COMPARISON IN PRESCRIBING-PATTERNS OF ANTIBACTERIAL DRUGS IN SALMONIDFARMING IN NORWAY DURING THE PERIODS 1980-1988 AND 1989-1994 (REPRINTED FROM DEN-NORSKE-VETERINOERFORENING, VOL 106, PG 711-721, 1994)

The choice of antibacterial drugs for the treatment of bacterial disea ses in farmed salmonids changed dramatically during the period 1980-19 94. In terms of treatment doses, oxytetracycline chloride was the most frequently prescribed antibacterial drug during the periods 1980-1983 and 1985-1986. In 1984, prescriptions changed in favour of furazolido ne and trimethoprim/sulphadiazine (1:5). Oxolinic acid was introduced for use in farmed fish in Norway in 1987, and immediately became the d rug of choice, comprising 36% and 50% of the prescribed treatment dose s in 1987 and 1988, respectively. In 1989, flumequine was temporarily approved for use in farmed salmonids, and during the period 1989-1994 antibacterial drug therapy in farmed salmonids acquired the character of a 'mono-therapy' with the quinolones flumequine and oxolinic acid, This rapid change-over in the choice of drug may partly be explained b y the development of bacterial drug resistance in farmed salmonids, bo th to oxytetracycline and trimethoprim/sulphadiazine, The prescribing of furazolidone declined to zero during the study period. The morbidit y caused by bacterial infections was defined as the number of treatmen t doses of antibacterial drugs per kg biomass of farmed salmonids per year. It was estimated that during the period 1988-1995, an average of 39% (mean value) of farmed salmon received, in theory, an antibacteri al cure once each year, In comparison, the corresponding figure for th e period 1981-1988 was 60%. However, in 1993 this figure fell to 13%, and declined even further in 1994 to 2.3%, The practice of on-farm mix ing of medicated feed, using prescribed raw materials (pure drug subst ances) or premix formulations, declined significantly during the perio d 1992-1994. This was due to the introduction, in 1992, of new regulat ions on the prescribing of drugs to farmed fish.