Pharmacokinetic interactions with methotrexate: is 7-hydroxy-methotrexate the culprit?
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Anti-Inflammatory Agents, Non-Steroidal↗
Biomedical subjects
L Slørdal
Publications and source records attributed to L Slørdal.
Interactions with the protein binding of 7-hydroxy-methotrexate in human serum in vitro.
7-Hydroxy-methotrexate (7-OH-MTX), the major extracellular methotrexate (MTX) metabolite, is 90-95% bound in human serum, with albumin (HSA) as the major binding protein. Reports of an interaction with concomitantly administered non-steroidal antiinflammatory drugs (NSAIDs) during MTX therapy led us to investigate whether these compounds could reduce the binding of 7-OH-MTX in vitro. Equilibrium dialysis experiments demonstrated that naproxen and indomethacin concentration dependently reduced the binding of 1 microM 7-OH-MTX. After ingestion of 1000 mg naproxen, per cent unbound 7-OH-MTX in sera from volunteers increased 2-3-fold in vitro, positively correlated to naproxen concentrations (P less than 0.00015). In addition, etacrynic acid, bilirubin, sulphamethizole and acetylsalicylic acid displaced 7-OH-MTX from its binding protein(s) in a competitive manner. The data suggest that 7-OH-MTX interacts with several exogenous and endogenous substances associated with HSA in human serum. Displacement of 7-OH-MTX from HSA may contribute to the interaction between NSAIDs and MTX.
Adult↗
Catecholamine binding and concentrations in acute phase plasma after surgery.
The present study was undertaken to decide whether the bound fractions and/or total concentrations of catecholamines were determinative for the variability of biologically active concentrations in human plasma. The binding and concentrations of noradrenaline (NA) and adrenalin (Adr) were determined in acute phase plasma after major hip surgery in five subjects. The bound fractions before surgery were 23.0% and 18.4% for NA and Adr, respectively. The binding of catecholamines increased in the post-operative period. Five days after surgery the binding of NA and Adr was 30.9% and 24.0%, respectively. The surgical trauma induced an acute phase reaction in plasma with a decrease of albumin (HSA) concentrations whereas the concentrations of alpha-1 acid glycoprotein (AAG) increased. The catecholamine concentrations showed a considerable inter- and intraindividual variability. However, the present work shows that the variability of the biologically active catecholamine concentrations is mainly dependent on the total plasma concentrations and not the plasma protein binding.
Acute-Phase Reaction↗
Pharmacokinetics of 7-hydroxy-methotrexate and methotrexate in the rat.
To investigate the pharmacokinetics of the active metabolite of methotrexate (MTX), 7-hydroxy-methotrexate (7-OH-MTX), 1 mg/kg of the compound was administered as single intravenous bolus injections to 6 unanaesthetized rats. For comparison, 1 mg/kg of the parent drug MTX was given to the same number of animals. Venous blood samples were drawn at intervals for a total of 120 min., and thereafter the rats were sacrificed and tissue samples were obtained from the brain, lungs, liver, kidneys, testes, fat, and muscle. Pharmacokinetics of 7-OH-MTX and MTX were biphasic, with a significantly (P less than 0.05) smaller central compartment of distribution (Vc) and a longer second phase half-life (t1/2(beta)) for 7-OH-MTX. MTX tissue concentrations exceeded those of 7-OH-MTX in all tissues examined. The highest 7-OH-MTX concentrations were found in renal tissue. It is implied that 7-OH-MTX is less extensively distributed than the parent compound.
Animals↗
Distribution of 7-hydroxymethotrexate in human blood.
We have examined the in-vitro distribution of 7-hydroxymethotrexate (7-OH-MTX), a cytotoxic metabolite of methotrexate (MTX), in human blood, and its protein binding in serum. The distribution of 7-OH-MTX (10(-6) M) in fresh samples of whole blood was studied at 37 degrees C and pH 7.51 +/- 0.05 (mean +/- s.d.), and its protein binding was assessed by equilibrium dialysis of serum against Krebs Ringer phosphate buffer at 37 degrees C and pH 7.41 +/- 0.07 (mean +/- s.d.). 7-OH-MTX had a mean cell/plasma concentration ratio of 0.03 (range 0-0.27, n = 18). It was extensively bound in human serum, with a bound fraction of 90.4 +/- 3.3% (mean +/- s.d.) in healthy volunteers (n = 11), and significantly lower, 82.3 +/- 4.0% (mean +/- s.d.), in hypoalbuminaemic surgical patients (n = 7). The binding of 7-OH-MTX was correlated with serum albumin (HSA) concentrations (r = 0.72, P less than 0.0007, n = 18). Blood distribution data support the contention that 7-OH-MTX has a small volume of distribution, and HSA appears to be mainly responsible for the high degree of its protein binding in serum.
Adult↗
Effect of anticancer drugs on drug metabolism.
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Animals↗
Distribution of nortriptyline in human blood: effects of temperature, pH, and drug concentration.
An in vitro study of putative factors causing postvenipuncture redistribution of the tricyclic antidepressant nortriptyline (NT) in blood was carried out in blood samples from a single subject. The influence of varying temperature, pH, and drug concentration on the protein binding of NT was assessed by equilibrium dialysis. The influence of the same variables on the distribution of NT in whole blood was measured by calculating the cell/plasma (C/P) drug concentration ratios after centrifugation of blood samples. Variation in temperature did influence the distribution of NT in blood considerably. From 4 to 37 degrees C, the C/P ratio was found to increase from 1.0 +/- 0.1 to 1.7 +/- 0.2, and protein binding expressed as unbound fraction from 2.9 +/- 0.2 to 7.0 +/- 1.1% (mean +/- SD). Neither pH variations within the 7.0-7.6 range, nor variations in drug concentration, were found to alter NT distribution at 37 degrees C. The observed effect of temperature on NT distribution shows that handling of blood samples from patients taking NT should be standardized in order to avoid errors of interpretation.
Buffers↗
High-dose metoclopramide and chlorpromazine in the treatment of cisplatin-induced emesis.
Twenty patients with lung cancer, treated with cisplatin and etoposide, were divided into two groups at random and given antiemetic therapy consisting of either high-dose metoclopramide (MCL) intravenously (8 mg/kg over 7 hours) and chlorpromazine (CPZ) (50 mg orally), or a reduced dose of MCL (6 mg/kg over 7 hours) and CPZ (50 mg orally). Serum MCL concentrations were monitored during the infusions. In the two groups, 33% and 38% vomited during and after the courses, and antiemetic control was achieved in 83% and 75% of the patients. There was no significant difference between the groups, and side effects were negligible. MCL concentrations exceeded 0.7 microgram/ml in all patients, with great inter-individual variation.
Adult↗
High-dose methotrexate therapy (6-8 g/m2) in childhood malignancies: clinical tolerability and pharmacokinetics.
Five children, ages 2.5 to 12 years (mean 6.2 years), with acute lymphoblastic leukemia or non-Hodgkin's lymphoma were given 22 courses of high-dose methotrexate (HD-MTX) therapy (6-8 g/m2/24 h). No serious clinical complications were encountered, but stomatitis occurred after three (14%) of the courses. First-phase elimination half-lives (t1/2(alpha)) of MTX and 7-hydroxy-methotrexate (7-OH-MTX) after 21 infusions were 2.7 +/- 0.4 h and 6.5 +/- 1.8 h (mean +/- SD). In one course (4.5%) there was delayed systemic MTX elimination, with first-phase elimination half-lives (t1/2(alpha] for MTX and 7-OH-MTX of 4.2 and 9.9 h, respectively, and second-phase elimination half-lives (t1/2(beta)) of 43 and 58 h. Significant decreases in white blood cell count, increases in serum creatinine, and increases in alanine aminotransferase and/or aspartate aminotransferase during the first 2-6 days were present in five (23%), three (14%), and six (27%) of the courses, respectively. The regimen was tolerated well by the children.
Antineoplastic Combined Chemotherapy Protocols↗
Lactoferrin and C-reactive protein in response to cytostatic drugs with emphasis on methotrexate.
In this study plasma concentrations of lactoferrin (LF) and C-reactive protein (CRP) are examined in 9 children with different kinds of cancer but without any intercurrent infections. New, sensitive enzyme-linked immunosorbent assay for LF and CRP are described. The samples are drawn before, during, and after the cytotoxic drugs are given. The cytotoxic courses include cis-platinum, vincristine, adriamycin, cytarabine, and methotrexate (6 g/m2/24 h and 33.6 g/m2/24 h). During the infusion of methotrexate 33.6 g/m2 the concentrations of LF are increased, only a small increase of CRP is observed, and for the other groups there is no changes of both parameters.
Adult↗
Distribution of methotrexate in human blood in vitro: independence of temperature, pH and drug concentration.
Distribution of methotrexate (MTX) in blood samples from a single donor as a function of incubation time, temperature, pH and drug concentration was investigated. Equilibrium, as expressed by the cell/plasma (C/P) partition ratio, was reached rapidly and was constant for 5 to 30 min following incubation. The C/P ratio was unaffected by temperature variations in the 4 to 37 degrees C range, pH variations from 7.06 to 7.82 and varying drug concentrations from 5 X 10(-5) M to 5 X 10(-10) M. Contradicting an earlier investigation, this implies that MTX can be monitored in plasma or serum samples without undue worries about hitherto unexplained and unusual distribution kinetics for this drug in blood.
Adult↗
A simple HPLC method for measuring metoclopramide in serum.
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Chromatography, High Pressure Liquid↗
Pharmacokinetics of methotrexate and 7-hydroxy-methotrexate after high-dose (33.6 g/m2) methotrexate therapy.
We have measured MTX and 7-OH-MTX in plasma and urine samples from a 9-year-old boy treated with six consecutive 24-h IV high-dose MTX courses (33.6 g/m2) after a relapse of ALL. The between-course pharmacokinetics of MTX and 7-OH-MTX were found to be highly reproducible. Both MTX and 7-OH-MTX elimination followed a biphasic curve, initial half-lives (t1/2(alpha] being 2.86 +/- 0.44 h and 5.14 +/- 0.46 h (mean +/- SD) and second-phase biological half-lives (t1/2(beta] being approximately 18 and 16 h, respectively. The apparent volume of distribution for MTX was 0.8 L/kg, whereas the corresponding value for 7-OH-MTX was threefold less. Since clearance of MTX was within the range reported for lower doses, the data suggest that MTX pharmacokinetics are not dose-dependent up to 33.6 g/m2.
Child↗
Induction of HL-60 cell differentiation by 3-deaza-(+/-)-aristeromycin, an inhibitor of S-adenosylhomocysteine hydrolase.
The metabolically stable inhibitor of S-adenosylhomocysteine hydrolase (AdoHcyase), 3-deaza-(+/-)-aristeromycin (dzAri) has recently been shown to induce differentiation in HL-60 cells. The present study was undertaken to characterize the cytostatic, cytotoxic, and differentiation inducing properties of dzAri in HL-60 cells and to investigate biochemical consequences of AdoHcyase inhibition. A dye exclusion test and a clonogenic assay were used to test cytotoxic and cytostatic properties. dzAri had reversible cytostatic effects on HL-60 cells at concentrations lower than 10 microM and partially reversible cytotoxic effects above 10 microM. The induction of differentiation was dependent upon concentration and time of exposure, with maximal effect after 6 days incubation with 5-10 microM dzAri. Washout experiments demonstrated that the cells were not committed to differentiation after 48 h of incubation with dzAri. The AdoHcyase of HL-60 cells was inhibited with a Ki of 20 nM. The concentration of S-adenosylhomocysteine increased dose dependently 48 h after incubation with 0.1-100 microM dzAri. The incorporation of [3H]methyl from [methyl-3H]methionine into 5-methylcytosine of DNA was reduced by 26% at 5 microM dzAri. The findings indicate that continuous presence of dzAri is necessary to induce differentiation and inhibit proliferation in HL-60 cells. The inhibition of AdoHcyase perturbs levels of transmethylation metabolites and the incorporation of [3H]methyl into 5-methyl-cytosine of DNA.
Adenosine↗
Methotrexate measurements in plasma: comparison of enzyme multiplied immunoassay technique, TDx fluorescence polarization immunoassay, and high pressure liquid chromatography.
One hundred nine patient plasma samples were examined for methotrexate (MTX) levels by enzyme multiplied immunoassay technique (EMIT), fluorescence polarization immunoassay (TDx), and high pressure liquid chromatography (HPLC). EMIT analysis was performed twice within a time span of 18 months. All three methods measure MTX with a high degree of specificity, sensitivity, and precision. There was no evidence of decay of MTX concentrations in samples stored at -20 degrees C for 1.5 years. EMIT, TDx, and HPLC are adequate methods for MTX quantification in the clinical laboratory.
Chromatography, High Pressure Liquid↗
Microsomal metabolism of antipyrine in rats treated with antineoplastic drugs.
Pretreatment with antineoplastic drugs for at least 1 week is known to reduce in vivo metabolic clearance of antipyrine in rats tested after 24 h of fasting and restraining. In this study hepatic metabolism of 14C-antipyrine was investigated in 9,000 g supernatants of fed, unrestrained rats pretreated with cyclophosphamide, 5-fluorouracil or methotrexate. Total antipyrine metabolites formed were measured by a radiometric assay. Apparent Vmax and Km values were estimated and transformed to intrinsic (hepatic) clearance and total (body) clearance for comparison with in vivo terms of metabolic rate. Hepatic microsomal metabolism of antipyrine in control rats expressed as intrinsic clearance, 0.12 +/- 0.03 ml (g liver min)-1, and total clearance, 4.8 +/- 1.2 ml (kg body wt min)-1, was not significantly changed after antineoplastic pretreatment, indicating that the previously observed inhibitory action of these drugs on in vivo antipyrine metabolism may be modulated by factors such as fasting and stress.
Animals↗
The effect of antineoplastic drugs on the pharmacokinetics of antipyrine in the rat.
The pharmacokinetics of antipyrine was investigated in individual rats pretreated with cyclophosphamide, 5-fluorouracil and methotrexate. Before oral dosing a complete emptying of the rat stomach was obtained by 24 hours of fasting and prevention of coprophagy. Antipyrine was given intravenously via a cannula in an inguinal vein and repeated samples of blood were drawn from a cannula in an inguinal artery. Systemic availability of oral antipyrine was studied in rats given the 14C-labelled drug intravenously and the 3H-labelled drug orally after pretreatment with cyclophosphamide. The log plasma concentration versus time curve of antipyrine given orally showed a short absorption and distribution phase followed by a linear elimination phase. Peak antipyrine concentrations were reached 3-6 minutes after oral dosing in control rats. The rate of absorption of antipyrine was moderately decreased by methotrexate. All drugs increased the area under the curve (AUC) of antipyrine. The systemic availability of oral antipyrine after cyclophosphamide pretreatment (0.88) was not changed, but the metabolic clearance of the drug was reduced. The apparent elimination rate constant was decreased by methotrexate and the apparent volume of distribution was decreased by cyclophosphamide and 5-fluorouracil. The results indicate that antineoplastic agents may change drug kinetics in different ways in rats.
Animals↗
Qualitatively different mechanisms of resistance to doxorubicin, both involving altered glutathione pools, in two myeloid cell lines in vitro.
Subclones of the two well-characterized myeloid cell lines HL-60 and KG1a were selected for doxorubicin resistance by systematic exposure to increased concentrations of the drug in vitro. Both subclones demonstrated a threefold increased resistance to the drug as evident from cell growth in liquid culture and clonogenicity in a semisolid matrix. Both resistant subclones displayed a similar degree of reduced total and nuclear doxorubicin levels. The HL-60 and the KG1a cells differed qualitatively and quantitatively with respect to glutathione (GSH) levels during culture, with markedly elevated concentrations in the resistant HL-60 subclone during 1 week of culture. Total GSH pools in resistant and sensitive KG1a cells were similar, but maximum GSH levels were reached earlier in the resistant KG1a clones than in the parental cells. Northern blot analysis suggests that resistance was accompanied by increased mdr1 expression in the KG1a but not in the HL-60 cells, whereas alterations in the glutathione S-transferase P1-1 and topoisomerase II message was evident in the latter. The results demonstrate the complex, multifactorial mechanisms behind the in vitro induction of even moderate resistance in anthracyclines.
Antibiotics, Antineoplastic↗