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Hello dear colleagues,
Has anyone ever heard that hard water could effect the outcome of a
tetracycline treatment? I got the question - if hard water could effect
the absorption of tetracyclines - from a Norwegian doctor who is working
in Albania. Locally they have very hard water. His letter didn't tell if
it really was a clinical problem. I am aware of the fact that there are
differences between the tetracyclines if it comes to the interaction
with polyvalent cations. What amounts of the different polyvalent
cations can affect tetracycline absorption?
Erik Pomp, DI-pharmacist, Norway
(PS! Norway-Brazil - 2-1)
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From: "Tata, Prasad"
To: "'PharmPK.aaa.pharm.cpb.uokhsc.edu'"
Subject: RE: PharmPK Hard water - tetracycline Interaction?
Date: Thu, 25 Jun 1998 10:43:17 -0400
MIME-Version: 1.0
Hard Water is known to have multi-valent metals which are known to form
complex with tetracyclines. Just check early reviews on Tetracylcine
Bioavailability reviews.
Prasad Tata
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Date: Fri, 26 Jun 1998 08:52:28 +0200
From: Hans Markus Bender
MIME-Version: 1.0
To: PharmPK.-at-.pharm.cpb.uokhsc.edu
CC: Multiple recipients of PharmPK - Sent by
Subject: Re: PharmPK Hard water - tetracycline Interaction?
X-Priority: 3 (Normal)
Dear Erik,
tetracyclines underly formation of complexes (chelates) with cations
with two or three valences. These complexes will not be absorbed. Since
hard water contains large concentrations of Ca++ and/or Mg++ it will
depress enteral absorption of tetracyclines in a quantity of clinical
relevance.
Best regards
Hans Markus Bender
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At the World Aquaculture meeting in February a couple of papers were
presented that indicated that more extensive bacterial resistance developed
to tetracyclines in seawater than in the freshwater tested. Since seawater
also contains multivalent metals, this could explain why greater resistance
developed in the seawater than in a freshwater (that may have been
relatively soft). The complex with the metals in the seawater probably
interferes with the stronger binding to clay or other particulate/sediment
matrix in the water. The binding to sediment/particulate would tend to
remove the tetracycline from the water and reduce bacterial exposure.
Without the strong binding there could be greater exposure of bacteria to a
reversibly complexed (bound) tetracycline. The individuals doing the
research on the effects of tetracycline useon microbial communities who
reported the resistance are Christin Forney, Beverly Dixon and Donald
Weston at California State University, Department of Biological Sciences,
Hayward, CA 94542.
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