Formulation and process factors influencing product quality and in vitro performance of ophthalmic ointments.

Owing to its unique anatomical and physiological functions, ocular surface presents special challenges for both design and performance evaluation of the ophthalmic ointment drug products formulated with a variety of bases. The current investigation was carried out to understand and identify the appropriate in vitro methods suitable for quality and performance evaluation of ophthalmic ointment, and to study the effect of formulation and process variables on its critical quality attributes (CQA). The evaluated critical formulation variables include API initial size, drug percentage, and mineral oil percentage while the critical process parameters include mixing rate, temperature, time and cooling rate. The investigated quality and performance attributes include drug assay, content uniformity, API particle size in ointment, rheological characteristics, in vitro drug release and in vitro transcorneal drug permeation. Using design of experiments (DoE) as well as a novel principle component analysis approach, five of the quality and performance attributes (API particle size, storage modulus of ointment, high shear viscosity of ointment, in vitro drug release constant and in vitro transcorneal drug permeation rate constant) were found to be highly influenced by the formulation, in particular the strength of API, and to a lesser degree by processing variables. Correlating the ocular physiology with the physicochemical characteristics of acyclovir ophthalmic ointment suggested that in vitro quality metrics could be a valuable predictor of its in vivo performance.

Cold flow of estradiol transdermal systems: influence of drug loss on the in vitro flux and drug transfer across human epidermis.

The objective was to quantify drug loss due to cold flow (CF) in marketed estradiol transdermal drug delivery systems (TDDS), and study its influence on the in vitro flux and drug transfer across contacting skin. TDDS samples (products-A and B) were induced with CF at 25 and 32°C/60% RH by applying 1-kg force for 72h. CF was measured as percent dimensional change and amount of drug loss/migration in CF region. In vitro drug permeation studies were conducted across human epidermis from TDDS excluding CF region, and CF region alone against control (without CF). In both products, significantly higher percentage of CF (dimensional change and drug migration) was observed at 32°C compared to 25°C. In vitro flux from both products excluding CF region either at 25 or 32°C was the same, but significantly lower compared to control. Drug transferred from CF region of product-A after 8h was the same at 25 and 32°C, but significantly higher in product-B. Flux from both products together with CF region at 32°C was significantly lower than that observed at 25°C. Results showed that excessive CF at storage (25°C) and clinical usage (32°C) conditions may have implications on product performance and safety of estradiol TDDS.

Disintegration of highly soluble immediate release tablets: a surrogate for dissolution.

The purpose of the work was to investigate correlation between disintegration and dissolution for immediate release tablets containing a high solubility drug and to identify formulations where disintegration test, instead of the dissolution test, may be used as the acceptance criteria based on International Conference on Harmonization Q6A guidelines. A statistical design of experiments was used to study the effect of filler, binder, disintegrating agent, and tablet hardness on the disintegration and dissolution of verapamil hydrochloride tablets. All formulation variables, i.e., filler, binder, and disintegrating agent, were found to influence tablet dissolution and disintegration, with the filler and disintegrating agent exerting the most significant influence. Slower dissolution was observed with increasing disintegration time when either the filler or the disintegrating agent was kept constant. However, no direct corelationship was observed between the disintegration and dissolution across all formulations due to the interactions between different formulation components. Although all tablets containing sodium carboxymethyl cellulose as the disintegrating agent, disintegrated in less than 3 min, half of them failed to meet the US Pharmacopeia 30 dissolution criteria for the verapamil hydrochloride tablets highlighting the dependence of dissolution process on the formulation components other than the disintegrating agent. The results identified only one formulation as suitable for using the disintegration test, instead of the dissolution test, as drug product acceptance criteria and highlight the need for systematic studies before using the disintegration test, instead of the dissolution test as the drug acceptance criteria.