Two-treatment Crossover Design Research Articles

Plasma atropine concentrations associated with decreased intestinal motility in horses.

IntroductionAtropine is an essential part of the treatment protocol for equine uveitis. Topical atropine administration has been associated with decreased intestinal motility and abdominal pain in horses. Experimental studies have indicated that frequent dosing is associated with a higher risk than dosing every 6 h. Unfortunately, no quantitative pharmacodynamic data for inhibition of the equine gut are published.Materials and methodsEight standardbred horses were assigned to receive either atropine or saline (control) to be infused over 30 min in a two-treatment cross-over design. Atropine concentrations in plasma were measured using ultra-high-performance liquid chromatography–tandem mass spectrometry. Intestinal motility was measured using borborygmi frequency and electrointestinography (EIG). Experimental data were analyzed using a non-linear mixed effects model. The model was then used to simulate different dosing regimens.ResultsAtropine significantly decreased borborygmi response and EIG response. Six horses developed clinical signs of abdominal pain. The pharmacokinetic typical values were 0.31, 1.38, 0.69, and 1.95 L/kg·h for the volumes of the central, the highly perfused, the scarcely perfused compartments, and the total body clearance, respectively. The pharmacodynamic typical values were 0.31 μg/L and 0.6 and 207 nV27 cpm for the plasma concentration at 50% of the maximum response and the maximum response and the baseline of cecal EIG response, respectively. Six different dosing regimens of topical atropine sulfate to the eye (0.4 and 1 mg every hour, every 3 h, and every 6 h) were simulated.ConclusionThe IV PK/PD data coupled with simulations predict that administration of 1 mg of topical atropine sulfate administered to the eye every hour or every 3 h will lead to atropine accumulation in plasma and decreased intestinal myoelectric activity. Administration every 6 h predicted a safe dosing regimen in full-sized horses. Clinical studies would be valuable to confirm the conclusions. For smaller equids and horses put at risk for colic due to othercauses, droplet bottles that deliver 40 μl of 1% atropine sulfate per drop or less may be used to lower the risk further.

Application of HPLC method using normal phase column in a comparative pharmacokinetic study of two sulpiride tablet formulations

An HPLC method using normal phase column eluted with an aqueous solvent and detected by fluorescence was applied to analyze sulpiride concentrations in plasma samples obtained from a comparative pharmacokinetic study. This comparative study was conducted to determine the bioequivalence of two tablet products (Dogmatyl and Sulpin) containing sulpiride on 12 normal healthy Chinese male volunteers in a single-dose, two-period, two-sequence, two-treatment crossover design. The pharmacokinetic parameters, AUC 0-last, AUC 0-inf, and C max, were calculated from plasma data and compared using the SAS General Linear Model computer program. A two one-sided t distribution test was also performed, as well as the 90% confidence interval method, to determine the mean difference of these three pharmacokinetic parameters. The results suggest that these two sulpiride tablet products are bioequivalent when orally administered in a 400 mg single dose of two tablets.

Optimal Crossover Designs for Generalized Linear Models

We identify locally D-optimal crossover designs for generalized linear models. We use generalized estimating equations to estimate the model parameters along with their variances. To capture the dependency among the observations coming from the same subject, we propose six different correlation structures. We identify the optimal allocations of units for different sequences of treatments. For two-treatment crossover designs, we show via simulations that the optimal allocations are reasonably robust to different choices of the correlation structures. We discuss a real example of multiple-treatment crossover experiments using Latin square designs. Using a simulation study, we show that a two-stage design with our locally D-optimal design at the second stage is more efficient than the uniform design, especially when the responses from the same subject are correlated.

Odds ratio based two-stage group sequential analysis for two-treatment two-period crossover trials

We consider a two-treatment and two-period crossover design where the treatment responses are binary. The outcome from each patient under such trial can be represented by a two-component vector which follows a bivariate binomial distribution. We develop a two-stage group sequential test procedure for equivalence based on the estimates of odds ratio. Various error spending functions are studied in this context. Simulation studies are carried out. An illustration with some real data example is also given.

Impact of an Individually Tailored Light Mask on Sleep Parameters in Older Adults With Advanced Phase Sleep Disorder

ABSTRACTObjective: This study investigated whether light delivered through the eyelids of sleeping persons might create phase delay in older adults who are adversely affected by advanced sleep phase disorder. Participants: Thirty-two cognitively intact, community-dwelling participants aged ≥ 50 years (20 females, 12 males) with Pittsburgh Sleep Quality Index scores ≥ 5 (poor sleep) completed the study. Methods: This within-subjects, randomized, two-treatment crossover design study exposed participants to an active “blue” (λmax = 480 nm) lighting intervention or a placebo “red” (λmax = 640 nm) control through closed eyelids during sleep for 8 weeks. Conditions were administered 1 hr after bedtime using custom-built light masks delivering a train of 2-s duration light pulses presented every 30 s for ≤ 2 hr (approximately 240 pulses/night). Dependent variables were subjective measures of sleep and depression (questionnaires) and objective measures of sleep (wrist actigraphy), analyzed using linear mixed models with treatment, period, and carryover as fixed effects. Results: The actigraphy analysis found no effect of the intervention or the control condition on sleep start time, total sleep time, number of sleep bouts, or sleep efficiency, either compared to baseline or to one another. Subjective responses of study participants, however, indicated statistically significant (p < 0.05) improvement in seven of eight reported measures of sleep quality with both the intervention and the control condition, but no difference between the two conditions. Conclusions: The participants reported improvement in sleep quality, but the intervention did not confer additional advantages after adjusting for period and carryover effects.

Incorporating baseline measurements into the analysis of crossover trials with time‐to‐event endpoints

Two-period two-treatment (2×2) crossover designs are commonly used in clinical trials. For continuous endpoints, it has been shown that baseline (pretreatment) measurements collected before the start of each treatment period can be useful in improving the power of the analysis. Methods to achieve a corresponding gain for censored time-to-event endpoints have not been adequately studied. We propose a method in which censored values are treated as missing data and multiply imputed using prespecified parametric event time models. The event times in each imputed data set are then log-transformed and analyzed using a linear model suitable for a 2×2 crossover design with continuous endpoints, with the difference in period-specific baselines included as a covariate. Results obtained from the imputed data sets are synthesized for point and confidence interval estimation of the treatment ratio of geometric mean event times using model averaging in conjunction with Rubin's combination rule. We use simulations to illustrate the favorable operating characteristics of our method relative to two other methods for crossover trials with censored time-to-event data, ie, a hierarchical rank test that ignores the baselines and a stratified Cox model that uses each study subject as a stratum and includes period-specific baselines as a covariate. Application to a real data example is provided.

Amifampridine phosphate in the treatment of muscle-specific kinase myasthenia gravis: a phase IIb, randomized, double-blind, placebo-controlled, double crossover study

Objective:The aim of this study is to determine the safety and the efficacy of amifampridine phosphate in muscle-specific kinase antibody-positive myasthenia gravis, in a 1:1 randomized, double-blind, placebo-controlled, switchback, double crossover study.Methods:Eligible patients had muscle-specific kinase myasthenia gravis, >18 years of age, and Myasthenia Gravis Foundation of America class II–IV with a score of ⩾9 on Myasthenia Gravis Composite scale. After the run-in phase, during which amifampridine phosphate was titrated to a tolerable and effective dosage, patients were randomized to receive placebo–amifampridine–placebo sequence or amifampridine–placebo–amifampridine sequence daily for 7 days. Then, patients switched treatment arms twice, for a total of 21 days of double-blind treatment. Safety was determined by serial assessments of adverse events/serious adverse events, physical examinations, and clinical and laboratory tests. The co-primary outcome measures included changes from baseline of Quantitative Myasthenia Gravis score and Myasthenia Gravis–specific Activities of Daily Living Profile score. The secondary outcome measures comprised changes from baseline of Myasthenia Gravis Composite score, Myasthenia Gravis Quality of Life scale—15 questions, Fatigue Severity Scale, and Carlo Besta Neurological Institute–Myasthenia Gravis scale. Statistical analyses were assessed using a switchback model for three-period, two-treatment crossover design.Results:A total of 10 patients were screened, enrolled, and treated. Transient paresthesias (60%) were the only amifampridine phosphate–related adverse events reported. Four patients were randomized to receive placebo–amifampridine–placebo sequence and three patients to receive amifampridine–placebo–amifampridine sequence. The co-primary objectives were statistically met (Quantitative Myasthenia Gravis score: p = 0.0003 and Myasthenia Gravis–specific Activities of Daily Living Profile score: p = 0.0006), as well as all the secondary endpoints (Myasthenia Gravis Composite score: p < 0.0001, Myasthenia Gravis Quality of Life scale—15 questions: p = 0.0025, Fatigue Severity Scale: p = 0.0061, and Carlo Besta Neurological Institute–Myasthenia Gravis scale: p = 0.0014).Conclusion:Despite the low number of patients, MuSK-001 study provided evidence that amifampridine phosphate, in the range of 30–60 mg daily dose, was safe and effective in treating muscle-specific kinase myasthenia gravis, suggesting the need for a large multi-center trial to confirm these results.

Comparative Bioavailability of Two Oral Perampanel Formulations in Healthy Subjects: A Randomized, Open Label, Single-Dose, 2-Way Crossover Study

Background: Perampanel is a glutamate non-competitive receptor antagonist that is effective as adjunctive treatment for epilepsy. No studies regarding comparative bioavailability between a generic perampanel formulation and the brand-name product have been published in the literature. Therefore, the goal of the present investigation was to compare the bioavailability and to evaluate the bioequivalence between a novel pharmaceutical equivalent 12 mg film-coated tablet formulation and the reference product. Methods: An open label, randomized-sequence, two-period, two-treatment, single-dose, crossover design study in healthy volunteers(n=24) was conducted. The treatment was split out by a 42 days wash-out period. The informed consent was signed by all volunteers. Healthy subjects of both genders, including non-pregnant and nonlactating females between 21-55 years with Quetelet index between 19-29 kg/m2 were enrolled. Blood samples were withdrawn in vacutainers with EDTA over 168 h and plasma levels of perampanel were measured by HPLC/ fluorescence method. Pharmacokinetic (PK) variables (Cmax, AUC0-last, and AUCinf) after a single oral administration dose of the test and reference treatments were analyzed by a non-compartmental PK model using natural logtransformed data and were compared by ANOVA for a two-treatment crossover design. Bioequivalence between the two formulations was evaluated using the 90% Confidence Interval (CI) comprised between 80-125% corresponding to the ratio of the geometric means for log-transformed PK parameters. Results: A similar bioavailability between products was determined. Test and reference formulations showed no statistically significant differences in relation to the fixed effect of period, sequence, treatment and volunteers within sequence as random effect for PK variables. The estimated point and 90% CI of the ratios of Cmax, AUC0-last and AUCinf were 0.92 (0.83-1.03), 1.04(0.98-1.10) and 0.98 (0.86-1.11), respectively. The formulations showed comparable safety and tolerability. Conclusion: The new pharmaceutical equivalent perampanel 12 mg film-coated tablet formulation was also bioequivalent to the reference product. Therefore, both drugs are interchangeable.

Bioequivalence evaluation of sparse sampling pharmacokinetics data using bootstrap resampling method

ABSTRACTBioequivalence studies are an essential part of the evaluation of generic drugs. The most common in vivo bioequivalence study design is the two-period two-treatment crossover design. The observed drug concentration–time profile for each subject from each treatment under each sequence can be obtained. AUC (the area under the concentration–time curve) and Cmax (the maximum concentration) are obtained from the observed drug concentration–time profiles for each subject from each treatment under each sequence. However, such a drug concentration–time profile for each subject from each treatment under each sequence cannot possibly be available during the development of generic ophthalmic products since there is only one-time point measured drug concentration of aqueous humor for each eye. Instead, many subjects will be assigned to each of several prespecified sampling times. Then, the mean concentration at each sampling time can be obtained by the simple average of these subjects’ observed concentration. One profile of the mean concentration vs. time can be obtained for one product (either the test or the reference product). One AUC value for one product can be calculated from the mean concentration–time profile using trapezoidal rules. This article develops a novel nonparametric method for obtaining the 90% confidence interval for the ratio of AUCT and AUCR (or CT,max/CR,max) in crossover studies by bootstrapping subjects at each time point with replacement or bootstrapping subjects at all sampling time points with replacement. Here T represents the test product, and R represents the reference product. It also develops a novel nonparametric method for estimating the standard errors (SEs) of AUCh and Ch,max in parallel studies by bootstrapping subjects treated by the hth product at each time point with replacement or bootstrapping subjects treated by the hth product at all sampling time points with replacement, h = T, R. Then, 90% confidence intervals for AUCT/AUCR and CT,max/CR,max are obtained from the nonparametric bootstrap resampling samples and are used for the evaluation of bioequivalence study for one-time sparse sampling data.

Checking distributional assumptions for pharmacokinetic summary statistics based on simulations with compartmental models

ABSTRACTBioequivalence (BE) studies are an essential part of the evaluation of generic drugs. The most common in vivo BE study design is the two-period two-treatment crossover design. AUC (area under the concentration–time curve) and Cmax (maximum concentration) are obtained from the observed concentration–time profiles for each subject from each treatment under each sequence. In the BE evaluation of pharmacokinetic crossover studies, the normality of the univariate response variable, e.g. log(AUC)1 or log(Cmax), is often assumed in the literature without much evidence. Therefore, we investigate the distributional assumption of the normality of response variables, log(AUC) and log(Cmax), by simulating concentration–time profiles from two-stage pharmacokinetic models (commonly used in pharmacokinetic research) for a wide range of pharmacokinetic parameters and measurement error structures. Our simulations show that, under reasonable distributional assumptions on the pharmacokinetic parameters, log(AUC) has heavy tails and log(Cmax) is skewed. Sensitivity analyses are conducted to investigate how the distribution of the standardized log(AUC) (or the standardized log(Cmax)) for a large number of simulated subjects deviates from normality if distributions of errors in the pharmacokinetic model for plasma concentrations deviate from normality and if the plasma concentration can be described by different compartmental models.

Adaptive two-stage bioequivalence trials with early stopping and sample size re-estimation

Bioequivalence between two products has to be demonstrated as an essential part of the generic approval process (new formulation vs. innovator product), bridging an innovator’s product from the formulation used in clinical phase III to the marketed formulation, or in case of major variations of an approved product. The most common design of bioequivalence studies is a twosequence two-period two-treatment crossover design, where inclusion of 90% confidence intervals of pharmacokinetic metrics in a pre-defined acceptance range has to be shown. Alternatively, bioequivalence can be established by using Two One-Sided Tests (TOST) each at an alpha level of 5%. However, this fixed sample approach offers no flexibility if in the planning phase parameters were misspecified. We propose a two-stage adaptive design based using combination tests to combine stagewise p-values. This will strictly control the type I error rate in case data-driven design modification have to be performed at an interim analysis. We derive 90%-repeated confidence intervals for the adaptive TOST approach. We investigate different sample size reassessment strategies using conditional power arguments. We discuss how futility stopping can be sensible implemented. The operating characteristics will be assessed by clinical trial simulations. Furthermore, the proposed adaptive design would allow to switch from a classical two-period design to a more complex replicate design if it turns out the reference product is highly variable and the within subject-variability has to be determined as well. Another application of the proposed method would be for establishing biosimilarity of two products. Authors’ details Lancaster University, Lancaster, UK. Medical University Vienna, Vienna, Austria. Baxter Innovations GmbH, Vienna, Austria. BEBAC Consultancy Services for Bioequivalence and Bioavailability Studies, Vienna, Austria. University Koln, Koln, Germany.

The pharmacokinetics of pimobendan enantiomers after oral and intravenous administration of racemate pimobendan formulations in healthy dogs.

Pimobendan is a benzimidazole-pyridazinone derivative, marketed as a racemic mixture for the management of canine heart failure. Pharmacokinetics of the enantiomers of pimobendan and its oral bioavailability have not been described in dogs. The aim of this study was to describe pharmacokinetics of three formulations of pimobendan in healthy dogs: the licensed capsule product, and novel liquid and intravenous formulations. A three-period, nested randomized two-treatment crossover design was used. Pimobendan was administered p.o. at 0.25 and i.v. at 0.125 mg/kg. Blood and plasma samples were analysed by liquid chromatography-mass spectrometry. Noncompartmental modelling was used to describe the pharmacokinetics. Parameters were compared between formulations using a general linear model. Bioequivalence of the oral formulations was tested using CI90 for AUC(0-∞) and Cmax . Bioavailability of pimobendan after oral dosing was 70%. Liquid and capsule formulations were bioequivalent only for AUC. The positive enantiomer of pimobendan (PE) had a larger volume of distribution than the negative enantiomer (NE) (281 ± 48 vs. 215 ± 68 mL/kg; P = 0.003) and a shorter half-life (21.7 vs. 29.9 min; P = 0.004). The NE was distributed more quickly than the PE into blood cells. Enantiomers of pimobendan have differing absorption, distribution and elimination. The pharmacokinetics of pimobendan in healthy dogs was described.

Crossover design in clinical trials for binary response

In this paper, we consider a binary response model for the analysis of the two-treatment, two-period and four-sequence crossover design. We have introduced intra-patient drug dependency parameter in the model and provide two tests for the hypothesis of equality of treatment effects. We employ Monte Carlo simulation to compare our tests and a test that works under parallel design on the basis of type I error rate and power. We find that our procedures are dominant over the competitor with respect to power. Finally, we use a data set to illustrate the applicability of our procedure.

Nonparametric analysis of the two-period two-treatment crossover design

The paper describes a nonparametric model for the analysis of the two-treatment, two-period, four-sequence crossover design. Tests for the equality of treatment effects and for the absence of carryover effects are provided. Some relevant asymptotic results of the proposed tests are obtained and compared with the existing nonparametric and parametric competitors via simulation. It is shown that the proposed tests are comparable to or better than the competitors in terms of type I error and power.

Prevention of dental erosion of a sports drink by nano-sized hydroxyapatitein situstudy

To evaluate the inhibitory effects of the sports drink containing nano-sized hydroxyapatite (nano-HA) on dental erosion in situ. The study had a single-blind, two-treatment crossover design. The two treatment groups were a control group (CG; Powerade only) and an experimental group (EG; 0.25% wt/vol nano-HA was added to Powerade). Ten subjects wore removable palatal appliances containing bovine enamel specimens. The appliances were immersed in each drink for 10mins, 4 times a day for 10days. The tooth surface microhardness (SMH) was tested, and the erosion depth and the morphology of the tooth surface were observed. The data were analysed by repeated measures anova and t-test. Between the baseline and the 10th day, SMH was decreased by 80% in the specimens of the CG (P<0.001), whereas there was only a 6% decrease in the SMH of the specimens in the EG. An erosion depth of 12.70±4.66μm and an irregular tooth surface were observed on the 10th day in the specimens of the CG. No dental erosions, however, was observed in the specimens of the EG. The sports drink containing 0.25% nano-HA was effective in preventing dental erosion in situ.

Demand Valve Oxygen: A Promising New Oxygen Delivery System for the Acute Treatment of Cluster Headache

To show that demand valve oxygen is an effective acute treatment for cluster headache and to compare this oxygen delivery technique with standard cluster headache therapy of continuous flow oxygen. Single-center, open-label, two-period, two-treatment crossover design, pilot study was used. Subjects treated with one of two sequences: first, headache treated with continuous flow oxygen (100% oxygen at 15 liters per minute), and subsequent with demand valve oxygen, or vice versa. Treatment began when pain was at least moderate. Subjects taught a specific breathing technique for demand valve oxygen that included initial period of hyperventilation. Primary end point was headache response (moderate-to-very-severe pain reduced to mild or none) after 30 minutes of treatment. Three subjects completed the trial, while a fourth completed demand valve oxygen only. All had chronic cluster headache. All subjects treated with demand valve oxygen became pain-free (time in minutes: 15, 19, 6, 8). Three of four had no recurrence within 24 hours. Demand valve oxygen reduced cranial autonomic symptoms in all and resolved them in two subjects. For continuous flow oxygen, two of three subjects became pain-free (20, 10 minutes). Continuous flow oxygen reduced but did not eliminate cranial autonomic symptoms. Continuous flow oxygen had higher recurrence rates. No adverse events noted with either treatment. Demand valve oxygen appears to be an effective acute treatment for cluster headache. All subjects became headache-free. Time to pain freedom was fast (average 12 minutes). The small number of study subjects does not allow a direct comparison of efficacy between demand valve oxygen and continuous high flow oxygen.

Two-period, two-treatment crossover designs subject to non-ignorable missing data

In common with most forms of designed experiment, crossover trials can be affected by missing data. Attempts to devise designs that can mitigate the possible effects of missing data, such as loss of efficiency, or even inestimability of certain contrasts, have been proposed. However, a potentially serious effect of missing data that has not been addressed in designs hitherto is that the treatment effects may be biassed because of the nature of the missingness process. We investigate this problem in two-treatment, two-period crossover designs. In particular, we consider the robustness of the analysis under a missing at random assumption when, in fact, the data are non-ignorably missing. We show that the conventional AB/BA design still has good properties, although the design with sequences AB, BA, AA, and BB may be preferred if the chance of dropout depends primarily on the difference between the responses in the two periods.

Effects of duodenal infusion of free α-linolenic acid on the plasma and milk proteome of lactating dairy cows

This study is an exploratory analysis for understanding the effect of a duodenal infusion of an α-linolenic acid (LNA) on the plasma and milk proteome of lactating dairy cows. Four primiparous Holstein cows were fitted with duodenal cannulas and received 0, 100, 200, 300 and 400 g/day of LNA in a two-treatment crossover design. Blood and milk were collected for determination of protein composition by two-dimensional gel electrophoresis. Alteration of protein spots was detected and identified using matrix-assisted laser desorption/ionization time-of-flight/time-of-flight tandem mass spectrometry (MALDI-TOF-TOF MS). Plasma haptoglobin levels, and milk β-casein A2, αs1-casein variant and albumin, did not differ in cows after infusion of 0, 100, 200 and 300 g/day of LNA, but were increased after the cows received duodenal infusion of 400 g/day of LNA. Western blot analysis of haptoglobin expression in plasma confirmed the alterations in protein expression seen using MS. This study demonstrated that infusion of high doses of LNA by duodenal cannula can result in metabolic stress within the bovine intestine and in changes in milk composition.

A response-adaptive design in crossover trial

In the present work, whenever the response variables are binary, we frame an adaptive allocation rule for a two-treatment two-period crossover design in the presence of possible carry-over effects. The proposed rule is a combination of the play-the-winner and randomized play-the-winner rules. We study various properties of the proposed rule through asymptotics and simulations. Some related inferential problems are also considered. The proposed procedure is compared with some possible competitor.

Bioequivalence in dogs of a meloxicam formulation administered as a transmucosal oral mist with an orally administered pioneer suspension product

A mucosal mist formulation of meloxicam, administered as a spray into the mouth (test article), was compared for bioequivalence to a pioneer meloxicam suspension for oral administration (reference article). Pharmacokinetic profiles and average bioequivalence were investigated in 20 dogs. The study design comprised a two-period, two-sequence, two-treatment cross-over design, with maximum concentration (C(max)) and area under plasma concentration-time curve to last sampling time (AUC(last)) used as pivotal bioequivalence variables. Bioequivalence of the products was confirmed, based on relative ratios of geometric mean concentrations (and 90% confidence intervals within the range 0.80-1.25) for C(max) of 101.9 (97.99-106.0) and for AUC(last) of 97.24 (94.44-100.1). The initial absorption of meloxicam was more rapid for the test article, despite virtually identical C(max) values for the two products. Mean elimination half-lives were 29.6 h (test article) and 30.0 h (reference article). The meloxicam plasma concentration-time profiles were considered in relation to published data on the inhibition of the cyclooxygenase-1 (COX-1) and COX-2 isoenzymes by meloxicam.