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Thursday, 1 September 1994
Page: 865

(Question No. 1471)


Senator Bell asked the Minister for Primary Industries and Energy, upon notice, on 10 June 1994, with reference to the public release summary on clorsulon:

  (1) What reference can be cited to support the claim that `rapid depletion followed'.

  (2) On what basis is the statement made that `there was no evidence for any interaction between active ingredients', and what research was used to justify this assertion.

  (3) What guarantee can be given that a warning on the label not to administer `when milk or milk products are to be used for human consumption' will be followed.


Senator Collins —The answer to the honourable senator's question is as follows:

  (1) The results of two trials carried out by Merck, Sharp and Dohme using cattle were evaluated by the Chemical Safety Unit of the Department of Human Services and Health using an analytical method suitable for residue analysis of clorsulon in cattle meat and offal. The method has a limit of determination for unchanged clorsulon of 0.1 mg/kg, which is also the level set for the maximum residue limit. Both trials demonstrated that the level of clorsulon residues had fallen to below the level of analytical determination by 21 to 28 days after dosing.

  From those trials it was concluded that there was adequate data to support maximum residue limits of 0.1 mg/kg in both cattle meat and offal. The withholding period of 42 days is more than adequate for clorsulon given the above depletion rates.

  (2) Ivermectin and clorsulon have quite different modes of action and therefore different spectra of activity. From this it can be predicted that additive effects between these two therapeutic agents is unlikely. In studies of rodents and other species, clorsulon and ivermectin exhibit quite different patterns of toxic signs at greatly different dose levels.

  Toxicological studies as required by the National Registration Authority for Agricultural and Veterinary Chemicals (NRA) were carried out by Merck, Sharp and Dohme and assessed by the Chemical Safety Unit. These studies included acute toxicity, short-term repeat dose studies, sub-chronic studies, long term studies, as well as reproduction, developmental and genotoxicity studies.

  Those studies support the expectation from pharmacological and mode of action studies that ivermectin and clorsulon will not interact with each other. In acute toxicity testing on rodents, the toxicity of the formulation containing both compounds is similar in signs and dose level to that of ivermectin given alone. There was no evidence that the toxicity of either compound was affected by the concurrent administration of the other.

  (3) State control-of-use laws make it a criminal offence to administer Ivomec-Plus (ivermectin plus clorsulon) to cows within 28 days prior to calving or during lactation.

  For the purpose of detecting residues of clorsulon the maximum residue limit has been set at the minimum limit of analytical determination. Strict monitoring of residues in milk is undertaken by milk authorities, together with traceback procedures to the point of use if residue limits have been exceeded. Dairy farmers are aware of the consequences, including commercial consequences, in the event that residues of a chemical product are detected in the milk supplied by them.

  Technical details in respect of the above studies can be obtained from the NRA.