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Hi,
I'm working with a compound that results in an acute toxicity upon IV
bolus injection. It has been decided that one of the screening
criteria for new compounds is a quick assesment of this acute
reaction in mice. The original compound is water soluble but the
first variant is not, at least to the extent I desire for injection.
What recommendation would people have for dealing with this? I would
like to come up with a standard screening protocol that does not
involve looking for novel excipients that may change the kinetics or
extent of toxicity for each variant. It has been suggested that I
simply dilute each compound to my desired concentration in water and
then filter thru a 0.45 micron any particulate matter. I have
problems with this because I will never be sure of the exact dose,
although I assume I could quantitate the filtrate by LCMS, but that
requires some additional work too. I know people on this board have
discussed the pros and cons of injecting in straight DMSO, but I'm
not sure if that is the answer either. Any advice or suggestions
would be greatly appreciated - especially information about how this
is routinely dealt with in the industry, if at all.
Thanks so much,
Noelle
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The following message was posted to: PharmPK
Hi Noelle,
it's always a pleasure to answer your questions.
As you anticipate the solubilization/filtration process is not
suitable for PK studies where you should ensure that you deliver the
right dose.
DMSO is definitely not the right answer too as it shows intrinsic
toxicity.
I used to assess the feasibility of cyclodextrin formulations in tox
studies when I was supplying toxicologists with drug formulations. As
compared to other "standard" excipients this is a roughly inert one
with good solubilizing properties if you take into account the
complexation issues.
I hope this helps,
best regards,
Frederic Doc
www.acriter-consulting.com
ex-Pfizer formulation scientist
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The following message was posted to: PharmPK
Dear Noelle,
I can't answer all your questions but we always check all our solutions
spectrophotometrically against a reference spectrum before we administer
to animals. This provides both a qualitative & quantitative check.
Obviously, you'll need a chromophore in your molecules.
I hope you don't mind me asking but are you planning to measure plasma
concentrations? Because without knowing the concentrations in the
central compartment (internal dose, if you like) your screening approach
will be fatally flawed IMHO.
HTH
Frederik Pruijn
Frederik B. Pruijn PhD MSc (Senior Research Fellow)
Experimental Oncology Group
Auckland Cancer Society Research Centre
Faculty of Medical and Health Sciences
The University of Auckland
Private Bag 92019
Auckland
New Zealand
Phone: +64-9-3737 599 x86939 or x86090
Fax: +64-9-3737 571
E-mail: f.pruijn.-a-.auckland.ac.nz
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The following message was posted to: PharmPK
Dear Noelle,
You could try 10% DMSO in buffer or in combination with PEG300 or
PEG400.
With 10% DMSO hemolysis is acceptable (final concentration in blood
approx. 0.5%). An alternative is the infusion of a small amount of 100%
DMSO for several minutes to prevent precipitation and other toxic
effects,
but the concentration of your compound should be as low as possible.
Almost
all formulations will show an influence on PK (as a function of
concentration used). You must find an acceptable compromise.
Kind regards
Thomas
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Dear Thomas,
I am concerned that such a formulation is likely to show massive
precipitation at the injection site, isn't it ?
Does it really work as a standard way to dose animals ?
Best reagrds,
Frederic
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Hi
Some questions to start with: what is the nature of the acute
toxicity; what is the molar concentration, pH and osmolarity of the
formulation of the original compound? Is there any solvent of
crystallisation in the compound as provided?
The blood buffers can usually cope with some deviation from pH 7.4
provided the concentration is not too high. Osmolarity below 300
milliosmoles is bad news but quite high values can be tolerated.
As a toxicologist - iv DMSO is to be avoided if at all possible!
Even if the animal tolerates it, it will obscure the presentation of
toxic signs due to your compound. PEGs 300 or 400 are OK and can be
admixed with PG or ethanol, but my favourite is hydroxy-propyl beta
cyclodextrin. Or you could ask you chemist to make more water-
soluble compounds.
When it comes to comparing toxicity, try to ensure this is undertaken
at comparable exposures rather than comparable doses. Many compounds
thought not to be toxic after oral dosing are just not absorbed! As
you are dosing iv. a couple of blood samples, say at 30 mins and 90
mins will give you some idea of the blood concentration vs time profile.
Hope this helps
Ian
Ian Smith
Independent Consultant in Preclinical Safety
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Dear Frederic,
we have seen no sign of precipitation with this approach. There will
be no
standard protocol to dose aninmals, but this approach is a good starting
point. In the past, we had compounds like a rock and it worked.
Regards
Thomas
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The following message was posted to: PharmPK
Dear Noelle,
I suggest the combination of DMSO and cyclodextrin for
solubilization. DMSO solubilized compounds precipitates
upon dilution, try to dilute with aqueous cyclodextrin or
buffered cyclodextrin solution with different CD
concentrations. The drug precipitation can be sustained or
even prevented. I still stress the application of
methylated cyclodextrin derivatives, DIMEB or RAMEB in case
of rock-like compounds, they prooved to be more effective
than the other CD-s. DMSO concentration can be reduced
below 5 % while maintaining the compound in solution at a
relatively high concentration. You can calculate the dose
and need not quantitation in case of clear solutions at
the starting phase.
I think it is not surely you are looking for, but it might
be useful in some cases.
Best regards, Maria Vikmon
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