Selective, Accurate, and Precise Quantitation of Glutarylcarnitine in Human Urine from a Patient with Glutaric Acidemia Type I

Background

Although correctly used in expanded newborn screening programs to identify patients with possible diseases, flow-injection tandem mass spectrometry (MS/MS) acylcarnitine “profiles” are inadequate for standard clinical uses owing to their limited quantitative accuracy and lack of selectivity. We report the application of our selective, accurate, and precise method for quantification of acylcarnitines, applied to urine glutarylcarnitine from a patient with glutaric acidemia type I (GAI).

Methods

A previously validated acylcarnitine ultra-HPLC-MS/MS method was used, with a focus on analysis of glutarylcarnitine. Calibrants and samples were isolated by solid-phase extraction and derivatized with pentafluorophenacyl trifluoromethanesulfonate. Acylcarnitine pentafluorophenacyl esters were eluted in 14-min chromatograms. Standardized calibrants and a 13-point, 200-fold concentration range calibration curve were used for accurate quantification of glutarylcarnitine. Quality control samples validated method accuracy and long-term analytic stability.

Results

Quantification of glutarylcarnitine in urine from a patient with GAI is reported. Long-term analytical stability of the method over a 5-year period is shown.

Conclusions

Our method for acylcarnitine quantification is shown to be selective, accurate, and precise; thus, we recommend it for confirmatory testing and monitoring of plasma and urine samples from patients with GAI.

Selective and accurate C5 acylcarnitine quantitation by UHPLC-MS/MS: Distinguishing true isovaleric acidemia from pivalate derived interference

Tandem MS acylcarnitine "profiles" are extremely valuable. Although used appropriately in newborn screening programs to identify patients with possible diseases, their inadequate quantitative accuracy and lack of selectivity is problematic for confirmatory testing. In this report, we show the application of our validated, selective, accurate, precise, and robust UHPLC-MS/MS method for quantitation of acylcarnitines, specifically to C5 acylcarnitines: pivaloyl-, 2-methylbutyryl-, isovaleryl-, and valerylcarnitine. Standardized calibrants were used to generate 13-point, 200-fold concentration range calibration curves. Samples were isolated by solid-phase extraction and derivatized with pentafluorophenacyl trifluoromethanesulfonate. Acylcarnitine pentafluorophenacyl esters were eluted in 14min chromatograms. Data demonstrating quantitative stability and method robustness over a five year time period are shown and these results validate the method's accuracy and robustness. Urine from patients with isovaleric acidemia (with the disease marker isovalerylcarnitine) and with pivaloylcarnitine present are shown. These results demonstrate the method's ability to distinguish true isovaleric acidemia from pivalate derived interference. Our method for acylcarnitine quantitation is shown to be accurate, precise, and robust for selective quantitation of isovalerylcarnitine, and thus is recommended for confirmatory testing of suspected isovaleric acidemia patients.

Correcting false positive medium-chain acyl-CoA dehydrogenase deficiency results from newborn screening; synthesis, purification, and standardization of branched-chain C8 acylcarnitines for use in their selective and accurate absolute quantitation by UHPLC-MS/MS

While selectively quantifying acylcarnitines in thousands of patient samples using UHPLC-MS/MS, we have occasionally observed unidentified branched-chain C8 acylcarnitines. Such observations are not possible using tandem MS methods, which generate pseudo-quantitative acylcarnitine "profiles". Since these "profiles" select for mass alone, they cannot distinguish authentic signal from isobaric and isomeric interferences. For example, some of the samples containing branched-chain C8 acylcarnitines were, in fact, expanded newborn screening false positive "profiles" for medium-chain acyl-CoA dehydrogenase deficiency (MCADD). Using our fast, highly selective, and quantitatively accurate UHPLC-MS/MS acylcarnitine determination method, we corrected the false positive tandem MS results and reported the sample results as normal for octanoylcarnitine (the marker for MCADD). From instances such as these, we decided to further investigate the presence of branched-chain C8 acylcarnitines in patient samples. To accomplish this, we synthesized and chromatographically characterized several branched-chain C8 acylcarnitines (in addition to valproylcarnitine): 2-methylheptanoylcarnitine, 6-methylheptanoylcarnitine, 2,2-dimethylhexanoylcarnitine, 3,3-dimethylhexanoylcarnitine, 3,5-dimethylhexanoylcarnitine, 2-ethylhexanoylcarnitine, and 2,4,4-trimethylpentanoylcarnitine. We then compared their behavior with branched-chain C8 acylcarnitines observed in patient samples and demonstrated our ability to chromographically resolve, and thus distinguish, octanoylcarnitine from branched-chain C8 acylcarnitines, correcting false positive MCADD results from expanded newborn screening.

Quantitative acylcarnitine determination by UHPLC-MS/MS--Going beyond tandem MS acylcarnitine "profiles"

Tandem MS "profiling" of acylcarnitines and amino acids was conceived as a first-tier screening method, and its application to expanded newborn screening has been enormously successful. However, unlike amino acid screening (which uses amino acid analysis as its second-tier validation of screening results), acylcarnitine "profiling" also assumed the role of second-tier validation, due to the lack of a generally accepted second-tier acylcarnitine determination method. In this report, we present results from the application of our validated UHPLC-MS/MS second-tier method for the quantification of total carnitine, free carnitine, butyrobetaine, and acylcarnitines to patient samples with known diagnoses: malonic acidemia, short-chain acyl-CoA dehydrogenase deficiency (SCADD) or isobutyryl-CoA dehydrogenase deficiency (IBD), 3-methyl-crotonyl carboxylase deficiency (3-MCC) or ß-ketothiolase deficiency (BKT), and methylmalonic acidemia (MMA). We demonstrate the assay's ability to separate constitutional isomers and diastereomeric acylcarnitines and generate values with a high level of accuracy and precision. These capabilities are unavailable when using tandem MS "profiles". We also show examples of research interest, where separation of acylcarnitine species and accurate and precise acylcarnitine quantification is necessary.

Validated method for the quantification of free and total carnitine, butyrobetaine, and acylcarnitines in biological samples

A validated quantitative method for the determination of free and total carnitine, butyrobetaine, and acylcarnitines is presented. The versatile method has four components: (1) isolation using strong cation-exchange solid-phase extraction, (2) derivatization with pentafluorophenacyl trifluoromethanesulfonate, (3) sequential ion-exchange/reversed-phase (ultra) high-performance liquid chromatography [(U)HPLC] using a strong cation-exchange trap in series with a fused-core HPLC column, and (4) detection with electrospray ionization multiple reaction monitoring (MRM) mass spectrometry (MS). Standardized carnitine along with 65 synthesized, standardized acylcarnitines (including short-chain, medium-chain, long-chain, dicarboxylic, hydroxylated, and unsaturated acyl moieties) were used to construct multiple-point calibration curves, resulting in accurate and precise quantification. Separation of the 65 acylcarnitines was accomplished in a single chromatogram in as little as 14 min. Validation studies were performed showing a high level of accuracy, precision, and reproducibility. The method provides capabilities unavailable by tandem MS procedures, making it an ideal approach for confirmation of newborn screening results and for clinical and basic research projects, including treatment protocol studies, acylcarnitine biomarker studies, and metabolite studies using plasma, urine, tissue, or other sample matrixes.

Management of 3-aminopyridine-2-carboxaldehyde thiosemicarbazone-induced methemoglobinemia

The anticancer agent 3-aminopyridine-2-carboxaldehyde thiosemicarbazone is a ribonucleotide reductase inhibitor. It inactivates ribonucleotide reductase by disrupting an iron-stabilized radical in ribonucleotide reductase's small subunits, M2 and M2b (p53R2). Unfortunately, 3-aminopyridine-2-carboxaldehyde thiosemicarbazone also alters iron II (Fe(2+)) in hemoglobin. This creates Fe(3+) methemoglobin that does not deliver oxygen. Fe(2+) in hemoglobin normally auto-oxidizes to inactive Fe(3+) methemoglobin at a rate of nearly 3% per day and this is counterbalanced by a reductase system that normally limits methemoglobin concentrations to less than 1% of hemoglobin. This balance may be perturbed by symptomatic toxicity levels during 3-aminopyridine-2-carboxaldehyde thiosemicarbazone therapy. Indications of 3-aminopyridine-2-carboxaldehyde thiosemicarbazone sequelae attributable to methemoglobinemia include resting dyspnea, headaches and altered cognition. Management of methemoglobinemia includes supplemental oxygen, ascorbate and, most importantly, intravenously administered methylene blue as a therapeutic antidote.

Preliminary clinical and pharmacologic investigation of photodynamic therapy with the silicon phthalocyanine photosensitizer pc 4 for primary or metastatic cutaneous cancers

Photodynamic therapy (PDT) for cutaneous malignancies has been found to be an effective treatment with a range of photosensitizers. The phthalocyanine Pc 4 was developed initially for PDT of primary or metastatic cancers in the skin. A Phase I trial was initiated to evaluate the safety and pharmacokinetic profiles of systemically administered Pc 4 followed by red light (Pc 4-PDT) in cutaneous malignancies. A dose-escalation study of Pc 4 (starting dose 0.135 mg/m(2)) at a fixed light fluence (135 J/cm(2) of 675-nm light) was initiated in patients with primary or metastatic cutaneous malignancies with the aim of establishing the maximum tolerated dose (MTD). Blood samples were taken at intervals over the first 60 h post-PDT for pharmacokinetic analysis, and patients were evaluated for toxicity and tumor response. A total of three patients (two females with breast cancer and one male with cutaneous T-cell lymphoma) were enrolled and treated over the dose range of 0.135 mg/m(2) (first dose level) to 0.54 mg/m(2) (third dose level). Grade 3 erythema within the photoirradiated area was induced in patient 2, and transient tumor regression in patient 3, in spite of the low photosensitizer doses. Pharmacokinetic observations fit a three-compartment exponential elimination model with an initial rapid distribution phase (∼0.2 h) and relatively long terminal elimination phase (∼28 h), Because of restrictive exclusion criteria and resultant poor accrual, the trial was closed before MTD could be reached. While the limited accrual to this initial Phase I study did not establish the MTD nor establish a complete pharmacokinetic and safety profile of intravenous Pc 4-PDT, these preliminary data support further Phase I testing of this new photosensitizer.

Phase I clinical and pharmacokinetic study of oxaliplatin, irinotecan and capecitabine

PURPOSE

To determine the maximum tolerated dose (MTD) and dose-limiting toxicity (DLT) of the combination of weekly oxaliplatin x 4, weekly irinotecan x 4 and capecitabine Monday through Friday for 4 weeks of every 6 week cycle in patients with solid tumors; to determine the pharmacokinetic profile of these agents in this combination; to observe patients for clinical anti-tumor response.

METHODS

Twenty-two patients with metastatic solid tumors received oxaliplatin 60 mg/m(2) weekly x 4, irinotecan beginning at a dose of 40 mg/m(2) weekly x 4, and capecitabine Monday through Friday for 4 weeks of every 6 week cycle, initially at 1,000 mg twice daily (bid).

RESULTS

The MTD was oxaliplatin 60 mg/m(2) weekly x 4, irinotecan 50 mg/m(2) weekly x 4 and capecitabine 450 mg bid Monday through Friday for 4 weeks of every 6 week cycle. One of six patients at this dose level developed DLT of nausea, vomiting, and diarrhea. Among patients treated with a constant capecitabine dose of 450 mg bid, there was a higher mean AUC of 5-FU in women than in men (mean +/- SD: 892 +/- 287 nM h vs. 537 +/- 182 nM h; Mann-Whitney two-tailed, P = 0.02). There was one complete response in a patient with gastric cancer.

CONCLUSION

The novel schedule of weekly oxaliplatin, weekly irinotecan, and capecitabine Monday through Friday, all administered for 4 weeks of every 6 week cycle, evaluated in this phase I trial is well-tolerated and demonstrated activity in a patient with gastric cancer.

Quantification of carnitine and acylcarnitines in biological matrices by HPLC electrospray ionization-mass spectrometry

BACKGROUND

Analysis of carnitine and acylcarnitines by tandem mass spectrometry (MS/MS) has limitations. First, preparation of butyl esters partially hydrolyzes acylcarnitines. Second, isobaric nonacylcarnitine compounds yield false-positive results in acylcarnitine tests. Third, acylcarnitine constitutional isomers cannot be distinguished.

METHODS

Carnitine and acylcarnitines were isolated by ion-exchange solid-phase extraction, derivatized with pentafluorophenacyl trifluoromethanesulfonate, separated by HPLC, and detected with an ion trap mass spectrometer. Carnitine was quantified with d(3)-carnitine as the internal standard. Acylcarnitines were quantified with 42 synthesized calibrators. The internal standards used were d(6)-acetyl-, d(3)-propionyl-, undecanoyl-, undecanedioyl-, and heptadecanoylcarnitine.

RESULTS

Example recoveries [mean (SD)] were 69.4% (3.9%) for total carnitine, 83.1% (5.9%) for free carnitine, 102.2% (9.8%) for acetylcarnitine, and 107.2% (8.9%) for palmitoylcarnitine. Example imprecision results [mean (SD)] within runs (n = 6) and between runs (n = 18) were, respectively: total carnitine, 58.0 (0.9) and 57.4 (1.7) micromol/L; free carnitine, 44.6 (1.5) and 44.3 (1.2) micromol/L; acetylcarnitine, 7.74 (0.51) and 7.85 (0.69) micromol/L; and palmitoylcarnitine, 0.12 (0.01) and 0.11 (0.02) micromol/L. Standard-addition slopes and linear regression coefficients were 1.00 and 0.9998, respectively, for total carnitine added to plasma, 0.99 and 0.9997 for free carnitine added to plasma, 1.04 and 0.9972 for octanoylcarnitine added to skeletal muscle, and 1.05 and 0.9913 for palmitoylcarnitine added to skeletal muscle. Reference intervals for plasma, urine, and skeletal muscle are provided.

CONCLUSIONS

This method for analysis of carnitine and acylcarnitines overcomes the observed limitations of MS/MS methods.

Strategy for the isolation, derivatization, chromatographic separation, and detection of carnitine and acylcarnitines

A strategy for detection of carnitine and acylcarnitines is introduced. This versatile system has four components: (1) isolation by protein precipitation/desalting and cation-exchange solid-phase extraction, (2) derivatization of carnitine and acylcarnitines with pentafluorophenacyl trifluoromethanesulfonate, (3) sequential ion-exchange/reversed-phase chromatography using a single non-end-capped C8 column, and (4) detection of carnitine and acylcarnitine pentafluorophenacyl esters using an ion trap mass spectrometer. Recovery of carnitine and acylcarnitines from the isolation procedure is 77-85%. Derivatization is rapid and complete with no evidence of acylcarnitine hydrolysis. Sequential ion-exchange/reversed-phase HPLC results in separation of reagent byproducts from derivatized carnitine and acylcarnitines, followed by reversed-phase separation of carnitine and acylcarnitine pentafluorophenacyl esters. Detection by MS/MS is highly selective, with carnitine pentafluorophenacyl ester yielding a strong product ion at m/z 311 and acylcarnitine pentafluorophenacyl ester fragmentation yielding two product ions: (1) loss of m/z 59 and (2) generation of an ion at m/z 293. To demonstrate this analytical strategy, phosphate buffered serum albumin was spiked with carnitine and 15 acylcarnitines and analyzed using the described protein precipitation/desalting and cation-exchange solid-phase extraction isolation, derivatization with pentafluorophenacyl trifluoromethanesulfonate, chromatography using the sequential ion-exchange/reversed-phase chromatography HPLC system, and detection by MS and MS/MS. Successful application of this strategy to the quantification of carnitine and acetylcarnitine in rat liver is shown.

Development of beta-lapachone prodrugs for therapy against human cancer cells with elevated NAD(P)H:quinone oxidoreductase 1 levels

beta-Lapachone, an o-naphthoquinone, induces a novel caspase- and p53-independent apoptotic pathway dependent on NAD(P)H:quinone oxidoreductase 1 (NQO1). NQO1 reduces beta-lapachone to an unstable hydroquinone that rapidly undergoes a two-step oxidation back to the parent compound, perpetuating a futile redox cycle. A deficiency or inhibition of NQO1 rendered cells resistant to beta-lapachone. Thus, beta-lapachone has great potential for the treatment of specific cancers with elevated NQO1 levels (e.g., breast, non-small cell lung, pancreatic, colon, and prostate cancers). We report the development of mono(arylimino) derivatives of beta-lapachone as potential prodrugs. These derivatives are relatively nontoxic and not substrates for NQO1 when initially diluted in water. In solution, however, they undergo hydrolytic conversion to beta-lapachone at rates dependent on the electron-withdrawing strength of their substituent groups and pH of the diluent. NQO1 enzyme assays, UV-visible spectrophotometry, high-performance liquid chromatography-electrospray ionization-mass spectrometry, and nuclear magnetic resonance analyses confirmed and monitored conversion of each derivative to beta-lapachone. Once converted, beta-lapachone derivatives caused NQO1-dependent, mu-calpain-mediated cell death in human cancer cells identical to that caused by beta-lapachone. Interestingly, coadministration of N-acetyl-l-cysteine, prevented derivative-induced cytotoxicity but did not affect beta-lapachone lethality. Nuclear magnetic resonance analyses indicated that prevention of beta-lapachone derivative cytotoxicity was the result of direct modification of these derivatives by N-acetyl-l-cysteine, preventing their conversion to beta-lapachone. The use of beta-lapachone mono(arylimino) prodrug derivatives, or more specifically a derivative converted in a tumor-specific manner (i.e., in the acidic local environment of the tumor tissue), should reduce normal tissue toxicity while eliciting tumor-selective cell killing by NQO1 bioactivation.

A phase I and pharmacodynamic study of fludarabine, carboplatin, and topotecan in patients with relapsed, refractory, or high-risk acute leukemia

PURPOSE

A novel regimen designed to maximize antileukemia activity of carboplatin through inhibiting repair of platinum-DNA adducts was conducted in poor prognosis, acute leukemia patients.

EXPERIMENTAL DESIGN

Patients received fludarabine (10 to 15 mg/m(2) x 5 days), carboplatin (area under the curve 10 to 12 by continuous infusion over 5 days), followed by escalated doses of topotecan infused over 72 hours (fludarabine, carboplatin, topotecan regimen). Twenty-eight patients had acute myelogenous leukemia (7 untreated secondary acute myelogenous leukemia, 11 in first relapse, and 10 in second relapse or refractory), 1 patient had refractory/relapsed acute lymphoblastic leukemia, and 2 patients had untreated chronic myelogenous leukemia blast crisis. Six patients had failed an autologous stem cell transplant. Patients ranged from 19 to 76 (median 54) years. Measurement of platinum-DNA adducts were done in serial bone marrow specimens.

RESULTS

Fifteen of 31 patients achieved bone marrow aplasia. Clinical responses included 2 complete response, 4 complete response with persistent thrombocytopenia, and 2 partial response. Prolonged myelosuppression was observed with median time to blood neutrophils >/=200/microl of 28 (0 to 43) days and time to platelets >/=20,000/microl (untransfused) of 40 (24 to 120) days. Grade 3 or greater infections occurred in all of the patients, and there were 2 infection-related deaths. The nonhematologic toxicity profile was acceptable. Five patients subsequently received allografts without early transplant-related mortality. Maximum tolerated dose of fludarabine, carboplatin, topotecan regimen was fludarabine 15 mg/m(2) x 5, carboplatin area under the curve 12, and topotecan 2.55 mg/m(2) over 72 hours. An increase in bone marrow, platinum-DNA adduct formation between the end of carboplatin infusion and 48 hours after the infusion correlated with bone marrow response.

CONCLUSIONS

Fludarabine, carboplatin, topotecan regimen is a promising treatment based on potential pharmacodynamic interactions, which merits additional study in poor prognosis, acute leukemia patients.

A phase IB clinical and pharmacokinetic study of the angiogenesis inhibitor SU5416 and paclitaxel in recurrent or metastatic carcinoma of the head and neck

PURPOSE

SU5416 is a novel small organic molecule that non-competitively inhibits the phosphorylation of the VEGF tyrosine kinase receptor, Flk-1. This phase IB study was performed to determine the safety, pharmacokinetics, and preliminary efficacy of the combination of SU5416 and paclitaxel in recurrent or metastatic carcinoma of the head and neck.

METHODS

Enrolled in the study were 12 patients with biopsy-proven recurrent or metastatic carcinoma of the head and neck. Six patients received intravenous SU5416 110 mg/m2 on days 1, 15, 18, 22 and 25, and paclitaxel 70 mg/m2 on days 8, 15 and 22. Since two patients experienced a dose-limiting toxicity (DLT) in cohort 1, the next six patients received identical treatment as above except the paclitaxel dose was reduced to 55 mg/m2 per week.

RESULTS

A total of 42 cycles at two different dose levels were given. In cohort 1 there were two deep venous thromboses that were DLTs. In the second cohort there was a DLT consisting of a transient ischemic attack after receiving SU5416. Most of the other toxicities seen were grade 1 or 2 in nature and consisted of headache, facial flushing, and fatigue. Two patients developed extensive ulcerative cavities at sites of prior radiation. There were no significant changes in the pharmacokinetic parameters of SU5416 given with paclitaxel. Four patients had prolonged freedom from progression of 18, 28, 42, and 60 weeks duration.

CONCLUSIONS

The combination of SU5416 with paclitaxel had a higher than expected incidence of thromboembolic events and prophylactic anticoagulation should be considered for future trials that combine an angiogenesis inhibitor with cytotoxic chemotherapy. Although the future development of SU5416 as a chemotherapeutic agent is unclear, there was a clinical benefit seen with this combination in 36% of the patients. This trial supports the use of developing antiangiogenic combinations, using molecular targeted agents, in head and neck carcinoma.

Pharmacokinetics of O6-benzylguanine (NSC637037) and its metabolite, 8-oxo-O6-benzylguanine

O6-Benzylguanine and its metabolite, 8-oxo-O6-benzylguanine, are equally potent inhibitors of the DNA repair enzyme, O6-alkylguanine-DNA alkyltransferase. Pharmacokinetic values are derived from cancer patients participating in a phase I trial (10 or 20 mg/m2 of O6-benzylguanine in a single bolus dose or 10 to 120 mg/m2 as a 60-min constant infusion). A two-compartment model fits the plasma concentration versus time profile of O6-benzylguanine. O6-Benzylguanine is eliminated rapidly from the plasma compartment in humans (t1/2 alpha and t1/2 beta are 2 +/- 2 min and 26 +/- 15 min [mean +/- SD, n = 7], respectively), and its plasma clearance (513 +/- 148 mL/min/m2) is not dose dependent. Metabolite kinetics are evaluated using both a novel approach describing the relationship between O6-benzylguanine and 8-oxo-O6-benzylguanine and classical metabolite kinetics methods. With increasing doses of O6-benzylguanine, the plasma clearance of 8-oxo-O6-benzylguanine, decreases, prolonging elimination of the metabolite. This effect is not altered by coadministration of BCNU. The urinary excretion of drug and metabolites is minimal.

A phase I and pharmacodynamic study of sequential topotecan and etoposide in patients with relapsed or refractory acute myelogenous and lymphoblastic leukemia

We designed a pharmacokinetic and pharmacodynamic phase I study of sequential topotecan (2.55-6.3mg/m2) by 72h infusion followed by five daily doses of etoposide for patients with refractory acute leukemia based upon synergistic anti-tumor activity of topoisomerase I and II inhibitors in vitro. Eight of the 29 patients achieved bone marrow aplasia and two patients achieved clinical remission. Common grade 3-4 toxicities included hepatic and gastrointestinal dysfunction, and correlated with increased steady-state plasma topotecan concentration. The predicted up-regulation of topoisomerase II activity by topoisomerase I inhibition was not observed at this dose and schedule and may provide insight into the modest anti-leukemia activity of the regimen.

Phase I clinical and pharmacokinetic study of rebeccamycin analog NSC 655649 given daily for five consecutive days

PURPOSE

Rebeccamycin analog (NSC 655649) is active against a variety of both solid and nonsolid tumor cell lines. We performed a phase I trial to determine the maximum-tolerated dose (MTD) of rebeccamycin analog when given on a daily x 5 schedule repeated every 3 weeks, characterize the toxicity profile using this schedule, observe patients for antitumor response, and determine the pharmacokinetics of the agent and pharmacodynamic interactions.

PATIENTS AND METHODS

Thirty assessable patients received a total of 153 cycles according to the following dose escalation schema: 60, 80, 106, 141, and 188 mg/m(2)/d x 5 days.

RESULTS

Grade 2 phlebitis occurred in all patients before the use of central venous access, placed at dose level 4 and higher. Dose-limiting toxicity (DLT), grade 4 neutropenia, occurred at 188 mg/m(2)/d x 5 days in both previously treated and chemotherapy-naive patients. Pharmacokinetic analysis revealed a three-compartmental model of drug elimination and a long terminal half-life (154 +/- 55 hours). The percentage drop in absolute neutrophil count correlates with the area under the curve infinity. The presence of a second peak during the elimination phase as well as a high concentration of NSC 655649 in biliary fluid compared with the corresponding plasma measurement (one patient) is suggestive of enterohepatic circulation. Two partial responses, two minor responses, and six prolonged (> 6 months) cases of stable disease were observed. Of these, three patients with gallbladder cancer and one patient with cholangiocarcinoma experienced either a minor response or a significant period of freedom from progression.

CONCLUSION

The recommended phase II dose for NSC 665649 on a daily x 5 every 3 weeks schedule is 141 and 165 mg/m(2)/d for patients with prior and no prior therapy, respectively, with DLT being neutropenia. During this phase I trial, encouraging antitumor activity was been observed.

Phase II and pharmacokinetic/pharmacodynamic trial of sequential topoisomerase I and II inhibition with topotecan and etoposide in advanced non-small-cell lung cancer

PURPOSE

In vitro and in vivo preclinical models have demonstrated synergistic activity when topoisomerase I and II inhibitors are administered sequentially. Topoisomerase I inhibitors increase topoisomerase II levels and increase cell kill induced by topoisomerase II poisons. We evaluated this hypothesis in a cohort of patients with advanced non-small-cell lung cancer (NSCLC).

METHODS

A group of 19 patients with advanced NSCLC (70% adenocarcinoma) received topotecan at a dose of 0.85 mg/m2 per day as a continuous 72-h infusion from days 1 to 3. Etoposide was administered orally at a dose of 100 mg twice daily for 3 days on days 7-9 (schedule and dose derived from prior phase I trials). Total and lactone topotecan concentrations were measured at the end of the 72-h infusion. Blood samples were obtained immediately after each 72-h topotecan infusion in order to measure the mutational frequency at the hypoxanthine phosphoribosyl transferase (HPRT) locus in peripheral lymphocytes.

RESULTS

A total of 55 cycles were administered. Toxicity was mainly hematologic with grade 4 neutropenia occurring in 7% of courses. Only one partial response and two stable diseases were observed. The 1-year survival rate was 33%. There was a statistically significant difference between steady-state lactone concentrations between cycle 1 and cycle 2 with decreasing concentrations with cycle 2 (P = 0.02). This was explained by a statistically significant increase in the clearance of topotecan lactone during cycle 2 (P = 0.03). Total but not lactone concentrations correlated with nadir WBC, ANC and platelet levels. Steady-state plasma lactone levels correlated with the mutational frequency at the HPRT locus (P = 0.06). In the one patient with a partial response a sixfold increase in HPRT mutational frequency was observed, which was not seen in patients with progressive disease.

CONCLUSION

The combination of topotecan and etoposide in this schedule of administration has minimal activity in adenocarcinoma of the lung. This lack of activity may be due to the delay in administration of etoposide after the topotecan as studies have shown that the compensatory increase in topoisomerase II levels after treatment with topoisomerase I inhibitors is shortlived (<24 h). The HPRT mutational frequency results suggest that the lack of clinical response may be associated with failure to achieve sufficient cytotoxic dose as indicated by a lack of increase in mutational frequency in those patients with progressive disease. HPRT mutational frequency may correlate with plasma steady-state topotecan lactone levels. Future studies should be directed toward earlier administration of topoisomerase II inhibitors after topoisomerase I inhibition.

A phase II and pharmacokinetic study of weekly 72-h topotecan infusion in patients with platinum-resistant and paclitaxel-resistant ovarian carcinoma

BACKGROUND

As suggested by preclinical trials, prolonged administration of topotecan, a reversible inhibitor of topoisomerase-I, may have a therapeutic advantage. Following a phase I trial of weekly 72-h topotecan infusion, we performed a phase II trial utilizing this schedule in ovarian carcinoma.

METHODS

Eligibility included platinum-/paclitaxel-resistant ovarian carcinoma, measurable disease, and adequate hematologic, renal, and hepatic function. A dose of 2.0 mg/m(2) of topotecan was administered as a 72-h infusion weekly via an ambulatory pump. Plasma topotecan concentrations were determined prior to and at the completion of each weekly course.

RESULTS

Twenty-four patients were entered and 23 patients were evaluable for toxicity and response. Two hundred eighteen weekly courses of therapy were administered (median 7 weeks, range 4-46 weeks). Toxicity was mild with grade 3 leukopenia, neutropenia, and anemia occurring in 13, 13, and 17% of patients, respectively. Two of 23 patients (9.1%) (CI 1-28%) had partial responses of 2 and 3 months' duration and 6 had stable disease. Steady state plasma topotecan lactone concentrations were a median of 1.2 ng/ml (range 0.4-8.00 ng/ml) following the first week of infusion. Steady state topotecan lactone concentrations after the first week of infusion were highest in 2 patients with partial responses. Mean steady state plasma topotecan lactone concentrations after the first week of infusion were 4.6, 2.0, and 1.3 ng/ml for partial response, stable disease, and progressive disease, respectively. An analysis of variance of steady state plasma topotecan concentrations after the first week of infusion over all administered cycles demonstrated a significant difference in steady state plasma topotecan lactone concentrations between patients with partial response and stable disease and between partial response and no response (significant at the 0.05 level after adjustment for multiple comparisons). Controlling for cycle number, steady state topotecan lactone concentrations are significantly greater for patients with responding or stable disease than those with progressive disease (P = 0.0003) and have a lower bound of > or = 1.9 ng/ml (95% confidence level).

CONCLUSION

Steady state topotecan lactone concentrations are associated with responding or stable disease in platinum- and paclitaxel-resistant ovarian cancer. Steady state topotecan concentrations could potentially be utilized to modify tumor exposure and response.

O6-benzylguanine: a clinical trial establishing the biochemical modulatory dose in tumor tissue for alkyltransferase-directed DNA repair

Early phase evaluation of anticancer drugs has traditionally used toxicity (usually hematological) rather than efficacy end points to establish appropriate dosing schedules. To establish a biochemical efficacy end point for overcoming alkylguanine DNA alkyltransferase (AGT)-mediated tumor cell resistance to 1,3-bis(2-chloroethyl)-1-nitrosourea, we performed a novel dose escalation clinical trial for the AGT-depleting agent O6-benzylguanine (BG). The dose of BG required to deplete AGT to undetectable levels (BMD(T)) in sequential computed tomography-guided tumor tissue biopsies before BG and 18 h after BG was determined. Thirty patients received doses of BG ranging from 10 to 120 mg/m2. In tumor tissue, AGT depletion >86% of baseline was demonstrated at all doses tested. Residual tumor AGT activity, present 18 h after BG doses of 10-80 mg/m2, was eliminated at the 120 mg/m2 dose and is thus the BMD(T) of BG. BG pharmacokinetics are characterized by the rapid, dose-independent clearance of BG from plasma Metabolism of BG to its biologically active metabolite, 8-oxo-benzylguanine (8-oxo-BG), was found. The t(1/2) of 8-oxo-BG is longer than BG. Plasma concentrations of 8-oxo-BG well above 200 ng/ml 18 h after the end of the BG infusion were observed at the highest dose levels tested and appeared to correlate with depletion of AGT activity to undetectable levels in tumor tissue. AGT activity in peripheral blood mononuclear cells at baseline did not correlate with tumor tissue AGT activity. Depletion of AGT activity to undetectable levels in peripheral blood mononuclear cells occurred at lower doses and was not a reliable predictor for tumor tissue depletion. No serious side effects were observed with administration of BG alone or in combination with 13 mg/m2 1,3-bis(2-chloroethyl)-1-nitrosourea. This is the first clinical study in which biochemical analyses from pre- and posttreatment tumor biopsies have been used as an efficacy end point for the clinical development of an anticancer agent. From our tumor tissue biopsy data, we have established that a BG dose of 120 mg/m2 infused over 1 h should be used in Phase II clinical trials.

Simultaneous determination of O6-benzylguanine and 8-oxo-O6-benzylguanine in human plasma by reversed-phase high-performance liquid chromatography

A high-performance liquid chromatographic assay for the quantification of O6-benzylguanine (O6BG) in human plasma was modified to include the metabolite, O6-benzyl-8-oxo-guanine (8-oxo-O6BG). O6-(p-Chlorobenzyl)guanine was used as the internal standard. Plasma samples were extracted with ethyl acetate and chromatographed on a C18 base-deactivated reversed-phase column. Separation was accomplished by gradient elution with mobile phases consisting of acetonitrile and phosphate buffer, pH 3.60. Eluted compounds were observed with diode array detection at 288 nm (O6BG) and 292 nm (8-oxo-O6BG). Standard curves were linear from 12.5 ng/ml to 1000 ng/ml, with an average regression coefficient of 0.999 (n=5) for both compounds. The lowest limit of quantitation was 25 ng/ml, with a signal-to-noise ratio of 8:1. The within-day relative standard deviations for O6BG quality control samples (n=18) with concentrations of 735 ng/ml, 305 ng/ml and 38 ng/ml were 2.4%, 4.2% and 5.3%, respectively. The within-day relative standard deviations for 8-oxo-O6BG quality control samples (n=18) at concentrations of 735 ng/ml, 420 ng/ml and 42 ng/ml were 2.2%, 4.0% and 7.1%, respectively. The day-to-day relative standard deviations for the same control specimens were 3.1%, 4.8% and 7.1% for O6BG, respectively, and 2.3%, 4.7% and 11.0% for 8-oxo-O6BG, respectively. This method was applied to plasma samples obtained from patients in a clinical trial of O6-benzylguanine. O6-Benzyl-8-oxo-guanine was identified in patient plasma specimens by liquid chromatography-electrospray mass spectrometry by comparison with spectral data acquired from reference material.

Atypical urinary opiate excretion pattern

Heroin is rapidly metabolized in humans to 6-acetylmorphine (6-AM), which is further metabolized to morphine and morphine conjugates. Urinary 6-AM is the best diagnostic indicator of heroin abuse. This metabolite however, is usually present in urine at less than 3% of the concentration of urinary total morphine (MOR). We present two case studies of 43-year-old, apparently identical, male twins who displayed an atypical pattern of opiate metabolism. The subjects had a history of opiate abuse, and they are currently in a substance-abuse treatment program. Urine specimens submitted by these subjects for periodic clinical urine drug testing occasionally gave positive responses for opiates by enzyme immunoassay. These samples were then submitted for confirmation analysis using a mixed-mode solid-phase extraction sample preparation, trimethylsilyl derivatization, and capillary gas chromatography-electron impact-mass spectrometry confirmation analysis. These specimens contained as much as 2000 ng/mL of 6-AM with less than 350 ng/mL of MOR, which yielded 6-AM/MOR ratios as large as 1100%. Additional urine samples from these subjects that screened negative for opiates were also tested for the presence of 6-AM. Clinically significant concentrations of 6-AM were found in some of these samples.

Determination of O6-benzylguanine in human plasma by reversed-phase high-performance liquid chromatography

A high-performance liquid chromatographic assay for O6-benzylguanine utilizing liquid-liquid extraction and reversed-phase chromatography has been developed. Plasma samples were alkalinized, extracted into ethyl acetate, evaporated, and the residues were reconstituted and chromatographed. Separation was accomplished by gradient elution with a mobile phase of methanol, acetonitrile, and phosphate buffer, pH 3.2. Eluted compounds were detected spectrophotometrically at 280 nm. Sample quantitation was obtained from the regression line of six-point standard curves ranging from 25 to 400 ng/ml. O6-Benzylguanine peak heights were compared to peak heights of O6-(p-chlorobenzyl)guanine (internal standard). The average regression coefficient was 0.999 (n = 4). High concentration (305 ng/ml) and low concentration (38 ng/ml) quality control samples were determined with a day-to-day relative standard deviation of 7 and 8%, respectively (n = 18). The within-day relative standard deviations were 2.7 and 3.0% (n = 18) for the high and low concentration quality control specimens, respectively. Sample quantitation was reliable to 25 ng/ml with a signal-to-noise ratio of 8:1. This method was applied to plasma samples obtained from patients in a clinical trial of O6-benzylguanine.

Quantification of carnitine, acetylcarnitine, and total carnitine in tissues by high-performance liquid chromatography: the effect of exercise on carnitine homeostasis in man

A method for the quantitative determination of carnitine, acetylcarnitine, and total carnitine in tissue was developed for application to clinical research and diagnosis. Human skeletal muscle and heart specimens (10-20 mg) were homogenized in 1 ml of water. Aliquots of the resulting homogenates (50 microliters) were extracted with 1.0 ml of acetonitrile:methanol (3:1) and the carnitine-related compounds were isolated using columns containing 300 mg of silica gel. Samples were then derivatized with 4'-bromophenacyl trifluoromethanesulfonate for spectrophotometric detection or 2-(2,3-naphthalimino)ethyl trifluoromethanesulfonate for fluorescence detection and quantified by high-performance liquid chromatography. Fluorometric detection of 2-(2,3-naphthalimino)ethyl ester derivatives afforded a 500-fold increase in sensitivity when compared to derivatization with 4'-bromophenacyl trifluoromethanesulfonate. This methodology permitted detection of acetylcarnitine in dilute human muscle homogenates at quantities of 790 fmol of acetylcarnitine injected. The method was applied to a series of human skeletal muscle biopsy samples obtained from subjects performing exercise at high work loads. The method permitted quantification of carnitine, acetylcarnitine, and total carnitine (sum of carnitine and all acylcarnitines) and demonstrated the specific redistribution of the carnitine pool from carnitine to acetylcarnitine with exercise above the lactate threshold. This HPLC method is facile, and provides a sensitive and specific approach for use in human biopsy specimens.

Determination of plasma non-esterified fatty acids and triglyceride fatty acids by gas chromatography of their methyl esters after isolation by column chromatography on silica gel

Non-esterified fatty acids (NEFA) and triglycerides were isolated from human plasma by column chromatography on silica gel. Eight principal fatty acids of each of these lipid classes were determined by gas chromatography of their methyl ester derivatives and quantified relative to multipoint standard curves. Within-day relative standard deviations for plasma non-esterified fatty acid and triglyceride fatty acid determinations were 2.4 and 3.2%, respectively. Day-to-day relative standard deviations for plasma non-esterified fatty acid and triglyceride fatty acid determinations were 1.4 and 1.1%, respectively. The total plasma concentration and the relative proportions of the eight non-esterified fatty acids determined by this method were significantly different from results obtained according to two generally accepted methods for direct plasma non-esterified fatty acid determination without a specific isolation step. These comparisons suggested that considerable fatty acid ester lipid hydrolysis occurred during these direct determination procedures, and that this hydrolysis resulted in 3-fold overestimation of plasma NEFA content by those methods. Measured levels of arachidonic acid are substantially overestimated by these direct determination methods in which non-esterified fatty acids are not isolated before derivatization.

Method for isolation of non-esterified fatty acids and several other classes of plasma lipids by column chromatography on silica gel

A method is described for isolation from human plasma of non-esterified fatty acids, cholesteryl esters, triglycerides, cholesterol and diglycerides, monoglycerides, and some phospholipids by extraction and silica gel column chromatography. All of these lipid classes except diglycerides and cholesterol were separated cleanly in seven elution steps. Diglycerides and cholesterol were isolated together. Recovery of model compounds which represent the most significant classes of plasma lipids during the column chromatographic step was nearly complete. The overall recovery of added heptadecanoic acid from plasma specimens was 81% after both sample isolation steps. The overall recovery of added synthetic pentadecanoic acid and heptadecanoic acid ester lipid homologues from plasma was 80-91% after both sample preparation steps. About 6 h are required for extraction and isolation in duplicate of these lipid classes from twenty plasma specimens. Alternatively, non-esterified fatty acids can be isolated from twenty plasma specimens in duplicate within 4 h by a variation of the full procedure.

High-performance liquid chromatographic separation of acylcarnitines following derivatization with 4'-bromophenacyl trifluoromethanesulfonate

A high-performance liquid chromatographic method for the separation of acylcarnitines after derivatization with 4'-bromophenacyl trifluoromethanesulfonate is presented. Derivatization of acylcarnitines was achieved at room temperature within 10 min. Separation of the acylcarnitine 4'-bromophenacyl esters was accomplished by high-performance liquid chromatography using as the analytical column a Resolve-PAK 5-microns C18 radially compressed cartridge eluted with a tertiary gradient containing varying proportions of water, acetonitrile, tetrahydrofuran, triethylamine, potassium phosphate, and phosphoric acid. Acylcarnitine 4'-bromophenacyl esters were detected spectrophotometrically at 254 nm. Baseline separation was obtained for a standard mixture (5 nmol of each injected) containing carnitine, acetyl-, propionyl-, butyryl-, valeryl-, hexanoyl-, heptanoyl-, octanoyl-, nonanoyl-, decanoyl-, lauroyl-, myristroyl-, palmitoyl-, and stearoylcarnitine. Nearly complete separation was obtained for a standard mixture containing butyryl-, isobutyryl-, isovaleryl-, and 2-methylbutyrylcarnitine. The method was applied to a normal human urine and then to this same urine spiked with the acylcarnitine standards. Urinary acylcarnitine profiles from patients having propionic acidemia, isovaleric acidemia, and medium-chain acyl-CoA dehydrogenase deficiency were performed. Urinary isovalerylcarnitine was quantified in the patient with isovaleric acidemia using heptanoylcarnitine as an internal standard.

An enzymatic method for the determination of butyrobetaine via conversion to carnitine after isolation by high performance liquid chromatography

An improved procedure for the determination of butyrobetaine [4-(N,N,N-trimethylammonio)butanoate] in plasma and tissue is described. Butyrobetaine was isolated by ion-exchange chromatography and high performance liquid chromatography. The isolation procedure was internally standardized with [3H]butyrobetaine. The recovery of butyrobetaine was greater than 90%. Following isolation butyrobetaine was enzymatically converted to carnitine using butyrobetaine hydroxylase and the resulting carnitine was assayed using carnitine acetyltransferase and [14C]acetylcoenzyme A. The conversion of butyrobetaine to carnitine and of carnitine to [14C]acetylcarnitine was greater than 98% as determined by high performance liquid chromatography. Using this method was analysed human sera (healthy controls) and tissues (autopsy) and found the following values: serum, 4.67 nmol/ml; kidney 17.6 nmol/g; liver, 26.5 nmol/g. The serum butyrobetaine values of twins suffering from carnitine deficiency were normal (3.78 and 3.87 nmol/ml), while the carnitine supplementation therapy caused an increase. Animal samples were analyzed and the values were 3-4 times higher than previously reported by others.

Rapid high-performance liquid chromatography of 3-methylhistidine in human urine

An internally standardized method for the determination of 3-methylhistidine in human urine is presented. This methylated amino acid and the chemically analogous internal standard 3-ethylhistidine were isolated from human urine specimens using small columns of cation-exchange resin. Quantification was accomplished by high-performance liquid chromatography using post-column derivatization with o-phthalicdicarboxaldehyde-2-mercaptoethanol followed by fluorometric detection. Sample-to-sample and day-to-day reproducibility were shown to have respective relative standard deviations of 2 and 5% for a human urine specimen containing 250 nmol/ml 3-methylhistidine when using 250 microliter urine per analysis. The chromatographic separation was evaluated in terms of various peak descriptors (capacity factor and retention time) and "Chromatographic Figures of Merit" (peak symmetry and chromatographic efficiency). The utility of the method was demonstrated by its successful application to 1000 human urine specimens.

Improved high-performance liquid chromatographic method for the determination of 6-N,N,N-trimethyllysine in plasma and urine: biomedical application of chromatographic figures of merit and amine mobile phase modifiers

An internally standardized method for the determination of 6-N,N,N-trimethyllysine in human plasma, human urine, rat plasma, rat urine and hydrolyzed rat urine is described. This methylated amino acid and the procedural internal standard 6-N,N,N-trimethyllysine were isolated from the sample matrices using short ion-exchange columns and detected following high-performance liquid chromatography using a postcolumn reaction (o-phthalic-dicarboxaldehyde-2-mercaptoethanol) and fluorometric detection. The reliable detection limit for 6-N,N,N-trimethyllysine was 0.2 nmol/ml in 200 microliters of human plasma. The chromatographic separation exploits the unique properties of a novel tertiary amine mobile phase modifier, 3-(N,N-dimethylamino)-1,2-propanediol. The capacity factor and "Chromatographic Figures of Merit" (including peak asymmetry and relative system efficiency) were calculated for the chromatographic peak representing 6-N,N,N-trimethyllysine in over 2200 injections made while evaluating 900 biological specimens.

Determination of carnitine, butyrobetaine, and betaine as 4'-bromophenacyl ester derivatives by high-performance liquid chromatography

A method for determination of carnitine, 4-(N,N,N-trimethylammonio)butanoate (butyrobetaine), and 2-(N,N,N-trimethylammonio)acetate (betaine) is described. These omega-trimethylammonio carboxylates and the chemically analogous internal standards 4-(N,N-dimethyl-N-propylammonio)-3-hydroxybutanoate or 6-(N,N,N-trimethylammonio)hexanoate were derivatized by reaction with 4'-bromophenacyl triflate in the presence of N,N-diisopropylethylamine. The trialkylammonio carboxylate 4'-bromophenacyl ester derivatives were separated from other sample constituents by reversed-phase ion-pair high-performance liquid chromatography with spectrophotometric detection at 254 nm. Standard curves were linear over a sample concentration range of 10-100 nmol/ml. Quantities of 2.5 nmol of omega-trialkylammonio acid derivatives injected into the chromatograph were detected with signal-to-noise ratios greater than 50.

Determination of free trimethyllysine in plasma and tissue specimens by high-performance liquid chromatography

A method for the determination of 6-N-trimethyllysine in tissues and plasma is described. Trimethyllysine and the chemically analogous 6-N-triethyllysine (internal standard) were isolated from acid-soluble fractions of tissue homogenates or plasma by combined ion-exchange--ion-exclusion chromatography. Trimethyllysine and triethyllysine were separated from other sample constituents by reversed-phase ion-pair high-performance liquid chromatography, derivatized post-column by reaction with o-phthalicdicarboxaldehyde and 2-mercaptoethanol, and detected fluorometrically. Standard curves were linear over a sample concentration range of 0.5--4 nmol/ml. The detection limit corresponded with 25 pmol trimethyllysine injected into the chromatograph. The procedure was used for the determination of trimethyllysine in plasma, liver, kidney, and mixed skeletal muscle of rat.

Derivatization of carboxylic acids by reaction with 4′-bromophenacyl trifluoromethanesulfonate prior to determination by high-performance liquid chromatography

The use of 4'-bromo-2-hydroxyacetophenone trifluoromethanesulfonate ester (4'-bromophenacyl triflate) in the preparation of carboxylic acid 4'-bromophenacyl ester derivatives for spectrophotometric detection in high-performance liquid chromatography is described. The reagent is prepared in 66% yield by the reaction of 4'-bromo-2-diazoacetophenone with trifluoromethanesulfonic acid in anhydrous sulfur dioxide and is stable for 3-6 months. Reactions of 10(-6) M carboxylate N,N-diisopropylethylammonium salts with this reagent in acetonitrile at room temperature proceed to completion in 1-5 min. Optimal rates of reaction are obtained with a 10-fold equivalent excess of alkylating agent and 5 equivalents of N,N-diisopropylethylamine present. The process has been applied successfully to mono-, di- and tricarboxylic and sterically hindered carboxylic acids.

Determination of 6-N-trimethyllysine in urine by high-performance liquid chromatography

A method for determination of 6-N-trimethyllysine in urine is described. Trimethyllysine and the chemically analogous 6-N-triethyllysine internal standard were isolated from aqueous samples by microcolumn ion-exclusion chromatography. The specimens were derivatized by reaction with 1-fluoro-2,4-dinitrobenzene and reaction byproducts extracted by organic solvents. The trimethyllysine and internal standard derivatives were separated easily from other sample constituents by reversed-phase paired-ion high-performance liquid chromatography with spectrophotometric detection at 405 nm. Standard curves were linear over a sample concentration range of 10-150 nmol/ml; the detection limit corresponded with 0.1 nmol trimethyllysine injected into the chromatograph. The procedure was used for determination of trimethyllysine in human urine.

Furosemide kinetics in patients with hepatic cirrhosis with ascites

Furosemide, 20 mg, was given intravenously as a bolus to seven patients with cirrhotic ascites and a 10-mg intravenous bolus dose was given to three normal subjects. Furosemide concentrations were measured by a specific high-performance liquid chromatographic analytic method. The median plasma elimination half-life (t1/2), volume of distribution at a steady state (VdSS), and VDarea of furosemide were 0.70 hr, 91 ml/kg, and 119 ml/kg in normal subjects. In the cirrhotic patients elimination t1/2 and Vd at steady state doubled and the Vdarea of furosemide was almost double that of the normal. There were no differences in plasma clearance or renal and nonrenal clearance between patients and controls, but five of the seven patients had lower renal clearances than controls. The water and sodium response to furosemide was directly related to the urinary furosemide excretion rate. We identified a subset of cirrhotic patients who responded poorly (125 ml/hr urinary output in the first 4 hr after furosemide compared to 300 ml/hr in the other patients and 400 ml/hr in the controls) to furosemide. These "poor responders" had the lowest renal clearance of furosemide and the lowest urinary furosemide excretion rates. Our data indicate that furosemide kinetics are altered in patients with cirrhotic ascites and lack of response in a subset of these patients is due to lack of delivery of furosemide to the renal site of its action.