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S M Blaney

Publications and source records attributed to S M Blaney.

At least 37 records · Page 2Linked to original sources
PubMed1997

Phase I trial and pharmacokinetic study of all-trans-retinoic acid administered on an intermittent schedule in combination with interferon-alpha2a in pediatric patients with refractory cancer.

PURPOSE: To determine the maximum-tolerated dose (MTD) of all-trans-retinoic acid (ATRA) administered on an intermittent oral schedule with interferon-alpha2a (IFN-alpha2a) in children with refractory cancer, and whether the marked reduction in plasma ATRA concentrations observed with chronic daily oral dosing could be circumvented with an intermittent dosing schedule. PATIENTS AND METHODS: Thirty-three children with refractory cancer (stratified by age, < or = 12 and > 12 years) were treated with ATRA 3 consecutive days per week and IFN-alpha2a 3 x 10(6) U/m2 5 consecutive days per week, both repeated weekly. The starting dose of ATRA was 60 mg/m2/d divided into three doses, with planned escalations to 90 and 120 mg/m2/d. Because severe headaches have been noted to occur on the initial day of ATRA administration, only two of three doses of ATRA were administered on day 1 of each week. RESULTS: Pseudotumor cerebri or dose-limiting headache was observed in two of five patients older than 12 years treated at the 120-mg/m2/d dose level and in one of six < or = 12 years at the 90-mg/m2/d level. Other non-dose-limiting toxicities of ATRA included reversible elevations in hepatic transaminases and triglycerides, dry skin, cheilitis, and nausea/vomiting. One child with recurrent neuroblastoma had an objective response of 6 months' duration, and one with recurrent Wilms' tumor had histologic maturation of multiple tumors. This intermittent schedule allowed for exposure to relatively high plasma concentrations of ATRA on a repetitive basis. Following 30-mg/m2 doses, the ATRA area under the concentration-time curve (AUC) decreased from 96 +/- 14 micromol/L/min on day 1 to 26 +/- 24 micromol/L/min by day 3 of drug administration, but on day 1 of the fourth consecutive week of therapy, the AUC averaged 110 +/- 16 micromol/L/min. The recommended pediatric phase II dose of ATRA administered on this schedule is 90 mg/m2/d. CONCLUSION: An intermittent schedule of ATRA administration appears to circumvent the low plasma drug exposure that is a result of the sustained upregulation of metabolism when this drug is administered on a chronic daily schedule. Based on the results of this trial, a phase II trial of ATRA/IFN-alpha2a in neuroblastoma and Wilms' tumor using this schedule is in progress.

Adolescent↗
PubMed1997

Phase I trial of docetaxel administered as a 1-hour infusion in children with refractory solid tumors: a collaborative pediatric branch, National Cancer Institute and Children's Cancer Group trial.

PURPOSE: A phase I trial of docetaxel was performed to determine the maximum-tolerated dose (MTD), the dose-limiting toxicities, and the incidence and severity of other toxicities in children with refractory solid tumors. PATIENTS AND METHODS: Forty-four children received 103 courses of docetaxel administered as a 1-hour intravenous infusion every 21 days. Doses ranged from 55 to 150 mg/m2, MTD was defined in heavily pretreated and less heavily pretreated (< or = 2 prior chemotherapy regimens, no prior bone marrow transplantation [BMT], and no radiation to the spine, skull, ribs, or pelvic bones) patients. RESULTS: Dose-related neutropenia was the primary dose-limiting toxicity. The MTD in the heavily pretreated patient group was 65 mg/m2, but the less heavily pretreated patients tolerated a significantly higher dose of docetaxel (maximum-tolerated dose, 125 mg/m2). Neutropenia and constitutional symptoms consisting of malaise, myalgias, and anorexia were the dose-limiting toxicities at 150 mg/m2 in the less heavily pretreated patients. Thrombocytopenia was not prominent, even in patients who experienced dose-limiting neutropenia. Common nonhematologic toxicities of docetaxel included skin rashes, mucositis, and mild elevations of serum transaminases. Neuropathy was uncommon. Peripheral edema and weight gain were observed in two of five patients who received more than three cycles of docetaxel. A complete response (CR) was observed in one patient with rhabdomyosarcoma, a partial response (PR) in one patient with peripheral primitive neuroectodermal tumor (PPNET), and a minimal response (MR) in two patients with PPNET. Three of the four responding patients were treated at doses > or = 100 mg/m2. CONCLUSION: The recommended phase II dose of docetaxel administered as a 1-hour intravenous infusion in children with solid tumors in 125 mg/m2. Because neutropenia was the dose-limiting toxicity and thrombocytopenia was mild, further escalation of the dose should be attempted with granulocyte colony-stimulating factor (G-CSF) support.

Adolescent↗
PubMed1996

Phase II evaluation of topotecan for pediatric central nervous system tumors.

BACKGROUND: Topotecan is a topoisomerase I inhibitor that has good penetration across the blood-brain barrier and significant antitumor activity against human brain tumor xenografts. In a Phase I trial in children with refractory cancer, topotecan was well tolerated when administered as a 24-hour infusion. The maximum tolerated dose was 5.5 mg/m2 and the dose-limiting toxicity was myelosuppression. This Phase II study of topotecan was performed to assess the activity of topotecan against childhood brain tumors. METHODS: Forty-five children with either a previously treated primary brain tumor that was refractory to standard therapy, or an untreated brain stem glioma or glioblastoma multiforme, received topotecan administered as a 24-hour intravenous infusion every 21 days. The initial dose was 5.5 mg/m2 with escalation to 7.5 mg/m2 on the second and subsequent doses in patients who did not experience dose-limiting toxicity. RESULTS: There were no complete or partial responses in the patients with high grade glioma (n=9), medulloblastoma (n=9), or brain stem glioma (n=14). One of 2 patients with a low grade glioma had a partial response lasting more than 17 months; 3 patients with a brain stem glioma had stable disease for 12 to 28 weeks; and 1 patient with a malignant neuroepithelial tumor and 1 patient with an optic glioma had stable disease for 41 weeks and 22 weeks, respectively. Dose escalation from 5.5 mg/m2 to 7.5 mg/m2 was well tolerated in the first 11 patients enrolled on this study who had not received prior craniospinal radiation therapy. The starting dose was subsequently increased to 7.5 mg/m2 for patients without prior craniospinal radiation. CONCLUSIONS: Topotecan administered as a 24-hour infusion every 21 days is inactive in high grade gliomas, medulloblastomas, and brain stem tumors.

Adolescent↗
PubMed1996

Pharmacologic strategies for the treatment of meningeal malignancy.

There have been significant strides in the treatment and prevention of meningeal cancer, particularly meningeal leukemia, during the past thirty years. These advantages are a direct result of innovative therapeutic approaches specifically designed to overcome the limitations of systemically administered chemotherapy. Such approaches include the administration of intrathecal chemotherapy by intralumbar or intraventricular injection, the administration of very high-dose systemic chemotherapy, and the administration of cranial or craniospinal irradiation. A better understanding of the central nervous system pharmacokinetics of commonly used anticancer agents has also resulted in improvements in the treatment of meningeal cancer. In this article, the clinical pharmacology of the most commonly used intrathecal agents and pharmacologic strategies for the treatment of meningeal cancer will be discussed. In addition, an overview of new agents for intrathecal administration and other novel CNS targeted therapies will be presented.

Antineoplastic Agents↗
PubMed1996

Central nervous system leukemia.

The treatment of central nervous system (CNS) leukemia still poses a significant challenge to the clinical oncologist despite significant advances in therapeutic strategies that are directly targeted at the CNS. This article reviews the evolving definition of CNS leukemia, the current status of therapy for the prevention and treatment of overt CNS leukemia, pharmacological considerations in the treatment of CNS leukemia, and the longterm sequelae of CNS-directed therapy, focusing on articles that have been published in the past 2 years. New agents and treatment strategies for the treatment and prevention of CNS leukemia are also discussed.

Antibodies, Monoclonal↗
PubMed1995

A phase I trial of amifostine (WR-2721) and melphalan in children with refractory cancer.

Melphalan has a steep dose-response curve, but the use of high doses results in unacceptable myelosuppression. Strategies to circumvent this dose-limiting myelosuppression would allow for the administration of higher, more effective doses of melphalan. Amifostine (WR-2721) has been shown in preclinical studies to protect the bone marrow from the myelotoxicity of melphalan, and in clinical trials, to protect from the myelotoxicity of other alkylating agents. A Phase I trial of the combination of amifostine and melphalan was performed in children with refractory cancers to: (a) define the acute toxicities of amifostine and its maximum tolerated dose (MTD); and (b) to determine whether the dose of melphalan could be safely escalated when administered in combination with amifostine. Amifostine was administered i.v. as a 15-min infusion 30 min before melphalan. The starting dose of amifostine was 750 mg/m2, with planned dose escalations in 30% increments. Melphalan was administered as a 5-min infusion using the previously defined MTD in heavily pretreated patients, 35 mg/m2, as the starting dose. The dose of melphalan was escalated by 30% increments. Nineteen patients, ranging in age from 3 to 24 years (median, 15 years), were entered on trial. The dose of amifostine was escalated to 2700 mg/m2, which is approximately 3-fold higher than the adult recommended dose, without reaching a MTD. Fifteen patients experienced nondose-limiting (< 25%), transient decreases in blood pressure after the amifostine infusion. Other nondose-limiting toxicities of amifostine included mild nausea and vomiting, flushing, anxiety, diarrhea, and urinary retention. Six patients, three each at the 2100 and 2700 mg/m2 amifostine dose levels were treated with an escalated dose of melphalan (45 mg/m2). All of these patients experienced grade 4 neutropenia (< 500/mm3), and five of six patients had grade 4 thrombocytopenia. The duration of this dose-limiting myelosuppression exceeded 7 days in four of six patients. Although no dose-limiting (grade 3 or 4) toxicity was attributed to amifostine, significant anxiety and reversible urinary retention occurred at the two highest amifostine dose levels. A dose of 1650 mg/m2 for pediatric Phase II trials is recommended. High doses of amifostine, however, do not appear to allow for escalation of melphalan beyond its single agent MTD of 35 mg/m2.

Adolescent↗
PubMed1995

Intrathecal administration of topotecan in nonhuman primates.

The cerebrospinal fluid (CSF) pharmacokinetics of topotecan were studied in a nonhuman primate model following intraventricular administration of 0.1 mg. Lactone and total drug concentrations were measured using a reverse-phase HPLC method with fluorescence detection. The mean peak concentrations of lactone and total drug in ventricular CSF were 83 +/- 18 microM and 88 +/- 25 microM, respectively. CSF drug elimination of the lactone was bi-exponential with a terminal half-life of 1.3h. The mean clearance from ventricular CSF was 0.075 ml/min for the lactone and 0.043 ml/min for total drug. The ventricular CSF drug exposure (AUC) to lactone was 450-fold greater following intraventricular administration of 0.1 mg topotecan than after systemic intravenous administration of a 40-fold higher dose (10 mg/m2). Peak lumbar concentrations (n = 1), which occurred 2 h after intraventricular drug administration, were 0.98 microM and 2.95 microM for the lactone and total drug, respectively. A transient CSF pleocytosis was observed in one animal following intralumbar topotecan administration and in one animal following intralumbar topotecan administration. No other acute or chronic neurologic or systemic toxicities were observed following a single intraventricular dose or weekly (x4) intralumbar topotecan. Compared with systemic topotecan, intrathecal administration provided a significant pharmacokinetic advantage in terms of CSF drug exposure and did not produce any significant neurotoxicity in a nonhuman primate model. Intrathecal topotecan should be evaluated clinically as a potential alternative therapy for refractory meningeal tumors.

Animals↗
PubMed1995

Pharmacokinetics of lamivudine and BCH-189 in plasma and cerebrospinal fluid of nonhuman primates.

2'-Deoxy-3'-thiacytidine is a dideoxycytidine analog with a sulfur in place of the 3' carbon of the ribose. There are two enantiomeric forms of the compound, both of which inhibit human immunodeficiency virus type 1 and 2 replication in vitro. However, the (-) enantiomer (lamivudine) appears to be significantly less cytotoxic to uninfected lymphocytes than is the (+) enantiomer. Lamivudine has entered initial clinical trials, and the present study was designed to describe the pharmacokinetic behavior of this compound in both plasma and cerebrospinal fluid (CSF) of primates. Lamivudine was administered as an intravenous bolus dose of 20 mg/kg for 24 h for administration. Urine samples were also obtained from two animals. The same dose of the racemate (BCH-189) was administered to one animal. The drug was quantitated in CSF and plasma with a reverse-phase high-pressure liquid chromatography technique. Elimination of lamivudine from plasma was biexponential, with a mean alpha phase half-life of 5.4 min, a mean beta phase half-life of 84 min, and a total clearance of 6.1 liters/h. The total clearance of the same dose of BCH-189 in a single animal was 11.0 liters/h. In two animals from which urine was obtained for 12 h postadministration, 32 and 59% of the drug was recovered unchanged. The deamination product of lamivudine was not detected. The CSF/plasma ratio of lamivudine was significantly higher when the drug was measured in the lumbar CSF (mean, 0.41) than when it was measured in the ventricular CSF (mean, 0.079). The measured CSF/plasma ratio for ventricular CSF is equivalent to that of other dideoxycytidine analogs, confirming the importance of the nucleobase in determining the degree of CSF penetration. The difference in lamivudine exposure in ventricular and lumbar CSF suggests that there is a transport mechanism for efflux of cytidine analogs from ventricular CSF.

Animals↗
PubMed1995

Effect of body position on ventricular CSF methotrexate concentration following intralumbar administration.

PURPOSE: Intralumbar methotrexate is one of the primary therapeutic modalities for the prevention and treatment of meningeal leukemia. However, methotrexate distribution to the ventricles is limited and highly variable following intralumbar dosing, and cytotoxic concentrations of methotrexate are not always achieved or sustained in the ventricular CSF. We used a nonhuman primate model to determine the effect of body position on the caudal distribution of an intralumbar dose of methotrexate. METHODS: Methotrexate (1.0 mg) was administered by intralumbar injection to four animals, which were then immediately placed either in an upright sitting position or in a prone position for 1 hour, then upright. Each animal served as its own control and was studied in each position on at least one occasion. RESULTS: The mean peak ventricular methotrexate concentration was 0.12 mumol/L (range, 0.091 to 0.20) in animals that were immediately placed upright, compared with 2.81 mumol/L (range, 0.21 to 8.9) in animals that remained prone for 1 hour. The mean area under the concentration-versus-time curves (AUC) was 0.51 mumol/L.h (range, 0.26 to 1.1) in the upright animals and 12.0 mumol/L.h (range, 0.9 to 35.4) in the prone animals. CONCLUSION: Maintaining a prone position for 1 hour after an intralumbar dose increased the peak methotrexate concentration and drug exposure in ventricular CSF. CSF drug distribution following intralumbar therapy can be influenced by body position after the injection.

Animals↗
PubMed1994

A pharmacokinetic model of topotecan clearance from plasma and cerebrospinal fluid.

We present a physiological pharmacokinetic model that describes the plasma and cerebrospinal fluid (CSF) concentrations of topotecan [(S)-9-dimethylaminomethyl-10-hydroxyamptothecin hydrochloride, SK&F 104864-A, NSC 609699] following i.v. and intraventricular administrations in monkeys. The model consists of three physical spaces: the CSF, the plasma, and a body compartment. The model incorporates such processes as reversible conversion of topotecan lactone to an inactive hydroxy acid form, microvascular exchange between CSF and plasma, bulk CSF flow, exchange between plasma and body compartments, and elimination of drug from the plasma compartment. Several parameters in the model were obtained from published literature on the physiology of the monkey. The model was then fit to the plasma and CSF data to deduce the other parameters. Calculated clearances of topotecan lactone and total drug from the CSF after intraventricular injection were 3.9 and 2.2 ml/h, respectively. Clearances of topotecan lactone and total drug from the plasma following a 10-min infusion were 26.3 liters/h/m2 and 17.8 liters/h/m2, respectively. The calculated ratios of the area under the concentration curve in the CSF following i.v. infusion to the area under the concentration curve in plasma were 0.11 and 0.19 for topotecan and total drug, respectively, indicating significant CSF penetration. The volume of distribution was 0.77 liters/kg, which represents distribution in a volume approximating total body water. The forward and reverse rate constants for the lactone-to-hydroxy acid conversion were 1.0 and 0.29 h-1, respectively. Comparison of the clearances (normalized to body surface area) with values reported for mice and humans shows reasonable similarity across species. This pharmacokinetic model may help guide future development and refinement of clinical protocols, especially in the treatment of diseases of the central nervous system.

Animals↗
PubMed1994

Acute pancreatitis after ifosfamide therapy.

Acute pancreatitis is an uncommon but serious complication of cancer chemotherapy. A 16-year-old girl with metastatic osteosarcoma experienced recurrent bouts of symptomatic pancreatitis 24 hours after treatment with ifosfamide administered as a single agent. To the authors' knowledge, this is the first report of an association between ifosfamide and pancreatitis. Because serum amylase levels are not monitored routinely during treatment with most chemotherapeutic agents, subclinical cases of pancreatitis with ifosfamide and other agents may go undetected.

Acute Disease↗
PubMed1993

Mechanism of resistance to cyclopentenyl cytosine (CPE-C) in Molt-4 lymphoblasts.

Cyclopentenyl cytosine (CPE-C), a carbocyclic analogue of cytidine, has preclinical antineoplastic activity against ara-C resistant murine leukemias and a broad spectrum of human tumor xenografts. CPE-C is a prodrug and requires intracellular phosphorylation to cyclopentenyl cytosine triphosphate (CPE-CTP) which depletes endogenous CTP pools. The initial step in this activation process is catalyzed by uridine/cytidine kinase. We studied the mechanism of resistance to CPE-C in a Molt-4 T-cell leukemia line made resistant to CPE-C (Molt-4R) by culturing it in the continuous presence of increasing concentrations of CPE-C. Using a tetrazolium based colorimetric assay to assess cytotoxicity, the IC90 for the parent Molt-4 cells (Molt-4WT) was 0.5 microM after a 24 hr drug exposure. In contrast, cytotoxicity was not observed at concentrations as high as 1 mM in the Molt-4R cells. Following a brief exposure to 1 microM CPE-C, parent drug could be detected intracellularly in the resistant and sensitive cell lines. However, CPE-CTP formation was reduced markedly in the resistant cell line. Measurement of the activity of anabolic and catabolic enzymes in the Molt-4WT and Molt-4R cells revealed equivalent activities of alkaline and acid phosphatases as well as cytidine and dCMP deaminase but there was a significant reduction in uridine/cytidine kinase activity in Molt-4R cells. Endogenous ribonucleotide pools and CPE-CTP pools were measured in the absence and presence of CPE-C. CTP pools were reduced markedly in Molt-4WT cells following exposure to CPE-C. However, CTP pools in Molt-4R cells exposed to 100 microM CPE-C were two times greater than in the untreated Molt-4WT cells. At high concentrations of CPE-C (10 and 100 microM), Molt-4R cells were able to generate amounts of CPE-CTP equivalent to that seen in Molt-4WT cells exposed to 1 microM CPE-C (a cytotoxic concentration of drug in Molt-4WT cells), but no cytotoxic effect was seen in Molt-4R cells. Therefore, in addition to decreased uridine/cytidine kinase activity, a second mechanism of resistance that is the result of alterations in CTP synthetase activity also appears to be operative. Elucidation of the mechanism of resistance in vitro may provide insight into the mechanism of action of the drug and potential mechanisms of resistance in vivo.

Antineoplastic Agents↗
PubMed1993

Pediatric phase I trial and pharmacokinetic study of topotecan administered as a 24-hour continuous infusion.

Topotecan, a water-soluble semisynthetic analogue of camptothecin, is the first topoisomerase I inhibitor to undergo evaluation in pediatric patients with refractory malignancies. A phase I and pharmacokinetic study was performed to determine the maximum tolerated dose (MTD) and dose-limiting toxicities, the incidence and severity of other toxicities, and the pharmacokinetics of topotecan in children. Twenty-nine patients received 42 courses of i.v. topotecan administered as a 24-h continuous infusion every 21 days at doses ranging from 2.0 to 7.5 mg/m2. Dose-related hematological toxicity was the dose-limiting toxicity. Leukopenia, neutropenia, and thrombocytopenia occurred sporadically at the 3.0- to 5.5-mg/m2 dose levels, but at 7.5 mg/m2 4 of 5 patients experienced dose-limiting thrombocytopenia (grade 4) and 2 of 5 had dose-limiting neutropenia (grade 4). No other dose-limiting toxicities were observed. Nausea and vomiting were mild and occurred in < 20 and 10% of patients, respectively. Grade 2 hematuria occurred in one patient. No objective responses were observed. Pharmacokinetic studies revealed a linear relationship between the steady-state topotecan concentration and dose. The mean steady-state concentration at the MTD was 18.2 +/- 3.7 nmol/liter and the total body clearance was 28.3 +/- 6.5 liters/h/m2. Elimination was biexponential with a t1/2 alpha of 14.4 +/- 1.8 min and a t1/2 beta of 2.9 +/- 1.1 h. The recommended starting dose for phase II pediatric trials is 5.5 mg/m2. Although this dose exceeds the MTD identified in heavily pretreated adult patients receiving topotecan on the same schedule, it is less than the MTD for minimally pretreated adult patients. Therefore, dose escalation to 7.5 mg/m2 in phase II pediatric trials should be considered for patients who tolerate treatment well at the 5.5-mg/m2 dose.

Adolescent↗
PubMed1993

Plasma and cerebrospinal fluid pharmacokinetic study of topotecan in nonhuman primates.

Topotecan, a water soluble semisynthetic analogue of camptothecin, is a topoisomerase I inhibitor that has recently entered phase II clinical trials. Topotecan has shown significant preclinical activity in refractory murine tumors and in human tumor xenograft models. In addition, objective antineoplastic activity has been observed in recent adult phase I clinical trials. Topotecan is unstable in solution and is rapidly and spontaneously converted to a less active open ring form which predominates at physiological pH. This study was undertaken to better define the pharmacokinetic behavior of this highly unstable compound in both plasma and cerebrospinal fluid (CSF) and to measure the degree of CSF penetration of this novel antineoplastic agent. Three nonhuman primates with indwelling Ommaya reservoirs received 10 mg/m2 i.v. topotecan administered as a 10-min infusion. Frequent plasma and CSF samples were obtained and immediately extracted and assayed with a reverse phase high performance liquid chromatography assay to quantitate the concentration of topotecan (lactone). Samples were then acidified and reinjected to quantitate total drug (lactone ring plus open ring). Peak plasma concentrations of topotecan ranged from 0.27 to 0.45 microM. Plasma disappearance of the lactone ring was biexponential with a distribution half-life (t1/2 alpha) of 22 +/- 5 min and an elimination half-life (t1/2 beta) of 1.3 +/- 0.1 h. Total body clearance of topotecan was 72.1 +/- 15.8 liters/h/m2. The volume of distribution at steady state was 88.6 +/- 33.2 liters/m2. Peak CSF concentrations of topotecan occurred at 30 min following drug administration and ranged from 0.044 to 0.074 microM. CSF disappearance paralleled that in plasma. The mean ratio of the area under the CSF concentration-time curve to that in plasma was 0.32 (range, 0.29 to 0.37). The mean CSF penetration of topotecan exceeds 30%, which is significantly greater than the penetration of most structurally similar chemotherapeutic agents. The impact of chemotherapy on the survival of patients with primary or metastatic central nervous system malignancies is very limited. Therefore, this novel antineoplastic agent is an excellent candidate for further study in patients with high risk or refractory central nervous system tumors.

Animals↗
PubMed1992

Modulation of the cytotoxic effect of cyclopentenylcytosine by its primary metabolite, cyclopentenyluridine.

Cyclopentenylcytosine (CPE-C), a synthetic cytidine analogue with significant preclinical antitumor activity against both solid tumor xenografts and 1-beta-D-arabinofuranosylcytosine resistant murine leukemia cell lines, will soon enter phase I clinical trials. Unlike 1-beta-D-arabinofuranosylcytosine which is activated by deoxycytidine kinase, the enzyme responsible for the phosphorylation of CPE-C is uridine/cytidine kinase. Preclinical pharmacokinetic studies of CPE-C in nonhuman primates revealed that the primary route of elimination in this species was deamination to cyclopentenyluridine (CPE-U), an inhibitor of uridine/cytidine kinase. Since CPE-C is likely to be deaminated in humans, we investigated the modulating effect of CPE-U on the in vitro cytotoxicity of CPE-C in Molt-4 lymphoblasts. Concurrent exposure of cells to cytotoxic concentrations of CPE-C and 50 microM CPE-U resulted in the rescue of 50% of cells and exposure to CPE-U concentrations in excess of 100 microM resulted in the rescue of greater than 90% of cells. Progressive attenuation of the rescue effect was observed with delayed administration of CPE-U and no cells were rescued when addition of CPE-C was delayed for more than 2 h. At the intracellular level it was observed that the formation of the cytotoxic metabolite, cyclopentenylcytosine triphosphate, was blocked by increasing concentrations of CPE-U presumably secondary to inhibition of uridine/cytidine kinase by CPE-U. Although CPE-U can modulate the cytotoxic effects of CPE-C in vitro, the minimum CPE-U levels that are required for modulation coupled with the available preclinical pharmacokinetic data from nonhuman primates suggests that this modulation is not likely to impact on the antitumor effects of CPE-C in humans.

Cell Survival↗
PubMed1992

Clinical pharmacology of 2',3'-dideoxyinosine in human immunodeficiency virus-infected children.

The pharmacokinetics of intravenous and oral 2',3'-dideoxyinosine (ddI) and the relationships between pharmacokinetic parameters and measures of response were studied in 48 human immunodeficiency virus-infected children. Disappearance of ddI from plasma after the intravenous dose was rapid and biexponential, with half-lives of 12 min and 1.0 h and a total clearance of 510 +/- 180 ml/min/m2. After oral administration, ddI absorption was limited and variable (mean bioavailability, 19% +/- 17%). A plasma ddI concentration-response relationship was observed for both decline in viral p24 antigen levels and improvement in intelligence quotient score. A limited sampling model was developed that accurately predicts the area under the ddI plasma concentration-time curve from one to three plasma samples. Although this pharmacokinetic study was done in children, the results also have relevance to adults and suggest that individualization of dose and schedule through therapeutic drug monitoring may be necessary to achieve optimal response.

Absorption↗