Average plasma concentrations of ceftriaxone following a single 30-minute intravenous (IV) infusion of a 0.5, 1 or 2 g dose and intramuscular (IM) administration of a single 0.5 (250 mg/mL or 350 mg/mL concentrations) or 1g dose in healthy subjects are presented in Table 1.
TABLE 1. Ceftriaxone Plasma Concentrations After Single Dose Administration| Dose/Route | Average Plasma Concentrations (mcg/mL) |
| | 0.5 hr | 1 hr | 2 hr | 4 hr | 6 hr | 8 hr | 12 hr | 16 hr | 24 hr |
| 0.5 g IV* | 82 | 59 | 48 | 37 | 29 | 23 | 15 | 10 | 5 |
0.5 g IM 250 mg/mL | 22 | 33 | 38 | 35 | 30 | 26 | 16 | ND | 5 |
0.5 g IM 350 mg/mL | 20 | 32 | 38 | 34 | 31 | 24 | 16 | ND | 5 |
| 1 g IV* | 151 | 111 | 88 | 67 | 53 | 43 | 28 | 18 | 9 |
| 1 g IM | 40 | 68 | 76 | 68 | 56 | 44 | 29 | ND | ND |
| 2 g IV* | 257 | 192 | 154 | 117 | 89 | 74 | 46 | 31 | 15 |
* IV doses were infused at a constant rate over 30 minutes. ND = Not determined. |
Ceftriaxone was completely absorbed following IM administration with mean maximum plasma concentrations occurring between 2 and 3 hours post-dose. Multiple IV or IM doses ranging from 0.5 to 2 g at 12- to 24-hour intervals resulted in 15% to 36% accumulation of ceftriaxone above single dose values.
Ceftriaxone concentrations in urine are shown in Table 2.
TABLE 2. Urinary Concentrations of Ceftriaxone After Single Dose Administration| Dose/Route | Average Urinary Concentrations (mcg/mL) |
| | 0-2 hr | 2-4 hr | 4-8 hr | 8-12 hr | 12-24 hr | 24-48 hr |
| 0.5 g IV | 526 | 366 | 142 | 87 | 70 | 15 |
| 0.5 g IM | 115 | 425 | 308 | 127 | 96 | 28 |
| 1 g IV | 995 | 855 | 293 | 147 | 132 | 32 |
| 1 g IM | 504 | 628 | 418 | 237 | ND | ND |
| 2 g IV | 2692 | 1976 | 757 | 274 | 198 | 40 |
| ND = Not determined. |
Thirty-three percent to 67% of a ceftriaxone dose was excreted in the urine as unchanged drug and the remainder was secreted in the bile and ultimately found in the feces as microbiologically inactive compounds. After a 1 g IV dose, average concentrations of ceftriaxone, determined from 1 to 3 hours after dosing, were 581 mcg/mL in the gallbladder bile, 788 mcg/mL in the common duct bile, 898 mcg/mL in the cystic duct bile, 78.2 mcg/g in the gallbladder wall and 62.1 mcg/mL in the concurrent plasma.
Over a 0.15 to 3 g dose range in healthy adult subjects, the values of elimination half-life ranged from 5.8 to 8.7 hours; apparent volume of distribution from 5.78 to 13.5 L; plasma clearance from 0.58 to 1.45 L/hour; and renal clearance from 0.32 to 0.73 L/hour. Ceftriaxone is reversibly bound to human plasma proteins, and the binding decreased from a value of 95% bound at plasma concentrations of < 25 mcg/mL to a value of 85% bound at 300 mcg/mL. Ceftriaxone crosses the blood placenta barrier.
The average values of maximum plasma concentration, elimination half-life, plasma clearance and volume of distribution after a 50 mg/kg IV dose and after a 75 mg/kg IV dose in pediatric patients suffering from bacterial meningitis are shown in Table 3. Ceftriaxone penetrated the inflamed meninges of infants and pediatric patients; CSF concentrations after a 50 mg/kg IV dose and after a 75 mg/kg IV dose are also shown in Table 3.
TABLE 3. Average Pharmacokinetic Parameters of Ceftriaxone in Pediatric Patients With Meningitis| | 50 mg/kg IV | 75 mg/kg IV |
| Maximum Plasma Concentrations (mcg/mL) | 216 | 275 |
| Elimination Half-life (hr) | 4.6 | 4.3 |
| Plasma Clearance (mL/hr/kg) | 49 | 60 |
| Volume of Distribution (mL/kg) | 338 | 373 |
| CSF Concentration - inflamed meninges (mcg/mL) | 5.6 | 6.4 |
| Range (mcg/mL) | 1.3-18.5 | 1.3-44 |
| Time after dose (hr) | 3.7 (± 1.6) | 3.3 (± 1.4) |
Compared to that in healthy adult subjects, the pharmacokinetics of ceftriaxone were only minimally altered in elderly subjects and in patients with renal impairment or hepatic dysfunction (Table 4); therefore, dosage adjustments are not necessary for these patients with ceftriaxone dosages up to 2 g per day. Ceftriaxone was not removed to any significant extent from the plasma by hemodialysis; in six of 26 dialysis patients, the elimination rate of ceftriaxone was markedly reduced.
TABLE 4. Average Pharmacokinetic Parameters of Ceftriaxone in Humans| Subject Group | Elimination Half-Life (hr) | Plasma Clearance (L/hr) | Volume of Distribution (L) |
| | | | |
| Healthy Subjects | 5.8-8.7 | 0.58-1.45 | 5.8-13.5 |
| Elderly Subjects (mean age, 70.5 yr) | 8.9 | 0.83 | 10.7 |
| Patients With Renal Impairment | | | |
Hemodialysis Patients (0-5 mL/min)* | 14.7 | 0.65 | 13.7 |
Severe (5-15 mL/min) | 15.7 | 0.56 | 12.5 |
Moderate (16-30 mL/min) | 11.4 | 0.72 | 11.8 |
Mild (31-60 mL/min) | 12.4 | 0.70 | 13.3 |
| Patients With Liver Disease | 8.8 | 1.1 | 13.6 |
*Creatinine clearance.
The elimination of ceftriaxone is not altered when Ceftriaxone for Injection is co-administered with probenecid.
Pharmacokinetics in the Middle Ear Fluid: In one study, total ceftriaxone concentrations (bound and unbound) were measured in middle ear fluid obtained during the insertion of tympanostomy tubes in 42 pediatric patients with otitis media. Sampling times were from 1 to 50 hours after a single intramuscular injection of 50 mg/kg of ceftriaxone. Mean (± SD) ceftriaxone levels in the middle ear reached a peak of 35 (± 12) mcg/mL at 24 hours, and remained at 19 (± 7) mcg/mL at 48 hours. Based on middle ear fluid ceftriaxone concentrations in the 23 to 25 hour and the 46 to 50 hour sampling time intervals, a half-life of 25 hours was calculated. Ceftriaxone is highly bound to plasma proteins. The extent of binding to proteins in the middle ear fluid is unknown.
Interaction with Calcium: Two in vitro studies, one using adult plasma and the other neonatal plasma from umbilical cord blood have been carried out to assess interaction of ceftriaxone and calcium. Ceftriaxone concentrations up to 1 mM (in excess of concentrations achieved in vivo following administration of 2 grams ceftriaxone infused over 30 minutes) were used in combination with calcium concentrations up to 12 mM (48 mg/dL). Recovery of ceftriaxone from plasma was reduced with calcium concentrations of 6 mM (24 mg/dL) or higher in adult plasma or 4 mM (16 mg/dL) or higher in neonatal plasma. This may be reflective of ceftriaxone-calcium precipitation.
Microbiology: The bactericidal activity of ceftriaxone results from inhibition of cell wall synthesis. Ceftriaxone has a high degree of stability in the presence of beta-lactamases, both penicillinases and cephalosporinases, of gram-negative and gram-positive bacteria.
In an in vitro study antagonistic effects have been observed with the combination of chloramphenicol and ceftriaxone.
Ceftriaxone has been shown to be active against most strains of the following microorganisms, both in vitro and in clinical infections described in the INDICATIONS AND USAGE section.
Aerobic gram-negative microorganisms:
Acinetobacter calcoaceticus
Enterobacter aerogenes
Enterobacter cloacae
Escherichia coli
Haemophilus influenzae (including ampicillin-resistant and beta-lactamase producing strains)
Haemophilus parainfluenzae
Klebsiella oxytoca
Klebsiella pneumoniae
Moraxella catarrhalis (including beta-lactamase producing strains)
Morganella morganii
Neisseria gonorrhoeae (including penicillinase- and nonpenicillinase-producing strains)
Neisseria meningitidis
Proteus mirabilis
Proteus vulgaris
Serratia marcescens
Ceftriaxone is also active against many strains of Pseudomonas aeruginosa.
NOTE: Many strains of the above organisms that are resistant to multiple antibiotics, e.g., penicillins, cephalosporins, and aminoglycosides, are susceptible to ceftriaxone.
Aerobic gram-positive microorganisms:
Staphylococcus aureus (including penicillinase-producing strains)
Staphylococcus epidermidis
Streptococcus pneumoniae
Streptococcus pyogenes
Viridans group streptococci
NOTE: Methicillin-resistant staphylococci are resistant to cephalosporins, including ceftriaxone. Most strains of Group D streptococci and enterococci, e.g., Enterococcus (Streptococcus) faecalis, are resistant.
Anaerobic microorganisms:
Bacteroides fragilis
Clostridium species
Peptostreptococcus species
NOTE: Most strains of Clostridium difficile are resistant.
The following in vitro data are available, but their clinical significance is unknown. Ceftriaxone exhibits in vitro minimal inhibitory concentrations (MICs) of ≤ 8 mcg/mL or less against most strains of the following microorganisms, however, the safety and effectiveness of ceftriaxone in treating clinical infections due to these microorganisms have not been established in adequate and well-controlled clinical trials.
Aerobic gram-negative microorganisms:
Citrobacter diversus
Citrobacter freundii
Providencia species (including Providencia rettgeri)
Salmonella species (including Salmonella typhi)
Shigella species
Aerobic gram-positive microorganisms:
Streptococcus agalactiae
Anaerobic microorganisms:
Prevotella (Bacteroides) bivius
Porphyromonas (Bacteroides) melaninogenicus