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The following message was posted to: PharmPK
All,
In planning for a PK experiment a CRO told me that they can only obtain
one blood sample from a guinea pig. They take this from the heart and
then sacrifice the animal. Is this common standard or can you obtain
several samples? If so how?
Thanks.
Jack
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Blood can be collected from either one of the metatarsal veins or from
the saphenous vein (if my memory serves me correctly; although this does
require practice and a high degree of skill). Also, consider a
cannulated (jugular vein) animal.
Sincerely,
Joe
--
Joseph V. Rutkowski, PhD, DABT
Sr. Director
Preclinical Pharmacology and Toxicology
Predix Pharmaceuticals
4 Maguire Road
Lexington, MA 02421
T: 781-372-3260 ext. 1078
F: 781-372-3267
jrutkowski.at.predixpharm.com
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Check the literature for orbital bleeding.
Stanley.Cotler.at.roche.com
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Jack
You may look into microdialysis probing for drug sampling
--
Luis M. Pereira, Ph.D.
Assistant Professor, Biopharmaceutics and Pharmacokinetics
Massachusetts College of Pharmacy and Health Sciences
179 Longwood Ave, Boston, MA 02115
Phone: (617) 732-2905
Fax: (617) 732-2228
Luis.Pereira.aaa.bos.mcphs.edu
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Thanks,
The drug we are sampling is a high molecular weight protein so I am
afraid
that microdialysis will not be working....
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Jack
Blood sampling volume to be collected also depends on the starting
sampling volume that your analytical method needs (according to
validation). If you need 500 uL plasma, then you might have to
collect 1 mL of blood, and therefore disabling several sampling
collection like it is common in clinical trials with human subjects.
As far as I know, animal trials generally use sets of 6-8 animals per
sampling time.
The following reference might help to clarify the issue:
Diehl KH, Hull R, Morton D, Pfister R, Rabemampianina Y, Smith D,
Vidal JM, van de Vorstenbosch C 2001. A good practice guide to the
administration of substances and removal of blood, including routes
and volumes. J Appl Toxicol 21(1):15-23.
Please let me know personally if you want me to send you the above
reference
Best regards
Nuno Silva
Faculty of Pharmacy, U.L.
Biopharmaceutics and Pharmacokinetics Dept.
Av. Prof. Gama Pinto
1649 003 Lisbon / Portugal
Tel: 21 7946473
Fax: 21 7946470
E-mail: nmens.aaa.ff.ul.pt
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The following message was posted to: PharmPK
Hi Nuno
Please just think about it. Especially with in vivo sampling you must
not choose your blood sample volume as a function of your analytical
method, but rather the other way around. In fact, the key issue is
not really the volume but instead the concentration of your analyte
versus your LOQ. If a regular GC or HPLC procedure is not good, we
need to look for a LC-MS or something better rather than immediately
thinking about getting more blood.
Cheers
Luis
--
Luis M. Pereira, Ph.D.
Assistant Professor, Biopharmaceutics and Pharmacokinetics
Massachusetts College of Pharmacy and Health Sciences
179 Longwood Ave, Boston, MA 02115
Phone: (617) 732-2905
Fax: (617) 732-2228
Luis.Pereira.-a-.bos.mcphs.edu
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The following message was posted to: PharmPK
Hi Jack:
While it is certainly easier to do a cardiac puncture, it is not the
only way. The one animal-per-timepoint approach necessitates a lot more
animals to deal with the interanimal variability. We've collected up to
24 samples (12 after each of 2 doses with a 24 hour washout in between
doses) from individual and freely-moving guinea pigs for drug-drug
interaction studies. These were females, 400-425 g, outbred Hartleys.
Each was cannulated with two catheters: one in the femoral artery and
the other in the jugular vein. Dosing was done automatically by
programmed delivery of one test article, followed 48 hours later by the
same test article in combination with another compound (in a common
vehicle)that competed for the same CYP. Dosing was done via the JV
catheter, while the FA catheter was connected to an automated blood
sampler.
In the 6 subject study, we collected 144 samples of heparinized whole
blood. Not more than 150 microliters was required per timepoint (~ 70 uL
plasma) due to the LCMSMS assay used. In the model that you mentioned,
it would have required at least 144 subjects. As a rule of thumb, you'd
expect to pay about 2x to 3x per subject vs. a rat study.
Surgical procedures to implant 2 catheters into guinea pigs are much
more difficult than rats (relatively easy) and similar to mice (quite
difficult), so it's not something to be attempted lightly. Nonetheless,
it is achievable if you're committed to guinea pigs as a model -- and
they are indeed good models for some diseases (e.g. the best rodent
model
for screening MAO inhibitors because like humans they have both the A
and B forms of the oxidase enzyme). Another consideration is that the
use of guinea pigs is governed by USDA licensure. While many shops can
use rats and mice (no license required yet), work in guinea pigs
requires a higher level of governance.
Candice Kissinger
BASi
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Hi Luis
I agree with you on this issue. Of course in vivo trials design
involving drug concentration analysis ideally should not depend on
the analytical method. Although, and according to my experience, in
practice sometimes blood volume is important, especially with low
dose, low bioavailability, high Vd drugs. For these cases,
concentration quantification can be tricky, even for MS-MS current
technology. For example, for drugs with Cmax around 500 pg/mL and
lower t1/2, developing an analytical method with a very low LOQ in
order to get a well define pk profile is not so simple as for a drug
with cmax around 1 ug/mL. For this situation, and for current HPLC/MS/
MS technology, increasing the sampling starting volume sometimes
helps a lot.
Maybe with nano HPLC technology this issue is not a problem, but I
don't have any experience with it. Maybe other group members could
share their experience.
Best regards
Nuno Silva
Faculty of Pharmacy, U.L.
Biopharmaceutics and Pharmacokinetics Dept.
Av. Prof. Gama Pinto
1649 003 Lisbon / Portugal
Tel: (+351) 217 946 406
Fax: (+351) 217 937 703
E-mail: nmens.-at-.ff.ul.pt
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