Comparative simulation of intraperitoneal aminoglycoside regimens for patients with peritonitis on automated peritoneal dialysis.

BACKGROUND: Intraperitoneal (IP) aminoglycosides (AGs) continue to be the cornerstone of empiric management of peritonitis. AG dosing during automated peritoneal dialysis (APD), however, has not been well studied in patients with peritonitis. We sought to identify differences in AG exposure in the peritoneum and plasma for two different dosing regimens with little supporting evidence in patients on APD with peritonitis. METHODS: A retrospective design that utilised the peritoneal and plasma concentration-time data from a prior study of 18 continuous ambulatory peritoneal dialysis (CAPD) patients with peritonitis to generate an in silico peritoneal and plasma PK model. This model was then used to compare via simulation using Phoenix© WinNonlin Software with IP AG dosing for a loading-dose regimen (1.5 mg/kg first dose) versus a fixed-dose regimen (0.6 mg/kg/d) in patients on APD with peritonitis. RESULTS: Outcome measures were (1) percentage of time where peritoneal peak concentrations/minimal inhibitory concentration (MIC) ratio >10, (2) AUC/MIC > 74 and (3) plasma Cmin concentrations. Both regimens resulted in > 90% optimal peak/MIC ratio and AUC/MIC ratios on days 1 and 5 of the dose protocol. The loading-dose regimen resulted in IP exposures that were 2.5 times greater in the peritoneal compartment on day 1. By day 5, both protocols resulted in similar accumulation of AG plasma Cmin concentrations of 2.5-3.4 mg/L versus 2.4-3.3 mg/L, respectively, for the loading-dose regimen versus fixed-dose regimen. CONCLUSIONS: The current international guidelines for the treatment of peritoneal dialysis-associated peritonitis can continue to recommend the fixed-dose regimen for those on APD with the addition of plasma Cmin monitoring after 3 days to assess for drug accumulation.

An updated vancomycin dosing protocol for initiating therapy in patients undergoing intermittent high-flux hemodialysis.

PURPOSE: To design an updated vancomycin dosing protocol for initiating therapy in patients undergoing chronic intermittent high-flux hemodialysis (iHFHD) that is congruent with the revised 2020 consensus guidelines for therapeutic drug monitoring (TDM). METHODS: Monte Carlo simulation methods were used to study vancomycin dosing for patients on iHFHD. Vancomycin regimens were constructed as intravenous infusions (for intradialytic administration) of a loading dose and maintenance doses 3 times weekly during subsequent dialysis sessions. Vancomycin plasma concentrations were simulated, and the probability of target attainment (PTA) for a 24-hour area under the time-concentration curve (AUC24) of 400 to 700 mg · h/L was determined. Standardized weight-based (ie, dose-banding) regimens were investigated, and an optimized protocol was selected based on TDM target attainment and practical considerations for use in the dialysis setting. RESULTS: The proposed vancomycin dosing protocol (for intradialytic administration) specifies 3 regimens: (1) a 1,500-mg loading dose and 750-mg maintenance doses for patients weighing 50 kg to 69 kg; (2) a 2,000-mg loading dose and 1,000-mg maintenance doses for patients weighing 70 kg to 89 kg; and (3) a 2,500-mg loading dose and 1,250-mg maintenance doses for patients weighing 90 kg to 110 kg. In a simulated hemodialysis population (n = 5,000), the proposed protocol delivered median (interquartile range [IQR]) loading and maintenance doses of 25.0 (23.4-26.6) mg/kg and 12.5 (11.8-13.3) mg/kg, respectively. The PTA for an AUC24 of 400 to 700 mg · h/L was 74.7% on day 1 and 70.8% on day 8, with less than 10% of values exceeding the target range. CONCLUSION: Our proposed dosing protocol for patients undergoing iHFHD offers an updated and practical approach for initiating vancomycin therapy that can be optimized with early TDM.

Prophylactic tranexamic acid use in non-cardiac surgeries at high risk for transfusion.

BACKGROUND: Tranexamic acid (TXA) reduces transfusion in a wide range of surgical populations, although its real-world use in non-cardiac surgeries has not been well described. The objective of this study was to describe prophylactic TXA use in non-cardiac surgeries at high risk for transfusion. METHODS: This is a retrospective cohort study of all adult patients undergoing major non-cardiac surgery at ≥5% risk of perioperative transfusion at five Canadian hospitals between January 2014 and December 2016. Canadian Classification of Health Interventions procedure codes within the Discharge Abstract Database were linked to transfusion and laboratory databases. TXA use was ascertained electronically from The Ottawa Hospital Data Warehouse and via manual chart review for Winnipeg hospitals. For each surgery, we evaluated the percentage of patients who received TXA as well as the specifics of TXA dosing and administration. RESULTS: TXA use was evaluable in 14 300 patients. Overall, 17% of surgeries received TXA, ranging from 0% to 68% among individual surgeries. TXA use was more common in orthopaedic (n = 2043/4942; 41%) and spine surgeries (n = 239/1322; 18%) compared to other surgical domains (n = 109/8036; 1%). TXA was commonly administered as a bolus (n = 2097/2391; 88%). The median TXA dose was 1000 mg (IQR 1000-1000 mg). CONCLUSION: TXA is predominantly used in orthopaedic and spine surgeries, with little uptake in other non-cardiac surgeries at high risk for red blood cell transfusion. Further studies are needed to evaluate the effectiveness and safety of TXA and to understand the barriers to TXA administration in a broad range of non-cardiac surgeries.

Evaluation of Transfusion Practices in Noncardiac Surgeries at High Risk for Red Blood Cell Transfusion: A Retrospective Cohort Study.

Perioperative bleeding is a major indication for red blood cell (RBC) transfusion, yet transfusion data in many major noncardiac surgeries are lacking and do not reflect recent blood conservation efforts. We aim to describe transfusion practices in noncardiac surgeries at high risk for RBC transfusion. We completed a retrospective cohort study to evaluate adult patients undergoing major noncardiac surgery at 5 Canadian hospitals between January 2014 and December 2016. We used Canadian Classification of Health Interventions procedure codes within the Discharge Abstract Database, which we linked to transfusion and laboratory databases. We studied all patients undergoing a major noncardiac surgery at ≥5% risk of perioperative RBC transfusion. For each surgery, we characterized the percentage of patients exposed to an RBC transfusion, the mean/median number of RBC units transfused, and platelet and plasma exposure. We identified 85 noncardiac surgeries with an RBC transfusion rate ≥5%, representing 25,607 patient admissions. The baseline RBC transfusion rate was 16%, ranging from 5% to 49% among individual surgeries. Of those transfused, the median (Q1, Q3) number of RBCs transfused was 2 U (1, 3 U); 39% received 1 U RBC, 36% received 2 U RBC, and 8% were transfused ≥5 U RBC. Platelet and plasma transfusions were overall low. In the era of blood conservation, we described transfusion practices in major noncardiac surgeries at high risk for RBC transfusion, which has implications for patient consent, preoperative surgical planning, and blood bank inventory management.

Antimicrobial Prophylaxis for Patients Undergoing Cardiac Surgery: Intraoperative Cefazolin Concentrations and Sternal Wound Infections.

This study characterizes the pharmacodynamics of antimicrobial prophylaxis and sternal wound infections following cardiac surgery. Duration of surgery and cefazolin plasma concentration during wound closure were independently associated with surgical site infection at 30 days. Furthermore, a duration of surgery of >346 min and a total cefazolin closure concentration of <104 mg/liter were significant thresholds for an increased risk of infection. This study provides new data that informs dosing strategies for effective antimicrobial prophylaxis (AP) in patients undergoing cardiac surgery with cardiopulmonary bypass.

Limitations of ceftriaxone compared with cefazolin against MSSA: an integrated pharmacodynamic analysis.

Objectives: Despite the convenience of once-daily dosing, the use of ceftriaxone for Staphylococcus aureus infections has significant limitations, including scarce clinical evidence and increasingly questionable pharmacodynamic activity. Our goal was to conduct an integrated pharmacokinetic-pharmacodynamic analysis of the appropriateness of ceftriaxone compared with cefazolin for treating serious MSSA infections. Methods: Ceftriaxone and cefazolin activity against five clinical MSSA isolates was characterized in an in vitro pharmacodynamic model. Monte Carlo simulations were then used to evaluate various dosing regimens of ceftriaxone and cefazolin based on relevant patient pharmacokinetic data, significant pharmacodynamic targets derived from the in vitro studies (55%ƒT>MIC for bacteriostasis, 75%ƒT>MIC for 1 log10 bacterial kill, 100%ƒT>MIC for ≥3 log10 bacterial kill) and MIC distributions for MSSA from national surveillance data. Results: Ceftriaxone at 1 g once daily had poor activity against MSSA with net bacterial growth predicted in 76% of simulated subjects. The standard 2 g of ceftriaxone once daily had predicted bacterial growth or bacteriostasis in 54% of cases with bactericidal effects in only 17%. Cefazolin at 2 g once daily was notably similar to ceftriaxone in expected target attainments. Cefazolin at 2 g twice daily demonstrated maximal pharmacodynamic activity with bactericidal effects in 97% of simulated subjects. Conclusions: Given the limited activity of ceftriaxone against S. aureus, particularly for serious infections when bacterial kill is desired, the convenience of once-daily dosing should be weighed against the risks of using an overly broad, suboptimal therapy. Cefazolin warrants further consideration, particularly as optimal pharmacodynamics against MSSA may be achieved with twice-daily dosing in most patients.

The Pharmacokinetics and Pharmacodynamics of Carfentanil After Recreational Exposure: A Case Report.

Carfentanil and related fentanyl analogs have been linked to a number of overdose deaths from drug users in several cities across North America. Diagnosis of carfentanil exposure requires a very high index of clinical suspicion, especially because available laboratory narcotic screens do not detect this agent. We describe a 34-year-old man admitted with depressed level of consciousness and in respiratory failure after recreational exposure to a white powder later inferred to contain carfentanil. Urine and whole blood samples were obtained for conventional preliminary drug screen immunoassays for unknown exposures, in addition to utilizing a high-pressure liquid chromatography-tandem mass spectrometry assay for quantification of carfentanil and its metabolite. The patient was intubated and required mechanically assisted ventilation for 31 hours until he was able to breathe safely on his own. Pharmacokinetic modeling of three timed blood samples identified the elimination half-life as 5.7 hours for carfentanil and 11.8 hours for the norcarfentanil metabolite. Awakening and breathing spontaneously corresponded to an interpolated blood carfentanil concentration of 0.52 ng/ml. This is the first pharmacokinetic and pharmacodynamic case report on the recreational use of carfentanil. Critical care clinicians should anticipate long periods of ventilatory support in the care of patients exposed to carfentanil.

Evaluation of cefazolin antimicrobial prophylaxis during cardiac surgery with cardiopulmonary bypass.

Objectives: Although clinical practice guidelines recommend standard cefazolin antimicrobial prophylaxis (AP) dosing for cardiac surgery, limited data exist as to whether adequate concentrations are achieved in this patient population. The goal of our study was to characterize intraoperative cefazolin concentrations particularly at wound closure with regards to maintaining target cefazolin closure concentrations ≥40 mg/L. Methods: Adults undergoing cardiac surgery with cardiopulmonary bypass (CPB) and receiving cefazolin AP according to protocol were studied. Blood samples were collected after the preoperative cefazolin dose, prior to intraoperative cefazolin doses and at wound closure. Intraoperative trough and closure concentrations were characterized and evaluated against a target threshold of ≥ 40 mg/L (≥8 mg/L unbound, assuming 80% protein binding). Results: Fifty-five subjects (64.9 ±âŸ10.4 years, 89.7 ±âŸ16.5 kg, CLCR >50 mL/min/72 kg) completed the study. Total cefazolin concentrations were <40 mg/L in 40% (12 of 30) of intraoperative trough samples and 9.8% (5 of 51) of closure samples. Below-target concentrations at some time during surgery were documented in 30.9% (17 of 55) of subjects. In multivariate analyses, lower body weight (P = 0.027) and shorter duration of surgery (P = 0.045) were significant predictors of closure concentrations <40 mg/L. A total cefazolin exposure (preoperative and intraoperative doses) of ≥ 7.6 mg/kgdosing weight for every hour of surgery (intermittent dosing) was required to achieve target closure concentrations. Conclusions: The standard cefazolin AP regimen was not reliable in maintaining target closure concentrations ≥40 mg/L in patients with normal renal function undergoing elective cardiac surgery with CPB. The findings supported a cefazolin AP regimen consisting of at least 2 g preoperatively and every 3 h during surgery.

No role for patient body weight on renal function assessment for drug dosing.

Objectives: To evaluate the ability of body-weight-driven renal function assessment (RFA) formulae to predict on-target elimination rate ranges for gentamicin in patients with varying degrees of renal function. Methods: A 6 year retrospective pharmacokinetic study was conducted at a university teaching hospital. Results: A total of 85 patients met the inclusion criteria and 127 pharmacokinetic files were analysed from patients on medical-surgical wards (53%) and medical-surgical ICUs (13%) receiving intravenous gentamicin for treatment, as well as those for patients receiving it for surgical prophylaxis (34%). Each RFA formula was examined against standard dosing tables for gentamicin. A table of acceptable elimination rates was generated using a traditional peak of 8 mg/L and trough between 0.5 and 2 mg/L associated with each of the dosing interval extensions. The ability of each RFA formula to select on-target elimination rates was evaluated. The RFA formula assuming a normalized body weight of 72 kg and a modified creatinine reagent adjustment factor of 90% provided the most accurate on-target elimination rate selection. This method was superior to dosing interval selection based on the Modification in Diet Renal Disease (MDRD) formula, Sanford's guide method, as well as the Cockcroft-Gault formulae using total body weight, ideal body weight or lean body weight ( P < 0.0001). Conclusions: Based on the use of gentamicin as a surrogate guide for renally adjusted drugs, these results support dosing interval selection based on a normalized body weight method and a formula reagent adjustment factor of 90% within the Cockcroft-Gault formula.

Comparison of Fentanyl and Morphine in the Prehospital Treatment of Ischemic Type Chest Pain.

In the treatment of acute coronary syndromes, reduction of sympathetic stress and catecholamine release is an important therapeutic goal. One method used to achieve this goal is pain reduction through the systemic administration of analgesia. Historically, morphine has been the analgesic of choice in ischemic cardiac pain. This randomized double-blind controlled trial seeks to prove the utility of fentanyl as an alternate first-line analgesic for ischemic-type chest pain in the prehospital setting. Successive patients who were treated for suspected ischemic chest pain in the emergency medical services system were considered eligible. Once chest pain was confirmed, patients received oxygen, aspirin, and nitroglycerin therapy. If the ischemic-type chest pain continued the patient was randomized in a double-blinded fashion to treatment with either morphine or fentanyl. Pain scale scores, necessity for additional dosing, and rate of adverse events between the groups were assessed every 5 minutes and were compared using t-testing, Fisher's Exact test, or Analysis of Variance (ANOVA) where appropriate. The primary outcome of the study was incidence of hypotension and the secondary outcome was pain reduction as measured by the visual analog score and numeric rating score. A total of 207 patients were randomized with 187 patients included in the final analysis. Of the 187 patients, 99 were in the morphine group and 88 in the fentanyl group. No statistically significant difference between the two groups with respect to hypotension was found (morphine 5.1% vs. fentanyl 0%, p = 0.06). Baseline characteristics, necessity for additional dosing, and other adverse events between the two groups were not statistically different. There were no significant differences between the changes in visual analog scores and numeric rating scale scores for pain between the two groups (p = 0.16 and p = 0.15, respectively). This study supports that fentanyl and morphine are comparable in providing analgesia for ischemic-type chest pain. Fentanyl appears to be a safe and effective alternative to morphine for the management of chest pain in the prehospital setting.

Post-operative nausea and vomiting in the cardiac surgery population: who is at risk?

OBJECTIVES: Post-operative nausea and vomiting (PONV) is a common and distressing complication following cardiac surgery. Therefore, our primary objective was to explore the predictors of severe PONV in the cardiac surgery population. METHODS: A retrospective study was completed on cardiac surgery patients (N = 150). A modified preoperative PONV risk assessment tool was utilized to identify patients at high and low risk for PONV. RESULTS: 54% of the high-risk group versus 13% of the low-risk group experienced ≥2 nausea events in the early post-operative period (p < 0.0001). The high-risk group had a uniquely elevated and sustained number of PONV events post-operatively. History of PONV (p = 0.03) and female gender (p = 0.01) emerged as significant predictors of any nausea event. CONCLUSIONS: A specific PONV risk assessment tool may be useful for predicting those at highest risk following cardiac surgery. Further research is required to identify strategies to reduce PONV.

Preoperative therapeutic apheresis for severe medically refractory amiodarone-induced thyrotoxicosis: a case report.

INTRODUCTION: Amiodarone is associated with thyroid dysfunction and life-threatening thyrotoxicosis. In medically refractory cases, or where medical therapy is contraindicated, thyroidectomy may be required. To decrease perioperative thyroid storm and to reduce overall surgical risk, apheresis may be considered preoperatively to restore euthyroidism. CASE DESCRIPTION: We report a 46-year-old female with a history of cardiac arrhythmia and tachycardia-induced cardiomyopathy for which she received amiodarone. Months after discontinuation of amiodarone, the patient presented with wide complex tachycardia and symptoms of thyrotoxicosis. Laboratory testing confirmed severe thyrotoxicosis which was subsequently refractory to medical therapy. Total thyroidectomy was required. Following a total of 10 apheresis treatments, thyroid hormone levels were reduced to near normal levels and the patient's symptoms improved. Thyroidectomy was performed without intraoperative or postoperative complication. DISCUSSION: In the setting of life-threatening, medically refractory amiodarone-induced thyrotoxicosis, therapeutic apheresis can effectively reduce thyroid hormone levels and restore a state of clinical and biochemical euthyroidism.

Successful treatment of pulmonary blastomycosis with continuously infused amphotericin B deoxycholate after failure with liposomal amphotericin B.

OBJECTIVE: To describe a case of successful treatment of severe pulmonary blastomycosis with amphotericin B deoxycholate after failure of liposomal amphotericin B. CASE SUMMARY: A 35-year-old male was exposed to damp decomposing wood while cleaning his basement. He subsequently developed a cough, malaise, fever, nausea, vomiting, and diarrhea. He was admitted to the hospital and intubated for worsening pulmonary symptoms. Microscopic examination of his sputum indicated Blastomyces dermatitidis. Liposomal amphotericin B was administered for 6 days, but the patient's temperature reached 39.6 °C and his white blood cell (WBC) count reached 52,300/µL. Extensive consolidation of both lungs fields was observed on chest X-ray. Because of progressive clinical deterioration, the treatment was switched to amphotericin B deoxycholate by continuous infusion. That change resulted in clinical improvement, with abrupt reductions (within 48 hours) in temperature and the WBC count. By day 14 of therapy (day 8 of amphotericin B deoxycholate), the chest X-ray showed improvement in diffuse airspace filling. After 16 days of amphotericin B treatment, intravenous followed by oral voriconazole was administered for 3 months. Eight months later the patient's strength had improved significantly, but he still had occasional episodes of shortness of breath. DISCUSSION: The management of blastomycosis is challenging because of the lack of clinically supporting data. The gold standard for severe pulmonary blastomycosis had been amphotericin B deoxycholate; however, improved safety data with liposomal amphotericin B for other fungal infections has suggested this as an effective alternative. This report describes a patient with severe pulmonary blastomycosis failing 6 days of liposomal amphotericin B, yet he tolerated and clinically responded to continuous infusion of amphotericin B deoxycholate. Based on this case report and a simulated pharmacokinetic/pharmaco dynamic analysis, continuous infusion of amphotericin B deoxycholate may be a reasonable option for enhanced efficacy and minimal toxicity in patients with blastomycosis. CONCLUSIONS: Ours is the first case report to use continuous infusion of amphotericin B deoxycholate for the management of pulmonary blastomycosis. These results suggest that liposomal amphotericin B may not be adequate in some patients for the management of B. dermatitidis pulmonary infections.

Integrating pharmacokinetics, pharmacodynamics and MIC distributions to assess changing antimicrobial activity against clinical isolates of Pseudomonas aeruginosa causing infections in Canadian hospitals (CANWARD).

OBJECTIVES: To study antimicrobial pharmacodynamic (PD) activity over time against clinical isolates of Pseudomonas aeruginosa in Canadian hospitals. METHODS: Integrated pharmacokinetic (PK)/PD analyses with Monte Carlo simulations were used to study cefepime, meropenem, piperacillin/tazobactam, ciprofloxacin, amikacin, gentamicin and colistin. Profiles of P. aeruginosa infections were modelled using CANWARD data from January 2007 to June 2012 inclusive. The probability of target attainment (PTA) was the proportion of cases achieving a %ƒT>MIC ≥ 50% for cefepime, meropenem and piperacillin/tazobactam, an ƒAUC/MIC ≥ 90 for ciprofloxacin and the aminoglycosides, and a total AUC/MIC ≥ 60 for colistin. RESULTS: Some 2126 P. aeruginosa isolates were identified. There were no significant trends over time in the PTA for cefepime (0.93-1.0), meropenem (0.89-0.92) or piperacillin/tazobactam (0.74-0.79) (data shown for the highest recommended doses). The PD activity for ciprofloxacin (PTA 0.48-0.64) was variable. There were notable improvements in the PTA for amikacin (from 0.21 to 0.55, P = 0.027), gentamicin (from 0.10 to 0.51, P = 0.035) and colistin (from 0.04 to ~0.20, P = 0.05), which were not reliably detected by MIC indices. There was a decline over time in the PTA for piperacillin/tazobactam from 0.73 to 0.61 against P. aeruginosa isolated from intensive care units (ICUs) (Pearson correlation coefficient -0.99, P = 0.003). Neither MIC50 nor MIC90 detected this reduction in PD activity. CONCLUSIONS: The overall PD activity against P. aeruginosa was stable from 2007 to 2012 for cefepime, meropenem and piperacillin/tazobactam, was variable and unreliable for ciprofloxacin, and improved significantly but remained relatively low for the aminoglycosides and colistin. There was a progressive reduction over time in the PD activity of piperacillin/tazobactam against ICU isolates, which was not detected by simply assessing MIC indices.

Initial vancomycin dosing protocol to achieve therapeutic serum concentrations in patients undergoing hemodialysis.

BACKGROUND: Although recent consensus guidelines proposed more aggressive vancomycin troughs of >10 or 15-20 mg/L for complicated Staphylococcus aureus infections, dosing information to achieve these targets in patients undergoing hemodialysis (HD) is scarce. METHODS: We used Monte Carlo simulation (MCS) methods with a previously published population-pharmacokinetic model and relevant patient demographics to evaluate and revise our existing vancomycin dosing protocol (1000-mg load followed by 500-mg maintenance dose, with doses infused during the last hour of dialysis). A new protocol (1000-mg load followed by 500-mg maintenance dose for patients <70 kg, 1250-mg followed by 750-mg for those 70-100 kg, and 1500-mg followed by 1000-mg for those >100 kg) was developed and prospectively validated to achieve therapeutic serum troughs in patients undergoing high-flux HD. RESULTS: MCSs predicted that our existing protocol would be suboptimal in more than one-third of patients. Simulations predicted that the new vancomycin dosing protocol would achieve maintenance (pre-HD) troughs of 10-20 mg/L in 86.0% of cases including 15-20 mg/L in 35.2%. In prospective validation, the observed postload trough (pre-HD session 2) was 13.5 ± 3.4 mg/L with 76.9% of levels (20 of 26) between 10 and 20 mg/L. The observed maintenance trough was 17.3 ± 4.0 mg/L with 65.5% (19 of 29) between 10 and 20 mg/L and 89.7% (26 of 29) within 10% of the upper limit (ie, 10-22 mg/L). CONCLUSIONS: In this study, a practical vancomycin dosing protocol for patients undergoing HD was developed and prospectively validated to achieve therapeutic serum concentrations in the clinical setting.

The influence of sparse data sampling on population pharmacokinetics: a post hoc analysis of a pharmacokinetic study of morphine in healthy volunteers.

BACKGROUND: Intensive sampling of patients for drugs with complex pharmacokinetic profiles is difficult to perform in the clinic or hospitalized patient setting. We seek to address whether sparse sampling can obtain pharmacokinetic parameter values similar to those with traditional modeling from a post hoc analysis of 2 previous clinical trials. OBJECTIVE: This study investigated whether population-guided, sparse-sampling pharmacokinetic analysis of morphine in 14 healthy volunteers allowed for optimal characterization of concentration-time profiles for a validation population of 5 young male patients receiving morphine. METHODS: Data were analyzed using nonparametric adaptive grid (NPAG) population modeling to investigate optimal compartmental structure and the influence of sparse sampling (ie, 9 versus 3 samples per subject) on parameter identification. These results were compared with traditional standard 2-stage (STS) pharmacokinetic modeling. The coefficients of determination (R(2)), mean error (ME), and root-mean-square error were used to assess the predictive performance of the various sampling models against a validation population. RESULTS: Seventy-nine percent of the healthy volunteers were male, with a mean age of 36 (17) years and a mean weight of 68 (10) kg. NPAG modeling identified that intravenous morphine was best represented by a 3-compartment pharmacokinetic profile and that sparse sampling with a least 3 blood samples per subject resulted in virtually identical measures of central tendency as the more intensively sampled dataset. A validation cohort of 5 male patients undergoing elective surgery had a mean age of 26 (4) years and a mean weight of 80 (13) kg. Using mean parameter estimates generated from sparse sampling and the 3-compartment model structure, simulated profiles were compared against measured concentrations in this validation cohort. Sparse sampling using NPAG achieved similar values of predictive performance as mean parameter values from the more intensively sampled, with an ME of -1.0 ng/mL and precision of 26.2 ng/mL compared with 0.76 ng/mL and 25.8 ng/mL, respectively. Traditional (STS) modeling techniques resulted in the greatest degree of underprediction within the validation group (ME = 4.43 versus 0.76 ng/mL, STS and NPAG-9, respectively; P < 0.0001). CONCLUSIONS: This post hoc analysis suggests that intensive sampling for discerning complex, 3-compartment pharmacokinetic models, such as morphine, may not be necessary. Sparse sampling achieved accurate model structure recognition and parameter identification for predicting concentrations of very complex drug-dosage regimens.

Sedation and analgesia usage in severe pandemic H1N1 (2009) infection: a comparison to respiratory failure secondary to other infectious pneumonias.

BACKGROUND: During the 2009 H1N1 pandemic (pH1N1), patients requiring mechanical ventilation for respiratory failure received high doses of sedation and analgesia. OBJECTIVE: To examine sedation and analgesia use among patients with respiratory failure due to severe pH1N1 infection compared to other infectious pneumonias. METHODS: In this observational cohort study of intensive care unit (ICU) patients with respiratory failure, we compared doses of sedatives and analgesics administered to patients with pH1N1, non-pH1N1 viral pneumonia, and adult respiratory distress syndrome (ARDS) secondary to bacterial pneumonia, on days 1, 3, 7, 14, and 28 of ICU admission. Cumulative drug use, daily drug use, and weight-adjusted medication doses were examined. RESULTS: The study population consisted of 37 patients with pH1N1 infection, 22 patients with non-pH1N1 viral pneumonia, and 46 patients with ARDS secondary to bacterial pneumonia. To achieve similar levels of sedation using the Richmond Agitation Sedation Scale, patients with pH1N1 were administered the highest cumulative median doses of fentanyl (11,230 µg; interquartile range [IQR] 3240-21,000), compared to 2400 µg (IQR 130-7130) in viral pneumonia and 2880 µg (IQR 600-6950) in ARDS (p < 0.001). Patients with pH1N1 were also administered the highest cumulative median doses of midazolam at 820 mg (IQR 330-1160), compared to 160 mg (IQR 20-390) in viral pneumonia and 160 mg (IQR 20-480 mg) in ARDS (p < 0.001). The pH1N1 group received the highest median daily fentanyl and midazolam doses on all study days. The pH1N1 group did not differ significantly in cumulative propofol dose compared with the other 2 study groups. CONCLUSIONS: Sedative and analgesic use may be uniquely higher in critically ill patients with pH1N1 infection compared to patients with other infectious pneumonias. This finding may be important for resource planning in future pandemics. Further study is required to explore the underlying mechanisms for potentially higher sedative and analgesic requirements in this patient population.

Neuroleptic malignant syndrome versus serotonin syndrome: the search for a diagnostic tool.

OBJECTIVE: To evaluate the use of urine dopamine and catecholamine concentrations as diagnostic aids in a patient with neuroleptic malignant syndrome (NMS) in the emergency department setting. CASE SUMMARY: A 61-year-old female on multiple medications, including several antipsychotics, rapidly deteriorated, with fever, lead-pipe rigidity, and decreased level of consciousness. The patient died 20 days after initial presentation to an emergency department. The Naranjo probability scale indicated probable causality for NMS due to quetiapine, haloperidol, and risperidone in this patient, whereas the Naranjo scale assigned only possible causality for serotonin syndrome developing with serotonergic agents. Laboratory investigations of blood and urine revealed elevations in dopamine, metanephrines, and epinephrines, as well as trazodone and risperidone. Serotonin metabolites were not elevated. DISCUSSION: NMS is a rare and potentially severe adverse effect associated with the use of antipsychotic medications. It is mainly characterized by hyperthermia, altered mental state, hemodynamic dysregulation, elevated serum creatine kinase, and rigors. It has been associated with multisystem organ failure potentially leading to rhabdomyolysis, acute respiratory distress syndrome, and disseminated intravascular coagulation. The prevalence of this syndrome is associated with the use of neuroleptics. Serotonin syndrome is another adverse drug reaction leading to NMS associated with elevated serotonin. It occurs when multiple serotonergic medications are ingested and is associated with rapid onset of altered mental status, myoclonus, and autonomic instability. Differentiating between NMS and serotonin syndrome can be challenging because of their similar clinical presentation. This case highlights the importance of a diagnostic aid being available to help distinguish between the 2 syndromes. CONCLUSIONS: We propose that laboratory findings that include dopamine and serotonin metabolites can be used as adjuncts to clinical and prescription histories in the diagnosis of NMS. The use of urinary catecholamine as a diagnostic aid in NMS needs further evaluation.