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Long duration of antibiotic helps improve clinical outcome after APP challenge

3 May 2021, at 10:30am

Pigs treated with one intramuscular dose of Draxxin® (tulathromycin) and then challenged with a virulent strain of Actinobacillus pleuropneumoniae (APP) had significantly reduced mortality and lung lesions compared to untreated controls.1

Previous studies have shown that a single 2.5 mg/kg bodyweight dose of Draxxin is rapidly released from the injection site and reaches maximum plasma concentrations in less than 1 hour. The AUC was more than 61 times greater for the lung than for plasma. AUC stands for “area under the curve” and is a measure of the drug in plasma based on drug concentration and time.2 Draxxin is slowly released from lung tissue.3

“We wanted to confirm that the pharmacologic profile of Draxxin translates into an improved clinical outcome,” says Lucina Galina, DVM, PhD, director, swine technical services, Zoetis.

Study design

For the study, 240 clinically healthy female and castrated male pigs about 6 weeks of age were acclimated for 10 days. Investigators then randomly assigned the pigs into six groups.

One group was not treated and served as the control, and the remaining five groups received 2.5 mg/kg of bodyweight of Draxxin on assigned days before challenge (Table 1), Galina says.

APP was selected for the challenge because it’s one of the primary causes of swine respiratory disease (SRD). The strain used for the challenge, serotype 5, was highly virulent and administered intranasally, she explains.

Significant differences

Mortality was evaluated for pigs that received Draxxin 11, 9, 7, 5 or 3 days before challenge. Mortality in pigs treated 9, 7 and 5 days before challenge was 7.5% (3/40) in each of these groups, which was significantly lower compared to mortality among controls.

In pigs treated 3 days before challenge, mortality was only 2.5% (1/40) — again significantly lower compared to controls and compared to pigs treated 11 days before challenge (Figure 1), Galina continues.

The investigators also weighted the gross involvement of each lung lobe to come up with the percentage of “total lung with lesions.” They evaluated pigs treated with Draxxin 11, 9, 7, 5 and 3 days before challenge with APP. Pigs treated with Draxxin 5 or 3 days before challenge had significantly less weighted lung lesions compared to controls, she reports.

Longer exposure of bacteria

Draxxin is a macrolide antimicrobial developed exclusively for veterinary use. Macrolide efficacy depends on the length of time bacterial pathogens are exposed to an antimicrobial. The extended presence of Draxxin in the lungs — thought to be due to the slow rate at which it metabolizes — likely explains its long duration of efficacy, Galina says.

“The results of the challenge study clearly show that the pharmacologic profile of Draxxin translates into practical clinical benefits. When only one dose is needed, sick pigs need to be handled less often. Labor costs are reduced compared to treatments that require repeat dosing. In addition, the withdrawal requirement for Draxxin is only 5 days,” she says.

A special formulation of Draxxin for nursery pigs — Draxxin 25 — is also available, Galina notes.

“Improved clinical results, reduced labor costs and a short withdrawal time all translate into savings for producers,” she says.

Draxxin is approved for treatment of SRD associated with APP as well as Pasteurella multocida(PM), Bordetella bronchiseptica, Haemophilus parasuis and Mycoplasma hyopneumoniae(M. hyo) and for control of SRD associated with APP , PM and M. hyo in groups of pigs where SRD has been diagnosed.

Important Safety Information for Swine: Withdraw Draxxin/Draxxin 25 five (5) days prior to slaughter in swine. Do not use in animals known to be hypersensitive to the product. Click here to see prescribing information for Draxxin.

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References
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1 Waag TA, et al. Duration of effectiveness of tulathromycin injectable solution in an Actinobacillus pleuropneumoniae respiratory-disease challenge model in swine. J Swine Health and Prod. May and June 2008.
2 Benchaoui HA, et al. Pharmacokinetics and lung tissue concentrations of tulathromycin in swine. J Vet Pharmacol Ther. 2004;27:203-210.
3 Waag TA, et al. Duration of effectiveness of tulathromycin injectable solution in an Actinobacillus pleuropneumoniae respiratory-disease challenge model in swine. J Swine Health and Prod. May and June 2008.

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