Intraoperative Methadone in Next-day Discharge Outpatient Surgery: A Randomized, Double-blinded, Dose-finding Pilot Study.

BACKGROUND: Contemporary perioperative practice seeks to use less intraoperative opioid, diminish postoperative pain and opioid use, and enable less postdischarge opioid prescribing. For inpatient surgery, anesthesia with intraoperative methadone, compared with short-duration opioids, results in less pain, less postoperative opioid use, and greater patient satisfaction. This pilot investigation aimed to determine single-dose intraoperative methadone feasibility for next-day discharge outpatient surgery, determine an optimally analgesic and well-tolerated dose, and explore whether methadone would result in less postoperative opioid use compared with conventional short-duration opioids. METHODS: This double-blind, randomized, dose-escalation feasibility and pilot study in next-day discharge surgery compared intraoperative single-dose IV methadone (0.1 then 0.2, 0.25 and 0.3 mg/kg ideal body weight) versus as-needed short-duration opioid (fentanyl, hydromorphone) controls. Perioperative opioid use, pain, and side effects were assessed before discharge. Patients recorded pain, opioid use, and side effects for 30 days postoperatively using take-home diaries. Primary clinical outcome was in-hospital (intraoperative and postoperative) opioid use. Secondary outcomes were 30-day opioid consumption, pain, opioid side effects, and leftover opioid counts. RESULTS: Median (interquartile range) intraoperative methadone doses were 6 (5 to 7), 11 (10 to 12), 14 (13 to 16), and 18 (15 to 19) mg in 0.1, 0.2, 0.25, and 0.3 mg/kg ideal body weight groups, respectively. Anesthesia with single-dose methadone and propofol or volatile anesthetic was effective. Total in-hospital opioid use (IV milligram morphine equivalents [MME]) was 25 (20 to 37), 20 (13 to 30), 27 (18 to 32), and 25 (20 to 36) mg, respectively, in patients receiving 0.1, 0.2, 0.25 and 0.3 mg/kg methadone, compared to 46 (33 to 59) mg in short-duration opioid controls. Opioid-related side effects were not numerically different. Home pain and opioid use were numerically lower in patients receiving methadone. CONCLUSIONS: The most effective and well-tolerated single intraoperative induction dose of methadone for next-day discharge surgery was 0.25 mg/kg ideal body weight (median, 14 mg). Single-dose intraoperative methadone was analgesic and opioid-sparing in next-day discharge outpatient surgery.

Morphine and Hydromorphone Effects, Side Effects, and Variability: A Crossover Study in Human Volunteers.

BACKGROUND: Balancing between opioid analgesia and respiratory depression continues to challenge clinicians in perioperative, emergency department, and other acute care settings. Morphine and hydromorphone are postoperative analgesic standards. Nevertheless, their comparative effects and side effects, timing, and respective variabilities remain poorly understood. This study tested the hypothesis that IV morphine and hydromorphone differ in onset, magnitude, duration, and variability of analgesic and ventilatory effects. METHODS: The authors conducted a randomized crossover study in healthy volunteers. Forty-two subjects received a 2-h IV infusion of hydromorphone (0.05 mg/kg) or morphine (0.2 mg/kg) 1 to 2 weeks apart. The authors measured arterial opioid concentrations, analgesia in response to heat pain (maximally tolerated temperature, and verbal analog pain scores at discrete preset temperatures to determine half-maximum temperature effect), dark-adapted pupil diameter and miosis, end-expired carbon dioxide, and respiratory rate for 12 h after dosing. RESULTS: For morphine and hydromorphone, respectively, maximum miosis was less (3.9 [3.4 to 4.2] vs. 4.6 mm [4.0 to 5.0], P < 0.001; median and 25 to 75% quantiles) and occurred later (3.1 ± 0.9 vs. 2.3 ± 0.7 h after infusion start, P < 0.001; mean ± SD); maximum tolerated temperature was less (49 ± 2 vs. 50 ± 2°C, P < 0.001); verbal pain scores at end-infusion at the most informative stimulus (48.2°C) were 82 ± 4 and 59 ± 3 (P < 0.001); maximum end-expired CO2 was 47 (45 to 50) and 48 mmHg (46 to 51; P = 0.007) and occurred later (5.5 ± 2.8 vs. 3.0 ± 1.5 h after infusion start, P < 0.001); and respiratory nadir was 9 ± 1 and 11 ± 2 breaths/min (P < 0.001), and occurred at similar times. The area under the temperature tolerance-time curve was less for morphine (1.8 [0.0 to 4.4]) than hydromorphone (5.4°C-h [1.6 to 12.1] P < 0.001). Interindividual variability in clinical effects did not differ between opioids. CONCLUSIONS: For morphine compared to hydromorphone, analgesia and analgesia relative to respiratory depression were less, onset of miosis and respiratory depression was later, and duration of respiratory depression was longer. For each opioid, timing of the various clinical effects was not coincident. Results may enable more rational opioid selection, and suggest hydromorphone may have a better clinical profile.

Intravenously administered interleukin-7 to reverse lymphopenia in patients with septic shock: a double-blind, randomized, placebo-controlled trial.

BACKGROUND: Profound lymphopenia is an independent predictor of adverse clinical outcomes in sepsis. Interleukin-7 (IL-7) is essential for lymphocyte proliferation and survival. A previous phase II study showed that CYT107, a glycosylated recombinant human IL-7, administered intramuscularly reversed sepsis-induced lymphopenia and improved lymphocyte function. Thepresent study evaluated intravenous administration of CYT107. This prospective, double-blinded, placebo-controlled trial was designed to enroll 40 sepsis patients, randomized 3:1 to CYT107 (10 µg/kg) or placebo, for up to 90 days. RESULTS: Twenty-one patients were enrolled (fifteen CYT107 group, six placebo group) at eight French and two US sites. The study was halted early because three of fifteen patients receiving intravenous CYT107 developed fever and respiratory distress approximately 5-8 h after drug administration. Intravenous administration of CYT107 resulted in a two-threefold increase in absolute lymphocyte counts (including in both CD4+ and CD8+ T cells (all p < 0.05)) compared to placebo. This increase was similar to that seen with intramuscular administration of CYT107, was maintained throughout follow-up, reversed severe lymphopenia and was associated with increase in organ support free days (OSFD). However, intravenous CYT107 produced an approximately 100-fold increase in CYT107 blood concentration compared with intramuscular CYT107. No cytokine storm and no formation of antibodies to CYT107 were observed. CONCLUSION: Intravenous CYT107 reversed sepsis-induced lymphopenia. However, compared to intramuscular CYT107 administration, it was associated with transient respiratory distress without long-term sequelae. Because of equivalent positive laboratory and clinical responses, more favorable pharmacokinetics, and better patient tolerability, intramuscular administration of CYT107 is preferable. TRIAL REGISTRATION: Clinicaltrials.gov, NCT03821038. Registered 29 January 2019, https://clinicaltrials.gov/ct2/show/NCT03821038?term=NCT03821038&draw=2&rank=1 .

Methadone pharmacogenetics in vitro and in vivo: Metabolism by CYP2B6 polymorphic variants and genetic variability in paediatric disposition.

AIMS: Methadone metabolism and clearance are determined principally by polymorphic cytochrome P4502B6 (CYP2B6). Some CYP2B6 allelic variants affect methadone metabolism in vitro and disposition in vivo. We assessed methadone metabolism by CYP2B6 minor variants in vitro. We also assessed the influence of CYP2B6 variants, and P450 oxidoreductase (POR) and CYP2C19 variants, on methadone clearance in surgical patients in vivo. METHODS: CYP2B6 and P450 oxidoreductase variants were coexpressed with cytochrome b5 . The metabolism of methadone racemate and enantiomers was measured at therapeutic concentrations and intrinsic clearances were determined. Adolescents receiving methadone for surgery were genotyped for CYP2B6, CYP2C19 and POR, and methadone clearance and metabolite formation clearance were determined. RESULTS: In vitro, CYP2B6.4 was more active than wild-type CYP2B6.1. CYPs 2B6.5, 2B6.6, 2B6.7, 2B6.9, 2B6.17, 2B6.19 and 2B6.26 were less active. CYPs 2B6.16 and 2B6.18 were inactive. CYP2B6.1 expressed with POR variants POR.28, POR.5 and P228L had lower rates of methadone metabolism than wild-type reductase. In vivo, methadone clinical clearance decreased linearly with the number of CYP2B6 slow metabolizer alleles, but was not different in CYP2C19 slow or rapid metabolizer phenotypes, or in carriers of the POR*28 allele. CONCLUSIONS: Several CYP2B6 and POR variants were slow metabolizers of methadone in vitro. Polymorphisms in CYP2B6, but not CYP2C19 or P450 reductase, affected methadone clearance in vivo. CYP2B6 polymorphisms 516G>T and 983T>C code for canonical loss of function variants and should be assessed when considering genetic influences on clinical methadone disposition. These complementary translational in vitro and in vivo results inform on pharmacogenetic variability affecting methadone disposition in patients.

IL-7 Immunotherapy in a Nonimmunocompromised Patient With Intractable Fungal Wound Sepsis.

A nonimmunocompromised patient developed life-threatening soft tissue infection with Trichosporon asahii, Fusarium, and Saksenaea that progressed despite maximum antifungal therapies and aggressive debridement. Interleukin-7 immunotherapy resulted in clinical improvement, fungal clearance, reversal of lymphopenia, and improved T-cell function. Immunoadjuvant therapies to boost host immunity may be efficacious in life-threatening fungal infections.

Plasma and cerebrospinal fluid pharmacokinetics of ondansetron in humans.

AIMS: Changes in serotonergic sensory modulation associated with overexpression of 5-HT3 receptors in the central nervous system (CNS) have been implicated in the pathophysiology of neuropathic pain after peripheral nerve damage. 5-HT3 receptor antagonists such as ondansetron can potentially alleviate neuropathic pain, but have limited effectiveness, due potentially to limited CNS access. However, there is currently limited information on CNS disposition of systemically-administered 5-HT3 receptor antagonists. This study evaluated the cerebrospinal fluid (CSF) disposition of ondansetron, as a surrogate of CNS penetration. METHODS: Fifteen patients were given a single 16 mg intravenous 15 minute infusion of ondansetron, followed by serial blood and a single CSF sampling. Population pharmacokinetic (PK) modelling was implemented to describe the average and individual plasma and CSF profiles of ondansetron. A two-compartmental model was used to capture ondansetron plasma PK with a single CSF compartment to describe distribution to the CNS. RESULTS: The individual model-estimated CSF to plasma partition coefficients of ondansetron were between 0.09 and 0.20. These values were mirrored in the calculated CSF penetration ratios, ranging from 0.08 to 0.26. CONCLUSIONS: After intravenous administration, CSF concentrations of ondansetron were approximately 7-fold lower than those observed in the plasma. A model could be developed to describe individual CSF concentration-time profiles of ondansetron based on a single CSF data point. The low CSF penetration of ondansetron may explain its limited analgesic effectiveness, and affords an opportunity to explore enhancing its CNS penetration for targeting conditions such as neuropathic pain.

Severe immunosuppression and not a cytokine storm characterizes COVID-19 infections.

COVID-19-associated morbidity and mortality have been attributed to a pathologic host response. Two divergent hypotheses have been proposed: hyperinflammatory cytokine storm; and failure of host protective immunity that results in unrestrained viral dissemination and organ injury. A key explanation for the inability to address this controversy has been the lack of diagnostic tools to evaluate immune function in COVID-19 infections. ELISpot, a highly sensitive, functional immunoassay, was employed in 27 patients with COVID-19, 51 patients with sepsis, 18 critically ill nonseptic (CINS) patients, and 27 healthy control volunteers to evaluate adaptive and innate immune status by quantitating T cell IFN-É£ and monocyte TFN-α production. Circulating T cell subsets were profoundly reduced in COVID-19 patients. Additionally, stimulated blood mononuclear cells produced less than 40%-50% of the IFN-É£ and TNF-α observed in septic and CINS patients, consistent with markedly impaired immune effector cell function. Approximately 25% of COVID-19 patients had increased IL-6 levels that were not associated with elevations in other canonical proinflammatory cytokines. Collectively, these findings support the hypothesis that COVID-19 suppresses host functional adaptive and innate immunity. Importantly, IL-7 administered ex vivo restored T cell IFN-É£ production in COVID-19 patients. Thus, ELISpot may functionally characterize host immunity in COVID-19 and inform prospective therapies.

Stereoselective Steady-State Disposition and Bioequivalence of Brand and Generic Bupropion in Adults.

The antidepressant bupropion is stereoselectively metabolized and metabolite enantiomers have differential pharmacologic effects, but steady-state enantiomeric disposition is unknown. Controversy persists about bupropion XL 300 mg generic equivalence to brand product, and whether generics might have different stereoselective disposition leading to enantiomeric non-bioequivalence and, thus, clinical nonequivalence. This preplanned follow-on analysis of a prospective, randomized, double-blinded, crossover study of brand and 3 generic bupropion XL 300 mg products measured steady-state enantiomeric plasma and urine parent bupropion and primary and secondary metabolite concentrations and evaluated bioequivalence and pharmacokinetics. Steady-state plasma and urine bupropion disposition was markedly stereoselective, with up to 40-fold differences in plasma concentrations of the active metabolite S,S-hydroxybupropion vs. R,R,-hydroxybupropion. Urine metabolite glucuronides were prominent, but glucuronidation was metabolite-specific and enantioselective. There were no differences between any generic and brand, or between generics, in plasma enantiomer concentrations of bupropion or the major metabolites. All generic products satisfied formal bioequivalence criteria (peak plasma concentration (Cmax ) and area under the plasma concentration-time curve over 24 hours (AUC0-24 )) using enantiomers for bupropion as well as for metabolites, and generics were comparable to each other, and were considered bioequivalent, based on enantiomeric analysis. Enantiomeric bioequivalence explains the previously observed therapeutic equivalence of bupropion generics and brand in treating major depression. These results have important implications for understanding the clinical therapeutic effects of bupropion based on complex and stereoselective metabolism.

Intraoperative Methadone in Same-Day Ambulatory Surgery: A Randomized, Double-Blinded, Dose-Finding Pilot Study.

BACKGROUND: Approximately 50 million US patients undergo ambulatory surgery annually. Postoperative opioid overprescribing is problematic, yet many patients report inadequate pain relief. In major inpatient surgery, intraoperative single-dose methadone produces better analgesia and reduces opioid use compared with conventional repeated dosing of short-duration opioids. This investigation tested the hypothesis that in same-day ambulatory surgery, intraoperative methadone, compared with short-duration opioids, reduces opioid consumption and pain, and determined an effective intraoperative induction dose of methadone for same-day ambulatory surgery. METHODS: A double-blind, dose-escalation protocol randomized 60 patients (2:1) to intraoperative single-dose intravenous methadone (initially 0.1 then 0.15 mg/kg ideal body weight) or conventional as-needed dosing of short-duration opioids (eg, fentanyl, hydromorphone; controls). Intraoperative and postoperative opioid consumption, pain, and opioid side effects were assessed before discharge. Patient home diaries recorded pain, opioid use, and opioid side effects daily for 30 days postoperatively. Primary outcome was in-hospital (intraoperative and postoperative) opioid use. Secondary outcomes were 30 days opioid consumption, pain intensity, and opioid side effects. RESULTS: Median (interquartile range) methadone doses were 6 (5-6) and 9 (8-9) mg in the 0.1 and 0.15 mg/kg methadone groups, respectively. Total opioid consumption (morphine equivalents) in the postanesthesia care unit was significantly less compared with controls (9.3 mg, 1.3-11.0) in subjects receiving 0.15 mg/kg methadone (0.1 mg, 0.1-3.3; P < .001) but not 0.1 mg/kg methadone (5.0 mg, 3.3-8.1; P = .60). Dose-escalation ended at 0.15 mg/kg methadone. Total in-hospital nonmethadone opioid use after short-duration opioid, 0.1 mg/kg methadone, and 0.15 mg/kg methadone was 35.3 (25.0-44.0), 7.1 (3.7-10.0), and 3.3 (0.1-5.8) mg morphine equivalents, respectively (P < .001 for both versus control). In-hospital pain scores and side effects were not different between groups. In the 30 days after discharge, patients who received methadone 0.15 mg/kg had less pain at rest (P = .02) and used fewer opioid pills than controls (P < .0001), whereas patients who received 0.1 mg/kg had no difference in pain at rest (P = .69) and opioid use compared to controls (P = .08). CONCLUSIONS: In same-day discharge surgery, this pilot study identified a single intraoperative dose of methadone (0.15 mg/kg ideal body weight), which decreased intraoperative and postoperative opioid requirements and postoperative pain, compared with conventional intermittent short-duration opioids, with similar side effects.

Bioequivalence and Therapeutic Equivalence of Generic and Brand Bupropion in Adults With Major Depression: A Randomized Clinical Trial.

Controversy persists about bupropion XL 300 mg generic equivalence to brand product. A prospective, randomized, double-blinded crossover in 70 adults with major depression in stable remission taking any bupropion XL 300 mg tested bioequivalence and therapeutic equivalence of available XL 300 mg products. After a 4-week lead-in on patients' existing bupropion, four 6-week phases evaluated brand and three generics. Patients were uninformed of switching. Drug overencapsulation ensured blinding. There were no differences between any generic and brand, or between generics, in peak plasma concentration (Cmax ) and area under the plasma concentration-time curve over the 24-hour dosing interval (AUC0-24 ) for racemic bupropion or major metabolites. All generics met formal bioequivalence criteria for bupropion and metabolites. There were no differences between generics and brand, or between generics, in depression symptoms or side effects, assessed by every 3-week in-person interview and daily smartphone-based self-report. There were no differences in patients' perceptions of bupropion products. Results show three bupropion XL 300 mg generic products are both bioequivalent and not therapeutically different from brand drug and each other.

Interleukin-7 restores lymphocytes in septic shock: the IRIS-7 randomized clinical trial.

BACKGROUND: A defining pathophysiologic feature of sepsis is profound apoptosis-induced death and depletion of CD4+ and CD8+ T cells. Interleukin-7 (IL-7) is an antiapoptotic common γ-chain cytokine that is essential for lymphocyte proliferation and survival. Clinical trials of IL-7 in over 390 oncologic and lymphopenic patients showed that IL-7 was safe, invariably increased CD4+ and CD8+ lymphocyte counts, and improved immunity. METHODS: We conducted a prospective, randomized, double-blind, placebo-controlled trial of recombinant human IL-7 (CYT107) in patients with septic shock and severe lymphopenia. Twenty-seven patients at academic sites in France and the United States received CYT107 or placebo for 4 weeks. Primary aims were to determine the safety of CYT107 in sepsis and its ability to reverse lymphopenia. RESULTS: CYT107 was well tolerated without evidence of inducing cytokine storm or worsening inflammation or organ dysfunction. CYT107 caused a 3- to 4-fold increase in absolute lymphocyte counts and in circulating CD4+ and CD8+ T cells that persisted for weeks after drug administration. CYT107 also increased T cell proliferation and activation. CONCLUSIONS: This is the first trial of an immunoadjuvant therapy targeting defects in adaptive immunity in patients with sepsis. CYT107 reversed the marked loss of CD4+ and CD8+ immune effector cells, a hallmark of sepsis and a likely key mechanism in its morbidity and mortality. CYT107 represents a potential new way forward in the treatment of patients with sepsis by restoring adaptive immunity. Such immune-based therapy should be broadly protective against diverse pathogens including multidrug resistant bacteria that preferentially target patients with impaired immunity. TRIAL REGISTRATION: Trials registered at clinicaltrials.gov: NCT02640807 and NCT02797431. FUNDING: Revimmune, NIH National Institute of General Medical Sciences GM44118.

Methadone Pharmacogenetics: CYP2B6 Polymorphisms Determine Plasma Concentrations, Clearance, and Metabolism.

BACKGROUND: Interindividual variability in methadone disposition remains unexplained, and methadone accidental overdose in pain therapy is a significant public health problem. Cytochrome P4502B6 (CYP2B6) is the principle determinant of clinical methadone elimination. The CYP2B6 gene is highly polymorphic, with several variant alleles. CYP2B6.6, the protein encoded by the CYP2B6*6 polymorphism, deficiently catalyzes methadone metabolism in vitro. This investigation determined the influence of CYP2B6*6, and other allelic variants encountered, on methadone concentrations, clearance, and metabolism. METHODS: Healthy volunteers in genotype cohorts CYP2B6*1/*1 (n = 21), CYP2B6*1/*6 (n = 20), and CYP2B6*6/*6 (n = 17), and also CYP2B6*1/*4 (n = 1), CYP2B6*4/*6 (n = 3), and CYP2B6*5/*5 (n = 2) subjects, received single doses of IV and oral methadone. Plasma and urine methadone and metabolite concentrations were determined by tandem mass spectrometry. RESULTS: Average S-methadone apparent oral clearance was 35 and 45% lower in CYP2B6*1/*6 and CYP2B6*6/*6 genotypes, respectively, compared with CYP2B6*1/*1. R-methadone apparent oral clearance was 25 and 35% lower in CYP2B6*1/*6 and CYP2B6*6/*6 genotypes, respectively, compared with CYP2B6*1/*1. R- and S-methadone apparent oral clearance was threefold and fourfold greater in CYP2B6*4 carriers. IV and oral R- and S-methadone metabolism was significantly lower in CYP2B6*6 carriers compared with that of CYP2B6*1 homozygotes and greater in CYP2B6*4 carriers. Methadone metabolism and clearance were lower in African Americans in part because of the CYP2B6*6 genetic polymorphism. CONCLUSIONS: CYP2B6 polymorphisms influence methadone plasma concentrations, because of altered methadone metabolism and thus clearance. Genetic influence is greater for oral than IV methadone and S- than R-methadone. CYP2B6 pharmacogenetics explains, in part, interindividual variability in methadone elimination. CYP2B6 genetic effects on methadone metabolism and clearance may identify subjects at risk for methadone toxicity and drug interactions.

The hematological effects of nitrous oxide anesthesia in pediatric patients.

BACKGROUND: Prolonged administration of nitrous oxide causes an increase in plasma homocysteine in children via vitamin B12 inactivation. However, it is unclear whether nitrous oxide doses used in clinical practice cause adverse hematological effects in pediatric patients. METHODS: This retrospective study included 54 pediatric patients undergoing elective spinal surgery: 41 received nitrous oxide throughout anesthesia (maintenance group), 9 received nitrous oxide for induction and/or emergence (induction/emergence group), and 4 did not receive nitrous oxide (nitrous oxide-free group). Complete blood counts obtained before and up to 4 days after surgery were assessed for anemia, macrocytosis/microcytosis, anisocytosis, hyperchromatosis/hypochromatosis, thrombocytopenia, and leukopenia. The change (Δ) from preoperative to the highest postoperative value was calculated for mean corpuscular volume (MCV) and red cell distribution width (RDW). RESULTS: No pancytopenia was present in any patient after surgery. All patients had postoperative anemia, and none had macrocytosis. Postoperative MCV (mean [99% confidence interval]) peaked at 86 fL (85-88 fL), 85 fL (81-89 fL), and 88 fL (80-96 fL) and postoperative RDW at 13.2% (12.8-13.5%), 13.3% (12.7-13.8%), and 13.0% (11.4-14.6%) for the maintenance group, the induction/emergence group, and the nitrous oxide-free group. Two patients in the maintenance group (5%) developed anisocytosis (RDW >14.6%), but none in the induction/emergence group or in the nitrous oxide-free group (P = 0.43). Both ΔMCV (P = 0.52) and ΔRDW (P = 0.16) were similar across all groups. CONCLUSIONS: Nitrous oxide exposure for up to 8 hours is not associated with megaloblastic anemia in pediatric patients undergoing major spinal surgery.

Cyclosporine-inhibitable cerebral drug transport does not influence clinical methadone pharmacodynamics.

BACKGROUND: Interindividual variability and drug interaction studies suggest that blood-brain barrier drug transporters mediate human methadone brain biodistribution. In vitro and animal studies suggest that methadone is a substrate for the efflux transporter P-glycoprotein, and that P-glycoprotein-mediated transport influences brain access and pharmacologic effect. This investigation tested whether methadone is a transporter substrate in humans [corrected]. METHODS: Healthy volunteers received oral (N=16) or IV (N=12) methadone in different crossover protocols after nothing (control) or the validated P-glycoprotein inhibitor cyclosporine (4.5 mg/kg orally twice daily for 4 days, or 5 mg/kg IV over 2 h). Plasma and urine methadone and metabolite concentrations were measured by mass spectrometry. Methadone effects were measured by miosis and thermal analgesia (maximally tolerated temperature and verbal analog scale rating of discreet temperatures). RESULTS: Cyclosporine marginally but significantly decreased methadone plasma concentrations and apparent oral clearance, but had no effect on methadone renal clearance or on hepatic N-demethylation. Cyclosporine had no effect on miosis or on R-methadone concentration-miosis relationships after either oral or IV methadone. Peak miosis was similar in controls and cyclosporine-treated subjects after oral methadone (1.4±0.4 and 1.3±0.5 mm/mg, respectively) and IV methadone (3.1±1.0 and 3.2±0.8 mm, respectively). Methadone increased maximally tolerated temperature, but analgesia testing was confounded by cyclosporine-related pain. CONCLUSIONS: Cyclosporine did not affect methadone pharmacodynamics. This result does not support a role for cyclosporine-inhibitable transporters mediating methadone brain access and biodistribution.

Cyclosporine-inhibitable blood-brain barrier drug transport influences clinical morphine pharmacodynamics.

BACKGROUND: The blood-brain barrier is richly populated by active influx and efflux transporters influencing brain drug concentrations. Morphine, a drug with delayed clinical onset, is a substrate for the efflux transporter P-glycoprotein in vitro and in animals. This investigation tested whether morphine is a transporter substrate in humans. METHODS: Fourteen healthy volunteers received morphine (0.1 mg/kg, 1-h IV infusion) in a crossover study without (control) or with the infusion of validated P-glycoprotein inhibitor cyclosporine (5 mg/kg, 2-h infusion). Plasma and urine morphine and morphine glucuronide metabolite concentrations were measured by mass spectrometry. Morphine effects were measured by miosis and analgesia. RESULTS: Cyclosporine minimally altered morphine disposition, increasing the area under the plasma morphine concentration versus time curve to 100 ± 21 versus 85 ± 24 ng/ml·h (P < 0.05) without changing maximum plasma concentration. Cyclosporine enhanced (3.2 ± 0.9 vs. 2.5 ± 1.0 mm peak) and prolonged miosis, and increased the area under the miosis-time curve (18 ± 9 vs. 11 ± 5 mm·h), plasma effect-site transfer rate constant (k(e0), median 0.27 vs. 0.17 h(-1)), and maximum calculated effect-site morphine concentration (11.5 ± 3.7 vs. 7.6 ± 2.9 ng/ml; all P < 0.05). Analgesia testing was confounded by cyclosporine-related pain. CONCLUSIONS: Morphine is a transporter substrate at the human blood-brain barrier. Results suggest a role for P-glycoprotein or other efflux transporters in brain morphine access, although the magnitude of the effect is small, and unlikely to be a major determinant of morphine clinical effects. Efflux may explain some variability in clinical morphine effects.

Postoperative QT interval prolongation in patients undergoing noncardiac surgery under general anesthesia.

BACKGROUND: Abnormal cardiac repolarization, indicated by a prolongation of the QT interval, increases the risk for torsades de pointes, a potentially life-threatening arrhythmia. Many perioperatively administered drugs and conditions prolong the QT interval. Despite several reports of perioperative torsades de pointes, systematic evidence regarding perioperative QT interval prolongation is limited. METHODS: Serial postoperative 12-lead electrocardiograms were obtained from 469 adult patients undergoing major noncardiac surgery under general anesthesia. Heart rate corrected QT-interval duration (Fridericia formula) was the primary outcome. All perioperatively administered drugs were recorded. Emphasis was placed on absolute QTc prolongation greater than 500 ms and relative increases of 30 and 60 ms. RESULTS: At the end of surgery, 80% of the patients (345 of 429) experienced a significant QTc interval prolongation (ΔQTc 23 ± 26 ms (mean and SD), 95% CI 20-25 ms, P less than 0.001). Approximately 51% (219 of 429) had a QTc greater than 440 ms, and 4% (16 of 429) a QTc greater than 500 ms. In 39% (166 of 429), the ΔQTc was greater than 30 ms, in 8% (34 of 429) >60 ms, and in greater than 0.5% (2 of 429) >100 ms. No changes in ΔQTc occurred at subsequent time points. One patient developed torsades de pointes with a ΔQTc: 29 ms (0.4% incidence rate). Several drugs had a large effect on ΔQTc: isoflurane, methadone, ketorolac, cefoxitin, zosyn, unasyn, epinephrine, ephedrine, and calcium. Postoperative body temperature had a weak negative correlation with ΔQTc (r = -0.15, P = 0.02); serum magnesium, potassium, and calcium concentrations were not correlated. CONCLUSION: Postoperative QT-interval prolongation is common. Several perioperatively administered drugs are associated with a substantial QT-interval prolongation. The exact cause and its clinical relevance are, however, unclear. Nevertheless, an association between postoperative QT prolongation and risk for torsades de pointes is likely.

Perioperative pharmacokinetics of methadone in adolescents.

BACKGROUND: Methadone is frequently administered to adults experiencing anesthesia and receiving pain treatment. Methadone pharmacokinetics in adults are well characterized, including the perioperative period. Methadone is also used in children. There is, however, no information on methadone pharmacokinetics in children of any age. The purpose of this investigation was to determine the pharmacokinetics of intravenous methadone in children undergoing surgery. Perioperative opioid-sparing effects were also assessed. METHODS: Eligible subjects were children 5-18 yr undergoing general anesthesia and surgery, with an anticipated postoperative inpatient stay exceeding 3 days. Three groups of 10 to 11 patients each received intravenous methadone hydrochloride after anesthetic induction in ascending dose groups of 0.1, 0.2, and 0.3 mg/kg (up to 20 mg). Anesthetic care was not otherwise changed. Venous blood was obtained for 4 days, for stereoselective determination of methadone and metabolites. Pain assessments were made each morning. Daily and total opioid consumption was determined. Perioperative opioid consumption and pain was determined in a second cohort, which was matched to age, sex, race, ethnicity, surgical procedure, and length of stay, but not receiving methadone. RESULTS: The final methadone study cohort was 31 adolescents (14 ± 2 yr, range 10-18) undergoing major spine surgery for a diagnosis of scoliosis. Methadone pharmacokinetics were linear over the dose range 0.1-0.3 mg/kg. Disposition was stereoselective. Methadone administration did not dose-dependently affect postoperative pain scores, and did not dose-dependently decrease daily or total postoperative opioid consumption in spinal fusion patients. CONCLUSIONS: Methadone enantiomer disposition in adolescents undergoing surgery was similar to that in healthy adults.

Nitrous oxide anesthesia and plasma homocysteine in adolescents.

BACKGROUND: Nitrous oxide inactivates vitamin B(12), inhibits methionine synthase, and consequently increases plasma total homocysteine (tHcy). Prolonged exposure to nitrous oxide can lead to neuropathy, spinal cord degeneration, and even death in children. We tested the hypothesis that nitrous oxide anesthesia causes a significant increase in plasma tHcy in children. METHODS: Twenty-seven children (aged 10-18 years) undergoing elective major spine surgery were enrolled, and serial plasma samples from 0 to 96 hours after induction were obtained. The anesthetic regimen, including the use of nitrous oxide, was at the discretion of the anesthesiologist. Plasma tHcy was measured using standard enzymatic assays. RESULTS: The median baseline plasma tHcy concentration was 5.1 µmol/L (3.9-8.0 µmol/L, interquartile range) and increased in all patients exposed to nitrous oxide (n = 26) by an average of +9.4 µmol/L (geometric mean; 95% confidence interval, 7.1-12.5 µmol/L) or +228% (mean; 95% confidence interval, 178%-279%). Plasma tHcy peaked between 6 and 8 hours after induction of anesthesia. One patient who did not receive nitrous oxide had no increase in plasma tHcy. Several patients experienced a severalfold increase in plasma tHcy (maximum +567%). The increase in plasma tHcy was strongly correlated with the duration and average concentration of nitrous oxide anesthesia (r = 0.80; P < 0.001). CONCLUSIONS: Pediatric patients undergoing nitrous oxide anesthesia develop significantly increased plasma tHcy concentrations. The magnitude of this effect seems to be greater compared with adults; however, the clinical relevance is unknown.