Whether in the era of compound drugs, where the formulation technology of various veterinary drug manufacturers played a key role, or in the current period dominated by national standard single drugs, effective medication technology is always based on a thorough understanding and unique insight into the drugs used. Understanding comes from professional knowledge, while the ability to apply that knowledge depends on personal perception and the lessons learned from practice. Below is a summary of the experience in effective treatment medication compiled by a veteran veterinarian who has spent their entire career diagnosing and treating livestock and poultry diseases. This is for those interested in learning and reference. First and foremost, the effective use of antimicrobial and anti-mycoplasma drugs follows specific principles and methods.

The effectiveness of treatment is directly linked to accurate diagnosis of the disease. Therefore, in addition to relying on on-site diagnostics like visual examination and palpation, combining laboratory-based simple diagnostic techniques with on-site clinical observations can help validate diagnoses and eliminate the misjudgment often made in traditional disease diagnosis. For example, by taking sputum samples with swabs and examining them under a microscope, veterinarians can roughly determine whether the pathogen infecting the livestock or poultry is a Gram-positive or Gram-negative bacterium, and whether it is a Gram-positive coccus or a Gram-negative bacillus. This approach greatly improves the targeting of antimicrobial drug selection.

In the treatment of pneumonia in livestock and poultry, the pathogens typically include Streptococcus pneumoniae, Streptococcus haemolyticus, Staphylococcus aureus, Pasteurella haemolytica, anaerobes, respiratory viruses, mycoplasmas, and chlamydia. Commonly used antimicrobial agents include macrolides, tetracyclines, penicillins, lincosamides, and cephalosporins. The selection of antimicrobial drugs for bacteria and mycoplasmas should be based on sensitivity test results, choosing drugs that are highly sensitive, broad-spectrum, cost-effective, and have low toxicity and side effects. In the absence of sensitivity test results, drugs effective against common Gram-negative rods, Pseudomonas aeruginosa, and Gram-positive cocci should be selected.

Furthermore, it is important to avoid relying on a single drug or administering drugs one by one in treatment, as this deviates significantly from the practical goal of combined drug therapy. When using two or more drugs, scientific and rational compatibility must be considered. In preventive treatment, if a single antimicrobial drug is sufficient, combination therapy should be avoided. However, for serious infections where the pathogens are unknown, or when livestock or poultry have underlying conditions such as heart and lung failure, immune dysfunction, or mixed infections, combination therapy should be employed to achieve synergistic effects and enhance efficacy. This helps improve treatment effectiveness and reduces the development of bacterial resistance.

The rational compatibility of combined drugs should follow the principle of using bactericidal agents during the reproductive phase in conjunction with those active during the dormant phase. For example, combining β-lactam antibiotics with aminoglycosides can achieve a synergistic antimicrobial effect. Combining bactericidal agents for the dormant phase with rapid-acting inhibitors, such as combining aminoglycosides with macrolides, can produce an additive synergistic effect for anti-mycoplasmal and antimicrobial action. Similarly, combining penicillins with cephalosporins can continuously inhibit bacterial cell wall synthesis, leading to a synergistic bactericidal effect. However, it should be noted that rapid-acting inhibitors should not be combined with reproductive phase bactericidal agents, such as combining macrolides with β-lactams, as rapid-acting inhibitors suppress bacterial protein synthesis quickly, preventing bacteria from entering the reproductive phase and reducing the effectiveness of the reproductive phase bactericidal agents, thus causing antagonistic effects.

Next, the antibiotic post-antibiotic effect (PAE) and the dosing interval play a crucial role in the effectiveness of medication. The post-antibiotic effect refers to the ability of an antibiotic to continue inhibiting bacterial growth even after the drug concentration in the body has fallen below the minimum inhibitory concentration (MIC). Different antibiotics have varying degrees of PAE against Gram-positive cocci. However, for Gram-negative bacilli, only aminoglycosides and quinolones show satisfactory PAE. Carbapenems and fourth-generation cephalosporins exhibit moderate PAE against Gram-negative bacilli, while penicillins and first-, second-, and third-generation cephalosporins almost have no PAE.

The dosing interval for antibiotics depends on the drug's half-life, PAE, and whether the antibacterial action is concentration-dependent. Generally, concentration-dependent antibiotics should have their daily dose concentrated into one administration to achieve a higher peak concentration. In contrast, time-dependent antibiotics, whose bactericidal effect is mainly determined by the duration the drug concentration exceeds the MIC of the pathogen, should have their dosing intervals shortened to ensure the concentration remains above the MIC for at least 60% of the 24-hour period.

Time-dependent antibiotics (with non-concentration-dependent bactericidal action and no or very short PAE) include penicillins, first-, second-, and third-generation cephalosporins, and aztreonam. These should be administered every 6-8 hours to extend the period during which the blood concentration exceeds the MIC of the pathogen. Concentration-dependent antibiotics (with bactericidal action that is concentration-dependent and good PAE) include aminoglycosides and quinolones. These should be administered at higher doses and with appropriate extended intervals.

For drugs that are intermediate between concentration- and time-dependent (with non-concentration-dependent bactericidal action and some PAE), such as carbapenems, fourth-generation cephalosporins, macrolides, lincosamides, and vancomycin, the dosing method should fall somewhere between the two principles mentioned above. In addition to sensitivity testing, the dosing interval should also take into account the drug's toxicity and the relationship between blood concentration and side effects. For example, aminoglycosides are concentration-dependent antibiotics, but their toxicity is not directly related to the blood concentration, regardless of their half-life.

For animals with normal renal function, administering the daily dose once a day is equally or more effective than splitting it into two to three doses, and it also reduces nephrotoxicity and ototoxicity. However, for animals with impaired renal function, aminoglycosides should be given at half the dose on the first day to maintain therapeutic blood concentrations, with subsequent doses calculated based on the creatinine clearance rate and split into two administrations. Similarly, for quinolones, which are also concentration-dependent antibiotics, toxicity is related to blood concentration. Except for those with a very long half-life, quinolones are typically administered every 12 hours rather than once daily.

In clinical practice, especially when pathogen results are unavailable, empirical medication should be adapted to local and temporal conditions (as bacterial spectra vary by region and the prevalence of bacterial species changes over time).