Overview
Gamithromycin is a novel 15-membered ring semi-synthetic azalide macrolide antibiotic for animal use only. Its primary mechanism of action involves binding to the 50S subunit of bacterial ribosomes, thereby blocking polypeptide chain elongation and inhibiting bacterial protein synthesis. Gamithromycin exhibits bacteriostatic activity against Mannheimia haemolytica, Pasteurella multocida in cattle, and Actinobacillus pleuropneumoniae, Pasteurella multocida, and Haemophilus parasuis in swine. The alkylated nitrogen at the 7a position of the gamithromycin lactone ring allows for rapid absorption under physiological pH conditions and sustained action in the lung tissue of target animals. It is indicated for the treatment of swine and bovine respiratory disease (SRD, BRD), as well as foot lesions and lameness in sheep. Gamithromycin boasts significant advantages such as rapid absorption and onset of action, long-lasting efficacy, low residue levels, and high safety. A single administration can achieve therapeutic or preventative effects, aligning with the future development trends of the domestic and international livestock industries and holding broad application prospects in veterinary clinics.
Pharmacological Action
Pharmacodynamics
Gamithromycin belongs to the macrolide antibiotic class. It is a 15-membered ring semi-synthetic azalide macrolide that primarily acts by binding to the 50S subunit of bacterial ribosomes, inhibiting bacterial protein synthesis by preventing polypeptide chain elongation. In vitro studies have demonstrated that gamithromycin exerts bacteriostatic effects against Mannheimia haemolytica, Pasteurella multocida in cattle, and Actinobacillus pleuropneumoniae, Pasteurella multocida, and Haemophilus parasuis in swine. The alkylated nitrogen at the 7a position of the gamithromycin lactone ring facilitates rapid absorption under physiological pH conditions and allows for prolonged therapeutic concentrations in the lung tissue of target animals.
Pharmacokinetics
In cattle, a single subcutaneous dose of gamithromycin at 6 mg/kg body weight administered in the neck results in peak plasma concentrations within 30 to 60 minutes, with a bioavailability >98% and no gender differences. In vitro plasma protein binding studies indicate a free drug concentration of 74%. The apparent volume of distribution is 25 L/kg. Gamithromycin reaches high concentrations in the lungs within less than 24 hours, with a lung/plasma concentration ratio >264, indicating rapid absorption into the target tissue for combating respiratory diseases. The plasma elimination half-life is long (>2 days). The drug is primarily excreted unchanged via bile.
In swine, a single intramuscular dose of gamithromycin at 6 mg/kg body weight administered in the neck results in peak plasma concentrations within 5 to 10 minutes, with a bioavailability >92%. In vitro plasma protein binding assays show a free drug concentration of 77%. The apparent volume of distribution is 39 L/kg. Gamithromycin is rapidly absorbed into the target tissues to combat respiratory diseases. The concentration of gamithromycin in the lungs is significantly higher than in the blood, and the plasma elimination half-life is long (approximately 4 days). The drug is primarily excreted unchanged via bile.
Indications
For the treatment of bovine respiratory disease (BRD) associated with Mannheimia haemolytica, Pasteurella multocida, and Mycoplasma spp. susceptible to gamithromycin; and swine respiratory disease (SRD) associated with Actinobacillus pleuropneumoniae, Pasteurella multocida, and Haemophilus parasuis susceptible to gamithromycin.
Dosage and Administration
Calculated based on gamithromycin.
Subcutaneous injection (cattle): A single dose of 6 mg per kg body weight (equivalent to 1 ml per 25 kg body weight). The administered volume at each injection site should not exceed 10 ml.
Intramuscular injection (swine): A single dose of 6 mg per kg body weight (equivalent to 1 ml per 25 kg body weight). The administered volume at each injection site should not exceed 5 ml.
Adverse Reactions
Following subcutaneous injection in cattle or intramuscular injection in swine, transient swelling and occasional mild pain may occur at the injection site.
Precautions
- Do not use in animals hypersensitive to macrolide antibiotics.
- Do not administer concurrently with other macrolide or lincosamide antibiotics.
- Do not use in lactating dairy cows.
- Do not use in pregnant cows within 2 months of the expected calving date.
- The safety of this product in pregnant sows has not been evaluated; use according to the veterinarian’s risk assessment.
- Gamithromycin may be irritating to eyes and/or skin; avoid contact with skin and/or eyes. If accidental contact occurs, rinse immediately with water.
- In case of accidental self-injection, seek immediate medical attention and provide the product label or package insert to the physician.
- Wash hands after use.
- Keep out of reach of children.
- Once the vial is opened, the contents are valid for 28 days. Discard any unused portion after this period.