Un recorrido por la pared abdominal: evaluación de las hernias por tomografía computada multidetector / A tour of the abdominal wall: assessment of hernias by multidetector computed tomography

Si bien el diagnóstico de hernias de la pared abdominal es clínico y el estudio más indicado es la ecografía, en una gran cantidad de casos es difícil su evaluación o no se sospecha su presencia debido al biotipo del paciente, la ausencia de síntomas, la aparición de complicaciones o corresponde a algún tipo de hernia poco frecuente. Además, la debilidad de la pared abdominal generada por una cirugía predispone a la eventración de órganos, a veces poco habituales, como el hígado, la vejiga o el apéndice. La utilización de la tomografía computada multidetector (TCMD) brinda grandes ventajas cuando resulta dificultoso establecer el diagnóstico por otros métodos. También puede ser un hallazgo incidental a tener en cuenta por sus posibles complicaciones futuras. En el presente trabajo describimos los principales hallazgos por TCMD de las hernias y eventraciones de la pared abdominal (como la umbilical, epigástrica, hipogástrica, inguinal, de Spiegel, lumbar, obturatriz, intercostal e incisional) y su contenido.

Although the diagnosis of abdominal wall hernias is clinical, and the most appropriate study is ultrasound, in a lot of cases they are difficult to evaluate, or their presence is not suspected because of the biotype of the patient, the absence of symptoms, the presence of complications, or the appearance of rare hernias. Surgery weakness generated in the wall leads to organ hernia, sometimes unusual, as in the liver, bladder, or appendix. The use of multidetector computed tomography (MDCT) is a great advantage in these situations where the diagnosis can be difficult to determine with other methods. It also can be an incidental finding to consider eventual complications. In this paper, the main MDCT findings in abdominal wall hernias are described, including umbilical, epigastric, hypogastric, inguinal, Spiegel, lumbar, obturator, intercostal, and incisional, as well as their content.

Hemorragia abdominal espontánea: evaluación por imágenes / Abdominal hemorrhage spontaneous: imaging evaluation

Se define como hemorragia intraabdominal espontánea a aquella que no es de causa traumática. Su presentación clínica es inespecífica, por lo que el diagnóstico suele realizarse en base a los hallazgos imagenológicos. El estudio de imágenes cumple tres funciones básicas: realizar el diagnóstico al detectar la presencia de sangre intraabdominal, localizar el origen del sangrado y determinar la presencia o no de extravasación arterial activa. Las causas del hemoperitoneo no traumático son diversas y se pueden clasificar, según el órgano de origen, en hepáticas, esplénicas, pancreáticas, adrenales, renales, gineco-obstétricas, vasculares y de partes blandas (peritoneales y musculares)

It defines spontaneous abdominal hemorrhage that is not traumatic. Its clinical presentation is nonspecific and usually not suspected by the emergency physician, so the diagnosis is usually made based on imaging findings. The study of images serves three basic functions, which are to perform the diagnosis by detecting the presence of blood intraabdominal, locating the source of bleeding and determining the presence or absence of active arterial extravasation. The causes of non traumatic hemoperitoneum are diverse and can be classified according to the organ of origin in liver, spleen, pancreas, adrenal, kidney, obstetric-gynecology, vascular and soft tissue (peritoneal and muscular)

Hemorragia abdominal espontánea: evaluación por imágenes

Se define como hemorragia intraabdominal espontánea a aquella que no es de causa traumática. Su presentación clínica es inespecífica, por lo que el diagnóstico suele realizarse en base a los hallazgos imagenológicos. El estudio de imágenes cumple tres funciones básicas: realizar el diagnóstico al detectar la presencia de sangre intraabdominal, localizar el origen del sangrado y determinar la presencia o no de extravasación arterial activa. Las causas del hemoperitoneo no traumático son diversas y se pueden clasificar, según el órgano de origen, en hepáticas, esplénicas, pancreáticas, adrenales, renales, gineco-obstétricas, vasculares y de partes blandas (peritoneales y musculares).(AU)

It defines spontaneous abdominal hemorrhage that is not traumatic. Its clinical presentation is nonspecific and usually not suspected by the emergency physician, so the diagnosis is usually made based on imaging findings. The study of images serves three basic functions, which are to perform the diagnosis by detecting the presence of blood intraabdominal, locating the source of bleeding and determining the presence or absence of active arterial extravasation. The causes of non traumatic hemoperitoneum are diverse and can be classified according to the organ of origin in liver, spleen, pancreas, adrenal, kidney, obstetric-gynecology, vascular and soft tissue (peritoneal and muscular).(AU)

Surgical management of intestinal malrotation in adults: comparative results for open and laparoscopic Ladd procedures.

BACKGROUND: This study aimed to characterize the clinical features of intestinal malrotation in adults, and to compare the results for the open and laparoscopic Ladd procedures. METHODS: Between 1984 and 2003, 21 adult patients with a mean age of 36 years (range, 14-89 years) were surgically treated for intestinal malrotation. The clinical data collected included age, gender, presenting symptoms, diagnostic tests, type of operation, operative time, narcotic requirement, time to oral intake, length of hospital stay, and outcome. The groups (open vs laparoscopic) were comparatively analyzed using two-sample t-tests and Wilcoxon rank sum tests. RESULTS: The two groups were similar in terms of age, clinical presentation, and diagnostic tests performed. The most common presenting symptoms were chronic abdominal pain, nausea, and repeated vomiting. Upper gastrointestinal barium studies (UGI/SBFT) were diagnostic for all patients with malrotation as compared with computed tomography (CT) scanning, which was falsely negative in 25% of patients. A total of 21 patients underwent the Ladd procedure, either open (n = 10) or laparoscopic (n = 11). Three laparoscopic procedures were converted to open. Overall, the laparoscopic group resumed oral intake earlier than the open group (1.8 vs 2.7 days; p = 0.092), had a shorter hospital stay (4.0 vs. 6.1 days; p = 0.050), and required less intravenous narcotics on postoperative day 1 (4.9 vs 48.5 mg; p = 0.002). The laparoscopic group underwent a longer operation (194 vs 143 min; p = 0.053). Sixteen of eighteen patients available for follow-up reported complete resolution of symptoms, 2 felt greatly improved. No patient required a second operation related to volvulus or recurrent symptoms. CONCLUSIONS: The laparoscopic Ladd procedure is feasible, safe, and as effective as the standard open Ladd procedure for the treatment of adults who have intestinal malrotation without midgut volvulus. Patients also benefit from this minimally invasive approach, as manifested by an earlier oral intake, a decreased need for intravenous narcotics, and an earlier discharge from the hospital.

Characterization of tubular functional capacity in humans using para-aminohippurate and famotidine.

BACKGROUND: Renal drug excretion by glomerular filtration and active tubular secretion may be altered by factors such as acute and chronic renal disease, nephrotoxins, and drug interactions. Thus, accurate and reproducible methods for quantitation of glomerular filtration rate (GFR) and tubular functional capacity are critical. METHODS: We utilized a four-step sequential infusion method to characterize anionic [para-aminohippurate (PAH)] and cationic (famotidine) tubular functional capacity in healthy volunteers. Filtration and secretion rates were quantitated from renal clearance and iothalamate-derived GFR determinations. RESULTS: Concentration-dependent renal clearance of PAH was observed at plasma concentrations> 100 mg/L; renal clearances were 442 +/- 131 (mean +/- SD), 423 +/- 94, 233 +/- 45, and 152 +/- 18 mL/min/1.73 m2 at plasma concentrations of 18 +/- 2, 92 +/- 5, 291 +/- 47 and 789 +/- 28 mg/L, respectively. The apparent affinity (Km) and maximum secretory capacity (TmPAH) were 141 +/- 70 mg/L and 71 +/- 16 mg/min/1.73 m2, respectively. The unbound renal clearance and tubular secretory clearance of famotidine were 384 +/- 70 and 329 +/- 78 mL/min/1.73 m2, respectively, and were not significantly correlated with the unbound plasma concentrations, which ranged from 126 to 2659 ng/mL. The rate of tubular secretion was linear at unbound plasma concentrations up to 2659 ng/mL. CONCLUSIONS: These data indicate that a sequential infusion method using PAH may be used to characterize the anionic secretory component of proximal tubular function. The tubular clearance of famotidine may be a suitable index of the cationic secretory capacity of the proximal tubule in humans. Saturation of the cationic secretory pathway was not observed, and further investigation into parallel pathways of cationic secretion, such as p-glycoprotein, may be warranted.

Effect of ceftazidime on systemic cytokine concentrations in rats.

The effect of a single dose of ceftazidime on circulating concentrations of interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) in a rat model of sepsis was studied. IL-6 concentrations were significantly elevated (100 to 200 times the baseline) 6 h after ceftazidime administration in both septic and nonseptic (control) rats. TNF-alpha concentrations increased significantly in nonseptic (approximately 40 times the baseline) rats but not septic (approximately 2 to 3 times the baseline) rats. Ceftazidime administration was not associated with an increase in endotoxin concentrations. These findings suggest that ceftazidime modulation of proinflammatory cytokine concentrations may be independent of its antimicrobial properties.

Nephrology pharmaceutical care preceptorship: a programmatic and clinical outcomes assessment.

OBJECTIVE: The University of Pittsburgh Nephrology Pharmaceutical Care Preceptorship (NPCP) program was conceived to acquaint health system pharmacists with the pharmacotherapeutic management of dialysis patients, enhance the delivery of pharmaceutical care, and improve clinical outcomes through the development of specialized professional skills. A survey designed to determine the impact of the NPCP program was sent to all 145 participants of the program. METHODS: The survey, designed to collect demographic information and data about the participants' practice sites, professional activities prior to and after the completion of the program, and markers of disease status, was mailed to all participants in September 1997. The 96 respondents (66.2%) were involved in a wide variety of clinical practices; inpatient management of peritoneal dialysis, hemodialysis, or renal transplant patients were most commonly reported. RESULTS: More than 80% of the participants believed that the educational content of the NPCP program was sufficient to allow them to establish a specialized service for the management of dialysis patients. However, two-thirds would have preferred to have more contact time (an additional 1-2 d) with the preceptorship faculty. The percentage of the pharmacists' time devoted to the provision of pharmaceutical care for dialysis patients almost doubled, from 13.1% to 25.2% (p < 0.001). The components of pharmaceutical care performed by these pharmacists also changed as a result of their completion of the NPCP program. Time devoted to clinical services and the provision of educational programs (inservices) increased significantly, while the time allocated to distributive activities decreased from a mean of 32.4% to 26.4% (almost 20% from baseline). The number of pharmacists who provided some component of pharmaceutical care for ambulatory dialysis patients increased significantly, from 10 to 33, after completion of the program. In the survey given after the preceptorship, almost 70% of these 33 pharmacists self-reported that the mean hematocrit of their ambulatory dialysis patients increased; 45% reported that the epoetin dose was lower. Parenteral iron use was also reported to have increased in 78.8% of the dialysis units, and an increase in serum ferritin and transferrin saturation was observed in 54.5% and 60.6% of the units. respectively. Although far fewer pharmacists (n = 15) initiated a renal osteodystrophy management program, 73.3% of those who did so reported an increase in their patients' compliance with phosphate binder therapy, which was reflected in a drop in serum phosphorous in 40% of the units. CONCLUSIONS: The NPCP program resulted in changes in the professional activities of the participants: fewer distributive activities and increased clinical and educational activities. These significant changes were noted in all areas of outpatient care. Participation in the NPCP program enhanced the delivery of pharmaceutical care to dialysis patients and improved the markers of disease status.

Determinants of ceftriaxone clearance by continuous venovenous hemofiltration and hemodialysis.

STUDY OBJECTIVE: To guide individual ceftriaxone dosages in patients receiving continuous renal replacement therapy. DESIGN: Prospective, outpatient study. SETTING: University-affiliated general clinical research center. PATIENTS: Eight patients receiving hemodialysis. INTERVENTION: We performed controlled clearance studies with three hemofilters: an acrylonitrile copolymer 0.6 m2 (AN69), polymethylmethacrylate 2.1 m2 (PMMA), and polysulfone 0.65 m2 (PS). MEASUREMENTS AND MAIN RESULTS: Subjects received ceftriaxone 1000 mg intravenously before the start of a clearance study. The concentration of ceftriaxone in multiple plasma and dialysate-ultrafiltrate samples was determined by high-performance liquid chromatography. The diffusional clearances (Cl(diffusion)) and sieving coefficients (SC) of ceftriaxone, urea, and creatinine were compared by a mixed-model repeated-measures analysis of variance with filter and blood, dialysate inflow, or ultrafiltration rate as the main effect and patient as a random effect. The fraction of ceftriaxone bound to plasma proteins was 43 +/- 15% (range 13-92%). Concentration dependence was evident in all three groups. The fraction unbound to plasma proteins (f(up)) at the time that SCs were determined was significantly lower in the PS group (0.16 +/- 0.07) than the AN69 group (0.30 +/- 0.17, p<0.01), but similar to that in the PMMA group (0.27 +/- 0.12). Despite the higher f(up), the SC of unbound ceftriaxone with the AN69 filter (0.48 +/- 0.13) was significantly lower than values for the PMMA (0.86 +/- 0.33) and PS (0.82 +/- 0.22) groups (p<0.05). Continuous venovenous hemofiltration clearance of urea and unbound ceftriaxone increased significantly only for the PMMA (p=0.006) and PS (p=0.015) filters when the ultrafiltration rate was increased. Significant linear relationships (p<0.0001) were observed between Cl(diffusion) of unbound ceftriaxone and clearance of urea for all three filters: AN69 slope = 0.57, PMMA slope = 0.90, and PS slope = 1.02. The slope of this relationship for the AN69 filter was significantly lower than for the other two filters. CONCLUSION: Ceftriaxone clearance was significantly increased and membrane dependent during continuous venovenous hemofiltration and continuous venovenous hemodialysis. Thus individual ceftriaxone dosages for patients receiving continuous renal replacement therapies should incorporate extracorporeal clearance.

Unintended immunomodulation: part I. Effects of common clinical conditions on cytokine biosynthesis.

Cytokines are low molecular weight proteins that act in an autocrine, paracrine and endocrine fashion to regulate and integrate immune effector cell function. Cytokine production is tightly controlled by a complex network of co-stimulatory and feedback loops. The systemic concentrations of some cytokines, most notably tumor necrosis factor and various interleukins, correlate with the extent of inflammation, and the severity of critical illness and patient outcome. Thus, cytokine expression is often monitored and/or manipulated as a therapeutic target in studies of sepsis and other inflammatory conditions. Unfortunately, some therapies designed to modify cytokine response have failed to improve outcomes in sepsis, and some of these therapies have actually been harmful. Several common clinical conditions, as well as, therapeutic interventions significantly influence cytokine expression. Furthermore, the magnitude and extent of these effects may be greater than those produced by immunomodulating therapies. In contrast, other conditions may not produce clinically significant changes in cytokine expression, and must simply be considered when interpreting studies designed to determine the effects of immunomodulation. Some conditions may even result in changes in the inflammatory response and may thus add to the inflammatory burden of a critically ill patient. This review provides intensivists and other clinicians with an overview of the effects of altered physiologic conditions on cytokine expression. This information is important so that studies measuring cytokines can be correctly interpreted and clinical circumstances in which cytokine manipulation is undesirable can perhaps be avoided.

Unintended immunomodulation: part II. Effects of pharmacological agents on cytokine activity.

Cytokines are proteins that are produced by immune and non-immune cells, and they function as mediators to facilitate cellular communication. Their production is regulated by a complex network of co-stimulatory and feedback loops that responds to a variety of stimuli. Several pharmacological agents have been found to alter systemic concentrations and/or the activity of different cytokines via a variety of mechanisms, including changes in biosynthesis, secretion, and/or stability. Many of the agents that modulate cytokine levels commonly are used in the management of critically ill patients. Catecholamines for example, have been found to promote the secretion of anti-inflammatory cytokines, and, therefore, may alter acute inflammatory processes such as sepsis. Antimicrobials have multiple effects on cytokine production, either secondary to the release of endotoxins from gram-negative bacteria or via direct activity on cytokine expression at the transcriptional and/or post-transcriptional level. Pentoxifylline has multiple effects on the immune system, but inhibition of pro-inflammatory cytokine release predominates. The reminder of the known drug-cytokine interactions and their effect on the inflammatory process are discussed. Information on the pharmacodynamic effect of drugs is limited, and our understanding of the clinical significance of these observations awaits further investigation. This review was designed to provide intensivists and other clinicians with useful information regarding the effect of medications on cytokine activity. It is also intended to help researchers and clinicians to optimize the design of studies of pharmacotherapeutic modulation of cytokines and to avoid the use of some agents in clinical circumstances in which cytokine manipulation is undesirable.

Determinants of ceftazidime clearance by continuous venovenous hemofiltration and continuous venovenous hemodialysis.

Although several dosage adjustment regimens have been proposed, there is little quantitative information to guide the initiation of ceftazidime therapy in patients who are receiving continuous renal replacement therapy. To determine the clearance of ceftazidime by continuous venovenous hemofiltration (CVVH) and continuous venovenous hemodialysis (CVVHD), we performed controlled clearance studies with stable hemodialysis patients with three hemofilters: a 0.6-m(2) acrylonitrile copolymer (AN69; Hospal) filter, a 2.1-m(2) polymethylmethacrylate filter (PMMA; Toray) filter and a 0.65-m(2) polysulfone (PS; Fresenius) filter. Subjects received 1,000 mg of ceftazidime intravenously prior to the start of a clearance study. The concentration of ceftazidime in multiple plasma and dialysate or ultrafiltrate samples was determined by high-performance liquid chromatography. The diffusional clearances (CI(diffusion)) and sieving coefficients of ceftazidime were compared by a mixed-model repeated-measures analysis of variance with filter and blood, dialysate inflow, or ultrafiltration rate as the main effect and the patient as a random effect. The fraction of ceftazidime bound to plasma proteins was 17%+/-7% (range, 10 to 25%). The clearances of ceftazidime, urea, and creatinine by CVVHD were essentially constant at blood flow rates of 75 to 250 ml/min for all three filters. Significant linear relationships (P<0.0001) were observed between CI(diffusion) of ceftazidime and clearance of urea for all three filters: AN69 (slope = 0.83), PMMA (slope = 0.89), and PS (slope = 1.03). Ceftazidime clearance was membrane independent during CVVH and CVVHD. CVVH and CVVHD can significantly augment the clearance of ceftazidime. Dosing strategies for initiation of ceftazidime therapy in patients receiving CVVH and CVVHD are proposed.

Evaluation of the influence of diabetes mellitus on antipyrine metabolism and CYP1A2 and CYP2D6 activity.

STUDY OBJECTIVE: To evaluate the metabolism of antipyrine, a general metabolic probe, caffeine, a probe for cytochrome P450 (CYP) 1A2 and N-acetyltransferase activity, and dextromethorphan, a specific probe for CYP2D6 activity in patients with type 1 or 2 diabetes mellitus. DESIGN: Prospective, controlled study. SETTING: Research facility. Patients. Fifteen patients with type 1 and 16 with type 2 diabetes, and 16 healthy controls. INTERVENTION: Each subject simultaneously received antipyrine 10 mg/kg, caffeine 100 mg, and dextromethorphan 30 mg. MEASUREMENTS AND MAIN RESULTS: The pharmacokinetics of antipyrine and its primary metabolites were determined from saliva and urine samples. Type 1 diabetes had marked effects on antipyrine metabolism whereas type 2 disease did not alter the metabolism of any of the probe drugs. The apparent oral clearance of antipyrine was increased 72% in patients with type 1 disease compared with controls (p=0.0001). In addition, formation clearances of 4-hydroxyantipyrine and 3-hydroxymethylantipyrine were increased by 74% and 137% in those patients relative to controls. The caffeine metabolic index (paraxanthine/caffeine) was increased 34% (p=0.11), and N-acetylation and CYP2D6 phenotype were not altered. CONCLUSION: The metabolism of antipyrine is increased in patients with type 1 diabetes. Based on in vitro reports of antipyrine metabolism and current caffeine metabolic index data, the predominant effect of type 1 diabetes appears to be an increase in CYP1A2 activity. Assessment of the effect of the disease on other specific CYP metabolic pathways is warranted.

Comparison of iothalamate clearance methods for measuring GFR.

STUDY OBJECTIVE: To evaluate the bias and precision of three methods of measuring glomerular filtration rate (GFR) relative to a standard method. DESIGN: Prospective, outpatient study. SETTING: University-affiliated general clinical research center. PATIENTS: Twenty-six patients with various degrees of renal function (GFR range 25-151 ml/min/1.73 m2). INTERVENTIONS: Each patient received iothalamate twice during the study visit, first as a bolus injection and then as a priming dose followed by a constant-rate infusion for 2.5 hours. MEASUREMENTS AND MAIN RESULTS: Plasma (ClpIVB) and renal clearances (ClrIVB) after bolus injection and plasma clearance during constant-rate infusion (ClpINF) were compared with standard renal clearance during constant-rate infusion (ClrINF). All three measures were highly correlated with ClrINF (r>0.90, p<0.001). The mean ClrIVB was not significantly different from ClrINF (106.3+/-30.4 vs 104.2+/-28.5 ml/min/1.73 m2) and provided a precise (8.8%, 95% CI 6.5-11.1%) and unbiased measure of GFR. Both ClpIVB and ClpINF were positively biased; values exceeded ClrINF by 11.8+/-11.1 (p=0.0001) and 10.5+/-12.5 ml/min/1.73 m2 (p=0.0003), respectively. Use of a nonrenal correction factor of 9.8 and 10.5 ml/min/1.73 m2 for infusion and bolus plasma clearance values, respectively, eliminated bias and improved the precision of these methods. CONCLUSIONS: Iothalamate renal clearance after bolus injection is a simple, accurate, and precise measurement of GFR and may be a useful alternative to the standard infusion method in clinical investigations. The corrected plasma clearance provides a simple index of GFR for clinical practice.

Cefazolin as empiric therapy in hemodialysis-related infections: efficacy and blood concentrations.

Concern about the increasing incidence of vancomycin-resistant organisms has tempered the enthusiasm for indiscriminate vancomycin use. Cefazolin has an antibacterial activity profile similar to vancomycin against most pathogens encountered in the hemodialysis (HD) population. We evaluated the clinical efficacy and serum concentrations that were achieved during empiric cefazolin use. Fifteen consecutive HD patients (five, conventional HD; five, high-efficiency HD; and five, high-flux HD) with suspected or documented infections warranting antibiotic intervention, including access-related, respiratory tract, urinary tract, or wound infections, were enrolled. Each patient received intravenous cefazolin (20 mg/kg actual body weight rounded to the nearest 500-mg increment [range, 1 to 2 g]) after each dialysis treatment for at least three doses. Cefazolin concentrations were obtained before and immediately after the next three consecutive dialysis treatments. Thirteen patients were evaluated for efficacy and all 15 were evaluated for toxicity and cefazolin blood concentrations. All patients showed at least a short-term (3-week) clinical resolution of infection with cefazolin treatment. No central nervous system toxicities were noted and no other adverse events were expressed by the patients during the course of cefazolin treatment. Predialysis cefazolin concentrations, as determined by high-performance liquid chromatography, were 70.2 +/- 42.7 (conventional HD), 45.6 +/- 18.9 (high-efficiency HD), and 41.6 +/- 23.9 mg/L (high-flux HD) over the three dialysis sessions. Cefazolin at doses of approximately 20 mg/kg administered post-HD appears to be a safe and effective empiric therapy and yields predialysis cefazolin concentrations of 2.5 times or greater than those considered to be the minimum inhibitory concentration breakpoint (16 mg/L) for susceptible organisms. These data support the broader use of cefazolin for empiric treatment in the HD population, allowing vancomycin to be reserved for confirmed resistant organisms.

Determinants of vancomycin clearance by continuous venovenous hemofiltration and continuous venovenous hemodialysis.

The clearance of vancomycin is significantly reduced in patients with acute, as well as, chronic renal failure. Although multiple-dosage regimen adjustment techniques have been proposed for these patients, there is little quantitative data to guide the individualization of vancomycin therapy in acute renal failure patients who are receiving continuous renal replacement therapy (CRRT). To determine appropriate vancomycin dosing strategies for patients receiving continuous venovenous hemofiltration (CVVH) and continuous venovenous hemodialysis (CVVHD), we performed controlled clearance studies in five stable hemodialysis patients with three hemofilters: an acrylonitrile copolymer 0.6 m2 (AN69), polymethylmethacrylate 2.1 m2 (PMMA), and polysulfone 0.65 m2 (PS). Patients received 500 mg of vancomycin intravenously at least 12 hours before the start of the clearance study. The concentration of vancomycin in multiple plasma and dialysate/ultrafiltrate samples was determined by EMIT (Syva, Palo Alto, CA). The diffusional clearance and sieving coefficient (SC) of vancomycin were compared by a mixed-model repeated-measures analysis of variance (ANOVA) with filter and blood (Q(B)), dialysate inflow (Q(DI)), or ultrafiltration rate (Q(UF)) as the main effects and patient as a random effect. Vancomycin was moderately protein bound in these patients; free fraction ranged from 49% to 83%. The SCs of the three filters were similar and significantly correlated with the free fraction of vancomycin (P = 0.01; r2 = 0.465). Significant linear relationships were observed between the diffusional clearance of vancomycin and Q(DI) for all three filters: AN69 (slope = 0.482; r2 = 0.880); PMMA (slope = 0.853; r2 = 0.966); and PS (slope = 0.658; r2 = 0.887). The slope of this relationship for the PMMA filter was significantly greater than that of the AN69 and PS filters. The clearance of vancomycin, urea, and creatinine, however, was essentially constant at all Q(B)s for all three filters. Thus, the clearance of vancomycin was not membrane dependent during CVVH. However, during CVVHD, membrane dependence of vancomycin clearance was noted at a Q(DI) greater than 16.7 mL/min; vancomycin clearance with PMMA at a Q(DI) of 25 mL/min was 66% and 43% greater than that with the AN69 and PS filters, respectively. CVVH (62% to 262%) and CVVHD (90% to 540%) can significantly augment the clearance of vancomycin in acute renal failure patients. Dosing strategies for individualization of vancomycin therapy in patients receiving CVVH and CVVHD are proposed.

Use of chlorzoxazone as an in vivo probe of cytochrome P450 2E1: choice of dose and phenotypic trait measure.

Chlorzoxazone is being developed and proposed for use as a probe to measure in vivo cytochrome P4502E1 activity, but the phenotypic trait measures that are used vary. Although the doses proposed for phenotyping range from 250 mg to 750 mg, the effect of dose on chlorzoxazone hydroxylation has not previously been evaluated. The purpose of this study was to characterize the pharmacokinetics of chlorzoxazone in normal healthy volunteers (N = 6) after single randomized oral doses of 250 mg and 750 mg. An additional 10 volunteers underwent a detailed pharmacokinetic study using the 250-mg dose to further evaluate proposed phenotypic trait measures (N = 16). Timed blood and urine samples were obtained for 10 hours for chlorzoxazone and 6-hydroxychlorzoxazone determination by HPLC. Pharmacokinetic parameter estimates were estimated using noncompartmental methods. Evaluation of phenotypic trait measures show that 6-hydroxychlorzoxazone to chlorzoxazone plasma concentration ratios at 2 to 4 hours after drug administration demonstrated the highest correlations with metabolite formation clearance (r = 0.9; P < 0.001). Urine-based parameters (e.g., total recovery) were not significantly related to formation clearance (r = 0.5; P > 0.05). Dose dependency in chlorzoxazone metabolism was shown by a 30% increase (P < 0.05) in the dose-normalized area under the concentration-time curve (AUC) of chlorzoxazone and lower incremental dose-normalized urinary recovery of 6-hydroxychlorzoxazone at early timepoints after the 750-mg dose. In addition, the plasma ratio of 6-hydroxychlorzoxazone to chlorzoxazone at 4 hours was reduced by 48% in 5 of 6 subjects after the 750-mg dose (P > 0.05). These data suggest that 6-hydroxylation was saturated at the higher dose and illustrate the importance of dose selection in phenotyping. The results of this study indicate that a chlorzoxazone dose of 250 mg should be used and that a single plasma ratio obtained 2 to 4 hours after dosing is reflective of chlorzoxazone 6-hydroxylation and thus may serve as a cytochrome P4502E1 phenotypic trait measure.

A primer on continuous renal replacement therapy for critically ill patients.

OBJECTIVES: To characterize the multiple continuous renal replacement therapy (CRRT) techniques available for the management of critically ill adults, and to review the indications for and complications of use, principles of drug removal during CRRT, drug dosage individualization guidelines, and the influence of CRRT on patient outcomes. DATA SOURCES: MEDLINE (January 1981-December 1996) was searched for appropriate publications by using terms such as hemofiltration, ultrafiltration, hemodialysis, hemodiafiltration, medications, and pharmacokinetics; selected articles were cross-referenced. STUDY SELECTION: References selected were those considered to enhance the reader's knowledge of the principles of CRRT, and to provide adequate therapies on drug disposition. DATA SYNTHESIS: CRRTs use filtration/convection and in some cases diffusion to treat hemodynamically unstable patients with fluid overload and/or acute renal failure. Recent data suggest that positive outcomes may also be attained in patients with other medical conditions such as septic shock, multiple organ dysfunction syndrome, and hepatic failure. Age, ventilator support, inotropic support, reduced urine volume, and elevated serum bilirubin concentrations have been associated with poor outcomes. Complications associated with CRRT include bleeding due to excessive anticoagulation and line disconnections, fluid and electrolyte imbalance, and filter and venous clotting. CRRT can complicate the medication regimens of patients for whom it is important to maintain drug plasma concentrations within a narrow therapeutic range. Since the physicochemical characteristics of a drug and procedure-specific factors can alter drug removal, a thorough assessment of all factors needs to be considered before dosage regimens are revised. In addition, an algorithm for drug dosing considerations based on drug and CRRT characteristics, as well as standard pharmacokinetic equations, is proposed. CONCLUSIONS: The use of CRRT has expanded to encompass the treatment of disease states other than just acute renal failure. Since there is great variability among treatment centers, it is premature to conclude that there is enhanced survival in CRRT-treated patients compared with those who received conventional hemodialysis. This primer may help clinicians understand the need to individualize these therapies and to prospectively optimize the pharmacotherapy of their patients receiving CRRT.