MSD K.K. (Japan)

OBJECTIVE: To quantify the incidence of anemia and red blood cell (RBC) transfusion practice in critically ill patients and to examine the relationship of anemia and RBC transfusion to clinical outcomes. DESIGN: Prospective, multiple center, observational cohort study of intensive care unit (ICU) patients in the United States. Enrollment period was from August 2000 to April 2001. Patients were enrolled within 48 hrs of ICU admission. Patient follow-up was for 30 days, hospital discharge, or death, whichever occurred first. SETTING: A total of 284 ICUs (medical, surgical, or medical-surgical) in 213 hospitals participated in the study. PATIENTS: A total of 4,892 patients were enrolled in the study. MEASUREMENTS AND MAIN RESULTS: The mean hemoglobin level at baseline was 11.0 +/- 2.4 g/dL. Hemoglobin level decreased throughout the duration of the study. Overall, 44% of patients received one or more RBC units while in the ICU (mean, 4.6 +/- 4.9 units). The mean pretransfusion hemoglobin was 8.6 +/- 1.7 g/dL. The mean time to first ICU transfusion was 2.3 +/- 3.7 days. More RBC transfusions were given in study week 1; however, in subsequent weeks, subjects received one to two RBC units per week while in the ICU. The number of RBC transfusions a patient received during the study was independently associated with longer ICU and hospital lengths of stay and an increase in mortality. Patients who received transfusions also had more total complications and were more likely to experience a complication. Baseline hemoglobin was related to the number of RBC transfusions, but it was not an independent predictor of length of stay or mortality. However, a nadir hemoglobin level of <9 g/dL was a predictor of increased mortality and length of stay. CONCLUSIONS: Anemia is common in the critically ill and results in a large number of RBC transfusions. Transfusion practice has changed little during the past decade. The number of RBC units transfused is an independent predictor of worse clinical outcome.

Purpose Patients who receive combined modality treatment for stage I and II Hodgkin lymphoma (HL) have an excellent outcome. Early response evaluation with positron emission tomography (PET) scan may improve selection of patients who need reduced or more intensive treatments. Methods We performed a randomized trial to evaluate treatment adaptation on the basis of early PET (ePET) after two cycles of doxorubicin, bleomycin, vinblastine, and dacarbazine (ABVD) in previously untreated-according to European Organisation for Research and Treatment of Cancer criteria favorable (F) and unfavorable (U)-stage I and II HL. The standard arm consisted of ABVD followed by involved-node radiotherapy (INRT), regardless of ePET result. In the experimental arm, ePET-negative patients received ABVD only (noninferiority design), whereas ePET-positive patients switched to two cycles of bleomycin, etoposide, doxorubicin, cyclophosphamide, vincristine, procarbazine, and prednisone (BEACOPPesc) and INRT (superiority design). Primary end point was progression-free survival (PFS). Results Of 1,950 randomly assigned patients, 1,925 received an ePET-361 patients (18.8%) were positive. In ePET-positive patients, 5-year PFS improved from 77.4% for standard ABVD + INRT to 90.6% for intensification to BEACOPPesc + INRT (hazard ratio [HR], 0.42; 95% CI, 0.23 to 0.74; P = .002). In ePET-negative patients, 5-year PFS rates in the F group were 99.0% versus 87.1% (HR, 15.8; 95% CI, 3.8 to 66.1) in favor of ABVD + INRT; the U group, 92.1% versus 89.6% (HR, 1.45; 95% CI, 0.8 to 2.5) in favor of ABVD + INRT. For both F and U groups, noninferiority of ABVD only compared with combined modality treatment could not be demonstrated. Conclusion In stage I and II HL, PET response after two cycles of ABVD allows for early treatment adaptation. When ePET is positive after two cycles of ABVD, switching to BEACOPPesc + INRT significantly improved 5-year PFS. In ePET-negative patients, noninferiority of ABVD only could not be demonstrated: risk of relapse is increased when INRT is omitted, especially in patients in the F group.

Purpose Clonal hematopoiesis of indeterminate potential (CHIP) is an age-related condition characterized by somatic mutations in the blood of otherwise healthy adults. We hypothesized that in patients undergoing autologous stem-cell transplantation (ASCT) for lymphoma, CHIP at the time of ASCT would be associated with an increased risk of myelodysplastic syndrome and acute myeloid leukemia, collectively termed therapy-related myeloid neoplasm (TMN), and other adverse outcomes. Methods We performed whole-exome sequencing on pre- and post-ASCT samples from 12 patients who developed TMN after autologous transplantation for Hodgkin lymphoma or non-Hodgkin lymphoma and targeted sequencing on cryopreserved aliquots of autologous stem-cell products from 401 patients who underwent ASCT for non-Hodgkin lymphoma between 2003 and 2010. We assessed the effect of CHIP at the time of ASCT on subsequent outcomes, including TMN, cause-specific mortality, and overall survival. Results For six of 12 patients in the exome sequencing cohort, mutations found in the TMN specimen were also detectable in the pre-ASCT specimen. In the targeted sequencing cohort, 120 patients (29.9%) had CHIP at the time of ASCT, which was associated with an increased rate of TMN (10-year cumulative incidence, 14.1% v 4.3% for those with and without CHIP, respectively; P = .002). Patients with CHIP had significantly inferior overall survival compared with those without CHIP (10-year overall survival, 30.4% v 60.9%, respectively; P < .001), including increased risk of death from TMN and cardiovascular disease. Conclusion In patients undergoing ASCT for lymphoma, CHIP at the time of transplantation is associated with inferior survival and increased risk of TMN.

Physical therapists require an accurate, reliable method for measuring muscle strength. They often use manual muscle testing or hand-held dynametric muscle testing (DMT), but few studies document the reliability of MMT or compare the reliability of the two types of testing. We designed this study to determine the intrarater reliability of MMT and DMT. A physical therapist performed manual and dynametric strength tests of the same five muscle groups on 11 patients and then repeated the tests two days later. The correlation coefficients were high and significantly different from zero for four muscle groups tested dynametrically and for two muscle groups tested manually. The test-retest reliability coefficients for two muscle groups tested manually could not be calculated because the values between subjects were identical. We concluded that both MMT and DMT are reliable testing methods, given the conditions described in this study. Both testing methods have specific applications and limitations, which we discuss.

PURPOSE: The phase II single-arm KEYNOTE-052 study evaluated the efficacy and safety of first-line pembrolizumab for patients with locally advanced or metastatic cisplatin-ineligible urothelial carcinoma (UC). PATIENTS AND METHODS: Three hundred seventy patients received pembrolizumab 200 mg intravenously every 3 weeks for up to 24 months. Positive tumor programmed death ligand 1 (PD-L1) expression was defined as combined positive score (CPS) ≥ 10. Response was assessed by independent central review every 9 weeks per RECIST v1.1. The primary end point was objective response rate (ORR). RESULTS: At data cutoff (September 26, 2018), the minimum follow-up was 2 years since the last patient enrolled. ORR was 28.6% (95% CI, 24.1% to 33.5%); 33 patients (8.9%) and 73 patients (19.7%) achieved complete and partial response, respectively. The median duration of response was 30.1 months (95% CI, 18.1 months to not reached [NR]); responses lasted ≥ 12 and ≥ 24 months in 67% and 52% of patients, respectively. Forty patients with complete or partial response completed 2 years of study treatment, and 32 had ongoing response at completion. Median overall survival (OS) was 11.3 months (95% CI, 9.7 to 13.1 months), and 12- and 24-month OS rates were 46.9% and 31.2%, respectively. In patients with CPS ≥ 10, ORR was 47.3% (95% CI, 37.7% to 57.0%) and median OS was 18.5 months (95% CI, 12.2 to 28.5 months). In patients with lymph node-only disease, ORR was 49.0% (95% CI, 34.8% to 63.4%), and median OS was 27.0 months (12.4 months to NR). There were no new safety signals. CONCLUSION: First-line pembrolizumab confers meaningful and durable clinical response in cisplatin-ineligible patients with advanced UC and is associated with prolonged OS, particularly with PD-L1 CPS ≥ 10 and lymph node-only disease.

Histamine diphosphate was shown to selectively attract human eosinophils from mixed granulocyte populations when over 20% eosinophils were used in a modified Boyden chamber chemotactic assay system. This effect of histamine is abolished by incubation with diamine oxidase (histaminase) and was generated by decarboxylation of L-histidine. A linear dose dependent increase in eosinophil migration was observed between 3 X 10(-7) M and 1.25 X 10(-6) M, while higher concentrations of histamine inhibited the migration of eosinophils. The attractant activity of histamine was not inhibited by H-1 or H-2 receptor antagonists, however, the inhibition of migration observed at higher histamine concentrations was reversed by metiamine, an H-2 receptor antagonist. The effects of histamine upon eosinophil migration were demonstrable using three different assays: (a) counting cells that had traversed 5-mum pore, 12-mum thick polycarbonate filters, (b) counting cells that had migrated various distances into a 3-mum pore, 145-mum cellulose nitrate filters, or (c) measuring the number of cells that had traversed an upper polycarbonate filter and migrated into a lower cellulose nitrate filter using 15Cr-labeled cells. The ability of histamine to enhance eosinophil migration was shown to be dependent upon the presence of a concentration gradient; histamine did not cause a dose-dependent increase in random motility. Furthermore, preincubation of the eosinophils with histamine deactivate the cells to further stimulation by histamine or by C5a. It is concluded that in low doses histamine is a chemoattractant for human eosinophils, while in higher doses histamine inhibits eosinophil migration. These observations may relate to the influx and localization of eosinophils in immediate hypersensitivity reactions.

BACKGROUND: Peroxisome proliferator-activated receptors (PPARs) are transcription factors of the nuclear receptor superfamily. It has been reported that the thiazolidinediones, which are antidiabetic agents and high-affinity ligands for PPARgamma, regulate growth of vascular cells. In the present study, we examined the role of PPARgamma in angiotensin II (Ang II)-induced hypertrophy of neonatal rat cardiac myocytes and in pressure overload-induced cardiac hypertrophy of mice. METHODS AND RESULTS: Treatment of cultured cardiac myocytes with PPARgamma ligands such as troglitazone, pioglitazone, and rosiglitazone inhibited Ang II-induced upregulation of skeletal alpha-actin and atrial natriuretic peptide genes and an increase in cell surface area. Treatment of mice with a PPARgamma ligand, pioglitazone, inhibited pressure overload-induced increases in the heart weight-to-body weight ratio, wall thickness, and myocyte diameter in wild-type mice and an increase in the heart weight-to-body weight ratio in heterozygous PPARgamma-deficient mice. In contrast, pressure overload-induced increases in the heart weight-to-body weight ratio and wall thickness were more prominent in heterozygous PPARgamma-deficient mice than in wild-type mice. CONCLUSIONS: These results suggest that the PPARgamma-dependent pathway is critically involved in the inhibition of cardiac hypertrophy.

Biotransformation of the imidazobenzodiazepine midazolam to its alpha-hydroxy and 4-hydroxy metabolites was studied in vitro using human liver microsomal preparations. Formation of alpha-hydroxy-midazolam was a high-affinity (Km = 3.3 mumol/L) Michaelis-Menten process coupled with substrate inhibition at high concentrations of midazolam. Formation of 4-hydroxy-midazolam had much lower apparent affinity (57 mumol/L), with minimal evidence of substrate inhibition. Based on comparison of Vmax/Km ratios for the two pathways, alpha-hydroxy-midazolam formation was estimated to account for 95% of net intrinsic clearance. Three azole antifungal agents were inhibitors of midazolam metabolism in vitro, with inhibition being largely consistent with a competitive mechanism. Mean competitive inhibition constants (Ki) versus alpha-hydroxy-midazolam formation were 0.0037 mumol/L for ketoconazole, 0.27 mumol/L for itraconazole, and 1.27 mumol/L for fluconazole. An in vitro-in vivo scaling model predicted inhibition of oral midazolam clearance due to coadministration of ketoconazole or itraconazole; the predicted inhibition was consistent with observed interactions in clinical pharmacokinetic studies. The selective serotonin reuptake inhibitor (SSRI) antidepressant fluoxetine and its principal metabolite, norfluoxetine, also were inhibitors of both pathways of midazolam biotransformation, with norfluoxetine being a much more potent inhibitor than was fluoxetine itself. This finding is consistent with results of other in vitro studies and of clinical studies, indicating that fluoxetine, largely via its metabolite norfluoxetine, may impair clearance of P450-3A substrates.

PURPOSE: Lynch syndrome due to pathogenic variants in the DNA mismatch repair genes MLH1, MSH2, and MSH6 is predominantly associated with colorectal and endometrial cancer, although extracolonic cancers have been described within the Lynch tumor spectrum. However, the age-specific cumulative risk (penetrance) of these cancers is still poorly defined for PMS2-associated Lynch syndrome. Using a large data set from a worldwide collaboration, our aim was to determine accurate penetrance measures of cancers for carriers of heterozygous pathogenic PMS2 variants. METHODS: A modified segregation analysis was conducted that incorporated both genotyped and nongenotyped relatives, with conditioning for ascertainment to estimates corrected for bias. Hazard ratios (HRs) and corresponding 95% CIs were estimated for each cancer site for mutation carriers compared with the general population, followed by estimation of penetrance. RESULTS: In total, 284 families consisting of 4,878 first- and second-degree family members were included in the analysis. PMS2 mutation carriers were at increased risk for colorectal cancer (cumulative risk to age 80 years of 13% [95% CI, 7.9% to 22%] for males and 12% [95% CI, 6.7% to 21%] for females) and endometrial cancer (13% [95% CI, 7.0%-24%]), compared with the general population (6.6%, 4.7%, and 2.4%, respectively). There was no clear evidence of an increased risk of ovarian, gastric, hepatobiliary, bladder, renal, brain, breast, prostate, or small bowel cancer. CONCLUSION: Heterozygous PMS2 mutation carriers were at small increased risk for colorectal and endometrial cancer but not for any other Lynch syndrome-associated cancer. This finding justifies that PMS2-specific screening protocols could be restricted to colonoscopies. The role of risk-reducing hysterectomy and bilateral salpingo-oophorectomy for PMS2 mutation carriers needs further discussion.

Vascular calcification is clinically important in the development of cardiovascular disease. It is reported that hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitors (statins) inhibited vascular calcification in several clinical trials. However, the mechanism is poorly understood. Recently, it has been suggested that apoptosis is one of the important processes regulating vascular smooth muscle cell (VSMC) calcification. In this study, we investigated the effect of statins on VSMC calcification by testing their effect on apoptosis, focusing in particular on regulation of the survival pathway mediated by growth arrest-specific gene 6 (Gas6), a member of the vitamin K-dependent protein family, and its receptor, Axl. In human aortic smooth muscle cells (HASMC), statins significantly inhibited inorganic phosphate (Pi)-induced calcification in a concentration-dependent manner (reduced by 49% at 0.1 micromol/L atorvastatin). The inhibitory effect of statins was mediated by preventing apoptosis, which was increased by Pi in a concentration-dependent manner, and not by inhibiting sodium-dependent phosphate cotransporter (NPC) activity, another mechanism regulating HASMC calcification. Furthermore, the antiapoptotic effect of statins was dependent on restoration of Gas6, whose expression was downregulated by Pi. Restoration of Gas6 mRNA by statins was mediated by mRNA stabilization, and not by an increase in transcriptional activity. Suppression of Gas6 using small interfering RNA and the Axl-extracellular domain abolished the preventive effect of statins on Pi-induced apoptosis and calcification. These data demonstrate that statins protected HASMC from Pi-induced calcification by inhibiting apoptosis via restoration of the Gas6-Axl pathway.

BACKGROUND: We conducted a phase I study with a granulocyte macrophage colony stimulating factor (GMCSF)-expressing oncolytic adenovirus, ONCOS-102, in patients with solid tumors refractory to available treatments. The objectives of the study were to determine the optimal dose for further use and to assess the safety, tolerability and adverse event (AE) profile of ONCOS-102. Further, the response rate and overall survival were evaluated as well as preliminary evidence of disease control. As an exploratory endpoint, the effect of ONCOS 102 on biological correlates was examined. METHODS: The study was conducted using a classic 3 + 3 dose escalation study design involving 12 patients. Patients were repeatedly treated intratumorally with ONCOS-102 plus daily low-dose oral cyclophosphamide (CPO). Tumor response was evaluated with diagnostic positron emission tomography (PET) and computed tomography (CT). Tumor biopsies were collected at baseline and after treatment initiation for analysis of immunological correlates. Peripheral blood mononuclear cells (PBMCs) were collected at baseline and during the study to assess antigen specificity of CD8+ T cells by interferon gamma (IFNγ) enzyme linked immunospot assay (ELISPOT). RESULTS: No dose limiting toxicity (DLT) or maximum tolerated dose (MTD) was identified for ONCOS-102. Four out of ten (40 %) evaluable patients had disease control based on PET/CT scan at 3 months and median overall survival was 9.3 months. A short-term increase in systemic pro-inflammatory cytokines and a prominent infiltration of TILs to tumors was seen post-treatment in 11 out of 12 patients. Two patients showed marked infiltration of CD8+ T cells to tumors and concomitant systemic induction of tumor-specific CD8+ T cells. Interestingly, high expression levels of genes associated with activated TH1 cells and TH1 type immune profile were observed in the post-treatment biopsies of these two patients. CONCLUSIONS: ONCOS-102 is safe and well tolerated at the tested doses. All three examined doses may be used in further development. There was evidence of antitumor immunity and signals of clinical efficacy. Importantly, treatment resulted in infiltration of CD8+ T cells to tumors and up-regulation of PD-L1, highlighting the potential of ONCOS-102 as an immunosensitizing agent for combinatory therapies with checkpoint inhibitors. TRIAL REGISTRATION: NCT01598129. Registered 19/04/2012.

BACKGROUND: Sarcopenia, the age-related loss of muscle mass [defined as appendicular LBM/Height2 (aLBM/ht2) below peak value by>1SD], strength and function, is a major contributing factor to frailty in the elderly. MK-0773 is a selective androgen receptor modulator designed to improve muscle function while minimizing effects on other tissues. OBJECTIVES: The primary objective of this study was to demonstrate an improvement in muscle strength and lean body mass (LBM) in sarcopenic frail elderly women treated with MK-0773 relative to placebo. DESIGN: This was a randomized, double-blind, parallel-arm, placebo-controlled, multicenter, 6-month study. Participants were randomized in a 1:1 ratio to receive either MK-0773 50mg b.i.d. or placebo; all participants received Vitamin D and protein supplementation. SETTING: General community. PARTICIPANTS: 170 Women aged ≥65 with sarcopenia and moderate physical dysfunction. MEASUREMENTS: Dual energy X-ray absorptiometry, muscle strength and power, physical performance measures. RESULTS: Participants receiving MK-0773 showed a statistically significant increase in LBM from baseline at Month 6 vs. placebo (p<0.001). Participants receiving both MK-0773 and placebo showed a statistically significant increase in strength from baseline to Month 6, but the mean difference between the two groups was not significant (p=0.269). Both groups showed significant improvement from baseline at Month 6 in physical performance measures, but there were no statistically significant differences between participants receiving MK-0773 and placebo. A greater number of participants experienced elevated transaminases in the MK-0773 group vs. placebo, which resolved after discontinuation of study therapy. MK-0773 was generally well-tolerated with no evidence of androgenization. CONCLUSIONS: The MK-0773-induced increase in LBM did not translate to improvement in strength or function vs. placebo. The improvement of strength and physical function in the placebo group could be at least partly attributed to protein and vitamin D supplementation.

Abstract Immune checkpoint inhibitors (ICI) have revolutionized treatment for various cancers; however, durable response is limited to only a subset of patients. Discovery of blood-based biomarkers that reflect dynamic change of the tumor microenvironment, and predict response to ICI, will markedly improve current treatment regimens. Here, we investigate CX3C chemokine receptor 1 (CX3CR1), a marker of T-cell differentiation, as a predictive correlate of response to ICI therapy. Successful treatment of tumor-bearing mice with ICI increases the frequency and T-cell receptor clonality of the peripheral CX3CR1 + CD8 + T-cell subset that includes an enriched repertoire of tumor-specific and tumor-infiltrating CD8 + T cells. Furthermore, an increase in the frequency of the CX3CR1 + subset in circulating CD8 + T cells early after initiation of anti-PD-1 therapy correlates with response and survival in patients with non-small cell lung cancer. Collectively, these data support T-cell CX3CR1 expression as a blood-based dynamic early on-treatment predictor of response to ICI therapy.

An antimetabolite, THX, was isolated from fermentation broths of the thienamycin producer, Streptomyces cattleya, when the organism was grown in the presence of a fluorine-containing substrate. THX was subsequently identified as one of the four possible stereoisomers of 4-fluorothreonine. Inorganic fluoride or any one of a number of organofluorine compounds can be used as precursors of 4-fluorothreonine. In addition, 19F NMR has provided evidence that the organism synthesizes fluoroacetate under the same fermentation conditions. The in vitro antibacterial spectrum of 4-fluorothreonine is also presented.

Summary As a result of previous in‐vitro studies on the a‐adrenergic receptor activity of the human prostate and prostatic capsule a trial was made of a‐adrenergic blockers for the relief of obstructive prostatic symptoms. Considerable benefit was obtained in several groups of patients, as demonstrated either by the relief or prevention of complete retention, or by diminution in residual urine or improvement in urinary flow‐rate recordings. A number of illustrative cases are described, and the indications for the use of this treatment are suggested. It is emphasised that this treatment provides symptomatic relief only, and in no sense purports to be a treatment of the enlarged prostate itself.

Three new angiotensin converting-enzyme inhibitors were given orally to 20 men in single doses ranging from 1.25 to 40 mg. Two of them induced comparable marked inhibition of both the blood pressure response to exogenous angiotensin I and plasma converting-enzyme activity. Onset of action was relatively slow, but 21 to 24 hr after drug plasma converting-enzyme activity was still clearly reduced. The third was less active. There was a close correlation between blood pressure response on administration of angiotensin I and plasma converting-enzyme activity. There were no adverse effects. These new drugs are interesting because of their long duration of action. The measurement of plasma converting-enzyme activity seems useful for monitoring efficacy of converting-enzyme blockade and compliance to therapy.

The effects of "ischaemia" (glucose-free Krebs-bicarbonate medium gassed with N2/CO2) on the release of glutamate and other major neurotransmitters in the retina were examined using the isolated rat and rabbit retina. Amino acid transmitters, acetylcholine, and dopamine were measured by HPLC. The release of glutamate, aspartate, GABA, and glycine from ischaemic retinas was more than doubled after 30 min, and after 90 min of ischaemia the release of amino acids was approximately 15-20-fold that of control values. Ischaemia also produced large increases in the release of dopamine from both the rat and especially the rabbit retina. In contrast, the release of acetylcholine from the rat retina was significantly decreased by ischaemia, although the release of choline was increased. Because the ischaemia-induced release of glutamate, aspartate, and GABA from the rat retina was completely Ca independent, and exposure of the retina to high K (50 mM) did not stimulate amino acid release, it is concluded that the mechanisms underlying the ischaemia-induced release do not involve an initial release of K or an influx of calcium.

Two radical-based approaches have been developed to effect the trifluoromethylation of aryl C-H bonds in native peptides either using stoichiometric oxidant or visible light photoredox catalysis. The reported methods are able to derivatize tyrosine and tryptophan sidechains under biocompatible conditions, and a number of examples are reported involving fully unprotected peptides with up to 51 amino acids. The development of this chemistry adds to the growing array of chemical methods for selectively modifying amino acid residues in the context of complex peptides. The direct incorporation of trifluoromethyl groups into biopolymers enables the study of a range of biological and biochemical systems, and preliminary results indicate this method can be extended to the incorporation of other fluoroalkyl groups for bioconjugation applications.

With the intent of achieving greater spatiotemporal control of PROTAC-induced protein degradation, a light-activated degrader was designed by photocaging an essential E3 ligase binding motif in a BRD4 targeting PROTAC. Proteolysis was triggered only after a short irradiation time, the kinetics of which could be monitored by live-cell video microscopy.

There is a ceiling to the reduction of enflurane MAC by fentanyl in the dog. Sufentanil (SUF), a more potent narcotic, may be more efficacious in reducing enflurane MAC. To test this hypothesis, 25 mongrel dogs were studied in three groups. Group 1 (n = 8) received SUF in progressively increasing infusion rates from 0.005 micrograms . kg-1 . min-1 to a maximum of 1.215 micrograms . kg-1 . min-1. MAC was determined at stable SUF concentrations in plasma [SUF] during each infusion rate. Group 2 (n = 10) received SUF at a dose rate (0.007 micrograms . kg-1 . min-1) designed to produce approximately 35% MAC reduction, and MAC determinations were made at regular intervals over a mean infusion time of 7.6 +/- 0.43 h (mean +/- SEM). Group 3 (n = 7) received 1.215 micrograms . kg-1 . min-1 and were studied as in group 2 over an infusion time of 6.7 +/- 0.42 h. In group 1, the highest infusion rate (1.215 micrograms . kg-1 . min-1) produced [SUF] = 48 ng/ml and reduced MAC by 71 +/- 6%. This was not statistically different from the reduction which occurred at [SUF] = 0.92 ng/ml (57 +/- 7%; infusion rate 0.015 micrograms . kg-1 . min-1; P = 0.21). In group 2, the degree of MAC reduction achieved by stable [SUF] (0.54 +/- 0.08 ng/ml) declined over time (MAC reduction at start = 34 +/- 2% versus 18 +/- 4.0% at the end of the infusion; P = 0.001), suggesting the development of tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)