Abstract
Pharmacokinetics of oxytetracycline (OTC) were studied in 4 cows after administration of either a conventional (OTC-C) or a long-acting (OTC-LA) preparation. After intravenous administration of OTG-G the elimination half-life for OTG was found to be 6 h. Intramuscular injection of OTC-C and OTC-LA resulted in almost identical plasma concentrations of OTC with peak values after 6–8 h. For both preparations the bioavailability after i.m. administration was 100 % and about 60 % of the dose was excreted in the urine during the first week. Plasma concentrations above 0.5 μg/ml were with both preparations maintained for approximately 60 h, indicating no retard effect of OTC-LA as compared to OTC-C.
Key words: Oxytetracycline, pharmacokinetics, cattle
Sammendrag
Oxytetracyklin (OTC) findes som injektionsvaeske til veterinser brug i en konventionel (OTG-C) og en „long-acting” (OTÓLA) præparation. I den foreliggende undersøgelse er de to praeparater sam-menlignet i 12 forsøg på 4 køer.
Efter intravenøs injektion of OTG-G fandtes eliminationshalve-ringstiden for OTG til 6 timer og 55–60 % af den injicerede dosis blev udskilt med urinen i løbet af den første uge.
Intramuskulaer injektion af ens doser af OTG-G og OTC-LA resul-terede i naesten identiske plasmakoncentrationskurver med højeste koncentration efter 6–8 timer. Sammenlignet med de plasmavaBrdier, der opnåedes ved intravenøs injektion, fandtes biotilgængeligheden for begge præparater efter intramuskulaer administration at vaere ca. 100 %, og ca. 60 % af dosis kunne genfindes i urinen.
Plasmakoncentrationer over 0.5 μg/ml kunne for så vel OTG-G som OTG-LA opretholdes i ca. 60 timer efter en intramuskulaer injektion af 20 mg/kg lgv.
Da der således ikke kunne påvises en forlaenget virkningstid for OTG-LA siammenlignet med OTC-C, og da det i andre unders0gelser er vist, at OTG-LA fremkalder betydelig mere vaevsbeskadigelse på injektionsstedet end OTC-G, må det konkluderes, at hos kvæg frem-byder OTG-LA ingen fordele i forhold til OTC-C.
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