A new benchtop system that uses novel milling technology aims to reduce drastically the time taken for routine pharmaceutical sample preparation. Technical sales manager Mike Pollard and business director Mark Fish, Drug Delivery Automation, RTS Life Science, describe how
?Sample preparation is one of the most time consuming activities for analytical scientists working in pharmaceutical laboratories today. In the pharmaceutical development process, large numbers of samples are prepared and analysed as part of stability and impurity studies. In a quality control environment, assay and content uniformity testing is a requirement of the pharmacopeia. In addition, increasingly complex controlled release dose forms are creating real challenges for traditional sample preparation techniques and technologies.
In theory, the extraction of a substance from a tablet should be a simple and straightforward process. This can be achieved by placing the tablet in a suitable quantity of solvent and waiting for it to dissolve. However, the reality is somewhat different.
resistance to dissolution
In most cases, tablet formulations are designed to allow them to be easily handled by the patient, swallowed and then passed into the stomach without breaking up. These characteristics provide the tablets with some inherent resistance to dissolution. Hard gel capsules present special physical challenges: for example, they may float, often requiring capsules to be split prior to extraction.
Modified and controlled release drugs are designed to deliver their active ingredients with a controlled dosing profile - in some cases, releasing the active ingredient slowly over a period of 24 hours. Consequently, such formulations are the most challenging to put into solution.
Laboratory analysts typically employ a number of techniques to assist the dissolution of a tablet, thereby reducing the time required to achieve liquid- solid extraction. The following are among the most widely adopted instruments used for sample preparation:
i. stirrers and shakers
When using a shaker bath the analyst places the tablets into a volumetric flask together with a suitable volume of solvent, typically in the range 250- 500ml. The equipment agitates the solution to encourage tablets to dissolve. Stirrers and shakers are cost- effective and easy to use. However, they require a large amount of desk space as multiple units are usually required. Extended run times are also required for many formulations.
ii. sonication baths
Sonication baths are used in much the same way as stirrers and shakers. However, rather than a stirring or shaking action, the sonication bath uses ultrasonic energy to disrupt the physical structure of the tablets. Sonication baths can be faster in their operation than stirrer baths. However, care must be taken to avoid the accelerated degradation of the formulation.
Ultrasonic baths and probes rely on cavitation to break down samples. Cavities are formed and collapse in microseconds, which releases tremendous energy within the liquid. This not only causes rapid generalised heating of the solution, but in other applications is used to accelerate chemical reactions.
The rapid heating and cavitation effects mean care must be taken to avoid increased rates of drug product degradation. Sonication baths can also be noisy devices, needing careful placement within the laboratory environment. Despite the high energies involved, some challenging tablet formulations can still take longer than 30 minutes to be homogenised by this method.
iii. rotor stator homogenisation
This type of homogeniser employs a high speed rotor, tightly fitted inside a toothed stator element, driven by a high-speed motor. The high sheer homogenisers require the introduction of the homogenising probe into the flask or beaker containing the tablets. Homogenisers are faster than stirrer baths and typically faster than sonication baths. However, they are noisy and potentially dangerous devices due to the high speed rotating elements used to break up the tablets mechanically.
The introduction of an external tool of this type requires careful method development around the cleaning of the tool. Performance characteristics can also vary between instruments, or over time as components wear. Failure to address these points can result in unpredictable recovery levels, or potential cross sample contamination.
iv. microwave assisted extraction
This technique uses microwave radiation to heat solvents in contact with the tablet to extract the soluble constituents from the tablet into the solvent. Some success has been reported for this technique in analysis of immediate release dose forms. However, wider application can be limited by tablet coatings and dose form. Many dose forms are resistant to disruption without some mechanical influence. The availability of practical laboratory-scale processing equipment is limited.
When discussing manual sample preparation methods it is also interesting to consider the associated costs. Some of these costs include equipment, analyst time and throughput, glassware, solvents supply and disposal and consumables. When evaluating new equipment, or assessing the need for automation, it is invaluable to review the cost associated with the current laboratory processes. The true cost of analysis must be considered alongside other factors such as efficiency, throughput and data quality benefits.
sample preparation
For the higher throughputs associated with quality control/batch release environments, pharmaceutical companies often look for automated solutions to perform sample preparation activities. These techniques allow the laboratory to process more samples with similar levels of resourcing, while also providing benefits in terms of data quality and reproducibility.
Typically, an analyst using purely manual methods will take anywhere from 20 minutes to two hours or more to prepare a tablet sample for HPLC analysis. Current automated systems can achieve cycle times of 20 minutes or better. In all cases, the cycle times will depend on dosage form and method used (see fig.1).
Automating sample preparation reduces manual working time and helps control inconsistencies in the preparation methods, by using robots or automation in place of the operator. This approach helps control sources of analytical variability as environment, method or operator factors are either removed, measured or controlled.
Automated workstations offer the benefits of unattended operation, but will still require some time for set-up and solvent preparation. Manual methods, by comparison, require operator involvement in most stages of the process, with the exception of steps like stirring or shaking where manual equipment can be left unattended for a short duration.
The adoption of automated technology is not without challenges.4,5,6 Most automation systems have taken the existing benchtop paradigms and introduced robots and software to carry out the task an operator would usually perform. This means that the limitations previously described for manual methods may still be inherent in systems, with the automation adding complexity in the forms of software and compliance issues and additional failure modes. For example, the filtration step adds extra cost due to the higher price of automation-friendly filters. It also introduces challenges in liquid handling because the system must aspirate solution, eject it through a filter and then be thoroughly washed to ensure that there is no carryover.
Transferring existing manual methods to an automated system can be a considerable challenge. Proving equivalence to current manual techniques is often a pre-requisite, and inevitable in the case that manual testing has been used to establish the registration or product specification. This process can be simplified where the constituents of the automation are available in benchtop form, facilitating a phased transition to an automated process.
alternatives to automation
The RTS SolidPrep is a new solution to address issues with existing pharmaceutical preparation methods, using techniques proven in the preparation of biological samples.
The system employs a novel milling technique to deliver extremely fast liquid-solid phase extraction. The short homogenisation times achieved by this technology offer radical improvements in throughput compared with traditional instruments, making it an ideal benchtop alternative to high-throughput automation. The instrument is bench mounted, requiring a similar amount of benchroom to a single stirrer plate.
As with all new technology, there are aspects of the new instrument that need to be considered. A key benefit of the equipment is the use of disposable vessels for the extraction process. This eliminates the need to find and clean suitable glassware and the risks of sample cross contamination (see figure 2).
Each tube contains a metered amount of specially selected ceramic milling media. In use, the analyst will take a fresh tube, add the tablets for extraction along with a metered volume of extraction media, load the tubes in the RTS SolidPrep instrument, and process the samples for the required amount of time. Post processing, the solutions will require clarification prior to analysis, which can be easily achieved by centrifuging or filtration.
Existing sample preparation methods will be based around alternative homogenisation instruments. Fortunately, existing methods can, in most cases, be easily adapted to work with the RTS SolidPrep, so that comparison and equivalence studies are simple to perform. Some attention needs to be paid to the smaller working volume, and in exceptional cases the solvent systems may require adjustment or optimisation to work within a lower volume window.
Dilution may be required prior to analysis to realise the same target analyte concentrations as established sample preparations. If a large number of tablets are being dissolved then their solubility should be compared with the vessel volume restriction.
RTS has developed a package of recommended apparatus and consumables with optimised workflows that simplify the transfer of existing methods, and maximise the productivity gain, ensuring that the new system can be used in a highly effective manner.
With most new instruments there is a lack of documentary evidence to support reliability claims. However, in this case, the core technology used by the instrument has been used in other non-pharmaceutical sample preparation methods for a number of years.
To prove its efficiency, this pioneering development has been tested by a large pharmaceutical company. The company tested its existing homogenisation method against the SolidPrep method, obtaining comparable homogenisation in each case.
In addition, RTS has carried out extensive tests both in-house and in partnership with an analytical laboratory in order to improve the efficiency of the instrument, demonstrate that the process gives comparable or better drug recovery and ensure that the new technique does not introduce new problems such as over heating.
the rewards
Sample preparation is a time-consuming but essential laboratory activity in the development and quality control testing of new drugs. As pharma companies develop increasingly complex dose forms, the limitations of current manual methods are becoming increasingly evident. In addition, established manual methods are struggling to meet modern laboratory demands in terms of throughput and cycle time.
Automation of sample preparation has the potential to offer significant benefits in drug development and quality control by increasing throughput and reducing the requirement for analyst intervention. Such technology, however, requires a considerable capital investment and the dedication of significant resources and time to transfer existing methods and maintain the equipment in use.
New effective benchtop equipment, such as the RTS SolidPrep, can offer significant improvements over current manual processes, by reducing cycle times and improving throughput without the complexity of an automated system.
The adoption of more effective manual testing technology will allow companies to take a staged approach to increasing their laboratory capacity as a precursor or alternative to automated sample preparation.
Boosting throughput
RTS SolidPrep provides high-speed preparation of tablets and other solid dose pharmaceuticals for assay, impurity and dose content uniformity applications. Using the SolidPrep, most laboratories will be able to achieve at least three times the throughput when compared with current manual methods. This improvement in efficiency gives a typical payback period of less than two months.
As well as dramatically reducing sample preparation time by more than 90%, RTS SolidPrep provides benefits including significant reductions in solvent use and waste, and reproducible homogenisation without localised heating or increased drug degradation.
In addition, this solution offers disposable in-vessel
processing. As a result, this eliminates the need to find and clean glassware and significantly reduces the risk of
sample cross talk and operator drug exposures.
RTS is able to provide a technical evaluation programme to companies interested in improving their solid dose form sample preparation processes.