An automated dissolution method can be a powerful tool to test drug products at all phases of their development. With minimal automated method validation, this tool can be used early in the drug-evaluation process. And with additional validation efforts, an automated method can be extended to the testing of Phase IV stability batches. Validating an automated dissolution-test method requires an understanding of the potential effects from filtration parameters, system interference, carry-over, cleaning..As the pace of product development accelerates, the approach to dissolution-method development must advance beyond a manual method and an assay. A natural progression of the method-development process must include the transfer of the manual method onto automated instrumentation.
Validating the automated method is the primary challenge when transferring from the manual method. A dissolution scientist must understand the potential effects from filtration, system interference, carry-over, cleaning parameters, and media replacement. Automated dissolution instrumentation can help generate good manufacturing practice (GMP) data only when validated testing parameters can negate these influences, so the dissolution scientist can be confident that results do not differ between the manual and the automated methods. In addition, all laboratory equipment used to support or generate GMP data about automated instrumentation must follow an instrument "chain of compliance." Proper documentation must exist that proves each piece of equipment has been properly qualified and calibrated for its intended use.
Product development life cycle
It is advantageous for a dissolution chemist to validate individual automated parameters even if comparable results are obtained between the automated and manual dissolution tests. This process provides additional information about the product and the automated procedure, which may be useful as the formulation evolves. In addition, by validating individual automated parameters, a dissolution chemist can demonstrate to the US Food and Drug Administration a high level of control and understanding of the automated procedures used to evaluate the performance of the drug product. The individual automated parameters to be validated should include filtration, system interference, carry-over, cleaning parameters, and media replacement for off-line sample collection. A dissolution chemist always must be aware that the dissolution of the product itself is validated, not a particular formula. With this fact in mind, it is beneficial to conduct the validation experiments after final formulas have been determined. If future formulations change drastically, experience and scientific judgment must be used to determine the necessity of revalidation of individual automation parameters.
Filtration. Although automated filtration parameters should be established first, the filtration procedures for manual dissolutions may not always transfer exactly to the automated instrument. Incompatible or inadequate automated filtration procedures are the most likely cause for different results between the manual and automated dissolution tests. A side-by-side comparison between a manual test and an automated test is the quickest way to evaluate compatibility between the two methods. Because results typically approach 100% drug released at later time points, samples taken at the earlier time points provide the best information. At minimum, it is advantageous to test two lots of drug product at the highest and lowest dosage strengths.
Experience in performing manual dissolutions should help determine the type of experiment to be conducted. The comparison can be performed two different ways. For highly variable batches, where the result relative standard deviation is >20% at the 10-min time point or >10% at later time points, USP recommends performing an automated dissolution and collecting manual samples simultaneously during the automated sampling. To ensure that the automated sampling probe is not affecting the hydrodynamics of the dissolution, however, a dissolution scientist should first perform the automated dissolution using only manual sampling. These results could be compared with the manual dissolution. For less variable batches, USP recommends comparing the results between separate manual and automated dissolutions tests. The acceptance criteria proposed under USP " <1092> Intermediate Precision guidelines state the difference should not exceed 10% with less than 85% dissolved and the difference should not exceed 5% for remaining time points above 85% dissolved (1, 2). 1092>
System interference. After acceptable filtration parameters have been established, a dissolution chemist should determine whether system interference is affecting the results generated with the automated instrumentation. This parameter is an important variable to investigate and hopefully eliminate as a potential source of difference between the manual and automated tests.
An example of system interference is any binding of the API to tubing or sampling needles when using sampling parameters described in the automated method. Once automated sampling occurs, the API often must travel through very long lines of tubing, thus generating the potential for system interference. The test may be performed by preparing a 20% API and a 100% placebo solution. The amount of API is measured with and without the automated system. A portion of the prepared API solution is placed into each of the six dissolution vessels. Sample aliquots should be withdrawn manually and filtered simultaneously as the automated system is sampling. The difference between the two responses should not exceed 2.0%. Because system interference is more likely to be observed with a 20% API solution, the information generated from this experiment is useful when analyzing results from dissolution-profile testing. Low levels of system interference from higher API concentrations may be less likely to be noticed. If system interference is not observed with a 20% API solution, a dissolution chemist is more likely to be assured that accurate data are obtained at earlier time points of automated dissolution profile testing. Conversely, if the results between the manual and the automated dissolution tests are not equivalent, especially at the earlier time points of profile testing, it may be determined that system interference is the cause of the nonequivalent automated results. Although only the results at Q time will pass or fail a batch, system interference is an important parameter to evaluate because it demonstrates to FDA a high level of control and understanding of the automated procedures used to evaluate the performance of the drug product.
Carry-over. If it has been determined that system interference is not a factor for the product, the elimination of carry-over must be validated for an automated dissolution testing system. Carry-over of an API may occur between sampling time points during dissolution-profile testing and between batches during multiple batch runs. To determine whether carry-over exists between sampling time points, perform a sampling sequence using solutions equivalent to 100% of the highest dosage form and a blank solution. The solutions must be sampled according to the already established automated filtration and sampling procedures. The sequence of the sampling should be as follows: 100% solution, blank, 100% solution.
The API in the blank solution should not exceed 1.0%, and the result for the second 100% sampled solution must be equivalent to 99.0–101.0% of the result of the first 100% sampled solution. If results exceed these acceptance criteria, increased sampling flush volumes, filter changes between time points, different filters, or any combination of these three parameters may need to be altered to obtain acceptable results.
Potential drug product carry-over between batches must be validated and eliminated if possible. This process allows the automated testing system to be used to its fullest potential so that multiple batches can be tested in a single run. The validation can be conducted by performing dissolution tests with the highest dosage strength batch followed immediately with a blank batch (no dosage forms). The API in the blank batch must not exceed an average of 1.0% for six vessels. The samples should be taken and compared at the infinity time point when results are expected to approach 100% API released. Cleaning parameters may need to be increased if results exceed this acceptance criterion.
Cleaning parameters. It is important to clean the automated dissolution-testing system between batches of a single run and between product changes. Clean the dissolution vessels, stirring shafts, sampling needles, and the entire length of all sampling lines. Potential problems may occur, especially between product changes, if a surfactant was used previously. Results from future batches may be inaccurately high if surfactant remains in the system from a previous run.
Adequate cleaning procedures must be validated to ensure no carry-over occurs between batches of a single run or after product changes. Validation of the cleaning parameters may be determined at the same time as the carry-over between batches experiments. If the carry-over results between batches exceed the acceptance criteria, increased cleaning parameters may solve the problem. The amount of dissolution media or hot water flushed through the lines at the end of a dissolution test may be set at the maximum allowable volume for that particular automated dissolution-testing system. In addition, the highest number of vessel washes and the volume of dissolution media or hot water used for the vessel washes may be set at the maximum allowable volume for that particular automated system. If even the most extensive cleaning parameters do not prevent an acceptable level of carry-over from an API, a dissolution chemist may decide that the dissolution procedure for this particular product is not "automatable."
Media replacement. A media-replacement process between time points for off-line sample collection should be validated with an automated dissolution-testing system. The media-replacement option corrects for sampling loss. This option allows a dissolution chemist to replace fresh media into each dissolution vessel after each sampled time point. The replacement media may be the primary dissolution media or a secondary media, typically used to affect the pH of the media already present in the dissolution vessel. The secondary media may be used for enteric-coated products that require a media pH change.
Automated off-line sampling collection differs greatly from manual sampling. Typically, larger sample volumes are removed for automated sampling, which has the potential to affect results for dissolutions with multiple time points. For each time point, a cumulative sample volume is removed. The total volume removed includes the flush volume, the tubing dead volume, the filter-deaeration volume, and the sample-collection volume. The flush volume is the volume of sample used to saturate the filter to prevent loss of the API on the filter. The tubing dead volume is the amount of sample that must fill the lines between the dissolution vessels and the sample-collection vials. The filter-deaeration volume is the amount of sample that is used to prepare the filter for filtration (used in certain automated dissolution testing systems). The sample-collection volume is the amount of sample that is collected for the off-line assay. A dissolution chemist must take into consideration the entire sample volume removed at each time point and decide whether an equivalent amount of fresh media is to be replaced into each vessel after each sampling time point. The large amounts of sample volumes removed and replaced may affect dissolution results. Potentially, large amounts of undissolved drug substance are removed for each sample, which may inaccurately lower the results of subsequent samples. Alternately, large amounts of replacement media may inaccurately dissolve the dosage form, which may affect the results of subsequent samples.
Validation is required to determine the necessity of media replacement. A dissolution chemist should perform dissolutions with and without media replacement and compare the results to manual dissolutions. The technique that produces results that more closely resemble manual results should be used in the automated dissolution test.
Instrument qualification and calibration
Equipment qualification. In addition to all of the validation work that must be completed for each product tested on the automated dissolution system, an instrument "chain of compliance" must be established and well documented for all primary, secondary, and tertiary instruments used to support GMP data generated by the automated system. Instrument qualifications and calibrations must be completed for all components on the entire automated system. These components may include the dissolution apparatus, any on-line ultraviolet or high-performance liquid chromatography instrumentation, and any ancillary equipment. The supporting equipment used to calibrate each component periodically on the automated system includes balances, weights, stopwatches, timers, thermometers, eccentricity meters, and vibration meters. Each piece of supporting equipment must maintain a documented and current calibration status. Although the company ultimately is responsible for GMP compliance when using automated instrumentation, the company may choose to follow qualification acceptance criteria established by the US Pharmacopeia, the instrument vendor, or their own company standard operating procedures (SOPs).
Initially, an installation qualification (IQ) and operation qualification (OQ) must be completed successfully and documented for each component of the automated dissolution-testing system. The customer should request from the vendor the test-script documentation that will be followed to complete initial qualifications. It is advantageous to have the compliance department review the documentation to be certain it fulfills the requirements for the instrument to be used in a GMP environment. If one chooses to have the vendor complete the IQ and OQ activities, one must be certain the company provides training documentation for their service technicians indicating that they are qualified to complete the qualification activities.
Preventive maintenance. The qualification practices do not end after the instrument is initially installed, qualified, and calibrated. Periodic preventive maintenance and calibration schedules must be established according to company SOPs. A qualified vendor is the best choice to perform the preventive-
maintenance activities for the automated instrument. These activities may include a periodic performance qualification of the instrument, which evaluates the overall performance and operation of the system. The preventive maintenance may also include the replacement of general components necessary for the continued smooth operation of the system. These components may include tubing, belts, sampling lines, lamps, and so forth. It is important to understand that the level of maintenance or repair performed on the instrument may necessitate a requalification, recalibration, or a change control. As stricter requirements are placed on the GMP environment, company SOPs should be reviewed to ensure that preventive maintenance activities do not push the instrument out of compliance.
Calibration checks. A periodic calibration schedule must be established for each component on the automated system. The schedule may include semiannual, quarterly, weekly, and daily activities designed to confirm the proper operation of the system. For the automated dissolution-testing system, the quarterly activities may include balance and temperature-probe calibrations. In addition, weekly or daily calibrations may include a quick balance check. For the dissolution apparatus, a semiannual performance calibration must be completed using USP calibrators. Trial dissolutions must be performed on disintegrating ( e.g., prednisone) and nondis-integrating ( e.g., salicylic acid) USP calibrators. Each dissolution test must pass the USP acceptance criteria established for the lot of drug tested. Semiannual physical testing must also pass USP acceptance criteria. The physical specifications include shaft and basket eccentricities, bath level, shaft verticality, and vessel and shaft centering. In addition, even though USP acceptance criteria have not yet been established for vibration, bath vibration is an important variable that should be measured periodically, especially if mechanical components have been changed on any of the components of the automated system. New mechanical components may increase bath vibration, which may increase dissolution results inaccurately. Daily physical specifications that must pass USP acceptance criteria include proper paddle–basket height, initial and final temperatures in all vessels, and shaft rotational speed (rpm).
Automated instrumentation for dissolution testing offers several advantages such as the ability to perform unattended testing and the ability to screen several batches with varying parameters. But, automated instrumentation also poses challenges for a dissolution chemist, including the need to have an overall understanding of the the automated system. Parameters such as filtration, system interference, carry-over, cleaning parameters, and media replacement are factors that must be addressed and validated to ensure equivalent results are obtained with manual and automated methods. The automated system can be used to generate GMP data only if all components on or supporting the system maintain a documented and current qualification and calibration status.
The author thanks Ron Mamajek, John Ballard, Ronnie McDowell, Dr. Michael Breslav, Dr. Daniel Kroon, Dr. Weiyong Li, and Dr. Brigitte Segmuller for their valuable suggestions.
1. " <1092> The Dissolution Procedure: Development and Validation," Pharmacopeial Forum, 30 (1), 351–363 (Jan.–Feb. 2004). 1092>
2. " <1092> The Dissolution Procedure: Development and Validation," Pharmacopeial Forum, 31 (5), 1463–1475 (Sep.–Oct. 2005). 1092>
David Fortunato is a scientist in the Chem Pharm division of Analytical Development, US, Johnson and Johnson Pharmaceutical Research and Development, LLC, Welsh and McKean Rds., Spring House, PA 19477, tel. 215.628.5098, fax 215.540.4684, dfortuna@PRDUS.JNJ.com [firstname.lastname@example.org]
Submitted: Feb. 22, 2006. Accepted: Apr. 7, 2006.
Keywords: Analytical testing, process automation, regulation validation and compliance, solid dosage forms