Mycoplasma synoviae (MS) and Mycoplasma gallisepticum (MG) are two of the most serious infections in poultry, causing financial losses across the globe. Antibiotics treatment can lessen the clinical signs of MG and MS infection in birds and help restrict the spread of these infections. However, the rise of antibiotics multidrug resistance (MDR) among poultry diseases is still a problem for the world's health. Minimum inhibitory concentration (MIC) is crucial to resolving this issue since it helps ensure correct antibiotic use and fights the development of antibiotic resistance. This investigation aims to assess the in vitro and in vivo efficacy of several antibiotics (tilmicosin, tylosin, erythromycin, spiramycin, lincomycin, and doxycycline) against MG and MS field isolates, in addition to guava leaves extract (GLE) against MG. For in vivo study, 510, one day old chicks were randomly split into 17 groups the birds were experimentally infected at 3 days old and supplied with different treatments in drinking waters for 5 successive days at 18 days old. The results of in vitro study showed that tilmicosin was the most effective against MG isolates with MIC values ranging from 0.0078 to 0.0156 μg/ml and spiramycin considered effective against MS with MIC values ranging from 0.015625 to16μg/ml and MIC value of GLE was 0.25 μg/ml that was considered as moderate sensitive to MG infection. The in vivo study revealed that tilmicosin and spiramycin were able to significantly lower the clinical score, lesion score, and re-isolation rate of MG and MS, respectively in the treated birds at p-value < 0.05 in contrast with control positive infected untreated groups. Additionally, the treated groups with tilmicosin in MG infection and spiramycin in MS infection showed significantly higher mean body weights (MBW) compared to the infected untreated ones at p-value < 0.05. The current study demonstrates that MG and MS's sensitivity to many of the most popular drugs changed as in tylosin become low sensitive and erythromycin become resistant. GLE has moderate sensitivity antibacterial effect against MG isolates both in vivo and in vitro and can be used as a natural antibiotic alternative. Therefore, we recommend periodical monitoring of the sensitivity of the circulation MG and MS strains using MIC test to overcome MDR of avian mycoplasmas with further suggestion to evaluate GLE as nano-preparation against MG infection.

Pharmacokinetic determinants of spiramycin and its distribution into the respiratory tract were studied in 2 groups of calves, 4 to 10 weeks old. Group-A calves (n = 4) were used to determine pharmacokinetic variables of spiramycin after IV (15 and 30 mg/kg of body weight) and oral administrations of the drug (30 mg/kg) and to measure distribution of spiramycin into nasal and bronchial secretions. Group-B calves (n = 4) were used to determine distribution of spiramycin into lung tissue and bronchial mucosa. Spiramycin disposition was best described by use of an open 3-compartment model. Mean (+/- SD) elimination half-life was 28.7 +/- 12.3 hours, and steady-state volume of distribution was 23.5 +/- 6.0 L/kg. Bioavailability after oral administration was 4 +/- 3%. High and persistent concentrations of spiramycin were achieved in the respiratory tract tissues and fluids. Tissue-to-plasma concentration ratio was 58 for lung tissue and 18 for bronchial mucosa at 3 hours after spiramycin administration and 137 and 49, respectively at 24 hours. Secretion-toplasma concentration ratio was 4 for nasal secretions and 7 for bronchial secretions, and remained almost constant with time. Thus, spiramycin penetrates well into the respiratory tract, although the value in bronchial secretions is lower than that in lung tissues and bronchial mucosa. Calculations indicate that a loading dose of 45 mg/kg, administered IV, followed by a maintenance dose of 20 mg/kg, IV, once daily is required to maintain active concentrations of spiramycin against bovine pathogens in bronchial secretions.

Impaired abomasal motility is common in cattle with abomasal disorders. The macrolide erythromycin has been demonstrated to be an effective prokinetic agent in healthy calves and in adult cattle with abomasal volvulus or left displaced abomasum. We hypothesized that 2 structurally related macrolides, spiramycin and tulathromycin, would also be effective prokinetic agents in cattle. Six milk-fed, male, Holstein-Friesian calves were administered each of the following 4 treatments: spiramycin, 75 000 IU/kg BW, IM, this dose approximates 25 mg/kg BW, IM; tulathromycin, 2.5 mg/kg BW, SC; 2 mL of 0.9% NaCl (negative control); and erythromycin, 8.8 mg/kg BW, IM (positive control). Calves were fed 2 L of cow's milk containing acetaminophen (50 mg/kg body weight) 30 min after each treatment was administered and jugular venous blood samples were obtained periodically after the start of sucking. Abomasal emptying rate was assessed by the time to maximal plasma acetaminophen concentration. Spiramycin, tulathromycin, and the positive control erythromycin increased abomasal emptying rate compared to the negative control. We conclude that the labeled antimicrobial dose of spiramycin and tulathromycin increases the abomasal emptying rate in healthy milk-fed calves. Additional studies investigating whether spiramycin and tulathromycin exert a prokinetic effect in adult cattle with abomasal hypomotility appear indicated.