Samar Elgammal

The present investigation was conducted to compare bile and serum concentrations of doxycycline
(DOX) in turkeys after single intramuscular (IM) and oral administrations of 20 mg/kg body weight (b.w.).
Furthermore, the entero-hepatic circulation and absolute bioavailability from gastrointestinal tract of DOX
after oral dose were accessed. Three groups of male turkeys of five each received DOX at a dose rate of 20
mg/kg b.w. intravenously, intramuscularly and orally. Samples of serum and bile excreted were taken at
predetermined intervals during 6 h. DOX concentrations of were determined by a reverse phase high-
performance liquid chromatography (HPLC) with UV detection at 347 nm. After intravenous (IV) injection
the elimination half-life (T1/2), the total body clearance (Cltot) and the volume of distribution (Vss) were
3.90 h, 0.55 L/h/kg and 2.39 L/kg, respectively. The maximal serum concentrations (Cmax) of DOX in
turkeys were 4.38 and 3.17 µg/ml, with time to peak concentration (Tmax) values of 0.74 and 1.00 h and
absolute bioavailability were 71.83 % and 48.81 %, after IM and oral administrations respectively. The bile
concentrations were up to 100 times higher than those in serum. The cumulative biliary excretion of the
administered dose DOX was about 7% and 3% recovered from the bile within the first 6 hr after IM and
oral dosing, respectively. After oral dose the entero-hepatic circulation model is based on the classical one
compartment model with bile elimination half-life (T1/2k1g) of 5.36 h and the maximal bile concentrations
(Cmax) was 222.39 µg/ml. Therefore DOX could be relevant for treatment of cholecyctitis and enteric
infectious diseases.

Background: The site of intramuscular (i.m.) injections can affect the serum and tissue concentration profiles and so alter bioavailability of drug. The variation in the pattern of absorption can be attributed to regional differences in blood flow to skeletal muscles. Materials and Methods: The pharmacokinetics and systemic bioavailability of gentamicin in broiler chickens were compared after single intravenous (i.v.) and intramuscular (i.m.) in two sites thigh and pectoral muscles injections of 5 mg kg-1 b.wt. Tissue residue profiles (kidney, liver, lung and muscles) of gentamicin were also compared after both sites of i.m. injections. The concentrations of gentamicin in serum and tissues were measured by microbiological assay using Bacillus subtilis ATCC 6633 as test organism. Results: Following i.v. injection, serum concentration-time curves were best described by a two compartment open model. The decline in serum drug concentration was bi-exponential with half-lives of (t1/2α) 0.09 h and (t1/2β) 2.25 h for distribution and elimination phases, respectively. After i.m. injections in thigh and pectoral muscles, serum concentrations were significantly lower in those injected gentamicin through thigh muscles. The peak serum concentrations of gentamicin (Cmax) were 32.44 and 39.34 μg mL-1 and were obtained at 0.44 and 0.42 h (Tmax), respectively and the elimination half-lives (t1/2el) were 1.74 and 2.39 h, respectively. The systemic i.m. bioavailabilities were 83 and 105.20%, after thigh and pectoral muscles injections, respectively. In vitro protein binding percent of gentamicin was 3.4%. The tissue levels following i.m. injections in thigh and pectorals muscles were highest in kidney, liver and decreased in the following order: Serum, lung and muscle. No gentamicin residues were detected in tissues and serum after 12 h with both routes of administration, gentamicin was found in both the liver and kidney after 48 h. Conclusion: This study recommend that injectable antibiotics should be injected in pectoral muscles in poultry farms to achieve high efficacy and avoid rapid elimination by renal portal system.