Pharmacokinetic analysis of acute and dietary exposure to piperonyl butoxide in the mouse

Piperonyl butoxide (PBO) is a popular insecticide synergist present in thousands of commercial, agricultural, and household products. PBO inhibits cytochrome P450 activity, impairing the ability of insects to detoxify insecticides. PBO was recently discovered to also inhibit Sonic hedgehog signaling, a pathway required for embryonic development, and rodent studies have demonstrated the potential for in utero PBO exposure to cause structural malformations of the brain, face, and limbs, or more subtle neurodevelopmental abnormalities. The current understanding of the pharmacokinetics of PBO in mice is limited, particularly with respect to dosing paradigms associated with developmental toxicity. To establish a pharmacokinetic (PK) model for oral exposure, PBO was administered to female C57BL/6J mice acutely by oral gavage (22-1800 mg/kg) or via diet (0.09 % PBO in chow). Serum and adipose samples were collected, and PBO concentrations were determined by HPLC-MS/MS. The serum concentrations of PBO were best fit by a linear one-compartment model. PBO concentrations in visceral adipose tissue greatly exceeded those in serum. PBO concentrations in both serum and adipose tissue decreased quickly after cessation of dietary exposure. The elimination half-life of PBO in the mouse after gavage dosing was 6.5 h (90 % CI 4.7-9.5 h), and systemic oral clearance was 83.3 ± 20.5 mL/h. The bioavailability of PBO in chow was 41 % that of PBO delivered in olive oil by gavage. Establishment of this PK model provides a foundation for relating PBO concentrations that cause developmental toxicity in the rodent models to Sonic hedgehog signaling pathway inhibition.

Single-Dose Psilocybin Treatment for Major Depressive Disorder: A Randomized Clinical Trial

Importance

Psilocybin shows promise as a treatment for major depressive disorder (MDD).

Objective

To evaluate the magnitude, timing, and durability of antidepressant effects and safety of a single dose of psilocybin in patients with MDD.

Design, Setting, and Participants

In this phase 2 trial conducted between December 2019 and June 2022 at 11 research sites in the US, participants were randomized in a 1:1 ratio to receive a single dose of psilocybin vs niacin placebo administered with psychological support. Participants were adults aged 21 to 65 years with a Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition diagnosis of MDD of at least 60 days' duration and moderate or greater symptom severity. Exclusion criteria included history of psychosis or mania, active substance use disorder, and active suicidal ideation with intent. Participants taking psychotropic agents who otherwise met inclusion/exclusion criteria were eligible following medication taper. Primary and secondary outcomes and adverse events (AEs) were assessed at baseline (conducted within 7 days before dosing) and at 2, 8, 15, 29, and 43 days after dosing.

Interventions

Interventions were a 25-mg dose of synthetic psilocybin or a 100-mg dose of niacin in identical-appearing capsules, each administered with psychological support.

Main Outcomes and Measures

The primary outcome was change in central rater-assessed Montgomery-Asberg Depression Rating Scale (MADRS) score (range, 0-60; higher scores indicate more severe depression) from baseline to day 43. The key secondary outcome measure was change in MADRS score from baseline to day 8. Other secondary outcomes were change in Sheehan Disability Scale score from baseline to day 43 and MADRS-defined sustained response and remission. Participants, study site personnel, study sponsor, outcome assessors (raters), and statisticians were blinded to treatment assignment.

Results

A total of 104 participants (mean [SD] age, 41.1 [11.3] years; 52 [50%] women) were randomized (51 to the psilocybin group and 53 to the niacin group). Psilocybin treatment was associated with significantly reduced MADRS scores compared with niacin from baseline to day 43 (mean difference,-12.3 [95% CI, -17.5 to -7.2]; P <.001) and from baseline to day 8 (mean difference, -12.0 [95% CI, -16.6 to -7.4]; P < .001). Psilocybin treatment was also associated with significantly reduced Sheehan Disability Scale scores compared with niacin (mean difference, -2.31 [95% CI, 3.50-1.11]; P < .001) from baseline to day 43. More participants receiving psilocybin had sustained response (but not remission) than those receiving niacin. There were no serious treatment-emergent AEs; however, psilocybin treatment was associated with a higher rate of overall AEs and a higher rate of severe AEs.

Conclusions and Relevance

Psilocybin treatment was associated with a clinically significant sustained reduction in depressive symptoms and functional disability, without serious adverse events. These findings add to increasing evidence that psilocybin-when administered with psychological support-may hold promise as a novel intervention for MDD.

Trial Registration

ClinicalTrials.gov Identifier: NCT03866174.

Clinical utility of a regional precision medicine molecular tumor board and challenges to implementation

Purpose

Molecular tumor boards provide precision treatment recommendations based on cancer genomic profile. However, practical barriers limit their benefits. We studied the clinical utility of the precision medicine molecular tumor board (PMMTB) and described challenges with PMMTB implementation.

Methods

An observational cohort study included patients reviewed by the PMMTB between September 2015 to December 2017. Patients who had consented to the registry study were included. The primary endpoint of this study was time on treatment (ToT) ratio. Clinical utility was established if the primary endpoint had least 15% of patients achieving a ToT ratio of ≥1.3.

Results

Overall, 278 patients were presented to the PMMTB and 113 cases were included in the final analysis. The PMMTB identified at least one nonstandard of care (SOC) clinically actionable mutation for 69.0% (78/113) of cases. In patients who received non-SOC treatment, 43.8% (7/16) achieved a ToT ratio of 1.3 or more (p < 0.001). Fifty-nine patients did not receive non-SOC recommendations. Reasons for not pursuing treatment included 35.6% having response to current treatment, 20.3% died prior to starting or considering PMMTB recommendations, 13.6% pursued other treatment options based on clinician discretion, another 10.2% pursued other treatment options because clinical trials recommended were not geographically accessible, 8.5% had rapid decline of performance status, 6.8% lacked of financial support for treatment, and 5.1% were excluded from clinical trials due to abnormal laboratory values.

Conclusion

The regional PMMTB non-SOC recommendations benefitted a majority of patients and additional processes were implemented to assist with non-SOC treatment accessibility.

A Phase 1 and pharmacokinetic study evaluating daily or weekly schedules of the humanized anti-GD2 antibody hu14.18K322A in recurrent/refractory solid tumors

Hu14.18K322A is a humanized anti-GD2 monoclonal antibody with a single point mutation that reduces complement-mediated cytotoxicity, with a maximum tolerated dose (MTD) of 60 mg/m² daily for 4 days in children with recurrent/refractory neuroblastoma. We report additional results of a Phase 1 trial to determine the MTD and safety profile of hu14.18K322A in patients with osteosarcoma, and of an alternative schedule of weekly hu14.18K322A administration in patients with neuroblastoma or osteosarcoma. Eligible patients with recurrent/refractory osteosarcoma received hu14.13K22A daily x4 every 28 days in a Phase 1 traditional 3 + 3 dose escalation design. Additional patients with osteosarcoma were then enrolled to receive hu14.18K322A once weekly for 4 weeks per course. Patients with recurrent/refractory neuroblastoma were also enrolled on the weekly schedule at 50 mg/m²/dose. Six patients with osteosarcoma treated on the daily schedule received a median of 2 (range 1-6) courses; the recommended daily dose was established as 60 mg/m². Three patients had stable disease (SD) as best overall response. Five patients (3 neuroblastoma, 2 osteosarcoma) enrolled on the weekly schedule received a median of 1 (1-3) course; 2 achieved SD as best overall response. Pain, fever, hematologic toxicities, hyponatremia, and ocular/visual abnormalities were common toxicities among both schedules. Dose-limiting toxicities attributed to hu14.18K322A included anorexia and fatigue (n = 1). Pharmacokinetic profiles were similar between daily and weekly schedules. The recommended dose for patients with osteosarcoma receiving daily hu14.18K322A x4 is 60 mg/m². Patients receiving the weekly schedule experienced similar pharmacokinetics and toxicity profile as the daily schedule.

Phase II study of antidisialoganglioside antibody, dinutuximab, in combination with GM-CSF in patients with recurrent osteosarcoma (AOST1421): A report from the Children’s Oncology Group

10508

Background: Treatment of patients with recurrent osteosarcoma (OS) is challenging and novel effective therapies are urgently needed. This study evaluated disease control rate (DCR) in patients with recurrent pulmonary OS, when treated with dinutuximab plus cytokine therapy as compared to a historical benchmark. The rationale for dinutuximab was the ubiquitous ( > 95%) GD2 positivity in OS tumors and cell lines. Methods: AOST1421 was a single-arm phase 2 study. Patients with recurrent pulmonary OS in complete surgical remission were eligible. Patients received five cycles of dinutuximab 70mg/m2/cycle with GM-CSF. Two different dinutuximab infusion schedules were used - 35mg/m2/day over 20 hours (2-day) and 17.5mg/m2/day over 10 hours (4-day) schedule. Primary end point was DCR, defined as proportion of patients event-free at 12 months from enrollment. Events were progressive disease or death within 12 months attributed to treatment or progression. The historical benchmark was AOST0221 with a 12-month DCR of 20% (95% CI 10-34%). Success was defined as ≥16/ 39 patients ( > 40%) event-free at 12 months from enrollment. Secondary objectives included toxicity evaluation and dinutuximab pharmacokinetics (PK). Results: Forty-one patients were enrolled from Nov 2015 - Jan 2018. Thirty nine were eligible and evaluable (age 7-26 yr; median 15 yr). Data current to December 31, 2019 was used for analysis. Accrual rate was higher than expected (22.1 vs. 19.2 patients/ yr.) despite a concurrently open competing study. One of 136 administered therapy cycles met criteria for unacceptable toxicity when one patient receiving the 2-day schedule died after cycle 2 due to an unknown cause, attributed as probably related to protocol therapy. The protocol was revised to allow only the 4-day schedule. Other ≥ Grade 3 toxicities occurring in > 10 % participants were expected dinutuximab toxicities such as pain, diarrhea, hypoxia and hypotension. Dinutuximab did not demonstrate sufficient evidence of efficacy as 27/ 39 patients experienced an event for a DCR of 30.7% (95% CI 17- 47%). PK studies are pending and will be reported. Conclusions: Dinutuximab toxicity in adolescent and young adult OS patients was similar to younger patients. While GD2 remains a relevant target in OS, combination of dinutuximab with GM-CSF did not meet the targeted successful DCR in patients with completely resected tumor. Other strategies for targeting GD2 or dinituximab combination therapy may still be warranted. Clinical trial information: NCT02484443.

Exposure-Response Analysis to Assess the Concentration-QTc Relationship of Psilocybin/Psilocin

Psilocybin is being developed for treating major depressive disorder. Psilocybin is readily dephosphorylated to psilocin upon absorption. The potential for psilocin proarrhythmic effect was assessed using a concentration-QTc interval (C-QTc) analysis from an open-label single ascending dose study of psilocybin. Psilocybin doses ranged from 0.3 to 0.6 mg/kg. This trial showed a significant but shallow C-QTc relationship. At the clinical dose of 25 mg, the mean psilocin maximum concentration is 18.7 ng/mL, and the associated mean (upper 90% confidence interval of mean) QTcF change is 2.1 (6.6) milliseconds. Given the short half-life of psilocin of about 4 hours, there would be no accumulation after monthly oral doses used in clinical trials. The upper limit of the 90% confidence interval of the model-predicted mean ΔQTcF crossed 10 milliseconds at a psilocin concentration of 31.1 ng/mL. At a supraclinical psilocin maximum concentration of about 60 ng/mL, ΔQTcF remains low, with a mean (upper limit of the 90% confidence interval) of 9.1 (17.9) milliseconds. This analysis enabled the characterization of the C-QTc relationship and prediction of QTc prolongation at the expected clinical and possible higher psilocybin doses.

High dose psilocybin is associated with positive subjective effects in healthy volunteers

AIM

The aim of the current study was to investigate the relationship between escalating higher doses of psilocybin and the potential psilocybin occasioned positive subjective effects.

METHODS

Healthy participants ( n=12) were given three escalating doses of oral psilocybin (0.3 mg/kg; 0.45 mg/kg; 0.6 mg/kg) or (18.8-36.6 mg; 27.1-54.0 mg; 36.3-59.2 mg) a minimum of four weeks apart in a supervised setting. Blood and urine samples, vital signs, and electrocardiograms were obtained. Subjective effects were assessed using the Mystical Experience Questionnaire and Persisting Effects Questionnaire.

RESULTS

There was a significant linear dose-related response in Mystical Experience Questionnaire total score and the transcendence of time and space subscale, but not in the rate of a complete mystical experience. There was also a significant difference between dose 3 compared to dose 1 on the transcendence of time and space subscale, while no dose-related differences were found for Mystical Experience Questionnaire total scores or rate of a mystical experience. Persisting Effects Questionnaire positive composite scores 30 days after completion of the last dose were significantly higher than negative composite scores. Persisting Effects Questionnaire results revealed a moderate increase in sense of well-being or life satisfaction on average that was associated with the maximum Mystical Experience Questionnaire total score. Pharmacokinetic measures were associated with dose but not with Mystical Experience Questionnaire total scores or rate of a mystical experience.

CONCLUSIONS

High doses of psilocybin elicited subjective effects at least as strong as the lower doses and resulted in positive persisting subjective effects 30 days after, indicating that a complete mystical experience was not a prerequisite for positive outcomes.

Compatibility of cefepime and vancomycin during simulated Y-site administration of prolonged infusion

PURPOSE

The physical and chemical compatibility of cefepime and vancomycin at concentrations typically used in prolonged-infusion cefepime infusions was assessed.

METHODS

Samples from a typical Y-site configuration of standard-infusion vancomycin and prolonged-infusion cefepime were collected at various time points during the simulated 4-hour infusion. Samples were analyzed by visual inspection, spectrophotometry, and high-performance liquid chromatography (HPLC). Infusion antibiotics were reconstituted in pairwise combinations of 0.9% sodium chloride injection and 5% dextrose injection to determine the effects of solvent selection on stability. Infusion simulations were performed in triplicate without light protection under fluorescent lighting at room temperature (22.5 °C). Experimental replicates were not run simultaneously but on sequential days due to the considerable time (~12 hours) required to analyze samples obtained from a single infusion simulation and the known time-dependent instability of reconstituted cefepime beyond 24 hours. Physical stability was assessed visually for evidence of particulate formation, haze, precipitation, color change, and gas evolution. Samples were also assessed spectrophotometrically at 600 nm at the time of collection and 24 hours after collection.

RESULTS

Cefepime was compatible with vancomycin at the concentrations tested. The solvent selected (0.9% sodium chloride or 5% dextrose) to reconstitute either antibiotic had no impact on compatibility. Solutions were indistinguishable from positive and negative controls (heat-degraded cefepime and freshly reconstituted cefepime, respectively) at all time points assessed in terms of visual clarity, spectrophotometric absorbance, and HPLC recovery.

CONCLUSION

Cefepime and vancomycin were physically and chemically compatible during simulated Y-site administration of prolonged-infusion cefepime.

Resolution of chronic bacterial-induced prostatic inflammation reverses established fibrosis

BACKGROUND

Prostatic inflammation has been suggested to contribute to the etiology of lower urinary tract symptoms by inducing fibrosis. We previously used a well-characterized mouse model of bacterial-induced prostate inflammation to demonstrate that chronic prostatic inflammation induces collagen deposition. Here, we examined stability of the newly synthesized collagen in bacterial-induced prostatic inflammation and the reversibility of fibrosis after resolution of infection and inflammation.

METHODS

Uropathogenic Escherichia coli 1677 was instilled transurethrally into adult C3H/HeOuJ male mice to induce chronic prostatic inflammation. Collagen was labeled by (3) H-proline administration for 28 days post-inoculation and (3) H-hydroxyproline incorporation measured to determine stability of the newly synthesized collagen. Inflammation score was graded using a previously established system and total collagen content was measured by picrosirius red staining quantitation and hydroxyproline content. Resolution of inflammation and reversal of collagen deposition was assessed after treatment with antibiotic enrofloxacin for 2 weeks on day 28 post-inoculation followed by an 8-week recovery period.

RESULTS

Decay analysis of incorporated (3) H-hydroxyproline revealed the half-life of newly synthesized collagen to be significantly shorter in infected/inflamed prostates than in controls. Treatment with antibiotic enrofloxacin completely eradicated bacterial infection and allowed resolution of inflammation. This was followed by marked attenuation of collagen content and correlation analysis verified a positive association between the resolution of inflammation and the reversal of collagen deposition.

CONCLUSIONS

These data demonstrate, for the first time, that inflammation-induced prostatic fibrosis is a reversible process.

Prostatic inflammation induces fibrosis in a mouse model of chronic bacterial infection

Inflammation of the prostate is strongly correlated with development of lower urinary tract symptoms and several studies have implicated prostatic fibrosis in the pathogenesis of bladder outlet obstruction. It has been postulated that inflammation induces prostatic fibrosis but this relationship has never been tested. Here, we characterized the fibrotic response to inflammation in a mouse model of chronic bacterial-induced prostatic inflammation. Transurethral instillation of the uropathogenic E. coli into C3H/HeOuJ male mice induced persistent prostatic inflammation followed by a significant increase in collagen deposition and hydroxyproline content. This fibrotic response to inflammation was accompanied with an increase in collagen synthesis determined by the incorporation of ³H-hydroxyproline and mRNA expression of several collagen remodeling-associated genes, including Col1a1, Col1a2, Col3a1, Mmp2, Mmp9, and Lox. Correlation analysis revealed a positive correlation of inflammation severity with collagen deposition and immunohistochemical staining revealed that CD45+VIM+ fibrocytes were abundant in inflamed prostates at the time point coinciding with increased collagen synthesis. Furthermore, flow cytometric analysis demonstrated an increased percentage of these CD45+VIM+ fibrocytes among collagen type I expressing cells. These data show–for the first time–that chronic prostatic inflammation induces collagen deposition and implicates fibrocytes in the fibrotic process.

Addition of ceftaroline to daptomycin after emergence of daptomycin-nonsusceptible Staphylococcus aureus during therapy improves antibacterial activity

Antistaphylococcal beta-lactams enhance daptomycin activity and have been used successfully in combination for refractory methicillin-resistant Staphylococcus aureus (MRSA) infections. Ceftaroline possesses MRSA activity, but it is unknown if it improves the daptomycin potency comparably to other beta-lactams. We report a complex patient case of endocarditis who was treated with daptomycin in combination with ceftaroline, which resulted in clearance of a daptomycin-nonsusceptible strain. An in vitro pharmacokinetic/pharmacodynamic model of renal failure was used to simulate the development of daptomycin resistance and evaluate the microbiologic effects of daptomycin plus ceftaroline treatment. Combination therapy with daptomycin and ceftaroline restored daptomycin sensitivity in vivo and resulted in clearance of persistent blood cultures. Daptomycin susceptibility in vitro was increased in the presence of either ceftaroline or oxacillin. Daptomycin at 6 mg/kg of body weight every 48 h was bactericidal in the model but resulted in regrowth and daptomycin resistance (MIC, 2 to 4 μg/ml) with continued monotherapy. The addition of ceftaroline at 200 mg every 12 h after the emergence of daptomycin resistance enhanced bacterial killing. Importantly, daptomycin plus ceftaroline as the initial combination therapy produced rapid and sustained bactericidal activity and prevented daptomycin resistance. Both in vivo- and in vitro-derived daptomycin resistance resulted in bacteria with more fluid cell membranes. After ceftaroline was added in the model, fluidity was restored to the level of the initial in vivo isolate. Daptomycin-resistant isolates required high daptomycin exposures (at least 10 mg/kg) to optimize cell membrane damage with daptomycin alone. Ceftaroline combined with daptomycin was effective in eliminating daptomycin-resistant MRSA, and these results further justify the potential use of daptomycin plus beta-lactam therapy for these refractory infections.

3, 4-Didehydroretinol kinetics differ during lactation in sows on a retinol depletion regimen and the serum:milk 3, 4-didehydroretinol:retinol ratios are correlated

3, 4-Didehydroretinol (DR) metabolism was previously followed in vitamin A (VA)-replete lactating sows. This study followed DR appearance and clearance after dosage in serum and milk during 2 lactation cycles in sows (n = 8) fed VA-free feed for 3 gestation-lactation cycles. During lactations 2 and 3, 35 μmol 3, 4-didehydroretinyl acetate was given orally after overnight food deprivation. Blood and milk were collected at 0, 1.5, 3, 5, 7, 9, 16, 24, 36, 48, 60, and 72 h; livers were obtained at kill. Samples were analyzed for DR, retinol (R), and 3, 4-didehydroretinyl esters. During lactations 2 and 3, the 5-h serum DR:R ratios were 0.028 ± 0.017 and 0.069 ± 0.042, respectively, and serum R concentrations were 0.75 ± 0.23 and 0.86 ± 0.37 μmol/L, respectively. The DR:R ratio and serum R were 0.018 ± 0.013 and 0.94 ± 0.12 μmol/L, respectively, in VA-replete sows from the same herd. After lactation 3, liver VA was 0.23 ± 0.05 μmol/g, indicating low-normal VA status. Serum DR area-under-the curve from 0 to 48 h increased as liver stores decreased. Thirteen to 23% of DR dose was secreted into milk, consistent with VA-replete sows. Milk DR concentrations were greater during lactation 3 than 2. Peak concentration occurred earlier and the half-life was shorter for milk DR in the more VA-depleted sows. The milk and serum DR:R were correlated from 3 to 9 h (r = 0.70; P < 0.0001) and increased as VA stores decreased regardless of serum R concentration. Milk DR:R may replace serum measurements during lactation.

Pharmacodynamic effect of clinical vancomycin exposures on cell wall thickness in heterogeneous vancomycin-intermediate Staphylococcus aureus

OBJECTIVES

Heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) have a higher predisposition to select for VISA with thickened cell walls upon vancomycin exposure, but the pharmacodynamic relationship of this occurrence with clinical doses is unknown. This study investigates the impact of clinical vancomycin dose simulations on cell wall thickness (CWT) and the emergence of resistance in hVISA in an in vitro pharmacodynamic model.

METHODS

In an in vitro pharmacokinetic/pharmacodynamic model, we simulated 125-2000 mg of vancomycin every 12 h (ƒAUC/MIC 24-225) over a 72 h period against three clinical hVISA and two standard control S. aureus strains. Pharmacodynamic activity, susceptibility and resistance populations were assessed, and CWT was determined at the end of the exposure.

RESULTS

Bactericidal activity occurred in hVISA only with vancomycin ƒAUC/MIC ≥ 164 exposures, but regrowth occurred after 24 h, regardless of initial activity. Following vancomycin exposure, CWT correlated with MIC increases (r = 0.66; P  < 0.0001). A significant increase in CWT occurred in hVISA with any vancomycin simulation, including the high-dose ƒAUC/MIC 225 regimen (24.4% increase in hVISA versus 3.3% with control; P < 0.001). Any vancomycin exposure in two of the three hVISA strains resulted in isolates with MICs ≥ 3 mg/L and as high as 8 mg/L, which corresponded with a more resistant VISA population profile.

CONCLUSIONS

High-dose vancomycin exposures in hVISA cannot prevent cell wall thickening, but prudent therapeutic strategies including treatment doses ≥ 1500 mg every 12 h (AUC/MIC ≥ 364) in conjunction with avoidance of long-term vancomycin exposure may avert further reduced susceptibility.

Effect of acetyl-l-carnitine on ovarian cancer cells' proliferation, nerve growth factor receptor (Trk-A and p75) expression, and the cytotoxic potential of paclitaxel and carboplatin

OBJECTIVES

The incidence of chemotherapy induced peripheral neuropathy (CIPN) is 15-25% with platinum and taxanes. CIPN can be permanent and often requires dose reduction or change in chemotherapy. Acetyl-l-carnitine (ALCAR), an ester of l-carnitine, is used to treat CIPN in humans and in animal models. The goals of this study are: 1) examine the effects of ALCAR on ovarian cancer cells, 2) determine if ALCAR affects the cytotoxicity of standard chemotherapy on ovarian cancer cells.

METHODS

OVCAR-3 and SKOV-3 ovarian cancer lines were incubated in ALCAR containing media. Viability, proliferation, and expression of the nerve growth factor receptors (NGFR) Trk-A and p-75 were determined by flow cytometry. Cytotoxicity assays examining ALCAR's effect on paclitaxel and carboplatin were done by flow cytometry and infrared plate-reader.

RESULTS

Flow cytometry showed no change in percent live (p = 0.87) or proliferation (p = 0.95) of OVCAR-3 cells when comparing controls with up to 100 microM ALCAR. However, there was a slight but significant decrease in the proliferation of SKOV-3 cells incubated at higher ALCAR concentrations (p = < 0.01). Flow cytometry showed no difference in the viability of OVCAR-3 cells when comparing ALCAR: +/- paclitaxel (p = 1), +/- carboplatin (p = 0.8), or both (p = 0.4). Proliferation assays indicated that paclitaxel's cytotoxicity on OVCAR-3 and SKOV-3 cells was unchanged at higher ALCAR concentrations (p = < 0.01-0.4). ALCAR did not affect the expression of NGFR on OVCAR-3 or SKOV-3 cells.

CONCLUSION

ALCAR does not affect the cytotoxicity of paclitaxel or carboplatin. There was no increase in proliferation, or NGFR of OVCAR-3 or SKOV-3 cells exposed to ALCAR.

Dose- and route-dependent teratogenicity, toxicity, and pharmacokinetic profiles of the hedgehog signaling antagonist cyclopamine in the mouse

The Hedgehog (Hh) signaling pathway is an essential regulator of embryonic development and appears to play important roles in postnatal repair and cancer progression and metastasis. The teratogenic Veratrum alkaloid cyclopamine is a potent Hh antagonist and is used experimentally both in vitro and in vivo to investigate the role of Hh signaling in diverse biological processes. Here, we set out to establish an administration regimen for cyclopamine-induced teratogenicity in the mouse. The dysmorphogenic concentration of cyclopamine was determined in vitro via mouse whole-embryo culture assays to be 2.0 microM. We administered cyclopamine to female C57BL/6J mice at varied doses by oral gavage, ip injection, or osmotic pump infusion and assessed toxicity and pharmacokinetic (PK) models. Bolus administration was limited by toxicity and rapid clearance. In vivo cyclopamine infusion at 160 mg/kg/day yielded a dam serum steady-state concentration of approximately 2 microM with a corresponding amniotic fluid concentration of approximately 1.5 microM. Gross facial defects were induced in 30% of cyclopamine-exposed litters, with affected embryos exhibiting cleft lip and palate. This is the first report describing the PKs and teratogenic potential of cyclopamine in the mouse and demonstrates that transient Hh signaling inhibition induces facial clefting anomalies in the mouse that mimic common human birth defects.

Effect of medical castration on CYP3A4 enzyme activity using the erythromycin breath test

PURPOSE

Testosterone administration can lead to increased antipyrine clearance in humans. Medical or surgical castration is a standard treatment of progressive prostate carcinoma, but the effect of the subsequent fall of testosterone concentrations upon drug metabolism has not been reported.

METHODS

Eleven men with a biopsy-proven diagnosis of progressive prostate cancer were enrolled after providing informed consent. CYP3A4 activity was determined using the erythromycin breath test (EBT) in each patient prior to their beginning with an LHRH-agonist (leuprolide or goserelin). No patients had elected to undergo orchiectomy during the period of subject accrual. Each subject underwent a second EBT 2 months after beginning LHRH suppression. Blood samples were collected at these time points to determine changes in testosterone and leutinizing hormone.

RESULTS

All subjects had a predictable drop in serum testosterone concentrations over the 8-week course of the study, but concentrations in three did not fall below castrate levels (<50 ng/dl). There was no statistically significant change in CYP3A4 activity using the EBT method (p = 0.88). The extent and direction of changes in CYP3A4 activity was highly variable, with three subjects experiencing an increase in activity, and five demonstrating a decrease in activity.

CONCLUSION

There is no clinically significant change in CYP3A4 activity after medical castration. No changes in the clearance of docetaxel or other CYP3A4 substrates are likely during and after medical castration. Although similar findings are expected after orchiectomy, we were not able to test this presumption because of patient preference for medical castration.

A randomized, double-masked, placebo-controlled pilot trial of extended IV lidocaine infusion for relief of ongoing neuropathic pain

OBJECTIVES

To determine the dose-response effect and safety of IV lidocaine at different dose infusion rates on spontaneous ongoing neuropathic pain.

METHODS

In this double-masked, placebo-controlled, parallel study conducted in an outpatient clinical research center, patients with peripheral neuropathic pain received a 6-hour infusion of three doses (1, 3, and 5 mg/kg) of lidocaine or placebo. The main outcome measure was relief of pain intensity (percentage pain intensity difference [PID %]). Other measures were responder rate, adverse events, and correlation between lidocaine levels and PID %.

RESULTS

There was a significant difference in the median PID % between the group treated with lidocaine 5 mg/kg/h (-34.60) and the placebo group (-11.96, P=0.012). Such effect began 4 hours after the onset of treatment and lasted until the end of the study. Lidocaine at lower infusion rates was no better than placebo in relieving pain. A modest but significant correlation was found between methylethylglycinexylidide (MEGX) levels and pain relief (R=0.60). There were no serious adverse events, but in two patients lidocaine was stopped prematurely.

CONCLUSIONS

Lidocaine at 5 mg/kg/h was more effective than placebo at relieving neuropathic pain. The effect started 4 hours after the onset of treatment and continued for at least 4 hours after the end of the infusion. Additional research is needed using higher infusion rates with larger sample sizes to confirm these results and to explore the role of MEGX in the relief of neuropathic pain.

Effect of exemestane on tamoxifen pharmacokinetics in postmenopausal women treated for breast cancer

PURPOSE

Rodent models of human breast cancer suggest that the combination of the steroidal aromatase inhibitor exemestane with tamoxifen may have additive activity. Clinical trials combining tamoxifen with letrozole or anastrazole have shown minor pharmacokinetic drug interactions. We did an open-label crossover clinical trial of the effect of exemestane on tamoxifen pharmacokinetics.

DESIGN

Thirty-two postmenopausal women who were clinically disease-free following primary treatments for breast cancer receiving tamoxifen for at least 3 months were studied. Blood was collected for pharmacokinetic analysis after at least 4 months of receiving 20 mg tamoxifen daily. Subjects then began 8 weeks of oral exemestane (25 mg daily), followed by another set of blood samples.

RESULTS

There were no serious toxicities noted when the two drugs were combined. There was no significant effect of exemestane on the area under the plasma concentration versus time curve (AUC) of tamoxifen at steady state before [3.04 mg h/L; 90% confidence interval (90% CI), 2.71-3.44] and during exemestane treatment (3.05 mg h/L; 90% CI, 2.72-3.41). There were no significant changes in the formation of primary tamoxifen metabolites. Oral clearance of exemestane averaged 602 L/h based on an average plasma exemestane AUC of 41.5 microg h/L (90% CI, 36.7-62.6). Plasma concentrations of estradiol, estrone, and estrone sulfate decreased when exemestane was begun; estradiol concentrations consistently decreased below the limit of quantitation.

CONCLUSIONS

There is no pharmacokinetic interaction between tamoxifen and exemestane. No modification in the standard regimen of either drug seems to be indicated if they are used in combination. The combination of the two drugs was well tolerated during the 8-week evaluation period.

Endocrine Effects of Tamoxifen Plus Exemestane in Postmenopausal Women with Breast Cancer: Table 1

PURPOSE

In some specific circumstances, combined hormonal therapies for breast cancer seem to be more effective than single maneuvers. In two laboratory mammary cancer models, the combination of the aromatase inactivator exemestane plus tamoxifen gives a higher response rate than is found with either agent alone. To evaluate the endocrine effects of the combination of exemestane and tamoxifen, we studied 33 postmenopausal women disease-free following primary treatments for breast cancer who were taking tamoxifen for at least 3 months.

DESIGN

After observation for symptoms on tamoxifen for 4 weeks, blood samples were taken and patients were begun additionally on exemestane 25 mg p.o. qd. Eight weeks later, blood samples were again taken, and exemestane was discontinued.

RESULTS

A decrease in alkaline phosphatase was found with exemestane treatment (P = 0.06), whereas no change in osteocalcin level was observed. A decrease in high-density lipoprotein cholesterol level was found (P = 0.0025), whereas total cholesterol, low-density lipoprotein cholesterol and triglyceride levels showed no changes with exemestane treatment. Estradiol, estrone, and estrone sulfate levels decreased to immeasurable or very low levels with exemestane treatment (all P < 0.001). No significant changes in frequencies of common drug-associated side effects, such as vasomotor symptoms or weight change, were found.

CONCLUSIONS

Based on the absence of adverse endocrine effects with the addition of exemestane to tamoxifen therapy observed in this study, further clinical evaluation of the efficacy of this combination is warranted.

Liquid chromatographic determination of hydroxyproline in tissue samples

We describe a reversed-phase assay of hydroxyproline in rat lung tissue using sarcosine for the internal standard and pre-injection reaction with both o-phthalaldehyde (OPA) and 9-fluorenylmethylchloroformate (FMOC). Intra-assay variability in the concentration range of 25-500 microM hydroxyproline was less than 1%. Normal rat (left) lung was found to have a hydroxyproline content of 1.08+/-0.18 mg/lung. This ability to measure minute amounts of hydroxyproline is being applied to the measure of collagen and pathological fibrosis.

Population pharmacokinetic and adverse event analysis of topotecan in patients with solid tumors

OBJECTIVE

Our objective was to describe the pharmacokinetics and pharmacodynamics of topotecan in patients.

METHODS

Data were pooled from 9 clinical trials. Topotecan, as a single-agent therapy, was administered as a daily 30-minute intravenous infusion for 5 days on a 3-week cycle. Doses of 0.2 to 2.0 mg/m(2) were studied; concentration and neutropenic event data were obtained on multiple occasions. The pharmacokinetics were characterized with use of hierarchical nonlinear regression. The relationship between severity of neutropenia and exposure was characterized with use of logistic regression.

RESULTS

The pharmacokinetics of topotecan were described with a linear 2-compartment model. Compromised renal function, low body weight, and poor Eastern Cooperative Oncology Group performance status were determinants of lower clearance, resulting in elevated exposure. Application of covariates reduced interpatient variability in clearance. Logistic regression showed that topotecan area under the concentration-time curve from 0 to 24 hours was predictive of the severity of neutropenia; the only other significant covariate was the number of courses of previous treatment with platinum-based regimens.

CONCLUSIONS

Patients with compromised renal function, low body weight, or poor performance status had low topotecan clearance. Patients with high topotecan AUC had an increased probability of experiencing severe neutropenia, which was greater if the patient had been pretreated with platinum-based agents. The use of covariates to individualize dose would result in less variability in exposure, reducing the likelihood of severe neutropenia and potentially improving treatment benefit.

Methotrexate sequestration in an ovarian cyst

OBJECTIVE

Methotrexate has been documented to accumulate in pleural effusions and ascitic fluid, resulting in severe local and systemic toxicity. In the following case report, we publish results of intraoperative measurements of methotrexate levels in serum and an ovarian cyst and attempt to determine if ovarian cysts similarly act as a depot for methotrexate.

METHODS

After determining intraoperative measurements of serum and ovarian cystic levels of methotrexate, we compared demonstrated pharmacokinetics to those expected by using pharmacokinetic systems analysis software.

RESULTS

Intraoperative measurement of methotrexate levels on day 3 of a 5-day methotrexate regimen revealed a serum methotrexate concentration of 1.6 x 10(-7) M and a concentration of 3.1 x 10(-7) M within the 166.4 ml ovarian cyst.

CONCLUSIONS

The measured levels demonstrate that methotrexate is sequestered within an ovarian cyst resulting in higher local drug levels. Our pharmacokinetic analysis suggests that methotrexate doses less than 100 mg/m2 can be safely administered to patients with small ovarian cysts. However, computed simulations support the possibility of local and systemic toxicity arising from large ovarian cysts when using high doses of methotrexate.

Renal clearance, tissue distribution, and CA-125 responses in a phase I trial of suramin

Suramin was administered to 49 patients in a Phase I cancer trial with real-time pharmacokinetic monitoring and dose individualization to achieve targeted mean plasma concentrations of 210 and 155 mg/liter during the 7-day period between days 15 and 22. Pharmacokinetic sampling after doses on days 1, 3, 5, and 8 was used to modify weekly suramin doses, beginning on day 15, in an attempt to achieve specific averaged plasma concentrations of 210 and 155 mg/liter. A 200-mg test dose was not effective in prospectively determining individual pharmacokinetic parameters and dosage requirements. Patients with peak plasma suramin concentrations in excess of 350 mg/liter may be more likely to experience neurotoxicity (P = 0.06), but there was no statistically significant effect of peak suramin concentration or of cumulative dose. Biopsy and autopsy tissue samples demonstrated low penetration of suramin into brain tissue and muscle but good penetration into prostate and other visceral organs. Prospective use of surrogate substrates for CYP1A2, CYP3A3/4, and CYP2D6 showed no consistent effect of suramin on these enzymes. Although a correlation between creatinine clearance and suramin renal clearance was found (r2 = 0.38; P < 0.00005), there was no correlation between creatinine clearance and total suramin clearance (P = 0.21). No suramin dose modification for renal or hepatic dysfunction can be supported at this time. Three of four ovarian cancer patients demonstrated a drop in CA-125 serum concentrations during suramin treatment.

Meperidine attenuates the secretion but not the transcription of interleukin 1 beta in human mononuclear leukocytes

BACKGROUND

The infusion of amphotericin-B (AmB) often produces clinically distressing rigors and chills, which promptly abate with intravenous injection of meperidine, although its mechanism of action is unknown.

OBJECTIVE

To examine the effects of meperidine on the transcription or secretion of Interleukin 1 beta (IL-1 beta) in human mononuclear leukocytes (MNL) exposed in vitro to the lipopolysaccharide (LPS) contained in Escherichia coli endotoxin or to AmB.

METHODS

Blood was drawn from eight healthy adult volunteers. The blood was centrifuged, and the layer containing MNL was separated; incubated with various combinations of medium, meperidine, and AmB; then tested for IL-1 content to determine the effect of meperidine on MNL secretion of IL-1 beta. To determine the effect on MNL transcription of IL-1 beta, the RNA was extracted from cells and the IL-1 beta was measured using one of two different methods.

RESULTS

Incubation of human MNL in the presence of LPS or AmB significantly increased transcription of IL-1 beta mRNA and secretion of IL-1 beta. Addition of meperidine to these cultures significantly reduced LPS-induced, but not AmB-induced, secretion of IL-1 beta in vitro. Meperidine did not alter IL-1 beta mRNA levels in MNL exposed to LPS or AmB.

CONCLUSIONS

These data suggest that meperidine decreases rigors and chills in part by decreasing MNL secretion of IL-1 beta through a posttranscriptional mechanism.

Quantitation of beta-lapachone and 3-hydroxy-beta-lapachone in human plasma samples by reversed-phase high-performance liquid chromatography

beta-Lapachone is an o-naphthoquinone found to have in vitro cytotoxicity in cancer cells, type I human immunodeficiency virus, and fungi. Analytical methods for evaluating beta-lapachone in biological fluids using high-performance liquid chromatography (HPLC) have not been published. The reversed-phase HPLC method described in this report utilizes liquid extraction of a 0.5-ml plasma sample with average recoveries of 67+/-10.8% and 70+/-10.3% for beta-lapachone and 3-hydroxy-beta-lapachone, respectively. Sensitivity of the assay using ultraviolet (UV) detection at 256 nm is 15 ng ml(-1) from a 100 microl injection. Plasma standards for beta-lapachone and 3-hydroxy-beta-lapachone are linear with no significant difference in slope between the compounds. The retention times of 2.7 min for 3-hydroxy-beta-lapachone and 5.9 min for beta-lapachone result in a clean separation permitting use of the same assay procedure without modification for both compounds. This assay offers the advantage that either beta-lapachone or 3-hydroxy-beta-lapachone can serve as the internal standard, depending on which compound is being analyzed.

Pharmacokinetics and short-term clinicopathologic changes after intravenous administration of a high dose of methimazole in dogs

A bolus dose of methimazole (MMI) was administered IV over 1 minute to 5 healthy adult dogs at a dosage (40 mg/kg of body weight) known to impart protection against cisplatin-induced renal disease. Blood and urine samples for pharmacokinetic analysis were collected over a 24-hour period. Physical examination, CBC, determination of serum thyroid hormone concentrations, and serum biochemistry analysis were performed over a 10-day period to evaluate short-term toxicoses. At this dosage, MMI appears to be safe and well tolerated in dogs; only 1 of the 5 dogs had mild and transient increases in serum activity of hepatic enzymes. In addition, MMI did not alter serum thyroid hormone concentrations. Half-life of 8.82 hours and mean residence time of 12.18 hours were determined for MMI. Renal clearance of native MMI, along with sulfate and glucuronide conjugates, represented only 20% of total systemic clearance. Results of this study provide further information concerning clinical use of MMI in dogs and may contribute to better understanding of the mechanism of MMI protection against chemically induced nephrotoxicosis.

Evidence of an absorption phase after short intravenous suramin infusions

Suramin was given as an intravenous infusion to 16 cancer patients in a phase I trial. Individual pharmacokinetic parameters were calculated from a test dose given 1 week prior to the administration of a full-dose (350-700 mg/m2) regimen of 1-h loading and maintenance infusions. A distribution phase of 3.8 h was found. Plasma suramin concentrations were noted to increase following cessation of the intravenous test infusion in eight subjects. A model is proposed in which high-capacity, low-affinity binding of suramin to a shallow compartment adjacent to the intravascular space occurs rapidly during infusion, followed by absorption back into the measured blood pool with binding to plasma albumin. Despite the observable presence of this postinfusion peak shortly after the cessation of the brief suramin infusion, the pharmacokinetics of suramin were best characterized by a traditional two-compartment model. The dose-adjusted area under the concentration-time curve (AUC) increased with dose, supporting a hypothesis of sustained absorption of suramin to vascular endothelium but also raising the possibility of dose-dependent clearance.

Meperidine attenuates the febrile response to endotoxin and interleukin-1 alpha in rats

Intravenous meperidine is commonly used to treat rigors and chills in febrile patients, though its mechanism of action is unknown. Therefore a laboratory model of pyrogen-induced fever was used to evaluate the effects of meperidine on the febrile response of rats injected with bacterial endotoxin or IL-1 alpha. Fever was measured using a computerized biotelemetry system for the continuous monitoring of body temperature. Injection of meperidine blocked the onset of fever in rats injected with endotoxin and attenuated the febrile response in rats injected with IL-1 beta. Furthermore, incubation of human mononuclear leukocytes (MNL) in the presence of meperidine significantly reduced endotoxin-induced secretion of IL-1 beta in vitro. These data suggest that meperidine decreases rigors and chills by decreasing the "set point" for fever, perhaps by reducing MNL secretion of IL-1 beta.

Intradermal carboplatin and ifosfamide extravasation in the mouse

BACKGROUND

Carboplatin and ifosfamide are new antineoplastic agents with vesicant properties that have not been determined. Vesicant activity was investigated in Balb-c mice by administering carboplatin or ifosfamide intradermally in clinically relevant concentrations.

METHODS

Carboplatin concentrations tested were 15, 10, and 1 mg/ml; those of ifosfamide were 50, 20, and 1 mg/ml. Five female mice were tested with each concentration; and five animals were used as controls and received only saline.

RESULTS

Carboplatin concentrations of 15 mg/ml and 10 mg/ml produced mean peak ulcer areas of 10 square millimeters (mm2) and 21 mm2 within 2-3 days of injection, respectively. The 1 mg/ml carboplatin injection was not associated with any ulcer formation. Ifosfamide at 50 mg/ml induced skin ulcerations in four of five mice, with maximal effect (19.6 mm2) by 1-2 days. Lower concentrations of ifosfamide produced no ulcerations. All ulcerative lesions healed completely within 21 days.

CONCLUSIONS

These results suggest that extravasation of carboplatin at concentrations of greater than or equal to 10 mg/ml or ifosfamide at concentrations of greater than or equal to 50 mg/ml is likely to cause ulcers in humans.

Levamisole in the adjuvant treatment of colon cancer

The chemistry, pharmacology, pharmacokinetics, assay methodologies, adverse effects, and dosage of levamisole are described, and the clinical studies of levamisole therapy in patients with colorectal carcinoma are reviewed. Levamisole is a synthetic, orally active agent that has antihelmintic and immunomodulatory properties. It is capable of inducing T-cell differentiation and restoring depressed effector functions of peripheral lymphocytes and phagocytes to normal. The drug is well absorbed from the gastrointestinal tract after oral administration and is extensively metabolized by the liver. Gas chromatography and high-performance liquid chromatography are the most common methods used to measure concentrations of levamisole in biologic fluids. Levamisole combined with fluorouracil has been associated with a one-third reduction in recurrence and risk of death in patients with surgically resected Dukes stage C colon cancer; this combination is now recommended as standard therapy in these patients. Uses in patients with rectal carcinoma, Dukes stage B colon cancer, metastatic colon cancer, other malignancies, or nonmalignant disorders remain investigational. Common adverse effects include nausea, abdominal pain, vomiting, diarrhea, metallic or altered taste, flulike symptoms, mood elevation, insomnia, hyperalertness, dizziness, and headache. The most serious adverse effect associated with levamisole is granulocytopenia. The FDA-approved dosage of levamisole is 50 mg orally every eight hours for three days every two weeks. Levamisole therapy is to be initiated no earlier than 7 and no later than 30 days after surgery and is to be continued for one year. Levamisole combined with fluorouracil has been associated with a one-third reduction in recurrence and risk of death in patients with resected stage C colon cancer. Further research is needed to more clearly define the mechanism of action, optimum dose and scheduling, and clinical efficacy of levamisole in treating other malignancies.

Efficacy of oral sucralfate suspension in prevention and treatment of chemotherapy-induced mucositis

The efficacy of orally administered sucralfate suspension in preventing and treating chemotherapy-induced mucositis was evaluated in a double-blind trial. Forty-eight children and adolescents with newly diagnosed acute nonlymphocytic leukemia were randomized to receive suspensions of either sucralfate or placebo orally every 6 hours during the first 10 weeks of intensive remission-induction chemotherapy. Patients given sucralfate suspension were less likely than subjects receiving placebo to acquire colonization with potentially pathogenic microorganisms: 14 (58%) of 24 versus 22 (92%) of 24, respectively (p = 0.008). However, no effect on preexisting colonization was noted. Subjective reporting of discomfort, objective scoring of the severity of mucositis, and the maximal percent of body weight lost during therapy were similar; 58% of patients receiving sucralfate reported no oral pain compared with 25% receiving placebo (p = 0.06). Ten episodes of gastrointestinal bleeding, 25 documented infections, and 886 days with fever were also equally distributed between sucralfate and placebo groups. We conclude that sucralfate suspension is of limited, if any efficacy, in the prevention and treatment of chemotherapy-induced mucositis. Sucralfate administration can, however, reduce acquisition of alimentary colonization with potential pathogens, perhaps by interfering with adherence to mucosal membranes.

Methotrexate cerebrospinal fluid and serum concentrations after intermediate-dose methotrexate infusion

Twenty-nine children with acute lymphocytic leukemia were given 24-hr infusions of intermediate-dose methotrexate (MTX, 1000 mg/m2) with and without intrathecal (IT) MTX (12 mg/m2), followed by leucovorin rescue. There was substantial interpatient variability in MTX systemic clearance (98.3 +/- 51 ml/min/m2), inducing total steady-state serum MTX concentrations ranging from 5.4 to 33.7 microM. The cerebrospinal fluid (CSF) concentration at the end of the infusion was 0.27 (+/- 0.1) microM when no IT-MTX was given and correlated with total steady-state (24-hr) serum concentration of MTX. By stepwise regression, the CSF MTX concentration correlated better with the nonprotein bound (free) steady-state serum MTX concentration (r = 0.66, P less than 0.01) than with total steady-state serum MTX concentration. Mean CSF: serum MTX concentration ratio was 0.023 (+/- 0.04) when no IT MTX was given. When an IT MTX dose (12 mg/m2) was given at the start of the MTX infusion, the steady-state CSF MTX concentration was 1.1 (+/- 0.4) microM, leading to a mean CSF: serum ratio of 0.073 (+/- 0.05). Despite 7-hydroxy-MTX serum concentrations exceeding MTX concentrations immediately after infusion, 7-hydroxy-MTX was not detectable in CSF of most patients (21 of 29), and was less than 50% of the concurrent MTX concentration when detectable. These data establish the substantial interpatient variability in CSF distribution of MTX after intermediate-dose MTX infusions and establish a significant correlation between steady-state free concentration of MTX in serum and CSF MTX concentration.

Disposition of intermediate-dose methotrexate in children with acute lymphocytic leukemia

Intermediate-dose methotrexate (MTX 200 mg/m2 iv in a bolus dose, followed by 800 mg/m2 iv, infused over 24 hours) is being used as a component of therapy for children with acute lymphocytic leukemia. To define the extent of interpatient variability in MTX disposition, with this dosage and schedule, the systemic clearance of MTX was measured in 69 children (total doses, 717; median, 10 doses per patient). The mean (+/- SD) systemic clearance was 91.6 (+/- 25.2) ml/min/m2 and ranged from 50-161 ml/min/m2. Renal clearance was measured in 16 of these patients and averaged 50.7 (+/- 14) ml/min/m2 during the MTX infusion (0-24 h), at which time mean systemic clearance was 8.7 (+/- 19) and nonrenal clearance was 31.1 (+/- 11.8) ml/min/m2. Measurement of 7-hydroxy-methotrexate in serum and urine was consistent with the substantial amount of nonrenal (metabolic) clearance observed in these patients. Cerebrospinal fluid MTX concentrations, measured at 24 hours, were 0.26 (+/- 0.1) microM when only the intravenous MTX was given and 1.08 (+/- 0.8) microM when an intrathecal dose (12 mg/m2) was also given at the start of the 24-hour infusion. This study establishes that there is substantial interpatient variability in MTX disposition in children and suggests a possible cause of variable patient response to MTX.