A rapid method for the quantification of the enantiomers of Warfarin, Phenprocoumon and Acenocoumarol by two-dimensional-enantioselective liquid chromatography/electrospray tandem mass spectrometry.

We describe a new fully validated enantioselective LC-MS/MS method for stereospecific quantification of both the racemic forms of Warfarin (WF), Phenprocoumon and Acenocoumarol in human plasma. Measurement specificity was assessed by using different blank donor plasma samples, where no interfering reagent peak appeared at the retention time (RT) of the targeted analytes. Response was linear for all analytes. Typical linear regression coefficients have >0.99. The recoveries ranged from 98% to 118%. Determinations in 10 normal healthy individuals revealed a high reproducibility of RTs. These findings confer to the method suitability for large population studies.

Dissolution and ionization of warfarin.

It has been shown in recent studies that warfarin exists in the solid state and in some nonaqueous solvents as a cyclic hemiketal. The present study was undertaken to investigate the ionization and ionization kinetics of warfarin, to confirm the probable existence of the cyclic hemiketal in aqueous solution, and to determine the possible consequences of the cyclic hemiketal to acyclic enol equilibrium and ionization kinetics on the dissolution rate of warfarin. The equilibrium aqueous solubility of un-ionized warfarin acid at 25 degrees C and ionic strength 0.5 (with potassium chloride) was found to be 1.28 X 10(-5) M, and its observed macroscopic pK alpha was 5.03-5.06, depending on the method of determination. By comparing the aqueous pK alpha of warfarin to phenprocoumin, a hydroxycoumarin that cannot exist in the cyclic hemiketal form, the hemiketal-acyclic enol ratio was estimated to be approximately 20:1. By stop-flow spectrophotometry, the ionization rate of warfarin (pH 3.5 jumped to pH 6.5) was found to have t1/2 less than 1-2 X 10(-3) s. The dissolution rate of warfarin from a rotating disk (600 rpm), as a function of pH, was measured under nonbuffered but pH-stat conditions (mu = 0.5 with potassium chloride). The pH-dissolution rate profile for warfarin agreed with that calculated from an equation derived previously to describe the dissolution of instantaneous ionizing acids, i.e., the profile was not perturbed from that expected from an acid of aqueous solubility 1.28 X 10(-5) M (un-ionized form) and pK alpha 5.06.

Determination of phenprocoumon in plasma and urine using at-line solid-phase extraction-capillary electrophoresis.

The use of capillary electrophoresis (CE) for the analysis of biological samples is rather problematic because of the large number of interferences present in the matrix. One of the possibilities to solve such problems is to couple solid-phase extraction (SPE) at-line with CE, a technique developed in our laboratory. In this study at-line SPE-CE is performed for the determination of the anticoagulant phenprocoumon in biological fluids. Plasma samples are injected after the addition of 1 vol.% of formic acid to release the drug from binding proteins, while urine samples can be directly injected. The procedure is linear between 0.2 and 30 microg ml(-1) with a correlation coefficient, r2, of 0.9996. The detection limit in plasma is 0.1 microg ml(-1), which is fully adequate in view of the concentrations, that have to be dealt with in practice. The phenprocoumon concentration in a plasma sample of a patient treated with the anticoagulant was 3.8 microg ml(-1).

[Breast feeding and oral anticoagulants]. / Borstvoeding en orale anticoagulantia.

Oral anticoagulants are frequently prescribed during lactation. Because these drugs could affect the hemostasis of the newborn, we did a literature search to find out whether precautions should be taken. It appeared that acenocoumarol and warfarin are not detectable in human milk. Besides the usual daily supplementation of 25 micrograms vitamin K for every breast-fed infant, precautions are not necessary. Phenprocoumon, ethylbiscoumacetate and phenindione are excreted in human milk and could affect neonatal hemostasis.

Reverse phase high performance liquid chromatographic determination of phenprocoumon in tablets.

A high performance liquid chromatographic procedure has been developed for the assay of phenprocoumon in tablets. In comparison to the present official USP assay procedure, it is equivalent in precision and accuracy and is faster and more specific. A mobile phase consisting of a 1% solution of acetic acid in acetonitrile-water (4 + 3) separates phenprocoumon from warfarin internal standard on a 6 micrometer octadecylsilane (ODS) column with UV detection at 311 nm. The method enables the concurrent determination of phenprocoumon and possible contaminants such as salicylic acid.

Determination of the anticoagulant phenprocoumon in human plasma and urine by high-performance liquid chromatography.

The determination of the anticoagulant phenprocoumon in plasma, after acidification and extraction with 1,2-dichloroethane was effected through isocratic high-performance liquid chromatography; a C18 reversed-phase column was used as stationary phase using aqueous acetonitrile as eluent and UV detection at 313 nm; p-chlorophenprocoumon was used as internal standard. A high proportion of phenprocoumon in urine is eliminated as the glucuronide and must be hydrolyzed enzymatically before extraction; the same column and detector as for plasma were used, but with gradient elution. The method was used in the range 0.1-5 mg/1, the sensitivity was 0.1 mg/1 for plasma and 0.02 mg/1 for urine, the precision was in the range 3-5% and the absence of interference due to other anticoagulants, drugs or endogenous compounds allows the specific determination of phenprocoumon in plasma and urine from patients and volunteers in clinical relevant cases, drug interaction, compliance, toxicological and pharmacokinetic studies.

Liquid chromatographic determination of coumarin anticoagulants in tablets: collaborative study.

A liquid chromatographic method for the determination of coumarin anticoagulants in tablets was collaboratively studied by 7 laboratories. The method uses an octadecylsilane-bonded microparticulate column, tetrahydrofuran-methanol-water-acetic acid mobile phase, and photometric detection at 311 nm. Each collaborator received samples of warfarin sodium, phenprocoumon, and dicumarol as a synthetic composite and as commercial individual and composited tablets. Pooled average assay values for synthetic and commercial tablet samples of warfarin sodium were 101.6 and 99.5%, respectively, with a combined reproducibility SD of 2.38% (CV = 2.37%) and combined repeatability SD of 1.49% (CV = 1.49%). Pooled average (SD) assay values for dicumarol and phenprocoumon commercial samples were 98.0 (2.27) and 101.3% (4.00), respectively. The content uniformity determinations of 2 mg warfarin sodium and 25 mg dicumarol tablets indicated average tablet contents (range) of 99.5% (91.0-116.0) and 98.0% (89.8-108.8), respectively. The method has been approved interim official first action.

Collaborative study of a semiautomated method for the analysis of acenocoumarol, phenprocoumon, and potassium warfarin tablets.

This collaborative study was undertaken to determine if the anticoagulants acenocoumarol, phenprocoumon, and potassium warfarin could be analyzed by the automated analysis system described in the collaborative study for the analysis of sodium warfarin and dicumarol. Collaborators were supplied with a composited tablet sample of each anticoagulant. Results agreed well with the National Formulary methods for phenprocoumon and potassium warfarin, and an unpublished method for acenocoumarol. For acenocoumarol, coefficients of variation on individual sets of data ranged from 0.30 to 1.94% For phenprocoumon, coefficients of variation ranged from 0.52 to 1.20%. For potassium warfarin, coefficients of variation ranged from 0.54 to 1.79%. The results of this study show that acenocoumarol, phenprocoumon, and potassium warfarin can be analyzed by the official AOAC method for the analysis of sodium warfarin and dicumarol tablets.

Biliary excretion of phenprocoumon and metabolites.

To evaluate phenprocoumon elimination its possible biliary excretion was evaluated in addition to the known pathway of renal elimination. Bile samples were obtained during diagnostic endoscopy in patients receiving chronic phenprocoumon therapy and were analyzed for phenprocoumon and its metabolites by HPLC and GC-MS. The following substances were detected, mainly in conjugated form: unchanged phenprocoumon and the metabolites 7-hydroxy-, 4'-hydroxy-, and 6-hydroxy-phenprocoumon. The data provide direct evidence of the biliary elimination of unchanged phenprocoumon and its metabolites in humans.

Determination of the coumarin anticoagulant phenprocoumon and metabolites in human plasma, urine and breast milk by high-performance liquid chromatography after solid-phase extraction.

The coumarin anticoagulant phenprocoumon (PH) and metabolites (6-, 7- and 4'-hydroxyphenprocoumon) were analysed in plasma and urine samples from anticoagulated patients using solid-phase extraction and high-performance liquid chromatography with reversed-phase columns and ultraviolet and fluorescence detection; a simpler handling of samples, higher selectivity, precision, accuracy and analytical recovery were obtained compared to analysis using liquid-liquid extraction. Similarly, a method for the analysis of PH in human breast milk was developed to assess the passage of anticoagulants into breast milk in anticoagulated lactating women.

A stable isotope assay for phenprocoumon and its metabolites.

A gas chromatographic/mass spectrometric assay for quantifying phenprocoumon and its 4'-, 6-, 7- and 8-hydroxy metabolites in microsomal preparations is described. This assay which uses deuterium-labeled analogs of the phenprocoumon metabolites as internal standards has a lower limit of quantitation of 20 ng ml-1. Diazomethane is used to derivatize both metabolites and parent compound yielding along with the expected 4-methoxy derivative a minor amount of the 2-methoxychromone. Resolution of the methylated metabolites is accomplished by capillary gas chromatography.