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Lyophilisation or freeze-drying is widely used in the pharmaceutical industry for a variety of reasons.
(JANIS CHRISTIE/GETTY IMAGES)The production of lyophilised medicinal products raises many challenges, including identifying critical temperatures, ensuring that the product is processed accordingly, optimising cycles to reduce run times and manufacturing costs, making sure the right containers are used and fit for purpose, and ensuring product uniformity, activity and stability.
In the past few years, theories and practices in lyophilisation technology have largely remained the same except for small incremental changes, which means that the process as a whole tends to evolve slowly over time. Extensive research is still being conducted to produce a reliable and easy-to-implement endpoint identification method, negating the need for pressure rise tests or temperature probe monitoring. However, several processes and products have recently come on to the market that may benefit the pharma industry.
One recent innovation is Praxair's Control Lyo Nucleation technology, which allows the freezing point of solutions in freeze dryers to be precisely controlled. Generally, solutions are cooled to below their critical temperature before primary drying is commenced, but the freezing point of different vials can be somewhat random resulting in a non-uniform ice structure, which introduces variability in the drying rate. Praxair's solution could increase control of the process to decrease moisture variability within the product, leading to narrower moisture ranges and potentially reducing the secondary drying time required to achieve acceptable product quality.
Other developments have come onto the market in terms of packaging; Lyoseal technology (Biocorp) enables vials to be stoppered and crimped within the freeze dryer, potentially saving capping time and helping to ensure container seal integrity. Improvements in glass design, geometry and surface coatings have also helped to reduce vial breakage and cycle times; for example, Easy Lyo (SGD) vials are 30% lighter than traditional vials, and therefore feature improved heat transfer to reduce cycle times. Top Lyo (Adelphi) vials have an ultra-thin hydrophobic transparent layer (40-100 nm) on the internal surface of the vial that helps prevent the collapse of the lyophilisation cake and can almost completely reduce the residual volume. Enhanced vial geometry also provides improved thermal transfer and a dramatic reduction in vial breakage during lyophilisation. There are also products coming onto the market that enable remote temperature probe monitoring.
These products are relatively new and have yet to be widely used, but all offer potential advantages to the pharma industry in terms of product quality and cost.
The challenges of lyophilising bio-based products mainly relate to the identification of critical temperatures and product behaviour during the drying process. Freeze-drying microscopy (Lyostat3; Biopharma Technology) can be used to measure collapse or eutectic temperature and identify skin formation potential (which may prevent or slow the drying process), while the polarised light application can enable visual observation of the degree of crystallinity within a sample. Differential thermal analysis and impedance analysis (Lyotherm2; Biopharma Technology) enables the identification of glass transitions, crystallisation and changes in structural mobility. Modulated differential scanning calorimetry (MDSC) analysis (TA Instruments) can also provide information on the frozen state and dried product stability.
As well as the initial characterisation of the active ingredient, bio-based entities require appropriate formulation to protect them from freezing- or drying-induced damage. With proteins, it is important to prevent the molecule from unfolding (from which it can often not recover), which may, for example, require certain sugars to protect it whilst the water is being removed. Prokaryotic or eukaryotic cells may demand certain freezing rates or special processes to prevent cell breakage. Naturally-derived products can be particularly challenging because of their inherent variability; robustness needs to be built into the formulation and lyophilisation-cycle. Certain products, such as collagen, may also require the production of a consistent, specific pore size and shape to be effective. It is also important to ensure that the dried-state storage temperature is practical for the product being developed because this affects how long the product can be stored and what storage temperatures are required. Careful analysis and monitoring of the whole lyophilisation process is crucial to achieve the correct product parameters. This can involve monitoring the product temperature during drying, pressure rise tests or a capacitance manometer and pirani gauge. In addition, moisture analysis of samples (moisture is critical to product stability) should be performed along with stability/activity analysis relevant to the product. These activities, as well as characterisation of the frozen state prior to freeze drying, are important to ensure product quality.
As well as tackling the unique problems posed by biological products, there are a number of other issues that the industry must face. Regulation of the product manufacturing/development process in the pharma industry is ever increasing, but in particular there have been greater demands for quality assurance from a number of regulatory authorities. Regulators need to know that the process is justified, that critical parameters have been measured and that processes have been developed accordingly. In the case of lyophilisation, this refers to parameters such as the collapse temperature and glass transition (dried state), as well as product formulation, to ensure that the product maintains its activity over the required shelf life. The cycle must be monitored and developed to ensure the product is consistent and it is also important to understand the extent to which any deviations are acceptable. Robustness studies can assist in providing this information; for example, shelf and product temperature deviations, as well as pressure deviations, can be tried to see what effect they have on product quality. This can assist a company in assessing any deviations that may occur during production and identifying whether a batch needs to be rejected or not.
To fully demonstrate that a product consistently meets the required specification, extensive product development and robustness testing is required. Many companies are now trying to approach it from a quality-by-design (QbD) angle. The aim of this approach is to ensure that a sufficient design space is tested and that all the different product development parameters are understood (e.g., formulation, lyophilisation cycle and product packaging). Further development of this process is important; in a competitive market all parameters need to be understood, whilst avoiding prohibitive costs.
At Biopharma Technology, we have conducted research on headspace moisture analysis. Moisture analysis is a fundamental part of the complete freeze-drying process because the moisture level has a critical impact on product quality and storage. Headspace analysis is a rapid and non-destructive method that can demonstrate that 100% of product is within the targeted moisture range.
Another aspect we are looking at is the treatment of equipment, such as equipment sterility and cleaning validation. The Pharmaceutical & Healthcare Sciences Society and the Parenteral Drug Association both produce guidelines on how to approach these challenges. Ensuring actual product sterility is also important; the seal on the product must prevent microbial ingress during storage, as well as keeping out any external moisture. The method of testing required is often product specific and needs to be chosen carefully.
The company is also involved in a number of government- (TSB) and EU-funded projects. We have completed a six-month study into the lyophilisation of red blood cells (RBCs). Drying RBCs involves some difficult challenges: not only must postprocess structural integrity be maintained, but the RBC must function as an oxygen carrier with no oxidation of haemoglobin. Survival levels of 96% were achieved, and the use of a novel biopolymer led to haemoglobin oxidation levels below detectable limits.
We have also recently completed a six-month, TSB-funded study into the freeze-drying of probiotic bacteria. This project demonstrated the feasibility of combining a number of individually proven industrial processes into a commercially viable manufacturing platform for the production of stabilised probiotic organisms. This project has led to a further study investigating microencapsulation of probiotics, which could also apply to the pharmaceutical industry for the delivery of drug substances.
A further TSB-sponsored project involved lyophilisation cycle development for an innovative, dual-layer scaffold implant product used in the first-line surgical treatment of cartilage damage, which has since begun clinical trials. This product required careful development to maintain pore structure. Biopharma Technology Limited (BTL) is also an active participant in a number of development programmes for second-generation scaffold products and their impregnation with growth factors and other proteins.
These projects bring new skills and knowledge that can be applied to the lyophilisation of a wide range of products, such as bacteria, proteins and scaffolds. The outcomes of these projects could provide new insights into drug delivery processes and provide improved processing and storage capabilities.
Isobel Cook is a Principal Scientist at Biopharma Technology.