Direct Oral Anticoagulants Vs. Enoxaparin for Prevention of Venous Thromboembolism Following Orthopedic Surgery: A Dose-Response Meta-analysis.

We carried out a dose-response model-based meta-analysis to assess venous thromboembolism (VTE) and bleeding with factor Xa (FXa) inhibitors (apixaban, edoxaban, rivaroxaban) and a thrombin inhibitor (dabigatran) compared with European (EU) (40 mg q.d.) and North American (NA) (30 mg Q12H) dose regimens of a low molecular weight heparin (enoxaparin) following orthopedic surgery. Statistically significant differences in both VTE and bleeding outcomes were found between the NA and EU doses of enoxaparin, with odds ratios (95% confidence interval) for the NA vs. EU dose of 0.73 (0.71-0.76) and 1.20 (1.14-1.29) for total VTE and major bleeding, respectively. At approved doses, estimated odds ratios vs. both doses of enoxaparin for the three FXa inhibitors (range: 0.35-0.75 for VTE; 0.76-1.09 for bleeding) compared with those for dabigatran (range: 0.66-1.21 for VTE; 1.10-1.38 for bleeding) suggested generally greater efficacy and less bleeding for the FXa inhibitors.

Quantitative Evaluations of Time-Course and Treatment Effects of Systemic Agents for Psoriasis: A Model-Based Meta-Analysis.

Aggregate data model-based meta-analysis is a regression approach to compare the dose-response and/or time-course across different treatments using summary level data from the literature. Literature search and systematic review following the Cochrane approach yielded 912 sources for investigational and approved treatments for psoriasis. In addition, data for tofacitinib were obtained from an internal database. Tofacitinib is an oral Janus kinase inhibitor. Two mathematical models were developed for Psoriasis Area and Severity Index (PASI) response in moderate to severe psoriasis patients to quantify the time to maximum effect for PASI75 and to evaluate the dose-response relationship for PASI responders (PASI50, PASI75, PASI90, PASI100) at Week 12. Body weight exhibited an inverse effect on the placebo component of both models, suggesting that body weight affects the overall PASI response regardless of drug. This analysis provides a quantitative framework for efficacy comparisons across psoriasis treatments.

Prediction of clinical irrelevance of PK differences in atorvastatin using PK/PD models derived from literature-based meta-analyses.

To support the development of a fixed-dose combination (FDC) of ezetimibe and atorvastatin for the treatment of dyslipidemia, bioequivalence (BE) studies were conducted across a combined dose range (10/10, 10/20, 10/40, and 10/80 mg of ezetimibe/atorvastatin). In the BE trials, all parameters met traditional BE bounds except for atorvastatin peak plasma concentration (Cmax) at two intermediate doses. Literature-based metadata analysis predicted that the observed difference in Cmax between an ezetimibe+atorvastatin FDC and coadministration of these agents translates directly into a non-clinically significant change of <1.2% absolute difference in the percentage lowering of low-density-lipoprotein cholesterol . Both FDC doses were confirmed to be clinically equivalent to coadministration in the subsequent clinical equivalence trials. These data suggest that modeling of dose-response relationships may be useful in predicting clinical equivalence, lowering cost/timelines through effective powering of studies, and predicting the effectiveness of new dosage formulations without the need for additional clinical efficacy trials in regulatory settings.

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.CPT: Pharmacometrics & Systems Pharmacology (2013) 2, e58; doi:10.1038/psp.2013.32; published online 24 July 2013.

An adaptive-design dose-ranging study of PD 0348292, an oral factor Xa inhibitor, for thromboprophylaxis after total knee replacement surgery.

BACKGROUND: PD 0348292 is an oral, selective, direct and reversible factor Xa inhibitor. This was an adaptive dose-ranging study evaluating a 100-fold PD 0348292 dose range in subjects undergoing total knee replacement (TKR). OBJECTIVE: To assess the efficacy and safety of a dose range of PD 0348292 relative to enoxaparin for the prevention of venous thromboembolism (VTE). METHODS: Extensive dose-response modeling and trial simulations were used to select the PD 0348292 dose range for the Phase 2 study. Subjects were randomized to a blinded PD 0348292 dose (0.1 mg qd to 10 mg qd) or open-label enoxaparin (30 mg bid) for 6-14 days after TKR surgery. Efficacy was assessed by mandatory bilateral venography. Results were analyzed using a dose-response modeling approach. RESULTS: Observed VTE frequency ranged from 1.4-37.1% across PD 0348292 doses and was 18.1% for enoxaparin. The PD 0348292 dose-response relationship for VTE was statistically significant (P < 0.0001). The dose of PD 0348292 equivalent to enoxaparin 30 mg bid for VTE prevention was estimated to be 1.16 mg (95% CI = 0.56 mg, 2.41 mg) qd. Total bleeding ranged from 4.9% to 13.8% across PD 0348292 doses and was 6.3% with enoxaparin. The dose-response relationship for total bleeding was not statistically significant (P = 0.2464). Overall, PD 0348292 and enoxaparin were well tolerated. CONCLUSION: Characterization of the dose-response relationship for VTE and bleeding using an adaptive Phase 2 study design provided a strong quantitative basis for Phase 3 dose selection.

Model-based drug development: a rational approach to efficiently accelerate drug development.

The pharmaceutical industry continues to face significant challenges. Very few compounds that enter development reach the marketplace, and the investment required for each success can surpass $1.8 billion. Despite attempts to improve efficiency and increase productivity, total investment continues to rise whereas the output of new medicines declines. With costs increasing exponentially through each development phase, it is failure in phase II and phase III that is most wasteful. In today's development paradigm, late-stage failure is principally a result of insufficient efficacy. This is manifested as either a failure to differentiate sufficiently from placebo (shown for both novel and precedented mechanisms) or a failure to demonstrate sufficient differentiation from existing compounds. Set in this context, this article will discuss the role model-based drug development (MBDD) approaches can and do play in accelerating and optimizing compound development strategies through a series of illustrative examples.

Long-term follow-up of patients with Herlitz-type junctional epidermolysis bullosa.

BACKGROUND: Junctional epidermolysis bullosa, type Herlitz (JEB-H) is a rare, autosomal recessive disease caused by absence of the epidermal basement membrane adhesion protein laminin-332. It is characterized by extensive and devastating blistering of the skin and mucous membranes, leading to death in early childhood. OBJECTIVES: To present the results of the long-term follow-up of a cohort of patients with JEB-H, and to provide guidelines for prognosis, treatment and care. METHODS: All patients with JEB-H included in the Dutch Epidermolysis Bullosa (EB) Registry between 1988 and 2011 were followed longitudinally by our EB team. Diagnosis was established using immunofluorescence antigen mapping, electron microscopy and DNA analysis. RESULTS: In total, we included 22 patients with JEB-H over a 23-year period. Their average age at death was 5.8 months (range 0.5-32.6 months). The causes of death were, in order of frequency: failure to thrive, respiratory failure, pneumonia, dehydration, anaemia, sepsis and euthanasia. The pattern of initial weight gain was a predictor of lifespan in these patients. Invasive treatments to extend life did not promote survival in our patients. CONCLUSIONS: It is important to diagnose JEB-H as soon as possible after birth so that the management can be shifted from life-saving to comfort care. The palliative end-of-life care can take place in hospital, but is also safe in the home setting. Suffering in patients with JEB-H can become so unbearable that in some patients who do not respond to adequate analgesic and sedative treatment, newborn euthanasia, performed according to the Groningen protocol, is legally permitted in the Netherlands.

A dose-response meta-analysis for quantifying relative efficacy of biologics in rheumatoid arthritis.

We present a dose-response meta-analysis to quantify relative efficacy of biologic disease-modifying antirheumatic drugs (DMARDs) in patients with rheumatoid arthritis (RA). There is a strong rationale for this analysis because, although multiple biologics are available, information on head-to-head comparisons is limited. Data on the percentage of patients attaining American College of Rheumatology (ACR) 20, 50, and 70 responses were extracted from 50 randomized controlled trials representing 21,500 patients, five mechanisms of action, and nine biologics. The analysis showed that all tumor necrosis factor inhibitors (anti-TNFs) share the same dose-response relationship for ACR 20, 50, and 70, differing only in potency. Yet there are significant differences in efficacy among the anti-TNFs due to differences in the clinical dose ranges available. At the suggested starting dose, golimumab was the least efficacious, followed by infliximab, adalimumab, etanercept, and certolizumab. Significant differences in the dose-response relationship were found between anti-TNFs and other biologics, resulting in differences in efficacy and differential impact of dose titration.

Therapeutic index of anticoagulants for prevention of venous thromboembolism following orthopedic surgery: a dose-response meta-analysis.

Information on the comparative effectiveness of drugs is crucial for drug development decisions, in addition to being needed by regulators, prescribers, and payers. We have carried out a dose-response meta-analysis of three end points each for efficacy and bleeding for various anticoagulants evaluated for the prevention of venous thromboembolism (VTE) following orthopedic surgery to assess the comparative efficacy and safety of various classes of agents. Data obtained from 89 randomized controlled trials of 23 anticoagulants representing seven drug classes were analyzed. The analysis showed significant differences in the therapeutic index (TI), the ratio of the dose with an acceptable bleeding risk to the dose with a relevant risk reduction for VTE, across the drug classes but not for drugs within a class. The direct inhibitors of FXa, the activated form of factor X--also known as prothrombinase--were found to have a significantly higher TI than that of any other class of anticoagulants, including enoxaparin, suggesting that this mechanism of action provides the best safety-to-efficacy margin.

Model-based meta-analysis for comparative efficacy and safety: application in drug development and beyond.

High development cost, low development success, cost-disciplined health-care policies, and intense competition demand an efficient drug development process. New compounds need to bring value to patients by being safe, efficacious, and cost-effective as compared with existing treatment options. Model-based meta-analysis (MBMA) facilitates integration and utilization of summary-level efficacy and safety data, providing a quantitative framework for comparative efficacy and safety assessment. This Commentary discusses the application and limitations of MBMA in drug development.

[Anaphylaxis in two children caused by peanut and nut allergies; recommendations for treatment]. / Anafylaxie door pinda- en notenallergie bij 2 kinderen; aanbevelingen voor beleid.

Two girls aged 12 and 7 years with asthma and peanut and nut allergy developed anaphylactic shock after ingestion of peanuts and nuts from an unreported source. They were both given intramuscular epinephrine. The 12-year-old girl was treated clinically for shock and after two days was discharged from hospital. The 7-year-old girl died. Risk factors for life-threatening anaphylactic reactions are adolescent to young adult age, asthma, previous severe anaphylactic reactions to the food in question, previous reaction to small dose of the food in question and allergy to peanuts or tree nuts. A double-blind, placebo-controlled food challenge should be carried out to document the culprit food. The most important therapeutic intervention is the intramuscular administration of epinephrine. For patients with two or more risk factors the prescription of an epinephrine auto-injector should be considered.

Therapeutic benefit of eletriptan compared to sumatriptan for the acute relief of migraine pain--results of a model-based meta-analysis that accounts for encapsulation.

A novel model-based meta-analysis was used to quantify the dose-response relationship of sumatriptan and eletriptan for the proportion of patients that achieve migraine pain relief up to 4 h after treatment. The proportion of patients that became pain free was also evaluated. This analysis includes some unique features, allowing comparison of sumatriptan and eletriptan doses that have not been directly compared in a head to head study and also permitting comparison between the two drugs at multiple time points up to 4 h after treatment. Because the analysis allows comparison of response to blinded sumatriptan with that to marketed sumatriptan and contains timepoints as early as 0.5 h, it is especially suited to detection of possible effects of encapsulation on sumatriptan's therapeutic effectiveness and thus was employed to assess this also. Data from 19 randomized placebo controlled clinical trials were jointly analysed using a random-effects logistic regression model. The results of this analysis show a significant clinical benefit of eletriptan 40 mg compared to sumatriptan 100 mg at any point in time up to 4 h after treatment. The benefit of eletriptan 40 mg is greatest around 1.5-2 h after treatment with an absolute difference at 2 h of 9.1% (7.4-11.5%) more patients achieving pain relief and 7.3% (5.8-8.6%) more patient achieving pain free when compared to sumatriptan 100 mg. An absolute benefit of more than 5% of patients is maintained from 45 min up to 4 h after treatment for pain relief and from 1.5 h up to 4 h for pain free. Eletriptan 20 mg was superior to sumatriptan 50 mg and similar to sumatriptan 100 mg for pain relief while it was similar to sumatriptan 50 mg for pain free. The benefit of eletriptan 20 mg when compared to sumatriptan 50 mg is greatest around 1.5-2 h after treatment with an absolute difference at 2 h of 5.0% (2.9-8.1%) more patients achieving pain relief. An absolute benefit of more than 3% of patients was maintained from 1 h up to 3 h after treatment. No significant difference was found between eletriptan 20 mg and sumatriptan 50 mg for the fraction of patients that became pain free. No significant effect of encapsulation of sumatriptan was found on the time course of response up to 4 h after treatment when compared to commercial sumatriptan.

Quantification of pharmacodynamic interactions between dexmedetomidine and midazolam in the rat.

The pharmacodynamic (PD) interaction between the benzodiazepine agonist midazolam and the alpha(2)-adrenergic agonist dexmedetomidine was characterized for defined measures of anesthetic action and cardiovascular and ventilatory side effects in 33 rats. For various combinations of constant plasma concentrations of midazolam (0.1-20 microg/ml) and dexmedetomidine (0.3-19 ng/ml) obtained by target-controlled infusion, the whisker reflex (WR), righting reflex (RR), startle reflex to noise (SR), tail clamp response (TC), and corneal reflex (CR) were assessed. EEG (power in 0.5-3.5-Hz frequency band), mean arterial pressure, and heart rate were recorded continuously. Blood gas values and arterial drug concentrations were determined regularly. The nature and extent of PD interaction was quantified by the model parameter synergy (SYN < 0, antagonism; SYN = 0, additivity; and SYN > 0, synergy). With increasing drug concentrations WR was lost first, followed by RR, SR, TC, and CR. These effects were accompanied by an increase of the EEG measure. The drug interaction was synergistic for all stimulus-response measures and the degree of synergy increased with deeper levels of central nervous system depression (SYN was 7.3, 145, 560, 374, and 1490 for WR, RR, SR, TC, and CR, respectively). The cardiovascular side effects of dexmedetomidine, evaluated at similar PD endpoints, were reduced in the presence of midazolam. Ventilatory side effects were minor for all drug combinations. The nature and extent of the PD interactions were not reflected in the EEG measure.

Crusted (Norwegian) scabies in a patient with dystrophic epidermolysis bullosa.

A 13-year-old girl with severe non-mutilating recessive dystrophic epidermolysis bullosa (EB) was admitted to hospital because of a Staphyloccus aureussepsos, deterioration of her general condition and worsening of her skin disease, which itched severely. In addition to the blisters and erosions normally seen, she was covered from head to toe with scales and hyperkeratotic crusts. Despite intensive topical therapy, her skin condition did not improve significantly until scabies was detected and treated 1 week after admission. Because of the huge number of mites found and the crusted appearance, a diagnosis of crusted (Norwegian) scabies was made. She was successfully treated with two doses of ivermectin orally and one application of lindane ointment. Permethrin cream was not tolerated. In this patient crusted scabies may have developed because of: (i) a modified host response due to malnourishment; (ii) inability to scratch because of the absence of fingernails; and (iii) abnormal scratching behaviour because of the vulnerability of EB skin, or a combination of these factors. Limited isolation measures were taken on admission and full measures were taken immediately after the diagnosis of crusted scabies was made. Prophylactic treatment of ward personnel was not undertaken. Fortunately, there was not an outbreak of scabies in the hospital.

Anesthetic profile of dexmedetomidine identified by stimulus-response and continuous measurements in rats.

This study characterizes the anesthetic profile of dexmedetomidine on the basis of steady-state plasma concentrations using defined stimulus-response, ventilatory, and continuous electroencephalographic (EEG) and cardiovascular effect measures in rats. At constant plasma concentrations of dexmedetomidine (range, 0.5-19 ng/ml), targeted and maintained by target-controlled infusion, the whisker reflex, righting reflex, startle reflex (to noise), tail clamp response, hot water tail-flick latency, and attenuation of heart rate (HR) increase associated with tail-flick (sympathoadrenal block) and corneal reflex, were assessed in 22 rats. EEG (power in 0.5- to 3.5-Hz frequency band), mean arterial pressure, and HR were recorded continuously. Blood gas values and arterial drug concentrations were determined regularly. The following steady-state plasma EC(50) values of dexmedetomidine (mean +/- S.E. nanograms per milliliter) were estimated: HR decrease (0.51 +/- 0.04), EEG (1.02 +/- 0.08), whisker reflex (1.09 +/- 0.10), sympathoadrenal block (1.85 +/- 0.80), mean arterial blood pressure increase (1.99 +/- 0.44), righting reflex (2.13 +/- 0.15), tail-flick latency (3.65 +/- 0.87), startle reflex (3.75 +/- 0.64), tail clamp (5.49 +/- 1.34), and corneal reflex (24.5 +/- 12.3). At the EC(50) value of tail clamp, ventilatory depression was minor. In rats, dexmedetomidine creates bradycardia, sedation/hypnosis, sympathoadrenal blocking effects, and blood pressure-increasing effects at plasma concentrations below 2.5 ng/ml. Higher plasma concentrations are needed to loose the startle reflex, tail-flick, tail clamp, and corneal reflex responses. Ventilatory depressant effects are minor. The applied EEG measure seems to reflect sedation/hypnosis but seems to have limited value to predict the deeper levels of analgesia and anesthesia of dexmedetomidine.

Characterization of the pharmacodynamic interaction between parent drug and active metabolite in vivo: midazolam and alpha-OH-midazolam.

The pharmacodynamic interaction between midazolam and its active metabolite alpha-OH-midazolam was investigated to evaluate whether estimates of relevant pharmacodynamic parameters are possible after administration of a mixture of the two. Rats were administered 10 mg/kg of midazolam, 15 mg/kg of alpha-OH-midazolam, or a combination of 3.6 mg/kg of midazolam and 35 mg/kg of alpha-OH-midazolam. Increase in the 11.5- to 30-Hz frequency band of the electroencephalogram was used as the pharmacodynamic endpoint. The pharmacodynamics of midazolam and alpha-OH-midazolam after combined administration were first analyzed according to an empirical and a competitive interaction model to evaluate each model's capability in retrieving the pharmacodynamic estimates of both compounds. Both models failed to accurately estimate the true pharmacodynamic estimates of midazolam and alpha-OH-midazolam. The pharmacodynamic interaction was subsequently analyzed according to a new mechanism-based model. This approach is based on classical receptor theory and allows estimation of the in vivo estimated receptor affinity and intrinsic in vivo drug efficacy. The relationship between stimulus and effect is characterized by a monotonically increasing function f, which is assumed to be identical for midazolam and alpha-OH-midazolam. The pharmacodynamic interaction is characterized by the classical equation for the competition between two substrates for a common receptor site. This mechanism-based interaction model was able to estimate the pharmacodynamic parameters of both midazolam and alpha-OH-midazolam with high accuracy. It is concluded that pharmacodynamic parameters of single drugs can be estimated after a combined administration when a mechanistically valid interaction model is applied.

Pharmacokinetic-pharmacodynamic modeling of the anticonvulsant and electroencephalogram effects of phenytoin in rats.

In this study a pharmacokinetic-pharmacodynamic model is proposed for drugs with nonlinear elimination kinetics. We applied such an integrated approach to characterize the pharmacokinetic-pharmacodynamic relationship of phenytoin. In parallel, the anticonvulsant effect and the electroencephalogram (EEG) effect were used to determine the pharmacodynamics. Male Wistar-derived rats received a single intravenous dose of 40 mg . kg-1 phenytoin. The increase in the threshold for generalized seizure activity (TGS) was used as the anticonvulsant effect and the increase in the total number of waves in the 11.5 to 30 Hz frequency band was taken as the EEG effect measure. Phenytoin pharmacokinetics was described by a saturation kinetics model with Michaelis-Menten elimination. Vmax and Km values were, respectively, 386 +/- 31 microg . min-1 and 15.4 +/- 2.2 microg . ml-1 for the anticonvulsant effect in the cortical stimulation model and 272 +/- 31 microg . min-1 and 5.9 +/- 0.7 microg . ml-1 for the EEG effect. In both groups, a delay to the onset of the effect was observed relative to plasma concentrations. The relationship between phenytoin plasma concentrations and effect site was estimated by an equilibration kinetics routine, yielding mean ke0 values of 0.108 and 0.077 min-1 for the anticonvulsant and EEG effects, respectively. The EEG changes in the total number of waves could be fitted by the sigmoid Emax model, but Emax values could not be estimated for the nonlinear relationship between concentration and the increase in TGS. An exponential equation (E = E0 + Bn . Cn) derived from the sigmoid Emax model was applied to describe the concentration-anticonvulsant effect relationship, under the assumption that Emax values cannot be reached within acceptable electric stimulation levels. This approach yielded a coefficient (B) of 2.0 +/- 0.4 microA . ml . microg-1 and an exponent (n) of 2.7 +/- 0.9. The derived EC50 value of 12.5 +/- 1. 3 microg . ml-1 for the EEG effect coincides with the "therapeutic range" in humans.

Relevance of arteriovenous concentration differences in pharmacokinetic-pharmacodynamic modeling of midazolam.

In the present investigation, the extent of arteriovenous concentration differences of midazolam in rats was quantified, and the consequences of these differences on the pharmacodynamic estimates were determined. The arterial concentration-effect relationships where analyzed by a traditional-effect compartment model that characterizes the delay between blood and the effect site with the rate constant k(eo). Venous concentration-effect relationships where analyzed according to the traditional model and an extended-effect compartment model that, by incorporating an additional rate constant k(vo), can characterize the delay between the arterial and venous sampling site. Significant hysteresis was observed in the arterial but not the venous concentration-effect relationships. Rate constants for k(eo), k(vo) and terminal half-life were (mean +/- S.E.M.) 0.32 +/- 0.062, 0.093 +/- 0.013 and 0.0217 +/- 0.0008 min-1, respectively, indicating the existence of significant arteriovenous concentration differences. Pharmacodynamic estimates as determined on basis of the arterial concentrations and the traditional-effect compartment model were EC50 = 104 +/- 1 ng/ml, Emax = 151 +/- 4 microV/sec and gamma = 0.83 +/- 0.06. Analysis of the venous concentration-effect relationships on basis of the traditional- or extended-effect compartment model led to similar pharmacodynamic estimates, indicating that the observed arteriovenous concentration differences did not result in biased pharmacodynamic estimates. This is due to the fact that the effect relevant elimination rate constant of midazolam is relatively small compared with its k(eo). The observed results are consistent with earlier reports based on computer simulations.

Determination of dexmedetomidine in rat plasma by a sensitive [3H]clonidine radioreceptor assay.

This paper describes the development and implementation of a sensitive radioreceptor assay (RRA) for determining concentrations of dexmedetomidine, an alpha-2 adrenergic agonist with anesthetic properties, in rat plasma. Calf retina membranes were selected as the alpha-2 adrenergic receptor source, and the alpha-2 antagonist [3H]RX821002 and the alpha-2 agonist [3H]clonidine were evaluated as radioligands. We optimized the binding conditions for both radioligands and chose a radioligand for implementation in the RRA based on the characteristics of the inhibition binding curves with dexmedetomidine. The final method is based on competition between the radioligand [3H]clonidine and dexmedetomidine for high-affinity binding sites present in calf retina membranes. The assay has a coefficient of variation of 8% in the range 23.7-592 pg for 0.2 mL of plasma. This assay can be applied to pharmacokinetic-pharmacodynamic studies of dexmedetomidine.

Pharmacokinetics of SNX-111, a selective N-type calcium channel blocker, in rats and cynomolgus monkeys.

SNX-111, a selective N-type voltage-sensitive calcium channel blocker, is in clinical trials for the treatment of ischemia-induced brain injury and chronic pain. Pharmacokinetic studies were conducted in rats and cynomologus monkeys to determine the disposition of this compound when it is administered for 24 hr by continuous, constant-rate intravenous infusion. Venous blood samples for determination of SNX-111 plasma levels were collected at regular intervals immediately before, during, and after dosing. Plasma concentrations of SNX-111 equivalents were measured by radioimmunoassay. Pharmacokinetic parameters were derived from plasma SNX-111 concentration-time data using a two-compartment pharmacokinetic model. Results showed close correspondences between pharmacokinetic parameters determined for both species. There were no consistent gender- or dose-related differences in calculated kinetic parameters. In all cases, apparent steady-state plasma SNX-111 concentrations were achieved within 2-4 hr of initiating SNX-111 infusion. Steady-state volume of distribution values were approximately 40% of body weight, indicating extravascular dissemination of SNX-111 to both extracellular and intracellular fluids. Elimination curves contained two exponential components. The fast component (rat t1/2, alpha = 0.375 hr; monkey t1/2, alpha = 0.730 hr) accounted for approximately 97% of the unit impulse disposition function. The apparent terminal half-life ranged from 4.61 hr (rat) to 6.48 hr (monkey). Current findings constitute the first description of the pharmacokinetics of a member of the omega-conopeptide family of neuronal calcium channel blockers.