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May 2006

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From:
"Ambrus, Kate" <[log in to unmask]>
Reply To:
The Pharmaceutical Microbiology Forum Email List <[log in to unmask]>
Date:
Tue, 9 May 2006 08:29:47 -0700
Content-Type:
text/plain
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Hello all,

I checked out the mathematical rules for rounding off, and thought I'd
pass it on. The reason that 0.45 rounds off to 0, is that the rule says
that the final answer will depend on the value in the decimal place
immediately to the right of the value that you are trying to round to.
In the above example it is a 4. 4 rounds down to 0.

If you were rounding off to one decimal place (for USP for example), the
answer would be 0.5, because in 0.45 there is a five immediately to the
right of the 4 (the first decimal place). Which would of course be short
of 1.0, and a failure also.

0.4999999 still rounds down to 0 - because of the 4 next to the zero
decimal place. Only values of 0.5 and above would round up to 1.

Happy calculating!

Kate S. Ambrus
Manager, Eye Care R&D Microbiology
Advanced Medical Optics
[log in to unmask]
(714) 247-8318

-----Original Message-----
From: The Pharmaceutical Microbiology Forum Email List
[mailto:[log in to unmask]] On Behalf Of Ambrus, Kate
Sent: Monday, May 08, 2006 9:44 AM
To: [log in to unmask]
Subject: Re: [PMFLIST] Preservative testing

I would fail the first product, because 0.45 technically does not round
off to 1. It rounds off to 0.5 only if you are rounding to one decimal
place. But since you are rounding off to zero decimal places, it rounds
off to 0 (if in doubt - check in EXCEL). I am not a mathematician, but I
think it has something to do with the number of rounding off steps you
are allowed to make (one only). If you had obtained a log drop of 0.5 to
begin with, then I would round it up to 1 and pass it (although with
some reservations).

The results in B seem misleading. We always calculate log-drops on the
raw data, and then round off the final results. That is we do not round
off the plate counts - only the resulting log-drops. Your actual
log-drop was 1.23, which does not round up to 2 - as Example 2 would
seem to suggest.

Kate S. Ambrus
Manager, Eye Care R&D Microbiology
Advanced Medical Optics
[log in to unmask]
(714) 247-8318

-----Original Message-----
From: The Pharmaceutical Microbiology Forum Email List
[mailto:[log in to unmask]] On Behalf Of
[log in to unmask]
Sent: Sunday, May 07, 2006 7:15 PM
To: [log in to unmask]
Subject: [PMFLIST] Preservative testing

Can members of the forum offer their opinion on how to evaluate a
preservative efficacy result.

Given that the Ph.Eur states in the General Notices for Limits:

"In determining compliance with a numerical limit the calculated result
of
a test or assay is first rounded to the number of significant figures
stated, unless otherwise prescribed.
The last figure is increased by one when the part rejected is equal or
exceeds one half unit, whereas it is not modified when the part rejected
is
less than one half unit."

Consider the following example being a result for an oral product
challenged with A.niger where the requirement is for a log reduction in
the
viable count of log 1 at 14 days with no increase thereafter:
(Note: the log reduction is stated as 1 not 1.0)

Example A
                  Challenge   14 Days           28 days
Count/ml          480,000           170,000           28,000
Log (2 sig figures)     5.68        5.23        4.45
Log reduction           -           0.45        1.23

Example B
                  Challenge   14 Days           28 Days
Count/ml          480,000           170,000           28,000
Log (rounded)           6           5           4
Log reduction           -           1           2

Example A fails as a log 1 reduction is not achieved at 14 days.
Example B passes as a log 1 reduction is achieved at 14 days.

In this actual result if we apply the limit as defined in the Ph. Eur a
pass is achieved. In trying to apply greater accuracy with the use of
log
values to 2 decimal places a fail is achieved. Which result would you
accept?

Brendan Lincoln
Microbiologist
Pacific Pharmaceuticals Ltd


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The PMFList (http://microbiol.org/PMFList_info.htm) is operated from
The Microbiology Network (http://microbiol.org) and supported by
our sponsors (http://microbiol.org/sponsor.htm) as a service to
the scientific community.

Please take a second to visit our sponsors' web sites and say thank you
for their support of this service.

Accugenix - http://www.accugenix.com

American Type Culture Collection - http://www.atcc.org

ATS Laboratories - http://www.ats-labs.com

Biolog - http://www.biolog.com

Biomerieux - http://industry.biomerieux-usa.com

Dupont Qualicon - http://www.qualicon.com

EMD Chemicals - http://www.emdchemicals.com

EMSL Analytical, Inc. - http://www.emsl.com

Genomic Profiling Systems, Inc. - http://www.genprosys.com

MIDI, Inc. - http://www.midi-inc.com

Millipore - http://www.millipore.com

Pall - http://www.pall.com

NovaTek International - http://www.ntint.com

Raven Biological Labs - http://www.ravenlabs.com

Veltek Associates, Inc - http://www.sterile.com

=================================
The nature of this service is to provide a medium for communication.
The specific statements and endorsements of individuals participating in
the discussions are not necessarily those of The Microbiology Network,
Inc., the PMF, or the sponsors of the list.


------------------
The PMFList (http://microbiol.org/PMFList_info.htm) is operated from
The Microbiology Network (http://microbiol.org) and supported by
our sponsors (http://microbiol.org/sponsor.htm) as a service to
the scientific community.

Please take a second to visit our sponsors' web sites and say thank you for their support of this service.

Accugenix - http://www.accugenix.com

American Type Culture Collection - http://www.atcc.org

ATS Laboratories - http://www.ats-labs.com

Biolog - http://www.biolog.com

Biomerieux - http://industry.biomerieux-usa.com

Dupont Qualicon - http://www.qualicon.com

EMD Chemicals - http://www.emdchemicals.com

EMSL Analytical, Inc. - http://www.emsl.com

Genomic Profiling Systems, Inc. - http://www.genprosys.com

MIDI, Inc. - http://www.midi-inc.com

Millipore - http://www.millipore.com

Pall - http://www.pall.com

NovaTek International - http://www.ntint.com

Raven Biological Labs - http://www.ravenlabs.com

Veltek Associates, Inc - http://www.sterile.com

=================================
The nature of this service is to provide a medium for communication.  The specific statements and endorsements of individuals participating in the discussions are not necessarily those of The Microbiology Network, Inc., the PMF, or the sponsors of the list.

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