Operating characteristics of a partial-block randomized crossover bioequivalence study for dutasteride, a drug with a long half-life: investigation through simulation and comparison with final results

Studies to establish bioequivalence (BE) of a drug are important elements in support of drug applications. A typical BE study is conducted as a single dose, randomized, 2-period crossover design. For drugs with long half lives (≥ 48 hours) and evaluation of multiple BE objectives in 1 trial, this design may not be adequate. A parallel design may then be a more appropriate choice. However, parallel designs require increased sample size, which can become substantial. One option that is a compromise between the complete randomized block design and the parallel design is a partial-block crossover design. This approach came about during the development of a combination of dutasteride and tamsulosin. Previous experience with performing single-dose dutasteride studies suggested that 28 days of washout is needed between treatments because of its half-life of 7-9 days. Simulations were performed to assess the operating characteristics of this design using a previously developed PK model. Four scenarios were developed, and each scenario was simulated 500 times. The results showed that this design demonstrated acceptable consumer and producer risk. Partial-block crossover designs should be considered for studies when the half-life of the drug is long and there are more than 2 periods.

Pharmacokinetic profile of controlled-release carvedilol in patients with left ventricular dysfunction associated with chronic heart failure or after myocardial infarction

We compared the pharmacokinetic (PK) profiles of repeated dosing with the currently available immediate-release (IR) carvedilol (given twice daily) and a newly developed controlled-release (CR) formulation (given once daily) in patients with left ventricular dysfunction (LVD). We enrolled 188 patients with stable mild, moderate, or severe heart failure as well as survivors of a recent acute myocardial infarction (MI) with asymptomatic LVD (left ventricular ejection fraction </=0.40) in a crossover study. PK variables were initially assessed after patients had received carvedilol IR 3.125, 6.25, 12.5, or 25 mg twice daily for >/=2 weeks. Patients were then switched to the corresponding dose of carvedilol CR (10, 20, 40, or 80 mg once daily), and PK variables were reassessed after an additional 2 weeks. The primary measures included trough plasma concentration (C(tau)), maximum plasma concentration (C(max)), and area under the concentration-time curve (AUC([0-t])) for both enantiomers of carvedilol of each formulation of the drug. The AUC((0-t)) and the trough and maximum carvedilol concentrations for both the R(+) and S(-) enantiomers were similar when carvedilol IR was compared with carvedilol CR as follows: 3.125 mg twice daily versus 10 mg once daily, 6.25 mg twice daily versus 20 mg once daily, 12.5 mg twice daily versus 40 mg once daily, and 25 mg twice daily versus 80 mg once daily, respectively. Based on a pooled analysis, the AUC((0-t)), C(max), and C(tau) for both R(+) and S(-) were equivalent for the CR and IR formulations, with point estimates and 90% confidence intervals within the bioequivalence limits of 80%-125%. The fluctuation index (the CR-IR ratio for [C(max) - C(min)]/C(ss) where C(min) is the minimum observed concentration over the dosing interval and C(ss) is the concentration at steady state) for both R(+)- and S(-)-carvedilol was approximately 1, indicating that the peak-to-trough fluctuation in plasma concentration for carvedilol after use of carvedilol CR once daily was similar to that for carvedilol IR given twice daily. The median time to maximum observed plasma concentration (t(max)) was approximately 3 hours longer for both enantiomers after administration of carvedilol CR as compared with carvedilol IR. These data demonstrate that the new carvedilol CR formulation given once daily is equivalent to the currently available carvedilol IR formulation given twice daily in patients with heart failure and asymptomatic post-MI LVD.

Pharmacokinetic properties of a new controlled-release formulation of carvedilol

This review summarizes the pharmacokinetics (PK) of carvedilol after administration of a new once-daily controlled-release (CR) formulation. The plasma concentration-time profiles for both R(+)- and S(-)-carvedilol indicate that carvedilol CR will provide coverage over a 24-hour period similar to the current immediate-release (IR) twice-daily formulation. Exposures for both enantiomers, based on area under the curve (AUC), maximum plasma concentrations (C(max)), and trough concentrations, are equivalent for carvedilol CR compared with carvedilol IR. C(max) and AUC of the enantiomers of carvedilol increase in an approximate dose-proportional manner after administration of carvedilol CR over the dose range of 10-80 mg, indicating that the formulation provides consistent PK performance across the dose strengths proposed for marketing. The intrasubject and intersubject variability of carvedilol CR was comparable to carvedilol IR. For carvedilol CR, mean AUC and C(max) were increased <20% after a high-fat meal compared with a standard meal. The CR and IR formulations of carvedilol exhibited equivalent steady-state PK characteristics in the target hypertension and heart failure populations. The availability of once-daily dosing is expected to improve treatment adherence and thereby enhance the effectiveness of carvedilol in routine clinical use.

Development of a pharmacokinetic/pharmacodynamic model for carvedilol to predict beta1-blockade in patients with congestive heart failure

To determine whether the controlled-release (CR) formulation of carvedilol given once daily provides 24-hour beta1-receptor blockade similar to the currently marketed immediate-release (IR) formulation given twice daily, changes in exercise-induced heart rate after bicycle ergometry were measured. The pharmacokinetic (PK)/pharmacodynamic (PD) relation between S(-)-carvedilol concentration-the enantiomer with beta-blocking activity-and change in exercise-induced heart rate was defined in healthy subjects and was best described using a direct effect inhibitory E(max) model (with E(max) being the maximum effect). The population estimates for E(max) and concentration at 50% of the maximum effect (EC50) were 19.2 beats per minute (an approximately 13% maximum decrease in exercise-induced heart rate) and 7.7 ng/mL, respectively. The PK/PD model was used to predict PD effects in patients with mild-to-severe heart failure and in patients after myocardial infarction with left ventricular dysfunction who had received both the IR and CR formulations of carvedilol. In these patients, carvedilol CR had equivalent predicted overall PD (area under the effect curve) and trough (PD(min)) effects compared with carvedilol IR, indicating 24-hour beta-blocking coverage for the new CR formulation of carvedilol given once daily.

Pharmacokinetic and pharmacodynamic comparison of controlled-release carvedilol and immediate-release carvedilol at steady state in patients with hypertension

Carvedilol is indicated for the treatment of essential hypertension and mild-to-severe chronic heart failure, as well as the reduction of cardiovascular mortality in clinically stable post-myocardial infarction patients with left ventricular dysfunction. Carvedilol is a racemic mixture of R(+) and S(-) enantiomers that combines beta(1)-, beta(2)-, and alpha(1)-adrenoceptor blockade. For all indications, the immediate-release (IR) formulation of carvedilol is taken twice daily. A controlled-release (CR) formulation of carvedilol that allows once-daily dosing has recently been developed. In this double-blind, parallel-group, crossover study, 122 patients with essential hypertension were randomly allocated to receive low and high doses of carvedilol or placebo. Patients received either a constant low dose (CR 20 mg once daily or IR 6.25 mg twice daily) or were titrated to a high dose (CR 80 mg once daily or IR 25 mg twice daily) before being crossed over to an equivalent dose of the alternative formulation. The pharmacokinetic (PK) and pharmacodynamic (PD) profiles were compared between patients receiving carvedilol CR and carvedilol IR. The PK profiles for R(+)- and S(-)-carvedilol for the 2 formulations were equivalent (based on area under the curve, maximum plasma concentration [C(max)], and trough drug concentration). Consistent with an extended-release formulation, carvedilol CR delayed C(max) by 3.5 hours compared with carvedilol IR. For both carvedilol CR and IR, the attenuation of exercise-induced heart rate in patients with hypertension was maintained over the entire 24-hour period, and the 2 formulations demonstrated equivalent beta(1)-blocking effects at trough (end of the dosing interval [PD(min)]), suggesting that the rate of absorption does not interfere with the PD effect. In this first direct comparison of carvedilol CR and IR in subjects with hypertension, fewer adverse events were reported while subjects were receiving carvedilol CR (59.1% overall) compared with carvedilol IR (77.5% overall). This was true regardless of dose received. Headache was the most commonly reported adverse event for subjects receiving either formulation of carvedilol and placebo. Importantly, dizziness and headache were reported less often when subjects received carvedilol CR. This is the first study to show that both formulations had comparable beta(1)-adrenergic blockade in patients with essential hypertension under steady-state conditions. Notably, carvedilol CR provides consistent beta(1)-adrenergic blockade over 24 hours with a once-daily dose.

Pharmacodynamics and pharmacokinetics of oral contraceptives co-administered with alosetron (Lotronex)

The 5-HT3 receptor antagonist alosetron (Lotronex) is indicated for use in women with severe, chronic, diarrhea-predominant irritable bowel syndrome (IBS) who have failed conventional therapy. Oral contraceptives (OCs) and alosetron are potential co-medications in women of childbearing age. This study assessed the effect of alosetron co-administration on pharmacodynamic markers of contraceptive efficacy, on the pharmacokinetics of estrogen and progesterone OC components, and on the activity of biochemical markers for the risk of thrombosis. This was an open label, nonrandomized two-way crossover study in 18 healthy women stabilized for 3 months on a low-dose OC containing ethinyl estradiol (EE) and levonorgestrel (LN). Alosetron had no effect on serum concentrations of luteinizing hormone (LH) or follicle-stimulating hormone. Ovarian activity grades (assessing follicle size, progesterone, and 17beta-estradiol concentrations) were similar during OC use with and without alosetron. Steady-state (Day 21) AUC24, Cmax, and tmax of both LN and EE were similar during coadministration of alosetron with an OC. Concentrations and activity of biochemical markers of thrombosis risk were not different in the presence of alosetron. These results indicate that alosetron does not alter the pharmacokinetics or pharmacodynamic markers of efficacy for a low-dose combination OC. The results also suggest that thromboembolic risk is not increased when alosetron is co-administered with an OC.

Treatment with intranasal fluticasone propionate significantly improves ocular symptoms in patients with seasonal allergic rhinitis

BACKGROUND

If monotherapy with an intranasal corticosteroid can alleviate both nasal and ocular symptoms of allergic rhinitis, treatment may be simplified and costs may be reduced.

OBJECTIVE

The purpose of this study was to evaluate the efficacy of once-daily fluticasone propionate (FP) aqueous nasal spray 200 microg compared with vehicle placebo and oral loratadine (LOR) 10 mg in reducing ocular symptoms associated with seasonal allergic rhinitis.

METHODS

A total of 471 patients received vehicle placebo, LOR, or FP in this multi-centre, double-blind, double-dummy, randomized study. Patients were > or =12 years old with a history of seasonal allergic rhinitis and a positive skin test for a relevant allergen. During the baseline and treatment periods, patients rated the severity of eye itching, tearing, and redness via visual analogue scales that ranged from 0 (no symptoms) to 100 (most severe symptoms). The three ocular ratings were added to derive the total ocular symptom score (TOSS). Patients with a TOSS > or =120 on at least 4 of the 7 days before the randomization visit were enrolled. The primary outcome was the difference between FP and vehicle placebo in the mean change from baseline in the reflective TOSS overall (averaged over the 28-day treatment period). A difference between FP and vehicle placebo of 25.5 was considered clinically significant.

RESULTS

The overall mean change from baseline in the TOSS was significantly greater in the FP group compared with vehicle placebo (clinically significant difference of 28.8; P<0.001) and compared with LOR (difference of 16.2; P=0.028). Overall mean (SEM) changes were -59.9 (5.4) for the placebo group, -72.5 (5.4) for the LOR group, and -88.7 (5.3) for the FP group. The FP treatment group also showed significantly greater overall mean changes in ocular itching, tearing, and redness compared with vehicle placebo (P<0.001) and compared with LOR (P< or =0.045).

CONCLUSION

Patients treated with intranasal FP had clinically and statistically significant decreases in ocular symptom scores compared with vehicle placebo. Data also suggest that FP reduced ocular symptoms more than or comparable with oral LOR. Patients experiencing ocular symptoms associated with allergic rhinitis may benefit from monotherapy with intranasal FP.

Fluticasone propionate aqueous nasal spray provided significantly greater improvement in daytime and nighttime nasal symptoms of seasonal allergic rhinitis compared with montelukast

BACKGROUND

The safety and efficacy of intranasal corticosteroids for the treatment of allergic rhinitis is well documented in the literature. Additionally, an expert panel has concluded that intranasal corticosteroids are the first line of therapy when obstruction is a major component of rhinitis. Montelukast is a leukotriene receptor antagonist recently approved for the treatment of seasonal allergic rhinitis (SAR).

OBJECTIVE

This randomized, double-blind, double-dummy, parallel-group study was conducted to compare the effectiveness of a 15-day course of intranasal fluticasone propionate 200 microg, once daily (FP200QD), to oral montelukast 10 mg, once daily (MON10QD), in relieving daytime and nighttime nasal symptoms associated with SAR.

METHODS

The intent-to-treat (ITT) analysis population consisted of 705 eligible males and females (> or = 15 years) with SAR randomized to either FP200QD (N = 353) or MON10QD (N = 352). The primary efficacy endpoint was the mean change from baseline in subject-rated daytime total nasal symptom scores (the sum of four individual scores: nasal congestion, itching, rhinorrhea, and sneezing), evaluated via visual analog scales, and averaged over weeks 1 to 2. Secondary endpoints included the four daytime individual nasal symptom scores, the nighttime total, and individual nasal symptom scores (each evaluated on a four-point scale from 0 to 3).

RESULTS

Statistically significant differences favoring FP200QD over MON10QD were observed for the mean change from baseline in daytime total nasal symptom scores (P < 0.001), daytime individual nasal symptom scores (P < 0.001), nighttime total (P < 0.001), and all individual nasal symptom scores (P < or = 0.002) over the 15-day treatment period. FP200QD and MON10QD were both well tolerated.

CONCLUSIONS

The results of this well controlled study demonstrated that FP200QD was consistently superior to MON10QD with regard to every efficacy endpoint evaluated, including daytime and nighttime nasal congestion, in subjects with SAR.