Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) methods for the therapeutic drug monitoring of cytotoxic anticancer drugs: An update

In the era of precision medicine, there is increasing evidence that conventional cytotoxic agents may be suitable candidates for therapeutic drug monitoring (TDM)- guided drug dosage adjustments and patient's tailored personalization of non-selective chemotherapies. To that end, many liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) assays have been developed for the quantification of conventional cytotoxic anticancer chemotherapies, that have been comprehensively and critically reviewed. The use of stable isotopically labelled internal standards (IS) of cytotoxic drugs was strikingly uncommon, accounting for only 48 % of the methods found, although their use could possible to suitably circumvent patients' samples matrix effects variability. Furthermore, this approach would increase the reliability of cytotoxic drug quantification in highly multi-mediated cancer patients with complex fluctuating pathophysiological and clinical conditions. LC-MS/MS assays can accommodate multiplexed analyses of cytotoxic drugs with optimal selectivity and specificity as well as short analytical times and, when using stable-isotopically labelled IS for quantification, provide concentrations measurements with a high degree of certainty. However, there are still organisational, pharmacological, and medical constraints to tackle before TDM of cytotoxic drugs can be more largely adopted in the clinics for contributing to our ever-lasting quest to improve cancer treatment outcomes.

Gender medicine and oncology: report and consensus of an ESMO workshop

BACKGROUND

The importance of sex and gender as modulators of disease biology and treatment outcomes is well known in other disciplines of medicine, such as cardiology, but remains an undervalued issue in oncology. Considering the increasing evidence for their relevance, European Society for Medical Oncology decided to address this topic and organized a multidisciplinary workshop in Lausanne, Switzerland, on 30 November and 1 December 2018.

DESIGN

Twenty invited faculty members and 40 selected physicians/scientists participated. Relevant content was presented by faculty members on the basis of a literature review conducted by each speaker. Following a moderated consensus session, the final consensus statements are reported here.

RESULTS

Clinically relevant sex differences include tumour biology, immune system activity, body composition and drug disposition and effects. The main differences between male and female cells are sex chromosomes and the level of sexual hormones they are exposed to. They influence both local and systemic determinants of carcinogenesis. Their effect on carcinogenesis in non-reproductive organs is largely unknown. Recent evidence also suggests differences in tumour biology and molecular markers. Regarding body composition, the difference in metabolically active, fat-free body mass is one of the most prominent: in a man and a woman of equal weight and height, it accounts for 80% of the man's and 65% of the woman's body mass, and is not taken into account in body-surface area based dosing of chemotherapy.

CONCLUSION

Sex differences in cancer biology and treatment deserve more attention and systematic investigation. Interventional clinical trials evaluating sex-specific dosing regimens are necessary to improve the balance between efficacy and toxicity for drugs with significant pharmacokinetic differences. Especially in diseases or disease subgroups with significant differences in epidemiology or outcomes, men and women with non-sex-related cancers should be considered as biologically distinct groups of patients, for whom specific treatment approaches merit consideration.

[Use of antiepileptic drugs during breastfeeding : What do we tell the mother?]

BACKGROUND

Knowledge about the passage of various antiepileptic drugs into breast milk and its consequences for the infant is limited. Faced with this uncertainty, breastfeeding is often discouraged for these patients. The aim of this study was to comprehensively review the available data regarding antiepileptic drugs during breastfeeding, to compare these data with information provided by the summary of product characteristics (SmPCs), and to provide recommendations for the use of these drugs in breastfeeding women.

MATERIAL AND METHODS

We performed a systematic literature review on breastfeeding data for 23 antiepileptic drugs. A breastfeeding compatibility score was developed and validated. The estimated score based on the literature review was compared with the estimated score based on recommendations provided by the SmPCs.

RESULTS

We identified 75 articles containing exposure and safety data for 15 antiepileptic agents during breastfeeding. The comparison between the score values based on the literature review and on the SmPCs revealed a very low degree of concordance (weighted kappa: 0.08).

CONCLUSION

Phenobarbital, primidone, carbamazepine, valproate and levetiracetam are probably compatible with breastfeeding. Treatment with phenytoin, ethosuximide, clonazepam, oxcarbazepine, vigabatrin, topiramate, gabapentin, pregabalin, lamotrigine and zonisamide can be authorized during breastfeeding, provided breastfed infants are carefully monitored for side effects. Since data on the use of mesuximide, clobazam, rufinamide, felbamate, lacosamide, sultiame, perampanel and retigabine are insufficient to adequately assess the risk for breastfed infants, use in breastfeeding women is in principle not recommended and should be carefully evaluated on a case by case basis. In practice, a risk-benefit analysis should be performed for each mother under antiepileptic treatment wishing to breastfeed her child, so that individual risk factors can adequately be taken into account when counseling the patient.

The levels of vancomycin in the blood and the wound after the local treatment of bone and soft-tissue infection with antibiotic-loaded calcium sulphate as carrier material

AIMS

Calcium sulphate (CaSO₄) is a resorbable material that can be used simultaneously as filler of a dead space and as a carrier for the local application of antibiotics. Our aim was to describe the systemic exposure and the wound fluid concentrations of vancomycin in patients treated with vancomycin-loaded CaSO₄ as an adjunct to the routine therapy of bone and joint infections.

PATIENTS AND METHODS

A total of 680 post-operative blood and 233 wound fluid samples were available for analysis from 94 implantations performed in 87 patients for various infective indications. Up to 6 g of vancomycin were used. Non-compartmental pharmacokinetic analysis was performed on the data from 37 patients treated for an infection of the hip.

RESULTS

The overall systemic exposure remained within a safe range, even in patients with post-operative renal failure, none requiring removal of the pellets. Local concentrations were approximately ten times higher than with polymethylmethacrylate (PMMA) as a carrier, but remained below reported cell toxicity thresholds. Decreasing concentrations in wound fluid were observed over several weeks, but remained above the common minimum inhibitory concentrations for Staphylococcus up to three months post-operatively.

CONCLUSION

This study provides the first pharmacokinetic description of the local application of vancomycin with CaSO₄ as a carrier, documenting slow release, systemic safety and a release profile far more interesting than from PMMA. In particular, considering in vitro data, concentrations of vancomycin active against staphylococcal biofilm were seen for several weeks. Cite this article: Bone Joint J 2017;99-B:1537-44.

Clinical usefulness of therapeutic concentration monitoring for imatinib dosage individualization: results from a randomized controlled trial

PURPOSE

This study assessed whether a cycle of "routine" therapeutic drug monitoring (TDM) for imatinib dosage individualization, targeting an imatinib trough plasma concentration (C min) of 1,000 ng/ml (tolerance: 750-1,500 ng/ml), could improve clinical outcomes in chronic myelogenous leukemia (CML) patients, compared with TDM use only in case of problems ("rescue" TDM).

METHODS

Imatinib concentration monitoring evaluation was a multicenter randomized controlled trial including adult patients in chronic or accelerated phase CML receiving imatinib since less than 5 years. Patients were allocated 1:1 to "routine TDM" or "rescue TDM." The primary endpoint was a combined outcome (failure- and toxicity-free survival with continuation on imatinib) over 1-year follow-up, analyzed in intention-to-treat (ISRCTN31181395).

RESULTS

Among 56 patients (55 evaluable), 14/27 (52 %) receiving "routine TDM" remained event-free versus 16/28 (57 %) "rescue TDM" controls (P = 0.69). In the "routine TDM" arm, dosage recommendations were correctly adopted in 14 patients (median C min: 895 ng/ml), who had fewer unfavorable events (28 %) than the 13 not receiving the advised dosage (77 %; P = 0.03; median C min: 648 ng/ml).

CONCLUSIONS

This first target concentration intervention trial could not formally demonstrate a benefit of "routine TDM" because of small patient number and surprisingly limited prescriber's adherence to dosage recommendations. Favorable outcomes were, however, found in patients actually elected for target dosing. This study thus shows first prospective indication for TDM being a useful tool to guide drug dosage and shift decisions. The study design and analysis provide an interesting paradigm for future randomized TDM trials on targeted anticancer agents.

[Antiepileptics in women of childbearing age and during pregnancy: comparison of specialized information with the current state of knowledge in Germany and Switzerland]

BACKGROUND

Healthcare professionals regularly read the summary of product characteristics (SmPC) as one of the various sources of information on the risks of drug use in women of childbearing age and during pregnancy. The aim of this article is to present an overview of the teratogenic potential of various antiepileptic drugs and to compare these data with the information provided by the SmPCs.

METHODS

A literature search on the teratogenic risks of 19 antiepileptic agents was conducted and the results were compared with the information on the use in women of childbearing age and during pregnancy provided by the SmPCs of 38 commercial products available in Switzerland and Germany.

RESULTS

The teratogenic risk is discussed in all available SmPCs. Quantification of the risk for birth defects and the numbers of documented pregnancies are mostly missing. Reproductive safety information in SmPCs showed poor concordance with risk levels reported in the literature. Recommendations concerning the need to monitor plasma levels and possibly perform dose adjustments during pregnancy to prevent treatment failure were missing in five Swiss and two German SmPCs.

DISCUSSION

The information regarding use in women of childbearing age and during pregnancy provided by the SmPCs is heterogeneous and poorly reflects the current state of knowledge. Regular updates of SmPCs are warranted in order for these documents to be of reliable use for health care professionals.

Prevalence and determinants of QT interval prolongation in medical inpatients

BACKGROUND

QT interval prolongation carries an increased risk of torsade de pointes and death.

AIM

We sought to determine the prevalence of QT prolongation in medical inpatients and to identify determinants of this condition.

METHODS

We enrolled consecutive patients who were admitted to the internal medicine ward and who had an electrocardiogram performed within 24 h of admission. We collected information on baseline patient characteristics and the use of QT-prolonging drugs. Two blinded readers manually measured the QT intervals. QT intervals were corrected for heart rate using the traditional Bazett formula and the linear regression-based Framingham formula. We used logistic regression to identify patient characteristics and drugs that were independently associated with QTc prolongation.

RESULTS

Of 537 inpatients, 22.3% had a prolonged QTc based on the Bazett formula. The adjusted odds for QTc prolongation based on the Bazett correction were significantly higher in patients who had liver disease (OR 2.9, 95% CI: 1.5-5.6), hypokalaemia (OR 3.3, 95% CI: 1.9-5.6) and who were taking ≥1 QT-prolonging drug at admission (OR 1.7, 95% CI: 1.1-2.6). Overall, 50.8% of patients with QTc prolongation received additional QT-prolonging drugs during hospitalisation.

CONCLUSIONS

The prevalence of QTc prolongation was high among medical inpatients but depended on the method used to correct for heart rate. The use of QT-prolonging drugs, hypokalaemia and liver disease increased the risk of QTc prolongation. Many patients with QTc prolongation received additional QT-prolonging drugs during hospitalisation, further increasing the risk of torsade de pointes and death.

Abstract P6-04-05: Tamoxifen dose escalation based on endoxifen level: a prospective trial with genotyping, phenotyping and pharmacokinetics over 4 months

Background: Retrospective studies assessing the impact of tamoxifen (Tam) metabolism and its active metabolite, endoxifen, on the efficacy of the treatment produced conflicting results. The prospective CYPTAM-BRUT 2 trial is ongoing1. In the present study we assessed if the level of Tam metabolites could be improved by doubling tamoxifen dose in breast cancer patients (pts) with any CYP2D6 genotype, poor (PM), intermediate (IM) and also extensive metabolizer (EM).

Patients and methods: This multicenter, prospective, open-label trial included pts treated with Tam for ≥ 4 months. CYP2D6 activity was determined centrally by genotyping and phenotyping (dextromethorphan test). Liquid chromatography-tandem-mass spectrometry was used to measure Tam, N-desmethyltamoxifen (N-DMT), 4-hydroxytamoxifen (4-HT) and endoxifen twice at baseline (Tam 20 mg qd), then at days 30, 90 and 120 after having increased the dose to 20 mg bid. Endoxifen increase and the differences between genotype/phenotype subgroups were analyzed by ANOVA.

Results: 76 pts were analyzed. Steady-state concentrations for Tam and its metabolites were reached in 30 days after doubling the dose. A range of 1.6 to 1.8 fold increase was observed. Geometric mean plasma concentrations in ng/ml (CV%) were: at baseline and day 30 respectively 134 (48) and 246 (46) for tamoxifen (p < 0.0001); 246 (53) and 413 (48) for N-DMT (p < 0.0001); 2.3 (44) and 3.7 (51) for 4HT (p < 0.0001); 18.7 (89) and 31.1 (92) for endoxifen (p = 0.005).

The level of endoxifen increased 1.4 to 1.7 folds in all genotype subgroups with geometric mean plasma concentrations in ng/ml (CV%): 6.9 (36) to 9.7 (24) in PMs (p = 0.7); 14.2 (69) to 20.7 (76) in IMs (p < 0.0001); and 22.6 (76) to 38.7 (85) in EMs (p < 0.0001). Similar results were obtained while considering phenotype subgroups. Genotypes and phenotypes explained less than 30% of the variability in endoxifen levels.

The occurrence of hot flashes and night sweating were followed prospectively. Endoxifen levels did not predict an increase in HF/NS events' overall occurrence (OR = 1.01, CI95% 0.78–1.31 for HF and 1.01, CI95% 0.79–1.29 for NS). Twelve pts received CYP2D6 inhibitors. Nine pts did not complete the planned 4 months with tamoxifen 20 mg bid. The main reasons were mood disorders, hot flashes, headache and nausea. Self-reported treatment compliance assessed by monthly anonymous questionnaire was ≥ 95%, except 80–95% in 4 pts.

Conclusions: This is the first trial reporting the impact of the increase of tamoxifen dose in all CYP2D6 genotypes, including EMs. Dose escalation of tamoxifen increased significantly the plasma level of endoxifen by similar ratio in all genotype subgroups.

Because of a huge inter-individual variability genotyping and phenotyping are not adequate surrogate markers of endoxifen level. Very low endoxifen levels are observed even in pts classified as EM.

Future trials aiming to improve the plasma level of endoxifen should consider direct measurement of the metabolite in plasma and adjust tamoxifen dose according to the initial level of the metabolite independently of the genotype.

Reference

1. A. Dieudonné, Journal of Clinical Oncology, 2011; vol 29, No 15, suppl (May 20, 2011): TPS 140

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-04-05.

Pregnancy outcome following maternal exposure to statins: a multicentre prospective study

OBJECTIVE

This contribution addresses the risk associated with exposure to statins during pregnancy.

DESIGN

Multicentre observational prospective controlled study.

SETTING

European Network of Teratology Information Services.

POPULATION

Pregnant women who contacted one of 11 participating centres, seeking advice about exposure to statins during pregnancy, or to agents known to be nonteratogenic.

METHODS

Pregnancies exposed during first trimester to statins were followed up prospectively, and their outcomes were compared with a matched control group.

MAIN OUTCOME MEASURES

Rates of major birth defects, live births, miscarriages, elective terminations, preterm deliveries and gestational age and birthweight at delivery.

RESULTS

We collected observations from 249 exposed pregnancies and 249 controls. The difference in the rate of major birth defects between the statin-exposed and the control groups was small and statistically nonsignificant (4.1% versus 2.7% odds ratio [OR] 1.5; 95% confidence interval [95% CI] 0.5-4.5, P = 0.43). In an adjusted Cox model, the difference between miscarriage rates was also small and not significant (hazard ratio 1.36, 95% CI 0.63-2.93, P = 0.43). Premature birth was more frequent in exposed pregnancies (16.1% versus 8.5%; OR 2.1, 95% CI 1.1-3.8, P = 0.019). Nonetheless, median gestational age at birth (39 weeks, interquartile range [IQR] 37-40 versus 39 weeks, IQR 38-40, P = 0.27) and birth weight (3280 g, IQR 2835-3590 versus 3250 g, IQR 2880-3630, P = 0.95) did not differ between exposed and non-exposed pregnancies.

CONCLUSIONS

This study did not detect a teratogenic effect of statins. Its statistical power remains insufficient to challenge current recommendations of treatment discontinuation during pregnancy.

[Antimicrobial agents and renal elimination: towards individual dosage adjustment?]

The efficacy and safety of anti-infective treatments are associated with the drug blood concentration profile, which is directly correlated with a dosing adjustment to the individual patient's condition. Dosing adjustments to the renal function recommended in reference books are often imprecise and infrequently applied in clinical practice. The recent generalisation of the KDOQI (Kidney Disease Outcome Quality Initiative) staging of chronically impaired renal function represents an opportunity to review and refine the dosing recommendations in patients with renal insufficiency. The literature has been reviewed and compared to a predictive model of the fraction of drug cleared by the kidney based on the Dettli's principle. Revised drug dosing recommendations integrating these predictive parameters are proposed.

[Pharmacovigilance update]

Main pharmacovigilance updates are reviewed. Rosiglitazone and sibutramine have been suspended due to cardiovascular risks. The safety profile of H1N1 vaccines is similar to the established profile of seasonal influenza vaccines. Paroxetine reduces the benefit of tamoxifen. The use of serotoninergic antidepressants in pregnancy is still disputed. The risk of venous thromboembolism could be higher with oral combined contraceptives containing drospirenone compared to those containing levonorgestrel. Prolonged QT and PR intervals have been observed with saquinavir. The correct use of transdermal patches is reviewed with the example of rivastigmine. Aseptic meningitis is a rare adverse reaction of lamotrigine. An increased risk of fractures after long term use of proton pump inhibitors is suspected.

Abstract PD05-09: Prospective Assessment of CYP2D6 by Genotyping, Phenotyping and Measurement of Tamoxifen, 4-Hydroxy-Tamoxifen and Endoxifen in Breast Cancer Patients Treated with Tamoxifen

Background: CYP2D6 is genetically highly polymorphic and several studies support that patients classified as poor-or intermediate-metabolizers achieve less or no benefit from tamoxifen treatment probably because they have lower levels of endoxifen. Genotyping is currently the major method used in studies and in clinical practice. However the ability of genotyping to predict plasma levels of endoxifen is uncertain for an individual patient. We assessed prospectively CYP2D6 activity by genotyping, phenotyping and the measurement of tamoxifen and its metabolites. Methods: Patients were genotyped for CYP2D6 (*1, *3, *4, *5, *6 and *XN) polymorphism. The CYP2D6 phenotype was determined by the dextromethorphan test. Plasma was collected at 2 time points after at least 4 months of treatment with tamoxifen 20 mg daily: tamoxifen, 4-hydroxytamoxifen, N-demethyltamoxifen and endoxifen were measured with high performance liquid chromatography coupled to triple stage tandem mass spectrometry. Linear regression analyses were performed on log transformed concentrations of tamoxifen, its metabolites, and the ratios 4- hydroxytamoxifen/tamoxifen, endoxifen/N-demethyltamoxifen versus the different genotype groups (UM, EM, IM, PM) and the dextromethorphan/dextrorphan ratio.

Results: The data of 26 patients are currently available. Geometric mean plasma concentrations (coefficient of variation %) of tamoxifen, N-desmethyltamoxifen, 4-OH-tamoxifen and endoxifen were 377 nmol/L (39%), 482 nmol/L (36%), 5.9 nmol/L (52%) and 60.7 nmol/L (94%), respectively. Genetic variation in CYP2D6 was significantly correlated with endoxifen, 4-hydroxytamoxifen and the ratios of 4-hydroxytamoxifen/tamoxifen and endoxifen/N-demethyltamoxifen: determination coefficients (R-squared) of 44% (P=0.0002), 30% (P=0.0038), 57% (P= <0.0001) and 47% (P=0.0001), respectively. Phenotypes defined by the dextromethorphan/dextrorphan ratio were significantly correlated with endoxifen and the ratios of 4-hydroxytamoxifen/tamoxifen and endoxifen/N-demethyltamoxifen: determination coefficients of 47% (P=0.0002), 39% (P=0.0012) and 59% (P= <0.0001), respectively. Conclusions: Our data confirm a significant correlation between CYP2D6 activity defined by genotyping or by phenotyping and plasma levels of endoxifen. However, the important interindividual variability in the concentrations of the metabolites of tamoxifen remains largely unexplained, suggesting that CYP2D6 genotyping and phenotyping are not sufficient to predict plasma levels of the active metabolites of tamoxifen. These preliminary results are consistent with a potential superiority of monitoring the active metabolites themselves rather than genetic or phenotypic surrogates. The study is ongoing and more data will be presented.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD05-09.

[Pharmacovigilance update]

Main pharmacovigilance signals and alerts issued in 2009 are reviewed. Efalizumab was withdrawn from the market due to increased risks, including progressive multifocal leukoencephalopathy (PML) and questionable efficacy. New cases of PML are still being reported with rituximab and natalizumab. Rare cases of pure red cell aplasia have been observed with mycophenate. Gastrointestinal perforation, severe skin rashes and various ocular disorders have been reported during erlotinib use. Severe skin rashes have been related to etravirine. Acute renal failure and pancreatitis can occur with exenatide. A link between sitagliptin and pancreatitis is suspected. Raised concerns of causality between insuline glargine and malignant tumors are not supported by strong evidence. Proton pump inhibitors seem to blunt clopidogrel benefit. Aliskiren can cause angioedema.

[Drugs and breastfeeding: some facts to consider before deciding they are incompatible]

Breastfeeding is considered the ideal way of providing young infants with the required nutrients for healthy growth and development. An increase in the prevalence and duration of breastfeeding has been observed over the last years in response to promotion campaigns. When a medicamentous treatment is started, discontinuation of breastfeeding is often proposed, for fear of harmful consequences for the infant. Nevertheless such a decision is not unimportant, and it appears that many drugs can actually be used during breastfeeding without significant risk. An assessment of the real risk incurred by exposed children makes it possible to avoid unnecessary discontinuations of breastfeeding. This article aims to review the facts needed to assess amount of drug exposure to the child and to list the few drugs associated with significant effects on the nursing infant.

[Pharmacovigilance update]

The observations of pharmacovigilance reported during 2007 reflect an increasing attention towards drug-induced augmentation of the incidence of common disorders. New substances are thus to be added to the list of risk factors susceptible to favour cardiovascular events (tegaserod, rosiglitazone, erythropoïetin, aprotinine) or psychiatric disorders (dopaminergic agonists, rimonabant). The evaluation of the security profile of new medicines remains challenging. Besides biological investigations of questionable relevance and clinical trial of inconstant efficiency towards safety outcomes, the role of pharmacovigilance notifications by practitioners remains of paramount importance.

Determination of aciclovir and ganciclovir in human plasma by liquid chromatography–spectrofluorimetric detection and stability studies in blood samples

A sensitive HPLC method has been developed for the assay of aciclovir and ganciclovir in human plasma, by HPLC coupled with spectrofluorimetric detection. Plasma (1000 microl), with 9-ethyl-guanine added as internal standard, is submitted to protein precipitation with trichloroacetic acid solution 20%. The supernatant, evaporated to dryness at 37 degrees C, is reconstituted in 100 microl of a solution of sodium heptanosulfonate 0.4% adjusted with acetic acid to pH 2.60 and a 30 microl volume is then injected onto a Nucleosil 100-5 microm C18 column. Aciclovir and ganciclovir are analysed by spectrofluorimetric detection set at 260 nm (excitation) and 380 nm (emission) using a gradient elution program with solvents constituted of acetonitrile and a solution of sodium heptanosulfonate 0.4% adjusted to pH 2.60. The calibration curves are linear between 0.1 and 10 microg/ml. The mean absolute recovery of aciclovir and ganciclovir are 99.2+/-2.5 and 100.3+/-2.5%, respectively. The method is precise (with mean inter-day C.V.s within 1.0-1.6% for aciclovir and 1.2-3.5% for ganciclovir), and accurate (range of inter-day deviations -1.6 to +1.6% for aciclovir and -0.4 to -1.4% for ganciclovir). The method has been applied in stability studies of ganciclovir in patients' blood samples, demonstrating its good stability in plasma at -20 degrees C and at room temperature. The distribution of ganciclovir and aciclovir in plasma and red blood cells was also investigated in vitro in spiking experiments with whole blood, which showed an initial drop of ganciclovir and aciclovir levels in plasma (about -25%) due to the cellular uptake of aciclovir and ganciclovir by red blood cells. The method has been validated and is currently applied in a clinical study assessing the ganciclovir plasma concentration variability after administration of valganciclovir in a population of solid organ transplant patients.

Population pharmacokinetics of imatinib and the role of alpha-acid glycoprotein

AIMS

The aims of this observational study were to assess the variability in imatinib pharmacokinetics and to explore the relationship between its disposition and various biological covariates, especially plasma alpha1-acid glycoprotein concentrations.

METHODS

A population pharmacokinetic analysis was performed using NONMEM based on 321 plasma samples from 59 patients with either chronic myeloid leukaemia or gastrointestinal stromal tumours. The influence of covariates on oral clearance and volume of distribution was examined. Furthermore, the in vivo intracellular pharmacokinetics of imatinib was explored in five patients.

RESULTS

A one-compartment model with first-order absorption appropriately described the data, giving a mean (+/-SEM) oral clearance of 14.3 l h-1 (+/-1.0) and a volume of distribution of 347 l (+/-62). Oral clearance was influenced by body weight, age, sex and disease diagnosis. A large proportion of the interindividual variability (36% of clearance and 63% of volume of distribution) remained unexplained by these demographic covariates. Plasma alpha1-acid glycoprotein concentrations had a marked influence on total imatinib concentrations. Moreover, we observed an intra/extracellular ratio of 8, suggesting substantial uptake of the drug into the target cells.

CONCLUSION

Because of the high pharmacokinetic variability of imatinib and the reported relationships between its plasma concentration and efficacy and toxicity, the usefulness of therapeutic drug monitoring as an aid to optimizing therapy should be further investigated. Ideally, such an approach should take account of either circulating alpha1-acid glycoprotein concentrations or free imatinib concentrations.

Population pharmacokinetics of imatinib and the role of alpha-acid glycoprotein

AIMS

The aims of this observational study were to assess the variability in imatinib pharmacokinetics and to explore the relationship between its disposition and various biological covariates, especially plasma alpha1-acid glycoprotein concentrations.

METHODS

A population pharmacokinetic analysis was performed using NONMEM based on 321 plasma samples from 59 patients with either chronic myeloid leukaemia or gastrointestinal stromal tumours. The influence of covariates on oral clearance and volume of distribution was examined. Furthermore, the in vivo intracellular pharmacokinetics of imatinib was explored in five patients.

RESULTS

A one-compartment model with first-order absorption appropriately described the data, giving a mean (+/-SEM) oral clearance of 14.3 l h-1 (+/-1.0) and a volume of distribution of 347 l (+/-62). Oral clearance was influenced by body weight, age, sex and disease diagnosis. A large proportion of the interindividual variability (36% of clearance and 63% of volume of distribution) remained unexplained by these demographic covariates. Plasma alpha1-acid glycoprotein concentrations had a marked influence on total imatinib concentrations. Moreover, we observed an intra/extracellular ratio of 8, suggesting substantial uptake of the drug into the target cells.

CONCLUSION

Because of the high pharmacokinetic variability of imatinib and the reported relationships between its plasma concentration and efficacy and toxicity, the usefulness of therapeutic drug monitoring as an aid to optimizing therapy should be further investigated. Ideally, such an approach should take account of either circulating alpha1-acid glycoprotein concentrations or free imatinib concentrations.

[Effects of oral cannabis and dronabinol on driving capacity]

Two retrospective epidemiologic studies have shown that cannabis is the main psychoactive substance detected in the blood of drivers suspected of driving under the influence of psychotropic drugs. An oral administration double-blind crossover study was carried out with eight healthy male subjects, aged 22 to 30 years, all occasional cannabis smokers. Three treatments and one placebo were administered to all participants at a two week interval: 20 mg dronabinol, 16.5 mg D9-tétrahydrocannabinol (THC) and 45.7 mg THC as a cannabis milk decoction. Participants were asked to report the subjective drug effects and their willingness to drive under various circumstances on a visual analog scale. Clinical observations, a psychomotor test and a tracking test on a driving simulator were also carried out. Compared to cannabis smoking, THC, 11-OH-THC and THC-COOH blood concentrations remained low through the whole study (<13.1 ng THC/mL,<24.7 ng 11-OH-THC/mL and<99.9 ng THC-COOH/mL). Two subjects experienced deep anxiety symptoms suggesting that this unwanted side-effect may occur when driving under the influence of cannabis or when driving and smoking a joint. No clear association could be found between these adverse reactions and a susceptibility gene to propensity to anxiety and psychotic symptoms (genetic polymorphism of the catechol-O-methyltransferase). The questionnaires have shown that the willingness to drive was lower when the drivers were assigned an insignificant task and was higher when the mission was of crucial importance. The subjects were aware of the effects of cannabis and their performances on the road sign and tracking test were greatly impaired, especially after ingestion of the strongest dose. The Cannabis Influence Factor (CIF) which relies on the molar ratio of active and inactive cannabinoids in blood provided a good estimate of the fitness to drive.

[Risk of overtreatment: not to be neglected. The example of antiepileptic drugs]

Overtreatment (unnecessary treatment, excessive drug dosages, unjustified polypharmacy) alters the risk-benefit ratio. Its prevention requires the recognition of the situations and the understanding of the mechanisms leading to it. The pharmacological treatment of epilepsy exposes to such a risk and serves as an example for its detection and correction.

[Will good clinical practice domesticate human research?]

During recent years, an increasingly comprehensive set of rules and guidelines has been developed around clinical trials, to ensure their proper ethical, methodological, administrative and financial conduct. While initially limited to new drug development, this regulation is progressively invading all areas of clinical research, with limited respect for the heterogeneity in aims, resources, sponsors and epistemological grounds. No clinical study should be planned without consideration of a series of legal requirements, which are reviewed. Concerns about their practical implications are critically assessed.

[Generic drugs and legal incentives: which impact?]

The dispositions that regulate generic substitution in Switzerland have been recently revised, and impose definite incentives on prescribers. The benefits and drawbacks associated with the prescription of generic drugs are reviewed, considering the viewpoints of patients, practitioners and third party payers. While the initial prescription of a generic drug raises no specific concerns, the generic switch during long-term treatment may require some caution. The advantages of using International Nonproprietary Names (INN) for drug prescription are discussed. A renewal of prescription habits would be welcomed however several practical issues would have to find rational solutions.

[Trends in drug therapy]

This article reviews some recent aspects of pharmacovigilance, of interest to the practitioner: biphosphonates and osteonecrosis of the jaw, antidepressants and suicide, antipsychotics and increased mortality risk and cerebrovascular events, withdrawal syndrome after in utero exposure to antidepressants SSRI, NSAIDs and increased cardiovascular events, cancer and topical immunosuppressants, visual loss and treatment of erectile dysfunction, valvulopathy and dopaminergic agonists. Risk-benefit assessment of drugs is a dynamic process. One must keep in mind that the data on the relationship between drugs and the clinical picture are of variable quality and that the size of the risk is often difficult to assess.

Intracellular measurements of anti-HIV drugs indinavir, amprenavir, saquinavir, ritonavir, nelfinavir, lopinavir, atazanavir, efavirenz and nevirapine in peripheral blood mononuclear cells by liquid chromatography coupled to tandem mass spectrometry

A sensitive and accurate liquid chromatography-tandem mass spectrometric (LC-MS/MS) method for the intracellular determination of nine antiretroviral drugs in human peripheral blood mononuclear cells (PBMCs) is proposed. PBMCs are isolated by density gradient centrifugation using Vacutainer CPT tubes and cell count is performed with a Coulter instrument. Single-step extraction of drugs from PBMCs pellets is performed with MeOH 50% (with clozapine added as internal standard, I.S.) and the supernatant is injected onto a 2.1 mm x 30 mm SymmetryShield 3.5 microm-RP18 column equipped with a 2.1 x 10 mm guard column. Chromatographic separations are performed using a gradient program with a mixture of 2 mM ammonium acetate containing 0.1% formic acid and acetonitrile with 0.1% formic acid. Analytes quantification is performed by electro-spray ionisation-triple quadrupole mass spectrometry using the selected reaction monitoring (SRM) detection mode. The positive mode is used for the HIV protease inhibitors (PIs) indinavir, amprenavir, saquinavir, ritonavir, nelfinavir, lopinavir, atazanavir and the non-nucleoside reverse transcriptase inhibitors (NNRTIs) nevirapine, and the negative mode is applied for efavirenz. The calibration curves are prepared using blank PBMCs spiked with antiretroviral drugs at concentrations ranging from 0.5 to 100 ng/ml of cell extracts and fitted to a quadratic regression model weighted by 1/(concentration)(2). The lower limit of quantification is less than 0.5 ng/ml. The mean extraction recovery for all PIs/NNRTIs is always above 88%. The method is precise, with mean inter-day CV% within 0.6-10.2%, and accurate (range of inter-day deviation from nominal values -7.2 to +8.3%). This analytical method can be conveniently used in clinical research for the assessment of intracellular levels of all PIs/NNRTIs commercially available at present using a simple one-step cell extraction of PBMCs followed by liquid chromatography coupled with tandem triple quadripole mass detection.

[Multiple diseases: should we treat them all?]

Studies are demonstrating additional benefits of multiple drug treatment in specific diseases. However, when a patient suffers multiple diseases, the lack of adequate clinical data on which to base a therapeutic attitude is baffling. The practitioner is forced to prescribe without a strong evidence base or to withhold medications for fear of doing more harm than good. In such circumstances, a prudent and drug sparing approach is to be preferred: a patient, not disease, oriented approach, using a few principles of rational prescribing: clear therapeutic objectives, prioritisation according to the severity of diseases, efficacy and safety of available therapies, therapeutic individualisation and monitoring, patient implication and attention to his/her desires and expectations.

[The blood-brain barrier: recent insights]

The blood-brain barrier must not be regarded as a purely passive wall opposing low permeability to undesirable compounds circulating in blood. It limits the access of molecules to brain tissue by a joint interplay of cerebro-spinal fluid turnover and selective uptake and expulsion of compounds through active drug carriers. The inhibition of such transporters can increase brain penetration of substrates leading to drug interactions with neuropsychiatric manifestations; it can also be exploited to increase brain and CSF concentrations of anti-infective, anti-neoplastic or psychotropic agents. Genetic polymorphisms affecting transporters may modulate the brain exposure to drugs in selected individuals. Such observations improve our understanding of a key mechanism governing clinical neuro-psychopharmacology.

[Drug interaction computer programs: which choice?]

Adverse drug reactions represent a partly preventable cause of morbidity. Computer-based tools may be useful for the prevention of those events resulting from drug interactions. While several such tools are currently available to practitioners, they have rarely been compared regarding their performances and limits. This article presents a benchmark evaluation of seven drug interaction databases which may be elected by physicians or pharmacists as an aid to prescription on a regular basis. None of the databases tested appears to be perfect, and the systems vary in their overall completeness and ease of use.

Disposition of voriconazole during continuous veno-venous haemodiafiltration (CVVHDF) in a single patient

OBJECTIVES

To determine whether voriconazole dosage adjustment is required during continuous veno-venous haemodiafiltration (CVVHDF).

METHODS

Voriconazole pharmacokinetics were studied in a critically ill patient under CVVHDF. The analysis was carried out for 12 h following a 6 mg/kg dose. Voriconazole concentrations were measured by HPLC in blood inlet and outlet lines and in dialysate.

RESULTS

The total body clearance of voriconazole was 20.3 L/h, with a terminal half-life of 13.7 h and a distribution volume of 399 L. The estimated sieving coefficient was 0.53 and the filtration-dialysis clearance 1.2 L/h.

CONCLUSIONS

CVVHDF does not significantly affect voriconazole disposition and requires no dosage adjustment.

[Withdrawal of a drug from the market for safety reasons: process and communication]

Each year, drugs must be withdrawn from the market following the identification of serious adverse reactions. We report here on an enquiry addressed to persons involved in the recent withdrawal of nefazodone, and a survey of physicians and pharmacists. Our results show the complexities of such withdrawal decisions and the difficulty in communicating them through the network of health professionals down to the patients.

Pharmacokinetics and dosage adaptation of meropenem during continuous venovenous hemodiafiltration in critically ill patients

Meropenem, a carbapenem broad-spectrum antibiotic, is regularly used in patients undergoing continuous venovenous hemodiafiltration (CVVHDF). Its disposition was studied over one dosage interval in 15 patients under CVVHDF on a steady regimen of 500 or 1000 mg every 8 to 12 hours. Meropenem levels were measured in plasma and filtrate-dialysate by high-performance liquid chromatography (HPLC) with UV detection. The mean CVVHDF flow rates were 7.1 +/- 0.9 L/h for blood (mean +/- SD), 0.5 +/- 0.3 L/h for predilution solution, 1.2 +/- 0.3 L/h for countercurrent dialysate, and 1.8 +/- 0.5 L/h for the total filtrate-dialysate. The pharmacokinetic analysis was based both on a noncompartmental approach and on a four-compartment modeling. The mean (coefficient of variation [CV]) total body clearance, volume of distribution at steady state, and mean residence time were, respectively, 5.0 L/h (46%), 14.3 L (29%), and 4.8 h (36%). The hemodiafiltration clearances calculated from plasma data alone and plasma with filtrate-dialysate data were 1.2 L/h (26%) and 1.6 L/h (39%), respectively. The compartmental model was used to optimize the therapeutic schedule of meropenem, considering reference minimal inhibitory concentration (MIC) of sensitive strains (4 mg/L). The results indicate that two different therapeutic schedules of meropenem are equally applicable to patients receiving CVVHD: either 750 mg tid or 1500 bid.

Determination of imatinib (Gleevec®) in human plasma by solid-phase extraction–liquid chromatography–ultraviolet absorbance detection

A sensitive HPLC method has been developed for the assay of imatinib in human plasma, by off-line solid-phase extraction followed by HPLC coupled with UV-Diode Array Detection. Plasma (750 microl), with clozapine added as internal standard, is diluted 3 + 1 with water and subjected to a solid-phase extraction on a C18 cartridge. After matrix components elimination with 2000 microl of water (in two aliquots of 1000 microl), imatinib is eluted with 3 x 500 microl MeOH. The resulting eluate is evaporated under nitrogen at room temperature and is reconstituted in 180 microl 50% methanol. A 50 microl volume is injected onto a Nucleosil 100-5 microm C18 AB column. Imatinib is analyzed using a gradient elution program with solvent mixture constituted of methanol and water containing both 0.05% ammonium acetate. Imatinib is detected by UV at 261 nm. The calibration curves are linear between 0.1 and 10 microg/ml. The limit of quantification and detection are 0.05 and 0.01 microg/ml, respectively. The mean absolute recovery of imatinib is 96%. The method is precise with mean inter-day CVs within 1.1-2.4%, and accurate (range of inter-day deviations -0.6 to +0.7%). The method has been validated and is currently being applied in a clinical study assessing the imatinib plasma concentration variability in a population of chronic myeloid leukemia- and gastro-intestinal stromal tumor-patients.