Studies On The Doxycycline Hydrochloride Sustain-released Injection And Pharmacokinetics Of Doxycycline In Swine

Doxycycline(DOX) belongs to the family of Tetracyclines ,it is a broad-spectrum antimicrobial drug and has a spectrum of activity against lots of pathogens,such as gram-positive and gram-negative bacteria organisms, sprirochetes, rickettsias, Mycoplasmas, chlamydias, coccidians, amebic protozoa.Several doxycycline hydrochloride sustain-released injections were made by dissolving doxycycline hydrochloride after adding the retardant in this study.After the optimization of the best formula,a doxycycline hydrochloride sustain-released injections has been developed successfully.Stability and pharmacokinetics of this preparation were also studied in the paper.Stable life prediction for doxycycline hydrochloride sustain-released injections was carried out by permanent stability test and the content of doxycycline was detected by HPLC-UV. According to"the technological specification of stability test for veterinary drug (trial performance)", the thermal stress test(6 months,according to Jees-Davis method), light accelerater tests and long-term stability tests of doxycycline hydrochloride sustain-released injections were carried out. After the samples had been kept under ambient condition, illumination (4500±500)Lx for 6 months,, and temperature (25±2)℃for 10 days, relative humidity (60±5)% for 18 months, Their appearance character, doxycycline content and pH were investigated.At the end of the test, except for color,all programs such as pellucidity, pH and decomposed product had no significant changes,the content of the preparation is consistented with the quality standard.The experimental results indicated that the preparation had good stability.We suggest that the period of validity about the injection could be temporarily determined at 2 years at room temperature.The pharmacokinetics of Doxycycline was investigated in 6 healthy pigs in a latine square desigh following single intravenous ,intramuscular administration of doxycycline hydrochloride injection and single intramuscular administration of doxycycline hydrochloride sustain-released injection,each administration is at a dose of 20mg·kg-1 body weight. Plasma samples were treated by 0.1M Na2EDTA-MacIlvaine buffer and 20% perchloric acid. Doxycycline concentration in plasma was determined by a HPLC.The HPLC equipped with a constant-flow pump was used ,together with a variable-wave-length UV detector operated at 365 nm.The separation was performed on C18 ( 5μm ,4.6mm×250mm I.D., Agilent ) with 0.01M aqueous oxalic acid solution-acetonitrile-methanol(60:25:15,v/v/v)as the mobile phase at a flow-rate of 1mL·min-1 at room temperature,and a 100μL sample was injected into the HPLC system .The HPLC method was established for determination of Doxycycline in swine plasma.A good linear relationship was obtained for DOX concentration from 0.10 to 12.80μg·mL-1 with r=0.9997, the limits of detection(LOD) and the limits of quantitation(LOQ) were 0.05μg·mL-1 and 0.1μg·mL-1 for Doxycycline in plasma,respectively;The mean relative recoveries of the plasma samples added doxycycline to 0.1, 0. 8 and 12.8μg·mL-1 were 93.4±3.2%,97.4±2.2% and 99.2±1.8% with coefficient of variation of 3.1%,1.9% and 1.9% in Intra-day precision and 7.3%,6.2% and 4.2% in Inter-day precision,respectively. This method offered a rapid, repeatable and accurate procedure and can be used to determine the concentration of doxycycline in swine lasma . The plasma concentration-time data derived from experiments were analyzed by non-compartmental method based on statistical moment theory.The main pharmacokinetic parameters after intravenous administration were as follows: AUC 108.15±13.25μg·h·mL-1,MRT 5.56±1.08h,Cl 187.19±22.21mL·h-1·kg-1,Vd(ss) 1.04±0.09 L·kg-1,t1/2 4.07±0.65h;The main pharmacokinetic parameters of the doxycycline hydrochloride injection and the doxycycline hydrochloride sustain- released injection administration were as follows,respectively: MRT 15.18±2.13h and 22.25±3.49h;Tmax 1.13±0.44h and 2.0±0.63h;Cmax 3.32±0.33μg·mL-1 and 3.097±0.291μg·mL-1;AUC 38.91±4.35 and 61.72±10.16μg·h·mL-1;F 36.66±7.88% and 57.66±10.75%.Compared with the doxycycline hydrochloride injection ,the Tmax of doxycycline hydrochloride sustain-released injections was delay about 0.87h,Cmax was reduced 0.25μg·mL-1, t1/2 was delay about 5.16h,and bioavailability was increased 57.28%.The experimental results showed that the doxycycline hydrochloride sustain-released injection had significant slow-released efficancy.In conclusion ,the doxycycline hydrochloride sustain-released injection had good stability,high bioavaibility,long active time and strong slow-released efficancy.Its successful development can provide a new formulation for veterinary clinical use of DOX.