Chlortetracycline chemical review

In 1995, the APVMA (formerly the NRA) began a review of chlortetracycline use in the pig industry because of residue concerns. This followed advice by the Queensland and Victorian departments of primary industries that chlortetracycline residues above the maximum residue limits (MRLs) had been found in pig offal and meat.

The APVMA began a review of chlortetracycline use in the pig industry because of toxicological concerns about residues in pork products. The APVMA then expanded the review to consider the use of chlortetracycline in all food-producing animals and in milk.

In June 1995, the APVMA released an interim report, Ad hoc review into the use of chlortetracycline in pigs. The report (which is available from the APVMA) identified off-label use of chlortetracycline for extended periods of treatment as the major contributing factor in the residue violations. A change in testing methods in the second half of 1993 was also identified as a possible contributor to the sudden increase in the detection of residue violations.

The interim report proposed increasing the Australian MRL from 0.05 ppm to 0.60 ppm in pig offal (kidney) to more closely align with the MRLs of the European Union, the United States and the Codex Alimentarius Commission.

At the start of the review, the use of chlortetracycline in cattle and sheep was not supported due to a lack of data and the uses were withdrawn. Temporary MRLs were set for sheep and cattle to allow the sale of existing stocks. The temporary MRLs were to expire on 31 December 1998.

During the data evaluation, the APVMA investigated not only residues in pigs but also residue-related aspects of all use patterns of chlortetracycline in commodities. Subsequently, the APVMA released the Draft review of chlortetracycline for public comment in November 1998 (the draft is available from the APVMA).

The APVMA re-examined the use of chlortetracycline in cattle and found that the existing MRLs for cattle were now supported by adequate data. The APVMA proposed confirming them as full MRLs.

The APVMA further proposed ceasing the uses of chlortetracycline in sheep, lambs and lactating animals as there were insufficient data to support them. The use of chlortetracycline in animals producing milk for human consumption was also not supported.

The APVMA completed the Chlortetracycline review final report in May 1999 but did not publish it because only a small number of registrants were involved (the report is available from the APVMA). The APVMA found that the registration and approvals of the products containing chlortetracycline could be varied to meet the current requirements for continued registration.

In the final review, the APVMA recommended:

• cancelling approval for the use of chlortetracycline in sheep, lambs and lactating animals
• cancelling approval for the use of chlortetracycline in animals producing milk for human consumption (product labels must carry the statement, ‘Do not use in lactating cows where milk or milk products may be used for human consumption.’)
• increasing withholding periods for pigs, poultry, and cattle for some use patterns
• withdrawing MRLs for milk, sheep, lambs and lactating animals
• establishing new MRLs for pig offal (liver and kidney)
• establishing MRLs for cattle, eggs and poultry.

Chlortetracycline as a topical application is currently listed in Table 5 of the MRL standard; Table 5 applies to ‘uses of substances where maximum residue limits are not necessary’.