Application of Ceftiofur Hydrochloride Injection in Animals

1. Structure and mechanism of action

Ceftiofur is a 7-aminocephalosporin nucleus that replaces the 7-β-aminoacyl group with an oxyiminothiazole group. The 3rd position of ceftiofur is furanoic acid thioester, making it a unique alternative to the third-generation cephalosporins. The main metabolite of ceftiofur, namely defuroyl ceftiofur, is the product of the hydrolysis of the thioester bond to release furanoic acid. The dimer of defuroyl ceftiofur (DFC) is the product of the condensation of DFC and itself, which retains the β-lactam ring and oxyimino-aminothiazolyl group of ceftiofur.

The mechanism of action of ceftiofur is the same as that of other β-lactam antibiotics. It can bind to penicillin-binding proteins (PBPs) on the bacterial cytoplasmic membrane, causing the loss of PBPs activity, hindering the cross-linking of mucins in sensitive bacteria, and causing cell wall defects. The high osmotic pressure in the bacteria causes the extracellular water to continuously penetrate into the bacteria, causing the bacteria to swell and deform, and activating autolytic enzymes, causing the bacteria to lyse and die, achieving the effect of efficient sterilization during the reproductive period.

2. Pharmacodynamics

After biotransformation in cattle and horses, ceftiofur is mainly metabolized by removing the furan carbonyl group on the third thio group to generate defurancarbonyl ceftiofur (DFC) with a complete β-lactam ring. Since the lactam ring is not destroyed, its antibacterial activity is basically the same as that of ceftiofur. Moreover, for respiratory bacteria, both ceftiofur and defurancarbonyl ceftiofur show good antibacterial activity against respiratory bacteria, and the MIC value does not exceed 0.3μg/mL.

Table 1. MIC Values of Ceftiofur Against Bovine Respiratory Pathogens

Bacterial Species	MIC50 (µg/mL)	MIC90 (µg/mL)
Mannheimia haemolytica (n=48)	≤0.0039	≤0.0039
Desfuroylceftiofur	0.0078	0.0078
Pasteurella multocida (n=42)	0.0078	0.0078
Desfuroylceftiofur	0.015	0.015
Histophilus somni (n=59)	≤0.0019	≤0.0019
Desfuroylceftiofur	≤0.0019	≤0.0019
Staphylococcus aureus (n=10)	1.0	1.0
Desfuroylceftiofur	4.0	8.0
Streptococcus uberis (n=15)	0.03	0.03
Desfuroylceftiofur	0.5	0.5
Streptococcus agalactiae (n=15)	≤0.0039	≤0.0039
Desfuroylceftiofur	0.015	0.015

After administration of ceftiofur, the metabolism in pigs is similar to that of cattle and horses, and defurancarbonyl ceftiofur is also the main antibacterial active drug, and the antibacterial activities of the two are similar. Ceftiofur shows extremely low drug resistance to pig respiratory bacteria, and the in vitro antibacterial activity is ≤0.125μg/mL. Actinobacillus pleuropneumoniae and Pasteurella show high sensitivity to ceftiofur.

Table 2. MIC Values of Ceftiofur Against Porcine Respiratory Pathogens

Bacterial Species/Pig	MIC50 (µg/mL)	MIC90 (µg/mL)
Pasteurella multocida (n=50)
Ceftiofur	≤0.0039	≤0.0039
Desfuroylceftiofur	≤0.0039	0.0078
Actinobacillus pleuropneumoniae (n=50)
Ceftiofur	≤0.0039	≤0.0078
Desfuroylceftiofur	0.0078	0.015
Salmonella choleraesuis (n=48)
Ceftiofur	0.5	1.0
Desfuroylceftiofur	0.25	1
Streptococcus suis (n=49)
Ceftiofur	0.0078	0.13
Desfuroylceftiofur	0.015	0.25

3. Pharmacokinetics

Whether the salt form of ceftiofur is administered intramuscularly or subcutaneously, the pharmacokinetic parameters (AUCs, etc.) of the two forms of the salt are statistically similar. The data show that both salt forms have similar therapeutic effects and systemic safety regardless of the route of administration. Similar equivalent therapeutic results were also observed in pigs, where two treatment levels of each salt (3.0 and 5.0 mg/kg) by the IM route gave essentially the same plasma concentrations, plasma concentrations (C max ), areas under the curve (AUCs), and elimination half-lives (t 1/2 ). Therefore, both salt forms are likely to produce the same therapeutic effects. In addition, for either salt, the residual concentrations in edible tissues should be the same regardless of the route of administration.

Table 4. Comparative Pharmacokinetics of Ceftiofur Hydrochloride and Ceftiofur Sodium After Single-Dose Administration in Cattle

Parameter	Ceftiofur Hydrochloride	Ceftiofur Sodium
	IM	SC
Cmax (mg/mL)	11.0 ± 1.69	8.56 ± 1.89
Tmax (h)	1-4	1-5
AUC(0-∞) (mg·h/mL)	160 ± 30.7	95.4 ± 17.8
t1/2 (h)	12.00 ± 2.63	11.50 ± 2.57

4. Safety

Ceftiofur hydrochloride injection was well tolerated after 9 consecutive days of administration at 1, 3, and 5 times the recommended dose for cattle. No significant changes related to ceftiofur were observed in clinical observations, clinical pathology, and histopathological examinations. Continuous administration had no effect on the feed intake, water intake and weight gain of all experimental cattle. In this study, the average body temperature of cattle in each group increased after the first administration and then stabilized. This shows that the experimental cattle developed tolerance to the drug and injection after the stress of administration. Body weight is a reflection of food consumption and normal growth. The results of the study showed that the drug had no effect on the normal growth of animals. The clinical pathological results did not show any trend of tissue or cell damage. Combined with the results of histopathological examination, there was no obvious pathological damage to the tissue at 5 times the recommended dose when used continuously. Therefore, ceftiofur hydrochloride injection has good safety in clinical use.

Table 5. Pre-experimental Bovine Hematological Analysis

Parameter	0x	1x	3x	5x
	Female	Male	Female	Male
WBC	9.71±1.70	7.89±1.19	8.44±1.29	8.27±0.95
LYM	5.77±0.58	4.74±1.08	5.61±0.90	4.89±0.24
MON	0.57±0.13	0.39±0.13	0.44±0.12	0.44±0.24
NEU	3.28±1.06	2.68±0.57	2.31±0.68	2.87±2.00
EOS	0.08±0.04	0.07±0.03	0.07±0.03	0.05±0.02
BAS	0.03±0.02	0.06±0.09	0.02±0.01	0.02±0.01
RBC	9.15±0.46	241.91±465.39	9.72±0.70	10.15±0.20
HGB	9.80±0.55	9.70±0.56	10.40±0.58	10.45±0.62
HCT	35.78±0.96	36.18±2.70	38.58±1.82	37.30±2.77
MCV	39.50±1.30	39.00±0.82	39.75±2.63	36.75±3.10
MCH	10.73±0.66	10.50±0.29	10.73±0.51	10.33±0.66
CHC	27.40±1.01	26.80±0.38	27.00±0.80	28.10±0.88
PLT	227.75±45.99	219.75±38.77	219.25±37.21	294.25±20.45
MPV	5.90±0.27	5.65±0.31	5.78±0.22	5.85±0.39
PCT	0.14±0.03	0.13±0.03	0.13±0.03	0.17±0.01

Terminology:

WBC: White Blood Cell

LYM: Lymphocyte

MON: Monocyte

NEU: Neutrophil

EOS: Eosinophil

BAS: Basophil

RBC: Red Blood Cell

HGB: Hemoglobin

HCT: Hematocrit

MCV: Mean Corpuscular Volume

MCH: Mean Corpuscular Hemoglobin

CHC: Mean Corpuscular Hemoglobin Concentration

PLT: Platelet

MPV: Mean Platelet Volume

PCT: Plateletcrit

Table 6. Post-experimental Bovine Serum Biochemical Analysis

Parameter	0x	1x	3x	5x
	Female	Male	Female	Male
WBC	8.73±2.60	7.38±1.35	8.14±1.71	7.15±0.46
LYM	5.93±0.91	4.73±1.23	4.96±1.21	4.40±0.62
MON	0.46±0.21	0.50±0.10	0.37±0.23	0.38±0.25
NEU	2.22±1.48	2.11±0.64	2.57±0.47	2.21±0.79
EOS	0.09±0.03	0.09±0.03	0.19±0.11	0.12±0.03
BAS	0.03±0.02	0.02±0.01	0.05±0.03	0.04±0.01
RBC	9.46±0.61	9.83±1.06	9.76±0.65	10.08±0.68
HGB	10.28±1.13	10.78±1.33	10.63±1.02	10.53±0.51
HCT	35.97±2.90	37.15±3.21	38.92±3.88	36.64±3.11
MCV	38.00±1.63	38.00±1.41	40.00±2.00	36.25±1.89
MCH	10.90±0.80	10.93±0.40	10.85±0.64	10.45±0.54
CHC	28.60±1.51	28.85±1.52	27.35±0.90	28.83±1.20
RDWc	24.98±1.89	24.80±0.68	25.53±0.70	24.60±2.47
RDWs	38.88±3.45	38.28±1.42	41.43±2.22	36.15±2.14
PLT	218.25±61.05	207.50±30.39	203.00±32.62	247.75±36.35
MPV	5.95±0.24	5.88±0.50	5.93±0.26	5.98±0.41
PCT	0.13±0.04	0.12±0.02	0.12±0.02	0.14±0.01
PDWc	30.75±1.90	30.30±2.40	30.50±2.34	30.63±2.61
PDWs	8.38±1.13	8.15±1.50	8.38±1.12	8.35±1.59

Figure: Histopathological Examination Results of Experimental Cattle at 0x and 5x Doses