Impact of product design parameters on in vitro release from intrauterine systems

Tailoring drug release from long-acting contraceptive levonorgestrel intrauterine systems

The wide array of polydimethylsiloxane (PDMS) variants available on the market, coupled with the intricate combination of additives in silicone polymers, and the incomplete understanding of drug release behavior make formulation development of levonorgestrel intrauterine systems (LNG-IUSs) formidable. Accordingly, the objectives of this work were to investigate the impact of excipients on formulation attributes and in vitro performance of LNG-IUSs, elucidate drug release mechanisms, and thereby improve product understanding. LNG-IUSs with a wide range of additives and fillers were prepared, and in vitro drug release testing was conducted for up to 12 months. Incorporating various additives and/or fillers (silica, silicone resins, silicone oil, PEG, etc.) altered the crystallization kinetics of the crosslinked polymer, the viscosity, and the microstructure. In addition, drug-excipient interactions can occur. Interestingly, additives which increased matrix hydrophobicity and hindered PDMS crystallization facilitated dissolution and permeation of the lipophilic LNG. The influence of additives and lubricants on the mechanical properties of LNG-IUSs were also evaluated. PDMS chemical substitution and molecular weight were deemed to be most critical polymer attributes to the in vitro performance of LNG-IUSs. Drugs with varying physicochemical characteristics were used to prepare IUSs, modeling of the release kinetics was performed, and correlations between release properties and the various physicochemical attributes of the model drugs were established. Strong correlations between first order release rate constants and both drug solubility and Log P underpin the partition and diffusion-based release mechanisms in LNG-IUSs. This is the first comprehensive report to provide a mechanistic understanding of material-property-performance relationships for IUSs. This work offers an evidence-based approach to rational excipient selection and tailoring of drug release to achieve target daily release rates in vivo. The novel insights gained through this research could be helpful for supporting development of brand and generic IUS products as well as their regulatory assessment.

Solid implantable devices for sustained drug delivery

Implantable drug delivery systems (IDDS) are an attractive alternative to conventional drug administration routes. Oral and injectable drug administration are the most common routes for drug delivery providing peaks of drug concentrations in blood after administration followed by concentration decay after a few hours. Therefore, constant drug administration is required to keep drug levels within the therapeutic window of the drug. Moreover, oral drug delivery presents alternative challenges due to drug degradation within the gastrointestinal tract or first pass metabolism. IDDS can be used to provide sustained drug delivery for prolonged periods of time. The use of this type of systems is especially interesting for the treatment of chronic conditions where patient adherence to conventional treatments can be challenging. These systems are normally used for systemic drug delivery. However, IDDS can be used for localised administration to maximise the amount of drug delivered within the active site while reducing systemic exposure. This review will cover current applications of IDDS focusing on the materials used to prepare this type of systems and the main therapeutic areas of application.

Impact of drug loading on release from levonorgestrel intrauterine systems

Levonorgestrel intrauterine systems (LNG-IUSs) are polydimethylsiloxane (PDMS) based non-biodegradable complex drug-device combination products providing efficacy for up to several years based on the strength. A large amount of LNG (e.g., 52 mg in Mirena and Liletta) must be loaded in the LNG-IUS products to maintain the long-acting effect even though LNG is a potent hormone. However, the high amount of LNG not only poses the potential risk of dose dumping, but also leads to drug waste due to incomplete drug utilization close to the end of usage. It has been unclear whether the duration of usage of these products should be extended for full drug utilization or products with lower drug loading should be developed. Therefore, it is critical to understand the impact of strength (or drug loading) on drug release from LNG-IUSs. In the current study, drug reservoirs with a broad range of drug loading (from 0.5% w/w to 50% w/w) were prepared and assembled into LNG-IUSs. Different accelerated release conditions were used to perform release testing of LNG-IUSs with different drug loading. 5% to 10% variation in excipient of the LNG-IUSs did not significantly alter the drug release profiles of the LNG-IUSs. The release rate of LNG-IUSs is inversely proportional to their drug loading at high drug loading (10% w/w, 25% w/w and 50% w/w). Drug release was incomplete for LNG-IUS with low drug loading (2.5% w/w and 1% w/w) and no drug release could be detected for the LNG-IUS with 0.5% w/w drug loading. In addition, the burst effect of the LNG-IUSs with different drug loading was investigated. This is the first research report covering ultra-long duration (more than four years) of real-time drug release from LNG-IUSs with different drug loading (0.5%-50% w/w). The amount of excipient (PDMS) used in the reservoir of LNG-IUSs was determined to be not a critical quality parameter in the formulation design since LNG-IUSs (50% w/w drug loading) with up to 10% variation in excipient did not show significant differences in their release profiles. The drug release kinetics/mechanism remained the same for LNG-IUSs with drug loading ranging from 1% to 50%. In addition, the accelerated release testing methods were confirmed to be representative of the real-time release profiles and this can give confidence in extending the duration of usage for these products provided that the device remains physically intact (no tearing or damage in the outer membrane) and the release rate is within the therapeutic window. It is recommended to perform both real-time and accelerated release testing simultaneously for LNG-IUSs to understand the burst effect as well as the complete release characteristics. Lastly, drug/polymer interaction may play a role when designing LNG-IUS formulations with low drug loading (<5% w/w) since drug/polymer interaction is significant when only a small amount of drug present.

Long-acting intrauterine systems: Recent advances, current challenges, and future opportunities

Levonorgestrel intrauterine systems (LNG-IUSs) are complex drug-device combination products designed to release a hormonal contraceptive drug for up to 7 years. These drug delivery systems offers a great promise as a modern method of long-acting reversible contraceptives (LARCs) to improve women's health. Unfortunately, there are some scientific challenges associated with the development of these products which are among the major reasons contributing to the availability of relatively few IUS products on the market. This review summarizes the formulation considerations (drug and excipient attributes), manufacturing methods, advances in characterization and in vitro drug release testing of IUSs, as well as factors influencing drug release from IUSs. A critical discussion on the major challenges to IUS product development is presented. Specifically, insights on bioequivalence evaluation, in vitro-in vivo correlation (IVIVC) establishment, and regulatory challenges are detailed. Lastly, methodological tools to overcome some of these hurdles to product development are proposed. The knowledge furnished through this review will be helpful towards obtaining better product understanding. Such understanding will facilitate the development of these complex drug products, as well as their regulatory approval process.

Biopredictive tools for the development of injectable drug products

INTRODUCTION

Biopredictive release tests are commonly used in the evaluation of oral medicines. They support decision-making in formulation development and allow predictions of the expected in-vivo performances. So far, there is limited experience in the application of these methodologies to injectable drug products.

AREAS COVERED

Parenteral drug products cover a variety of dosage forms and administration sites including subcutaneous, intramuscular, and intravenous injections. In this area, developing biopredictive and biorelevant methodologies often confronts us with unique challenges and knowledge gaps. Here, we provide a formulation-centric approach and explain the key considerations and workflow when designing biopredictive assays. Also, we outline the key role of computational methods in achieving clinical relevance and put all considerations into context using liposomal nanomedicines as an example.

EXPERT OPINION

Biopredictive tools are the need of the hour to exploit the tremendous opportunities of injectable drug products. A growing number of biopharmaceuticals such as peptides, proteins, and nucleic acids require different strategies and a better understanding of the influences on drug absorption. Here, our design strategy must maintain the balance of robustness and complexity required for effective formulation development.

Effect of crosslinking on the physicochemical properties of polydimethylsiloxane-based levonorgestrel intrauterine systems

Polydimethylsiloxane (PDMS)-based levonorgestrel intrauterine systems (LNG-IUSs) such as Mirena® are long-acting drug-device combination products designed to release LNG for contraceptive purposes up to 6 years. LNG-IUSs consist of a hollow cylindrical drug-PDMS reservoir mounted with a polyethylene frame and covered by an outer PDMS membrane. PDMS is the release-controlling excipient present in both the matrix and the outer membrane. The degree of PDMS crosslinking is a key parameter in LNG-IUS manufacturing, dictating the elasticity and mechanical strength (which are critical parameters in molding and demolding of the cylindrical reservoirs). In addition, elasticity and mechanical strength are also important to prevent deformation during insertion into the uterine cavity. The objectives of this study were to investigate the impact of PDMS crosslinking on the physicochemical properties of LNG-IUSs and to develop appropriate testing methods for characterization of their mechanical strength. Formulations with different degrees of crosslinking were prepared by varying the ratio of the PDMS elastomer base and the crosslinking agent. A novel solvent swelling and extraction method was developed to determine the degree of PDMS crosslinking. The extent of crosslinking was also characterized via FTIR, Raman, ¹H NMR, DSC, TGA and dynamic mechanical analysis. As expected, formulations with higher degrees of crosslinking showed lower crystallinity. Interestingly, the less crystalline formulations showed higher Tg values and storage moduli compared to the high crystalline formulations, implying that crosslinking is the predominant parameter governing the physicochemical and mechanical properties in LNG-IUSs. Correlations were established between PDMS crosslinking and the physicochemical properties of LNG-IUSs which will be useful for quality control purposes during formulation screening and development. A better understanding of the physicochemical characteristics of these complex products will facilitate drug product development.

Refining the in vitro release test method for a dapivirine-releasing vaginal ring to match in vivo performance

Previously reported in vitro release test methods for drug-releasing vaginal rings containing poorly water-soluble drugs have described use of water-alcohol systems or surfactant solutions in efforts to maintain sink conditions. Here, as part of efforts to more closely match in vitro and in vivo release for the 25 mg dapivirine matrix-type silicone elastomer vaginal ring for HIV prevention, we have investigated alternatives to the 1:1 v/v water/isopropanol medium described previously. Specifically, we evaluated dapivirine release from rings into (i) monophasic water/isopropanol mixtures of varying compositions and (ii) biphasic buffer/octanol systems using pH 4.2 and pH 7.0 buffers. The rate and mechanism of dapivirine release were dependent upon the isopropanol concentration in the release medium, in accordance with the observed trend in drug solubility. At 0 and 10% v/v isopropanol concentrations, dapivirine release followed a partition-controlled mechansim. For media containing ≥ 20% v/v isopropanol, in vitro release of dapivirine was significantly increased and obeyed permeation-controlled kinetics. Cumulative release of ~3.5 mg dapivirine over 28 days was obtained using a water isopropanol mixture containing 20% v/v isopropanol, similar to the ~4 mg dapivirine released in vivo. Dapivirine release into the biphasic buffer/octanol system (intended to mimic the fluid/tissue environment in vivo) was constrained by the limited solubility of dapivirine in the buffer component in which the ring resided, such that cumulative dapivirine release was consistently lower than that observed with the 20% v/v isopropanol in water medium. Release into the biphasic system was also pH dependent, in line with dapivirine's pK_a and with potential implications for in vivo release and absorption in women with elevated vaginal pH.

RP-HPLC method validation for fast extraction and quantification of Levonorgestrel drug from silicone based intrauterine device intended for in-process and finished formulation

BACKGROUND

To develop and validate a simple and consistent reversed phase high performance liquid chromatography (RP-HPLC) method for the estimation of Levonorgestrel (LNG) drug from silicone based intrauterine device.

METHODS

Sample solution was prepared using tetrahydrofuran (THF) as solvent for the drug extraction, and RP-HPLC analysis was performed using Luna C18 analytical column (150 × 4.6 mm, 5 μm, 100 Å - Phenomenex), with a mobile phase consisting of a mixture of acetonitrile and water (50:50, v/v) at a flow rate of 1.0 ml/min and injection volume of 20 μl. Detection was carried out at 241 nm in PDA detector, with a total run time of 15 min. The method was validated in accordance with ICH guidelines. Method applicability was tested for optimizing formulation using quality-by-design approach, to check the stability and content uniformity of levonorgestrel-silicone mixture (core blend), and quantifying the amount of LNG from commercially available silicone based formulation.

RESULTS

The retention time for LNG drug was obtained at 8.5 min (± 0.3 min). A linear relationship was observed over the concentration range of 2.6-15.6 μg/ml with the correlation coefficient (r) value 0.9999. The method was found to be precise within the acceptable limit (RSD < 2%) and the drug recovery from the intrauterine device was found in the range 99.78-100.0%. Content uniformity for different prototypes developed was observed in the range of 91.6-101.4%, and assay of optimized core blend was in the range of 97.78-106.79% during the 10 days of retention period for stability studies.

CONCLUSION

The validated method is found to be a simple, accurate, precise, reproducible, and hence can be used for the routine analysis of LNG such as in-process, quality control and stability assays of silicone based intrauterine devices by RP-HPLC.

Impact of Formulation Parameters on In Vitro Release from Long-Acting Injectable Suspensions

The development of long-acting injectable (LAI) suspension products has increased in recent years. A better understanding of the relationship between the physicochemical properties of these products and their in vitro as well as in vivo performance is expected to further facilitate their development and regulatory review. Using Depo-SubQ Provera 104® as the reference listed drug (RLD), four qualitatively and quantitatively (Q1/Q2) equivalent LAI suspensions with different formulation properties were prepared. Two recrystallization methods (solvent evaporation and antisolvent) were utilized to obtain active pharmaceutical ingredient (API) with different properties and solid-state characterization was performed. In addition, two different sources of the major excipient were used to prepare the Q1/Q2 equivalent suspensions. Physiochemical characterization and in vitro release testing of the prepared Q1/Q2 equivalent suspension formulations and the RLD were conducted. In vitro drug release was dependent not only on the particle size, the morphology, and the crystallinity of the API but also on the residual solvent in the API. The excipient source also affected the drug release rates.