The aim of this study was to apply quality-by-design principles to build in a more scientific and risk-based multifactorial
strategy in the development of an ultrahigh-pressure liquid chromatography (UHPLC) method for omeprazole and its related impurities.
The quality-by-design concept was outlined years ago by Joseph M. Juran (1) and is used in many industries to improve the
quality of products and services simply by planning quality from the beginning. Since the US Food and Drug Administration
(FDA) announced its "Pharmaceutical Current Good Manufacturing Practices (cGMPs) for the 21st Century" initiative (2) in 2002,
a quality-by-design approach has also been sought in the pharmaceutical industry.
Through the International Conference on Harmonization (ICH), this concept resulted in ICH guideline Q8(R2) in which quality-by-design
is defined as "a systematic approach to development that begins with predefined objectives and emphasizes product and process
understanding and process control, based on sound science and quality risk management" (3).
Although ICH guideline Q8(R2) doesn't explicitly take analytical method development into account and no other regulatory guideline
has been issued, the quality-by-design concept can be extended to a systematic approach that includes the definition of the
methods goal, risk assessment, design of experiments, developing a design space, verification of the design space, implementing
a control strategy, and continual improvement to increase method robustness and knowledge (4). The novelty and opportunity
in this approach is that working within the design space of a specific method can be seen as an adjustment and not a postapproval
A systematic approach should replace the still common "screening," also known as a trial-and-error approach, in which one
factor at a time (OFAT) is varied until the best method is found. The OFAT approach is time-consuming and often results in
a nonrobust method because interactions between factors are not considered.
Today, systematic concepts use experimental design plans as an efficient and fast tool for method development. In a full or
fractional, factorial design, a couple experiments are carried out in which one or more factors are changed at the same time.
By using statistical software tools (for example, Design Expert from Stat-Ease, Inc.), the effect of each factor on the separation
can be calculated and the data can be used to find the optimum separation (4). In our laboratory, this concept is used when
the development of nonchromatographic methods is necessary.
However, the easiest and fasted way of developing a liquid chromatographic method is by using chromatography modeling, especially
in combination with ultrahigh-pressure liquid chromatography (UHPLC) technology. Based on a small number of experiments, these
software applications can predict the movement of peaks when parameters such as eluent composition or pH, flow rate, column
temperature, column dimensions, and particle size are changed (5–11). When necessary, the developed method can be transferred
(back) to high performance liquid chromatography (HPLC).
In our laboratory we have been using visual chromatographic modeling (software packages) for many years now in HPLC and UHPLC
method development and it has resulted in very robust methods (4,12–14). The aim of this study was to apply quality-by-design
principles to build in a more scientific and risk-based, multifactorial strategy in the development of a new UHPLC method
for testing the purity of omeprazole.
Omeprazole belongs to the group of proton-pump inhibitors and is one of the most widely prescribed drugs. It suppresses gastric
acid secretion by specific inhibition of the enzyme hydrogen-potassium adenosine triphosphatase (H+, K +-ATPase). Omeprazole
formulations are used to treat acid reflux, heartburn, ulcer disease, and gastritis (15).
Omeprazole is described in the monograph of the European Pharmacopeia (EP) (16). Purity testing for omeprazole is accomplished by using HPLC with UV detection on a 125 mm × 4.6 mm, 5-μm d
p C8 column in isocratic mode with an eluent consisting of 27 vol% acetonitrile and 73 vol% disodium hydrogen phosphate solution
(pH 7.6) and a flow rate of 1.0 mL/min. On the basis of the synthetic route, the monograph recommends testing the impurities
A, B, C, D, E, H, and I by HPLC, and the impurities F and G have to be tested by a photometric method (chemical structures
are shown in Figure 1). A typical chromatogram of a selectivity standard solution containing omeprazole and its related impurities
A–I obtained using the EP method is given in Figure 2 and shows that the method was developed without any chromatography knowledge. Some of the impurity
peaks show coelution, but the last three peaks are separated from each other with a huge distance of 10 min each.
Figure 1: Chemical structures of omeprazole and its related impurities.
Several analytical procedures for the determination of omeprazole and its related impurities have been described. A review
of the analytical methodologies for the determination of omeprazole, mostly in plasma and urine, was published in 2007 (17).
Only some recent publications focus on stability-indicating methods for the analysis of impurities and degradation products
in omeprazole formulations (18–20). As far as we know, no analytical method has been published that would separate all synthesis
impurities and degradation products mentioned in the EP monograph. Therefore, there is a need for a simple, fast, and reliable purity method for the determination of omeprazole
and its related impurities in the active pharmaceutical ingredient (API) and in pharmaceutical formulations.
Figure 2: Typical chromatogram of a selectivity standard solution containing omeprazole and its related impurities A–I by
using the purity method published in the European Pharmacopoeia. Column: 125 mm × 4.6 mm, 5-μm dp Symmetry C8 column; mode: isocratic; eluent: 27 vol% acetonitrile and 73 vol% disodium hydrogen phosphate [1.4 g/L], adjusted
with phosphoric acid to pH 7.6; flow rate: 1 mL/min.