Stability Articles

The current regulatory guidances governing forced degradation studies of biological pharmaceuticals are extremely general. They itemize broad principles and approaches with few practical instructions. There is no single document that comprehensively addresses issues related to stress studies such as objectives, timing, selection of stress conditions, and extent of degradation. We will attempt to fill that gap by summarizing regulatory guidance for stress studies of biological products and present some examples of their practical applications.

In the ibuprofen (IBP) bulk drug (1) and tablet (2) assay methods (high-performance liquid chromatography [HPLC]) of the United States Pharmacopeia (USP), valerophenone (ISTD) is used in standard solutions for system-suitability determination and as an internal standard for the quantitation of ibuprofen in bulk drug and tablets. ISTD is prepared in a solution of 1% chloroacetic acid (pH 3.0
0.05):acetonitrile (40:60). This ISTD solution is used as an extraction solvent for IBP tablets (tablet assay preparation) and for IBP bulk drug substances (bulk drug assay preparation) as well as for the preparation of system-suitability standard solutions. The HPLC mobile phase for this method is 1% chloroacetic acid (pH 3.0
0.05):acetonitrile (40:60). The peak response ratios of IBP and 4-isobutylacetophenone (4-IBAP) to ISTD are factored in the quantitation of IBP and 4-IBAP in bulk drug and tablet assay samples.

Stability is defined as the capacity of a drug substance or drug product to remain within established specifications to maintain its identity, strength, quality, and purity throughout the retest or expiration dating periods (1). Physical, chemical, and microbiological data are  generated as a function of time and storage conditions (e.g., temperature and relative humidity [RH]). Stability testing provides evidence that the quality of a drug substance or drug product under the influence of various environmental factors changes with time (2). Although the storage conditions are relatively constant, the distribution environment can vary greatly, especially when a drug product is shipped between various climatic zones (1). Seasonal changes, mode of transportation, and the number of drop-off points are also variables that should be considered within the pharmaceutical supply chain.

Buffers used to formulate proteins should not serve as substrates or inhibitors. They should exhibit little or no change in pH with temperature, show insignificant penetration through biological membranes, and have maximum buffer capacity at a pH where the protein exhibits optimal stability. In conformity with the proposition that “Nature designs the optimum molecules,” buffers should mimic the antidenaturant properties of nature exhibited by osmolytes (1–5) that are independent of the evolutionary history of the proteins (6, 7). Such properties may include preferential exclusion from the protein domain (8–11) and stabilization without changing the denaturation Gibbs energy (
Gd) (12).

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Out-of-specification (OOS) regulatory issues have been well documented in the literature (1). Out-of-trend (OOT) stability data identification and investigation is rapidly gaining regulatory interest. An OOT result is a stability result that does not follow the expected trend, either in comparison with other stability batches or with respect to previous results collected during a stability study. The result is not necessarily OOS but does not look like a typical data point. This article discusses the regulatory and business basis, possible statistical approaches, and implementation challenges to the identification of OOT stability data. Representatives from PhRMA member companies met to consider these topics, review current practices, and summarize various approaches to potentially address this issue. It is noted that the identification of OOT results is a complicated issue and that further research and discussion is needed.

Once a candidate drug reaches use in humans, all stability storage and testing must be
conducted according to current good manufacturing practices  (CGMPs). The regulatory mandate for stability testing in the United States is contained in 21 CFR Part 211 Section 166, which states that There shall be a written testing program designed to assess the stability characteristics of drug products. The results of such stability testing shall be used in determining appropriate storage conditions and expiration dates. The written program shall be followed and shall include…. Although 21 CFR addresses stability data treatment and reporting for expiration dating, it says almost nothing about how to ensure control within the stability storage operation or how to design stability protocols. There are many ways to run a stability operation in a GMPcompliant manner, but the bottom line is to have written procedures and protocols with documented evidence that they are followed.

Forced degradation or stress testing is undertaken to demonstrate specificity when developing stability-indicating methods, particularly when little information is available about potential degradation products. These studies also provide information about the degradation pathways and degradation products that could form during storage. Forced degradation studies may help facilitate pharmaceutical development as well in areas such as formulation development, manufacturing, and packaging, in which knowledge of chemical behavior can be used to improve a drug product.

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Tablet Relaxation and Physiocomechanical Stability of Lactose, Microcrystalline Cellulose, and Dibasic Calcuim Phosphate01

This
study reports on the effects that water absorbed into amorphous sodium
indomethacin (NaIMC) can have on simultaneous tendencies to crystallize
to its trihydrate form and to undergo base-catalyzed hydrolysis because
of the plasticizing effects of water on molecular mobility. Measurement
of water vapor absorption at 30°C and powder x-ray diffraction patterns
as a function of relative humidity (RH) reveal that upon exposure to
21% RH, NaIMC does not crystallize over a 2-month period. Measurements
of the glass transition temperature as a function of such exposure
reveals a change in Tg from 121°C, dry, to 53°C at 21% RH, such that Tg
at 21% RH is ~13°C above the highest storage temperature of 40°C used
in the study. At 56% RH and higher, however, crystallization to the
trihydrate occurs rapidly; although over the 2-month period,
crystallization was never complete. Assessment of chemical degradation

The purpose of this study was to prepare poly(ethylene glycol) (PEG)ylated octreotide and investigate the stability against acylation by polyester polymers such as poly(lactic acid) and poly(lactic-co-glycolic acid). Octreotide was modified by reaction with monomethoxy PEG-propionaldehyde (molecular weight 5,000) in the presence of sodium cyanoborohydride. The mono-PEGylated fraction was isolated by reversed-phase high-performance liquid chromatography (HPLC) and characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Circular dichroism demonstrated no significant secondary structural differences between mono-PEGylated octreotide (mono-PEG-octreotide) and intact octreotide. As a test system for the stability study against acylation reaction, lactic acid (LA) solutions with various concentrations and pH values were prepared with water dilution and subsequent accelerated equilibration at 90°C for 24 hours.