Effects of diltiazem upon metabolism and immunosuppressive action of cyclosporine in kidney graft recipients

It is widely believed that calcium antagonists such as diltiazem exert immunosuppressive effects in kidney graft recipients--however, the mechanism is unclear. In a randomized controlled trial, kidney graft recipients who received diltiazem during transplantation and for an average of 12 months thereafter experienced significantly fewer rejection episodes than patients treated with cyclosporine and steroids alone. Furthermore, 1-year (97% vs. 85%) and 4-year (80% vs. 70%) graft survival rates were higher in diltiazem-treated patients, but the difference was not statistically significant. In vitro, diltiazem had little immunosuppressive activity. Concentrations of diltiazem which blocked the proliferation of PHA-stimulated human peripheral blood mononuclear cells, or prevented activation-associated accumulation of interleukin-2 mRNA, or p50- and p70-IL-2 receptor mRNA exceeded pharmacological concentrations by more than 100-fold. Both, CsA and high doses of diltiazem caused an increase of IL-6 mRNA. In contrast to these findings, the IL-6 plasma concentrations were comparable in both groups, whereas the serum concentration of soluble IL-2 receptors was decreased in patients treated with diltiazem. Administration of diltiazem caused an alteration of CsA metabolism. The whole-blood concentration of CsA metabolite 17 was significantly increased in diltiazem-treated patients, resulting in a five-times-higher concentration of this metabolite in the cellular blood compartment compared with the parent drug. Changes in metabolites 1, 8, and 18 levels were less pronounced. Although direct immunosuppressive properties of diltiazem are unlikely, diltiazem could support immunosuppression by altering CsA metabolism, and promoting accumulation of certain metabolites.

Evaluation of proposed sulphoxidation pathways of carbocysteine in man by HPLC quantification

A quantitative study has been made of the metabolism of S-carboxymethyl-L-cysteine (CMC) and its sulphoxides in volunteers by HPLC. Precolumn derivatization was applied prior to gradient reversed phase HPLC separation and fluorescence detection. For CMC and its metabolites containing a primary amino group the reagent 9-fluorenylmethylchloroformate was used. The other metabolites of CMC were derivatized at their carboxylic group with 1-pyrenyldiazomethane to give stable fluorescent products. Urine samples were collected for 8 h after oral administration of 1.125 g CMC to 33 healthy volunteers. Elimination of CMC in urine as sulphoxides did not account for more than 1% of the dose in any of the volunteers. Thus, CMC-sulphoxide metabolites are not quantitatively important. Recovery of the original substance in 8-hour urines ranged from 10 to 30% and a further 2 to 20% was recovered as the metabolite thiodiglycolic acid. Oral doses of 0.19, 1.125, and 2.25 g CMC in a second group of 12 healthy volunteers did not reveal dose dependence of the urinary excretion of the sulphoxides or of thiodiglycolic acid. Serum concentration-time-curves of CMC, (S)- and (R)-CMC sulphoxide were measured in a group of 9 healthy volunteers. The CMC sulphoxides in serum reached 1.5% of the parent substance after 4 hours. The ratio of CMC to its sulphoxide metabolites was similar in serum and urine. Pharmacogenetic polymorphism of sulphoxidation was not confirmed by the specific HPLC methods used.

Acute poisoning with bromofosmethyl (bromophos)

One hour after suicidal ingestion of about 20 mL of a 38% solution of bromofosmethyl, CAS: 2104-96-3 (bromophos), a 52 year-old female was admitted to the hospital with extreme miosis, hypersalivation, hyperperistalsis and muscular fibrillation. Gastric lavage was performed and activated charcoal administered. Cholinergic symptoms were antagonized by repeated doses of 0.5 mg atropine. Because of the high dose of bromophos, hemoperfusion was performed with amberlite XAD4. The bromophos clearance during hemoperfusion was 95 mL/min (flow 200 mL/min). The patient received two doses of 500 mg obidoxime for recurrent muscular fibrillation. The further clinical course was uneventful. On day 4, the patient was transferred to a psychiatric ward because of persistent suicidality. In contrast to poisoning by most organophosphates, red blood cell acetyl cholinesterase was only minimally depressed but the plasma butyryl cholinesterase was initially decreased and normalized within a few days. The records of 25 patients reported to our Poison Control Center with ingestion of more than 1 g bromophos were also evaluated. The most frequent symptoms were miosis, hyperperistalsis, hypersalivation, agitation, nausea/vomiting and convulsions. Nine of the patients had no symptoms. Bromophos is relatively less toxic than its phosphate derivative, parathion.

Clearance of ceftriaxone in critical care patients with acute renal failure

Serum concentrations of ceftriaxone (RocephinTM), a third generation cephalosporin, were monitored in 5 operative intensive care patients suffering from acute renal failure (ARF) and compared to those of 7 patients without renal disturbance. For a period of 7 days, a fixed dose of 2 g/day was given by a 15 min infusion. Pharmacokinetic parameters were calculated by fitting all serum and urine data measured over the period of treatment. Ceftriaxone free fraction was measured on days 2 and 7. There was no evidence for an intraindividual change in ceftriaxone-clearance during the observation period. Ceftriaxone renal clearance was closely dependent on creatinine clearance according to a linear regression expressed by Clren = 0.14 Clcrea + 2.2 (r = 0.951, p less than 0.0001). Total clearance was also associated with creatinine clearance: Cltot = 0.19 Clcrea + 8.2 (r = 0.964, p less than 0.0001). Related to the free fraction, renal clearance was in the range of the glomerular filtration rate. Non-renal clearance was strongly decreased when related to the free fraction indicating that biliary excretion is also impaired in patients with acute renal failure. Obviously no compensatory increase in hepatic ceftriaxone clearance takes place. It is concluded that elimination of ceftriaxone may be strongly impaired during acute renal failure in surgical intensive care patients and that dosage should be restricted according to degree of the impairment of creatinine clearance.

Pharmacokinetic interaction between cyclosporin and diltiazem

Previous reports have indicated that administration of the calcium antagonist diltiazem results in major changes in the pharmacokinetics of cyclosporin A (CyA). A new clinical trial was undertaken in 22 renal transplant patients receiving a constant dose of cyclosporin to further explore this interaction. Coadministration of diltiazem for one week produced an increase in the blood concentration of CyA and its metabolites 17 and 18 in almost all patients, but no increase in CyA metabolites 1 and 21. The mean whole blood CyA trough level determined by HPLC rose from 117 ng.ml-1 to 170 ng.ml-1 after one week on diltiazem, and the mean trough level of metabolite 17 rose similarly from 184 ng.ml-1 before to 336 ng.ml-1. Based on experiments with microsomes from human liver the effect of diltiazem was due to noncompetitive inhibition of CyA-metabolism by diltiazem, and the increased concentration of metabolite 17 might have been due to stronger inhibition of its secondary metabolism steps.

Cyclosporin drug monitoring: comparison of four immunoassays and HPLC

Cyclosporin blood trough levels were measured with four different immunoassays and high-performance liquid chromatography in 12 patients receiving low-dose steroids and CsA after kidney transplantation. These patients represent a selection with an uncomplicated posttransplant course and received no drugs with a known influence on CsA pharmacokinetics. The use of specific antibodies against the parent drug yielded levels comparable to those detected by HPLC. CsA levels measured with nonspecific antibodies exceeded those measured with specific ones by a factor of two to three. All immunoassay-detected CsA levels correlated significantly with the HPLC-determined CsA levels. In addition, blood levels of the CsA metabolites 1, 17, 18, and 21 were determined by HPLC. In one additional patient, who was under tuberculostatic treatment and had a transitory deterioration of liver function, levels of nonspecific-antibody-determined CsA rose, as confirmed by rising levels of metabolite 17, while those of the parent drug fell. We conclude that routine drug monitoring should include at least one immunoassay with a specific antibody detecting the unchanged CsA, and a supplementary immunoassay with a nonspecific antibody detecting a composition of cross-reacting metabolites plus the unchanged substance. If available, HPLC should be used to confirm levels of CsA and its metabolites in patients with suspected alteration of their CsA metabolism.

Stereochemistry of aromatic phenytoin hydroxylation in various drug hydroxylation phenotypes in humans

Phenytoin pharmacokinetics exhibit large intersubject differences and coinheritance of phenytoin metabolism with known drug hydroxylation polymorphisms was therefore suspected. To study the inherited enzymatic mechanisms underlying phenytoin disposition in humans, we have investigated the rate and the stereochemical course of aromatic phenytoin hydroxylation in subjects with and without genetic drug hydroxylation deficiencies for mephenytoin or debrisoquine. For the separate analysis of S- and R-enantiomers of 5-(4-hydroxyphenyl)-5-phenylhydantoin (HPPH; the major phenytoin metabolite), a chiral ligand exchange chromatography system was used. The S-enantiomer of HPPH was the major urinary phenytoin metabolite irrespective of the various drug hydroxylation phenotypes studied. By contrast, the formation of the HPPH R-enantiomer was significantly decreased in poor metabolizer phenotypes of mephenytoin leading to a bimodal distribution of the urinary HPPH S/R-ratio in humans which was correlated closely with the mephenytoin hydroxylation index. Thus, HPPH S/R-values greater than 40 are likely to occur in S-mephenytoin hydroxylation-deficient phenotypes. Analysis of HPPH S/R-ratios in urine samples in a population of 122 randomly selected epileptic patients under chronic phenytoin treatment showed that product-stereoselective aromatic phenytoin hydroxylation is preserved after chronic drug administration. In subjects with and without genetic S-mephenytoin hydroxylation deficiency, extensive HPPH formation was confirmed by a pronounced NIH-shift of the tritium isotope during the product-stereoselective hydroxylation of the pro-S phenyl ring of phenytoin. Substrate-stereoselective glucuronidation of R- and S-HPPH (and related enantiomeric hydantoin metabolites) could be excluded based on identical urinary excretion of p.o. administered pure metabolite enantiomers.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics of hexobarbital and dipyrone in critical care patients receiving high-dose pentobarbital

The effect of pentobarbital treatment in a mean dose of 30 mg/kg/day on the clearance of hexobarbital (Evipan) and dipyrone (Novalgin) has been evaluated in critical care patients receiving a large number of drugs as comedication. Eleven patients treated with pentobarbital showed a hexobarbital half-life of 2.79 h and a total plasma clearance of 9.80 ml X min-1 X kg-1 as compared to 10 patients without pentobarbital administration in whom there was a significantly longer half life (6.92 h) and lower clearance (2.97 ml X min-1 X kg-1). The kinetics of hexobarbital were correlated with the urinary excretion of D-glucaric acid, a non-invasive parameter of drug metabolising activity. In 10 patients on pentobarbital, the total plasma clearance of N-4-methyl-aminoantipyrine, the active form of dipyrone, did not differ from that in 8 patients not receiving pentobarbital. As drug kinetics show great variability in these patients, it is difficult to discriminate enzyme induction from other mechanisms, for example competitive inhibition or changes in volume of distribution. In the presence of pentobarbital, however, induction of drug metabolising enzymes should be considered as a possible reason for the higher clearance of hexobarbital.

Monitoring of pentobarbital plasma levels in critical care patients suffering from increased intracranial pressure

Pentobarbital plasma levels were determined in 16 critical care patients receiving a dose of approximately 30 mg/kg/day and suffering from severe head injury. In 10 patients monitored more than six times, a continuous decrease in plasma concentrations, caused by a mean increase in pentobarbital total plasma clearance from 0.81 to 1.06 ml/min/kg, was found. This effect might be due to autoinduction of hepatic drug-metabolizing enzymes. As clearance values showed marked inter- and intraindividual variability, it is necessary to monitor pentobarbital plasma levels frequently to adapt the dosage to the changes in clearance. Infrequent determinations are of little clinical value, as the necessary changes in pentobarbital dosage will not be predicted precisely enough.

D-glucaric acid excretion in critical care patients--comparison with 6 beta-hydroxycortisol excretion and serum gamma-glutamyltranspeptidase activity and relation to multiple drug therapy

The incidence of increased drug metabolism activity as a consequence of multiple drug therapy at a surgical intensive care ward has been studied non-invasively by determinations of daily urinary D-glucaric acid (GA) excretion rates. Among 165 randomly selected patients, GA excretion was stimulated in 76 cases (= 46%). Exploratory data analysis showed that increases in GA excretion are primarily due to administration of barbiturates (pentobarbitone, Nembutal), miconazole (Daktar) and, to a lesser extent, neuroleptics. Surprisingly, the large number of simultaneously administered additional drugs failed to increase GA excretion. Urinary 6 beta-hydroxycortisol (6 beta-OHF) and 17-hydroxycorticosteroid (17-OHCS) excretion rates were correlated in 34 patients with GA excretion; patients not receiving known enzyme inducers showed low GA values but high 6 beta-OHF and 17-OHCS values, however, with a ratio of 6 beta-OHF/17-OHCS in the normal range. Patients receiving high dose pentobarbitone treatment failed to exhibit significantly increased 6 beta-OHF and 17-OHCS or 6 beta-OHF/17-OHCS values. Miconazole treatment resulted in a significantly increased ratio of 6 beta-OHF/17-OHCS. gamma-Glutamyltranspeptidase activity in serum showed no correlation with GA excretion (n = 91).

Benzo(a)pyrene metabolism in hepatic microsomes from female DA rats with a genetic sparteine oxidation deficiency

The impact of the genetic hydroxylation deficiency described for several drugs such as sparteine, debrisoquine, and phenformin, has been studied with respect to benzo(a)pyrene (BP) metabolite formation. 14C-BP (80 microM) was incubated with liver microsomes from female DA rats deficient in sparteine oxidation; microsomes from female Sprague-Dawley rats served as controls. BP metabolites were separated by high pressure liquid chromatography (HPLC). No significant differences were detected in the overall formation rate of 9,10-,4,5-, and 7,8-dihydrodiol-BP, of 4 quinones, or of 9-OH- and 3-OH-BP. Thus, the study suggested no association between genetic hydroxylation polymorphism (debrisoquine/sparteine type) and the formation of at least 6 BP metabolites.

Antipyrine metabolite formation and excretion in patients with chronic renal failure

In the present study the influence of chronic renal insufficiency on antipyrine clearance, metabolite formation and excretion was investigated in 8 patients. After oral administration of antipyrine, the parent compound, its metabolites and their conjugates were assayed in plasma and urine. Besides the parent drug, 3-hydroxymethylantipyrine (HMA) was present in plasma in the free and conjugated forms, whereas 4-hydroxyantipyrine (OHA) and norantipyrine (NORA) were found only in the conjugated form. The same was true for urine. The plasma concentrations of these metabolites are too low to be measured in subjects with normal renal function. Plasma antipyrine clearance in the patients was in the same range as in healthy subjects. Investigation of metabolite kinetics, however, revealed that the rate of formation of NORA was preferentially decreased, whereas that of OHA and HMA were unaltered. Renal clearance of the metabolites of antipyrine was severely impaired in patients with renal insufficiency, and the resulting accumulation made it possible for the first-time to measure the antipyrine metabolites in plasma. Mean residence times of metabolites were longer than that of the parent compound. Renal clearances of the conjugates were correlated with the creatinine clearance, but were somewhat higher. Renal clearance of free HMA was lower and was also correlated with creatinine clearance. The mean clearance for glucuronidation of HMA was 93.1 ml/min. The results suggest that in healthy subjects Phase I metabolism is the rate-limiting step in the elimination of antipyrine, which is essential for its application as a model drug in metabolism studies.

Oxidation and glucuronidation of valproic acid in male rats--influence of phenobarbital, 3-methylcholanthrene, beta-naphthoflavone and clofibrate

The influence of phenobarbital, clofibrate, 3-methylcholanthrene and beta-naphthoflavone on omega- and beta-oxidation as well as on glucuronidation of valproic acid (n-dipropylacetic acid) was evaluated in male Sprague-Dawley rats by determination of urinary excretion of its metabolites by GC-MS after administration of 100 mg/kg. In controls 12% of the dose was excreted within 24 hours, primarily as glucuronides; metabolites formed by oxidation amounted to about 4%. Phenobarbital treatment led to stimulation of 4-hydroxyvalproic acid [(omega-1)-oxidation], 5-hydroxyvalproic acid and n-propylglutaric acid (omega-oxidation) excretion. Clofibrate enhanced the excretion of 4-hydroxyvalproic acid and 3-keto-valproic acid, a product of peroxisomal beta-oxidation. beta-Naphthoflavone slightly increased the excretion of 5-hydroxyvalproic acid. The most specific effect was found for 3-methylcholanthrene, which was effective in stimulating the formation of 3-hydroxyvalproic acid which might be formed by (omega-2)-oxidation. The addition of fatty acids (olive oil in which 3-methylcholanthrene and beta-naphthoflavone were suspended) led to increased excretion of 3-keto-valproic, 4-hydroxyvalproic and n-propylglutaric acid. The excretion of 3-hydroxyvalproic acid was completely suppressed by olive oil. Such specific effects were not observed for glucuronidation of valproic acid and its metabolites, although stimulation was attained after phenobarbital, clofibrate and 3-methylcholanthrene treatment, because of instability of glucuronide conjugates. Stimulation of valproic acid metabolism was also shown by increased plasma clearance after treatment with phenobarbital. In contrast, clofibrate given once 1 hr before valproic acid inhibited excretion of valproic acid, possibly by competition during renal tubular secretion. Determination of valproic acid metabolites in urine provides a useful tool for evaluation of inducer specificity of short chain fatty acid metabolism and differentiation between microsomal and peroxisomal enzyme activity.

Studies on the mechanism of stimulation of microsomal H2O2 formation and benzo(a)pyrene hydroxylation by substrates and flavone

The addition of activators like flavone and hexobarbital to hepatic microsomes markedly stimulates H2O2 formation. The similar increase observed with flavone of microsomal hydroxylation of benzo(a)pyrene and its inhibition by catalase and methanol suggests but does not prove a necessary interaction of microsomal H2O2 production with benzo(a)pyrene hydroxylation. Hexobarbital and flavone-stimulated H2O2 formation is optimal at a stoichiometric relationship of these activators and NADPH. This implies either their direct participation as electron donors or their indirect involvement in electron transport by facilitation of stoichiometric substrate cytochrome P-450/NADPH flavoprotein interactions. Steady state kinetics data are consistent with a scheme in which the formation in microsomes of a complex of 1 mole of NADPH with NADPH-cytochrome P-450 reductase and 1 mole hexobarbital with cytochrome P-450 regulates H2O2 formation.

Urinary excretion of D-glucaric acid, an indicator of drug metabolizing enzyme activity, in patients with impaired renal function

The urinary excretion rate of D-glucaric acid, an in vivo parameter of the activity of drug metabolizing enzymes, has been determined in patients with chronic renal insufficiency (glomerular filtration rate 4.5-80 ml/min/1.73m2). The mean value of 22.3 mu moles/d (SD 7.2; n 28) was almost identical to that of healthy controls (22.1 mu moles/d, SD 7.3; n 22). Thus, no inhibitory or enhancing effect of renal insufficiency could be detected. The ability of this parameter to indicate alterations in the activity of hepatic drug metabolism, even in patients with renal insufficiency, was demonstrated by the increased excretion rate of glucaric acid (107 mu moles/d, SD 43.5; n 8; p less than 0.001) after treatment for 7 days with the enzyme inducer phenobarbital. No significant correlation was found between glucaric acid excretion and sex, age, body weight or body surface in 50 patients. Glucaric acid excretion, therefore, should not be related to the creatinine content of urine samples, since creatinine excretion decreases with severity of renal insufficiency and varies with sex, age, body weight and many other conditions. A single dose of dipyrone (Novalgin¿), a further in vivo indicator of drug metabolism, increased glucaric acid excretion on the same day, but no interference was found after a single dose of cortisol.

Hybrid information provided by the 14C-aminopyrine breath test. Studies with 14C-monomethylaminoantipyrine in the guinea pig

N-Demethylation of 14C-aminopyrine (14C-AP), labelled at the methyl groups of the tertiary amino group, yields H14 CHO and 14C-monomethylaminoantipyrine (14C-MMAAP) which also undergoes N-demethylation, however, at a slower rate as measured in hepatic microsomes. As after intraperitoneal application to male guinea pigs of 14C-AP (75 mg/kg; 50 muCi/kg), exhalation rate of 14CO2 declines in a biphasic manner, the hypothesis was tested whether the terminal part might reflect N-demethylation of MMAAP. The application of 14C-MMAAP (70 mg/kg; 10 muCi/kg), resulted in monophasic curves of 14CO2 exhalation rate. Their half lives were, however, longer than terminal half lives obtained after 14CAP. Obviously, this terminal phase does not represent 14CO2 formation from the metabolite MMAAP only, but 14C-AP might still contribute to 14CO2 production. Confirmation was obtained by HPLC determination of AP and MMAAP in serum after injection of AP. Shortly after injection, high concentrations of AP and low ones of MMAAP were found in blood from the portal vein and systemic circulation. Thus, initial parts of 14CO2-exhalation rate curves reflect predominantly AP metabolism whereas later phases provided hybrid information.

Demonstration of drug-ethanol interactions by changes in activity of hepatic microsomal oxidase/oxygenase cytochrome P-450 function

"Uncoupling" of microsomal hepatic oxygenases is characterized by a situation in which microsomal monooxygenases exhibit more oxidase than oxygenase activity with an increased formation of hydrogen peroxide at the expense of O2, NADPH and substrate hydroxylation. The importance of such in vitro observations with respect to physiological conditions "in vivo" has been tested by investigating elimination kinetics of ethanol. If hexobarbital, a substrate of mixed function oxygenase as well as an "uncoupler", is given to guinea pigs together with ethanol, changes in the elimination of ethanol occur. It is suggested that this is the consequence of an increased formation of H2O2 which contributes via peroxidatic reaction of catalase to the elimination of ethanol. The results also show additional interactions of hexobarbital as well as of ethylmorphine with ethanol elimination. Both compounds increased the initial blood levels of ethanol which precede accelerated elimination, probably by a first pass effect. At low concentrations of ethanol, ethylmorphine inhibits ethanol elimination by inhibition of ADH.

Evaluation of in vivo parameters of drug metabolizing enzyme activity in man after administration of clemastine, phenobarbital or placebo

The 24 h urinary excretion of 6beta-hydroxycortisol and D-glucaric acid, the plasma half lives and total clearances of aminopyrine, and serum gamma-glutamyl-transpeptidase activity have been measured in nineteen healthy male volunteers. The study was done double blind and was conducted as a test of induction of microsomal drug metabolizing enzymes during and after daily doses of 6 mg clemastine, 300 mg phenobarbital or a placebo. The urinary excretion of 6beta-hydroxycortisol and D-glucaric acid was significantly increased in the phenobarbital group, the standard for induction. No changes were observed after treatment with clemastine or placebo. Phenobarbital also reduced the half life of aminopyrine, but it was not affected by clemastine or placebo. Gamma-glutamyl-transpeptidase activity increased only in the phenobarbital group. The elimination constant k2 of aminopyrine and the excretion of glucaric acid in the pre-medication period were correlated (p less than 0.05) The results indicate that the tests were of diagnostic value in determination of microsomal enzyme induction by phenobarbital. Failure to observe similar changes after treatment with clemastine imply failure of induction of this activity under the experimental conditions.

Comparison of methods to study enzyme induction in man

A combination of several in vivo parameters has been applied in male healthy volunteers to test the suitability of these parameters to indicate enzyme induction in man: Urinary excretion of D-glucaric acid and 6 beta-hydroxycortisol, activity of serum gamma-glut amyltranspeptidase, and pharmacokinetics of aminopyrine respond significantly to phenobarbital treatment. Glucaric acid excretion is enhanced about 7-fold. Its response to induction overcomes the large individual and inter-individual variations which exist in the untreated state for glucaric acid excretion and the other parameters applied, as well. Total body clearance of aminopyrine as obtained after an oral test dose increases more than twofold from 251 to 551 ml/min upon phenobarbital treatment. This arises from increases in both the elimination constant and the apparent volume of distribution, as well. Urinary excretion of aminoantipyrine during 24 hr is about doubled, whereas the elimination of acetyl-aminotipyrine is not much affected. 6 beta-hydroxycortisol excretion in urine and activity of serum gamma-glutamyltranspeptidase are significantly augmented to about 150% of control values. Half life times of phenobarbital measured after termination of treatment are in normal range, suggesting no self-induction of phenobarbital metabolism. Because of the complexity of drug metabolizing enzymes only a combination of different parameters reliably indicates alterations in this enzyme system by inducing agents.