Evaluation of gender differences in the pharmacokinetics of oral zileuton nanocrystalline formulation using a rat model.

Zileuton is a leukotriene inhibitor used to treat asthma. As a BCS class II drug it exhibits challenges with solubility which likely impact its absorption. As patient gender significantly impacts the pharmacokinetics of many drugs, this study aimed to investigate potential gender-based pharmacokinetic differences after oral zileuton administration in rats. Male and female Sprague Dawley rats received single oral gavage doses of pure zileuton as an active pharmaceutical ingredient (30 mg/kg body weight (bw)), physical mixture (PM; at 30 mg/kg bw of the formulation contains zileuton, kollidon VA64 fine, dowfax2A1 and trehalose), and nanocrystalline formulation of zileuton (NfZ; at 30 mg/kg bw of the formulation). Plasma, tissue, and urine concentrations were quantified using high performance liquid chromatography (HPLC). Noncompartmental pharmacokinetic analysis showed higher zileuton levels in the plasma of female versus male rats across all evaluated forms of zileuton (API, PM, and NfZ). Female rats demonstrated higher peak plasma concentrations (Cmax) and increased area under the plasma concentration-time curve (AUC) relative to males, regardless of formulation. These findings reveal substantial gender disparities in the pharmacokinetics of zileuton in the rat model. This study emphasizes the critical need to evaluate gender differences during preclinical drug development to enable gender-based precision dosing strategies for equivalent efficacy/safety outcomes in male and female patients. Additional studies are warranted to investigate underlying mechanisms of such pharmacokinetic gender divergences.

Evaluation of mucosal immune profile associated with Zileuton nanocrystal-formulated BCS-II drug upon oral administration in Sprague Dawley rats.

Nanocrystal drug formulation involves several critical manufacturing procedures that result in complex structures to improve drug solubility, dissolution, bioavailability, and consequently the efficacy of poorly soluble Biopharmaceutics Classification System (BCS) II and IV drugs. Nanocrystal formulation of an already approved oral drug may need additional immunotoxic assessment due to changes in the physical properties of the active pharmaceutical ingredient (API). In this study, we selected Zileuton, an FDA-approved drug that belongs to BCS-II for nanocrystal formulation. To evaluate the efficacy and mucosal immune profile of the nanocrystal drug, 10-week-old rats were dosed using capsules containing either API alone or nanocrystal formulated Zileuton (NDZ), or with a physical mixture (PM) using flexible oral gavage syringes. Control groups consisted of untreated, or placebo treated animals. Test formulations were administrated to rats at a dose of 30 mg/kg body weight (bw) once a day for 15 days. The rats treated with NDZ or PM had approximately 4.0 times lower (7.5 mg/kg bw) API when compared to the micron sized API treated rats. At the end of treatment, mucosal (intestinal tissue) and circulating cytokines were measured. The immunological response revealed that NDZ decreased several proinflammatory cytokines in the ileal mucosa (Interleukin-18, Tumor necrosis Factor-α and RANTES [regulated upon activation, normal T cell expressed and secreted]). A similar pattern in the cytokine profile was also observed for the micron sized API and PM treated rats. The cytokine production revealed that there was a significant increase in the production of IL-1ß and IL-10 in the females in all experimental groups. Additionally, NDZ showed an immunosuppressive effect on proinflammatory cytokines both locally and systemically, which was similar to the response in micron sized API treated rats. These findings indicate that NDZ significantly decreased several proinflammatory cytokines and it displays less immunotoxicity, probably due to the nanocrystal formulation. Thus, the nanocrystal formulation is more suitable for oral drug delivery, as it exhibited better efficacy, safety, and reduced toxicity.

Pectin microparticles for peptide delivery: Optimization of spray drying processing.

Spray-dried pectin microparticles can potentially improve the oral bioavailability of peptides by virtue of their mucoadhesion. However, developing such formulations with desirable quality attributes is challenging due to the sensitivity of microparticle critical quality attributes towards changes in spray drying processing parameters. In this study, a central composite design approach was applied to investigate the influence of input temperature, aspirator rate, feed flow rate, polymer concentration and polymer feed weight on the yield and particle size of pectin microparticles prepared via spray drying. A mathematical model for the prediction of yield was statistically significant with good predictability. A maximum yield of 72.2% was achieved through optimizing the spray drying conditions. The particle size remained in a relatively narrow range (D50, 2.16-3.67 µm), and therefore was considered independent of the factors investigated. The model for yield prediction was further validated using octreotide acetate as a representative peptide. The presence of octreotide acetate in the pectin microparticles increased their surface roughness and decreased their melting enthalpy. In addition, it was determined that pectin with a high degree of esterification (72%, AU201) resulted in faster drug release compared to pectin with a lower degree of esterification (62%, CU401). Interestingly, the degree of esterification did not impact microparticle particle size, morphology or thermal properties. This study demonstrates the importance of DoE in optimization of the spray drying process for the development of pectin-based peptide microparticles. This is the first report using spray-dried pectin-based microparticles for octreotide delivery. The yield prediction model achieved using a central composite design may also be helpful for formulation development of similar drug products.

Formulation and evaluation of itraconazole liposomes for Hedgehog pathway inhibition.

Itraconazole (ITZ) is an FDA-approved antifungal agent that has recently been explored for novel biological properties. In particular, ITZ was identified as a potent inhibitor of the hedgehog (Hh) pathway, a cell signalling pathway that has been linked to a variety of cancers and accounts for ∼25% of paediatric medulloblastoma (MB) cases. To date, there is not a targeted therapeutic option for paediatric MB, resulting in long-term side effects such as hormone deficiency, organ damage and secondary cancers. A primary obstacle for developing targeted therapy for brain ailments is the presence of the blood-brain barrier (BBB), which protects the brain from potentially harmful substances. Due to its size and hydrophobicity, ITZ does not penetrate the BBB. Alternatively, liposomes are being increasingly used within the clinic to increase drug bioavailability, target specificity and BBB permeability. With this in mind, we have successfully developed ITZ-containing liposomes with an optimal size for BBB penetration (<100 nm) and encapsulation efficiency (∼95%) by utilizing a continuous manufacturing approach-turbulent coaxial jet in co-flow. Our preliminary in vitro data demonstrate that these liposomes inhibit the Hh pathway, albeit at a reduced level in comparison to free ITZ. (196/250 words).

In vitro-in vivo correlation of parenteral PLGA microspheres: Effect of variable burst release.

Development of IVIVCs is a very complicated process, especially for complex drug products such as parenteral PLGA microspheres with multiphasic drug release characteristics. Specifically, microspheres that exhibit an initial burst release phase are even more challenging since the in vitro and in vivo burst release phases may not be comparable if drug absorption is rate-limiting at this stage. Therefore, the objectives of the present work were: 1) to investigate the predictability of developed IVIVCs for the in vivo burst release phase based on the in vitro burst release phase of the formulations; and 2) to evaluate the impact of variable burst release on the predictability of the developed IVIVCs for two different types of microsphere-based drug products. Accordingly, Risperdal Consta® (Risperidone) and Lupron Depot® (Leuprolide acetate, LA) were selected as model products. Compositionally equivalent risperidone and LA formulations with variable burst release phases were prepared with manufacturing process changes (such as solvent systems and mixing methods). The prepared microspheres exhibited differences in critical physicochemical properties (such as particle size, porosity, average pore diameter, and drug distribution) and hence differences in their in vitro release characteristics (such as variable burst release and release rate). The in vitro and in vivo (rabbit model (intramuscular injection) burst release were similar for the risperidone microspheres but were significantly different for the LA microspheres. This had an impact on the complexity of the developed IVIVC models. Level A IVIVCs with the ability to predict various types of burst release were developed using time scaling and shifting factors. Moreover, it was observed that IVIVCs developed using formulations with less variation in burst release had better predictability and vice-versa. Thus, the present research has provided a comprehensive understanding of the impact of the burst release phase on the development, complexity, and predictability of IVIVCs for complex parenteral microspheres containing a variety of therapeutic molecules.

Development of Level A in vitro-in vivo correlations for peptide loaded PLGA microspheres.

Peptide loaded PLGA microsphere products are more complex in terms of manufacturing, drug release characteristics as well as release mechanism compared to small molecule loaded PLGA microsphere products. This is due to the complex structure of peptides, their hydrophilicity, charged state, large size and potential for instability. Moreover, therapeutic peptides are highly potent and therefore, any unintended change in the microsphere release profile may lead to undesirable side effects and toxicity. Accordingly, the objectives of the present work were: 1) to evaluate the impact of minor manufacturing changes on the quality and performance of peptide microspheres; and 2) to investigate the feasibility of developing Level A in vitro-in vivo correlations (IVIVCs) for peptide microspheres. Compositionally equivalent leuprolide acetate (LA) microspheres prepared with minor manufacturing changes (solvent system/homogenization speed) showed significant differences in their physicochemical properties (such as pore size, total porosity, particle size and surface distribution of peptide on the prepared microspheres). This, in turn, resulted in significant alteration in the release characteristics. Peptide-polymer interaction, in vitro degradation and microsphere morphology studies were conducted to facilitate understanding of the differences in the drug release characteristics. A rabbit model was used to determine the pharmacokinetic profiles of all the prepared formulations. The obtained in vivo release profiles showed the same rank order as the in vitro release profiles but with low burst release and overall faster in vivo release rates. The low in vivo burst release is considered to be due to the masking effect of the absorption phase from the intramuscular site, and this complicated the development of an IVIVC. Despite these challenges, an affirmative Level A IVIVC over the entire release profile was successfully developed in a rabbit model for peptide microspheres for the first time. The developed IVIVC was also predictive of the RLD product, Lupron Depot®. This work highlights the feasibility of developing IVIVCs for complex parenteral drug products such as peptide microspheres. In conclusion, these results indicate the sensitivity of peptide release, and hence, the safety and efficacy of highly potent peptide microspheres, to minor manufacturing changes. Accordingly, development of IVIVCs for such complex drug products is highly desirable.

Comprehensive quality by design approach for stable nanocrystalline drug products.

The novelty of the present research is application of a comprehensive quality by design (QbD) approach to minimize errors in product optimization and validation for the development of a stable nanocrystalline zileuton (BCS class II drug) formulation. A QbD approach was used to identify, optimize and validate the critical processes parameters (wet media milling and spray drying) and critical formulation parameters (drug and excipient concentrations). The milling time, milling speed, inlet temperature, aspirator rate, feed flow rate and drug concentration had a significant influence on the particle size and total product yield of the nanocrystalline zileuton. Trehalose compared to mannitol was determined to be a better stabilizer during spray drying processing. Stability studies revealed the following trend after 12 months: 4 °C (most stable) >25 °C/60% RH > 40 °C/75% RH (least stable) for the optimized spray-dried nanocrystalline zileuton in terms of physicochemical attributes, crystallinity and in vitro dissolution testing. Based on the comprehensive QbD approach, stable spray-dried nanocrystalline zileuton was obtained with exceptionally high total product yield (∼80% w/w) and small particle size (276.4 ±â€¯27.54 nm) with low PDI (0.109 ±â€¯0.056 units). Drug release from the formulations followed a particle size dependent dissolution trend. Additionally, pH switch dissolution testing indicated that complete drug release from the nanoformulations was observed at intestinal pH (pH 6.8) within 1-2 h of the shift from the stomach pH (pH 1.2).

Nanoamorphous drug products - Design and development.

Most of the recent drug compounds coming out of the drug discovery pipeline are labile (multiple polymorphs), and need to be developed into robust marketed oral drug formulations. There are only 22 oral macroamorphous drug products approved by FDA and till date none approved oral nanoamorphous drug products. However, there are several oral nanoamorphous drug formulations (including both labile and non-labile drugs) being researched and a few of these are in the clinical trials. Due to the labile nature of these drug compounds, there is a need to utilize a controlled strategy for design and development of robust nanoamorphous drug formulations in order to prevent any physicochemical instability. The present research focuses on the use of a novel integrated critical process parameters and critical formulation parameters (iCPP-CFPs) DoE approach for the design and development of stable nanoamorphous spironolactone (BCS class II compound with eight polymorphic forms). There are possibilities of the interconversion of these polymorphic forms during processing (manufacturing nanoamorphous particles) and during storage. In the present study, polymorphic transitions (amorphous to crystalline and anhydrous to hydrate) were carefully monitored via orthogonal solid-state characterization tools. Significant polymorphic transitions were observed in the formulations stored at 40 °C/75% RH over six months, however the formulations stored at 4 °C were stable. The significant iCPP-CFPs (solvent-to-antisolvent ratio, drug concentration and inlet temperature of the spray dryer) were critically investigated for their influence on different CQAs (critical quality attributes). Solvent-to-antisolvent ratio and inlet temperature were identified to be the significant iCPP-CFPs. Particle size and total product yield were identified to be the significant CQAs. Lab-scale manufacturing of the spray dried nanoamorphous spironolactone resulted in a remarkably high total product yield (82.4 ±â€¯3.91% w/w) with a uniform and homogenous particle size (244.2 ±â€¯23.32 nm). Furthermore, the physicochemical attributes and the drug release criteria of the nanoamorphous spironolactone were compared with two marketed products (spironolactone tablets, USP 100 mg (Pfizer and Mylan)) and other in-house formulations. In addition, nanoamorphous spironolactone showed a significantly superior kinetic solubility/dissolution rate (10-fold) with a longer supersaturation time (∼6h) compared to the in-house formulations.

In vitro release testing method development for ophthalmic ointments.

It is essential as well as challenging to develop a reliable in vitro release testing method for determining whether differences in release profiles exist between qualitatively and quantitatively equivalent ophthalmic ointment formulations. There is a lack of regulatory guidance on in vitro release testing methods for ophthalmic formulations. Three different in vitro release testing methods 1) USP apparatus 4 with semisolid adapters; 2) USP apparatus 2 with enhancer cells; and 3) Franz diffusion cells were investigated. Qualitatively and quantitatively equivalent ointments were prepared via hot melting and simple mixing methods using four different sources of excipients (i.e. white petrolatum). The ointment formulations were characterized for content uniformity, particle size, and rheological parameters. All the formulations showed adequate content uniformity and similar particle size. The ointments prepared via the hot melting processes showed higher rheological parameters, as did the ointments prepared using 'white' petrolatum that exhibited a yellowish color. The three in vitro release testing methods were compared and evaluated for reproducibility, discriminatory capability, and correlation with the rheological parameters. Compared with the compendial methods, the non-compendial method (Franz diffusion cells) showed poorer reproducibility. All three methods possessed the ability to discriminate between the ophthalmic ointments with manufacturing differences. However, the USP apparatus 4 method displayed the largest margin of discrimination between the release profiles of the different ophthalmic ointments. In addition, the in vitro release rate obtained using the USP apparatus 4 method showed the strongest logarithmic linear correlation with the rheological parameters (Power law consistency index (K value) and crossover modulus) compared to the other two methods.

Physicochemical attributes and dissolution testing of ophthalmic ointments.

The investigation of semisolid ophthalmic ointments is challenging due to their complex physicochemical properties and the unique anatomy of the human eye. Using Lotemax® as a model ophthalmic ointment, three different manufacturing processes and two excipient sources (Fisher® (OWP) and Fougera® (NWP)) were used to prepare loteprednol etabonate ointments that were qualitatively and quantitatively the same across the manufactured formulations. Physicochemical properties including drug content and uniformity, particle size and distribution, as well as rheological parameters (onset point, crossover modulus, storage modulus and Power law consistency index) were investigated. In addition, USP apparatus 2 with enhancer cells was utilized to study the in vitro drug release characteristics of the ophthalmic ointments. Both manufacturing processes and excipient sources had a significant influence on the physicochemical attributes and the in vitro drug release profiles of the prepared ointments. Ointments prepared via the hot melt processes exhibited higher rheological parameters and lower drug release rates compared to ointments prepared without hot melting. Ointments prepared with OWP demonstrated higher rheological parameters and lower in vitro drug release rates compared to ointments prepared with NWP. A strong correlation between the rheological parameters and in vitro drug release rate was shown using logarithmic linear regression. This correlation may be useful in predicting in vitro drug release from measured physicochemical properties, and identifying the critical quality attributes during the development of ointment formulations.

Pharmaceutical Amorphous Nanoparticles.

There has been a tremendous revolution in the field of nanotechnology, resulting in the advent of novel drug delivery systems known as nanomedicines for diagnosis and therapy. One of the applications is nanoparticulate drug delivery systems which are used to improve the solubility and oral bioavailability of poorly soluble compounds. This is particularly important because most of the molecules emerging from the drug discovery pipeline in recent years have problems associated with solubility and bioavailability. There has been considerable focus on nanocrystalline materials; however, amorphous nanoparticles have the advantage of synergistic mechanisms of enhancing dissolution rates (due to their nanosize range and amorphous nature) as well as increasing supersaturation levels (due to their amorphous nature). An example of this technology is NanomorphTM, developed by Soliqus/Abbott, wherein the nanosize drug particles are precipitated in an amorphous form in order to enhance the dissolution rate. This along with other simple and easily scalable manufacturing techniques for amorphous nanoparticles is described. In addition, the mechanisms of formation of amorphous nanoparticles and several physicochemical properties associated with amorphous nanoparticles are critically reviewed.

Formulation design space for stable, pH sensitive crystalline nifedipine nanoparticles.

Enteric coated formulations protect drugs from degrading in the harsh environment of the stomach (acidic pH and enzymes), and promotes drug delivery to and absorption into the duodenum and/or later parts of the intestine. Four DoE models were applied to optimize formulation parameters for the preparation of pH sensitive nifedipine nanoparticles. Stability studies were performed on the optimized formulations to monitor any possible variation in particle size distribution, homogeneity index, surface charge and drug release (pH 1.2 and pH 6.8). Stability studies were performed for 3 months at 4°C, 25°C and 40°C. A combination of Eudragit®L 100-55 and polyvinyl alcohol was determined to be the most effective in stabilizing the nanoparticle suspension. The average particle size distribution, polydispersity index and surface charge of the optimized pH sensitive nifedipine nanoparticles were determined to be 131.86±8.21nm, 0.135±0.008 and -7.631±0.146mV, respectively. Following three months storage, it was observed that the formulations stored at 4°C were stable in terms of particle size distribution, polydispersity index, surface charge, drug loading and drug release, whereas those stored at 25°C and 40°C were relatively unstable. A predictive model to prepare stable pH sensitive nifedipine nanoparticles, was successfully developed using multiple linear regression analysis.

Solid state drug-polymer miscibility studies using the model drug ABT-102.

Amorphous solid dispersions typically suffer storage stability issues due to: their amorphous nature, high drug loading, uneven drug:stabilizer ratio and plasticization effects as a result of hygroscopic excipients. An extensive solid state miscibility study was conducted to aid in understanding the mechanisms involved in drug/stabilizer interactions. ABT-102 (model drug) and nine different polymers with different molecular weights and viscosities were selected to investigate drug/polymer miscibility. Three different polymer:drug ratios (1:3, 1:1 and 3:1, w/w) were analyzed using: DSC, FTIR and PXRD. Three different techniques were used to prepare the amorphous solid dispersions: serial dilution, solvent evaporation and spray drying. Spray drying was the best method to obtain amorphous solid dispersions. However, under certain conditions amorphous formulations could be obtained using solvent evaporation. Melting point depression was used to calculate interaction parameters and free energy of mixing for the various drug polymer mixtures. The spray dried solid dispersions yielded a negative free energy of mixing which indicated strong drug-polymer miscibility compared to the solvent evaporation and serial dilution method. Soluplus was the best stabilizer compared to PVP and HPMC, which is probably a consequence of strong hydrogen bonding between the two CO moieties of soluplus and the drug NH moieities.

Formulation design and evaluation of amorphous ABT-102 nanoparticles.

Amorphous nanoparticles are able to enhance the kinetic solubility and concomitant dissolution rates of BCS class II and BCS class II/IV molecules due to their characteristic increased supersaturation levels, smaller particle size and greater surface area. A DoE approach was applied to investigate formulation and spray drying process parameters for the preparation of spray dried amorphous ABT-102 nanoparticles. Stability studies were performed on the optimized formulations to monitor physical and chemical changes under different temperature and humidity conditions. SLS/soluplus and SLS/PVP K25 were the best stabilizer combinations. Trehalose was used to prevent nanoparticle aggregation during spray drying. Particle size distribution, moisture content, PXRD, PLM, FTIR and in vitro dissolution were utilized to characterize the spray dried nanoparticle formulations. The formulations prepared using soluplus showed enhanced dissolution rate compared to those prepared using PVP K25. Following three months storage, it was observed that the formulations stored at 4°C were stable in terms of particle size distribution, moisture content, and crystallinity, whereas those stored at 25°C/60%RH and 40°C/75%RH were unstable. A predictive model to prepare stable solid spray dried amorphous ABT-102 nanoparticles, incorporating both formulation and process parameters, was successfully developed using multiple linear regression analysis.

Formulation and performance of danazol nano-crystalline suspensions and spray dried powders.

PURPOSE: This study focuses on the formulation optimization, in vitro and in vivo performance of differently sized nano-crystalline liquid suspensions and spray-dried powders of a poorly soluble BCS class II compound i.e. Danazol. METHODS: A DoE approach was utilized to optimize stabilizer concentration and formulate danazol (BCS class II) nano-crystalline suspensions and dry powders via wet milling followed by spray drying. Solubility studies were performed to select best stabilizers. Particle size, PXRD, contact angle measurement and in vitro dissolution were utilized in characterization of the liquid and spray-dried powder formulations. RESULTS: The liquid nano-crystalline suspensions followed particle size-dependent dissolution rates i.e. faster dissolution for smaller crystals. The spray-dried nano-crystal powders did not show fast dissolution profiles compared to the liquid nano-crystalline suspension. The poor dissolution of the spray-dried powder correlated to its high LogP value (i.e. LogP 4.53) and poor wetting (or polar surface-area). In vivo bioavailability studies showed superior performance of the liquid nano-crystalline suspensions compared to other milled and un-milled formulations. CONCLUSION: Wet-milling and spray-drying optimization for danazol nano-crystalline suspension was performed. This study indicates that drug candidates with high LogP values and low polar surface area may not be suitable for formulation as dry nano-crystals.

In Vitro and In Vivo Performance of Different Sized Spray-Dried Crystalline Itraconazole.

The objectives of the present study were to formulate and optimize different sized liquid and solid nanocrystalline formulations and evaluate their in vitro and in vivo performance to determine the effect of particle size on the oral bioavailability of solid nanocrystalline formulations. Nanotechnology is a promising approach to solve the problem of poor oral bioavailability of Biopharmaceutical Classification System class II/IV compounds. However, the highly exposed surface area of nanocrystals and hence their high Gibb's free energy poses a great challenge to nanocrystalline suspension stabilization. In this study, stabilization was achieved by preparing spray-dried nanocrystalline powders. A design of experiment approach was utilized to optimize the nanocrystalline suspensions/powders. On the basis of drug solubility studies, polyvinylpyrrolidone 40 KDa and sodium lauryl sulfate were selected for wet milling processing. Mannitol was chosen as the auxiliary excipient for spray-drying processing. In vitro dissolution utilizing a United States Pharmacopeia (USP) apparatus II showed superior release profiles for both liquid and nanocrystalline powder formulations compared with coarse-sized and unmilled formulations. Significantly, the oral bioavailability of nanocrystalline formulations with particle size of 280 nm was more than 20 times that of the unmilled formulation, whereas the nanocrystalline formulation with particle size of 750 nm showed only a 2.8 times increase in bioavailability compared with the unmilled formulation.

Effect of counterion on the solid state photodegradation behavior of prazosin salts.

The effect of counterion was evaluated on the photodegradation behavior of six prazosin salts, viz., prazosin hydrochloride anhydrous, prazosin hydrochloride polyhydrate, prazosin tosylate anhydrous, prazosin tosylate monohydrate, prazosin oxalate dihydrate, and prazosin camsylate anhydrous. The salts were subjected to UV-Visible irradiation in a photostability test chamber for 10 days. The samples were analyzed for chemical changes by a specific stability-indicating high-performance liquid chromatography method. pH of the microenvironment was determined in 10%w/v aqueous slurry of the salts. The observed order of photostability was: prazosin hydrochloride anhydrous>prazosin camsylate anhydrous~prazosin-free base>prazosin hydrochloride polyhydrate>prazosin tosylate anhydrous>prazosin oxalate dihydrate~prazosin tosylate monohydrate. Multivariate analysis of the photodegradation behavior suggested predominant contribution of the state of hydration and also intrinsic photosensitivity of the counterion. Overall, hydrated salts showed higher photodegradation compared to their anhydrous counterparts. Within the anhydrous salts, aromatic and carbonyl counterion-containing salts showed higher susceptibility to light. The pH of microenvironment furthermore contributed to photodegradation of prazosin salts, especially for drug counterions with inherent higher pH. The study reveals importance of selection of a suitable drug salt form for photosensitive drugs during preformulation stage of drug development.