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Things You Should Know About Tiamulin (Part 2)

Here is the continuation of the questions and answers of about the important things a pig farmer should know about tiamulin.

Does tiamulin have adverse interaction with other antibiotics?
Generally, tiamulin is a safe drug and may be used in the prevention and treatment of certain infections in pigs of any age. However, like other drugs, tiamulin may show adverse interaction with certain other antibiotics, most specifically with some members of the so-called ionophore (also called polyether) antibiotics such as salinomycin, monensin and narasin. These ionophore antibiotics are commonly used as growth promoters in pigs and ruminants, and as anticoccidial agents in poultry.

The term “ionophores” refers to substances that “punch” holes in the membrane coverings of bacterial cells resulting in their death. Although the ionophore antibiotics have selective effects on bacterial cells at the usual doses, they may also adversely affect the animal cells at high doses and/or in combination with tiamulin.

When using tiamulin you should always make sure that your pigs are not at the same time receiving salinomycin, monensin or narasin in feeds, water, or injections. Also, beware of the possibility of some commercial feeds containing any of these substances that may not be so-reflected in the label. If, however, treatment with an ionophore antibiotic and tiamulin at the same time is deemed necessary, two things may be done: (1) reduce the dose of the ionophore to 80 ppm (g/ton or mg/kg of medicated feeds) or lower, and (2) reduce the dose of tiamulin to 30 ppm.

Can tiamulin be safely used with similar erythromycin, lincomycin, or chloramphenicol?
Although tiamulin has no known adverse interactions with macrolides (example, erythromycin, tylosin, and spiramicin), licosamides (lincomycin and clindamycin) and chlorampheriicol derivatives such as florfenicol, I don’t advise using it in combination with these other drugs. All these drugs act similarly as tiamulin on bacterial pathogens; their simultaneous presence in the site of infection will lead to competition at the site of action making the effects of individual drugs less effective than when each is used alone.

What then are antibiotics with safe and useful interaction with tiamulin?
The tetracyclines have long been proved synergistic with tiamulin. Synergistic interaction or synergism means that the combined effect of drugs in combination is greater than the sum of their separate individual effects.

The tetracyclines (chlortetracycline, oxytetracycline, and doxycycline) that are commonly used in pigs exert the same antibacterial effects, and same synergistic interaction with tiamulin. They differ only in the way they are absorbed, distributed and eliminated from the body. The usual feed inclusion rates of tetracyclines when combined with the recommended dose of tiamulin are 400 g/ton (mg/kg) for chlortetracycline, 800 g/ton for oxytetracycline, and 300 g/ton for doxycycline. The lower inclusion rate of doxycycline and the higher inclusion rate of oxytetracycline than that of chlortetracycline are due to the rate of their absorption and excretion, and not so much to more potent antibacterial action.

If tiamulin and a tetracycline are synergistic, shouldn’t we expect the dose of one or both these drugs be reduced?

Ideally, that’s what we should expect, but it doesn’t work all the time. It’s the greater antibacterial effect of the combination rather than reduced dose that is more important. If either the dose of the tetracycline or of tiamulin is reduced, then the optimum concentration of each drug may not be attained at the site of infection to bring about synergism. The same principle applies to trimethoprim-sulfonamide combination, in which the dose of the sulfonamide is not necessarily reduced to affect synergism with trimethoprim.

Can tiamulin be combined with amoxicillin to cause a synergistic effect? Tiamulin is a bacteriostatic antibiotic while amoxicillin is bacteriocidal. An old rule in antibiotic combination is that generally a “static” antibiotic should not be used together with a “cidal” antibiotic. However, test results reported last year by veterinarians at Chulalongkorn University in Thailand showed that tiamulin acts synergistically with amoxicillin in the treatment of cases of Hemophilus parasuis (HP) and Actinobacillus pleuropneumoniae (App) and Bordetella bronchiseptica (atrophic rhinitis) infections in pigs. The effect of the same combination on Strqptococcus suis and Pasteurella multocida are at best additive, that is the combined effect of tiamulin and amoxicillin is equal to the sum of their individual effects. No evidence of antagonism between tiamulin and amoxicillin has been observed.

Does tiamulin cause antibiotic residues in pork?
All antibiotics may leave drug residues in meat when the animals medicated with them are slaughtered for food before their assigned withdrawal periods. The required withdrawal period for tiamulin is 7 to 10 days, beyond which meat will no longer contain hazardous drug residues. However, if tiamulin is used in combination with a tetracycline or amoxicillin, the withdrawal period of the other drug, which may be different from that of tiamulin, should be observed.

Does tiamulin have a counterpart antibiotic in human medicine?
To date, no antibiotic used in the treatment of human infections is similar or the same as tiamulin. Tiamulin is used exclusively for animals. Unlike the macrolides, lincosamides, and tetracyclines, which are themselves, or closely related antibiotics, are used in treating human patients, tiamulin poses little, if any, danger of bacterial resistance in human pathogens.