (F), cortisone (E), prednisolone (PL), prednisone (PN), 6beta-hydroxycortisol (6beta-OHF) and 6beta-hydroxyprednisolone (6beta-OHP)] and an internal standard (6beta-hydroxycotortisone) were derivatized by treatment with 9-anthroyl nitrile (9-AN) in a mixture of basic catalysts (triethylamine and quinuclidine) to give the fluorescent esters through the 21-hydroxyl group. The GC derivatives so obtained were then cleaned by a straight-phase disposable cartridge and chromatographed on a straight-phase column with an isocratic HPLC technique. The fluorescence derivatives of the GCs, including the internal standard, were separated as clear single peaks and no interfering peaks were observed on the chromatograms. The lower limits of detection for F, E, PL and PN in plasma or urine were 0.1 ng/ml and those for 6beta-OHF and 6beta-OHP in plasma or urine were 0.5 ng/ml, at a signal-to-noise ratio of 3. The analytical recovery of known amounts of the GCs added to plasma or urine were almost 100%. This method can be applied to the determination of plasma or urinary F in renal transplant patients who received PL and can be applied for other metabolic investigations in relation to the change in blood pressure via 11beta-hydroxysteroid dehydrogenase or in hepatic metabolizing via CYP3A4.

A predictive model for area under the concentration versus time curve of cyclosporin A using several routine monitoring results in renal transplant patients

We created a predictive model for the area under the concentration versus time curve (AUC) of cyclosporin A (CsA) using routine monitoring results, and examined its clinical utility. Based on 48 clinical time courses accumulated from renal transplant patients, the AUC predictive model was created. An estimate of the AUC0-8 (integrated from time zero to 8 h) was then given as follows: AUC0-8 = 5673.1 x log(TL) + 9342.8 x log(OB) + 64.1 x Dprd x 869.4 x DTK - 168.9 x HCT - 161.2 x SCr - 11.3 x GPT + 3.0 x PL - 588.6 x SEX - 24794.5. In this model, the AUC0-8(ng.h/ml) is given as a function of the CsA through levels (TL, ng/ml), obesity (OB, %), daily dose of prednisolone (Dprd, mg/d), donor type of kidney (DTK), hematocrit (HCT, %), serum creatinine (SCr, mg/dl), glutamate-pyruvate transaminase activity (GPT, IU/l), plasma lipids (PL, mg/dl) and sex distinction (SEX). The Statistical significance of the multiple regression was p < 0.00001 (R2 = 0.862, n = 48), and the day after transplantation, neither the administered oral dose of CsA, or the patient's age had any contribution to the regression. The predictive performance of this model was almost equal to that of the existing method which used 3-point data on the concentration versus time curve. In clinical adaptation for renal transplant patients, the steady-state concentration of CsA (Css) based on the AUC0-8 predictive model was significantly decreased during acute gastroenteritis or before acute rejection, whereas nephrotoxicity was increased, even though CsA trough levels were within a normal therapeutic range (100-200 ng/ml). These findings suggest that the created AUC0-8 predictive model using routine monitoring results, i.e., the trough level of CsA, biochemical tests, a daily dose of predorinsolone (PRD), and basic patient information, is convenient as a monitoring device for CsA therapy, and is satisfactory in clinical practice.

Relationship between erythrocyte-to-plasma distribution ratio of cyclosporin and lymphocyte proliferation in renal transplant patients

OBJECTIVE

The aim of this study was to examine the relationship between erythrocyte-to-plasma distribution ratio of cyclosporin (CsA-EP) and lymphocyte proliferation as an indicator of immunosuppressive activity in renal transplant patients.

METHODS

A total of 113 whole blood samples obtained from 6 inpatients with renal transplantation were analysed. CsA concentrations in blood and plasma at trough were measured by fluorescence polarization immunoassay using monoclonal antibody, lymphocyte proliferation in response to phytohaemagglutinin was evaluated by the fluorimetric derivatization method using ethidium bromide and the stimulation index (SI) was calculated.

RESULTS

There was no correlation between CsA dose and trough levels (vs blood CsA, r2 = 0.052; vs plasma CsA, r2 = 0.054, n = 113). A significant negative correlation between the SI and the CsA-EP was found in individual or all samples (r2 = 0.224, p < 0.0001, n = 113), whereas CsA trough levels in blood or plasma had no correlation with the SI.

CONCLUSION

Although the degree of contribution of CsA-EP to the SI was 22%, the CsA-EP is a more useful predictor of changes in immunosuppressive response than CsA concentration in blood or plasma. The adoption of the CsA-EP as a monitoring index could be helpful in assessing the appropriateness of CsA immunosuppressive therapy.

A nomogram for predicting optimal dosage of cyclosporine in renal transplant patients: taking physiological factors into consideration for regimen during immunosuppressive therapy

We constructed a nomogram for determining the optimal regimen of cyclosporine (CyA), based on physiological changes that occur during immunosuppressive therapy. The nomogram consists of a fixed model and a variable model. In the fixed model, the oral dose of CyA (D, mg/kg) is given by the multiple linear function of logarithmic CyA trough level (TL, ng/ml), the surrogate apparent total body clearance of CyA (CL/fsu, l/h/kg, being equal to D/TL/12), and the erythrocyte-to-plasma distribution ratio of CyA (CyA-EP), as defined by: D = 4.938 x log(TL) + 1.5037 x CL/fsu - 0.0326 x CyA-EP - 10.7156. In the variable model, the CL/fsu is given by the CyA-EP and the patient's intrinsic parameters (P1, P2), using a nonlinear equation: CL/fsu = P1 x exp(P2 x CyA-EP)/CyA-EP. An optimal CyA dose to maintain a desired trough level was calculated, and the validity of the nomogram was found satisfactory for clinical use. This offers a very concise and practical method for the therapeutic monitoring of CyA. Because the pharmacokinetics of CyA depends on physiological changes due to several disease states, and because the CyA-EP reflects the pharmacokinetics of CyA and the patient's disease state, the proposed nomogram is believed to provide an optimal dosage adjustment, taking physiological factors into consideration.

Relationship between apparent total body clearance of cyclosporin A and its erythrocyte-to-plasma distribution ratio in renal transplant patients

To establish an optimal method for determining a cyclosporin A (CyA) regimen based on physiological changes that occur during immunosuppressive therapy, the relationship between apparent CyA body clearance (CL/f) and the CyA erythrocyte-to-plasma distribution ratio (CyA-EP) was examined using clinical time courses obtained during routine monitoring. The CyA-EP, which was calculated by a multiple regression formula using routine data, was increased during renal dysfunction involving the normal recovery phase after transplantation, during nephrotoxicity, during acute tubular necrosis, and during acute renal rejection. CyA total body clearance (CLt), calculated by multiplying CL/f and converted bioavailability, fc (which is equal to 0.009 x LD, where LD represents the CyA level in blood per dose ratio), showed hyperbolic decay with increasing CyA-EP (the mean CLt was defined as follows: CLt = 0.937/CyA-EP), whereas fc showed exponential decay with increasing CyA-EP (the mean fc was defined as follows: fc = 0.593 x exp(-0.155 x CyA-EP)). These findings suggest that total CyA body clearance and its bioavailability were suppressed during the renal dysfunction phase. Hence, the mean CL/f as a function of the CyA-EP was given by the following equation: CL/f = 1.390 x exp(0.204 x CyA-EP)/CyA-EP. Since the CyA-EP reflects a patient's disease state and alterations in the CyA pharmacokinetic profile, these model formulae should provide an adequate method for determining a CyA dosage regimen for several disease states after renal transplantation.

Pharmacokinetics of cyclosporin A after intravenous administration to rats in various disease states

We examine the pharmacokinetic profile of cyclosporin A (CyA) after intravenous administration to rats prepared as models of various disease states found in patients who receive organ transplantations. After intravenous bolus administration to normal rats, the total blood clearance (CLt) of CyA showed a dose-dependent increase. The CLt was reduced in anemic (ANE) rats prepared by venesection, in carbon tetrachloride-induced acute hepatic failure (AHF) rats, and in glycerol-induced acute renal failure (ARF) rats. On the other hand, the volume of distribution at a steady state (Vss) of CyA increased significantly in ANE and aged (AGE) rats. CyA distribution was tissue-specific, and the tissue CyA concentration was disease state-dependent. Linear relationships between the CyA concentration in whole blood and various tissues (liver, kidney and heart) were found in AGE, ANE and AHF animals. However, in ARF rats, tissue concentration was not increased to a great extent in comparison with the other disease models, even though the whole blood CyA concentration was increased. The tissue per blood concentration ratio (Kb), which represented the CyA tissue transfer from systemic circulation, was influenced by the disease state. In the liver, in particular, the Kb increased in the AHF and AGE groups, whereas it decreased in the ANE and ARF rats. The CLt of CyA was negatively related to the erythrocyte per plasma concentration ratio (E/P), and the E/P exhibited disease state-dependent changes, suggesting that this ratio is a valuable indicator for predicting variations in CyA total blood clearance in organ transplant patients during episodes of anemia, nephrotoxicity and hepatotoxicity.

Erythrocyte uptake and protein binding of cyclosporin A (CyA) in human blood: factors affecting CyA concentration in erythrocytes

To further the understanding of the complexity of cyclosporin A (CyA) pharmacokinetics, we conducted an erythrocyte uptake and efflux study, and a protein binding study in human blood. The uptake study showed that the transport of CyA from the extracellular fraction to erythrocytes was retarded by increased human serum albumin (HSA) and lipid levels in this fraction. In addition, the concentration of CyA in erythrocytes increased with increases in CyA concentration in blood and reductions in hematocrit. The efflux study showed that the transport of CyA from erythrocytes to the extracellular fraction was essentially enhanced by increases of HSA and lipid levels in that fraction, but that these effects were relatively small. There were two affinity binding sites for CyA in ghost-free erythrocyte hemolysate, but not in the plasma fraction. The affinity binding constants for these binding sites were reduced by elevations in temperature, and under physiological conditions, 37 degrees C, almost all the CyA in erythrocytes was bound to a CyA binding protein, namely, cyclophillin. These findings suggest that CyA distribution in blood is of two different types which are present in the erythrocyte and plasma fractions, respectively. Monitoring of blood biochemistry variables showed that the concentration of CyA in erythrocytes had an interlocking relationship with these physiological factors, which were related to patient disease state, i.e., hematocrit, lipids, albumin, and total protein; the concentration of CyA in erythrocytes could be predicted from these physiological factors.

Fluorimetric determination of mexiletine in serum by high-performance liquid chromatography using pre-column derivatization with fluorescamine

A simple, specific and sensitive micro-scale method for the assay of the antiarrhythmic agent mexiletine in human serum is described. The method uses high-performance liquid chromatography, with pre-column fluorimetric derivatization by fluorescamine. Following extraction with diethyl ether, mexiletine and 4-methylmexiletine (an internal standard) were derivatized with fluorescamine under weakly alkaline condition (pH 9.0) and chromatographed on a reversed-phase column with aqueous methanol-2-propanol as the mobile phase. The two fluorescent derivatives of mexiletine and the internal standard were separated as clear single peaks, and no interfering peaks were observed on the chromatograms. The detection limit for mexiletine was 0.005 micrograms/ml from only 100 microliters of serum, and the calibration curves in the range 0.01-5 micrograms/ml were linear, with an overall coefficient of variation of less than 5%. The analytical recovery of a known amount of mexiletine added to serum was almost 100%. This method proved to be effective in the rapid monitoring of the serum concentrations in patients who received this potent antiarrhythmic drug.

A model to account for the blood-to-plasma distribution of cyclosporin A in human blood

A mathematical model to account for the blood-to-plasma distribution of cyclosporin A (CyA) in human blood was derived, and alterations in the blood-to-plasma distribution of CyA under several influencing conditions were examined using this model. The model was derived on the assumption that there are two CyA binding sites in human blood, which exist in plasma and cellular fractions. In the plasma fraction, the CyA binding sites are mainly lipoproteins (LPs), in which CyA exhibits nonsaturable, low affinity binding with LPs independent of drug concentration. In the cellular fraction, the binding site of CyA is the CyA binding protein (CBP), in which CyA shows a specific binding in a temperature dependent, saturable process. The results obtained from simulative studies agreed with previous reports on the blood-to-plasma distribution of CyA, indicating the usefulness of this approach. And also, this model may be used to predetermine individual variations in the blood-to-plasma distribution of the drug in renal transplant patients.

Ozagrel hydrochloride monohydrate, a thromboxane synthase inhibitor, and its metabolites as inhibitors of hepatic microsomal drug metabolism

The change in the hepatic oxidative drug-metabolizing capacity in humans treated with ozagrel hydrochloride monohydrate (OZA), an imidazole derivative and a new thromboxane A2 synthase inhibitor, was studied and the inhibitory potencies of the metabolites of OZA (M-1 and M-2) on the mouse hepatic microsomal monooxygenase system in vitro were compared with that of OZA. In vitro, M-1 and M-2, which are the beta-oxidized form and the reduced form of OZA, respectively, inhibited aminopyrine N-demethylation, aniline hydroxylation and testosterone hydroxylations in mouse hepatic microsomes and produced type II difference spectra in the same manner as OZA. The kinetic data indicated that the inhibitory potencies and the affinities of these compounds for cytochrome P-450 were decreased in the order of M-2 greater than OZA greater than M-1. The ratio of 6 beta-hydroxycortisol (6 beta-OHF) to cortisol (F) in urine, used as an indicator of oxidative drug-metabolizing capacity in humans, did not change significantly during oral treatment with 400 mg/d of OZA, while the ratio decreased to 80-85% of the original level during treatment with 800 mg/d of OZA. Although the participation of the metabolites of OZA in the reduction of drug-metabolizing capacity in vivo is not yet clear, the results suggest that hepatic oxidative drug-metabolizing enzyme activities in humans are inhibited by treatment with a relatively high dose of OZA.

Effects of temperature and endogenous factors in blood on concentrations of cyclosporin in plasma measured by high-performance liquid chromatography

The effects of temperature, hematocrit (Hct), lipid level in plasma and cyclosporin A (CyA) level in whole blood on the concentration of CyA in plasma measured by high-performance liquid chromatography were studied in vitro. With rise in blood storage temperature before cells were removed, the concentration of CyA in plasma was increased in the temperature range between 10 degrees C and 37 degrees C, but was decreased between 4 degrees C and 10 degrees C. With rise in Hct, the concentration of CyA in plasma was decreased, and it was more markedly decreased at the blood storage temperature of 4 degrees C than at 37 degrees C. A lipid supplementation study showed that the concentration of CyA in plasma was increased with rise in plasma triglyceride level and in plasma cholesterol level at the storage temperature of 4 degrees C but not at 37 degrees C. Studies of the effect of CyA concentration in blood on the CyA distribution in blood demonstrated that the cellular/plasma concentration (C/P) ratio at low levels (less than 200 micrograms/ml) of plasma CyA ranged from 4 to 10 and was about 2 times higher than that at higher concentrations at 4 degrees C, but the ratio was relatively constant at 37 degrees C. The saturation capacity of the cellular fraction for CyA showed considerable individual variations, but there was no difference between the capacities at 4 degrees C and 37 degrees C. The separation of plasma after equilibration at 37 degrees C made it possible to avoid the variations in the distribution of CyA in whole blood associated with changes in Hct, lipid level in plasma and CyA level in whole blood, and to obtain a measurement reflecting the physiologically significant concentration of CyA in plasma.

Evaluation of fluorescence polarization immunoassay for determination of cyclosporin in plasma

The fluorescence polarization immunoassay (FPIA) method for determination of cyclosporin in plasma was evaluated and compared with the high-performance liquid chromatography (HPLC) and the radioimmunoassay (RIA) methods. The coefficients of variation for the within-run and between-run precision were less than 5 and less than 8%, respectively, for samples ranging in concentration from 50 to 600 ng/ml. Recoveries were determined by adding cyclosporin at concentrations from 25 to 1,000 ng/ml to patient plasma; they were, on average, 98.5%. The calibration curve was stable throughout a 10-week study period. There was no clinically significant interference due to hemolysis, icterus, lipemia, or other commonly used drugs. There was considerable variation of the ratio of the FPIA result to the HPLC result, whereas there was a good correlation between the FPIA and the RIA results (r = 0.975, n = 25, y = 1.2x - 36.4), when evaluated using specimens from renal transplant patients receiving cyclosporin orally. It was concluded that the FPIA is an appropriate, rapid method for patient cyclosporin analysis in plasma and serves as a practical alternative to the RIA.

Quantitative determination of cyclosporin A in whole blood and plasma by high performance liquid chromatography

A simple, specific and sensitive method for monitoring therapeutic levels of the immunosuppressive agent cyclosporin A (CyA) in whole blood and plasma has been developed which uses a high performance liquid chromatography and involves a simple liquid-liquid extraction procedure. Samples were delipolysed with 0.1 mM dextran sulfate sodium salt, extracted with n-hexane, and chromatographed on a Lichrosorb Si-60 column with UV detection at 215 nm. Each of CyA and internal standard (cyclosporin D) is resoluted clearly as a single peak and no interfering peaks are observed on the chromatograms. The detection limit is 5 ng/ml in whole blood and plasma. The reproducibility assessed by repeated analysis is satisfactory, that is to say, each coefficient of variation of the within-run and between-run precision is below 4%. The analytical recovery of added CyA is almost complete. This method is sensitive enough for monitoring whole blood and plasma levels of CyA in renal transplant patients in the therapeutic dose range, and is also applicable to the study on the distribution of CyA between plasma and non-plasma fractions of blood in patients with renal allografts.

A comparison of the dissolution rates of caffeine tablets in a rotating-basket with those in a Sartorius dissolution tester

Uncoated caffeine tablets of four different hardnesses were tested for dissolution rate by the Sartorius (S.S. method) and by the rotating basket method of the U.S.P. XVIII. In both methods the dissolution rate decreased with increasing hardness, and the rate obtained with the S.S. method was always less than that by the U.S.P. method. This result cannot be explained as being due only to the difference in the volume of dissolution medium. Also it was difficult to ensure that the characteristic changes in the process of dissolution paralleled the curves obtained from a plot of % caffeine dissolved vs time. Accordingly, the dissolution rate constants were calculated from the slope of each straight line in a plot of ln W infinity/(W infinity --W) vs time.

Interpretation of dissolution rate data from in vitro testing of compressed tablets

To find if theoretically and experimentally a relation existed between the dissolution rate theory of Kitazawa, Johno & others (1975) and that of Wagner (1969), a study was undertaken with uncoated caffeine, aspirin and proxyphylline tablets using two dissolution methods. Although the original treatment for surface area of drug available for dissolution was quite different between the two dissolution theories, the dissolution rate constants obtained were in fair agreement. Hence it might not be always necessary to take into consideration changes in the surface area as a function of dissolution rate, and the 1n W infinity/(W infinity) versus time plot devised by Kitazawa & others might be a useful and simple means of obtaining the dissolution rate constant of an active ingredient from a dosage form such as compressed tablet.