>From their registration:

>ADVERSE REACTIONS Increased mortality in worker bees was very commonly observed in the clinical and preclinical trials following treatment with VarroMed. This effect is considered to be associated with the oxalic acid in VarroMed, and increased with increasing doses and/or repeated treatments.



An EU assessment report can be downloaded at: 

http://www.ema.europa.eu/ema/index.jsp?curl=pages/medicines/veterinary/medicines/002723/vet_med_000342.jsp&mid=WC0b01ac058001fa1c

or go to http://www.ema.europa.eu/ema/ , find medicine, veterinary medicines, european public assessment reports, varromed, assessment history, pdf file: VarroMed : EPAR - Public assessment report



Lots of interesting data here, including a divergent opinion about varromed from some of the experts. 







>Note that Varromed uses sucrose as the humectant/sticker.  The sugar encourages the bees to consume some of the acids, which then has adverse effects upon the bees.  Replacing the sugar with 40% glycerin in water appears to be promising, since bees do not find glycerin attractive to eat.



Another oxalic based drug has been EU approved: Oxybee. The same EU evaluation as for varromed can be found on the ema website. This formulation also has glycerin as excipient, but also uses sugar to prepare the final solution. 

This drug can only be used as single dose winter treatment, but also has worker bee mortality as side effect, mostly after higher doses than recommended in the SPC.



As a side note: LD50 values were calculated in each drug file:

- varromed: The estimated LD50 values are 195 µg OAD/bee in the fixed combination.

- oxybee: the LD50 of OAD by topical application in bees is approximately in the range of 530–550 µg/bee



Interestingly, the calculated LD50 of varromed is lower than for oxybee, but side effects (worker mortality) seem similar.



Best regards, 

Kris, 

Belgium



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