Commentary on AAPS Workshop: dissolution testing for the twenty-first century: linking critical quality attributes and critical process parameters to clinically relevant dissolution.

This is a summary report of the workshop entitled "Dissolution Testing for the Twenty-first Century: Linking Critical Quality Attributes and Critical Process Parameters to Clinically Relevant Dissolution," organized by the In Vitro Release and Dissolution Testing Focus Group of the American Association of Pharmaceutical Scientists. Participants from the pharmaceutical industry, regulatory authorities, and academia in the US, Europe, and Japan attended this workshop to review, discuss, and explore the role of traditional dissolution testing in the new arena of Quality by Design (QbD) and Process Analytical Technology (PAT). Other areas of discussion were the use of the dissolution test to evaluate drug release from novel dosage forms, challenges in dissolution testing and specification setting, and dissolution apparatus calibration using performance verification tablets versus mechanical calibration. The workshop identified areas where further research and collaboration are needed to advance knowledge and understanding of the science of dissolution. Views expressed in this report are those of the authors and do not necessarily reflect those of the FDA and USP.

Methods to assess in vitro drug release from injectable polymeric particulate systems.

This review provides a compilation of the methods used to study real-time (37 degrees C) drug release from parenteral microparticulate drug delivery systems administered via the subcutaneous or intramuscular route. Current methods fall into three broad categories, viz., sample and separate, flow-through cell, and dialysis techniques. The principle of the specific method employed along with the advantages and disadvantages are described. With the "sample and separate" technique, drug-loaded microparticles are introduced into a vessel, and release is monitored over time by analysis of supernatant or drug remaining in the microspheres. In the "flow-through cell" technique, media is continuously circulated through a column containing drug-loaded microparticles followed by analysis of the eluent. The "dialysis" method achieves a physical separation of the drug-loaded microparticles from the release media by use of a membrane, which allows for sampling without interference of the microspheres. With all these methods, the setup and sampling techniques seem to influence in vitro release; the results are discussed in detail, and criteria to aid in selection of a method are stated. Attempts to establish in vitro-in vivo correlation for these injectable dosage forms are also discussed. It would be prudent to have an in vitro test method for microparticles that satisfies compendial and regulatory requirements, is user friendly, robust, and reproducible, and can be used for quality-control purposes at real-time and elevated temperatures.

Development of a dialysis in vitro release method for biodegradable microspheres.

The purpose of this research was to develop a simple and convenient in vitro release method for biodegradable microspheres using a commercially available dialyzer. A 25 KD MWCO Float-a-Lyzer was used to evaluate peptide diffusion at 37 degrees C and 55 degrees C in different buffers and assess the effect of peptide concentration. In vitro release of Leuprolide from PLGA microspheres, having a 1-month duration of action, was assessed using the dialyzer and compared with the commonly used sample and separate method with and without agitation. Peptide diffusion through the dialysis membrane was rapid at 37 degrees C and 55 degrees C in all buffers and was independent of peptide concentration. There was no detectable binding to the membrane under the conditions of the study. In vitro release of Leuprolide from PLGA microspheres was tri-phasic and was complete in 28 days with the dialysis technique. With the sample and separate technique, linear release profiles were obtained with complete release occurring under conditions of agitation. Diffusion through the dialysis membrane was sufficiently rapid to qualify the Float-a-Lyzer for an in vitro release system for microparticulate dosage forms. Membrane characteristics render it useful to study drug release under real-time and accelerated conditions.

Plasticizing effect of water on poly(lactide-co-glycolide).

The purpose of this research was to evaluate the effect and nature of hydration on the glass transition temperature (Tg) of poly(D,L-lactide-co-glycolide) and investigate the physical state of water within the polymer during hygrothermal aging. The polymer was incubated in water at 23, 30, 37 and 55 degrees C, while the vapor sorption studies were carried out at 37 degrees C using saturated salt solutions. The water content and the thermal behavior of PLGA-water system were assessed by Karl Fischer titration and modulated differential scanning calorimetry, respectively, the hygrothermal aging was monitored by gel permeation chromatography. Water depressed reversibly the Tg by about 15 degrees C regardless of the incubation conditions. The Tg then remained constant at approximately 30 degrees C for five days, except when degradation occurred. A broad ice melting peak was detected around 0 degrees C. In the sorption studies, a linear correlation (r2 0.9837) between the Tg and the moisture content was observed in the range of 0.3-2.6% w/w, but there was no discernible endothermic event associated with the melting of ice. Data were found to fit reasonably well to the Gordon-Taylor/Kelley-Bueche equation. There were no differences between bulk and vapor water aging. It is proposed that the water responsible for plasticizing the polymer was non-freezable (bound) water and the small fraction of such water which was absorbed at high relative humidity caused polymer degradation in the same manner as bulk water.

A model-dependent approach to correlate accelerated with real-time release from biodegradable microspheres.

The purpose of this study was to determine the feasibility of applying accelerated in vitro release testing to correlate or predict long-term in vitro release of leuprolide poly(lactide-co-glycolide) microspheres. Peptide release was studied using a dialysis technique at 37 degrees C and at elevated temperatures (50 degrees C-60 degrees C) in 0.1M phosphate buffered saline (PBS) pH 7.4 and 0.1M acetate buffer pH 4.0. The data were analyzed using a modification of the Weibull equation. Peptide release was temperature dependent and complete within 30 days at 37 degrees C and 3 to 5 days at the elevated temperatures. In vitro release profiles at the elevated temperatures correlated well with release at 37 degrees C. The shapes of the release profiles at all temperatures were similar. Using the modified Weibull equation, an increase in temperature was characterized by an increase in the model parameter, alpha, a scaling factor for the apparent rate constant. Complete release at 37 degrees C was shortened from approximately 30 days to 5 days at 50 degrees C, 3.5 days at 55 degrees C, 2.25 days at 60 degrees C in PBS pH 7.4, and 3 days at 50 degrees C in acetate buffer pH 4.0. Values for the model parameter beta indicated that the shape of the release profiles at 55 degrees C in PBS pH 7.4 (2.740) and 50 degrees C in 0.1M acetate buffer pH 4.0 (2.711) were similar to that at 37 degrees C (2.677). The E(a) for hydration and erosion were determined to be 42.3 and 19.4 kcal/mol, respectively. Polymer degradation was also temperature dependent and had an E(a) of 31.6 kcal/mol. Short-term in vitro release studies offer the possibility of correlation with long-term release, thereby reducing the time and expense associated with long-term studies. Accelerated release methodology could be useful in the prediction of long-term release from extended release microsphere dosage forms and may serve as a quality control tool for the release of clinical or commercial batches.

Assessment of fertility in male rats after extended chemical castration with a GnRH antagonist.

The purpose of this study was to assess whether male rats whose testosterone levels were suppressed to castration levels (<0.5 ng/mL) for a 1-year period by the sustained delivery of orntide acetate, a GnRH antagonist, would return to fertility (ie, produce offspring) after serum testosterone returned to control levels. Male rats comprising a treatment group (orntide microspheres, dose = 27 mg/kg/y), a vehicle control group, and a control group of proven male breeders were used. For the treatment and vehicle control groups, serum orntide and testosterone levels were monitored at periodic intervals for 14 months from the initiation of treatment. After serum testosterone levels returned to vehicle control levels and orntide serum levels were no longer discernible for the treated group, each of the animals was housed with 2 drug-naive, female, proven breeders. All the breeder females produced offspring with the exception of 1 female housed with a male rat from the treatment group and the 2 females housed with a single male rat from the vehicle control group. The mean size and weight of the litters from each group were not statistically different. Further, fertility of the offspring from each group was assessed. The male and female offspring studied were all shown to be fertile. The results suggest that lack of fertility due to testosterone suppression in male rats is reversible after cessation of treatment with the GnRH analog, orntide.

Orchidectomy, but not ovariectomy, regulates angiotensin II-induced vascular diseases in apolipoprotein E-deficient mice.

In humans, the incidence and severity of abdominal aortic aneurysms (AAA) are greater in males than in females. Chronic infusion of angiotensin II (AngII) into apolipoprotein E-deficient (apoE(-/-)) mice promotes atherosclerosis and causes the formation of AAAs. Just as human males are more susceptible to developing AAAs, male mice are more susceptible to AngII-induced AAAs. We hypothesized that sex steroid hormones mediate gender differences in AngII-induced AAA through regulation of the renin-angiotensin system. To define the role of ovarian hormones, female apoE(-/-) mice were subjected to ovariectomy or sham operation and infused with AngII (1000 ng/kg x min) for 28 d. Ovariectomy had no effect on AngII-induced atherosclerosis, nor did it influence the incidence or severity of AAA. To define the role of testicular hormones, male apoE(-/-) mice were subjected to orchidectomy (orx) or sham operation and infused with AngII (1000 ng/kg x min) for 28 d. Orx resulted in a profound reduction in AAA incidence (85% vs. 18%, sham vs. orx; P = 0.003) to the level observed in females (25%). However, orx had no effect on AngII-induced reductions in plasma renin concentration or spleen AngII receptor density. In contrast, orx resulted in an increase in atherosclerosis (0.46 +/- 0.07 vs. 1.20 +/- 0.21 mm(2), sham vs. orx; P = 0.002). These results suggest that estrogen does not mediate gender differences in AngII-induced AAA. In contrast, androgens mediate a higher incidence of AngII- induced AAA, through mechanisms that do not appear to involve circulating renin or angiotensin receptor density.