Impact of API Physicochemical Properties on Cleaning Method Design and Cleaning Validation
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PEER-REVIEWED Impact of API Physicochemical Properties on Cleaning Method Design and Cleaning Validation William R. Porter ABSTRACT purpose of a cleaning method is to minimize cross- Physicochemical properties of active pharmaceutical contamination from previously manufactured product ingredients (APIs) and excipients used in the manu- when the subsequent product is to be manufactured facture of pharmaceutical dosage forms play a critical on cleaned equipment. Cleaning validation serves to role in the successful design of robust and validated demonstrate that the cleaning method can achieve cleaning processes. The development and validation this goal. of these methods requires an understanding of the Prevention of cross contamination between differ- solubility properties and resistance to degradation ent product lots manufactured on shared equipment is of formulation components, including both API and accomplished by using a validated cleaning procedure excipients. Knowledge and understanding of physi- (the method). The cleaning method should be devel- cochemical characteristics is critical to cleaning agent oped according to scientific and technical principles, selection, cleaning procedure design, worst-case com- be validated in designated conformance trials, be pound identification, and analytical method selection well controlled in performance, and be monitored and development. Much of the information needed and maintained throughout the product lifecycle. concerning solubility (i.e., hydrophilicity/lipophi- The cleaning method is validated by demonstrating licity, ionizability, surface activity, and temperature that remaining residue on the equipment surfaces effects) and degradation (i.e., hydrolysis, oxidation, is below a calculated acceptable residue level that photochemical reactivity) is routinely obtained dur- provides clean equipment that can be safely used for ing preformulation studies on new API candidates, subsequent manufacturing. or can be efficiently obtained at that time. Points Critical to the development of a reliable and to consider and questions to ask relating to physico- robust cleaning procedure is consideration of chemical property identification that are relevant to appropriate scientific and technical knowledge of cleaning are reviewed. the properties of the product residue to be cleaned. Fundamental knowledge of the physicochemical properties of the active pharmaceutical ingredient INTRODUCTION (API) and other formulation components is essential Development and validation of cleaning processes in this regard. Understanding the solubility and for equipment used in the manufacture of pharma- stability properties of the residue to be cleaned are ceutical dosage forms is critical to the assurance of vital areas of study. Without knowledge of solubility efficacy, safety, and quality of the final product. The and stability characteristics of the active drug and ABOUT THE AUTHOR For more Author William R. Porter formerly served for more than 25 years as Pharmacist, Senior Pharmacist, Senior information, Pharmaceutical Scientist, and Associate Research Fellow in the Pharmaceutics group at Global Pharma- go to ceutical Research and Development, Abbott Laboratories, Illinois, USA. He may be reached by e-mail gxpandjvt.com/bios [ at [email protected]. gxpandjvt.com JOURNAL OF VALIDATION TECHNOLOGY [SPRING 2011] 87 PEER-REVIEWED inactive residue to be cleaned, the following cannot cleaning a surface, at least some of the undesirable be determined: residue must be dissolved, emulsified, or suspended • A rational selection of cleaning agent cannot to some extent by the cleaning agent, which in most be made cases is water fortified with additives to enhance the • A rational cleaning procedure cannot be solubilization process. Alternatively, alcohol may be developed required as a cleaning agent in some cases based on • Determination of the worst-case compound in favorable solubility of the API in alcohol. The follow- a cleaning matrix cannot be made ing is a review of the basic physicochemical concepts • A rational analytical testing of residues cannot that influence solubility. Several publications provide be accomplished. more detailed coverage of this topic (1, 2). The following topics related to solubility are briefly The above are fundamental to the development of discussed: cleaning methods and the conduct of cleaning valida- • Hydrophilicity/hydrophobicity (or lipophobicity/ tion. Solubility and stability properties are fundamen- lipophilicity) tal areas of interest in pharmaceutical R&D, but may • Ionization and the effect of pH not be generally known to cleaning method devel- • Effect of temperature opers. However, in most pharmaceutical product • Surface activity development programs, much of the physicochemical • Liquid and semisolid product vehicle polarity property information needed to assist developers of • Impact of solubility on cleaning procedures and cleaning methods will have been obtained as part of cleaning validation. preformulation studies typically performed early in the development process. Those charged with devel- Hydrophilicity/Hydrophobicity oping cleaning methods may have to ferret out this (or lipophobicity/lipophilicity) information if knowledge management procedures Like dissolves like. Water has a high dielectric con- are not in place in their organization to assure avail- stant (i.e., a measure of its polarity, or ability to ability of information. Cleaning method development become oriented in space by application of an exter- specialists, as customers for preformulation informa- nal electric field). Substances that also exhibit high tion, may need to make their special needs known to polarity, such as table salt (an ionic substance) or those who actually conduct physicochemical property sucrose (an electrically neutral substance containing elucidation studies to ensure that the physicochemical many polar hydroxyl substituents) intermix well with data needed to support cleaning method development water molecules–they are hydrophilic (“water-loving”) is acquired in a timely and economical manner. Sub- molecules. These molecules form solutions in which mitting a special request for studies to be conducted molecules of the polar substance are dispersed in a sea just to support cleaning method development is not of water molecules stabilized by dipole-dipole, dipole- cost-effective and may delay development. It is essen- charge, or hydrogen bonding interactions. Substances tial that the cleaning method stakeholders understand that do not exhibit high polarity, such as animal fats what they need and expect from preformulation col- (e.g., glycerol esters of long-chain fatty acids), do not leagues and makes those needs known well in advance mix well with water. They are hydrophobic (“water- of the time the information is actually wanted. This hating”) molecules. There are only limited ways, other review addresses specific applications of fundamental than van der Waals’ forces, in which molecules having principles of solubility and stability as well as how this low polarity can interact with water molecules. The information applies to cleaning method development introduction of a hydrophobic nonpolar molecule and cleaning validation. into liquid water actually forces the water molecules to become more ordered and less random in their SOLUBILITY orientation, because opportunities for water molecules The solubility properties of an API are part of the to engage in stronger interactions, such as hydrogen fundamental physicochemical properties determined bonding, are reduced in the direction of the nonpo- in preformulation studies. Knowledge of these proper- lar solute. Nonpolar (greasy) substances dissolve ties is useful in the development of cleaning methods more readily in nonpolar (lipophilic—“fat-loving”) and in the approach to cleaning at the commercial solvents. Conversely, polar substances have little manufacturing site. At some point in the process of affinity for nonpolar lipids (i.e., they are lipophobic— 88 JOURNAL OF VALIDATION TECHNOLOGY [SPRING 2011] ivthome.com WILLIAM R. PORTER “fat-hating”) and will tend to separate from fatty or though the parent substance from which they were nonpolar materials to form a new phase. derived is not. Substances that are weakly acidic in The determination of the relative hydrophilicity/ aqueous solution tend to be less soluble in acidic lipophilicity of new drug substances is critical to the cleaning media because the acidity of the cleaning development of new drug products and methods medium suppresses ionization of weak acids. Sub- for analyzing them, in addition to its impact on stances that are weakly basic in aqueous solutions cleanability. Conventionally, the affinity for a new tend to be less soluble in alkaline cleaning media API for polar and nonpolar media is represented by because the alkalinity of the cleaning medium sup- its octanol-water partition coefficient (3,4). Octa- presses ionization of weak bases. The manipulation nol-water partition coefficients are such important of cleaning solution pH is an easy tool for enhancing predictors of the behavior of chemical substances solubilization of troublesome residues. Lipophilic in solution that their determination is often one residues (e.g., from mixtures containing lubricants of the first activities performed in characterizing such as magnesium stearate) are often difficult to the physiochemical properties of a new API candi- remove from surfaces. Many commonly