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Dear all,
I am curious if anyone has any PK or PD information on
Guaifenesin? Does this expectorant act locally (gastric irritation &
reflexes ) or systemically, or both? Any info on this drug would be
highly appreciated. Thank you in advance. Val.
Harley07.-at-.istar.ca
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I believe that the mechanism has not been elucidated. In addition, I do
not believe that the clinical efficacy has been studied, especially not
with respect to the current scientific standards - this is a fairly old
drug. Even if efficacy was acheived, I don't think that it is unproven
whether expectoration has an impact on outcome. Water is probably a better
expectorant in clinical terms.
Best regards,
E. Migoya, PharmD
Novartis Pharmaceuticals
[I also like it (H20) as a mild cough suppresant - useless when trying to
sleep though ;-)].
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Sorry I don't have any answers to this - only another question. I am
interest in this as well. I thought that ipecac syrup worked as an
expectorant by a GI irritation-reflex action - true? I also wondered
whether the asthma associated with severe GERD (gastro-esophageal refux
disease) might be due to a similar mechanism (ie. irritation-reflex)? I
think the more common explanation is aspiration pneumonitis caused by an
incompetent esophageal sphincter.
Any response?
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Dear All,
Guaifenesin is not locally acting. It is a centrally-acting skeletal muscle
relaxant that selectively depresses or blocks nerve impulse transmission at
the internuncial neuron level of the spinal cord, brainstem, and subcortical
areas of the brain. It has been used in horses (since 1949) as an adjunct to
pre-anesthetic agents and barbiturates. It does not, however, depress
intercostal or diaphragmatic activity, as other peripheral-acting skeletal
muscle relaxants. If used alone, the IV dose is .-a-. 110 mg/kg and will produce
recumbency within minutes, and a light, surgical plane of anesthesia will last
~ 6 minutes. It is better to pre-med with a phenothiazine first though. When
used alone, a higher average respiratory rate and a lower, balanced pulse is
also seen, if followed by halothane. Other combinations do exist, and I would
suggest looking in the veterinary literature for more info.
Sincerely,
Russell Higbee, MS, PhD, DVM
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Hi,
I think you need to keep in mind what kind of doses are used for different
applications. In doses used in humans (100-400mg every four hours, not to
exceed 2400mg/day), I am not able to find any reference that suggests any
muscle relaxant effects or nerve impulse transmission blockage whatsoever.
Even at the 1200mg/day prescription strength (1200mg twice daily) you are
far from the 110mg/kg cited for veterinary use, and of course don't have
nearly the bioavailability of the IV form.
The most current reference I have (Facts & Comparisons, 1997) states that
guaifenesin, in humans, is claimed to "enhance the output of respiratory
tract fluid by reducing adhesivenesss and surface tension, facilitating the
removal of viscous mucus." However, "there is a lack of convincing studies
to document efficacy". Since the drug in not inhaled, this would have to
be a systemic effect (at least I've never heard of an inhaled form of the
drug).
Besides that I have some chemical information, but am not able to find any
kinetic information.
Bob Meyer, RPh
rjmeyer.at.globaldialog.com
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To all,
An excellent review of the historical development of medical uses of
guaifenesin has been written by K. A. Funk (1970) Equine Vet. J. 2:173. I
would suggest starting there for a more complete background. Also see Funk
(1973) Equine Vet. J. 5:15; Pedersoli (1972) Auburn Vet 29:6
Kinetic of disappearance of guaifenesin from plasma in the pony have been
studied by Davis and Wolff (1970) Am. J. Vet. Res. 31:469. Interestingly,
there seems to be a sex-related difference in the rate of clearance. Females
clear at a T1/2 of 59.6 plus or minus 4.8 min, whereas male ponies clear at a
T1/2 of 84.4 +/- 7.9 min. < I dunno.....??> This is the only kinetic study
that I'm aware of, but there may be more.
Russell Higbee, MS, PhD, DVM
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Copyright 1995-2010 David W. A. Bourne (david@boomer.org)