Development pharmaceutics of microbicide formulations. Part I: preformulation considerations and challenges

Designing Dual Compartment HIV Prevention Products: Women's Sensory Perceptions and Experiences of Suppositories for Rectal and Vaginal Use

Dual compartment suppositories are being developed to prevent HIV and other sexually transmitted infections. Such products, for use in the rectum, the vagina, or both, could have a significant public health impact by decreasing global incidence of these diseases. In this study, 16 women each used two rheologically distinct suppositories in their vagina and rectum. User Sensory Perception and Experience (USPE) scales assessed sensory experiences during sexual activity to understand whether, and how, women perceive formulation properties in the vagina and rectum. Qualitative data from individual in-depth interviews captured women's descriptions and comparisons of the experiences. Significant differences and large Cohen's d effect sizes between vaginal and rectal experiences of suppository-A were found for three scales: Application (APP): Product Awareness, SEX: Initial Penetration; and SEX: Effortful. Qualitative data provided user experience details that credibly align with these score differences. Near significant differences and large effect sizes were found for two additional scales: SEX: Perceived Wetness with suppository-A and SEX: Messiness with suppository-B. In addition, other scale scores showed medium-to-large effect sizes that correspond to hypothesized sensations associated with biophysical properties of the suppositories. Statistical significance combined with large effect sizes and qualitative data accurately represent the hypothesized perceptibility of suppository properties and identifies performance characteristics relevant to acceptability and adherence; together these data provide discernment of factors that can guide the development of dual compartment products. The Clinical Trial Registration number: NCT02744261.

Progress and Perspectives on HIV-1 microbicide development

The majority of HIV-1 infections occur via sexual intercourse. Women are the most affected by the epidemic, particularly in developing countries, due to their socio-economic dependence on men and the fact that they are often victims of gender based sexual violence. Despite significant efforts that resulted in the reduction of infection rates in some countries, there is still need for effective prevention methods against the virus. One of these methods for preventing sexual transmission in women is the use of microbicides. In this review we provide a summary of the progress made toward the discovery of affordable and effective HIV-1 microbicides and suggest future directions. We show that there is a wide range of compounds that have been proposed as potential microbicides. Although most of them have so far failed to show protection in humans, there are many promising ones currently in pre-clinical studies and in clinical trials.

Formulation and delivery of anti-HIV rectal microbicides: advances and challenges

Men and women engaged in unprotected receptive anal intercourse (RAI) are at higher risk of acquiring HIV from infected partners. The implementation of preventive strategies is urgent and rectal microbicides may be a useful tool in reducing the sexual transmission of HIV. However, pre-clinical and first clinical trials have been able to identify limitations of candidate products, mostly related with safety issues, which can in turn enhance viral infection. Indeed, the development of suitable formulations for the rectal delivery of promising antiretroviral drugs is not an easy task, and has been mostly based on products specifically intended for vaginal delivery, but these have been shown to provide sub-optimal outcomes when administered rectally. Research and development in the rectal microbicide field are now charting their own path and important information is now available. In particular, specific formulation requirements of rectal microbicide products that need to be met have just recently been acknowledged despite additional work being still required. Desirable rectal microbicide product features regarding characteristics such as pH, osmolality, excipients, dosage forms, volume to be administered and the need for applicator use have been studied and defined in recent years, and specific guidance is now possible. This review provides a synopsis of the field of rectal microbicides, namely past and ongoing clinical studies, and details on formulation and drug delivery issues regarding the specific development of rectal microbicide products. Also, future work, as required for the advancement of the field, is discussed.

Electrospun fibers for vaginal anti-HIV drug delivery

Diversity of microbicide delivery systems is essential for future success in the prevention and treatment of HIV in order to account for the varied populations of women all over the world that may benefit from use of these products. Recently, a novel dosage form for intravaginal drug delivery has been developed using drug-eluting fibers fabricated by electrospinning. There is a strong rationale to support the idea that drug-eluting fibers can be designed to realize multiple design constraints in a single product for topical HIV prevention: fibers are able to deliver a wide range of agents, incorporate multiple agents via composites, and facilitate controlled release over relevant time frames for pericoital and sustained (coitally-independent) use. It is also technologically feasible to scale-up production of fiber-based microbicides. Electrospun fibers may allow for prioritization of physical attributes that affect user perceptions without compromising biological efficacy. Challenges with using fibers as a microbicide include issues related to vehicle deployment, spreading and retention in the vaginal vault. In addition, studies will need to address the interaction of the fibers with the mucosal environment, including unknown safety and toxicity. Sustained release fiber microbicides capable of delivering multiple antiretroviral drugs while simultaneously exhibiting tunable degradation or dissolution of the fibers is also a challenge. However, electrospun fibers are a promising new platform for vaginal delivery of anti-HIV agents and future research will inform their place in the field. This article is based on a presentation at the "Product Development Workshop 2013: HIV and Multipurpose Prevention Technologies", held in Arlington, Virginia on February 20-21, 2013. It forms part of a special supplement to Antiviral Research.

Future strategies in microbicide development

The reduction in human immunodeficiency virus (HIV) infection in women demonstrated by pericoital use of tenofovir gel has encouraged the continued development of microbicides. Novel approaches include new ways to deliver tenofovir, as well as products that contain different antiretroviral drugs, either as single agents or as combinations of antiretroviral drugs. Indeed, emphasis has renewed on the development of multipurpose prevention technologies, products designed to address multiple sexually transmitted infections. Dual-purpose contraceptive antiretroviral products are also being designed to prevent HIV and pregnancy. Since consistent and correct use of these products will be critical to their effectiveness, the active pharmaceutical ingredients must be delivered in acceptable vaginal dosage forms, such as gels, films and sustained-release vaginal rings. The development of different dosage forms will help ensure that women can find a method to protect themselves from HIV, pregnancy, and potentially other sexually transmitted infections.

Early identification of availability issues for poorly water-soluble microbicide candidates in biorelevant media: a case study with saquinavir

In the search for a successful HIV microbicide, many poorly water-soluble antiviral agents are currently being investigated. Unfortunately, solubility and precipitation issues may limit intravaginal concentrations and thus availability of these agents upon application of an aqueous gel formulation. In the present study, we evaluated the in vitro precipitation behavior of the HIV protease inhibitor saquinavir in vaginal and seminal fluid simulants (VFS and SFS). Despite its limited solubility, the mesylate salt of saquinavir enables formulation of sufficiently high concentrations (2.5 mM, i.e. ca. 10(5)-fold in vitro IC(50) values) in a standard aqueous vehicle. While saquinavir stays in solution upon dilution with VFS, SFS induces precipitation of saquinavir, resulting in a 5-fold reduced availability and antiviral potency. Inclusion of the solubilizing excipients polyethylene glycol 1000 (12%) and hydroxypropyl-β-cyclodextrin (2.5%) was required to avoid saquinavir precipitation in SFS and to restore the antiviral potency of the formulation. This study illustrates the importance of identifying solubility and precipitation issues of microbicide candidates in biorelevant media and provides a simple in vitro procedure to implement this evaluation in early microbicide development.

Rectal microbicides: clinically relevant approach to the design of rectal specific placebo formulations

BACKGROUND

The objective of this study is to identify the critical formulation parameters controlling distribution and function for the rectal administration of microbicides in humans. Four placebo formulations were designed with a wide range of hydrophilic characteristics (aqueous to lipid) and rheological properties (Newtonian, shear thinning, thermal sensitive and thixotropic). Aqueous formulations using typical polymers to control viscosity were iso-osmotic and buffered to pH 7. Lipid formulations were developed from lipid solvent/lipid gelling agent binary mixtures. Testing included pharmaceutical function and stability as well as in vitro and in vivo toxicity.

RESULTS

The aqueous fluid placebo, based on poloxamer, was fluid at room temperature, thickened and became shear thinning at 37°C. The aqueous gel placebo used carbopol as the gelling agent, was shear thinning at room temperature and showed a typical decrease in viscosity with an increase in temperature. The lipid fluid placebo, myristyl myristate in isopropyl myristate, was relatively thin and temperature independent. The lipid gel placebo, glyceryl stearate and PEG-75 stearate in caprylic/capric triglycerides, was also shear thinning at both room temperature and 37°C but with significant time dependency or thixotropy. All formulations showed no rectal irritation in rabbits and were non-toxic using an ex vivo rectal explant model.

CONCLUSIONS

Four placebo formulations ranging from fluid to gel in aqueous and lipid formats with a range of rheological properties were developed, tested, scaled-up, manufactured under cGMP conditions and enrolled in a formal stability program. Clinical testing of these formulations as placebos will serve as the basis for further microbicide formulation development with drug-containing products.

Formulation development of retrocyclin 1 analog RC-101 as an anti-HIV vaginal microbicide product

RC-101 is a synthetic microbicide analog of retrocyclin, which has shown in vitro activity against X4 and R5 HIV-1. In an effort to develop a safe and effective RC-101 vaginal microbicide product, we assessed safety in ex vivo macaque and human models and efficacy using in vitro and ex vivo models. A polyvinyl-alcohol vaginal film containing RC-101 (100 μg/film) was developed. Formulation assessment was conducted by evaluating disintegration, drug content, mechanical properties, and stability. Efficacy was evaluated by in vitro peripheral blood mononuclear cells (PBMC) assay and ex vivo human ectocervical tissue explant model. Ex vivo safety studies were conducted by exposing RC-101 to an excised monkey reproductive tract and excised human ectocervical tissue. RC-101 100 μg films were shown to be safe to human and monkey tissue and effective against HIV-1 in vitro and ex vivo in human ectocervical tissue. The 90% inhibitory concentration (IC90) for RC-101 films at 2,000 μg (IC90=57.5 μM) using an ex vivo model was 10-fold higher than the IC90 observed using an in vitro model (IC90=5.0 μM). RC-101 films were stable for 1 month at 25°C, with in vitro bioactivity maintained for up to 6 months. RC-101 was developed in a quick-dissolve film formulation that was shown to be safe in an ex vivo model and effective in in vitro and ex vivo models. RC-101 film formulations were shown to maintain bioactivity for a period of 6 months. Findings from the present study contribute to the development of a safe and effective topical microbicide product.

Exploiting drug repositioning for discovery of a novel HIV combination therapy

The development of HIV drugs is an expensive and a lengthy process. In this study, we used drug repositioning, a process whereby a drug approved to treat one condition is used to treat a different condition, to identify clinically approved drugs that have anti-HIV activity. The data presented here show that a combination of two clinically approved drugs, decitabine and gemcitabine, reduced HIV infectivity by 73% at concentrations that had minimal antiviral activity when used individually. Decreased infectivity coincided with a significant increase in mutation frequency and a shift in the HIV mutation spectrum. These results indicate that an increased mutational load is the primary antiviral mechanism for inhibiting the generation of infectious progeny virus from provirus. Similar results were seen when decitabine was used in combination with another ribonucleotide reductase inhibitor. Our results suggest that HIV infectivity can be decreased by combining a nucleoside analog that forms noncanonical base pairs with certain ribonucleotide reductase inhibitors. Such drug combinations are relevant since members of these drug classes are used clinically. Our observations support a model in which increased mutation frequency decreases infectivity through lethal mutagenesis.

Nanoparticle-based vaginal drug delivery systems for HIV prevention

IMPORTANCE OF THE FIELD

Several strategies are being investigated for the prevention of heterosexual transmission of HIV. Of these, topical vaginal drug delivery systems, microbicides, are being actively pursued. HIV prevention by means of a topical microbicide has several drug delivery challenges. These challenges include the vaginal mucosal barriers and potential degradation of the drugs in the vaginal lumen due to pH and enzymes present. Also, new drugs being evaluated as microbicides have specific mechanisms of action, which in some cases require drug targeting to a specific site of action. Nanoparticles provide a delivery strategy for targeted or controlled delivery to the vagina which can be applied in the field of HIV prevention.

AREAS COVERED IN THE REVIEW

This review summarizes nanoparticulate systems and their use in mucosal delivery to date. The sexual transmission of HIV along with the various targets to prevent transmission are discussed as well as the potential opportunities, challenges and advantages in using a nanoparticle-based approach for microbicidal drug delivery.

WHAT THE READER WILL GAIN

This review provides a general understanding of vaginal drug delivery, its challenges, and nanoparticulate delivery systems. Additionally, insight will be gained as to the limited existing application of this technology to the field of HIV prevention.

TAKE HOME MESSAGE

To date, few studies have been published that exploit nanoparticle-based microbicidal delivery to the vagina. The use of nanoparticles for vaginal drug delivery provides an approach to overcome the existing barriers to success.

Development of topical microbicides to prevent the sexual transmission of HIV

Women comprise almost 50% of the population of people living with HIV and the majority of these women contracted the virus through sexual transmission in monogamous relationships in the developing world. In these environments, where women are not empowered to protect themselves through the negotiation of condom use, effective means of preventing HIV transmission are urgently needed. In the absence of an approved and effective vaccine, microbicides have become the strategy of choice to provide women with the ability to prevent HIV transmission from their infected partners. Topical microbicides are agents specifically developed and formulated for use in either the vaginal or rectal environment that prevent infection by sexually transmitted infectious organisms, including pathogenic viruses, bacteria and fungi. Although a microbicidal product will have many of the same properties as other anti-infective agents and would be similarly developed through human clinical trials, microbicide development bears its own challenges related to formulation and delivery and the unique environment in which the product must act, as well as the requirement to develop a product that is acceptable to the user. Herein, perspectives based on preclinical and clinical microbicide development experience, which have led to an evolving microbicide development algorithm, will be discussed. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of anti-retroviral drug discovery and development, Vol 85, issue 1, 2010.

Pharmaceutical development of microbicide drug products

HIV infection rates in the developing world remain a serious problem. One potential approach to reduce infection rates is to use products known as microbicides, referred to herein as microbicide drug products (MDPs). These are drugs capable of, when administered topically to the vagina (or rectum), interfering with infection by one or more mechanisms. This review article covers the latest pharmaceutical developments in the area of microbicides dosage forms and delivery systems. These products are principally designed for use in the developing world and must therefore address cultural and societal issues generally unknown in the developed world. The first-generation microbicides evaluated clinically were principally polyanions. These drugs, administered intravaginally as gels, were found to be ineffective in preventing transmission of HIV from men to women. Second-generation drugs such as tenofovir, dapivirine, and UC781 are reverse transcriptase inhibitors developed as gels formulations and intravaginal rings (IVRs). Gels are considered coitally-related products while IVRs are coitally-independent systems designed to release the drug over a four-week period or possibly longer (up to 3 or 4 months). Other dosage forms under development include fast dissolving films, tablets/capsules, and possibly vaginal sponges. Dual protection systems are also under development. These systems include formulations capable of preventing HIV infection along with a second drug capable of preventing conception or other viral infections such as HSV.

A novel itraconazole bioadhesive film for vaginal delivery: design, optimization, and physicodynamic characterization

The purpose of this work was to design and optimize a novel vaginal drug delivery system for more effective treatment against vaginal candidiasis. Itraconazole was formulated in bioadhesive film formulations that could be retained in the vagina for prolonged intervals. The polymeric films were prepared by solvent evaporation and optimized for various physicodynamic and aesthetic properties. In addition, percentage drug retained on vaginal mucosa was evaluated using a simulated dynamic vaginal system as function of time. A polymeric film containing 100 mg itraconazole per unit (2.5 cm x 2.5 cm) have been developed using generally regarded as safe listed excipients. The pH of vaginal film was found to be slightly acidic (4.90 +/- 0.04) in simulated vaginal fluid and alkaline (7.04 +/- 0.07) in water. The little moisture content (7.66 +/- 0.51% w/w) was present in the film, which helps them to remain stable and kept them from being completely dry and brittle. The mechanical properties, tensile strength, and percentage elongation at break (9.64 N/mm(2) and 67.56% for ITRF(65)) reveal that the formulations were found to be soft and tough. The films (ITRF(65)) contained solid dispersion of itraconazole (2.5)/hydroxypropyl cellulose (1)/polyethylene glycol 400 (0.5), which was found to be the optimal composition for a novel bioadhesive vaginal formulation, as they showed good peelability, relatively good swelling index, and moderate tensile strength and retained vaginal mucosa up to 8 h. Also, the film did not markedly affect normal vaginal flora (lactobacillus) and was noncytotoxic as indicated by the negligible decrease in cell viability.

Vaginal microbicides and the prevention of HIV transmission

Worldwide, nearly half of all individuals living with HIV are now women, who acquire the virus largely by heterosexual exposure. With an HIV vaccine likely to be years away, topical microbicide formulations applied vaginally or rectally are being investigated as another strategy for HIV prevention. A review of preclinical and clinical research on the development of microbicides formulated to prevent vaginal HIV transmission yielded 118 studies: 73 preclinical and 45 clinical. Preclinical research included in-vitro assays and cervical explant models, as well as animal models. Clinical research included phase I and II/IIb safety studies, and phase III efficacy studies. Whereas most phase I and phase II clinical trials have found microbicide compounds to be safe and well tolerated, phase III trials completed to date have not demonstrated efficacy in preventing HIV transmission. Topical microbicides are grouped into five classes of agents, based on where they disrupt the pathway of sexual transmission of HIV. These classes include surfactants/membrane disruptors, vaginal milieu protectors, viral entry inhibitors, reverse transcriptase inhibitors, and a fifth group whose mechanism is unknown. The trajectory of microbicide development has been toward agents that block more specific virus-host cell interactions. Microbicide clinical trials face scientifically and ethically complex issues, such as the choice of placebo gel, the potential for viral resistance, and the inclusion of HIV-infected participants. Assessment of combination agents will most likely advance this field of research.

Interpreting properties of microbicide drug delivery gels: analyzing deployment kinetics due to squeezing

Prophylactic efficacy of topical microbicidal drug delivery formulations against HIV may depend upon their abilities to coat and be retained on epithelial surfaces where infection begins. Rheological and surface properties play paramount roles in governing coating. While fundamental fluid mechanical studies of epithelial coating mechanisms have begun, their results have not previously addressed questions of practical value to formulators in the pharmaceutics community. The present theoretical study began this process. We focused upon squeezing flows of seven vaginal gels which are models for future microbicides or a candidate formulation in clinical trials. Each formulation is based upon one of three different macromolecules: cellulose, polyacrylic acid (PAA), or carrageenan. We addressed: (1) properties with greatest influence on squeezing flow; (2) alterations of properties to improve measures of coating dynamics; and (3) effects of polymer concentration and temperature on coating dynamics. We found that yield stresses dominated flows of PAA gels, and that surface slip, while small, significantly influenced coating by cellulose gels. Decreases in consistency, increases in shear-thinning, and increases in temperature led to thinner coatings. Details of altered coating rates depended upon parameter values and time. Specific polymer concentration effects differed between cellulose and PAA gels, though trends were similar.

Microbicides: a new frontier in HIV prevention

Microbicides are products that can be applied to vaginal or rectal mucosal surfaces with the goal of preventing, or at least significantly reducing, the transmission of sexually transmitted infections (STIs) including HIV-1. Despite more than two decades of HIV-1 vaccine research, there is still no efficacious HIV-1 vaccine, and the scientific community appears skeptical about the short or long-term feasibility of developing a vaccine that has the ability to induce sterilizing immunity against HIV-1. In this setting, microbicide research has gathered momentum. Currently, 16 candidate microbicides are in clinical development and five products are being evaluated in large-scale Phase 2B/3 effectiveness studies. Initial data from these trials will be available within the next 2-3 years, and it is feasible that there could be one or more licensed microbicides by the end of the decade. The first generation of surfactant microbicides had a non-specific mechanism of action. However, subsequent candidate microbicides have been developed to target specific steps in the process of viral transmission. The purpose of this article is to provide an overview of microbicide development and an update on the candidate pipeline.

Squeezing flows of vaginal gel formulations relevant to microbicide drug delivery

Efficacy of topical microbicidal drug delivery formulations against HIV depends in part on their ability to coat, distribute, and be retained on epithelium. Once applied to the vagina, a formulation is distributed by physical forces including: gravity, surface tension, shearing, and normal forces from surrounding tissues, i.e., squeezing forces. The present study focused on vaginal microbicide distribution due to squeezing forces. Mathematical simulations of squeezing flows were compared with squeezing experiments, using model vaginal gel formulations. Our objectives were: (1) to determine if mathematical simulations can accurately describe squeezing flows of vaginal gel formulations; (2) to find the best model and optimized parameter sets to describe these gels; and (3) to examine vaginal coating due to squeezing using the best models and summary parameters for each gel. Squeezing flow experiments revealed large differences in spreadability between formulations, suggesting different coating distributions in vivo. We determined the best squeezing flow models and summary parameters for six test gels of two compositions, cellulose and polyacrylic acid (PAA). We found that for some gels it was preferable to deduce model input parameters directly from squeezing flow experiments. For the cellulose gels, slip conditions in squeezing flow experiments needed to be evaluated. For PAA gels, we found that in the absence of squeezing experiments, rotational viscometry measurements (to determine Herschel-Bulkley parameters) led to reasonably accurate predictions of squeezing flows. Results indicated that yield stresses may be a strong determinant of squeezing flow mechanics. This study serves as a template for further investigations of other gels and determination of which sources of rheological data best characterize potential microbicidal formulations. These mathematical simulations can serve as useful tools for exploring drug delivery parameters, and optimizing formulations, prior to costly clinical trials.

Gels as vaginal drug delivery systems

The vagina has been used as a mucosal drug delivery route for a long time. Its single characteristics can be either limitative or advantageous when drug delivery is considered. Gels are semi-solid, three-dimensional, polymeric matrices comprising small amounts of solid, dispersed in relatively large amounts of liquid, yet possessing more solid-like character. These systems have been used and are receiving a great deal of interest as vaginal drug delivery systems. Gels are versatile and have been used as delivery systems for microbicides, contraceptives, labour inducers, and other substances. Although somewhat neglected in clinical studies, pharmaceutical characterization of vaginal gels is an important step in order to optimize safety, efficacy and acceptability. Indeed, the simple formulation of a gel can lead to different performances of systems containing the same amount of active substances. Therefore, this paper discusses and summarizes current use and research of vaginal drug delivery systems based in gels.

Effectiveness of female controlled barrier methods in preventing sexually transmitted infections and HIV: current evidence and future research directions

OBJECTIVES

To evaluate evidence for the effectiveness of female controlled physical and chemical barrier methods in preventing STI/HIV transmission, to examine recent reviews on microbicide development, and to highlight promising research directions. To discuss challenges in conducting effectiveness research and in translating results to public health intervention.

METHODS

Systematic review of articles that examined the disease prevention effectiveness of at least one female controlled barrier method. Review of conference abstracts that presented clinical and preclinical microbicide data.

RESULTS

Randomised controlled trials provide evidence that female condoms confer as much protection from STIs as male condoms. Observational studies suggest that the diaphragm protects against STI pathogens. Several microbicide effectiveness studies are under way and new directions, such as adaptation of therapeutic agents as preventive products, are being examined. Substantial attention is now given to product formulation and novel delivery strategies. Combining microbicide products with different mechanisms of action as well as combining chemical and physical barriers will be necessary to maximise prevention effectiveness.

CONCLUSIONS

Increased investment in the development and identification of female controlled barrier methods offers promise that additional products will be available in the years ahead. Generalizing trial results to a community setting, promoting products that may be less effective than male condoms, and bringing an effective product to scale introduce public health challenges that warrant attention. The need for female controlled barrier methods that provide women with the opportunity to take an active role in reducing their STI/HIV risk are urgently needed and constitute an essential tool to prevent continued spread of these infections.

Gravity-induced coating flows of vaginal gel formulations: in vitro experimental analysis

Efficacy of topical microbicidal drug delivery formulations against HIV depends in part on their coating distributions and retention on vaginal epithelium. This study focused on gravity-induced coating flows of vaginal gels, and effects of formulation composition and surface wettability on coating. We hypothesized that presence of a yield stress, and surface wettability, affect coating. Experiments imaged and analyzed coating flows of gels on inclined model hydrophilic or hydrophobic surfaces. The in vitro wettability conditions bracket those believed to exist on vaginal epithelium in vivo. Six commercial vaginal gels were studied: three polyacrylic acid-based (PAA) and three cellulose-based. Our research group uses these gels in complementary human in vivo studies and other in vitro experimental analyses; this study is a first step in linking the in vivo and in vitro measurements. Coating by PAA gels was different from cellulose-based gels: the former exhibited yield stresses, which prevented initial gel shape from deforming during sliding. Coating flows of cellulose gels depended upon surface wettability. The slipping rates of the PAA gels ranked inversely with fitted yield stress values. The coating flow rates of the cellulose gels (hydrophilic surface) did not correlate with consistency index, but ranked inversely with the shear-thinning index. This study introduces a simple methodology for comparing trial formulations and relating their flows to gel constituents and physical properties. It also suggests differences in coating by current commercial gels.

Development pharmaceutics of microbicide formulations. Part II: formulation, evaluation, and challenges

In recent years, AIDS and sexually transmitted diseases (STDs) have become a burgeoning problem and are spreading at an alarming rate. Microbicides are being developed as a new therapeutic category for prevention of transmission of sexually transmitted infections (STIs) and HIV. Many of the microbicide formulations (MF) may fail to elicit a protective response either because of a lack of efficacy or inadequate formulation. Manufacturing a stable, efficacious, safe, and optimal product is the main objective of formulation development programs. Preformulation parameters (PP), as discussed in Part I of this series, influence formulation development significantly and should be considered carefully before designing a formulation strategy. Initially, based on PP and market research, a target product profile (TPP) is generated, which defines product attributes that can be normally classified as "essential" and "desirable." A complex and dynamic process begins thereafter that takes into consideration myriad factors starting from selection of delivery system, selection of excipients, compatibility study, prototype composition, selection of process and optimization, stability testing, scale up, manufacturing under good manufacturing practices (GMP), and packaging development. Prototype formulations are evaluated for several performance characteristics (e.g., dispersion behavior, bioadhesion, retention, spreading, rheology). These compositions are also subjected to biologic evaluation by various in vitro and in vivo models. Such a well-planned, well-coordinated, and well-implemented formulation development program not only accelerates overall development but also minimizes failures in subsequent clinical development studies. The objective of this review is to highlight the importance of formulation science, outline the steps involved in this process, and explore how these can be exploited for achieving optimal MF.