Pharma Times - Vol. 44 - No. 12 - December 2012 29 The monitoring of bioburden, either as a product being manufactured, or prior to sterilization (be that through a sterilizing grade filter or through a terminal sterilization process) is an issue of FDA concern. A review of FDA warning letters between 2001 and 2011 indicates that seventy-nine companies have received a warning letter observation relating to bioburden testing. With some companies, multiple observations have been given within the same warning letter and 111 observations have been made in relation to bioburden testing for this period. The majority of the observations were made during the period 2004-2007, as indicated in the graph below. However, a number of warning letter observations continues to be issued each year with the current rate averaging at ten per year. Review of FDA warning letters for microbial bioburden issues (2001-2011) *Dr. Tim Sandle Head of Microbiology, BPL, UK Article Figure 1: Graph displaying the number of warning letters which mention a bioburden issue for the period 2001-211. The range of areas covered by the bioburden observations varies across a number of subject categories, of which the failure to conduct adequate bioburden testing for material prior to the point of filtration is the largest category. The second largest area relates to a failure to conduct adequate investigations into bioburden results which exceed alert or action levels. The third largest grouping was warning letter observations which relate to sampling (either an insufficient number of samples taken or samples not being taken at all). Together, these three most populated categories account for 65% of the warning letter observations. A categorization of bioburden warning letter observations is displayed in the chart below: Each of the categories is examined further below. Out of limits investigations Many 483 warning letter observation related the investigation of out-of-limits results for viable counts. These citations were divided into: a) Excursions above the action level not being investigated. *Email Id: tim.sandle@bpl.co.uk Figure 2: Categorization of warning letter observations in relation to bioburden for the period 2001-2011. b) Investigations having taken place into bioburden excursions, but at a level deemed inadequate in that the FDA inspectors considered that the root cause had not been identified. c) Investigations for which the root cause had been identified but where the corrective and preventative actions were considered to be inadequate in that sufficient safeguards had not been put in place to prevent the contamination event from re-occurring. d) Aspects of the investigation not being sufficiently recovered. For example, in one company (Genzyme Corporation), a potentially pathogenic microorganism had been isolated but this had not been commented upon by the company and no further investigation had taken place into the likely origin of the contamination or as a product impact assessment. Sampling Four comments were made in relation to samples from the warning letters where samples had been taken according to sampling plans but there was no evidence of the samples having been tested. These observations probably relate to laboratory error. There were twenty comments in relation to other sampling related issues. These have been categorized as: a) No rationale in place for why particular samples are taken. b) No sampling plans in plans. c) No clear procedures in place relating to how samples are taken. d) The size of the sample taken was insufficient for the type of bioburden test required. Two of these observations related to the assessment for the sample taken prior to final filtration and it is assumed that this was in relation to the membrane filtration method. e) An insufficient number of samples were taken for bioburden testing. This was by far the most common observation with sixteen 483 observations.