摘要:

Imatinib is a potent and selective inhibitor of the protein tyrosine kinase Bcr-Abl, platelet-derived growth factor receptors (PDGFRα and PDGFRβ) and KIT. Imatinib is approved for the treatment of chronic myeloid leukaemia (CML) and gastrointestinal stromal tumour (GIST), which have dysregulated activity of an imatinib-sensitive kinase as the underlying pathogenetic feature.Pharmacokinetic studies of imatinib in healthy volunteers and patients with CML, GIST and other cancers show that orally administered imatinib is well absorbed, and has an absolute bioavailability of 98% irrespective of oral dosage form (solution, capsule, tablet) or dosage strength (100mg, 400mg). Food has no relevant impact on the rate or extent of bioavailability. The terminal elimination half-life is approximately 18 hours. Imatinib plasma concentrations predictably increase by 2- to 3-fold when reaching steady state with 400mg once-daily administration, to 2.6 ± 0.8 μg/mL at peak and 1.2 ± 0.8 μg/mL at trough, exceeding the 0.5 μg/mL (1 μmol/L) concentrations needed for tyrosine kinase inhibitionin vitroand leading to normalisation of haematological parameters in the large majority of patients with CML irrespective of baseline white blood cell count.Imatinib is approximately 95% bound to human plasma proteins, mainly albumin and α1-acid glycoprotein. The drug is eliminated predominantly via the bile in the form of metabolites, one of which (CGP 74588) shows comparable pharmacological activity to the parent drug. The faecal to urinary excretion ratio is approximately 5 : 1.Imatinib is metabolised mainly by the cytochrome P450 (CYP) 3A4 or CYP3A5 and can competitively inhibit the metabolism of drugs that are CYP3A4 or CYP3A5 substrates. Interactions may occur between imatinib and inhibitors or inducers of these enzymes, leading to changes in the plasma concentration of imatinib as well as coadministered drugs.Hepatic and renal dysfunction, and the presence of liver metastases, may result in more variable and increased exposure to the drug, although typically not necessitating dosage adjustment. Age (range 18–70 years), race, sex and bodyweight do not appreciably impact the pharmacokinetics of imatinib.

ISSN:0312-5963    

出版商:ADIS    

年代:2005

数据来源: ADIS

摘要:

Microdialysis is a probe-based sampling method, which, if linked to analytical devices, allows for the measurement of drug concentration profiles in selected tissues. During the last two decades, microdialysis has become increasingly popular for preclinical and clinical pharmacokinetic studies. The advantage ofin vivomicrodialysis over traditional methods relates to its ability to continuously sample the unbound drug fraction in the interstitial space fluid (ISF). This is of particular importance because the ISF may be regarded as the actual target compartment for many drugs, e.g. antimicrobial agents or other drugs mediating their action through surface receptors. In contrast, plasma concentrations are increasingly recognised as inadequately predicting tissue drug concentrations and therapeutic success in many patient populations. Thus, the minimally invasive microdialysis technique has evolved into an important tool for the direct assessment of drug concentrations at the site of drug delivery in virtually all tissues. In particular, concentrations of transdermally applied drugs, neurotransmitters, antibacterials, cytotoxic agents, hormones, large molecules such as cytokines and proteins, and many other compounds were described by means of microdialysis.The combined use of microdialysis with non-invasive imaging methods such as positron emission tomography and single photon emission tomography opened the window to exactly explore and describe the fate and pharmacokinetics of a drug in the body. Linking pharmacokinetic data from the ISF to pharmacodynamic information appears to be a straightforward approach to predicting drug action and therapeutic success, and may be used for decision making for adequate drug administration and dosing regimens. Hence, microdialysis is nowadays used in clinical studies to test new drug candidates that are in the pharmaceutical industry drug development pipeline.

ISSN:0312-5963    

出版商:ADIS    

年代:2005

数据来源: ADIS

摘要:

Telithromycin is the first ketolide, which is a new class of antibacterial agents related to the macrolides that have structural modifications permitting dual binding to bacterial ribosomal RNA so that activity is retained againstStreptococcus pneumoniaewith macrolide-lincosamide-streptograminBresistance. Clinical experience in infectious patients has shown that oral telithromycin 800mg once daily for 5–10 days is effective for the treatment of community-acquired upper and lower respiratory tract infections. Absorption of telithromycin in humans is estimated to be ≥90%. Prior to entering the systemic circulation, telithromycin undergoes first-pass metabolism (mainly by the liver). Its absolute bioavailability is 57% and is unaffected by food. The volume of distribution of telithromycin after intravenous infusion is 2.9 L/kg. Telithromycin is 60–70% bound to serum proteins and has extensive diffusion into a range of target biological tissues, achieving concentrations above its minimum inhibitory concentration (MIC) against key respiratory pathogens throughout the dosing interval. After entering the systemic circulation, telithromycin is eliminated by multiple pathways (7% by biliary and/or intestinal excretion, 13% by renal excretion and 37% by hepatic metabolism).Telithromycin is metabolised via cytochrome P450 (CYP) 3A4 and non-CYP pathways. The identified metabolites show minimal antibacterial activity compared with the parent drug. In healthy subjects receiving telithromycin 800mg once daily, the peak plasma concentration achieved is 2.27 μg/mL. Plasma concentrations of telithromycin show a biphasic decrease over time, with an initial disposition half-life of 2.9 hours and a terminal elimination half-life of approximately 10 hours after multiple dose administration. Steady-state plasma concentrations are achieved within 2–3 days of once-daily administration. Owing to elimination by multiple pathways there is a small increase in exposure when one of these elimination pathways is impaired, as indicated by the results of studies in special patient populations (e.g. those with hepatic or renal impairment). Dosage reductions may be recommended in patients with severe renal impairment. Inhibition of CYP3A4 by potent inhibitors such as itraconazole and ketoconazole results in a 54% and 95% increase in telithromycin area under the plasma concentration-time curve, respectively. The potential for telithromycin to inhibit the CYP3A4 pathway is similar to that of clarithromycin. The once-daily administration of telithromycin is likely to limit the potential for drug interactions and clinically significant increases in exposure. In phase III clinical trials, the telithromycin 800mg once-daily dose has been shown to provide close to the maximum antimicrobial activity againstS. pneumoniae,Haemophilus influenzaeandStaphylococcus aureusin patients with community-acquired pneumonia.In conclusion, telithromycin has a well characterised and reproducible pharmacokinetic profile, with pharmacokinetic/pharmacodynamic relationships supporting an oral dosage regimen of 800mg once daily.

ISSN:0312-5963    

出版商:ADIS    

年代:2005

数据来源: ADIS

摘要:

The initiation of antiretroviral therapy has resulted in an impressive reduction in the rate of disease progression in AIDS and HIV-1-related deaths in children; however, there are still several major challenges to be faced in order to improve therapy. A major topic that needs to be dealt with is the establishment of the optimal dosage of antiretroviral therapy for children. This review presents the currently available peer-reviewed data on the pharmacokinetics of nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), protease inhibitors (PIs) and fusion inhibitors (FIs) in children. In addition, the data are discussed in relation to the currently available European and US guidelines and the US FDA-approved drug labels.High intra- and interpatient variability in pharmacokinetics are often observed for all antiretroviral drugs. The number of children included in the pharmacokinetic studies is often small and children are often divided into divergent groups using different dosage levels and/or drug formulations. For a substantial number of antiretroviral drugs, dosage recommendations, especially for young children, are still absent in the European and US guidelines. The recommended drug dosages in the guidelines are often different from that in the officially approved drug product label. In addition, the recommended drug dosages may deviate between the European and US guidelines. Thus, while practioners aim to meet the recommendations in the official guidelines, patients may receive highly divergent dosages of medication.The high intra- and interpatient variability in pharmacokinetics of antiretroviral drugs in children hampers the application of fixed dosages of antiretroviral drugs. For PIs and NNRTIs, plasma drug levels correlate with viral suppression and drug toxicity. NRTIs are prodrugs that are intracellularly converted to their active triphosphate form and, therefore, plasma NRTI levels correlate poorly with viral suppression. Therapeutic drug monitoring of PIs and NNRTIs should be considered to optimise HIV therapy in children.

ISSN:0312-5963    

出版商:ADIS    

年代:2005

数据来源: ADIS

摘要:

BackgroundTo study the pharmacokinetics and clinical outcome of gemcitabine (2′-2′-difluoro-deoxcytidine [dFdC]) during intra-arterial versus intravenous delivery in locally advanced and regionally metastatic pancreatic cancer.Patients and methodsSeven patients with unresectable pancreatic cancer received escalating intra-arterial doses of gemcitabine ranging from 800 to 1400 mg/m2, after selective embolisation of all pancreatic blood supply, except for the tumour-feeding arteries. Four patients received intravenous gemcitabine (control). Venous blood samples at different time intervals were taken throughout 270 minutes for pharmacokinetic analyses of gemcitabine and its inactive metabolite 2′-2′-difluorodeoxyuridine (dFdU).ResultsPharmacokinetic data revealed differences in plasma concentrations between intra-arterial and intravenous delivery routes. The plasma concentration-time curve of gemcitabine during and after cessation of intra-arterial pancreatic target administration through the proximal splenic artery showed a profile with an area under the plasma concentration-time curve from 0 to 270 minutes (intra-arterial 29.0 ± 0.4 vs intravenous 331.0 ± 2.7 ng · min/mL; p < 0.0001) and peak plasma concentration (intra-arterial 1.1 ± 0.2 vs intravenous 7.6 ± 2.0 ng/mL; p < 0.0001) significantly lower than that for the corresponding systemic intravenous route. A plot of ln (% of dose) versus time showed a bi-compartmentalised metabolic model for intravenous administration of gemcitabine, one indicating rapid conversion of gemcitabine to dFdU, and another at a significantly lower affinity resulting in no conversion. Hence, this could be the main reason why dFdU was not detected in the systemic circulation during pancreatic intra-arterial target delivery. Furthermore, during intravenous administration a pseudo first-order rate constant (≈0.20 min–1) forin vivoconversion of gemcitabine to dFdU was estimated, indicating a rapid cellular deamination which was not shown in the intra-arterial route. Clinically, one patient had a partial response and six patients had a stable disease after intra-arterial administration of gemcitabine. The median time to disease progression was 4 months and the median overall survival was 5 months. One patient survived for 26 months. No grade III or IV toxicity was documented.ConclusionIntra-arterial administration of gemcitabine has a major advantage related to reduced toxicity as increasing the dose through this administration route will eventually result in pancreatic cellular drug target delivery prior to systemic availability. Despite the low number of patients recruited, the clinical results are encouraging and this approach should be tested in a randomised study.

ISSN:0312-5963    

出版商:ADIS    

年代:2005

数据来源: ADIS

摘要:

Background and objectiveMoxifloxacin is a new generation fluoroquinolone antimicrobial agent used worldwide. In clinical practice in intensive care units, moxifloxacin may be frequently administered through a nasogastric feeding tube. In the absence of an oral liquid formulation and since the multivalent cations contained in enteral feeds may potentially impair absorption of moxifloxacin administered via this route, we studied the effect of concomitant enteral feeding on the pharmacokinetics and tolerability of moxifloxacin administered as a crushed tablet through the nasogastric tube.Participants and methodsThis was a single-centre, open-label, randomised, controlled, nonblinded, three-way crossover study. Twelve young healthy volunteers (nine females and three males) aged 20–42 years were included in the study. Each participant received three separate treatment regimens in a randomised fashion: an intact moxifloxacin 400mg tablet (regimen A, reference treatment), a crushed moxifloxacin 400mg tablet as a suspension through a nasogastric tube with water (regimen B) and a crushed moxifloxacin 400mg tablet as a suspension through a nasogastric tube with enteral feeding (regimen C). A washout period of 1-week followed each treatment. Concentrations of moxifloxacin in serum were measured by a validated high-performance liquid chromatography method. Pharmacokinetic parameters were calculated by noncompartmental methods. Additionally, the primary parameters indicative for changes in absorption (area under the serum concentration-time curve from time zero to infinity [AUC∞] and peak serum concentration [Cmax]), were tested for bioequivalence, assuming log-normally distributed data using ANOVA.ResultsAll moxifloxacin treatment regimens were well tolerated. The AUC∞was slightly, but not statistically significantly, decreased in treatments with regimens B and C. AUC∞(geometric means 39.6 [regimen A] vs 36.1 [regimen B] vs 36.1 mg · h/L [regimen C] and point estimates 91% for B : A and C : A) indicated bioequivalence of the treatments. Bioequivalence criteria of AUC∞and Cmaxwere met upon retrospective statistical analysis. Likewise Cmaxafter moxifloxacin administration through nasogastric tube with water (regimen B) and with tube feed (regimen C) were slightly decreased (geometric means 3.20 [regimen A] vs 3.05 [regimen B] vs 2.83 mg/L [regimen C]; point estimates 88% for B : A, and 95% for C : A). They were within the range seen in other studies conducted with oral administration of the drug. No statistically significant differences were observed in time to reach Cmax(tmax; median 1.75 [regimen A] vs 1.00 [regimen B] vs 1.75 hours [regimen C]). Thus, the rate of absorption of moxifloxacin was not affected by administration through a nasogastric tube. This route of ingestion seems to be associated with a slight loss of bioavailability independent of the carrier medium used (water vs enteral feed); no clinically relevant interaction with the multivalent cations contained in the enteral feed was observed, indicating that moxifloxacin and enteral nutrition can be administered concomitantly.ConclusionThere was no clinically relevant effect of enteral feeding on the pharmacokinetics of oral moxifloxacin in healthy volunteers. This result has to be evaluated in patients, particularly those from the intensive care unit, who are characterised by severe infectious and/or concomitant diseases that might influence absorption of moxifloxacin.

ISSN:0312-5963    

出版商:ADIS    

年代:2005

数据来源: ADIS

摘要:

ObjectiveTo compare the pharmacokinetics of milnacipran in extensive metabolisers (EMs) and poor metabolisers (PMs) of sparteine and mephenytoin, and to assess the influence of multiple administrations of milnacipran on the activity  of  cytochrome  P450  (CYP)  isoenzymes  through  its  own  metabolism and through various probes, namely CYP2D6 (sparteine/dextromethorphan), CYP2C19 (mephenytoin), CYP1A2 (caffeine) and CYP3A4 (endogenous 6-β-hydroxy-cortisol excretion).MethodsTwenty-five healthy subjects, 12 EMs for both sparteine/dextromethorphan and mephenytoin, nine EMs for mephenytoin and PMs for sparteine/dextromethorphan (PM2D6) and four PMs for mephenytoin and EMs for sparteine/dextromethorphan (PM2C19) were administered milnacipran as a single 50mg capsule on day 1 followed by a 50mg capsule twice daily for 7 days. The pharmacokinetics of milnacipran and its oxidative metabolites were assessed after the first dose (day 1) and after multiple administration (day 8), and were compared for differences between CYP2D6 and CYP2C19 PMs and EMs. Metabolic tests were performed before (day −2), during (days 1 and 8) and after (day 20) milnacipran administration.ResultsMilnacipran steady state was rapidly achieved. Metabolism was limited: approximately 50% unchanged drug, 30% as glucuronide and 20% as oxidative metabolite (mainly F2800 theN-dealkyl metabolite). Milnacipran administration to PM2D6and PM2C19subjects did not increase parent drug exposure or decrease metabolite exposure. Milnacipran oxidative metabolism is not mediated through CYP2D6 or CYP2C19 polymorphic pathways nor does it significantly interact with CYP1A2, CYP2C19, CYP2D6 or CYP3A4 activities.ConclusionLimited reciprocal pharmacokinetic interaction between milnacipran and CYP isoenzymes would confer flexibility in the therapeutic use of the drug when combined with antidepressants. Drug-drug interaction risk would be low, even if the combined treatments were likely to inhibit CYP2D6 and CYP2C19 isoenzyme activities.

ISSN:0312-5963    

出版商:ADIS    

年代:2005

数据来源: ADIS