Clinical Pharmacology of Elagolix: An Oral Gonadotropin-Releasing Hormone Receptor Antagonist for Endometriosis

The clinical pharmacology of elagolix was extensively evaluated in clinical studies in healthy subjects and in women with endometriosis. Elagolix pharmacokinetics (PK) show significant population variability, however they are minimally affected by patients' baseline characteristics and demographics, except for clinically relevant extrinsic and intrinsic factors such as coadministrated strong organic anion transporting polypeptide (OATP) 1B1 inhibitors and severe hepatic impairment, which are contraindications for the use of elagolix. These studies enabled a comprehensive understanding of elagolix mechanism of action and the downstream pharmacodynamic (PD) effects on gonadotropin and ovarian hormones, as well as full characterization of the PK/PD (PKPD) relationships of elagolix at various dosages, including the approved 150 mg once daily and 200 mg twice daily dosing regimens for the management of moderate to severe pain associated with endometriosis. Several model-based analyses have contributed to understanding of the benefit-risk profile of elagolix in patients with endometriosis, through characterization of the exposure relationship with responder rates, with changes in bone mineral density over time, as well as the interaction with coadministered drugs. Collectively, these studies and analyses served as supportive evidence for the effectiveness of the approved dosages and provided general dosing instructions of the first approved oral gonadotropin-releasing hormone receptor antagonist.

Impact of Target-Mediated Elimination on the Dose and Regimen of Evolocumab, a Human Monoclonal Antibody Against Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9)

Understanding the pharmacokinetic (PK) and pharmacodynamic (PD) relationship of a therapeutic monoclonal antibody against proprotein convertase subtilisin/kexin type 9 (PCSK9) exhibiting target-mediated drug disposition (TMDD) is critical for selecting optimal dosing regimens. We describe the PK/PD relationship of evolocumab using a mathematical model that captures evolocumab binding and removal of unbound PCSK9 as well as reduction in circulating low-density lipoprotein cholesterol (LDL-C). Data were pooled from 2 clinical studies: a single-dose escalation study in healthy subjects (7-420 mg SC; n = 44) and a multiple-dose escalation study in statin-treated hypercholesterolemic patients (14 mg weekly to 420 mg monthly [QM] SC; n = 57). A TMDD model described the time course of unbound evolocumab concentrations and removal of unbound PCSK9. The estimated linear clearance and volume of evolocumab were 0.256 L/day and 2.66 L, respectively, consistent with other monoclonal antibodies. The time course of LDL-C reduction was described by an indirect response model with the elimination rate of LDL-C being modulated by unbound PCSK9. The concentration of unbound PCSK9 associated with half-maximal inhibition (IC₅₀ ) of LDL-C elimination was 1.46 nM. Based on simulations, 140 mg every 2 weeks (Q2W) and 420 mg QM were predicted to achieve a similar time-averaged effect of 69% reduction in LDL-C in patients on statin therapy, suggesting that an approximate 3-fold dose increase is required for a 2-fold extension in the dosing interval. Evolocumab dosing regimens of 140 mg Q2W or 420 mg QM were predicted to result in comparable reductions in LDL-C over a monthly period, consistent with results from recently completed phase 3 studies.

A model-based meta-analysis of monoclonal antibody pharmacokinetics to guide optimal first-in-human study design

The objectives of this retrospective analysis were (1) to characterize the population pharmacokinetics (popPK) of four different monoclonal antibodies (mAbs) in a combined analysis of individual data collected during first-in-human (FIH) studies and (2) to provide a scientific rationale for prospective design of FIH studies with mAbs. The data set was composed of 171 subjects contributing a total of 2716 mAb serum concentrations, following intravenous (IV) and subcutaneous (SC) doses. mAb PK was described by an open 2-compartment model with first-order elimination from the central compartment and a depot compartment with first-order absorption. Parameter values obtained from the popPK model were further used to generate optimal sampling times for a single dose study. A robust fit to the combined data from four mAbs was obtained using the 2-compartment model. Population parameter estimates for systemic clearance and central volume of distribution were 0.20 L/day and 3.6 L with intersubject variability of 31% and 34%, respectively. The random residual error was 14%. Differences (> 2-fold) in PK parameters were not apparent across mAbs. Rich designs (22 samples/subject), minimal designs for popPK (5 samples/subject), and optimal designs for non-compartmental analysis (NCA) and popPK (10 samples/subject) were examined by stochastic simulation and estimation. Single-dose PK studies for linear mAbs executed using the optimal designs are expected to yield high-quality model estimates, and accurate capture of NCA estimations. This model-based meta-analysis has determined typical popPK values for four mAbs with linear elimination and enabled prospective optimization of FIH study designs, potentially improving the efficiency of FIH studies for this class of therapeutics.

Greater seasonal cycling of 25-hydroxyvitamin D is associated with increased parathyroid hormone and bone resorption

SUMMARY

This analysis assessed whether seasonal change in 25-hydroxyvitamin D concentration was associated with bone resorption, as evidenced by serum parathyroid hormone and C-terminal telopeptide concentrations. The main finding was that increased seasonal fluctuation in 25-hydroxyvitamin D was associated with increased levels of parathyroid hormone and C-terminal telopeptide.

INTRODUCTION

It is established that adequate 25-hydroxyvitamin D (25(OH)D, vitamin D) concentration is required for healthy bone mineralisation. It is unknown whether seasonal fluctuations in 25(OH)D also impact on bone health. If large seasonal fluctuations in 25(OH)D were associated with increased bone resorption, this would suggest a detriment to bone health. Therefore, this analysis assessed whether there is an association between seasonal variation in 25(OH)D and bone resorption.

METHODS

The participants were (n = 279) Caucasian and (n = 88) South Asian women (mean (±SD); age 48.2 years (14.4)) who participated in the longitudinal Diet, Food Intake, Nutrition and Exposure to the Sun in Southern England study (2006-2007). The main outcomes were serum 25(OH)D, serum parathyroid hormone (sPTH) and serum C-terminal telopeptide of collagen (sCTX), sampled once per season for each participant.

RESULTS

Non-linear mixed modelling showed the (amplitude/mesor) ratio for seasonal change in log 25(OH)D to be predictive of log sPTH (estimate = 0.057, 95 % CI (0.051, 0.063), p < 0.0001). Therefore, individuals with a higher seasonal change in log 25(OH)D, adjusted for overall log 25(OH)D concentration, showed increased levels of log sPTH. There was a corresponding significant ability to predict the range of seasonal change in log 25(OH)D through the level of sCTX. Here, the corresponding parameter statistics were estimate = 0.528, 95 % CI (0.418, 0.638) and p ≤ 0.0001.

CONCLUSIONS

These findings suggest a possible detriment to bone health via increased levels of sPTH and sCTX in individuals with a larger seasonal change in 25(OH)D concentration. Further larger cohort studies are required to further investigate these preliminary findings.

A semi-mechanistic model to characterize the pharmacokinetics and pharmacodynamics of brodalumab in healthy volunteers and subjects with psoriasis in a first-in-human single ascending dose study

Pharmacokinetic-pharmacodynamic (PK-PD) modeling can provide a framework for quantitative "learning and confirming" from studies in all phases of drug development. Brodalumab is a human monoclonal antibody (IgG2 ) targeting the IL-17 receptor A that blocks signaling by cytokines thought to play a central role in the pathogenesis of psoriasis (IL-17A, IL-17F, and IL-17A/F). We used semi-mechanistic modeling of single dose, first-in-human data to characterize the exposure-response relationship between brodalumab and the Psoriasis Area and Severity Index (PASI) in a Phase 1 clinical trial. Fifty-seven healthy volunteers and 25 subjects with moderate to severe psoriasis received single intravenous or subcutaneous administration of placebo or brodalumab (7-700 mg). A two-compartment model with parallel linear and nonlinear (Michaelis-Menten) elimination pathways described brodalumab PK. The PK-PASI relationship was characterized by linking a signaling compartment with an indirect response model of psoriatic plaques, where signaling suppressed plaque formation. The concentration of half-maximal inhibition IC50 was 2.86 µg/mL (SE: 50%). The endogenous psoriatic plaque formation rate of 0.862 (SE: 40%) PASI units/day was comparable with literature precedent. Despite the small sample size and single administration data, this semi-mechanistic modeling approach provided a quantitative framework to inform design of dose-ranging Phase 2 studies of brodalumab in psoriasis.

Clinical Trial Simulation to Inform Phase 2: Comparison of Concentrated vs. Distributed First-in-Patient Study Designs in Psoriasis

Clinical trial simulation (CTS) and model-based meta-analysis (MBMA) can increase our understanding of small, first-in-patient (FIP) trial design performance to inform Phase 2 decision making. In this work, we compared dose-ranging designs vs. designs testing only placebo and the maximum dose for early decision making in psoriasis. Based on MBMA of monoclonal antibodies in the psoriasis space, a threshold of greater than a 50 percentage point improvement over placebo effect at the highest feasible drug dose was required for the advancement in psoriasis. Studies testing only placebo and the maximum dose made the correct advancement decision marginally more often than dose-ranging designs in the majority of the cases. However, dose-ranging studies in FIP trials offer important design advantages in the form of dose–response (D–R) information to inform Phase 2 dose selection. CTS can increase the efficiency and quality of drug development decision making by studying the limitations and benefits of study designs prospectively.

Single-Dose Pharmacokinetics of Varenicline, a Selective Nicotinic Receptor Partial Agonist, in Healthy Smokers and Nonsmokers

Varenicline is a novel and selective alpha4beta2 nicotinic receptor partial agonist that is under development for smoking cessation. The primary objectives of this double-blind, placebo-controlled, single-dose, dose-escalation study were to determine the clinical pharmacology of single doses of varenicline in healthy smokers and nonsmokers under fed and fasted conditions and to determine the clinical pharmacology of varenicline administered in the morning and in the evening to smokers. Within each subject group, 4 subjects were randomized to varenicline and 2 subjects to placebo. Subjects received one single oral administration of varenicline or placebo: 6 doses (0.01, 0.03, 0.1, 0.3, 1.0, and 3.0 mg) were investigated in nonsmokers and 7 doses in smokers (0.01, 0.03, 0.1, 0.3, 1.0, 3.0, and 10.0 mg). Varenicline was well tolerated after single doses up to 3.0 mg in smokers and 1.0 mg in nonsmokers. Nausea and vomiting at doses above 3.0 mg in smokers and 1.0 mg in nonsmokers were dose limiting. Systemic exposure to varenicline and pharmacokinetic variability were similar between smokers and nonsmokers. Coadministration with food, smoking restriction, and time-of-day dosing did not affect the pharmacokinetics of varenicline.

Multiple-Dose Pharmacokinetics of the Selective Nicotinic Receptor Partial Agonist, Varenicline, in Healthy Smokers

Varenicline is a novel and selective alpha4beta2 nicotinic acetylcholine receptor partial agonist developed for smoking cessation. The primary objectives of this double-blind, placebo-controlled, dose-escalation study were to determine the pharmacokinetics, safety, and tolerability of multiple oral doses of varenicline given as tablets once (1 mg, 2 mg, and 3 mg) or twice (1 mg) daily to healthy adult smokers. Within each dose level, 8 subjects were randomized to varenicline and 4 subjects to placebo. Varenicline was well tolerated at doses up to and including 2 mg daily. Dose-proportional increases in maximum observed plasma concentrations and area under the plasma concentration-time curve from time zero to the end of the dosing interval values were observed between the 1-mg and 2-mg daily doses of varenicline. Once- and twice-daily dosing resulted, on average, in an approximate 2- and 3-fold increase in varenicline systemic exposure, respectively, compared with single dose. There was no evidence of concentration- or time-dependent changes in the pharmacokinetics of varenicline upon repeat dosing.

Quantitative model of the relationship between dipeptidyl peptidase-4 (DPP-4) inhibition and response: meta-analysis of alogliptin, saxagliptin, sitagliptin, and vildagliptin efficacy results

Dipeptidyl peptidase-4 (DPP-4) inhibition is a well- characterized treatment for type 2 diabetes mellitus (T2DM). The objective of this model-based meta-analysis was to describe the time course of HbA1c response after dosing with alogliptin (ALOG), saxagliptin (SAXA), sitagliptin (SITA), or vildagliptin (VILD). Publicly available data involving late-stage or marketed DPP-4 inhibitors were leveraged for the analysis. Nonlinear mixed-effects modeling was performed to describe the relationship between DPP-4 inhibition and mean response over time. Plots of the relationship between metrics of DPP-4 inhibition (ie, weighted average inhibition [WAI], time above 80% inhibition, and trough inhibition) and response after 12 weeks of daily dosing were evaluated. The WAI was most closely related to outcome, although other metrics performed well. A model was constructed that included fixed effects for placebo and drug and random effects for intertrial variability and residual error. The relationship between WAI and outcome was nonlinear, with an increasing response up to 98% WAI. Response to DPP-4 inhibitors could be described with a single drug effect. The WAI appears to be a useful index of DPP-4 inhibition related to HbA1c. Biomarker to response relationships informed by model-based meta-analysis can be leveraged to support study designs including optimization of dose, duration of therapy, and patient population.

Central nervous system pharmacokinetics of the Mdr1 P-glycoprotein substrate CP-615,003: intersite differences and implications for human receptor occupancy projections from cerebrospinal fluid exposures

The central nervous system (CNS) distribution and transport mechanisms of the investigational drug candidate CP-615,003 (N-[3-fluoro-4-[2-(propylamino)ethoxy]phenyl]-4,5,6,7-tetrahydro-4-oxo-1H-indole-3-carboxamide) and its active metabolite CP-900,725 have been characterized. Brain distribution of CP-615,003 and CP-900,725 was low in rats and mice (brain-to-serum ratio < 0.2). Cerebrospinal fluid (CSF)-to-serum ratios of CP-615,003 were 6- to 8-fold lower than the plasma unbound fraction in rats and dogs. In vitro, CP-615,003 displayed quinidine-like efflux in MDR1-expressing Madin-Darby canine kidney II cells. The brain-to-serum ratio of CP-615,003 in mdr1a/1b (-/-) mice was approximately 7 times that in their wild-type counterparts, confirming that impaired CNS distribution was explained by P-gp efflux transport. In contrast, P-gp efflux did not explain the impaired CNS penetration of CP-900,725. Intracerebral microdialysis was used to characterize rat brain extracellular fluid (ECF) distribution. Interestingly, the ECF-to-serum ratio of the P-gp substrate CP-615,003 was 7-fold below the CSF-to-serum ratio, whereas this disequilibrium was not observed for CP-900,725. In a clinical study, steady-state CSF exposures were measured after administration of 100 mg of CP-615,003 b.i.d. The human CSF-to-plasma ratios of CP-615,003 and CP-900,725 were both approximately 10-fold below their ex vivo plasma unbound fractions, confirming impaired human CNS penetration. Preliminary estimates of CNS receptor occupancy from human CSF concentrations were sensitive to assumptions regarding the magnitude of the CSF-ECF gradient for CP-615,003 in humans. In summary, this case provides an example of intersite differences in CNS pharmacokinetics of a P-gp substrate and potential implications for projection of human CNS receptor occupancy of transporter substrates from CSF pharmacokinetic data when direct imaging-based approaches are not feasible.

Displacement of serotonin and dopamine transporters by venlafaxine extended release capsule at steady state: a [123I]2beta-carbomethoxy-3beta-(4-iodophenyl)-tropane single photon emission computed tomography imaging study

Both positron emission tomography and single photon emission computed tomography (SPECT) studies suggest that saturation of serotonin transporters (SERT) is present during treatment with therapeutic doses of selective serotonin reuptake inhibitors (SSRIs). Selective serotonin reuptake inhibitors also appear to increase the availability of dopamine transporters (DAT). The current study measured SERT occupancy and modulation of DAT by the serotonin/norepinephrine reuptake inhibitor (SNRI) venlafaxine using [123I]2beta-carbomethoxy-3beta-(4-iodophenyl)-tropane SPECT. Eight healthy subjects were administered open-label venlafaxine extended release capsules (75 mg/d for 4 days followed by 150 mg/d for 5 days). Venlafaxine significantly inhibited [123I]beta-CIT binding to SERT in the brainstem (55.4%) and the diencephalon (54.1%). In contrast, venlafaxine increased [123I]beta-CIT binding to DAT in the striatum (10.1%) after 5 days of administration of 150 mg/d. The displacement of [123I]beta-CIT from brain SERT and the increase in striatal [123I]beta-CIT binding to DAT appear similar to previous work with the SSRI citalopram (40 mg/d). A literature review of SERT occupancy by marketed SSRIs and the SNRI venlafaxine using SPECT ([123I]beta-CIT) or positron emission tomography ([11C](N, N-Dimethyl-2-(2-amino-4-cyanophenylthio)-benzylamine) imaging suggests that therapeutic doses of SNRI are associated with virtual saturation of the serotonin transporter.

Absolute oral bioavailability of traxoprodil in cytochrome P450 2D6 extensive and poor metabolisers

BACKGROUND

Traxoprodil, a substituted 4-phenylpiperidine, is an N-methyl-D-aspartate (NMDA) receptor antagonist that is selective for receptors containing the NR2B subunit. In vivo and in vitro studies examining the disposition of traxoprodil have demonstrated that it is mainly metabolised by cytochrome P450 (CYP) 2D6, a major drug-metabolising enzyme that exhibits a genetic polymorphism.

OBJECTIVE

To assess the single-dose absolute oral bioavailability of traxoprodil in healthy male volunteers phenotyped as either CYP2D6 extensive or poor metabolisers.

METHODS

This was an open-label, three-way crossover study. Traxoprodil was administered as a single dose orally in solution of 50, 100 and 300mg and intravenously as a constant rate 2-hour infusion of 50 and 100mg. CYP2D6 phenotype was assigned following single-dose dextromethorphan administration.

RESULTS

In poor metabolisers (n = 6), oral bioavailability was approximately 80% and was consistent with a liver extraction ratio of approximately 20% (plasma clearance of approximately 4 mL/min/kg) indicating near complete absorption. Following intravenous administration, the mean volume of distribution at steady state (V(ss)) was moderate (approximately 6.5 L/kg) and the mean elimination half-life (t((1/2))) was approximately 20 hours. Following oral administration the mean maximum plasma concentration (C(max)) and area under the plasma concentration-time curve from time zero to infinity (AUC(infinity)) increased approximately proportionally with dose. In extensive metabolisers (n = 11), oral bioavailability was dose-dependent and nonlinear. At the 100mg dose, the absolute oral bioavailability was approximately 39.5%. Overall, the oral bioavailability ranged from 22.8% to 62.1% and its estimation was confounded by large differences in plasma concentrations at oral doses without equivalent intravenous doses. Following intravenous administration, plasma clearance was high (approximately 27 mL/min/kg), the V(ss) was moderate (approximately 4 L/Kg) and the t((1/2)) was approximately 2-4 hours. Following oral administration the C(max) and AUC(infinity) increased more than proportionally with dose. Apparent oral clearance decreased with increasing oral dose. However, t((1/2)) was approximately the same at all doses (approximately 4 hours).

CONCLUSION

The pharmacokinetics of traxoprodil were quite different in the two phenotypes. In extensive metabolisers, the oral bioavailability was nonlinear and dose-dependent, while in poor metabolisers, oral bioavailability appeared to be linear and dose-independent. Based on the pharmacokinetics in extensive and poor metabolisers, the nonlinear oral bioavailability in extensive metabolisers may be attributed to saturation of hepatic first-pass CYP2D6 metabolism. Thus, at a high oral dose, the impact of CYP2D6 metabolism on traxoprodil pharmacokinetics is minimal.

The impact of P-glycoprotein on the disposition of drugs targeted for indications of the central nervous system: evaluation using the MDR1A/1B knockout mouse model

Thirty-two structurally diverse drugs used for the treatment of various conditions of the central nervous system (CNS), along with two active metabolites, and eight non-CNS drugs were measured in brain, plasma, and cerebrospinal fluid in the P-glycoprotein (P-gp) knockout mouse model after subcutaneous administration, and the data were compared with corresponding data obtained in wild-type mice. Total brain-to-plasma (B/P) ratios for the CNS agents ranged from 0.060 to 24. Of the 34 CNS-active agents, only 7 demonstrated B/P area under the plasma concentration curve ratios between P-gp knockout and wild-type mice that did not differ significantly from unity. Most of the remaining drugs demonstrated 1.1- to 2.6-fold greater B/P ratios in P-gp knockout mice versus wild-type mice. Three, risperidone, its active metabolite 9-hydroxyrisperidone, and metoclopramide, showed marked differences in B/P ratios between knockout and wild-type mice (6.6- to 17-fold). Differences in B/P ratios and cerebrospinal fluid/plasma ratios between wild-type and knockout animals were correlated. Through the use of this model, it appears that most CNS-active agents demonstrate at least some P-gp-mediated transport that can affect brain concentrations. However, the impact for the majority of agents is probably minor. The example of risperidone illustrates that even good P-gp substrates can still be clinically useful CNS-active agents. However, for such agents, unbound plasma concentrations may need to be greater than values projected using receptor affinity data to achieve adequate receptor occupancy for effect.

Factors affecting the clinical development of cytochrome p450 3A substrates

The objective of this review is to evaluate the risks associated with the discovery and development of cytochrome p450 (CYP) 3A substrates. CYP3A is the most abundant p450 enzyme in human liver and is highly expressed in the intestinal tract. The enzyme contributes substantially to metabolism of approximately 50% of currently marketed drugs that undergo oxidative metabolism. As a result, drug-drug interactions involving inhibitors of CYP3A-mediated metabolism can be of great clinical consequence. It is the position of the authors that, because of the factors responsible for the broad substrate specificity of CYP3A, discovery and development of compounds across a large and broad portfolio that are completely devoid of CYP3A metabolism is not feasible. Thus, it is important that scientifically valid approaches to the discovery and development of compounds metabolised by CYP3A be realised. The clinical relevance of CYP3A metabolism is dependent on a multitude of factors that include the degree of intestinal and hepatic CYP3A-mediated first-pass extraction, the therapeutic index of the compound and the adverse event associated with inhibition of CYP3A metabolism. Thus, a better understanding of the disposition of a CYP3A-metabolised compound relative to the projected or observed therapeutic index (or safety margin) can provide ample evidence to support the continued development of a CYP3A substrate. This document will highlight current practices as well as the benefits and risks associated with those practices.

Microsomal protein concentration modifies the apparent inhibitory potency of CYP3A inhibitors

The effect of microsomal protein concentration on the inhibitory potency of a series of CYP3A inhibitors was assessed in vitro using diazepam 3-hydroxylation (yielding temazepam) as an index of CYP3A activity. With diazepam concentrations fixed at 100 micro M, inhibition of temazepam formation by fixed concentrations of ritonavir, ketoconazole, itraconazole, OH-itraconazole, norfluoxetine, and fluvoxamine decreased substantially as active protein concentrations increased from 0.0625 to 3.0 mg/ml. However protein concentration had only a small effect on the inhibitory activity of fluconazole. Equilibrium dialysis indicated extensive microsomal binding of all inhibitors except fluconazole; binding increased with higher protein concentrations. Based on the CYP3A content of liver microsomes, decrements in inhibitory potency of stronger inhibitors (ketoconazole and ritonavir) could be explained by specific binding, whereas nonspecific binding is anticipated to account for the effect on weaker inhibitors (norfluoxetine and fluvoxamine). Thus, microsomal binding (specific, nonspecific, or a combination of both) may have a major effect on estimation of inhibitory potency of p450 inhibitors and may contribute to variations among laboratories. The effect can be minimized by use of the lowest possible microsomal protein concentration for in vitro studies of metabolic inhibition.

Emergency department management of patients with seizures: a multicenter study

OBJECTIVES

Patients with seizure disorders are common in the emergency department (ED), yet little is known regarding the management of these patients. This study was performed to define the frequency of patients with seizure disorders in the ED patient population and to determine possible seizure etiologies, characteristics of diagnostic activities, treatments, and dispositions.

METHODS

Twelve EDs monitored all patients with a chief complaint related to seizure disorders presenting over 18.25 days (5% of the calendar year) in late 1997. Retrospective chart review was used to gather specific data regarding these consecutive cases.

RESULTS

Of the 31,508 patients who presented to these 12 EDs during the study period, 368 (1.2%) had complaints related to seizures. Three hundred sixty-two charts were available for analysis and make up the study population. Two hundred fifty-seven (71%) utilized emergency medical services (EMS) for transport and care. Advanced care, including intravenous access, laboratory work, cardiac monitoring, or oxygen administration, was utilized in 304 (84%) patients. Antiepileptic drugs were given in 199 (55%) patients. Ethanol withdrawal or low antiepileptic drug levels were implicated as contributing factors in 177 (49%) of patients. New-onset seizures were thought to be present in 94 (26%) patients. Status epilepticus occurred in only 21 (6%) patients. Ninety-eight (27%) of all patients were admitted to the hospital.

CONCLUSIONS

Patients with presenting complaints related to seizures are frequent in the ED population and make considerable demands on EMS and ED resources. Six percent of patients with seizure-related presentations were in status epilepticus and more than a fourth of all patients required hospitalization.

Ascorbic acid use in hyporesponders to Epoetin alfa

I.v. ascorbic acid has been used in an effort to mobilize ferritin stores in hyporesponsive HD patients receiving Epoetin alfa. However, not all patients who respond to i.v. ascorbic acid therapy will have subsequent decline in feritin stores (Gastaldello et al., 1995; Tarng & Huang, 1998). Additionally, predicting those patients who will overcome their Epoetin alfa hyporesponsiveness remains unclear. Ascorbic acid's effect on hemosiderin deposits may be another possible mechanism to the increased Epoetin alfa response observed in some HD patients (Hemosiderin is a pathologic deposition of iron in tissues including the spleen, small intestine, and bone marrow). Although there are no well-controlled studies evaluating hemosiderin and i.v. ascorbic acid, it should be noted that subjects with scurvy often present with excessive iron deposits in the tissues, indicating the possible effects of ascorbic acid on hemosiderin metabolism (Bothwell et al., 1964). Ascorbic acid deficiency is often present in many HD patients due to its removal during dialysis and lack of dietary intake (Ponka & Kuhlback, 1983). It remains controversial whether oral ascorbic acid supplementation is indicated in patients receiving HD. Therefore, the Recommended Daily Allowance (RDA) of 60 mg/day should be advised (Makoff, 1999). I.v. ascorbic acid should be considered as a possible adjuvant to therapy in patients who are "iron-overloaded" and hyporesponsive to Epoetin alfa. Although the long-term effects of i.v. ascorbic acid on HD patients is unknown, the potential risk of secondary oxalosis should be considered (Costello, 1991; Pru, Eaton, & Kjellstrand, 1985). It may be necessary to monitor plasma oxalate levels if long-term therapy with i.v. ascorbic acid is used. Clinical studies have examined i.v. ascorbic acid doses from 300 mg-500 mg given up to TIW for a maximum duration of 12 weeks without any significant deleterious effects (Gastaldello et al., 1995; Tarng & Huang, 1998; Tarng et al., 1999). However, large-scale, prospective, and controlled trails are needed to determine the long-term safety and efficacy of i.v. ascorbic acid therapy in iron overloaded HD patients receiving Epoetin alfa.

State of the art: therapeutic controversies in severe acute asthma

This is a transcript of the 1999 SAEM State-of-the-Art session on "Therapeutic Controversies in Severe Acute Asthma," presented at the 1999 SAEM annual meeting in Boston. The aim of this session was to address some of the current controversies in the management of acute asthma exacerbations, a major issue in emergency medicine. Despite many recent advances in asthma management, morbidity and mortality remain high. While many of us have strong feelings on how asthma patients should be treated, many of our assertions are not based on good science, and there are numerous areas of controversy. This discussion focuses on the controversy over beta agonist treatment for acute asthma, the physiology of corticosteroids in asthma, and the emergency use of leukotriene-modifying agents.

Value of point-of-care blood testing in emergent trauma management

BACKGROUND

No prospective study demonstrates the value of point-of-care laboratory testing (POCT) in the management of major trauma.

METHODS

In a prospective, noninterventional, study of 200 major trauma patients, we evaluated the influence of a blood POCT profile (hemoglobin, Na+, K+, Cl-, blood urea nitrogen, glucose, pH, PCO2, PO2, HCO3-, base deficit, and lactate) on emergent diagnostic and therapeutic interventions. Physicians responded to a standardized set of questions on their diagnostic and therapeutic plans before and after the availability of POCT results. Management plan changes were deemed emergently appropriate, if they were influenced by the POCT results and, within the ensuing 30 minutes, the change in management was likely to reduce morbidity or conserve resources.

RESULTS

For emergently appropriate plan changes, Na+, Cl-, K+, and blood urea nitrogen were never influential, whereas in each of 6.0% of cases (95% confidence interval [CI], 3.5%-10.2%) at least one of the remaining POCT parameters was influential. An emergently appropriate change was based on hemoglobin in 3.5% of cases (95% CI, 1.0%-6.1%), blood gas parameters in 3.0% of cases (95% CI, 0.64%-5.7%), lactate in 2.5% of cases (95% CI, 1.1%-5.7%), and glucose in 0.5% of cases (95% CI, 0.1%-2.8%). All of these cases involved blunt injury.

CONCLUSION

Na+, Cl-, K+, and blood urea nitrogen levels do not influence the initial management of major trauma patients. In patients with severe blunt injury, hemoglobin, glucose, blood gas, and lactate measurements occasionally result in morbidity-reducing or resource-conserving management changes.

Persistent inhibition of CYP3A4 by ketoconazole in modified Caco-2 cells

PURPOSE

The intestinal metabolism of some CYP3A substrates can be altered profoundly by co-administration of the potent inhibitor, ketoconazole. The present research was conducted to test the hypothesis that, unlike the inhibition kinetics observed with isolated microsomes, inhibition of CYP3A4 by ketoconazole in an intestinal cell monolayer is time-dependent and slowly reversible.

METHODS

Confluent, 1alpha,25-dihydroxy Vitamin D3-treated Caco-2 cells were exposed to 1 microM ketoconazole for two hours (Phase I) and then washed three times with culture medium containing no inhibitor. This was followed by a second incubation period (Phase II) that varied in the composition of the apical and basolateral culture medium: Condition 1. apical/basolateral differentiation medium (DM); Condition 2, apical/ basolateral DM + basolateral 2g/dL Human Serum Albumin (HSA); Condition 3, apical/basolateral DM + apical/basolateral 2 g/dL HSA. After various lengths of time for the second phase (0 to 4 hours), both apical and basolateral medium were exchanged with fresh DM. Midazolam (6 microM) was included in the apical medium for determination of CYP3A4 activity (Phase III).

RESULTS

Two-way ANOVA of the data revealed persistent inhibition of CYP3A4 under Conditions 1 and 2 (p < 0.001). In contrast, cells treated under Condition 3 exhibited rapid reversal of CYP3A4 inhibition. The level of CYP3A4 activity observed was inversely correlated with the amount of ketoconazole remaining in the cell monolayer at the end of Phase II.

CONCLUSIONS

These studies provide mechanistic evidence that ketoconazole can be sequestered into the intestinal mucosa after oral administration, producing a persistent inhibition of first-pass CYP3A4 activity.

Hydroxyurea in the treatment of HIV-1

OBJECTIVE

To describe the role of hydroxyurea in the treatment of HIV-1.

DATA SOURCES

Published clinical studies using hydroxyurea in HIV treatment were accessed through MEDLINE (January 1994-March 1999) and conference abstracts. All relevant studies were evaluated.

DATA SYNTHESIS

Adherence, expense, and resistance limit the pharmacotherapeutic options in the management of patients with HIV. Hydroxyurea may be an alternative to conventional HIV treatments.

CONCLUSIONS

Several potential advantages of adding hydroxyurea to antiretroviral treatment regimens include the drug's well-documented toxicity, convenient dosing, good tolerability and low cost, and its unique mechanism of action. Hydroxyurea may have synergistic effects that prove promising in initial and salvage therapy antiretroviral regimens. Larger, well-controlled clinical studies are needed to adequately define the role of hydroxyurea in the treatment of HIV.

Lateral line morphology and cranial osteology of the rubynose brotula, Cataetyx rubrirostris

Cranial osteology, canal neuromast distribution, superficial neuromast distribution and innervation, and cephalic pore structure were studied in cleared and stained specimens of the deep sea brotulid Cataetyx rubrirostris. The cranial bone structure of C. rubrirostris is similar to other brotulids (Dicrolene sp.) and zoarcids (Zoarces sp.), except for an unusual amount of overlapping of the bones surrounding the cranial vault. The superficial neuromasts are innervated by the anterodorsal, anteroventral, middle and posterior lateral line nerves and are organized similarly to those of the blind ophidioid cave fish Typhliasina pearsei. The cephalic pores open into a widened lateral line canal system. The canal is compartmentalized into a series of neuromast-containing chambers that probably amplify signals received by the system.

Effect of inhibitor depletion on inhibitory potency: tight binding inhibition of CYP3A by clotrimazole

The purpose of this work was to evaluate the effect of mutual unbound inhibitor and unbound enzyme depletion on the potency of three antifungal cytochrome P-450 (CYP)3A inhibitors with over 1000-fold range in enzyme affinity. Incubations were performed with human liver microsomal protein concentrations that varied from 25 to 1000 microg/ml. The effect of each inhibitor was evaluated using midazolam as a CYP3A probe. Clotrimazole was found to be a tight binding inhibitor of CYP3A with a Ki of 250 pM. Analysis of percent inhibition data by stepwise linear regression for the matrix of inhibitor and enzyme concentrations used showed that protein concentrations predicted the percent inhibition by clotrimazole (r2 = 0.60, p <.001). When clotrimazole concentrations were added to the model, the r2 improved to 0.81, p =.003. Clotrimazole concentrations alone were not a significant predictor of percent inhibition (r2 = 0. 21, p =.08). For ketoconazole, protein concentrations provided a weak prediction of the percent inhibition (r2 = 0.39, p =.006). Conversely, ketoconazole concentrations alone were a good predictor of percent inhibition (r2 = 0.55, p <.001). In contrast to results with clotrimazole and ketoconazole, percent inhibition by fluconazole was not dependent on protein concentrations (r2 = 0.06, p =.39). We conclude that microsomal inhibitory potency can be affected by incubation conditions that deplete the unbound concentration of inhibitor available to the enzyme. This may introduce serious error into a quantitative prediction of an in vivo drug-drug interaction based on an in vitro derived Ki value.

Prospective multicenter study of relapse following treatment for acute asthma among adults presenting to the emergency department. MARC investigators. Multicenter Asthma Research Collaboration

STUDY OBJECTIVE

To identify factors associated with relapse following treatment for acute asthma among adults presenting to the emergency department (ED).

DESIGN

Prospective inception cohort study performed during October 1996 to December 1996 and April 1997 to June 1997, as part of the Multicenter Asthma Research Collaboration.

SETTING

Thirty-six EDs in 18 states.

PATIENTS

ED patients, aged 18 to 54 years, with physician diagnosis of acute asthma. For the present analysis, we restricted the cohort to patients sent home from the ED (n = 971), then further excluded patients with comorbid respiratory conditions (n = 32). This left 939 eligible subjects to have follow-up data.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

Two weeks after being sent home from the ED, patients were contacted by telephone. A relapse was defined as an urgent or unscheduled visit to any physician for worsening asthma symptoms during the 14-day follow-up period. Complete follow-up data were available for 641 patients, of whom 17% reported relapse (95% confidence interval, 14 to 20). There was no significant difference in peak expiratory flow rate (PEFR) between patients who suffered relapse and those who did not. In a multivariate logistic regression analysis (controlling for age, gender, race, and primary care provider status), patients who suffered relapse were more likely to have a history of numerous ED (odds ratio [OD] 1.3 per 5 visits) and urgent clinic visits (OR 1.4 per 5 visits) for asthma in the past year, use a home nebulizer (OR 2.2), report multiple triggers of their asthma (OR 1.1 per trigger), and report a longer duration of symptoms (OR 2.5 for 1 to 7 days).

CONCLUSION

Among patients sent home from the ED following acute asthma therapy, 17% will have a relapse and PEFR does not predict who will develop this outcome. By contrast, several historical features were associated with increased risk. Further research should focus on ways to decrease the relapse rate among these high-risk patients. The clinician may wish to consider these historical factors when making ED decisions.

Inhibition of cytochrome P-450 3A (CYP3A) in human intestinal and liver microsomes: comparison of Ki values and impact of CYP3A5 expression

The purpose of this study was to compare the kinetics of intestinal and hepatic cytochrome P-450 3A (CYP3A) inhibition by using microsomal midazolam 1'-hydroxylation as a marker of enzyme activity. The effect of two antifungal agents commonly implicated in CYP3A drug-drug interactions was examined. Inhibition type and affinities were determined for human liver and intestinal microsomes screened for the presence or absence of CYP3A4 and CYP3A5, as well as for cDNA-expressed CYP3A4 and CYP3A5 microsomes. Ketoconazole and fluconazole were found to be noncompetitive inhibitors of both enzymes. Ketoconazole exhibited a Ki for cDNA-expressed CYP3A4 of 26. 7 +/- 1.71 nM, whereas the Ki for cDNA expressed CYP3A5 was 109 +/- 19.7 nM. Corresponding Ki values for fluconazole were 9.21 +/- 0.51 microM and 84.6 +/- 12.9 microM. For liver and intestinal microsomes that contained only CYP3A4, the average ketoconazole Ki was found to be 14.9 +/- 6.7 nM and 17.0 +/- 7.9 nM, respectively, whereas fluconazole yielded mean respective Ki values of 10.7 +/- 4.2 microM and 10.4 +/- 2.9 microM. Liver and intestinal microsomes that contained an equal or greater amount of CYP3A5, in addition to CYP3A4, were less susceptible to inhibition by both ketoconazole and fluconazole. These findings suggest that there can be significant differences in the affinity of these two enzymes for inhibitors. This may further broaden interindividual variability with respect to the magnitude of in vivo drug-drug interactions. We also conclude that there is no significant difference in inhibition type and affinity of ketoconazole and fluconazole for hepatic versus intestinal CYP3A4.

Spectral sensitivity of the goldfish Torus longitudinalis

We measured the photopic spectral sensitivity of multiunit activity in the torus longitudinalis and optic tectum of goldfish. Since negative contrast stimuli are most effective for exciting torus longitudinalis, spiking activity was evoked by the shadow of a disc moving through a monochromatic light beam projected upon a screen. The amount of activity evoked in torus longitudinalis generally increased with the monochromatic stimulus radiance at the same rate for all wavelengths, indicating a univariant response. Spiking activity in tectum, however, increased at different rates across the spectrum, indicating color-dependent responses. The action spectra for torus longitudinalis were all similar and relatively flat as expected of a homogeneous, broad-band luminance processing system, and about 1 log unit more sensitive than the tectal action spectra. The latter generally displayed sharp peaks and dips in sensitivity indicative of opponent processing.

EMT defibrillation does not increase survival from sudden cardiac death in a two-tiered urban-suburban EMS system

OBJECTIVE

The use of automatic external defibrillators (AEDs) by EMS initial responders is widely advocated. Evidence supporting the use of AEDs is based largely on the experience of one metropolitan area, with effect on survival in many systems not yet proved. We conducted this study to determine whether the addition of AEDs to an EMS system with a response time of 4 minutes for first-responder emergency medical technicians (FREMTs) and 10 minutes for paramedics would affect survival from cardiac arrest.

METHODS

This prospective, controlled, crossover study (AED versus no AED) of consecutive cardiac arrests managed by 24 FREMT fire companies took place from 1992 to 1995 in Charlotte, North Carolina, a city of 455,000. Patients were stratified using the Utstein criteria. The primary endpoint was survival to hospital discharge among patients with bystander-witnessed arrests of cardiac origin.

RESULTS

Of the 627 patients, 243 were bystander-witnessed arrests of cardiac origin. Survival to hospital discharge was accomplished in 5 of 110 patients (4.6%; 95% confidence interval [CI] 0.6% to 8.4%) with AED compared with 7 of 133 (5.3%, 95% CI 1.5% to 9.1%) without AED (P = .8). Both groups were comparable with regard to age, gender, history of myocardial infarction, congestive heart failure or diabetes, arrest at home, bystander CPR, and whether or not ventricular fibrillation (VF) was the initial rhythm. For arrests of any cause, witnessed by bystanders or EMS personnel, with an initial rhythm of VF or ventricular tachycardia (VT), 5 of 77 (6.5%, 95% CI 1.0% to 12.0%) with AED survived compared with 8 of 105 patients (7.6%, 95% CI 2.5% to 12.7%) without AED (P = .8). Statistically significant differences were noted in race and EMS response times between the two groups, which did not affect survival.

CONCLUSION

Addition of AEDs to this EMS system did not improve survival from sudden cardiac death. The data do not support routinely equipping initial responders with AEDs as an isolated enhancement, and raise further doubt about such expenditures in similar EMS systems without first optimizing bystander CPR and EMS dispatching.

Air medical transport services in North Carolina

Air medical transport is an important component of contemporary prehospital care for patients with time-sensitive conditions and those whose clinical needs exceed the expertise of local providers. Early contact with trained flight dispatchers facilitates air transport. Appropriate stabilization, effective communication, and transfer of medical documents ensure that transports are appropriate, timely, and safe.

The role of torus longitudinalis in equilibrium orientation measured with the dorsal light reflex

The torus longitudinalis (TL) is a paired elongated structure reciprocally connected with the optic tectum in actinopterygian fishes. Electrophysiological recordings have revealed a sustained neural discharge in TL inversely related to luminance [Northmore, 1984]. This photometric response may play a role in the comparison of light levels between the two eyes, which must occur for the dorsal light reflex (DLR) to orient the body in the environment. Based on the luminance response of TL, it was hypothesized that TL ablation would result in a reduced DLR. Individual goldfish (Carassius auratus) were observed with variable and constant light sources on opposite sides of a test tank. The DLR was measured with respect to angle (degree) and duration (seconds) of body tilt about the longitudinal axis. After baseline readings were obtained, the intertectal commissure was cut and TL was removed bilaterally. Surgical control fish had only the intertectal commissure cut. Following surgery, TL ablatees showed a significantly reduced DLR compared to controls. The results are consistent with the suggestion by Northmore [1984] that TL may be involved in the processing of luminance information.

Glutamine synthetase immunoreactivity is present in oligodendroglia of various regions of the central nervous system

Glutamine synthetase immunoreactive oligodendrocytes were identified in the cerebral cortex, cerebellum, brain stem, and spinal cord. They were mostly confined to the gray matter, particularly close to neurons and processes. The white matter showed few immunoreactive oligodendroglia. It was suggested that some type of oligodendrocytes, specially those in perineuronal location, might fulfill a functional role more akin to astrocytes than to the normally myelinating oligodendroglia.

Application of an immunofluorescence assay for Crohn's disease using primed nude mouse lymph nodes to a United States/Mexican border population

Previous studies using an indirect immunofluorescence (IF) technique found that sera from patients with Crohn's disease (CD) frequently contained antibody that recognized an antigen(s) in CD tissue filtrate-primed lymphoid tissue from athymic nude (nu/nu) mice. The present study examined the reproducibility of this IF assay in a different laboratory setting and used patients with infectious diarrhea. We examined the immunoreactivity of 113 sera from eight patients with Crohn's disease, 11 with ulcerative colitis, 62 patients with infectious diarrhea, 22 nondiarrheal disease controls, and ten normal adults. Sera were absorbed with nu/+BALB/c mouse serum proteins coupled to Sepharose 4B to remove nonspecific binding. All sera were coded and tested against at least 2 of 4 lymph nodes from nu/nu mice that were previously inoculated with either CD tissue filtrate or with a passaged CD-induced nu/nu lymphoma. Reference positive CD sera and negative control sera were run in parallel during each assay. Sera from three CD patients consistently showed positive IF. None of the sera from patients with infectious diarrhea, other disease controls, or normals were positive. These results demonstrate the reproducibility of the IF assay using CD tissue-primed nude mouse lymph nodes and the preferential immunoreactivity of CD sera.

[3H]thymidine labeling of astrocytes in experimental allergic encephalomyelitis

In acute experimental allergic encephalomyelitis (EAE), astrocytes in spinal cord tissue hypertrophy and stain intensely with antibody to the glial fibrillary acidic protein (GFAP). We attempted to determine if this activation is a result solely of hypertrophy of existing astrocytes or if astrocyte division might also occur. Lewis rats in various stages of acute EAE were injected with [3H]thymidine, the spinal cord sections were prepared, immunostained for GFAP and processed for radioautography. In spinal cords from rats administered thymidine on days 11-15 after sensitization a large number of mononuclear cells showed radioactive label. Many of these labeled cells, most likely monocytes and lymphocytes, were associated with inflammatory lesions, but others were located in the CNS parenchyma at great distances from the lesions. Most cells staining for the GFAP were hypertrophied with greatly extended cell processes, and the nuclei of some of these cells identified as astrocytes were overlaid with silver grains, indicating uptake of [3H]thymidine. In addition a few ependymal cells appeared to be labeled. No GFAP-stained cells from the Freund's adjuvant controls contained radioactive label. Similar studies using SJL/J mice with chronic relapsing EAE yielded very few labeled inflammatory cells or astrocytes. This study indicates that division takes place in some astrocytes in acute EAE, but occurs much less frequently in chronic EAE. Probably most of the increase in GFAP-stained material is a result of hypertrophy of astrocytes rather than of massive cell division.

Immunocytochemical localization of glutamic acid decarboxylase (GAD) and glutamine synthetase (GS) in the area postrema of the cat. Light and electron microscopy

The present study was designed to investigate the existence of two key enzymes involved in the metabolism of gamma-aminobutyric acid, glutamic acid decarboxylase (GAD) and glutamine synthetase (GS), in the area postrema (AP) of the cat. The results showed that punctuate structures of variable size corresponding to axon terminals, exhibited GAD-immunoreactivity and were distributed in varying densities. The greatest accumulation was present in the caudal and middle segment of the AP and particularly in the area subpostrema, where the aggregation of terminals was extremely dense. The population of the GAD-labelled axon profiles gradually decreased toward the solitary complex. No neuronal bodies were labelled in our preparations. The electron microscopic studies revealed a large variety of contacts between labelled terminals and unlabelled dendrites, axons or neurons. The possibility that the GAD-immunoreactive terminals might correspond to vagal afferent projections was discussed on the basis of our observations and of other studies that employed horseradish peroxidase or degeneration methods. GS-immunoreactivity was seen in ependymoglial cells of the AP, particularly toward the caudal region, and in astrocytes and their processes of the AP proper. The latter were frequently observed around capillaries. The presence of both GAD-immunoreactive profiles and GS-immunostained ependymoglial cells and astrocytes in the AP, provided further immunocytochemical evidence of the functional correlation between the two enzymes.

Axoglial contacts in the area postrema of the cat: an ultrastructural study

Axoglial contacts were observed in an ultrastructural study of the area postrema of the cat. According to the disposition of the electron-dense projections attached to the adjoining membranes these contacts were classified as symmetrical or asymmetrical. The axon profiles contained aggregations of clear vesicles randomly distributed or grouped in cluster adjacent to the electron-dense projections. Dense core vesicles were occasionally seen. The neuroglial profiles were either astrocytic or ependymoglial in nature. The astrocytes showed a clear cytoplasm, polymorphous vesicles, mitochondria, glycogen granules, and bundles of filaments. The ependymal cells, in contrast, had a more electron-dense and granular appearance, tubular structures, irregular vesicular formations, profiles of smooth reticuloendoplasm, and filaments grouped in bundles or isolated in the cytoplasm. The possibility that these contacts might play a role in the chemical transfer from neurons to glial cells is discussed on the basis of existing biochemical data.

Immunocytochemical localization of glial fibrillary acidic protein (GFAP) in the area postrema of the cat. Light and electron microscopic study

Glial fibrillary acidic protein (GFAP) was demonstrated in the cytoplasm and processes of ependymal cells and astroglial components of the area postrema of the cat. These observations differ from the findings in the ependyma of the ventricular cavities which are consistently negative for the protein. Since some studies have suggested sensory functions of the glial cells in this emetic chemoreceptor trigger zone, a careful consideration of morphological and biochemical attributes of these cells seems appropriate.