Studies Of Pharmacokinetics And Residues Of Doxycycline Hydrochloride After Intramuscular Injection In Pigs

High performance liquid chromatorgraphic method (HPLC) to detect Doxycyclinehydrochloride in pigs plasma and tissues were developed, pharmacokinetics and tissueresidues of Doxycycline hydrochloride were investigated, following intramuscularinjection at dose of 2.5 mg/kg body weight (b.w) in healthy pigs(n=6).chromatographyseparation was achieved on a Agilent Zorbax TC-C18 column using a mixature ofacetonitrile, methanol and 0.01M oxalic acid(v/v 20: 10: 70) as the mobile phase,thedetection wavelength is 350 nm and mobile speed is 0.8 ml/min. The Doxycyclinehydrochloride was extracted by by McIlvaine buffer from plasma and tissues. Thesupernatant was added 5% perchlorate to remove protein,and 60μl samples were injectedin high performance liquid chromatography to analyses after clean-up procedure bySPE HLB Oasis cartridge. Their linearity are all good over the concentration range(0.05～12.8μg/g) in plasma and tissues,The calibration of doxycycline hydrochloride andCorrelation coefficient(R) in plasma, muscle, liver, kidney, skin and fat were Y=0.0078X-0.0682(R=0.9999), Y=0.0042X-0.0291(R=0.9998), Y=0.0064X-0.0250(R=0.9997),Y=0.0060X-0.0276(R=0.9997), Y=0.0028X-0.0252(R=0.9999), respectively. Themean recoveries for all samples were all exceed 69.4%,Intra-day CV and inter-day CV areunder 5.90% and 9.60% respectively. The limits of detection (LOD) were 0.025μg/ml,0.0125μ/g in plasam, in tissues respectively. The limit of quatition (LOQ) were 0.05μg/ml, 0.025μg/g in plasam,in tissue respectively. Both can satisfy the need of theresidual detection.The kinetics of Doxycycline Hydrochloride had been fit to one compartment modelwith first order absorption after intramuscular injection at dose of 2.5 mg/kg body weight(b.w) in pigs. The main parameters were as follows: the half-lives of absorption (t_{1/2 ka})and elimination (t_{1/2 ke}) were0.400±0.312 h, and 9.530±0.956 h respectively, area underthe plasma drug concentration-time curve from 0 to∞(AUC) was 44.414±4.123μg.h/ml, the peak plasma concentration (C_max) was 2.811±0.136μg/ml, peaking at 1.910±0.213 h (T_pn)after dosing. Moreover, each healthy pig was administered DoxycyclineHydrochloride i.m. once a day at dose of 2.5 mg/kg body weight (b.w) for four days (n=6).The tissue residues of Doxycycline Hydrochloride were determined in muscle, liver,kidney, skin and fat. Tissue residues of Doxycycline Hydrochloride was to be lower to themaximum residue limit (MRL) after 16 days. The results indicated that the elimination ofDoxycycline Hydrochloride in tissue was slow. It is proposed that withdrawal periodshould be not less than 16 days after an intramuscular injection at a dose of 2.5 mg/kgb.w.