The role of nuclear receptors in pharmacokinetic drug–drug interactions in oncology

Drug-drug interactions can have a major impact on treatment outcome in cancer patients. These patients are at high risk of such interactions, because they are treated with combinations of multiple cytotoxic anticancer drugs or hormonal agents often co-administered with prophylactic antiemetics and analgesics to provide palliation. Interactions between drugs can affect the pharmacokinetics of concomitantly administered chemotherapeutic agents. Especially, due to the specific properties of anticancer drugs, such as a narrow therapeutic index and steep dose-toxicity curve, small pharmacokinetic changes can have significant clinical consequences like decreased therapeutic efficacy or increased toxicity. An important mechanism that underlies these interactions is the induction of enzymes or efflux transporters involved in the biotransformation and clearance of anticancer drugs. Several nuclear receptors, like the pregnane X receptor (PXR), constitutively androstane receptor (CAR), have been shown to regulate induction. Activation of these receptors will lead to induction of important enzymes like cytochrome P450 3A4 (CYP3A4), which is involved in the biotransformation of more than 50% of all clinically used drugs. Therefore, concomitant administration of agents that activate PXR will affect the pharmacokinetics of drugs that are substrate for PXRs target genes, which include CYP3A4 and MDR-1. Understanding of the molecular mechanisms that underlie enzyme induction and the identification of (new) drugs involved in pharmacokinetic drug-drug interactions may contribute to the predictability of drug-drug interactions and eventually help to develop safer anticancer regimens.

Breast cancer resistance protein (Bcrp1/Abcg2) is expressed in the harderian gland and mediates transport of conjugated protoporphyrin IX

Proper regulation of intracellular levels of protoporphyrin IX (PPIX), the direct precursor of heme, is important for cell survival. A deficiency in ferrochelatase, which mediates the final step in heme biosynthesis, leads to erythropoietic protoporphyria (EPP), a photosensitivity syndrome caused by the accumulation of PPIX in the skin. We have previously shown that mice with a deficiency in the ABC transporter Bcrp1/Abcg2 display a novel type of protoporphyria. This protoporphyria is mild compared with ferrochelatase-dependent EPP, and in itself not sufficient to cause phototoxicity, but it might exacerbate the consequences of other porphyrias. In this study, we identified the mouse harderian gland as a novel expression site of Bcrp1. Because of its pronounced role in porphyrin secretion, the harderian gland presents a useful tool to study the mechanism of Bcrp1-related protoporphyria and transport of porphyrins. Bcrp1−/− harderian gland displayed a highly increased accumulation of PPIX glycoconjugates, and a similar shift was seen in Bcrp1−/− liver. Tear- and hepatobiliary excretion data suggest that Bcrp1 controls intracellular levels of PPIX by mediating high affinity transport of its glycoconjugates and possibly low-affinity transport of unconjugated PPIX. This mechanism may allow cells to prevent or reduce cytotoxicity of PPIX under excess conditions, without spillage under physiological conditions where PPIX is needed.

A phase I, randomized, open-label, parallel-cohort, dose-finding study of elacridar (GF120918) and oral topotecan in cancer patients

PURPOSE

Breast cancer resistance protein (ABCG2) substantially limits the oral bioavailability of topotecan. Coadministration with elacridar, an inhibitor of breast cancer resistance protein-mediated drug transport, increases the bioavailability of topotecan. The aim of this study was to establish the lowest effective dose of elacridar to obtain maximum oral bioavailability of topotecan and to determine the optimal schedule of coadministration of oral topotecan and elacridar. In the second part of this study, dose-limiting toxicities and maximum tolerated dose of oral topotecan coadministered with elacridar, at a daily times five regimen administered every 21 days, were established.

EXPERIMENTAL DESIGN

In part I, 20 patients were randomized to receive 100, 300, 500, 700, or 1,000 mg of elacridar on days 1 and 8 1 h before or simultaneously with 2.0 mg oral topotecan, which was also randomized. On day 15, all patients were treated with 1.5 mg/m(2) i.v. topotecan. In part II of the study, patients were treated daily with oral topotecan and with the lowest effective dose of elacridar following from part I. The maximum tolerated dose and dose-limiting toxicity were determined in cohorts of three patients. Blood samples were taken on days 1, 8, and 15 of part I and on day 1 of cycles 1 and 2 of part II.

RESULTS

Complete apparent oral bioavailability of topotecan (102 +/- 7%) for all treatment arms with elacridar in both schedules was seen in part I. In the topotecan dose escalation part, two dose-limiting toxicities were seen at the 2.5 mg topotecan dose level.

CONCLUSION

The recommended schedule is 2.0 mg oral topotecan plus 100 mg elacridar administered concomitantly daily times five every 21 days.

SELDI-TOF MS serum protein profiles in breast cancer: assessment of robustness and validity

There is an urgent need for new serum markers that can be applied in e.g. the early detection of breast cancer. Following detection of new, potential biomarkers, such as those reported by Vlahou et al. (Clin Breast Cancer 2003;4:230-239) and Laronga et al. (Dis Markers 2003;19:229-238), assessment of both their robustness and validity is essential to confirm their clinical applicability. We therefore aimed to determine robustness and validity of biomarkers reported by the authors mentioned, by analysis of an independent sample set (breast cancer: n=47, normal women: n=45) in our laboratory, according to the methods described by both authors. Although all markers for the differentiation between breast cancer patients and normal women, discovered in the study of Vlahou et al., were recovered in our validation data set, none had sufficient performance to be applied as a classifier. The markers discovered by Laronga et al. in the differentiation between lymph node positive and -negative breast cancer patients were in part recovered from our validation data set, but were also not applicable as a classifier. In conclusion, although (part of) the proteins discovered and designated as markers by either author could be detected, their validity as biomarkers could not be confirmed by the current study. This finding stresses that, when reporting on a potential biomarker, confirmation of both robustness and validity is essential in obtaining its true clinical applicability.

Multidrug Resistance Proteins 2 and 3 Provide Alternative Routes for Hepatic Excretion of Morphine-Glucuronides

Glucuronidation is a major hepatic detoxification pathway for endogenous and exogenous compounds, resulting in the intracellular formation of polar metabolites that require specialized transporters for elimination. Multidrug resistance proteins (MRPs) are expressed in the liver and can transport glucuronosyl-conjugates. Using morphine as a model aglycone, we demonstrate that morphine-3-glucuronide (M3G), the predominant metabolite, is transported in vitro by human MRP2 (ABCC2), a protein present in the apical membrane of hepatocytes. Loss of biliary M3G secretion in Mrp2(-/-) mice results in its increased sinusoidal transport that can be attributed to Mrp3. Combined loss of Mrp2 and Mrp3 leads to a substantial accumulation of M3G in the liver, from which it is transported across the sinusoidal membrane at a low rate, resulting in the prolonged presence of M3G in plasma. Our results show that murine Mrp2 and Mrp3 provide alternative routes for the excretion of a glucuronidated substrate from the liver in vivo.

Quantification of farnesylmethylcysteine in lysates of peripheral blood mononuclear cells using liquid chromatography coupled with electrospray tandem mass spectrometry: pharmacodynamic assay for farnesyl transferase inhibitors

Biological effectiveness is an important parameter in determining optimal dosages of molecular targeted drugs, such as farnesyl transferase inhibitors. To determine concentration-effect relationships, robust and quantitative biological assays are a prerequisite. Here, we present a novel assay for protein farnesylation that is based on generation of the biomarker farnesylmethylcysteine (FmC). Quantification was performed with liquid chromatography coupled to tandem mass spectrometry. The assay has been validated based on the most recent FDA guidelines for bioanalytical validation, and all results were within requirements. FmC is formed under the action of an endogenous protease that is activated upon cell lysis. The biomarker could be detected in A549 human lung cancer cells as well as in human peripheral blood mononuclear cells. Incubation of A549 cells with AZD3409, a novel prenyl transferase inhibitor, resulted in a significant decrease of the FmC concentration in the lysates. These findings provide a very good starting point for use of this assay in preclinical and clinical dose finding studies with FTIs.

Simultaneous quantification of cyclophosphamide and its active metabolite 4-hydroxycyclophosphamide in human plasma by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC-MS/MS)

Cyclophosphamide is a cytotoxic prodrug with a very narrow therapeutic index. To study the clinical pharmacology of cyclophosphamide in a large cohort of patients a previously published method for the simultaneous quantitative determination of cyclophosphamide and 4-hydroxycyclophosphamide in human plasma using liquid chromatography tandem mass spectrometry (LC-MS/MS) was optimized. Addition of an isotopically labelled internal standard and adaptation of the gradient resulted in a fast, robust and sensitive assay. Because 4-hydroxycyclophosphamide is not stable in plasma, the compound is derivatized with semicarbazide immediately after sample collection. Sample preparation was carried out by protein precipitation with methanol-acetonitrile (1:1, v/v), containing isotopically labelled cyclophosphamide and hexamethylphosphoramide as internal standards. The LC separation was performed on a Zorbax Extend C18 column (150 mm x 2.1 mm ID, particle size 5 microm) with 1 mM ammonium hydroxide in water-acetonitrile (90:10, v/v) as the starting gradient, at a flow-rate of 0.40 mL/min with a total run time of 6 min. The lower limit of quantification (LLQ, using a 100 microL sample volume) was 200 ng/mL and the linear dynamic range extended to 40,000 ng/mL for cyclophosphamide and 50-5000 ng/mL for 4-hydroxycyclophosphamide. Accuracies as well as precisions were lower than 20% at the LLQ concentration and lower than 15% for all other concentrations. This method has been successfully applied in our institute to support ongoing studies into the pharmacokinetics and pharmacogenetics of cyclophosphamide.

Determinants of the elimination of methotrexate and 7-hydroxy-methotrexate following high-dose infusional therapy to cancer patients

AIMS

To characterize determinants of the elimination of methotrexate (MTX) and 7-hydroxy-methotrexate (7-OH-MTX) in patients receiving high-dose MTX therapy (HDMTX).

METHODS

24 and 48-h blood samples from 76 patients receiving HDMTX (dose range 300 mg m-2 to 12 g m-2) were analysed, and concentration-time data were subjected to population pharmacokinetic and covariate analysis using nonlinear mixed-effect modelling (NONMEM).

RESULTS

Treatment-related mortality was 1.3% (one patient with renal failure). Values for MTX clearance (CLMTX) and 7-OH-MTX clearance (CL7-OH-MTX) were estimated at 8.85 and 2 L-1, respectively. Baseline creatinine clearance correlated with CLMTX and CL7-OH-MTX. Concurrent administration of benzimidazoles led to a 27% decrease in CLMTX and a 39% decrease in CL7-OH-MTX. Prior administration of nonsteroidal anti-inflammatory drugs (NSAIDs) resulted in a 16% decrease in CLMTX and a 38% decrease in CL7-OH-MTX. Plasma MTX concentrations were significantly higher in patients also receiving benzimidazoles at 24 h (2.01 micromol L-1vs. 0.66 micromol L-1, P<10(-4)) and at 48 h (0.25 micromol L-1vs. 0.12 micromol L-1, P<10(-4)). 7-OH-MTX plasma concentrations were also significantly higher in patients with concurrent benzimidazoles as compared with patients without benzimidazoles at 24 h (4.47 micromol L-1vs. 2.52 micromol L-1, P=0.0009) and at 48 h (1.11 micromol L-1vs. 0.72 micromol L-1, P=0.031).

CONCLUSIONS

In patients receiving HDMTX, concurrent administration of benzimidazoles was associated with a significant decrease of CLMTX and CL7-OH-MTX, resulting in significantly higher plasma concentrations of MTX and 7-OH-MTX. The data suggest that benzimidazole treatment should be seen as a relative contraindication for HDMTX.

[The pharmacokinetics of monoclonal antibodies]

Monoclonal antibodies (MOABs) are, due to their specificity, increasingly being deployed for therapeutic purposes. MOABs are derived from immunoglobulins and are fully or partially of murine or human origin. They are administered parenterally: mostly intravenously, but subcutaneous or intramuscular administration is also possible, in which case absorption probably occurs through the lymphatic system. The distribution of MOABs from the bloodstream into the tissues is slow and is hampered by the high molecular size of the MOABs, which is a lesser problem for fragments of antibodies (Fab fragments). MOABs are metabolised to peptides and amino acids. This process takes place in many tissues of the body, but probably predominantly in epithelial cells. As a consequence of the saturable binding of the MOAB to its target, a dose-dependent (non-linear) elimination is often observed. Immune reactions can accelerate the elimination of antibodies, partially depending on the degree ofhumanisation of the antibody. Antibodies and endogenous immunoglobulins are protected from elimination by binding to protective receptors (neonatal Fc-receptor; FcRn), which explains their long half-lives (up to 4 weeks). Metabolic pharmacokinetic interactions with other drugs have not been reported and are not expected. It is expected that in the years to come, new MOABs directed towards new targets will appear on the market, as well as existing antibodies with improved pharmacokinetic properties.

Monitoring of platinum surface contamination in seven Dutch hospital pharmacies using inductively coupled plasma mass spectrometry

OBJECTIVE

To develop, validate, and apply a method for the determination of platinum contamination, originating from cisplatinum, oxaliplatinum, and carboplatinum.

METHODS

Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine platinum in wipe samples. The sampling procedure and the analytical conditions were optimised and the assay was validated. The method was applied to measure surface contamination in seven Dutch hospital pharmacies.

RESULTS

The developed method allowed reproducible quantification of 0.50 ng l(-1) platinum (5 pg/wipe sample). Recoveries for stainless steel and linoleum surfaces ranged between 50.4 and 81.4% for the different platinum compounds tested. Platinum contamination was reported in 88% of the wipe samples. Although a substantial variation in surface contamination of the pharmacies was noticed, in most pharmacies, the laminar-airflow (LAF) hoods, the floor in front of the LAF hoods, door handles, and handles of service hatches showed positive results. This demonstrates that contamination is spread throughout the preparation rooms.

CONCLUSION

We developed and validated an ultra sensitive and reliable ICP-MS method for the determination of platinum in surface samples. Surface contamination with platinum was observed in all hospital pharmacies sampled. The interpretation of these results is, however, complicated.

Human mass balance study of the novel anticancer agent ixabepilone using accelerator mass spectrometry

Ixabepilone (BMS-247550) is a semi-synthetic, microtubule stabilizing epothilone B analogue which is more potent than taxanes and has displayed activity in taxane-resistant patients. The human plasma pharmacokinetics of ixabepilone have been described. However, the excretory pathways and contribution of metabolism to ixabepilone elimination have not been determined. To investigate the elimination pathways of ixabepilone we initiated a mass balance study in cancer patients. Due to autoradiolysis, ixabepilone proved to be very unstable when labeled with conventional [¹⁴C]-levels (100 μCi in a typical human radio-tracer study). This necessitated the use of much lower levels of [¹⁴C]-labeling and an ultra-sensitive detection method, Accelerator Mass Spectrometry (AMS). Eight patients with advanced cancer (3 males, 5 females; median age 54.5 y; performance status 0–2) received an intravenous dose of 70 mg, 80 nCi of [¹⁴C]ixabepilone over 3 h. Plasma, urine and faeces were collected up to 7 days after administration and total radioactivity (TRA) was determined using AMS. Ixabepilone in plasma and urine was quantitated using a validated LC-MS/MS method. Mean recovery of ixabepilone-derived radioactivity was 77.3% of dose. Fecal excretion was 52.2% and urinary excretion was 25.1%. Only a minor part of TRA is accounted for by unchanged ixabepilone in both plasma and urine, which indicates that metabolism is a major elimination mechanism for this drug. Future studies should focus on structural elucidation of ixabepilone metabolites and characterization of their activities.

Phase I and pharmacokinetic trial of AP5346, a DACH–platinum–polymer conjugate, administered weekly for three out of every 4 weeks to advanced solid tumor patients

PURPOSE

To determine the maximum tolerated dose (MTD) safety and pharmacokinetics of AP5346, a copolymer-linked 1,2-diaminocyclohexane(DACH)-platinum compound, in advanced solid tumor patients.

EXPERIMENTAL DESIGN

AP5346 was administered as a 1-hour IV infusion on days 1, 8, 15 of a 28-day cycle. Seven dose levels (DL) were explored: DL1: 40 mg platinum (Pt)/m2 (1 patient); DL2: 80 (1); DL3: 160 (3); DL4: 320 (3); DL5: 640 (6); DL6: 850 (6); DL7: 1280 (6) mg Pt/m2. Dose-limiting toxicity (DLT) included infusion omission and cycle delay >2 weeks.

RESULTS

Twenty-six patients received 41 cycles (median 1/patient, range 1-4). No DLT occurred in DL 1-4; 1 DLT in DL5 (RD; renal insufficiency), two in DL6 (MTD; vomiting; fatigue) and 5 in DL7 (neutropenic infection with diarrhea; neutropenia with vomiting; vomiting with fatigue; renal insufficiency; and fatigue). Two deaths occurred due to renal insufficiency (DL5); in both cases patients had disease in or surrounding genitourinary tract whose contribution could not be accurately discerned. Grade 1-2 creatinine abnormalities occurred in seven patients. Nausea/emesis was frequent (92%), reaching grade 3-4 (23%), but controlled by antiemetics. Grade 2-4 allergic reactions occurred in 4 patients. Cmax and AUC increased linearly with dose for total plasma platinum and ultrafiltrate platinum. Antitumor activity included two partial responses in metastatic melanoma and ovarian cancer, and an additional CA-125 normalization (from 133 IU/l) in a suspected ovarian cancer.

CONCLUSIONS

AP5346 administered weekly for 3 weeks out of every four is tolerated up to a dose of 640 mg Pt/m2 on the first cycle when given with antiemetic prophylaxis. The pharmacokinetics of AP5346 indicates a prolonged half-life, and evidence of antitumor activity was observed at this dose level.

[Management recommendations in patients with methotrexate intoxication]

Intoxication due to insufficient renal clearance developed in 2 patients, a 54-year-old man and a 61-year-old woman, who were under treatment with methotrexate (MTX) for a primary cerebral lymphoma and a recurrence of large-cell B-cell-non-Hodgkin lymphoma, respectively. Both were treated with folinic acid rescue, thymidine, and alkalisation of the urine. MTX is a cytotoxic drug that is often used in oncology and rheumatology. Significant and even lethal toxicity can develop when the elimination ofMTX is delayed or when supportive care, such as folinic acid rescue, is inadequate. Delayed elimination can be caused by reduced renal function, by the 'third space' phenomenon such as in case of ascites, pleural fluid accumulation and oedema, and by drug-drug interactions leading to reduced renal function or a disturbance in the plasma protein binding ofMTX. Once toxicity has developed, the therapy must be directed at protection of the normal tissues, restoration of renal function and hence the renal elimination ofMTX, restoration of the alkalisation of the urine, and general supportive therapy.

Trabectedin (ET-743, Yondelis) is a substrate for P-glycoprotein, but only high expression of P-glycoprotein confers the multidrug resistance phenotype

Trabectedin (ET-743, Yondelis) is a novel anticancer drug currently undergoing phase II and III investigations. There are various and conflicting reports whether trabectedin is a substrate for P-glycoprotein (P-gp), an important factor in drug disposition and multi-drug resistance (MDR). We have now unambiguously shown that trabectedin is a P-gp substrate by investigating vectorial transport over monolayers of LLC-PK1 pig kidney and Madine-Darby Canine kidney (MDCK) cells and the mdr1a and/or MDR1 transfected subclones. We further characterized the cytotoxic effects and cellular accumulation of trabectedin in these cell lines as well as in a panel of other cell lines with high or moderate expression levels of P-gp. Trabectedin displayed the typical MDR phenotype only in highly P-gp expressing cell lines, but not in cell lines with expression levels more closely conforming to clinical samples, suggesting that P-gp will not confer resistance to trabectedin in cancer patients.

In vitro characterization of the human biotransformation pathways of aplidine, a novel marine anti-cancer drug

Aplidine is a potent marine anti-cancer drug and is currently being investigated in phase II clinical trials. However, the enzymes involved in the biotransformation of aplidine and thus its pharmacokinetics are not known yet. To assess the biotransformation pathways of aplidine and their potential implications for human pharmacology and toxicology, the in vitro metabolism of aplidine was characterized using incubations with human plasma, liver preparations, cytochrome P450 (CYP) and uridine diphosphoglucuronosyl transferase (UGT) supersomes in combination with HPLC analysis and cytotoxicity assays with cell lines. Aplidine was metabolised by carboxyl esterases in human plasma. Using CYP supersomes and liver microsomes, it was shown that aplidine was metabolised mainly by CYP3A4 and also by CYP2A6, 2E1 and 4A11. Four metabolites were observed after incubation with human liver microsomes, one formed by CYP2A6 (C-demethylation) and three by CYP3A4 (hydroxylation and/or C-dealkylation). No conjugation was observed in human liver S9 fraction. However, the aplidine metabolites formed by CYP were further conjugated by the phase II enzymes UGT, GST and SULT. In accordance with the findings in microsomes and CYP supersomes, a significant effect of specific CYP2A6, 2E1, 3A4 and 4A11 inhibitors on the cytotoxicity of aplidine in Hep G2 and IGROV-1 cells could be observed. These results provide evidence that CYP3A4 has a major role in metabolising aplidine in vitro with additional involvement of CYP2A6, 2E1, and 4A11. Further, the metabolites formed by CYPs can be conjugated by UGT, SULT and GST. These findings could help interpret the in vivo pharmacokinetics of aplidine.

EO-9 bladder instillations: Formulation selection based on stability characteristics and in vitro simulation studies

A bladder instillation of EO-9 (EOquin) is currently used in phase II clinical trials for the treatment of superficial bladder cancer. Three alternative formulations were developed to improve its pharmaceutical properties and clinical acceptability. Freeze-dried products composed of EO-9, 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD), tri(hydroxymethyl) aminomethane (Tris), and sodium bicarbonate (NaHCO(3)) were tested. Selection of one formulation for further development was based on stability studies. These studies comprised stability of the freeze-dried products, stability after reconstitution and dilution and stability during bladder instillation in an experimental set-up. The stability study of the freeze-dried products showed that the formulation composed of EO-9/HPbetaCD/Tris (4/600/1mg/vial) was most stable. After reconstitution and dilution all products were stable for at least 8h. The product composed of EO9/HPbetaCD/NaHCO(3) (4/600/20mg/vial) was the least stable product both as freeze-dried formulation and after reconstitution and dilution. The bladder instillation simulation experiment showed that all products were stable when mixed with urine of pH 8 and unstable in urine of pH 4 and 6. The degradation products formed in urine were EO-5a and EO-9-Cl. Based on these results, the product composed of EO-9/HPbetaCD/Tris (4/600/1mg/vial) was selected for further pharmaceutical development.

Validation of SELDI-TOF MS serum protein profiles for renal cell carcinoma in new populations

Currently, no suitable biomarker for the early detection or follow-up of renal cell carcinoma (RCC) is available. We aimed to validate previously reported potential serum biomarkers for RCC obtained with Surface Enhanced Laser Desorption Ionisation-Time of Flight Mass Spectrometry (SELDI-TOF MS) in our laboratory using distinct patient populations. Two sets of sera from RCC patients and healthy controls (HC) were gathered from different institutes and analysed according to published procedures. The first set (40 RCC, 32 HC) consisted of mainly presurgery samples from patients with disease stages I-IV. The second set (26 RCC, 27 HC) were mostly sera from patients with stage-IV disease, drawn after nephrectomy. Only the increased expression of the previously found serum amyloid-alpha (SAA) peak cluster could be validated in a similar RCC patient subset in both our populations in two independent analyses. It was seen both in early- and late-stage disease and in pre- and postsurgery samples. These results were also confirmed by ELISA. Other previously identified biomarker candidates (mass-to-charge ratio's (m/z) 3900, 4107, 4153, 5352 and 5987) proved difficult to reproduce upon duplicate analysis. Modification of the analytical protocol for these markers resulted in their detection, but we did not achieve satisfactory classification of patients and controls with these alleged biomarkers in any of our two sample sets. Instead, two new peaks (m/z 4289 and 8151) were identified with better performance (sensitivity and specificity approximately 65-90%) for separating patients from controls in the first sample set. Concluding, only the SAA peak cluster was validated as a robust RCC biomarker candidate, which is present in a specific subset of these patients, regardless of disease stage or nephrectomy status. In addition, two new peaks were seen which might prove useful as biomarkers, provided these are validated in new populations.

[Severe phenytoin intoxication in patients with hypoalbuminaemia]

Two patients, a 35-year-old woman and a 60-year-old man, developed severe neurological side effects during treatment with phenytoin: disorientation, myoclonia, hallucinations and drowsiness in the first patient and a comatose state in the second. The woman had spina bifida, a ventriculoperitoneal drain because of hydrocephalus, recurrent urinary-tract infection, and a history of status epilepticus. The man suffered from diabetic ketoacidosis complicated by epileptic convulsions. In both patients, the total phenytoin concentration in the blood was within the therapeutic range of 8-20 mg/l. However, both had low serum albumin concentrations, below 25 g/l. Low serum albumin levels are associated with increased concentrations of the free fraction of phenytoin. Toxic levels of free phenytoin were found: 4 and 8 mg/l, respectively, while the therapeutic range is 0.5-2 mg/l. The first patient recovered after treatment with phenytoin was stopped, after which she was placed on a lower dosage; the second patient died. When prescribing phenytoin to patients with hypoalbuminaemia, one should be aware of the risk of intoxication due to a high level of free phenytoin and consequently an increased risk of severe neurological side effects.

Novel paclitaxel formulations for oral application: a phase I pharmacokinetic study in patients with solid tumours

PURPOSE

To explore the pharmacokinetics (PKs) of paclitaxel and two major metabolites after three single oral administrations of a novel drinking solution and two capsule formulations in combination with cyclosporin A (CsA) in patients with advanced cancer. Moreover, the tolerability and safety of the formulations was studied. In addition, single nucleotide polymorphisms in the multidrug resistance (MDR1) gene were determined.

PATIENTS AND METHODS

Ten patients were enrolled and randomized to receive CsA 10 mg/kg followed by oral paclitaxel 180 mg given as (1) drinking solution (formulation 1), (2) capsule formulation 2B, and (3) capsule formulation 2C on day 1, 8, or 15.

RESULTS

The median C (max) of paclitaxel was 0.42 (0.23-0.96), 0.48 (0.08-0.59), and 0.39 (0.11-1.03) microg/ml and the area under the plasma concentration-time curve was 2.83 (1.69-5.12), 2.01 (1.57-3.04), and 2.67 (1.05-3.61) mug h/ml following administration of formulations 1, 2B, and 2C, respectively. The novel formulations were tolerated after single oral dose without causing relevant gastrointestinal or haematological toxicity.

CONCLUSIONS

The PK and metabolism of paclitaxel were comparable between the oral formulations co-administered with CsA.

Evaluation of pharmacotherapy in geriatric patients after performing complete geriatric assessment at a diagnostic day clinic

BACKGROUND

Elderly patients often take multiple drugs. It is known that polypharmacy, i.e. use of five or more drugs, may lead to drug interactions and adverse events. However, undertreatment of conditions or illnesses is also a concern in geriatric patients. A centralised review of both diagnoses and medication may play a key role in optimising pharmacotherapy in geriatric patients. The aims of this study were to evaluate the quality and appropriateness of medication after performing a complete geriatric assessment (CGA) and medication review at a diagnostic geriatric day clinic, to investigate reasons for drug changes, and to determine whether medication review leads to a reduction in the number of drugs used.

METHODS

A chart review was performed in 702 patients (mean age 82.0 years, range 57.1-104.1 years) who underwent a CGA at a diagnostic geriatric day clinic. Medication at admission, changes in medication and reasons for changes were noted.

RESULTS

Vitamins, for example folic acid and vitamin B(12) (cyanocobalamin), and trimethoprim for urinary tract infections were the most frequently started medications after CGA and medication review. The number of drugs used was reduced in only a minority of patients (11.7%); reasons for discontinuation were a diagnosis that was no longer relevant (38.8%), adverse events (33.2%) and identification of better pharmacotherapeutic options (22.0%). In 69.2% of the cases a new diagnosis was the reason for starting a new medication, followed by osteoporosis prophylaxis (15.0%) and improvement in pharmacotherapy (10.6%). At admission, patients were taking a mean number of 4.6 drugs (range 0-17). A mean of 0.8 drugs (range from reduction of 5 to addition of 7) had been added per patient, resulting in a mean number of 5.4 (range 0-18) prescribed drugs at discharge.

CONCLUSION

Evaluation of medication in patients after performing CGA at the geriatric day clinic investigated resulted in relevant medication changes. The main reason for prescribing new drugs was a new diagnosis. Absence of a relevant medical indication was the main reason for stopping drugs. CGA and medication review resulted in a mean net addition of 0.8 drugs per patient.

Development and validation of an assay for the quantitative determination of cladribine nucleotides in MDCKII cells and culture medium using weak anion-exchange liquid chromatography coupled with tandem mass spectrometry

The development and validation of an assay for the quantitative analysis of cladribine mono-, di- and triphosphate (2-chloro, 2'-deoxyadenosine 5'-mono-, di- and triphosphate or 2CdAMP, 2CdADP and 2CdATP) in culture medium (Optimem) and cell lysate is described. Cladribine mono- and diphosphate reference compounds were obtained by thermal degradation of cladribine triphosphate. The reference compounds were characterized using ion-pairing reversed-phase high-performance liquid chromatography with ultraviolet detection. The bioanalytical assay for 2CdAMP, 2CdADP and 2CdATP is based on weak anion-exchange liquid chromatography coupled with tandem mass spectrometry in the positive ion mode (WAXLC/MS/MS). A fused-silica electrospray capillary was used instead of a stainless steel electrospray capillary to minimize adsorption of analytes and thus decrease variation in the analyte signals. Dynamic ranges of 1.11-27.7, 0.550-55.0 and 1.31-52.3 nM for 2CdAMP, 2CdADP and 2CdATP, respectively, were validated in culture medium and cell lysate. Optimem samples required stabilization with 30% methanol to prevent conversion of 2CdATP into 2CdAMP and 2CdADP. All intra- and interday accuracies and precisions were within +/-20%. The stability of the compounds was assessed under various analytically relevant conditions. The method was successfully used to investigate cladribine nucleotide transport in vitro in Madin-Darby canine kidney II (MDCKII) cells.

Liquid chromatography–tandem mass spectrometric assay for the nucleoside reverse transcriptase inhibitor emtricitabine in human plasma

A liquid chromatography-tandem mass spectrometric assay for the determination of the antiretroviral nucleoside emtricitabine in human plasma was developed and validated using a simple sample pre-treatment procedure. After addition of 5'-deoxy-5-fluorocytidine as the internal standard and protein precipitation with acetonitrile, the supernatant was directly injected in the isocratic chromatographic system using a polar embedded reversed-phase column and formic acid in water-methanol as the eluent. The eluate was completely led into an electrospray interface with positive ionization and the analytes were quantified using triple quadrupole mass spectrometry. The assay was validated in the range 5-5000 ng/mL. Intra-day precisions were <or=7% and inter-day precisions were <or=10%. Accuracies between 92 and 99% were found. The analytes were chemically stable under all relevant conditions and the assay was applied in the analysis of plasma samples of HIV-infected patients treated with the drug.

Antiviral activity of HIV type 1 protease inhibitors nelfinavir and indinavir in vivo is not influenced by P-glycoprotein activity on CD4+ T cells

P-glycoprotein (P-gp) can compromise the antiretroviral effect of a protease inhibitor (PI)-containing regimen for HIV-1, but can also reduce HIV-1 replication. We studied the net effect of P-gp on the intracellular HIV-1 RNA and DNA load in vivo. CD4(+) T cells were isolated from 27 HIV-1 patients (13 without and 14 with a PI-containing regimen) and subsequently sorted in CD45RO(-) (naive) and CD45RO(+) (memory) subsets with either high (P-gp(high)) or low (P-gp(low)) P-gp activity. Unspliced HIV-1 RNA and HIV-1 DNA load were determined. For each patient P-gp(high) and P-gp(low) subsets were compared. In patients on a PI-containing regimen, intracellular unspliced HIV-1 RNA was significantly lower in P-gp(high)-naive CD4(+) cells compared to P-gp(low)-naive CD4(+) cells (p = 0.04). The same trend was seen in naive CD4(+) cells of treatment naive patients. In both treated and untreated patients HIV-1 DNA levels were significantly lower in P-gp(high) than in P-gp(low) memory CD4(+) cells (p = 0.02 and p = 0.04). High cellular P-gp activity coincided with a reduced intracellular HIV-1 load in vivo, both in therapy-naive and in PI-treated patients. Therefore we conclude that the potential efflux function of P-gp on PIs may be clinically less relevant than the effect of P-gp on intracellular HIV-1 replication.

Validated assay for the simultaneous determination of the anti-cancer agent gemcitabine and its metabolite 2',2'-difluorodeoxyuridine in human plasma by high-performance liquid chromatography with tandem mass spectrometry

A sensitive and specific high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) assay for the quantitative determination of gemcitabine (dFdC) and its metabolite 2',2'-difluorodeoxyuridine (dFdU) is presented. A 200-microL aliquot of human plasma was spiked with a mixture of internal standards, didanosine, lamivudine and fludarabine, and extracted using solid-phase extraction. Dried extracts were reconstituted in 1 mM ammonium acetate/acetonitrile (97:3, v/v) and 10-microL volumes were injected onto the HPLC system. Separation was achieved on a 150 x 2.1 mm C18 bonded phase endcapped with polar groups (Synergi Hydro-RP column) using an eluent composed of 1 mM ammonium acetate (pH 6.8)/acetonitrile (94:6, v/v). Detection was performed by positive ion electrospray ionization followed by MS/MS. The assay quantifies a range from 0.5 to 1000 ng/mL for gemcitabine and from 5 to 10,000 ng/mL for dFdU using 200 microL of human plasma sample. Validation results demonstrate that gemcitabine and dFdU concentrations can be accurately and precisely quantified in human plasma. This assay is used to support clinical pharmacologic studies with gemcitabine.