Venkatramana M. Rao

Reactive impurities in excipients: profiling, identification and mitigation of drug-excipient incompatibility.

Reactive impurities in pharmaceutical excipients could cause drug product instability, leading to decreased product performance, loss in potency, and/or formation of potentially toxic degradants. The levels of reactive impurities in excipients may vary between lots and vendors. Screening of excipients for these impurities and a thorough understanding of their potential interaction with drug candidates during early formulation development ensure robust drug product development. In this review paper, excipient impurities are categorized into six major classes, including reducing sugars, aldehydes, peroxides, metals, nitrate/nitrite, and organic acids. The sources of generation, the analytical method for detection, the stability of impurities upon storage and processing, and the potential reactions with drug candidates of these impurities are reviewed. Specific examples of drug–excipient impurity interaction from internal research and literature are provided. Mitigation strategies and corrective measures are also discussed.

Modeling of Pan Coating Processes: Prediction of Tablet Content Uniformity and Determination of Critical Process Parameters

We developed an engineering model for predicting the active pharmaceutical ingredient (API) content uniformity (CU) for a drug product in which the active is coated onto a core. The model is based on a two-zone mechanistic description of the spray coating process in a perforated coating pan. The relative standard deviation (RSD) of the API CU of the coated tablets was found to be inversely proportional to the square root of the total number of cycles between the spray zone and drying zone that the tablets undergo. The total number of cycles is a function of the number of tablets in the drying zone, the spray zone width, the tablet velocity, the tablet number density, and the total coating time. The sensitivity of the RSD to various critical coating process parameters, such as pan speed, pan load, spray zone width, as well as tablet size and shape was evaluated. Consequently, the critical coating process parameters needed to achieve the desired API CU were determined. Several active film coating experiments at 50, 200, and 400 kg using various pan coaters demonstrated that good correlation between the model predictions and the experimental results for the API CU was achieved.

Effect of Sodium Lauryl Sulfate in Dissolution Media on Dissolution of Hard Gelatin Capsule Shells

AbstractPurpose. Sodium lauryl sulfate (SLS) is a commonly used surfactant in dissolution media for poorly water soluble drugs. However, it has occasionally been observed that SLS negatively impacts the dissolution of drug products formulated in gelatin capsules. This study investigated the effect of SLS on the dissolution of hard gelatin capsule shells. Methods. The USP paddle method was used with online UV monitoring at 214 nm (peptide bond). Empty size # 0 capsule shells were held to the bottom of the dissolution vessel by magnetic three-prong sinkers. Results. SLS significantly slowed down the dissolution of gelatin shells at pH < 5. Visually, the gelatin shells transformed into some less-soluble precipitate under these conditions. This precipitate was found to contain a higher sulfur content than the gelatin control sample by elemental analysis, indicating that SLS is part of the precipitate. Additionally, the slowdown of capsule shell dissolution was shown to be dependent on the SLS concentration and the ionic strength of the media. Conclusions. SLS interacts with gelatin to form a less-soluble precipitate at pH < 5. The use of SLS in dissolution media at acidic pH should be carefully evaluated for gelatin capsule products.

Formation of reactive impurities in aqueous and neat polyethylene glycol 400 and effects of antioxidants and oxidation inducers

A 2,4-dinitrophenylhydrazine (DNPH) precolumn derivatization high-performance liquid chromatography-ultraviolet detection (HPLC-UV) method was developed to quantify levels of formaldehyde and acetaldehyde in polyethylene glycol (PEG) solutions. Formic acid and acetic acid were quantified by HPLC-UV. Samples of neat and aqueous PEG 400 solutions were monitored at 40°C and 50°C to determine effects of excipient source, water content, pH, and trace levels of hydrogen peroxide or iron metal on the formation of reactive impurities. The effects of antioxidants were also evaluated. Formic acid was the major degradation product in nearly all cases. The presence of water increased the rate of formation of all impurities, especially formic acid as did the presence of hydrogen peroxide and trace metals. Acidic pH increased the formation of acetaldehyde and acetic acid. A distribution of unidentified degradation products formed in neat PEG 400 disappeared upon addition of HCl with corresponding increase of formic acid, indicating they were likely to be PEG-formyl esters. Other unidentified degradation products reacted with DNPH to form a distribution of derivatized products likely to be PEG aldehydes. Antioxidants butylated hydroxyanisole, butylated hydroxytoluene, propyl gallate d-alpha tocopheryl polyethylene glycol-1000 succinate, and sodium metabisulfite were effective in limiting reactive impurity formation, whereas ascorbic acid and acetic acid were not.

Effect of force feeder on tablet strength during compression

Mechanical strength of tablets is an important quality attribute, which depends on both formulation and process. In this study, the effect of process variables during compression on tablet tensile strength and tabletability (the ratio of tensile strength to compression pressure) was investigated using a model formulation. Increase in turret and force feeder speeds reduced tablet tensile strength and tabletability. Turret speed affected tabletability through changes in dwell time under the compression cam and the kinetics of consolidation of granules in the die cavity. The effect of force feeder was attributed to the shearing of the granulation, leading to its over-lubrication. A dimensionless equation was derived to estimate total shear imparted by the force feeder on the granulation in terms of a shear number. Scale-independence of the relationship of tabletability with the shear number was explored on a 6-station Korsch press, a 16-station Betapress, and a 35-station Korsch XL-400 press. The use of this relationship, the exact nature of which may be formulation dependent, during tablet development is expected to provide guidance to the scale-up and interchangeability of tablet presses.

Effect of antioxidants and silicates on peroxides in povidone

Reactive peroxides in povidone often lead to degradation of oxidation-labile drugs. To reduce peroxide concentration in povidone, the roles of storage conditions, antioxidants, and silicates were investigated. Povidone alone and its physical mixtures with ascorbic acid, propyl gallate, sodium sulfite, butylated hydroxyanisole (BHA), or butylated hydroxytoluene (BHT) were stored at 25 °C and 40 °C, at 11%, 32%, and 50% relative humidity. In addition, povidone solution in methanol was equilibrated with silicates (silica gel and molecular sieves), followed by solvent evaporation to recover povidone powder. Peroxide concentrations in povidone were measured. The concentration of peroxides in povidone increased under very-low-humidity storage conditions. Among the antioxidants, ascorbic acid, propyl gallate, and sodium sulfite reduced the peroxide concentration in povidone, whereas BHA and BHT did not. Water solubility appeared to determine the effectiveness of antioxidants. Also, some silicates significantly reduced peroxide concentration in povidone without affecting its functionality as a tablet binder. Porosity of silicates was critical to their ability to reduce the peroxide concentration in povidone. A combination of these approaches can reduce the initial peroxide concentration in povidone and minimize peroxide growth under routine storage conditions.

Release mechanisms of a sparingly water-soluble drug from controlled porosity-osmotic pump pellets using sulfobutylether-β-cyclodextrin as both a solubilizing and osmotic agent

The purpose of this work is to delineate the release mechanisms of a sparingly water-soluble drug, prednisolone (PDL), from a microporous or controlled porosity-osmotic pump pellet (CP-OPP) using sulfobutylether-beta-cyclodextrin (CD) as both a solubilizing and osmotic agent. All factors, osmotic and diffusional, influencing drug release as described by the Theeuwes and Zentner equation were partially demonstrated in an earlier paper1 and are further quantitatively evaluated here to determine whether the equation may be applied to CP-OPPs. The PDL release rate from the CP-OPPs containing precomplexed PDL follows the zero-order kinetics for up to 30-40% of drug release during the first 1-2 h and subsequently nonzero order kinetics. The zero-order drug release phase reveals the main contribution is from osmotic pumping with a negligible diffusion component, resulting from the nearly constant driving forces in the system. The nonzero order drug release phase is associated with the dynamic changes in the system (e.g., declining osmotic driving force and greater diffusion component with time). In addition, the parameters related to membrane characteristics were determined, and the effect of viscosity was evaluated for the pellet system. The membranes coated on the CP-OPPs are less permeable to water or solutes than the membranes coated on the previously reported tablets. The viscosity due to the CD decreases as a function of CD concentration, which partly affects the observed drug release profiles. The viscosity effect of CD is significant and captured in a hydraulic permeability term.

Chapter 6 – Excipient Compatibility

Publisher Summary The excipient compatibility is related to the physical and chemical stability of the drug in solid dosage forms. Some of the common ways by which excipients may affect drug stability in the dosage form are by altering moisture content in the dosage form, changing microenvironmental pH in the dosage form, acting as general acid–base catalysts, directly reacting with drug or becoming a source of impurities that can either directly react with drug substances or participate as catalysts in the drug degradation. The excipients can also alter the physical and/or the chemical form of the drug through, for example, ion-exchange, transformation of polymorphs, and the formation of eutectic or solid solutions. The changes in physical or chemical state may in turn alter the chemical stability of the drug. Most drugs and excipients contain water, which may be either bound or unbound. The physical state of water in an excipient or the drug–excipient mixture determines its potential role in drug–excipient interactions. Presence of water in the solid-state systems has a significant impact on the stability, not only in causing the hydrolysis of drugs, e.g., of acetylsalicylic acid, but also its participation as a reaction medium, and in increasing the plasticity and molecular mobility of the system.

Recent Trends in Product Development and Regulatory Issues on Impurities in Active Pharmaceutical Ingredient (API) and Drug Products. Part 1: Predicting Degradation Related Impurities and Impurity Considerations for Pharmaceutical Dosage Forms

The American Association for Pharmaceutical Scientists (AAPS) Workshop on Predicting and Monitoring Impurities in API and Drug Products: Product Development and Regulatory Issues was held on October 13–14, 2012 at the McCormick Place in Chicago, IL, USA. The goal of the workshop was to discuss control strategies of chemical and physical changes of active pharmaceutical ingredients (API) and drug products in the drug development process. These changes can affect both the safety and efficacy of drugs; therefore, the ability to rapidly predict and assess the potential for drug product performance changes for impurity formation and the associated safety concerns are important parts of speeding the development of innovative drug therapies. The workshop consisted of four different sessions. Each session focused on separate fundamental issues to build a comprehensive understanding of the physical and chemical processes that impact drug degradation, the control of impurities and the impact of these factors on safety and regulatory areas. Taken together, this comprehensive understanding is used to achieve a more robust development process that enables predictability with a concomitant assurance of safety and efficacy. Innovative methodologies for development of effective stability control strategies were also presented. This article summarizes Sessions 1 and 2 of the American Association for Pharmaceutical Scientists (AAPS) Workshop on Predicting and Monitoring Impurities in API and Drug Products: Product Development and Regulatory Issues and addresses of predicting degradation related impurities and impurity considerations for pharmaceutical dosage forms. Sessions 3 and 4 of the American Association for Pharmaceutical Scientists (AAPS) Workshop on Predicting and Monitoring Impurities in API and Drug Products: Product Development and Regulatory Issues are summarized in Recent Trends in Product Development and Regulatory Issues on Impurities in Active Pharmaceutical Ingredient (API) and Drug Products Part 2: Safety Considerations of Impurities in Pharmaceutical Products and Surveying the Impurity Landscape published separately.

An active film-coating approach to enhance chemical stability of a potent drug molecule

Peliglitazar, a PPAR α/γ agonist, was found to undergo acid as well as base catalyzed degradation. The acid catalyzed degradation led to the formation of benzylic alcohol and glycine carbamate and the base catalyzed degradation led to formation of p-hydroxyanisole and an amine degradant. In capsule formulations, the capsules with the lowest drug-loading exhibited maximum instability even at 25°C/60% RH storage condition. Incorporation of pH-modifiers to maintain ‘micro-environmental pH’ acidic did not prevent the formation of the base-catalyzed degradants. Traditional dry granulated tablet formulation which is qualitatively similar to the capsule formulations showed the presence of acid-catalyzed degradants even without the presence of an acidifying agent. On the other hand, traditional wet granulated tablet formulation showed mainly base-catalyzed degradants. Stability problems of the tablet formulation were aggravated because the potent molecule required low tablet strengths which resulted in low drug to excipient ratio. To stabilize the molecule, an active film-coating approach was explored. In this approach, the drug was sprayed with the coating material onto non-active containing tablet cores. This approach of trapping the drug particles into the coating material provided tablets with satisfactory chemical stability. The stability enhancement observed in the active coating approach is attributed to the higher drug to excipient ratio in the film coat of non-reactive coating material compared to that in the traditional dry or wet granulated formulations.