Proposals for withdrawal period of sheep milk for some commonly used veterinary medicinal products: A review

This paper summarises the results of studies performed in Greece, in order to establish withdrawal time of sheep milk for some commonly used antimicrobial drugs. Several studies have been performed to establish milk withdrawal time for the following veterinary medicinal products, commonly used in the therapeutics of sheep: lincomycin, spectinomycin, procaine penicillin G, dihydrostreptomycin, kanamycin, oxytetracycline, trimethoprim and sulfadiazine, albendazole. For oxytetracycline, two pharmaceutical forms were tested, specifically long-acting injectable solution and spray. For albendazole, the pharmaceutical form of oral suspension was tested. For all the other antimicrobials, the pharmaceutical form of injectable solution was tested. The animal phase of all the trials was performed at the Veterinary Faculty of the University of Thessaly. Each product was administered at the highest recommended dose and the frequency currently licensed for administration to sheep. Subsequently, either liquid chromatography or liquid chromatography–mass spectrophotometry was used under GLP principles and as required each time, in order to establish residues of each antibiotic in milk. Most of the analytical work was carried out at GLP accredited laboratories. In each case, limit of detection and limit of quantification for each antibiotic tested were appropriately calculated. For calculation and proposal of a withdrawal period, the legally established minimum residue levels of each antibiotic and their concentrations detected in sheep milk were taken into account. The proposed withdrawal periods are as follows: lincomycin and spectinomycin inj. sol.: 4 milkings, procaine penicillin G and dihydrostreptomycin inj. sol.: 5 milkings, dihydrostreptomycin inj. sol.: 5 milkings, kanamycin inj. sol.: 4 milkings, oxytetracycline long-acting inj. sol.: 16 milkings, oxytetracycline spray: 0 milkings, trimethoprim and sulfadiazine inj. sol.: 7 milkings, albendazole or. susp.: 7 milkings after last administration of each test product. The above results provide standards and will help veterinarians to use the various veterinary pharmaceutical products in the therapeutics of dairy ewes.