Tilmicosin as a single injection treatment for respiratory disease of feedlot cattle.

Tilmicosin, a new semi-synthetic macrolide antibiotic, was evaluated in eight field trials as a single subcutaneous injection at dosages of 0 (placebo), 5, 10 and 20 mg/kg for the treatment of naturally occurring respiratory disease in feedlot cattle. Animals for these trials were selected from large groups of recently-shipped feeder cattle at the time clinical signs of respiratory disease and body temperature of 40.6 degrees C or higher were observed. Treated animals were evaluated daily for 10 days and finally at day 28. Each animal was weighed on the first day and again on day 28. Animals that died were necropsied. All treatment dosages were effective in significantly lowering mortality, improving weight gains, lowering body temperature, and reducing the severity of clinical signs when compared to the placebo-treated controls. Body temperature was the only variable with statistically significant differences among the dose levels.

Structure-activity studies of 20-deoxo-20-amino derivatives of tylosin-related macrolides.

Reductive amination of the C-20 aldehyde group of tylosin and related macrolides yielded a large series of derivatives with potentially useful antibiotic properties. Evaluation of these new compounds was conducted on the basis of: 1) Broad antimicrobial spectrum in vitro, with particular emphasis on inhibition of Pasteurella multocida and Pasteurella haemolytica; 2) in vivo efficacy, especially when given orally, against P. multocida in experimental infections in chicks; and 3) bioavailability after oral administration to laboratory animals. The most useful activity was found within a series of derivatives produced by reductive amination of desmycosin with secondary amines.

Synthesis and antimicrobial evaluation of 20-deoxo-20-(3,5-dimethylpiperidin-1-yl)desmycosin (tilmicosin, EL-870) and related cyclic amino derivatives.

A series of 20-deoxo-20-cyclic (alkylamino) derivatives of tylosin, desmycosin, macrocin and lactenocin was prepared by reductive amination of the C-20 aldehyde group. The majority of the compounds were prepared using metal hydrides (sodium cyanoborohydride or sodium borohydride) as the reducing agents and a suitable cyclic alkylamine. Subsequently, a more convenient procedure was developed using formic acid as a reducing agent. The C-20 amino derivatives prepared from desmycosin exhibited good in vitro antimicrobial activity against Pasteurella haemolytica and Pasteurella multocida (MIC range of 0.78 approximately 6.25 micrograms/ml) as well as Mycoplasma species (MIC range of 0.39 approximately 6.25 micrograms/ml). Several derivatives showed excellent oral efficacy against infections caused by P. multocida in chicks. One of these derivatives, 20-deoxo-20-(3,5-dimethylpiperidin-1-yl)desmycosin (tilmicosin or EL-870) was selected for development as a therapeutic agent for pasteurellosis in calves and pigs.

Single-dose treatment of neonatal calf pneumonia with the new macrolide antibiotic tilmicosin.

Tilmicosin, a new macrolide antibiotic, 20-deoxo-20-(3,5-dimethylpiperidin-l-yl)desmycosin, formerly identified as EL-870, has been evaluated in three experiments as a single subcutaneous injection at dosages of 10, 20 or 30 mg/kg for the treatment of naturally occurring pneumonia in neonatal calves. Male Holstein calves, under five days of age, were shipped from Wisconsin and housed in pens. They were assigned sequentially to a treatment group when their temperature was greater than or equal to 39.7 degrees C for two consecutive days or greater than or equal to 39.7 degrees C and signs of respiratory disease were present. Clinical signs were evaluated daily for 14 days after the tilmicosin treatment. Calves that died and those that survived for the 14 day experimental period were examined post mortem. Treatment with tilmicosin was effective at all dosage levels, as determined by significant (P less than or equal to 0.05) reductions in body temperature within 24 hours, in the number of animals that died, in the incidence and severity of clinical signs, in the number of Pasteurella species found in lung tissue and in the severity of the pneumonic lesions. In two of the three experiments severe outbreaks of cryptosporidiosis resulted in significant mortalities within a few days after the arrival of the calves. Treatment with tilmicosin was effective against respiratory disease even in the presence of this severe concurrent disease.

In vitro and in vivo evaluation of C-20- and C-23-modified derivatives of tylosin against veterinary pathogens.

Three series of semi-synthetic derivatives of tylosin-related macrolides were evaluated for utility in veterinary medicine. 23-Modified derivatives of 5-O-mycaminosyltylonolide (OMT) possessed potent activity in vitro against species of Pasteurella and Mycoplasma. An experimental infection in chicks caused by Pasteurella multocida was utilized to evaluate efficacy; several of these derivatives of OMT effectively treated the infection when given subcutaneously, but none were effective after oral administration in drinking water. Macrolides retaining the 4'-O-mycarosyl moiety (tylosin, DMT) had relatively poor activity against Pasteurella in vitro. Certain 20-modified derivatives of desmycosin demonstrated good oral bioavailability in chicks and a lead compound with oral efficacy in the Pasteurella infection model was discovered.

In vitro antibacterial properties of EL-870, a new semi-synthetic macrolide antibiotic.

A new macrolide antibiotic, EL-870, 20-deoxo-20-(3,5-dimethylpiperidin-1-yl)desmycosin, has been prepared by chemical modification of desmycosin. In vitro, against selected animal bacterial pathogens, it inhibited growth of Pasteurella multocida, Pasteurella haemolytica, Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae, Streptococcus suis, Actinomyces pyogenes and certain other bacteria at levels of 6.25 micrograms/ml or less. In general, the MICs for Gram-negative enteric bacteria have been greater than 50 micrograms/ml. Concentrations equivalent to 4 X the MIC value were bactericidal for Pasteurella sp. EL-870 had other antibacterial properties which were characteristic of macrolide antibiotics.

Comparison of the antimycoplasma activity of two commercially available tylosin premixes.

Two tylosin premixes (referred to in this report as Premix A and tylosin Premix B), obtained as commercial products from Japan, were analyzed microbiologically for tylosin and by high pressure liquid chromatography (HPLC) for macrolide content. They were evaluated in the feed at concentrations of 550 and 1100 ppm antibiotic activity for the treatment of chickens with induced Mycoplasma gallisepticum (MG) infection. The tylosin microbiological assay value for Premix A was 3.0% below and for Premix B, 7.5% above the tylosin concentration stated on the respective premix labels. Analyses by HPLC showed tylosin Premix A contained 84% tylosin and 16% other macrolide derivatives; whereas, tylosin Premix B contained 42.6% tylosin, 46.6% other macrolides, and 10.8% unidentified material. When the two premixes were administered in the feed for 5 days as treatments for MG-infected chickens, tylosin Premix A was significantly more effective than tylosin Premix B, as measured by reductions in mortality, air sac lesions, and infection as indicated by development of MG antibody. In experiments in pigs where individual macrolide derivatives were used, tylosin was more effective than the other macrolides, desmycosin or macrocin, for the treatment of Mycoplasma hyopneumoniae infection. It is apparent from these studies that commercially available tylosin products may contain varying quantities of tylosin and related macrolide antibiotics and that these differences may significantly affect the efficacy of the products.

Structure-activity studies among 16-membered macrolide antibiotics related to tylosin.

Although a substantial number of 16-membered macrolides related to tylosin have now been isolated and evaluated as antibiotics, none appeared to be superior to tylosin in treating bacterial or mycoplasmal infections caused by sensitive organisms. Nevertheless, this comparison of the antibiotic activity of 16-membered macrolides clearly indicates that novel antibiotics with potentially useful activity can be obtained from mutant strains which have been blocked at various steps in their biosynthesis of antimicrobial agents. The novel compounds thus produced may also be used as starting materials for additional chemical and microbiological modification. Furthermore, the mutant strains which produced these novel compounds should be useful recipients for interspecific genetic recombination by protoplast fusion or gene cloning to yield hybrid antibiotics. Even greater exploitation of these methods will be required in the continuing search for new antibiotics and improved methods for producing them.

Orally administered tylosin for the control of pneumonia in neonatal calves.

The effectiveness of orally administered tylosin tartrate for the control of naturally occurring pneumonia was determined in 287 neonatal calves. Tylosin tartrate was mixed with reconstituted milk replacer at the time of feeding. Daily doses of 1.0 g (0.5 g BID), 2.0 g (1.0 g BID) and 4.0 g (2.0 g BID) were evaluated for periods ranging from seven to 28 days. Tylosin at the optimum dose of 2.0 g daily reduced mortality to 12 out of 95 (12.6 per cent) compared to 38 out of 89 (42.7 per cent) in the non-medicated control calves. The 1.0 g daily dose did not reduce mortality. The number of calves with moderate to severe lung lesions was also reduced by treatment at 2.0 g daily to 13 out of 95 (13.7 per cent) compared to 45 out of 89 (50.6 per cent) in the control group. All dose levels had a similar effect in reducing the severity of clinical signs indicative of respiratory disease. Tylosin treatment at all dose levels reduced the number of Pasteurella multocida isolations from lung tissue to 15/146 (10.3 per cent) compared to 61/141 (43.3 per cent) for the controls. However, there were no differences between treated and controls in the number of P haemolytica isolations. The frequency of mycoplasma isolations from lung tissue were reduced significantly by tylosin treatment at the 4.0 g and 2.0 g dose levels to 36/93 (38.7 per cent) compared to 61/86 (70.9 per cent) for the control calves.

The incidence of Mycoplasma dispar, Ureaplasma and conventional Mycoplasma in the pneumonic calf lung.

This report describes the incidence of Mycoplasma dispar, ureaplasma and conventional (large colony) mycoplasma isolated from the pneumonic lungs of groups of young calves and the identification to species level of mycoplasmas in mixed populations with the aid of the indirect fluorescent antibody test. Pneumonic lung tissue yielded one or more mycoplasma species from 88% of the 153 calves cultured. The mycoplasmas identified and percent of the calves with lungs positive for each species were: M. dispar (56%), ureaplasma (44%), Mycoplasma bovis (37%), Mycoplasma arginini (33%) and Mycoplasma bovirhinis (23%). Conventional mycoplasmas isolated from two calves (1%) could not be identified using the antisera available.

Effects of feeding tylosin to layers exposed to Mycoplasma gallisepitcum.

Two experiments are reported in which the effect of tylosin upon the development of Mycoplasma gallisepticum (MG) infection in replacement layers was monitored by serological and cultural methods. Concentrations of tylosin tested included 0, 22, 38.5, and 55 ppm. Egg production and feed consumption data were collected for one year. Tylosin slowed the rate of spread of MG infection as measured by serological and cultural methods. The effect of tylosin on the spread of MG infection was dose related. Hen day egg production peaked at 85 to 87% in the mediated groups, while controls peaked at 81 to 84%. The magnitude of tylosin effect on production increased with time to a maximum difference of 10 to 12% at 52 weeks. Feed efficiency was markedly improved by all concentration of tylosin ranging from 5% at peak production to 12 to 18% at 52 weeks. The incidence of shell-less or soft shelled eggs was markedly reduced in the tylosin treated group.

Calfhood immunization against an experimental Parainfluenza and Pasteurella challenge.

An inactivated vaccine including Parainfluenza-3, PASTEURELLA MULTOCIDA and PASTEURELLA HEMOLYTICA stimulated good immunity in calves against an experimental shipping fever challenge. Calves were first vaccinated when 4 to 10 weeks old and revaccinated at weaning age. There were higher HI titers, lower temperatures, and less lung lesions recorded in the vaccinated group when compared to the control animals.