Pharmacokinetics of Midazolam in preterm neonates with an insight in brain Tissue: A PBPK approach

Physiological maturity is a gradual process taking place throughout infancy and childhood. Though for years anatomical growth has been the basis for dose calculation in pediatric population, physiological immaturity can-not be overlooked especially in neonates. The potential difference in physiology can significantly affect the outcomes of treatment and may result in under dosing or over-dosage. For many ethical and logistic constrains, carrying out pharmacokinetic studies of pharmacological agents in neonatal population remains a challenging task and such data is therefore, insufficient. This work presents Physiologically Based Pharmacokinetic modeling approach to predict the disposition of IV Midazolam in preterm neonates of different gestational ages, validated by the experimental studies. Furthermore, midazolam concentration in brain tissue of these neonates- the major site of its action- has been noted. The predicted and observed plasma pharmacokinetic parameters are comparable. This article demonstrates the usefulness of in-silico approach for finding out the PK parameters in neonates which may aid in deciding the frequency of drug administration in this population.

Sex-Related Differences in Drugs with Anti-Inflammatory Properties

There is increasing evidence of sex differences in the action of anti-inflammatory drugs, with women being at significantly higher risk of adverse effects. Nevertheless, clinicians' awareness of the implications of these sex differences on dosing and adverse event monitoring in routine practice is still in need of improvement. We reviewed the literature evaluating sex differences in terms of pharmacokinetics and pharmacodynamics of anti-inflammatory drugs. The anti-thrombotic activity of selective and non-selective COX-inhibitors tends to be stronger in men than women. Side effect profiles differ with regards to gastro-intestinal, renal and hepatic complications. Glucocorticosteroids were found to be more effective in men; women were more sensitive to corticosteroids when their oestradiol levels were high, a finding important for women taking hormonal contraception. TNF-alpha inhibitors have a longer half-life in men, leading to stronger immunosuppression and this a higher incidence of infections as side effects. Although research on sex differences in the effectiveness and safety of drugs is increasing, findings are often anecdotal and controversial. There is no systematic sex-differentiated reporting from clinical trials, and women are often under-represented. As personalized medicine is gaining in importance, sex, and gender aspects need to become integral parts of future research and policy making.

Enzyme and Transporter Kinetics for CPT-11 (Irinotecan) and SN-38: An Insight on Tumor Tissue Compartment Pharmacokinetics Using PBPK

BACKGROUND

Computational tools are becoming more and more powerful and comprehensive as compared to past decades in facilitating pharmaceutical, pharmacological and clinical practice. Anticancer agents are used either as monotherapy or in combination therapy to treat malignant conditions of the body. A single antineoplastic agent may be used in different types of malignancies at different doses according to the stage of the disease.

OBJECTIVE

To study the behavior of CPT-11 (Irinotecan) and its metabolite SN-38 in tumor tissue compartment through the Whole Body-Physiologically Pharmacokinetics (WB-PBPK) and to determine the activity of metabolic enzymes and transporters participating in the disposition of CPT-11 and SN-38 working in their physiological environment inside the human body.

METHODS

Whole body PBPK approach is used to determine the activity of different metabolic enzymes and transporters involved in the disposition of CPT-11 and its active metabolite, SN-38. The concentrations and pharmacokinetic parameters of the parent compound and its metabolite administered at clinically applicable dose via the intravenous route in the tumor tissue are predicted using this approach.

RESULTS

The activity rate constants of metabolic enzymes and transporters of CPT-11 are derived at their natural anatomic locations. Concentration-time curves of CPT-11 and SN-38 with their 5th to 95th percentage range are achieved at the tumor tissue level. Mean tumor tissue pharmacokinetics of both compounds are determined in a population of 100 individuals.

CONCLUSION

Tumor tissue concentration-time curves of CPT-11 and SN-38 can be determined via PBPK modeling. Rate constants of enzymes and transporters can be shown for healthy and tumor bearing individuals. The results will throw light on the effective concentration of active compound at its target tissue at the clinically applied IV dose.

Sex-Related Differences in Pharmacokinetics and Pharmacodynamics of Frequently Prescribed Drugs: A Review of the Literature

While there is considerable evidence about sex-related differences between men and women in drug metabolism, efficacy and safety of frequently prescribed drugs such as analgesics, tranquillizers, statins and beta-blockers, clinicians' awareness of the implications on dosing and adverse event monitoring in routine practice is inadequate. Some drugs are more effective in men than women (e.g. ibuprofen) or vice versa (e.g. opioids, benzodiazepine), typically owing to pharmacodynamic causes. The 5-hydroxytryptamine (5-HT) receptor 3 antagonist alosetron is approved for women only since it largely lacks efficacy in men. For statins, equal efficacy was demonstrated in secondary prevention of cardiovascular events, but primary prevention is still under debate. For some drugs (e.g. paracetamol, metoprolol), women are at significantly higher risk of adverse effects. Therefore, considering sex-specific features in clinical trials and therapeutic guidelines is warranted to ensure efficacy and safety of medicines.

WB-PBPK approach in predicting zidovudine pharmacokinetics in preterm neonates

Antiretroviral therapy has been the mainstay of treatment for neonates born to HIV infected mothers. Neonates born prematurely to HIV positive mothers are underdeveloped not only in anatomical terms but also in their physiological systems. Zidovudine, the first antiretroviral drug in clinical therapy for the treatment of HIV has been approved for use in preterm neonates both prophylactically and therapeutically. The present work describes the whole body physiologically based pharmacokinetic (WB-PBPK) model development for zidovudine in preterm neonates of varying gestational ages, to observe the pharmacokinetic behavior of the drug in this vulnerable group of the population. Along with the height, weight, post-natal, and gestational ages of the preterm neonates, metabolic enzymes CYP2A6, CYP2C8, etc. were incorporated for each neonate. The composition of the different organs in terms of water and lipid components, blood flow rates, etc. were specified during simulations according to the gestational ages of these neonates. The following PK parameters were estimated for preterm neonates using simulated plasma profiles: AUC 2686.41 ± 123.49 μmol min/L, C_max 6.46 ± 0.74 μmol/L, half-life 8.98 ± 2.36 hr, mean residence time 12.23 ± 3.43 hr, and total plasma clearance 1.48 ± 0.19 ml/min/kg in comparison with the observed PK parameters of a clinical study by Mirochknic et al. in preterm neonates with AUC 2020.04 μmol/min/L, C_max 6.10 μmol/L, and total plasma clearance 1.62 ml/min/kg. PBPK simulations provide an opportunity to visualize the possible impact of physiological maturity levels at varying gestational ages on the pharmacokinetic behavior of zidovudine in preterm neonates.

Hepatic arterial infusion of irinotecan and EmboCept® S results in high tumor concentration of SN-38 in a rat model of colorectal liver metastases

Intraarterial chemotherapy for colorectal liver metastases (CRLM) can be applied alone or together with embolization particles. It remains unclear whether different types of embolization particles lead to higher intratumoral drug concentration. Herein, we quantified the concentrations of CPT-11 and its active metabolite SN-38 in plasma, liver and tumor tissue after hepatic arterial infusion (HAI) of irinotecan, with or without further application of embolization particles, in a rat model of CRLM. Animals underwent either systemic application of irinotecan, or HAI with or without the embolization particles Embocept^® S and Tandem™. Four hours after treatment concentrations of CPT-11 and SN-38 were analyzed in plasma, tumor and liver samples by high-performance liquid chromatography. Additionally, DNA-damage and apoptosis were analyzed immunohistochemically. Tumor tissue concentrations of SN-38 were significantly increased after HAI with irinotecan and EmboCept^® S compared to the other groups. The number of apoptotic cells was significantly higher after both HAI with irinotecan and EmboCept^® S or Tandem™ loaded with irinotecan compared to the control group. HAI with irinotecan and EmboCept^® S resulted in an increased SN-38 tumor concentration. Both HAI with irinotecan and EmboCept^® S or Tandem™ loaded with irinotecan were highly effective with regard to apoptosis.

Zytoprotektion mit Amifostin (Ethyol®) in der Chemotherapie: Meta-Analyse zum pharmakokinetischen Interaktionspotential mit Zytostatika

The cytoprotective agent amifostine (AMI) is capable to protect healthy cells (contrary to tumor cells) due to higher activity of alkaline phosphatase at the membrane site of normal cells. In seven clinical trials the influence of AMI on the pharmacokinetics of different cytostatics was investigated. Preadministration of AMI increased Cmax of doxorubicin (+ 44 %, p < 0.06), epirubicin (+ 31 %, P < 0.08), mitomycin C (+ 41 %, p < 0.01) and docetaxel (+ 31 % and + 17 %, not significant). In contrary, the peak concentration of pirarubicin , the tetrahydropyranyl-prodrug of doxorubicin was decreased (- 50 %, P < 0.03), leading to an equal higher concentrationof doxorubicin in the blood . In accordance to the peak concentrations, the AUC'ast was increased by chemoprotection: doxorubicin + 53 % (p < 0.01) and epirubicin + 23 % (not significant), docetaxel + 25 % and + 31 % (not significant). AUC'ast of mitomycin C and paclitaxel seemed to be unaffected by preadministered AMI. A particular inhibition of the protein binding by AMI has been identified as one reason for higher serum concentrations of anthracycline drugs. After cytoprotection, a possible increase of the cytostatic's Serum concentrations should be taken into account for optimal dosage schedules.

Physiologically based pharmacokinetic modeling for predicting irinotecan exposure in human body

Colorectal cancer is the third leading cause of cancer-related deaths in the United States. Treatment of colorectal cancer remains a challenge to clinicians as well as drug developers. Irinotecan, a Camptothecin derivative, is successfully used for the treatment of this rapidly progressing malignancy and finds its place in the first line of therapeutic agents. Irinotecan is also effective in treating SCLC, malignant glioma and pancreatic adenocarcinoma. However, its adverse effects limit its clinical application. Mainly metabolized by hepatic route, and excreted through biliary tract, this dug has been found to possess high variation in patients in its pharmacokinetic (PK) profile. Physiologically based pharmacokinetic (PBPK) models using compartmental approach have attained their position to foresee the possible PK behavior of different drugs before their administration to patients and such models have been proposed for several anticancer agents. In this work, we used WB-PBPK technology to develop a model in a population of tumor patients who used IV irinotecan therapy. This model depicted the concentration of drug and its pharmacologically active metabolite in human body over a specific period of time. Knowledge about pharmacokinetic parameters is extracted from this profile and the model is evaluated by the observed results of clinical study presented in literature. The predicted behavior of the drug by this approach is in good agreement with the observed results and can aid in further exploration of PK of irinotecan in cancer patients, especially in those concomitantly suffer from other morbidity.

Evaluation of real-time data obtained from gravimetric preparation of antineoplastic agents shows medication errors with possible critical therapeutic impact: Results of a large-scale, multicentre, multinational, retrospective study

WHAT IS KNOWN AND OBJECTIVE

Medication errors are a significant cause of morbidity and mortality especially with antineoplastic drugs, owing to their narrow therapeutic index. Gravimetric workflow software systems have the potential to reduce volumetric errors during intravenous antineoplastic drug preparation which may occur when verification is reliant on visual inspection. Our aim was to detect medication errors with possible critical therapeutic impact as determined by the rate of prevented medication errors in chemotherapy compounding after implementation of gravimetric measurement.

DESIGN

A large-scale, retrospective analysis of data was carried out, related to medication errors identified during preparation of antineoplastic drugs in 10 pharmacy services ("centres") in five European countries following the introduction of an intravenous workflow software gravimetric system. Errors were defined as errors in dose volumes outside tolerance levels, identified during weighing stages of preparation of chemotherapy solutions which would not otherwise have been detected by conventional visual inspection.

KEY RESULTS

The gravimetric system detected that 7.89% of the 759 060 doses of antineoplastic drugs prepared at participating centres between July 2011 and October 2015 had error levels outside the accepted tolerance range set by individual centres, and prevented these doses from reaching patients. The proportion of antineoplastic preparations with deviations >10% ranged from 0.49% to 5.04% across sites, with a mean of 2.25%. The proportion of preparations with deviations >20% ranged from 0.21% to 1.27% across sites, with a mean of 0.71%. There was considerable variation in error levels for different antineoplastic agents.

WHAT IS NEW AND CONCLUSION

Introduction of a gravimetric preparation system for antineoplastic agents detected and prevented dosing errors which would not have been recognized with traditional methods and could have resulted in toxicity or suboptimal therapeutic outcomes for patients undergoing anticancer treatment.

Assessment of Pharmacokinetic Interaction Between Capecitabine and Cetuximab in Metastatic Colorectal Cancer Patients

AIM

This study focuses on the plasma disposition and metabolic activation of capecitabine (CCB) when administered alone or when combined with cetuximab (CTX).

PATIENTS AND METHODS

Twenty-four chemo-naïve patients with KRAS wild-type colorectal cancer were randomized into two arms and received either CCB alone (1,000 mg/m(2) bid p.o.), followed by CCB plus CTX (loading dose (LD)=400 mg/m(2) followed by 250 mg/m(2) weekly i.v. maintenance dose) (Arm A; n=12 patients (patients)) or CCB plus CTX followed by CCB alone (Arm B; n=12 patients). Plasma samples were collected from the cubital vein and CCB, 5'-desoxy-5-fluorocytidine (5'-DFCR) and 5'-desoxy-5 fluorouridine (5'-DFUR) were quantified by a sensitive, selective reversed phase high-performance liquid chromatography (HPLC) assay. Non-compartment pharmacokinetic parameters have been calculated by Phoenix WinNonlin.

RESULTS

No clinically relevant impact of CTX on CCB pharmacokinetic parameters and metabolic conversion could be detected in both arms after statistical evaluation (ANOVA).

CONCLUSION

From the pharmacokinetic point of view, co-administration of CTX to CCB seems to be safe.

Systemic side effects of eye drops: a pharmacokinetic perspective

When administering eye drops, even when completely correctly applied, several routes of absorption are possible and excess amounts can sometimes cause an unwanted systemic bioavailability of the drops when not completely absorbed into the eye. Furthermore, the concentration of active ingredients in such medicinal preparations is usually very high, so that despite the correct application of the recommended dose, considerable amounts may be absorbed in an unwanted manner through various routes. Children are subject to a much higher risk of systemic side effects because ocular dosing is not weight adjusted and physiological development (eg, liver status) differs from that of adults. There is a lack of information about pediatric dosing in the current literature. This review summarizes the most important clinically relevant systemic side effects that may occur during ophthalmic eye treatments. In this review, we discuss general pharmacokinetic considerations as well as the advantages, disadvantages, and consequences of administering drugs from some important drug groups to the eye.

Clinical pharmacokinetics and metabolism of paclitaxel after a three-hour infusion: comparison of two preparations

The clinical pharmacokinetics (PHK) of paclitaxel (PACLI) and its hydroxylated metabolites after three hours IV infusion (200 mg/m2) of two preparations were investigated in 13 patients receiving chemotherapy against breast cancer. Standard TaxolÒ was purchased from Bristol Myers Squibb and a test preparation ebetaxel (containing additional 2 mg/mL citric acid) was provided by Ebewe Pharma Austria. In the first cycle, either standard or test preparation was administered, then its alternative preparation in the second cycle (latin square, paired crossover design). In both treatment schedules the peak concentrations of PACLI occurred at the end of infusion after three hours. Mean peak concentration of PACLI was cmax5 505191131 ng/mL for the test preparation and cmax5 526991109 ng/mL for the standard preparation. No statistically significant differences in these plasma concentrations could be calculated. Mean tmax of metabolites was between 3.00 and 3.25 hours, their plasma concentrations were very similar: 6-OH-PACLI: cmax 4689266 ng/mL versus 4529212 ng/mL, 3Í-OH-PACLI: cmax 85938 ng/mL versus 90944 ng/mL, 3Í,6-DiOH-PACLI: cmax 87927 ng/mL versus 76931 ng/mL.

The PHK parameters of PACLI (AUC, Cltot, Vd) and its metabolites (AUC, t1/2 dis, t1/2 el) did not differ significantly between both preparations. Biotransformation of PACLI into its three hydro-xylated metabolites (expressed as their appearance in blood) was not affected by the content of citric acid in the test preparation.

A Simple Method for Comparing Enzymatic Capecitabine Activation in Various Mono- and Combination Chemotherapies

Before being able to develop a pharmacodynamic effect, a number of drugs have to be activated by enzymes, which are known to be potentially influenced by manifold factors, leading to a possible alteration of their activity behaviour. Based on capecitabine, we report a simple and rapid method for the estimation and comparison of the so-called ‘apparent enzyme activity' (R), not only intra- (different dose levels) but also inter-schedule, to contribute to therapeutic success. Dividing the area under the curve (AUC) of the product by the AUC of the precursor generates a factor which indicates the apparent activity of the enzyme involved in the biotransformation of a compound. Our own data as well as data from the literature was used to calculate those R levels revealing that the formation of 5′-DFUR - the immediate precursor of 5-fluorouracil - was not affected by concomitant medication within the dosing range investigated. Calculated hypothetical means of R for carboxylesterase (1.49 ± 0.66) and for cytidine deaminase (1.17 ± 0.65) were obtained. Additionally, it is important to note that the method described in this report is of general use and not limited to chemotherapeutic agents, as soon as enzymes are involved in drug activation.

Impact of co-administered drugs on drug monitoring of capecitabine in patients with advanced colorectal cancer

BACKGROUND

Drug monitoring is a useful tool for obtaining detailed information about the disposition of a drug in an individual patient during chemotherapy. According to the international guidelines, the analytical assay for quantification of a compound in biological samples must be validated. Among a number of parameters, peak purity is an important requirement.

MATERIALS AND METHODS

We analyzed pharmacokinetics in patients who received chemotherapy with capecitabine and up to 10 various co-medications.

RESULTS

Out of seven investigated co-administered drugs, we found evidence that the proton pump inhibitor pantoprazole causes peak interferences with capecitabine during high-performance liquid chromatography analysis. Therefore quantification of capecitabine in plasma samples can be inaccurate.

CONCLUSION

We recommend an altered time schedule for co-administered drugs or changing the mobile phase used in the assay.

Clinical pharmacokinetics of capecitabine and its metabolites in combination with the monoclonal antibody bevacizumab

AIM

Capecitabine, designed as a pro-drug to the cytotoxic agent 5-fluorouracil, is widely used in the management of colorectal cancer. This study was designed to investigate whether co-administration of the monoclonal antibody bevacizumab (BVZ) shows potential to modulate the plasma disposition of capecitabine (CCB) and its metabolites.

PATIENTS AND METHODS

Nine patients treated with CCB and BVZ for advanced colorectal cancer entered this pharmacokinetic study. In the first cycle CCB was given alone at doses of 1,250 mg/m2 bi-daily for two weeks with one week rest. In the second cycle BVZ co-administration started simultaneously with oral intake of CCB by short infusion of 7.5 mg/kg.

RESULTS

Mean plasma concentration time curves of CCB and its metabolites were insignificantly lower in the BVZ combination regimen compared to CCB monotherapy. After repeated cycles of BVZ no significant pharmacokinetic interaction was observed.

CONCLUSION

From the pharmacokinetic point of view and in agreement with numerous clinical study data, co-administration of BVZ with CCB appears to be safe and efficient.

Disposition of Erlotinib and Its Metabolite OSI420 in a Patient with High Bilirubin Levels

Erlotinib is an oral epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor approved for the treatment of non-small cell lung cancer and when combined with gemcitabine for pancreatic cancer. Dose reduction of erlotinib in patients with severe hepatic impairment has been established. We present the case of a male patient suffering from an adenocarcinoma of the pancreas with metastases in the liver and lung, whose disease progression led to highly elevated bilirubin levels of >14 mg/dl accompanied by icterus and pruritus. Despite the known contraindication, the patient agreed to be treated with 150 mg erlotinib p.o. per day. We performed therapeutic drug monitoring of erlotinib on day 1 after the first ingestion of erlotinib and then over a period of 19 days. One-compartment pharmacokinetics on day 1 were calculated, and, based on these data, a pharmacokinetic simulation for the following 19 days was run. On day 1 after the first erlotinib ingestion, plasma concentrations were identical to those described in the literature. On the following days, erlotinib plasma concentrations remained at a similar order of magnitude after daily ingestion. Compared with published data, OSI420 plasma concentrations were clearly higher from day 1 to 16. Due to disease progression, the last intake of erlotinib was on day 16, but plasma concentrations of the drug and metabolite increased excessively thereafter. The data give evidence that total bilirubin levels up to 14 mg/dl do not necessarily cause elevated plasma concentrations of erlotinib when given in doses of 150 mg per day.

Validation of a simple assay for the quantification of the capecitabine metabolites 5'-DFCR and 5'-DFUR for drug monitoring in patients receiving outpatient chemotherapy

A simple and precise analytical method for the determination of 5'deoxy-5-fluorocytidine (DFCR) and 5'deoxy-5-fluorouridine (DFUR), the enzymatically formed metabolites of capecitabine in plasma, was developed using a reversed-phase high performance liquid chromatography gradient method with external standard method. Blood samples were analyzed after separation of DFCR/DFUR by solid-phase extraction from matrix compounds using a C16 amide reversed-phase column operated at a flow rate of 0.8 ml/min in gradient elution mode with a mobile phase composed of water-methanol (10 mM ammonium acetate in water; m/v). Excellent recoveries in plasma ranging from 77.5-99.12% for DFCR and 84.70-99.15% for DFUR, respectively, were obtained. For both compounds the calibration curves were linear over the range from 0.156 to 5.0 μg/ml. The present assay is robust, selective and sensitive, and is being applied in our laboratories to monitor plasma concentrations of DFCR and DFUR in clinical phase I and phase II studies.

Acute Reversible Heart Failure Caused by Coronary Vasoconstriction due to Continuous 5-Fluorouracil Combination Chemotherapy

We present the case of a 51-year-old male patient who received adjuvant chemotherapy consisting of oxaliplatin, bolus and continuous 5-fluorouracil (5-FU) and leucovorin after anterior resection because of locally advanced rectal cancer. Preoperative chemotherapy with capecitabine (an oral 5-FU prodrug) had been well tolerated. Two days after initiation of the first course of chemotherapy, the patient reported typical chest pain. The ECG showed ST elevations and prominent T waves in almost all leads. Due to suspicion of a high-risk acute coronary syndrome, an urgent cardiac catheterization was performed. It showed a generally reduced coronary flow with multiple significant stenoses (including the ostia of the left and right coronary artery), as well as a highly reduced left ventricular function with diffuse hypokinesia. Due to the meanwhile completely stable situation of the patient after medical acute coronary syndrome treatment, no ad hoc intervention was performed to allow further discussion of the optimal management. Thereafter, the patient remained clinically asymptomatic, without any rise in cardiac necrosis parameters; only NT-pro-BNP was significantly elevated. A control cardiac catheterization 2 days later revealed a restored normal coronary artery flow with only coronary calcifications without significant stenoses, as well as a normal left ventricular ejection fraction. Cardiovascular symptoms occurred on the second day of continuous 5-FU treatment. As cardiotoxic effects seem to appear more frequently under continuous application of 5-FU, compared to the earlier established 5-FU bolus regimens, treating medical oncologists should pay special attention to occurring cardiac symptoms and immediately interrupt 5-FU chemotherapy and start a cardiologic work-up.

Metabolic activation of irinotecan during intra-arterial chemotherapy of metastatic colorectal cancer

Biotransformation of irinotecan (CPT-11) into its pharmacologic active metabolite SN-38 was investigated in patients treated for advanced colorectal cancer. A dose of 180 mg/m(2) CPT-11 was administered to 6 patients by 60 min hepatic intra-arterial infusion (HAI) via a surgically implanted Port-a-Cath® system. Blood samples were collected from 0 to 360 min after start of HAI, and CPT-11 plus metabolites were analysed by a selective reversed phase HPLC method. The objective of this study was to evaluate the extent to which SN-38 is generated after HAI of irinotecan given at a low dose of 180 mg/m(2). In a second investigation, CPT-11 was administered via conventional intravenous infusion (dose 180 mg/m(2), 60 min infusion time, 11 patients) and CPT-11 plus metabolites were quantified using identical analytical procedure. Compared to i.v. infusion, the pharmacokinetics of CPT-11 and SN-38 were altered by HAI. The mean c(max) of CPT-11 after HAI was reduced by 37%, whereas the mean c(max) of SN-38 increased by 60%. HAI resulted in a desired, increased metabolic conversion of CPT-11 into SN-38 and might improve the regional availability of the pharmacologic active metabolite SN-38 at the site of tumor. Plasma concentrations of the metabolites SN-38 glucuronide and APC remained unaffected by the route of administration.

A rapid and simple HPLC assay for quantification of capecitabine for drug monitoring purposes

AIM

Capecitabine, a 5-fluorouracil prodrug, has been integrated into the management of multiple cancer types. In order to obtain information about plasma levels of capecitabine in patients who had drug intake at home during chemotherapy, a simple HPLC method for capecitabine monitoring has been developed and validated.

PATIENTS AND METHODS

Capecitabine levels were quantified by a simple reversed-phase HPLC system with an external standard method. Plasma samples were obtained from 12 colorectal cancer patients who underwent chemotherapy with capecitabine alone (1000 mg/m(2)) or combined with oxaliplatin (130 mg/m(2)).

RESULTS

Although there was evidence that capecitabine had not been taken according to the chemotherapeutic schedule in two cases, the study demonstrated that its combination with oxaliplatin showed no significant drug-drug interactions.

CONCLUSION

Due to its robustness, specificity and sensitivity, the method is also well-suited for capecitabine analysis in other pharmacokinetic studies.

Pharmacokinetics of irinotecan in combination with biweekly cetuximab in patients with advanced colorectal cancer

BACKGROUND

The effect of biweekly cetuximab (CTX) on the pharmacokinetics of CPT-11 and its metabolites was evaluated in this prospective, paired, crossover study.

PATIENTS AND METHODS

Patients with epidermal growth factor receptor-positive advanced colorectal cancer received infusions of CPT-11 (180 mg/m(2); FOLFIRI schedule) every second week. CTX (500 mg/m(2) for 120 min) was infused on day 2, followed by biweekly infusions (500 mg/m(2) for 120 min). Plasma samples were analysed on day 1 of cycle 1 (CPT-11 monotherapy) and on day 1 of cycle 3 or 4 (CPT-11 plus CTX). The endpoint of this study was to evaluate differences in plasma concentrations of CPT-11 and metabolites between cycle 1 and cycle 3 (or 4).

RESULTS

Generally, there was little difference in CPT-11 pharmacokinetics when combined with CTX in the 11 enrolled patients. However, a significantly lower area under the concentration-time curve from 0-48 hours was observed for the SN-38 glucuronide metabolite with combination therapy versus monotherapy (by 27%, p<0.05).

CONCLUSION

CTX has no clinically relevant impact on the pharmacokinetics of CPT-11 or its activation into SN-38; however, there may be a delay in detoxification of SN-38 by beta-D-glucuronidation.

Doxorubicin pharmacokinetics following two different liposomal formulations (CAELYX™ vs MYOCET™) in advanced breast cancer patients

Abstract #2128

Background: Liposomal encapsulation of Doxorubicin (DOX) was designed to minimize healthy tissue distribution by altering pharmacokinetics (PK) thus reducing cardiotoxicity while preserving antitumour efficacy. Study objective was to compare the PK behaviour of the two main liposomal formulations of DOX, i.e. pegylated (Caelyx, C) versus non pegylated (Myocet, M), in a single center study including 17 MBC patients, all Anthracyclin pretreated with additional risk faktors.&#x2028; Methods: Cohort 1 consisted of 10pts (mean age 62, 49-77) treated by C as 1HR infusion of 50mg/m²/4 wks. Plasma samples were collected at timepoints min 0, 30, 60, 120, 180 and d1, 7, 14, 28. In cohort 2, 7 pts (mean age 58, 51 – 70) received M 75mg/m² 1H Infusion / 3wks, plasma levels determined at min 0, 30, 60, 90, 120, 180 and d1, 2, 3. Total amount of DOX was determined following the 1st infusion respectively, analytic procedure included solid phase extraction quantification by HPLC and PK analysis by Win Nonlin Pro. Doxorubicinol was detected after M only.&#x2028; Results: in Cohort1 after C, mean Cmax of 6.8 µg/ml surprisingly occured at a mean tmax of 2.3 d, log conc time curve showed linear decrease of DOX conc suggesting continuous release into the tissue (mean conc d 7 3.3, d 14 1.0, d 21 0.3, d 28 0.09 µg/ml) . No metabolites were found, AUC (does not represent reliable drug exposure and bioavailability of DOX) expressed as µg/ml.d was 54.6. In contrast AUClast of M was calculated as 35µg ml.H and mean Cmax by 7.5 µg/ml at infusion end. DOXol was measured in all M treated patients at a slower metabolisation rate and late appearance compared to conventional DOX. t/2 el of C was 6 times longer than that of M (HR 90 vs 15). Differences in plasma disposition and PK of M vs C are depicted in table 1 and compared to pooled data of conventional DOX derived from former studies (50 mg/m² 30min inf, n=40). Cltot of conv. DOX was 10 fold higher than M and 500 fold higher than C, Vss about 12 times that of M and 70 times that of C. These PK differences underlines a different toxicity profile between PEGL (C, PPE syndrome) and NPEGL (M, myelotox, nausea), both reducing cardiac tox by avoiding peak plasma levels due to prolonged circulation time.&#x2028; &#x2028;

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 2128.

[Pharmaceutical aspects of clinical trials: concepts of pharmacokinetic investigations]

Pharmacokinetic investigations of a drug - and of its pharmacologically active metabolite, if necessary - represent an essential part of clinical trials. The European Union (EMEA, European Medicines Agency) strictly regulates the separation and quantification of a drug from biological matrix, e.g. blood, urine, tissue, and others. These GCP (Good Clinical Practice) and GLP (Good Laboratory Practice) guidelines have to be considered and documented for the planning of the investigation, the administration of the test drug, the sampling, and the transport of samples. The following sample preparation, analytical measurements, and biometric calculations have to be performed only by validated procedures. Similar requirements are necessary for the final pharmacokinetic modelling, the statistical presentation of data, and the final report. In this article the most important aspects concerning the performance of a pharmacokinetic investigation will be presented.

Influence of bevacizumab on the plasma disposition of CPT 11 and its metabolites in advanced colorectal cancer patients

3540

Background: The monoclonal antibody (mab) bevacizumab (BEV) inhibits VEGF, downregulates angiogenesis and lowers interstitial pressure, by which blood tissue transfer and metabolism of a drug could be modulated. CPT 11 produced survival benefit combined with BEV and undergoes complex biotransformation by different enzymatic routes: carboxylesterase hCE2 (SN 38), UGT1A1 (detoxificition to SN 38 glucuronide) and CYP 3A4 (APC), the latter enzyme has been described to be reversibly inhibited by mabs. Therefore it seems worthwhile to investigate a potential influence of BEV on plasma disposition and pharmacokinetics (PK) of CPT11 and metabolites. Methods: 10 pts with advanced colorectal cancer (5 first line, 5 second line after FOLFOX) were treated by FOLFIRI schedule (with CPT 11 180 mg/m2 1HR infusion) preceeded by BEV 5 mg/kg (90–60–30 min infusion) every 2 weeks. At cycle 1, CPT 11 was applied before BEV to allow baseline PK analysis of CPT 11 and its metabolites, at cycle 4 (i.e. after 8 weeks) determination of CPT 11 plasma conc was repeated after a 30 min infusion of BEV. Plasma samples were collected every 30 min over 4 HR and analysed by HPLC. Results: PK of CPT 11 remained unaffected by BEV, only a small decrease in cmax and AUC was found. Contrary, SN 38 formation seemed to be delayed and formation rate decreased when combined with BEV, resulting in lower cmax (-24%) and AUC (-20%). SN 38 glucuronide levels were generally found to be higher than those of SN 38, cmax and AUC reduced by 35% when BEV was preadministered. A similar effect was also observed in PK parameters of APC (about 30% reduction of cmax and AUC). Conclusion: A changed plasma disposition of all 3 metabolites - generated by 3 different enzymatic pathways - is unlikely to be caused by BEV influencing CPT 11 metabolism. The observed effect could be explained by increased blood tissue transfer, alteration of microvasculature by BEV may favour tissue uptake of the drug.

[Table: see text]

No significant financial relationships to disclose.

In vivo disposition of irinotecan (CPT-11) and its metabolites in combination with the monoclonal antibody cetuximab

BACKGROUND

The present study was designed to investigate whether a combination of irinotecan and the monoclonal antibody cetuximab shows potential to modulate the pharmacokinetics of irinotecan and its metabolites.

PATIENTS AND METHODS

All patients, suffering from advanced colorectal cancer, received irinotecan (350 mg/m2) every third week and cetuximab as a loading dose (400 mg/m2) on day 2, followed by a weekly maintenance dose (250 mg/m2). Plasma samples were analysed after the first (MONO) and second (CMAB) irinotecan infusions.

RESULTS

No significant alterations in the plasma concentrations and pharmacokinetics of irinotecan and its metabolites were observed after combination with cetuximab. Only differentiation of irinotecan into lactone and carboxylate plasma concentrations resulted in a distinctly lower cmax of the active lactone in the CMAB and a significantly higherAUClast in the MONO schedule (p<0.02).

CONCLUSION

The results of this study indicated that cetuximab has no clinically relevant impact on the pharmacokinetics of irinotecan, its activation into SN-38, or its detoxification by beta-D-glucuronidation.

Disposition of paclitaxel (Taxol®) and its metabolites in patients with advanced breast cancer (ABC) when combined with trastuzumab (Hercpetin®)

Monoclonal antibodies are capable of modulating drug metabolising enzymes resulting in unexpected plasma concentrations of a drug when given concomitantly. Therefore plasma concentration of paclitaxel (PTX) and its metabolites has been monitored in 10 patients with advanced breast cancer during treatment with PTX alone or combined with trastuzumab (TMAB, paired cross over design). Compared to the MONO regimen PTX peak plasma concentrations were about 25% lower in the TMAB schedule: cmax = 3294 +/- 1174 ng/ml (MONO: 4368 +/- 1887 ng/ml). TMAB also caused lower peak plasma concentration of the main metabolite 6-hydroxy PTX (248 +/- 89 ng/ml) compared to the MONO schedule (194 +/- 82 ng/ml). Cmax of the minor metabolites was distinctly below 100 ng/ml and consequently differed negligible in both schedules. The similar apparent formation rate of the metabolites in both schedules (range from 30 to 50 min) as well as identical tmax values (range 170-190 min) suggested that TMAB had no influence on PTX metabolism. In accordance to plasma concentrations, AUClast of PTX was lower in the MONO schedule (733 +/- 197 microg/ml*min, AUClast = 669 +/- 248 microg/ml*min for TMAB) but without significance. In summary no indices for an altered plasma disposition of PTX and its metabolites could be found when TMAB was given concomitantly.

Pharmacokinetics and metabolism of irinotecan combined with capecitabine in patients with advanced colorectal cancer

BACKGROUND

Irinotecan (CPT-11) in combination with 5-fluorouracil/folinic acid is used successfully for first-line treatment of metastatic colorectal cancer. Capecitabine (CCB) represents a very convenient alternative to 5-fluorouracil, either as single agent or in a combination of regimens acting synergistically and with the potential to further improve efficacy. Both CPT-11 and CCB need to be activated by human carboxyl esterases, therefore a probable pharmacokinetic drug interaction was checked.

PATIENTS AND METHODS

Ten patients suffering from advanced colorectal cancer were enrolled in this trial. CPT-11 was administered as a 30-min i.v.-infusion (70 mg/m2) weekly. CCB was given p.o. twice daily for two weeks (2,000 mg/m2 daily) starting the day after the first CPT-11 infusion. Plasma samples were analysed during/after the first (MONO) and third (CAPIRI) CPT-11 infusion.

RESULTS

CCB did not alter CPT-11 plasma disposition, and no significant changes in c(max), AUC(last), Vdss and Cl(tot) during CAPIRI treatment could be observed. However, co-administration of CCB appeared to decrease SN-38 (the cytotoxic CPT-11 metabolite) plasma concentrations during the first three hours after initiation of CPT-11 infusion, with strongly time-dependent plasma percentage differences between control and CAPIRI treatment (p < 0.005, R = 0.981). Co-administration of CCB also had a similar impact on the initial plasma disposition of SN-38gluc, but not on that of the APC metabolite.

CONCLUSION

Overall, our findings indicate that, while the administration of CCB resulted in reversible lower formation rates of SN-38 and SN-38gluc, it did not have a significant impact on CPT-11 pharmacokinetics.

Pharmacokinetics of Gemcitabine Combined with Trastuzumab in Patients with Advanced Breast Cancer

BACKGROUND

Combining the monoclonal antibody trastuzumab (TMAB) with chemotherapy is a new strategy in treatment of advanced breast cancer in HER+++ overexpressing patients.

PATIENTS AND METHODS

The disposition of gemcitabine has been investigated in 8 breast cancer patients (prospective cross-over design). Gemcitabine was administered as a 30-min i.v. infusion (1,000 mg/m(2) in 250 ml) on day 1 weekly for 3 weeks. On day 2 TMAB was infused with a loading dose of 4 mg/kg (90-min infusion) followed by a weekly maintenance dose of 2 mg/kg (30-min infusion). Pharmacokinetic analysis was performed after the first (= MONO) and after the third gemcitabine infusion (= TMAB).

RESULTS

Cmax was 22.2 microg/ml (t(max) = 24 min) in the MONO and 24.6 microg/ml (t(max) = 23 min) in the TMAB schedule. Gemcitabine distributed rapidly from plasma within a few minutes and was eliminated with a t1/2el of about 80 min in both arms of the study. The metabolite difluorodeoxyuridine (dFdU) appeared in plasma with t1/2appin = 12.8 min (MONO) or t1/2appin = 10.2 min (TMAB) reaching a mean peak concentration of 35.9 microg/ml (MONO) or 30.4 microg/ml (TMAB), respectively.

CONCLUSION

The results gave evidence that TMAB does not affect the disposition of gemcitabine.

Clinical pharmacokinetics and metabolism of paclitaxel after polychemotherapy with the cytoprotective agent amifostine

BACKGROUND

Cytoprotection of healthy cells represents a new approach in cancer chemotherapy, but a pharmacokinetic drug interaction between the cytostatic and the cytoprotectant is undesired.

METHODS

The purpose was to evaluate the clinical pharmacokinetics (PHK) of paclitaxel (PACLI) and its metabolites under cytoprotection in patients suffering from breast cancer. PACLI was administered alone and in a second cycle in combination with amifostine (AMI) as a paired cross over.

RESULTS

In both treatment schedules the steady state of PACLI occurred after 3 hours, the tmax of metabolites between 3 and 4 hours. The mean steady-state concentration was cmax = 5432 +/- 1238 ng/ml in the control group and cmax = 5140 +/- 2407 ng/ml in the AMI group. For the serum metabolites, the findings were very similar: 6-OH-PACLI: cmax 413 +/- 153 ng/ml versus 432 +/- 304 ng/ml, 3"-OH-PACLI: cmax 99 +/- 103 ng/ml versus 123 +/- 98 ng/ml, 3",6-DiOH-PACLI: cmax 43 +/- 55 ng/ml versus 75 +/- 85 ng/ml. AUC values of metabolites were slightly higher in the AMI group, but PHK seemed equal.

CONCLUSION

The results gave evidence, that cytoprotection with AMI has no clinical consequences on PACLI pharmacokinetics and biotransformation.

[Binding of epirubicin to human plasma protein and erythrocytes: interaction with the cytoprotective amifostine]

The in vitro binding rate of epirubicin (EPR) to different plasma proteins, control serum, red blood cells and whole blood was investigated without and with the cytoprotective agent amifostine. The binding rate of EPR to plasma proteins fractions and red blood cells dependend on the concentration of the matrix components. EPR was bound more than 90% to human serum alpha-globulin (alpha-HSG), to human serum albumine (HSA) and human serum beta-globuline (beta-HSG) at 80 to 90%, in the case of human serum gamma-globulin (gamma-HSG) the binding rate amounted 75%. The binding rate of EPR to RBCs in whole blood samples reached 38%. Within the observed concentration range of proteins (1-40 micrograms/ml, depending on the protein concentration) AMI caused a reduction of the protein-bound amount of EPR in the range from 2 to 19% of HSA, 4 to 20 in the case of beta-HSG, 2 to 32% in the case of alpha-HSG and 17 to 21% for gamma-HSG. In the whole blood samples the binding of EPR to proteins dropped from 45 to 32% and RBC-partitioning from 38 to 32%. Two compounds with free thiol groups, cystein and glutathione, were compared with AMI in regard to lowering the binding rate of EPR to HSA: the effect was exactly in the same order of magnitude: -17% for AMI, -21.0% for cystein and -20.8% for glutahion (p < 0.002). For a negative control, cystin and phenylalanin were tested, too: both compounds showed no influence on the protein binding of EPR: 63.8% binding rate in the control group, 65.2% in the presence of cystin and 64.6% in the presence of phenylalanin (statistically not significant). The present results indicate, that binding of EPR to serum proteins is reduced in the presence of AMI by interaction of the thiol-group with the protein and that the thiophosphoric ester bond in the test solution must cleave rapidly.

Pharmacokinetic interaction between 4'-epidoxorubicin and the multidrug resistance reverting agent quinine

The serum and red blood cell (RBCs) disposition of epirubicin (EPR) after intravenous bolus injection without and with coadministered quinine ( QUI) was investigated in patients undergoing a cyclic chemotherapy with EPR. QUI possesses a statistical significant influence on the EPR serum concentrations and, as a consequence, on the pharmacokinetic parameters for the initial distribution phase of EPR. Within the first 15 min after administration, EPR was distributed from the central compartment distinctly faster in compare to the control, when QUI was preadministered (t(1/2) = 6 min for the control group and t(1/2) = 3 min with QUI; -46%, p < 0.05). Yet, in the beta-phase when drug-elimination predominates, no statistical significant influence of QUI in regard to EPR serum and RBC concentrations could be observed. Half-life of elimination was 0.5 h for the control group and 8.6 h for the QUI group (-10%). The mean initial serum concentration (co) was reduced significantly by QUI from 7359 +/- 506 ng/ml to 4351 +/- 1682 ng/ml (-42%, p < 0.005). Furthermore, QUI caused a reduction of the serum bioavailability of EPR (expressed as AUC(o-24)-values) from 3404 +/- 1008 ng/ml x h to 2359 +/- 1073 ng/ml x h (-31%, p < 0.05). Vd and Vdbeta were increased at about 90% and the mean total body clearance was accelerated from 45.3 to 1487 ml/min, but due to the large standard deviations the calculated difference for these parameters was not statistically significant. In the observed time interval of 24 h, the red blood cell coefficient of distribution k(rbc) of EPR was lower if QUI was coadministered (k(rbc) = 1.25 +/- 0.12 for the control group k(rbc) = 1.15 +/- 0.13 under QUI; p < 0.04). The results point out that QUI induces an accelerated distribution of EPR from the blood into the tissue and that QUI additionally may have influence on the red-blood cell partitioning of EPR.

[Drug interactions between interferon alpha 2b and 5-fluorouracil during continuous intravenous 5FU infusion]

The concentration-time profile of 5-fluorouracil (5FU) in serum of patients during continuous infusion of 5FU for five days was investigated. The coadministration of each of 5 million units interferon-alpha-2b (IFN) on day 2 and 4 of the infusion causes an accumulation of 5FU in the serum at about 120% on day 3 in compare to the control (day 1 of infusion without IFN). On day 5 of the infusion the mean 5FU serum concentrations are about 170% higher than on day 1 with a level of probability ranging from p < 0.0003 to p < 0.043. Mean AUC-values increase from 5454 ng/ml.h (day 1) to 12069 ng/ml.h (day 3, p < 0.05) and subsequently to 14919 ng/ml.h on day 5 (p < 0.005). IFN causes an decrease of the total body clearance from 2949 ml/h (day 1) to 1959 ml/h on day 3 and to 1258 ml/h on day 5 (p < 0.008), respectively. There might exist a linear correlation between the order of magnitude of the 5FU serum concentrations and its pharmacokinetic parameters on day 1, 3 and 5 and the administration of IFN, because a close correlation ranging from R = 0.972 to R = 0.999 have been found in regression analysis.

Pharmacokinetic interaction of 5-fluorouracil and interferon alpha-2b with or without folinic acid

The purpose of this study was to evaluate a potential pharmacokinetic (PK) interaction between fluorouracil (5-FU) and the biomodulating agent interferon alpha (IFN-alpha) in patients with metastatic colorectal carcinoma. 5-FU was applied as an intravenous bolus injection of 750 mg m-2 weekly and IFN-alpha 2b (IFN) 5 MU was injected 3 times weekly (TIW) subcutaneously. In the first study, 13 patients were treated by this schedule, 5-FU plasma levels were determined by HPLC on day (d) one as baseline before starting IFN; the analysis was repeated at the second or third cycle of 5-FU administration 1 hour after the last IFN injection respectively. In the second study, 10 patients additionally received folinic acid (FA) 200 mg m-2 as a short time infusion immediately before 5-FU, and a third analysis of FU kinetics was performed in order to compare the influence of a double modulation of IFN and FA to IFN alone. Combination of 5-FU and IFN resulted in a significant increase of the AUC of 5-FU (80%) and the fictive initial concentration (C0, 65%) obviously caused by a reduction of 5-FU clearance by 50%. However, when FA was added to this schedule, no significant changes of FU kinetics compared to 5-FU alone could be documented. Finally, in two pilot patients 5-FU 750 mg was given as a continuous infusion (CI) over 5 days and IFN 5 x 10(6) u was added daily from d2 to d5.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetic drug interaction between epirubicin and interferon-alpha-2b in serum and red blood cells

The influence of interferon-alpha-2b (CAS 99210-65-8, IFN) on the pharmacokinetics of epirubicin (CAS 56420-45-2, EPR) was investigated in 10 patients (4 male, 6 female). EPR was injected as an i.v. bolus over 2 min in a dose of 60 mg/m2 IFN was pre-administered 3 times a week in a dose of 5 x 10(6) IU as a s.c. injection. The comparison of the pharmacokinetics after injection of EPR and EPR+IFN did not show remarkable differences. A statistical significant influence in regard to the terminal elimination half-life (gamma-HL) and the total clearance (CLtot) was found, indicating a reduction of gamma-HL from 18.18 +/- 16.7 for EPR to 8.47 +/- 8.67 h for EPR+IFN and a reduction of the total clearance from 72.33 +/- 55.4 ml/min for EPR to 48.41 +/- 12.7 ml/min for EPR+IFN. The area under the concentration-time curve (AUC, according to the 3-compartment model) increases under the influence of IFN from 2004 +/- 1105 ng/ml.h for EPR up to 2582 +/- 1024 ng/ml.h for EPR+IFN. However, this increase is statistically irrelevant due to the high deviation ranges. Besides, the influence of IFN on the interactions of EPR with red blood cells (RBCs) was investigated in 6 patients under the above conditions. The percental concentration of EPR in RBCs is reduced from 35.4% to 34.7% after administration of IFN. Two metabolites, 13-dihydroepirubicin (M I) and 7-deoxydoxorubicinone (M II), were detected both in serum and RBCs, whereas IFN showed no significant interference with the metabolism or with the binding of the metabolites to RBCs.

In vitro and in vivo binding of epirubicin to red blood cells and human plasma proteins

In this study, the in vitro interaction of epirubicin (EPR), a cytostatic antibiotic, with plasma proteins (PP), namely alpha-HSA, gamma-HSG, alpha+beta-HSG and with isolated human red blood cells (RBCs) was investigated and further correlated with the in vivo pharmacokinetics and binding of EPR and two of its metabolites, 13-dihydroepirubicin and 7-deoxydoxorubicinone to RBCs. The in vitro encapsulation rate in isolated erythrocytes amounts to 52.9 +/- 2.8% and remains constant within the range of studied concentrations (2.5-20 micrograms/ml). EPR was found to bind differently to the various PP in vitro. Binding to alpha-HSA amounted up to 51.0 +/- 7.10%, to alpha+beta-HSG 79.45 +/- 2.7%, to gamma-HSG 57.1 +/- 2.8%. The in vivo-binding rate of EPR, dihydroepirubicin and deoxydoxorubicinone to RBCs after 5 min of injection was 32 +/- 6.96%, 11.6 +/- 3.1% and 10.05 +/- 3.5% respectively, their availability in serum was 42.6 +/- 11.8%, 2.4 +/- 0.4% and 1.2 +/- 0.67% respectively.

Pharmacokinetic interaction between epirubicin and the multidrug resistance reverting agent D-verapamil

The potential for a pharmacokinetic interaction between epirubicin and the second-generation multidrug resistance modulating agent D-verapamil (DVPM) has been investigated in six patients with advanced colorectal cancer. Our results indicate that a significant interaction takes place. Enhanced distribution of epirubicin from the serum and altered disposition might, in fact, explain the increased level of myelotoxicity in this pilot as well as in other clinical phase II studies involving DVPM.

Penetration of norfloxacin into the aqueous humor of the human eye

Forty six patients received a topical application of a 0.3% norfloxacin (Zoroxin; MSD, Austria) solution into the lower fornix at different time intervals and frequencies before undergoing planned extracapsular cataract extraction. Aqueous humor was sampled at the beginning of surgery and assayed for the level of the antibiotic with high performance liquid chromatography. The highest aqueous humor level observed 30 min after the administration of the last drop in four patients who received five drops of norfloxacin into the lower fornix was 660.25 +/- 378.2 ng/ml. These concentrations are above the minimum inhibitory concentration of norfloxacin for 90% (MIC90) of most of the gram-negative microorganisms, but below the MIC90 of most of the staphylococci (coagulase negative Staph. and Staphylococcus aureus range between 0.25-1 mg/ml).

[Pharmacokinetics of 5-fluorouracil in erythrocytes following i.v. administration]

The in vivo binding of the antineoplastic agent 5-fluorouracil (1) to erythrocytes in the whole blood of patients was investigated. The vascular availability of 1 is influenced by erythrocytes at 38.6 +/- 7.2% (calculated as AUC0-60-values), the coefficient of partition is 0.65 +/- 0.18. In comparison with serum, the volume of distribution and the total clearance are elevated by the erythrocytes, the half-lives of the compartment distribution and of the terminal elimination are not influenced.

[The binding of 5-fluorouracil to serum protein fractions, erythrocytes and ghosts under in vitro conditions]

The binding of 5-fluorouracil (1) to erythrocytes and to serum proteins under in vitro conditions was investigated. The binding rate of 1 to erythrocytes is dose-independent and amounts from 16.8 to 31.7% (concentration range 1 to 20 micrograms/ml). The mean coefficient of partition for erythrocytes is 0.25 (+/- 0.03), no binding to ghosts was observed. 1 is bound at about 4% to proteins, whereby 0.7% are bound to alpha-globulin, 0.8% to beta-globulin, 1.6% to gamma-globulin, and 0.8% to albumine. The mean partition coefficient for proteins is 0.04 (+/- 0.006).

[Ciprofibrate: erythrocyte partition coefficient and binding to serum protein]

The in vitro binding of the lipid lowering agent Ciprofibrat (1) to different plasma protein fractions and its red blood-cell partition coefficient were investigated. The binding-rate to albumin and alpha-globulin is dose-dependent (first order kinetic) and amounts to about 95% for albumin and to 25% for alpha-globulin. The affinity of 1 to beta- and gamma-globulin is non-specific and dose-independent (average binding-rate 8% and 10%, respectively). 1 shows only a weak affinity to erythrocytes, therefore, the red blood-cell partition coefficient is 0.02.

[Pharmacokinetics of carboplatin after intraperitoneal administration]

The concentration-profile of the antineoplastic agent carboplatinum in serum and intraperitoneal-fluid (IPF) of six female patients was studied. Pharmacokinetical analysis showed a rapid distribution-phase between both compartments within the first 4h after administration (t1/2 serum = 4.4 h, t1/2 IPF = 3.3 h). Elimination half-life of carboplatinum of 20.3 h from the blood-vessel-system was significantly higher than from the intraperitoneal-compartment (t1/2 = 10.6 h). The relative bioavailability (calculated as AUC-values) was at least 6 times higher for the IPF than for serum within the first 48 h. 98% of measured amount were eliminated from both compartments within this time. The desired high IPF-levels support this route of administration.