Transfer of Candesartan Into Human Breast Milk.

BACKGROUND: There are currently no data regarding the transfer of candesartan into human milk. This report provides data on this transfer, an estimation of the amount breastfed infants receive, and plasma concentrations from two breastfed infants. CASES: Three breastfeeding mothers, all stabilized on candesartan (8-32 mg/d), provided milk and plasma samples over one dosing interval (24 hours). Two infant plasma samples were obtained. The amount the infants ingested was estimated to be 0.09% (95% CI 0.07-0.11) of the maternal dose (weight-adjusted). Candesartan was undetectable (less than 0.2 micrograms/L) in infant plasma samples. CONCLUSION: A relative infant dose of 0.09% suggests that maternal benefit from candesartan at standard therapeutic doses may outweigh risk in breastfeeding healthy, term infants.

Development, validation and application of a novel liquid chromatography tandem mass spectrometry assay measuring uracil, 5,6-dihydrouracil, 5-fluorouracil, 5,6-dihydro-5-fluorouracil, α-fluoro-ß-ureidopropionic acid and α-fluoro-ß-alanine in human plasma.

The plasma 5,6-dihydrouracil/uracil (UH2/U) ratio is a possible phenotypic marker of dihydropyrimidine dehydrogenase (DPD) activity, hence an index of 5-fluorouracil (5-FU) response and toxicity. Studies have re-affirmed the value of 5-FU and 5,6-dihydro-5-fluorouracil (FUH2) for therapeutic drug monitoring (TDM). However, FUH2 has limited stability in plasma, necessitating expedited plasma separation and freezing, where routine compliance may not be easy. The metabolites α-fluoro-ß-ureidopropionic acid (FUPA) and α-fluoro-ß-alanine (FßAL) are stable in plasma and are probable candidates for TDM. This paper describes development, validation and application of an LC-MS/MS assay quantifying U, UH2, 5-FU, FUH2, FUPA and FßAL in human plasma. Extraction was by salt-assisted liquid-liquid extraction (LLE) in two-stages with pH adjustment. The supernatants were mixed, dried and reconstituted. Analytes were resolved on the Luna PFP (2) (150×2.00mm, 3µ) column by gradient elution and analyzed by tandem mass spectrometry via electrospray ionisation in positive polarity. The analytical response was linear (r2≥0.99) in the concentration (ng/mL) ranges: 50-10 000 for FßAL and FUH2, 50-5 000 for FUPA, 50-100 000 for 5-FU, 5-200 for U and 10-400 for UH2. Within- and between-run accuracy and precision were ≤ 10.2% and ≤ 9.8% respectively across the QC range and inclusive of LLOQ. The internal standard (IS) normalised matrix effects were within 93-112% with CV of ≤ 9.7% and normalised recoveries were within 91-107% with CV of ≤ 9.8%. This robust assay was successfully applied to samples from rectal and colorectal cancer patients (n=10) on 5-FU. Deviations ≤ 2.0% from the mean values were observed when incurred samples were reanalysed.

Quantification and clinical application of carboplatin in plasma ultrafiltrate.

Carboplatin is a chemotherapy drug used in a variety of cancers with the primary toxicity being exposure-dependant myelosuppression. We present the development and validation of a simple, robust inductively coupled plasma mass spectrometry (ICP-MS) method to measure carboplatin in plasma ultrafiltrate. Plasma ultrafiltrates samples were prepared using Amicon Ultra 30,000da cut-off filters and then diluted with ammonia EDTA before ICP-MS analysis. The assay was validated in the range 0.19-47.5mg/L carboplatin in ultrafiltrate. The assay was linear (r2>0.9999), accurate (<6% bias, 12% bias at LLOQ) and precise (intra- and inter-day precision of <3% coefficient of variation). No matrix effects were observed between plasma ultrafiltrate and aqueous platinum calibrators and recovery was complete. The assay was applied to 10 clinical samples from patients receiving carboplatin. Incurred sample reanalysis showed reproducible values over 3 analysis days (<6% CV). As plasma stability prior to ultrafiltration has been a major concern in previous clinical studies this was studied extensively at room temperature (22°C) over 24h. Carboplatin was found to be stable in both spiked plasma (n=3) and real patient samples (n=10) at room temperature for up to 8h before ultrafiltration. This makes routine measurement of carboplatin concentrations in clinical settings feasible.

Quantification of dabigatran and indirect quantification of dabigatran acylglucuronides in human plasma by LC-MS/MS.

BACKGROUND: An assay for the quantification of dabigatran and its active metabolites, dabigatran acylglucuronides, has not previously been described in detail. RESULTS: For the quantification of total dabigatran concentration (free dabigatran and acylglucuronides), samples were subjected to alkaline hydrolysis. For the quantification of free dabigatran, samples were acidified with ammonium formate. Following acetonitrile protein precipitation, the samples were analyzed by LC-MS/MS using gradient elution to ensure separation of dabigatran from dabigatran acylglucuronides. Mean recoveries ≥98% were achieved. The assay was validated over the range 2.5-1000 ng/ml dabigatran, imprecision was <9% CV (<15% at LLOQ) and accuracy was 101-114%. CONCLUSION: An assay for dabigatran with indirect quantification of dabigatran acylglucuronides in plasma was developed, validated and applied.

Transfer of doxazosin into breast milk.

To the best of our knowledge, there have been no published studies of doxazosin transfer into human milk. In rats, milk concentrations twentyfold higher than in plasma have been reported. Based on these animal data, some references advise to avoid breastfeeding during doxazosin therapy. However, the physicochemical properties of doxazosin suggest low transfer into human milk. A 37-year-old breastfeeding woman who was administered doxazosin 4 mg daily for 2 doses was studied. Doxazosin concentrations in milk and plasma were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The milk/plasma area under the concentration-time curve (AUC0-18 hours) ratio was 0.1. This finding is consistent with what could be predicted based on the physicochemical properties of doxazosin. The average and maximum milk concentrations were 2.9 and 4.2 µg/L. These values correspond to estimated relative infant doses of 0.06% and 0.09%, respectively, assuming standard infant milk intake. These values are well below the generally accepted cutoff of 10% for predicting safety during breastfeeding. A low relative infant dose of < 0.1% suggests that maternal doxazosin therapy may be compatible with breastfeeding after careful individual risk-benefit analysis.

Influence of adult age on the total and free clearance and protein binding of (R)- and (S)-warfarin.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: Hepatic drug clearance is thought to be reduced with age. However for highly protein bound drugs, which are cleared by capacity-limited metabolism, studies on total clearance have been conflicting. The hypothesis that protein binding decreases with age has been used to explain this. Warfarin is a highly protein bound drug, which is cleared by capacity-limited metabolism. There are conflicting or little data on the relationship between adult age and total and free clearance and protein binding of (R)- and (S)-warfarin. WHAT THIS STUDY ADDS: In a clinical study of 72 patients (18-89 years) on warfarin therapy, both total and free clearance of (R)-warfarin decreased with age. For (S)-warfarin there was a stronger signal of a decrease in free than total clearance. Protein binding was found not to correlate with age for (R)- and (S)-warfarin. In an ex vivo study, in which warfarin was spiked to plasma samples from 60 healthy subjects (19-87 years), no correlation between protein binding and age was found. These data support the hypothesis that hepatic drug clearance decreases with age. This should be taken into consideration when individualizing dosing, particularly in the elderly. AIMS: To test the hypothesis that the clearance (CL) of warfarin, a very highly protein bound drug with capacity-limited metabolism, decreases with age. METHODS: In a clinical study, a steady-state blood sample was taken from 72 patients (18-89 years) on routine treatment with warfarin. Concentrations of (R)- and (S)-warfarin were determined in plasma (total) and ultrafiltrate (free) by LC-MS/MS. Total and free CL and protein binding were determined and regressed against age and other covariates. In an ex vivo study, warfarin was spiked to plasma samples from 60 healthy subjects (19-87 years) and protein binding was regressed against age and other covariates. RESULTS: For (R)-warfarin a significant decrease with age was found for both total and free CL (P < 0.001). For (S)-warfarin there was a stronger signal of a decrease with age in free CL (P= 0.005) vs. total CL (P= 0.045). The decrease in CL of (R)- and (S)-warfarin was 0.3-0.5% per year. Other covariates influencing CL were lean body weight for both (R)- and (S)-warfarin and CYP2C9 genotype and blood sampling time for (S)-warfarin. Protein binding of (R)- and (S)-warfarin was not found to change significantly with age in either the clinical or the spiked samples, despite a slight decrease in albumin concentration with age. CONCLUSIONS: These data support the hypothesis that the CL of (R)- and (S)-warfarin decreases with age. More accurate information was gained when measuring free CL for (S)-warfarin. Warfarin protein binding did not change significantly with age.

Influence of ABCB1 (P-glycoprotein) haplotypes on nortriptyline pharmacokinetics and nortriptyline-induced postural hypotension in healthy volunteers.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: A single nucleotide polymorphism in ABCB1, which encodes P-glycoprotein, has retrospectively been associated with symptoms of nortriptyline-induced postural hypotension in depressed patients. This finding needs to be replicated in independent studies before recommendations regarding pharmacogenetic testing can be made. WHAT THIS STUDY ADDS: In a prospective study of healthy volunteers homozygous for ABCB1 (1236-2677-3435, TTT/TTT or CGC/CGC), a single dose of nortriptyline was administered, plasma exposure was determined and blood pressure and heart rate were monitored during posture change. No differences between ABCB1 haplotype groups were found in plasma exposure of nortriptyline and its active metabolites, E- and Z-10-hydroxynortriptyline. The heart rate response to posture change was increased with nortriptyline, whereas there was no difference in blood pressure response. However, no differences between haplotype groups were observed except that the pre dose heart rate response to standing was greater in the TTT than CGC homozygotes. The association between ABCB1 polymorphisms and nortriptyline-induced postural hypotension found in a previous study could not be confirmed. The results raise the possibility of a predisposition in heart rate response in the TTT homozygotes rather than an effect of nortriptyline. AIMS To investigate the influence of ABCB1 (1236-2677-3435) polymorphisms on nortriptyline pharmacokinetics and nortriptyline-induced postural hypotension in healthy volunteers. METHODS: Genetic screening of 67 healthy volunteers identified eight CGC homozygotes and nine TTT homozygotes of ABCB1 (1236-2677-3435), who were administered a single dose of nortriptyline 25 mg. Plasma exposure of nortriptyline and its active metabolites, E- and Z-10-hydroxynortriptyline, was determined over 72 h. Heart rate and blood pressure responses to posture change (active standing and passive head-up tilt) were measured continuously using finger plethysmography. RESULTS: There were no differences in plasma exposure between ABCB1 haplotype groups, as the geometric mean (95% CI) AUC(0,72 h) ratios were 0.98 (0.94, 1.03), 1.02 (0.96, 1.09) and 0.95 (0.80, 1.10) for nortriptyline, E- and Z-10-hydroxynortriptyline, respectively. The pre dose heart rate response to standing was greater in the TTT than CGC homozygotes (mean (95% CI) difference 7.4 (1.5, 13.4) beats min(-1) , P = 0.02). At t(max) at 8 h post dose, nortriptyline increased the heart rate response to posture change in all subjects with mean (95% CI) Δ heart rate values of 7.4 (3.6, 11.3) beats min(-1) on active standing (P = 0.0009) and 4.8 (2.0, 7.6) beats min(-1) on head-up tilt (P = 0.002), but no difference was observed between haplotype groups. There was no difference in blood pressure response to posture change in either group. CONCLUSION: The association between ABCB1 polymorphisms and nortriptyline-induced postural hypotension found in the previous study could not be confirmed. The results raise the possibility of a predisposition in heart rate response in the TTT homozygotes rather than an effect of nortriptyline.

Quantification of total and free concentrations of R- and S-warfarin in human plasma by ultrafiltration and LC-MS/MS.

A sensitive LC-MS/MS assay for quantification of total and free concentrations of R- and S-warfarin in plasma was required to support clinical studies on warfarin enantiomers. Several ultrafiltration devices were evaluated for separation of free warfarin from plasma proteins. The highest precision and lowest non-specific binding was obtained for Centrifree ultrafiltration devices. R- and S-warfarin were extracted from plasma (total) and ultrafiltrate (free) by liquid-liquid extraction with methyl tert-butyl ether using d(6)-warfarin as internal standard. Mean extraction recovery was 68 ± 4%. The enantiomers were separated on a Chirobiotic V column with isocratic elution using 40% methanol and 0.03% acetic acid in water. Negative mode electrospray ionisation was used for MS/MS detection, monitoring the ion transition m/z 307/161. Calibration curves (quadratic, weighted 1/x) were fitted over the range of 20-2,000 ng/ml (r(2)≥0.995) in plasma and 0.5-20 ng/ml (r(2)≥0.998) in ultrafiltrate. The lower limit of quantification for R- and S-warfarin was 0.5 ng/ml in ultrafiltrate. Intra- and interday precision (% RSD) and bias were within 10% in all cases, and matrix effects were negligible. The assay was applied successfully to analysis of samples from clinical studies.

Quantification of cyclizine and norcyclizine in human plasma by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

A rapid and simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay was developed and validated for quantification of cyclizine and its main metabolite norcyclizine in human plasma. Samples were prepared by protein precipitation with acetonitrile and cinnarizine was used as internal standard (recovery >87%). The analytes were eluted from a C8 50 mm×2.0 mm analytical column using a linear gradient of methanol and 0.05% formic acid with a total analysis time of 4 min. Analytes were detected by MS/MS using electrospray ionisation in the positive mode with multiple reactions monitoring (MRM) of the precursor ion/product ion transitions 267.2/167.2 for cyclizine and 253.2/167.2 for norcyclizine. Matrix effects were negligible. Standard curves for cyclizine and norcyclizine were linear (r(2)≥0.996) over the range 2-200 ng/mL, with 2 ng/mL representing the lower limit of quantification. Relative standard deviations were <14% for intra- and inter-day precision and the accuracy was within ±8%. The assay was successfully applied to a clinical study.

Investigation of the metabolic fate of 2-, 3- and 4-bromobenzoic acids in bile-duct-cannulated rats by inductively coupled plasma mass spectrometry and high-performance liquid chromatography/inductively coupled plasma mass spectrometry/electrospray mass spectrometry.

Inductively coupled plasma mass spectrometry (ICPMS) has been used to determine the rate and routes of excretion of bromine following the intraperitoneal administration (50 mg kg(-1)) of 2-, 3- and 4-bromobenzoic acids to male bile-duct-cannulated rats. Analysis of urine and bile for (79/81)Br using ICPMS showed that all three bromobenzoic acids were rapidly excreted (82-98%) within 48 h of dosing, primarily via the urine. High-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICPMS) was then used to obtain metabolite profiles for bile and urine. These profiles revealed that extensive metabolism had taken place, with the unchanged bromobenzoic acids forming a minor part of the total of compound-related material detected. Concomitant MS studies, supplemented by alkaline hydrolysis, enabled the identification of the major metabolite of all three of the bromobenzoic acids as a glycine conjugate. Ester glucuronide conjugates were also identified, but formed only a small proportion of total.

Application of inductively coupled plasma mass spectrometry and high-performance liquid chromatography--with parallel electrospray mass spectrometry to the investigation of the disposition and metabolic fate of 2-, 3- and 4-iodobenzoic acids in the rat.

ICP-MS, HPLC-ICP-MS and HPLC-ICP-MS/ESI-MS have been applied to determine the disposition and metabolic fate of 2-, 3- and 4-iodobenzoic acids following intraperitoneal administration at 50 mg kg(-1) to male bile duct cannulated rats. Quantitative excretion balance studies based on the determination of the total iodine content of urine and bile showed that all three iodobenzoic acids were rapidly excreted. Recoveries ranging from 95 to 105% of the administered doses were achieved within 24 h of administration. Metabolite profiles for urine and bile showed extensive metabolism with unchanged iodobenzoic acids forming a minor part of the total. A combination of alkaline hydrolysis and MS enabled the identification of the major metabolites of all three iodobenzoic acids as glycine and ester glucuronide conjugates with very little if any of the parent compounds excreted unchanged.

High-performance liquid chromatography/inductively coupled plasma mass spectrometry and tandem mass spectrometry for the detection of carbon-containing compounds.

High-performance liquid chromatography (HPLC) combined with inductively coupled plasma mass spectrometry (ICPMS) has been studied as a means for the detection of carbon to provide a 'universal' method for detecting organic compounds in chromatographic eluents. Carbon is particularly difficult to ionise and the amount of carbon present in normal chromatographic systems leads to high backgrounds, making detection a challenge. Novel separation approaches were therefore employed, using either entirely aqueous eluents (at temperatures of 60 and 160 degrees C, dependent on the column used) to eliminate the organic modifier completely, or isotopically enriched solvents. For the aqueous eluents, detection limits for sulphanilamide were found to be 2.26 microg, corresponding to 1.13 micromol (0.47 micromol of carbon), injected on a conventional 4.6 mm i.d. column. The use of a narrow bore column with highly isotopically enriched 12C-methanol (99.95 atom%) as organic modifier for the mobile phase enabled the detection of 86 micromol for 13C-triple-labelled caffeine and 79 micromol for 13C-double-labelled phenacetin. The sensitive detection of 12C-compounds with 13C-enriched methanol as organic modifier proved impractical due to a lower level of isotopic enrichment (99 atom%) of this solvent, with the residual 12C-methanol resulting in significant interference.

Sensitive sulphur-specific detection of omeprazole metabolites in rat urine by high-performance liquid chromatography/inductively coupled plasma mass spectrometry.

The use of high-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICPMS) with sulphur-specific detection was investigated as a method for obtaining metabolite profiles for the drug omeprazole administered as a 1:1 mixture of (32)S- and (34)S-labelled material. Analysis based on the monitoring of the chromatographic eluent at either m/z 32 or 34 was not successful due to insufficient sensitivity caused by interferences from polyatomic ions. However, reaction of sulphur with oxygen in the hexapole collision cell, combined with monitoring at m/z 48 (for (32)S) or m/z 50 (for (34)S), provided a facile method for metabolite profiling. Detection of m/z 48 was superior in sensitivity to detection of m/z 50.