OOS Investigation case study-6 (Assay)

In Pharmaceutical Industries OOS investigation and root cause identification is very important topic. If you are not able to identify the exact root cause, then your effort should be looked in your investigation.

Here I am sharing another case study to understand it in a better way-

OOS observed in Assay test. 

During investigation if you found any root cause in Preliminary or hypothesis testing, before planning of re-analysis, Use any of Investi pigation tools (5 Why, 6 M etc to rule out all other probabilities)Review it thoroughly and plan the negative experiment if required to make the investigation more adequate.

Description of Event:

OOS result observed in Assay test.

Result: 107.0%+-Limit: 95.0 - 105.0%.

Total 02 samples were planned in same sequence subject sample and other higher strength(2X) sample.

Preliminary investigation:

During preliminary investigation checked all possibilities for higher Assay results like Instrument error (No pressure fluctuation , no air bubble in mobile phase/Rinse line ) Calculation error (wrong weight, wrong potency etc.), Standard preparation error (recovery factor of standard and control standard is 99.8%) and all other possible causes for higher result, but no error is identified in preliminary investigation. Hence hypothesis testing is planned.

Re-measurement:

Hypothesis testing is performed to rule out instrument error, vial filling error, dilution error etc.Same vial result is found similar/higher to initial result  (112.0%), 02 injections injected from same vial and both injection results are similar in initial as well in hypothesis, hence Instrument error is ruled out.

Refilled (100.2%) and re-dilution (99.6%) results are found well with in specification limit.

Most of the investigator will plan the re-analysis" as Re-filled vial and re-dilution results are well within specification limit.

"Now the question is ,"Is above investigation and hypothesis outcome is sufficient evidence to plan the re-analysis?"

Yes ,we can ."But this is not complete investigation as other possibilities are not ruled out for higher results, this may not be acceptable to many of the Regulatory Auditors.

"So what is the additional investigation and efforts are missing."

My take.

"In above investigation re-filled from final sample solution result is with in specification limit and+ re-dilution from stock solution is also with in limit . So there is no issue with the productquality and no error in sample preparation.

There is something happened during sample vial filling.

How final solution gives higher result during initial analysis and with in specification result from same final solution in re-measurement.

Here we can use Systematic root cause analysis as 6M methodology to identify/Rule out other possibilities of higher results:

1-Man, 2-Machine, 3-Method, 4-Measurement, 

5-Mothar nature & 6-Material

In each section first write all the possibilities for higher results and systematically rule out till last 01 or 02 most probabilities and performed the protocol based experiment to identify the exact root cause for higher result.

“Check the peak purity of higher result on PDA, if peak purity is failed then possibilities that some extraneous contamination from vial which give response on same RT and if peak purity is passed then we go for below two possibilities.”

As per my opinion the last 02 most probable cause  are:

1- At the time of vial filling by mistake analyst rinse the vial with  higher strength (2X) sample solution, hence higher strength trace remains in the vial and give higher result, but as same vial result found higher side (about 5%) the possibility is ruled out.

2- As same vial result in hypothesis testing is found higher side about 5% from initial,

How is this possible? In diluents there is 90% of solvent, a slight amount of solvent evaporation from vial can give such higher results i.e. In general we filled about 1.6 ml solution in HPLC vial and only 0.1 ml solvent evaporation can give more than 6% higher result.

Based above investigation outcome , suppose when you again check the same HPLCvial and it is found that the cap is not properly fixed.

Perform the negative experiment using same solution (You can prepare standard solution of same concentration as sample) and inject one with properly fixed cap and other improper (As initial) and inject after about the same time difference as in initial analysis.If result found higher side in improper cap fixed on HPLC vial , then definitely it make our investigation strong and will support the root cause analysis.

Based on out come (if positive) , we can take CAPA to use snap type septa cap (Resistance to solvent evaporation) where solvent is more than 50%.

This experiment will support to our initial root cause. Even though if we did not find any support from above experiment, Our such efforts in investigation will give confidence to auditor."