All-cause mortality imbalance in the tigecycline phase 3 and 4 clinical trials

In 12 of 13 phase 3 and 4 comparative clinical trials, all-cause mortality was higher in the tigecycline group versus the comparator group. Study-level mortality risk differences were pooled using a random-effects meta-analysis. Statistical models evaluated the association between patient-level all-cause mortality and baseline factors using logistic regression, recursive partitioning [classification and regression tree (CART) analysis] and survival techniques. The estimated risk difference (tigecycline minus comparator) in all-cause mortality from the meta-analysis was 0.6% (95% confidence interval 0.1-1.2%). Statistical modelling identified baseline bacteraemia associated with mortality only in the tigecycline group. In patients with ventilator-associated pneumonia (VAP) and baseline bacteraemia, mortality was 50.0% (9/18) for tigecycline versus 7.7% (1/13) for the comparator group. Study-level and patient-level analyses have identified that patients in the hospital-acquired pneumonia trial, particularly those with VAP with baseline bacteraemia, were at a higher risk of clinical failure and mortality.

Population pharmacokinetics of oxycodone in children 6 months to 7 years old

Young children are often undertreated for pain. One barrier to effective pain treatment is understanding the pharmacokinetic behavior of analgesics in this age group. Oxycodone is a commonly prescribed opioid for severe pain, yet little is known about its pharmacokinetics in young children. This article used population pharmacokinetic modeling to synthesize pharmacokinetic data from several studies into a model. A single population model that described the observed pharmacokinetics was developed. The combined data were best described with a 2-compartment linear model with different first-order absorption rates depending on route of administration. Weight was found to significantly influence both clearance (CL) and volume of distribution (Vd). The following model adequately describes the population pharmacokinetic profile of oxycodone where absolute bioavailability (F) is estimated for each administration route: CL/F=55x(body weight/70)0.87; V/F=86x(body weight/70)1.16. The interindividual coefficients of variation in CL and Vd were 20.2 and 19.7%, respectively. This finding confirms that the allometric scaling using the above model explained most of the variability in exposure observed among children. This model confirms using a weight-based dose for oxycodone without adjustment for age between 6 months and 7 years and is valuable for evaluating dosing schedules and dosing routes.

The effect of azithromycin on ivermectin pharmacokinetics--a population pharmacokinetic model analysis

Background

A recent drug interaction study reported that when azithromycin was administered with the combination of ivermectin and albendazole, there were modest increases in ivermectin pharmacokinetic parameters. Data from this study were reanalyzed to further explore this observation. A compartmental model was developed and 1,000 interaction studies were simulated to explore extreme high ivermectin values that might occur.

Methods and Findings

A two-compartment pharmacokinetic model with first-order elimination and absorption was developed. The chosen final model had 7 fixed-effect parameters and 8 random-effect parameters. Because some of the modeling parameters and their variances were not distributed normally, a second mixture model was developed to further explore these data. The mixture model had two additional fixed parameters and identified two populations, A (55% of subjects), where there was no change in bioavailability, and B (45% of subjects), where ivermectin bioavailability was increased 37%. Simulations of the data using both models were similar, and showed that the highest ivermectin concentrations fell in the range of 115–201 ng/mL.

Conclusions

This is the first pharmacokinetic model of ivermectin. It demonstrates the utility of two modeling approaches to explore drug interactions, especially where there may be population heterogeneity. The mechanism for the interaction was identified (an increase in bioavailability in one subpopulation). Simulations show that the maximum ivermectin exposures that might be observed during co-administration with azithromycin are below those previously shown to be safe and well tolerated. These analyses support further study of co-administration of azithromycin with the widely used agents ivermectin and albendazole, under field conditions in disease control programs.

This paper describes the use of a modeling and simulation approach to explore a reported pharmacokinetic interaction between two drugs (ivermectin and azithromycin), which along with albendazole, are being developed for combination use in neglected tropical diseases. This approach is complementary to more traditional pharmacokinetic and safety studies that need to be conducted to support combined use of different health interventions. A mathematical model of ivermectin pharmacokinetics was created and used to simulate multiple trials, and the probability of certain outcomes (very high peak blood ivermectin levels when given in combination) was determined. All simulated peak blood levels were within ranges known to be safe and well tolerated. Additional field studies are needed to confirm these findings.

Dose-escalating study of the pharmacokinetics and tolerability of fesoterodine in children with overactive bladder

OBJECTIVE

To determine the pharmacokinetics, safety and tolerability of fesoterodine, and assess the utility of 3-day bladder diaries (exploratory objective) in pediatric subjects with neurogenic detrusor overactivity or idiopathic overactive bladder (OAB).

METHODS

In this 8-week open-label study, subjects (8-17 years, >25 kg) received fesoterodine 4 mg for 4 weeks, then 8 mg for 4 weeks. Blood samples were obtained at weeks 4 and 8.

RESULTS

Of 21 subjects enrolled, 11 had neurogenic detrusor overactivity and 10 had idiopathic OAB; 1 discontinued (personal reasons). Mean age and weight were 13.2 years and 54.0 kg for boys (n = 12) and 13.1 years and 49.2 kg for girls (n = 9). 5-Hydroxy-methyltolterodine plasma concentrations did not differ by diagnosis and were consistent with predictions based on adult data. Treatment-related adverse events (all mild or moderate) included 1 event each of dry mouth, constipation, dry eyes and blurred vision, and 2 events each of nausea and increased post-void residual volume. Three-day bladder diaries proved feasible.

CONCLUSIONS

Oral administration of fesoterodine in pediatric subjects (>25 kg) with idiopathic OAB or neurogenic detrusor overactivity produced steady-state plasma 5-hydroxy-methyltolterodine exposures similar to those in adults. The doses given were well tolerated.

Clinical Pharmacology and Pharmacokinetics of Once-Daily Hydromorphone Hydrochloride Extended-Release Capsules

Hydromorphone hydrochloride extended release (HHER) is a multiparticulate melt-extrusion pellet capsule formulation administered q24h. Study 1 investigated the bioavailability of 24-mg HHER fed, as well as 24-mg and 12-mg HHER and 8-mg hydromorphone hydrochloride immediate-release (HHIR) tablets fasting. No clinically significant food effect was observed on hydromorphone C(max) or AUC for the 24-mg HHER, and dose proportionality (AUC) was demonstrated between 12- and 24-mg HHER. Study 2 demonstrated dose strength proportionality for 3 x 12-mg HHER versus 1 x 32-mg HHER. Study 3 evaluated 12-mg HHER q24h versus 3-mg HHIR q6h at steady state. HHER produced relatively constant steady-state concentrations over 24 hours. HHER and HHIR were equivalent for AUC(ss). C(ssmax) was 26% lower for HHER than HHIR, C(ssmin) was 43% higher for HHER, and peak-to-trough fluctuation was 126% for HHER versus 328% for HHIR, which are ideal attributes of a once-daily oral extended-release dosage form. HHER administration resulted in fewer adverse events than HHIR in study 3.

Population pharmacokinetics of atorvastatin and its active metabolites in children and adolescents with heterozygous familial hypercholesterolemia: selective use of informative prior distributions from adults

The population pharmacokinetics (PPK) of atorvastatin and its principal active metabolite, o-hydroxyatorvastatin, were described in 6-17 years old pediatric hypercholesterolemia patients with a 2-compartment model for both parent and metabolite. Informative prior distributions on selected parameters, based on adult data, were required to stabilize the model and were implemented using a Bayesian penalty term on the likelihood function in the nonlinear mixed effects model (NONMEM VI with PRIOR). Concentrations below the limit of quantitation were treated as censored data using a conditional likelihood function. Atorvastatin apparent oral clearance (CL/F) was described as a function of body weight using an allometric equation. Based on the final model, the typical CL/F estimates for a Tanner Stage 1 patient (35 kg weight) and Tanner Stage ≥2 (50 kg weight), would be 553 and 543 L/hour, respectively. When scaled allometrically, CL/F was similar to values reported for adults. Variability in atorvastatin PK was primarily affected by weight.

Modeling dose-response relationships of the effects of fesoterodine in patients with overactive bladder

Background

Fesoterodine is an antimuscarinic for the treatment of overactive bladder, a syndrome of urgency, with or without urgency urinary incontinence (UUI), usually with increased daytime frequency and nocturia. Our objective was to develop predictive models to describe the dose response of fesoterodine.

Methods

Data from subjects enrolled in double-blind, placebo-controlled phase II and III trials were used for developing longitudinal dose-response models.

Results

The models predicted that clinically significant and near-maximum treatment effects would be seen within 3 to 4 weeks after treatment initiation. For a typical patient with 11 micturitions per 24 hours at baseline, predicted change was -1.2, -1.7, and -2.2 micturitions for placebo and fesoterodine 4 mg and 8 mg, respectively. For a typical patient with 2 UUI episodes per 24 hours at baseline, predicted change was -1.05, -1.26, and -1.43 UUI episodes for placebo and fesoterodine 4 mg and 8 mg, respectively. Increase in mean voided volume was estimated at 9.7 mL for placebo, with an additional 14.2 mL and 28.4 mL for fesoterodine 4 mg and 8 mg, respectively.

Conclusions

A consistent dose response for fesoterodine was demonstrated for bladder diary endpoints in subjects with overactive bladder, a result that supports the greater efficacy seen with fesoterodine 8 mg in post hoc analyses of clinical trial data. The dose-response models can be used to predict outcomes for doses not studied or for patient subgroups underrepresented in clinical trials.

Trial Registration

The phase III trials used in this analysis have been registered at ClinicalTrials.gov (NCT00220363 and NCT00138723).

Bioequivalence of long half-life drugs--informative sampling determination--using truncated area in parallel-designed studies for slow sustained-release formulations

A simulation study was done to determine if 72 h is the most informative sampling duration for bioequivalence (BE) determination in parallel-designed BE studies with drugs that have half-lives of at least 30 h. The impact of absorption and elimination half-lives on informative sampling was evaluated. Two-treatment parallel-designed BE studies using a one-compartment oral absorption model with half-lives of 30 and 350 h was simulated. Area under the curve (AUC) values were truncated at 12-360 h. Experimental BE data [median time to reach the maximum concentration (T(max) ) = 20 h and low clearance = 0.192 L/h) indicated a decrease and then an increase in the intrasubject variability [root mean square error (RMSE)] for truncated AUC as a function of time. Simulations supported these findings with the highest probability of passing the BE confidence interval criteria being between 60 and 96 h, depending on half-life and percent coefficient of variation. The 30-h simulation exhibited a minimum in RMSE at 24-h truncation that continued to increase up to 360 h, whereas the 350-h simulation exhibited a minimum at 60 h, which increased after 96 h. Power curves at the 350-h half-life showed higher probabilities of rejection of BE for true test/reference ratios greater than 0.9. For parallel-designed BE studies, sampling beyond 120 h will not affect the BE decision and therefore is unnecessary.