Danielle S. Fisher

Clinical pharmacokinetics of tyrosine kinase inhibitors: implications for therapeutic drug monitoring.

Abstract: The treatment of many malignancies has been improved in recent years by the introduction of molecular targeted therapies. These drugs interact preferentially with specific targets that are mutated and/or overexpressed in malignant cells. A group of such targets are the tyrosine kinases, against which a number of inhibitors (tyrosine kinase inhibitors, TKIs) have been developed. Imatinib, a TKI with targets that include the breakpoint cluster region–Abelson (bcr-abl) fusion protein kinase and mast/stem cell growth factor receptor kinase (c-Kit), was the first clinically successful drug of this type and revolutionized the treatment and prognosis of chronic myeloid leukemia and gastrointestinal stromal tumors. This success paved the way for the development of other TKIs for the treatment of a range of hematological malignancies and solid tumors. To date, 14 TKIs have been approved for clinical use and many more are under investigation. All these agents are given orally and are substrates of a range of drug transporters and metabolizing enzymes. In addition, some TKIs are capable of inhibiting their own transporters and metabolizing enzymes, making their disposition and metabolism at steady-state unpredictable. A given dose can therefore give rise to markedly different plasma concentrations in different patients, favoring the selection of resistant clones in the case of subtherapeutic exposure, and increasing the risk of toxicity if dosage is excessive. The aim of this review was to summarize current knowledge of the clinical pharmacokinetics and known adverse effects of the TKIs that are available for clinical use and to provide practical guidance on the implications of these data in patient management, in particular with respect to therapeutic drug monitoring.

LC-MS/MS of some atypical antipsychotics in human plasma, serum, oral fluid and haemolysed whole blood

Therapeutic drug monitoring (TDM) of atypical antipsychotics is common, but published methods often specify relatively complex sample preparation and analysis procedures. The aim of this work was to develop and validate a simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the analysis of amisulpride, aripiprazole and dehydroaripiprazole, clozapine and norclozapine, olanzapine, quetiapine, risperidone and 9-hydroxyrisperidone, and sulpiride in small (200 μL) volumes of plasma or serum for TDM purposes. The applicability of the method as developed to haemolysed whole blood and to oral fluid was also investigated. Analytes and internal standards were extracted into butyl acetate:butanol (9+1, v/v) and a portion of the extract analysed by LC-MS/MS (100 mm × 2.1 mm i.d. Waters Spherisorb S5SCX; eluent: 50 mmol/L methanolic ammonium acetate, pH* 6.0; flow-rate 0.5 mL/min; positive ion APCI-SRM, two transitions per analyte). Assay calibration (human plasma, oral fluid, and haemolysed whole blood calibration solutions) was performed by plotting the ratio of the peak area of the analyte to that of the appropriate internal standard. Assay validation was as per FDA guidelines. Assay calibration was linear across the concentration ranges studied. Inter- and intra-assay precision and accuracy were within 10% for all analytes in human plasma. Similar results were obtained for oral fluid and haemolysed whole blood, except that aripiprazole and dehydroaripiprazole were within 15% accuracy at low concentration (15 μg/L) in oral fluid, and olanzapine inter-assay precision could not be assessed in these matrices due to day-by-day degradation of this analyte. Recoveries varied between 16% (sulpiride) and 107% (clozapine), and were reproducible as well as comparable between human plasma, human serum, calf serum and haemolysed whole blood. For oral fluid, recoveries were reproducible, but differed slightly from those in plasma suggesting the need for calibration solutions to be prepared in this medium if oral fluid is to be analysed. LLOQs were 1-5 μg/L depending on the analyte. Neither ion suppression/enhancement, nor interference from some known metabolites of the antipsychotics studied has been encountered. The method has also been applied to the analysis of blood samples collected post-mortem after dilution (1+1, 1+3; v/v) in analyte-free calf serum.

Plasma, oral fluid, and whole-blood distribution of antipsychotics and metabolites in clinical samples

Background: Oral fluid provides a noninvasive method of sample collection. The aim of this study was to obtain oral fluid, plasma, and whole blood from patients prescribed amisulpride, aripiprazole, clozapine, quetiapine, risperidone, or sulpiride and to measure plasma:whole blood and plasma:oral fluid analyte distribution. Methods: Matched oral fluid, plasma and whole-blood samples were analyzed by liquid chromatography–tandem mass spectrometry. Results: There were 101 sets of samples from 90 (56 male, 34 female) patients (nine prescribed 2 antipsychotics, and one 3). There were ⩽5 samples for aripiprazole, amisulpride, and sulpiride. There was a good relationship between the plasma and hemolyzed whole-blood concentrations (R2 > 0.95), with plasma:whole-blood ratios varying between 0.7 (amisulpride) and 1.8 (aripiprazole). Amisulpride plasma and oral fluid concentrations were similar, whereas aripiprazole and dehydroaripiprazole oral fluid concentrations were approximately 8% of those in the plasma, reflecting the weak and strong plasma protein binding of these compounds, respectively. For the other analytes, plasma concentrations were 2–4 times higher than oral fluid concentrations. In general, there was a poor relationship (R2 = 0.3–0.7) between the plasma and oral fluid concentrations, possibly due to intrapatient saliva pH variation during sample collection. Conclusions: This work shows that hemolyzed whole-blood samples can be used for therapeutic drug monitoring purposes for the analytes of interest, provided that the plasma:whole-blood ratio is taken into account when interpreting results. For aripiprazole and dehydroaripiprazole, measurements in oral fluid will probably not be feasible. However, the relationship between plasma and oral fluid concentration for amisulpride, clozapine (and norclozapine), quetiapine (and possibly quetiapine metabolites), and risperidone/9-hydroxyrisperidone shows potential for oral fluid analysis.

Stability of some atypical antipsychotics in human plasma, haemolysed whole blood, oral fluid, human serum and calf serum

Long-term stability data of atypical antipsychotics in different matrices are not widely available. The aim of this work was to assess the stability of amisulpride, aripiprazole and dehydroaripiprazole, clozapine and norclozapine, olanzapine, quetiapine, risperidone and 9-hydroxyrisperidone, and sulpiride in human EDTA plasma, heparinised haemolysed human whole blood, oral fluid, human serum, and newborn calf serum stored in tightly capped plastic containers under a range of conditions. Measurements were performed by LC-MS/MS. Analyte instability was defined as a deviation of 15% or greater from the expected concentration. All analytes were stable following 3 freeze-thaw cycles in human plasma, and were stable in this matrix for at least 5 days at ambient temperature (olanzapine, 3 days); 4 weeks at 2-8°C (olanzapine, 2 weeks), and 2 years at -20°C (except for dehydroaripiprazole, olanzapine, and quetiapine, 1 year). In human serum, aripiprazole, dehydroaripiprazole, norclozapine, olanzapine, quetiapine, risperidone, 9-hydroxyrisperidone, and sulpiride were unstable after 5 days at ambient temperature, 3 weeks at 2-8°C, and 9 months at -20°C. Olanzapine was unstable in whole blood and oral fluid under most conditions studied, although prior addition of ascorbic acid had a moderate stabilising effect. All other analytes were stable in whole blood and oral fluid for at least 2 days at ambient temperature, 1 week at 2-8°C, and 2 months at -20°C (clozapine and norclozapine, 1 month whole blood). These results confirm that plasma (EDTA anticoagulant) is the sample of choice for TDM of atypical antipsychotics. Delayed (more than 1 week) analysis of patient samples should be undertaken with caution, especially with serum and with haemolysed whole blood. With olanzapine, only plasma collected and stored appropriately is likely to give reliable quantitative results.

Risperidone and Total 9-Hydroxyrisperidone in Relation to Prescribed Dose and Other Factors: Data From a Therapeutic Drug Monitoring Service, 2002-2010

Background: Information on the plasma risperidone and total 9-hydroxyrisperidone concentrations (‘total risperidone’) attained in clinical practice is scant. The aim of this work was to gather such information to better inform the interpretation of results. Method: This involved the audit of plasma total risperidone data from a risperidone therapeutic drug monitoring service 2002–2010. Results: There were 586 samples from 411 patients [289 (70%) males aged at the time of the first sample (median, range) 37 (7–83) years and 121 females aged 42 (10–91) years]. In patients aged 18 years and over, the mode of risperidone administration was oral: 242 samples (163 patients), risperidone long-acting injection (RLAI): 42 samples (39 patients), both oral and RLAI: 18 samples (12 patients), no information: 266 samples (211 patients). No risperidone/9-hydroxyrisperidone was detected in 10% of the samples, including 5 samples from patients prescribed RLAI. In the remainder, the mean (SD) total plasma total risperidone was all samples 35 (36), oral only 33 (29), RLAI only 23 (16), oral and RLAI 50 (21) &mgr;g/L. Overall, only 45% of the samples had plasma total risperidone within the range 20–59 mcg/L. Multiple linear regression analysis (95 samples) revealed that sex, smoking habit, and dose explained 21% of the variation in plasma total risperidone after oral dosage (dose alone only explained 11% of the variation). There was no discernable influence of age, body weight, and the plasma risperidone:total 9-hydroxyrisperidone ratio on plasma total risperidone. Conclusions: Risperidone therapeutic drug monitoring can help assess adherence and guide dosage even after RLAI.

Measurement of quetiapine and four quetiapine metabolites in human plasma by LC‐MS/MS

There is interest in monitoring plasma concentrations of N-desalkylquetiapine in relation to antidepressant effect. A simple LC-MS/MS method for quetiapine and four metabolites in human plasma (50 μL) has been developed to measure concentrations of these compounds attained during therapy. Analytes and internal standard (quetiapine-d8) were extracted into butyl acetate-butanol (10:1, v/v) and a portion of the extract analysed by LC-MS/MS (100 × 2.1 mm i.d. Waters Spherisorb S5SCX; eluent: 50 mmol/L methanolic ammonium acetate, pH* 6.0; flow-rate 0.5 mL/min; positive ion APCI-SRM, two transitions per analyte). Assay calibration (human plasma calibrators) was linear across the ranges studied (quetiapine and N-desalkylquetiapine 5-800, quetiapine sulfoxide 100-15,000, others 2-100 µg/L). Assay validation was as per FDA guidelines. Quetiapine sulfone was found to be unstable and to degrade to quetiapine sulfoxide. In 47 plasma samples from patients prescribed quetiapine (prescribed dose 200-950 mg/day), the (median, range) concentrations found (µg/L) were: quetiapine 83 (7-748), N-desalkylquetiapine, 127 (7-329), O-desalkylquetiapine 12 (2-37), 7-hydroxyquetiapine 3 (<1-48), and quetiapine sulfoxide 3,379 (343-21,704). The analyte concentrations found were comparable to those reported by others except that the concentrations of the sulfoxide were markedly higher. The reason for this discrepancy in unclear.

Plasma concentrations of quetiapine, N-desalkylquetiapine, o-desalkylquetiapine, 7-hydroxyquetiapine, and quetiapine sulfoxide in relation to quetiapine dose, formulation, and other factors.

Background: N-Desalkylquetiapine may be a pharmacologically active quetiapine metabolite. However, information on plasma concentrations of N-desalkylquetiapine and other quetiapine metabolites attained during quetiapine therapy is scant. The aim of this study was to investigate plasma concentrations of quetiapine, N-desalkylquetiapine, O-desalkylquetiapine, 7-hydroxyquetiapine, and quetiapine sulfoxide attained during therapy and analyze the data with respect to prescribed dose and other variables. Method: Quetiapine and its metabolites were measured in plasma samples submitted for quetiapine therapeutic drug monitoring (2009–2011). Concentration, metabolic ratio, and concentration corrected for dose (C/D) were investigated against quetiapine dose, age, sex, and formulation. Sample results were excluded if nonadherence with therapy was queried. Results: There were 99 samples from 59 patients. N-Desalkylquetiapine plasma concentrations showed the strongest correlation with dose of all analytes, but O-desalkylquetiapine and quetiapine sulfoxide were strongly correlated to plasma quetiapine concentrations. There was no significant difference in C/D for any analyte between males and females and no correlation to age. Quetiapine and quetiapine sulfoxide C/D were significantly different (P < 0.01) between patients prescribed immediate- and extended-release formulations. Quetiapine, 7-hydroxyquetiapine and quetiapine sulfoxide C/D showed significant variation (P < 0.02) between those samples taken 10–14 hours postdose as compared with that of 16–24 hours postdose, but there was no significant effect as regards N-desalkylquetiapine. Conclusions: Plasma quetiapine, O-desalkylquetiapine, 7-hydroxyquetiapine, and quetiapine sulfoxide concentrations were significantly affected by formulation and/or time since last dose. Plasma N-desalkylquetiapine concentrations were not affected by either factor therefore may be a better marker for quetiapine exposure than plasma quetiapine concentrations.

Unintentional domestic non-fire related carbon monoxide poisoning: Data from media reports, UK/Republic of Ireland 1986–2011

Context. Gathering information on the circumstances that give rise to unintentional domestic non-fire related carbon monoxide poisoning and the associated morbidity and mortality is not straightforward because the diagnosis is so often missed in life. Methods. We searched Newsbank and related databases (at least 332 sources, UK and Republic of Ireland) for reports of domestic carbon monoxide poisoning, 1986–end 2011 inclusive. The search terms were ‘carbon monoxide AND (house* OR home* OR caravan* OR tent*) NOT (work OR fire OR suicide*)’. Newsbank includes full-text articles from 19 UK national newspapers and over 140 UK & Irish regional and local newspapers and periodicals. Results and discussion. There were reports of 348 incidents (880 victims: 334 male, 352 female, 194 sex not stated). Reports of incidents increased from 1986 (1) to 2011 (28). There were 298 deaths (169 male, 124 female, 5 sex not reported). The likelihood of a fatal outcome increased with age for both males and females (28%, 1–9 years; 71%, 80 + years). The source of carbon monoxide was often a central heating or water boiler (48% of 244 incidents). Many incidents (49%) occurred in private dwellings. However, incidents in caravans, tents, sheds and outhouses had a much higher death rate. If a victim was discovered alive chances of survival were relatively good (87%), even if found unconscious. The estimated duration of carbon monoxide exposure ranged from minutes to years in both fatal and non-fatal incidents. Pets were recorded in 31 incidents (17 died). In 5 cases, carbon monoxide poisoning was identified through illness or death of a pet. Prosecutions were recorded in 49 incidents and at least 7 custodial (prison) sentences resulted, with 34 further convictions resulting in a fine. Charges were preferred against either an installer/maintenance engineer (42%), or the landlord (31%). Conclusion. Deaths and permanent injuries from unintentional domestic non-fire related carbon monoxide poisoning continue. Survival rates are relatively high if poisoning is diagnosed in life, but warning signs are often missed and inappropriate behavior such as placing barbecues in tents and failure to perform proper safety checks by gas appliance fitters still kills.

Fatal unintentional non-fire-related carbon monoxide poisoning: England and Wales, 1979–2012

Abstract Context. Unintentional carbon monoxide poisoning remains a significant cause of morbidity and mortality in England and Wales. Methods. Study design: observational case series. Data on fatal carbon monoxide poisoning in England and Wales from 1979 to 2012 were obtained from coroner reports. Data on unintentional non-fire-related carbon monoxide poisoning were extracted and were analysed by year of registration of death, sex, age group, and whether death occurred at a private house, flat, associated garage, or residential caravan (‘home’), or elsewhere. Results and discussion. There were 28,944 carbon monoxide-related deaths, of which 82% were male. Deaths increased from 965 (1979) to 1700 (1987), and then fell to 182 (2012). Of these 2208 (64% male) were recorded as unintentional non-fire-related deaths. Annual numbers of these latter deaths fell from 166 in 1979 to 25 in 2012 (i.e. from 3.37 to 0.44 per million population). Some 81 and 92% of such deaths in males and in females, respectively, occurred at ‘home’. A clear preponderance of male versus female deaths was seen in the 10–19, 20–39 and 40–64 years age groups, with similar numbers of deaths in males and in females in the younger (< 1 and 1–9 year) and higher (65–79 and 80 + years) age groups. A higher proportion of these excess deaths in males occurred outside the deceaseds ‘home’ in those aged 10–19, 20–39 and 40–64 years. Conclusion. Deaths from unintentional non-fire-related carbon monoxide poisoning are now much less common in England and Wales than in earlier years, but remain a cause for concern. Installation and proper maintenance of carbon monoxide alarms in dwellings and outhouses, for example, and education not only of the public, but also of health and other professionals as to the danger posed by carbon monoxide could help prevent such deaths.

A rapid and simple assay for lamotrigine in serum/plasma by HPLC, and comparison with an immunoassay

Monitoring serum/plasma concentrations of lamotrigine may be useful under certain circumstances. An HPLC column packed with strong cation-exchange (SCX)-modified microparticulate silica together with a 100% methanol eluent containing an ionic modifier permits direct injection of sample extracts. An HPLC-UV method developed using this principle for the measurement of serum/plasma lamotrigine is simple, sensitive and selective. The analysis time is less than 5 min. Intra- and inter-assay precision and accuracy meet acceptance criteria, and sample stability, and potential interferences from other compounds have been evaluated. There was good agreement with consensus mean results from external quality assessment samples (n = 32). Analysis of patient samples (n = 115) using the HPLC method and the Seradyn QMS® Lamotrigine immunoassay showed that the immunoassay over-estimated lamotrigine by 21% on average.