In pig farming production and the treatment of pig diseases, especially in the treatment of respiratory system diseases, many people use compound amoxicillin, amoxicillin, ceftiofur, and cefquinome in combination with tylosin and tilmicosin. But is this scientific and reasonable? Opinions vary.

So, is it really reasonable to prescribe a combination of amoxicillin, cefquinome, tylosin, and tilmicosin? Let's analyze it from the perspective of antibiotic classification and combination principles to provide a reference and exchange for frontline clinical veterinarians.

Antibiotic Classification

According to the nature of their action, antibiotics can be divided into four categories:

1. Bactericidal agents in the growth phase: Such as penicillins, cephalosporins, and fluoroquinolones.
2. Bactericidal agents in the stationary phase: Such as aminoglycosides and polymyxins.
3. Rapid bacteriostatic agents: Such as lincosamides, tetracyclines, chloramphenicol, and macrolides.
4. Slow bacteriostatic agents: Such as sulfonamides.

Analysis of Combination

When combining the above antibiotics, their effects can be synergistic, additive, unrelated, or antagonistic.

According to research and statistical reports, when two antibiotics are used together, about 25% show synergistic effects, about 60-70% show unrelated or additive effects (mostly unrelated), and about 5-10% show antagonistic effects.

Summary

• Combining bactericidal agents in the growth phase with those in the stationary phase increases the chances of synergistic effects.
• Combining rapid bacteriostatic agents with bactericidal agents in the growth phase can produce antagonistic effects.
• Combining rapid bacteriostatic agents generally results in additive effects.
• Combining rapid bacteriostatic agents with slow bacteriostatic agents also results in additive effects.

Combining bactericidal agents in the stationary phase with rapid bacteriostatic agents can produce synergistic and additive effects. Combining bactericidal agents in the growth phase with slow bacteriostatic agents results in unrelated effects. Combining bactericidal agents in the growth phase, stationary phase, and rapid bacteriostatic agents often results in synergistic and additive effects.

Results of Combination

Based on the above principles, the interaction results of combining different antibiotics are as follows:

1. Growth-phase bactericidal agent + Stationary-phase bactericidal agent = Synergistic (enhanced effect).
2. Growth-phase bactericidal agent + Rapid bacteriostatic agent = Antagonistic (reduced effect).
3. Stationary-phase bactericidal agent + Slow bacteriostatic agent = Synergistic or unrelated.
4. Rapid bacteriostatic agent + Slow bacteriostatic agent = Additive (complementary effect).
5. Rapid bacteriostatic agents combined generally result in additive or unrelated effects.
6. Stationary-phase bactericidal agent + Rapid bacteriostatic agent = Additive or synergistic.

Therefore, according to the above combination principles, combining amoxicillin, cefquinome, tylosin, and tilmicosin results in an "antagonistic" combination, reducing the therapeutic effect. Therefore, they should not be combined.

Indications for Combination Use

1. Severe infections where the pathogen has not yet been identified.
2. Severe infections that cannot be controlled by a single antibiotic.
3. Mixed infections of aerobic and anaerobic bacteria.
4. Infections by two or more compound pathogens.
5. Infections by multi-drug resistant pathogens.
6. Infections that require long-term treatment but where pathogens easily develop resistance to certain antibiotics, such as some fungal diseases or infections by pathogens with different growth characteristics, requiring drugs with different antibacterial mechanisms, such as tuberculosis and non-tuberculous mycobacteria.
7. Toxic antibiotics, where doses can be appropriately reduced when combined, provided there is clinical evidence of similar effectiveness.

Number of Drugs in Combination

When combining drugs, it is advisable to choose drugs with synergistic or additive effects, such as the combination of penicillins, cephalosporins, or other β-lactams with aminoglycosides. The number of drugs combined: typically, two drugs are used in combination, while combinations of three or more drugs are only suitable for individual cases, such as the treatment of more severe infections.

Cephalosporins are a widely used class of antibiotics in pig farms, with significant differences in antibacterial characteristics among different cephalosporins. Due to a lack of understanding in pig farms, cephalosporins are often used irrationally. This not only greatly increases drug costs but also misses the best time for prevention and treatment, causing unnecessary losses to the farm.