A clue about ethidium toxicity

[Tom Anderson]

On Sun, 17 Jun 2007, Undergrad wrote:

> As you know ethidium (aka homidium) is also used as trypanocide in cattle,
> sheep, goat ect... No ADI (admitted daily intake) are available for ethidium
> however there is one for isometamidium which is a closely related to
> homidium and also intercalate in DNA. Also it was found that isometamidium
> is transform in homidium in the body (less thant
> 1%)(http://www.inchem.org/documents/jecfa/jecmono/v31je10.htm).
>
> The ADI of isometamidium is 0-100 microgramme/kg
> (http://66.102.9.104/search?q=cache:7ct_Z9QkXWwJ:www.ipfsaph.org/cds_static/en/jecfa_veterinary_drug_residue_isometamidium_en_cthttpwwwfaoorgaosipfsaphinformat
> ionsourcejecfa_JECFAEVAL57.html+isometamidium+who+adi&hl=en&ct=clnk&cd=1&gl=uk).
>
> So if isomethidium give rise to 0.1% of homidium, the proportionnal ADI
> of homidium could be : 0.1 microgramme par kg so 6 microgramme for a 60
> kg person.
>
> In this study, it is shown that isometamidium have a strongest toxic
> effect than homidium:
> http://www.inchem.org/documents/jecfa/jecmono/v25je10.htm

Excellent info. So, assuming that these numbers apply to people (not
entirely unreasonable, if the vets think they apply to both rats and
cows!), it would seem 6 ug/day (possibly more, given the
EtBr/isometamidium data) would be a safe therapeutic dose for a
normal-sized person; my EtBr stock is at 10 mg/ml, which means i could
drink 6 ul a day and expect to have no ill effects. I imagine splashing it
on the skin leads to far less efficient absorbtion (although possibly a
more powerful local effect).

tom

-- 
Tom Anderson, MRC Laboratory for Molecular Cell Biology, UCL, London WC1E 6BT
(t) +44 (20) 76797264   (f) +44 (20) 76797805   (e) thomas.anderson from ucl.ac.uk