Methods of Controlling Pasteurella Infections

This invention relates to methods of controlling Pasteurella infections. In particular, this invention relates to methods of controlling Pasteurella infections which comprise administering to an infected or susceptible warm-blooded animal a compound selected from the group consisting of desmycosin, lactenocin, cirramycin A.sub.1, 23-deoxy-5-O-mycaminosyltylonolide (DOMT), antibiotic M-4365 G.sub.2 (repromicin), 9-dihydrodesmycosin, 9-dihydrolactenocin, 20-dihydrodesmycosin, 20-dihydrolactenocin, rosaramicin (rosamicin; M4365 A.sub.2 ; juvenimicin A.sub.3), and the pharmaceutically acceptable acid addition salts of these compounds.

Pasteurella infections cause serious economic losses in animals. Pasteurellosis, which is a respiratory disease in sheep, cattle and pigs, and fowl cholera are examples of severe diseases in which Pasteurella species are either the primary, or important secondary, etiological agents. P. multocida and P. haemolytica are the agents implicated in these diseases.

We have discovered that a certain group of macrolide antibiotics exhibit unexpectedly high antibacterial activity against certain gram-negative bacteria, i.e. Pasteurella species. More particularly, we have discovered that these compounds are effective in vivo as well as in vitro against Pasteurella species such as P. multocida and P. haemolytica.

The structures of the macrolide compounds which are useful in the method of this invention are shown in formula 1 and Table 1:

The compounds used in the methods of this invention are either known antibiotics or are readily prepared from known antibiotics. The preparation of desmycosin is described by R. L. Hamill et al. in U.S. Pat. No. 3,178,341, issued Apr. 13, 1965. The preparation of lactenocin is described by R. L. Hamill et al. in U.S. Pat. No. 3,326,759, issued June 20, 1967. Cirramycin A.sub.1 is prepared as described by H. Koshiyama et al., J. Antibiotics Ser. A16, 59-66 (1963) and S. Nash et al. in U.S. Pat. No. 4,252,898, issued Feb. 24, 1981. Antibiotic M-4365 G.sub.2 (repromicin) can be prepared as described by T. Furumai et al. in J. Antibiotics 30, 443-449 (1977) or as described by A. K. Ganguly in U.S. Pat. No. 3,975,372, issued Aug. 17, 1976. The preparation of 9-dihydrodesmycosin (dihydrodesmycosin) is described by E. H. Massey in U.S. Pat. No. 3,769,273, issued Oct. 30, 1973. 9-Dihydrolactenocin is prepared in an analogous manner. Rosaramicin can be prepared as described by M. J. Weinstein et al. in U.S. Pat. No. 4,234,690, issued Nov. 18, 1980.

20-Dihydrodesmycosin and 20-dihydrolactenocin can be prepared by chemical reduction using known procedures such as, for example, treatment with an approximately stoichiometric amount of sodium borohydride in an alcoholic solvent.

DOMT is identical to depoxyciramycin A.sub.1 (de-epoxycirramycin A.sub.1). The preparation and activity of depoxycirramycin A.sub.1 are described by H. Tsukiura et al. in J. Antibiotics 22 (3) 89-99, and 100-105 (1969). Tsukiura et al. prepare deoxycirramycin A.sub.1 by treating cirramycin A.sub.1 with potassium iodide in acetic acid.

Another method of preparing DOMT is described by Richard H. Baltz, Gene M. Wild, and Eugene T. Seno in their copending application entitled DE(MYCINOSYLOXY) TYLOSIN AND PROCESS FOR ITS PRODUCTION, Ser. No. 156,855, filed June 12, 1980, now U.S. Pat. No. 4,321,362. This method comprises preparing DOMT by mild acid hydrolysis of 23-de(mycinosyloxy)tylosin (DMOT). The structure of DMOT is shown in formula 2: ##STR5##

DMOT is prepared by fermentation of Streptomyces fradiae NRRL 12171 under submerged aerobic conditions until a substantial level of antibiotic activity is produced. DMOT can be extracted from basified broth filtrate with polar organic solvents and can be further purified by extraction, chromatography, and/or crystallization.

The DMOT-producing strain of Streptomyces fradiae has been deposited and made part of the stock culture collection of the Northern Regional Research Center, Agricultral Research, North Central Region, 1815 North University Street, Peoria, Ill., 61604, from which it is available to the public under the accession number NRRL 12171.

DOMT is prepared from DMOT by mild acid hydrolysis. Appropriate solutions having a pH of about four or below can be used to accomplish the hydrolysis. Temperatures of about 20.degree. to about 100.degree. C. can be used in this method. The reaction time needed to carry out the hydrolysis varies, depending upon the pH of the reaction mixture and the temperature used. At higher pH levels the reaction rate is slower, and at higher temperatures the reaction rate is faster. The reaction is carried out by treating DMOT with a mild acid solution for a time sufficient to effect removal of the mycarosyl group to give DOMT.

Alternatively, and sometimes preferably, DOMT can be prepared by treating DMOT in the fermentation broth in which it is produced, using mild acidic conditions as above described for a time sufficient to convert the DMOT to DOMT. DOMT thus prepared can be isolated from the fermentation using techniques known in the art.

In carrying out the method of this invention, a specified compound of formula 1 or a pharmaceutically acceptable acid addition salt thereof is administered parenterally to an infected or susceptible warm-blooded animal. The dose used to control Pasteurella infections will vary with the compound, the severity of the infection, and the age, weight, and condition of the animal. The total dose required for several days protection will generally, however, be in the range of from about 10 to about 400 mg/kg and preferably will be in the range of from about 25 to about 350 mg/kg. Protection for up to about seven days can be provided by a single injection; the length of protection will depend upon the dose given. The total dose can also be divided into smaller doses given at intervals, such as once daily for four to seven days. Obviously, other suitable dosage regimens can be constructed.

The compounds of this invention may be formulated for parenteral administration by methods recognized in the veterinary pharmaceutical art. Effective injectable compositions containing these compounds may be in either suspension or solution form. In the preparation of suitable formulations it will be recognized that, in general, the water solubility of the acid addition salts is greater than that of the corresponding free bases. Similarly, the free bases are more soluble in dilute acids or in acidic solutions than in neutral or basic solutions.

In the solution form a compound is dissolved in a physiologically acceptable vehicle. Such vehicles comprise a suitable solvent, preservatives such as benzyl alcohol, if needed, and buffers. Useful solvents include, for example, water and aqueous alcohols, glycols, and carbonate esters such as diethyl carbonate. Such aqueous solutions contain, in general, no more than 50% of the organic solvent by volume.

Injectable suspension compositions employ a liquid suspending medium, with or without adjuvants, as a vehicle. The suspending medium can be, for example, aqueous polyvinylpyrrolidone, inert oils such as vegetable oils or highly refined mineral oils, or aqueous carboxymethylcellulose.

Suitable physiologically acceptable adjuvants are necessary to keep the compound suspended in suspension compositions. The adjuvants may be chosen from among thickeners such as carboxymethylcellulose, polyvinylpyrrolidone, gelatin, and the alginates. Many surfactants are also useful as suspending agents. Lecithin, alkylphenol polyethylene oxide adducts, naphthalenesulfonates, alkylbenzenesulfonates, and the polyoxyethylene sorbitan esters are useful suspending agents.

Many substances which affect the hydrophilicity, density, and surface tension of the liquid suspending medium can assist in making injectable suspensions in individual cases. For example, silicone antifoams, sorbitol, and sugars can be useful suspending agents.

The compounds of this invention exhibit unexpectedly high antibacterial activity against Pasteurella species. For example, representative compounds were tested against avian, bovine and porcine Pasteurella species, using the conventional broth-dilution assay. The P. haemolytica strains are bovine strains; the P. multocida strains are avian, bovine and porcine strains. The minimal inhibitory concentrations (MIC's) of representative compounds against these species are summarized in Table II.

Examples 1 and 2 illustrate the useful in vivo activity of the compounds of this invention.

Representative compounds were evaluated in groups of ten one-day-old chicks at the specified dosage of subcutaneous injection given one and four hours post challenge of the chicks with Pasteurella multocida (0.1 ml of a 20-hour tryptose broth culture of an avian P. multocida given subcutaneously). The compounds (as free bases) were administered in an aqueous propylene glycol solution; non-medicated water and feed were provided to the animals ad libitum. The chicks were observed for the following five days. Results of these tests are summarized in Table III.

Cirramycin A.sub.1 and rosaramicin were evaluated in mice by subcutaneous injection given one and four hours post challenge of the mice with Pasteurella multocida (0.1 ml of a 10.sup.-5 dilution of a tryptose broth culture of a bovine isolate). Mortality was evaluated for the following seven days. The results are summarized in Table IV.

(A) Desmycosin base is added to propylene glycol. Water and benzyl alcohol are added so that the solution contains 50% (by volume) propylene glycol, 4% (by volume) benzyl alcohol and 200 mg/ml of desmycosin base.

(B) A desmycosin solution is prepared as described in Section A except that the solution contains 50 mg/ml of desmycosin base.

(C) A desmycosin solution is prepared as described in Section A except that the solution contains 500 mg/ml of desmycosin tartrate.

(D) A solution prepared as described in Section A but using lactenocin.

(E) A solution prepared as described in Section A but using 20-dihydrodesmycosin.

(F) A solution prepared as described in Section A but using 23-deoxy-5-O-mycaminosyltylonolide (DOMT).

(G) A solution prepared as described in Section A but using 9-dihydrodesmycosin.

(H) A solution prepared as described in Section C but using rosaramicin.

(I) A desmycosin suspension is prepared by adding finely ground desmycosin to carboxymethylcellulose with thorough mixing so that each ml of finished suspension contains 200 mg of desmycosin.

A lyophilized pellet of Streptomyces fradiae NRRL 12171 is dispersed in 1-2 ml of sterilized water. A portion of this solution (0.5 ml) is used to inoculate a vegetative medium (150 ml) having the following composition:

Alternatively, a vegetative culture of S. fradiae NRRL 12171, preserved in 1-ml volumes in liquid nitrogen, is rapidly thawed and used to inoculate the vegetative medium. The inoculated vegetative medium is incubated in a 500-ml Erlenmeyer flask at 29.degree. C. for about 48 hours on a closed-box shaker at 300 rpm.

This incubated vegetative medium (0.5 ml) is used to inoculate 7 ml of a production medium having the following composition:

The inoculated fermentation medium is incubated in a 50-ml bottle at 29.degree. C. for about 6 days on a closed-box shaker at 300 rpm.

In order to provide a larger volume of inoculum, 60 ml of incubated vegetative medium, prepared in a manner similar to that described in section A, is used to inoculate 38 L of a second-stage vegetative growth medium having the following composition:

Adjust pH to 8.5 with 50% NaOH solution.

This second-stage vegetative medium is incubated in a 68-liter tank for about 47 hours at 29.degree. C.

Incubated second-stage medium (4 L) thus prepared is used to inoculate 40 liters of sterile production medium having the following composition:

Adjust pH to 7.2 with 50% NaOH solution.

The inoculated production medium is allowed to ferment in a 68-liter tank for about 5 days at a temperature of 28.degree. C. The fermentation medium is aerated with sterile air to keep the dissolved oxygen level between about 30% and 50% and is stirred with conventional agitators at about 300 rpm.

Fermentation broth, obtained as described in Section B, and having a pH of 7.2, is filtered using a filter aid. Ethyl acetate (400 ml) is added to the filtrate (1450 ml). The pH of the solution is adjusted to 9.1 by the addition of sodium hydroxide. The solution is stirred 10 minutes, and the ethyl acetate is separated (filtering through a filter aid to clear any emulsion which forms). The filtrate is again extracted with ethyl acetate (200 ml). Water (200 ml) is added to the combined ethyl acetate extracts; the pH of this solution is adjusted to 4.1 with phosphoric acid. After extraction, the aqueous phase is separated, and the organic phase is discarded. The aqueous phase is adjusted to pH 9.1 with sodium hydroxide and then concentrated to a volume of about 100 ml under vacuum. An amorphous precipitate forms. After permitting the precipitate to stand overnight, it is separated by filtration. The precipitate is dissolved in acetone (20 ml); water (75 ml) is added. The solution is concentrated under vacuum to remove acetone. The precipitate which forms is separated by filtration and washed with water to give about 500 mg of DMOT (2). An additional 260 mg is obtained in a similar manner from the filtrate.

DMOT (11 g), prepared as described in Section C, is dissolved in a dilute hydrochloric acid solution (final pH 1.8). The resulting solution is allowed to stand for 24 hours at room temperature and then is adjusted to pH 9.0 by addition of sodium hydroxide. This basic solution is extracted with chloroform. The chloroform extract is evaporated under vacuum to give 9.65 g of DOMT.

DOMT is prepared from DMOT by treating DMOT in the fermentation broth in which it is produced with mild acid as described in Section D of Example 4. Isolation of DOMT is accomplished by a procedure similar to that described for DMOT in Section C of Example 4.