Protein binding characteristics and pharmacokinetics of ceftriaxone in intensive care unit patients

Aims

The aim of the present study was to assess the pharmacokinetics of total and unbound ceftriaxone in intensive care unit (ICU) patients and its protein binding characteristics.

Methods

Twenty patients (m/f 15/5, age 25–86 years, body weight 60–121 kg, APACHE II 7–40, estimated glomerular filtration rate 19–157 ml min^–1, albumin 11.7–30.1 g l^–1, total bilirubin <0.1–36.1 mg dl^–1) treated with intravenous ceftriaxone were recruited from two ICUs. Timed plasma samples were obtained using an opportunistic study protocol. Ceftriaxone concentrations were determined by high-performance liquid chromatography; unbound concentrations were determined after ultrafiltration using a new method which maintains physiological pH and temperature. The pharmacokinetics was described by a one-compartment model, the protein-binding characteristics by Michaelis–Menten kinetics.

Results

For total drug, the volume of distribution was 20.2 l (median; interquartile range 15.6–24.5 l), the half-life 14.5 h (10.0–25.5 h) and the clearance 0.96 l h^–1 (0.55–1.28 l h^–1). The clearance of unbound drug was 1.91 l h^–1 (1.46–6.20 l h^–1) and linearly correlated with estimated glomerular filtration rate (slope 0.85, y-intercept 0.24 l h^–1, r² = 0.70). The unbound fraction was higher in ICU patients (33.0%; 20.2–44.5%) than reported in healthy volunteers, particularly when renal impairment or severe hyperbilirubinaemia was present. In all patients, unbound concentrations during treatment with ceftriaxone 2 g once daily remained above the EUCAST susceptibility breakpoint (≤1 mg l^–1) throughout the whole dosing interval.

Conclusions

Protein binding of ceftriaxone is reduced and variable in ICU patients due to hypoalbuminaemia, but also to altered binding characteristics. Despite these changes, the pharmacokinetics of unbound ceftriaxone is governed by renal function. For patients with normal or reduced renal function, standard doses are sufficient.     

Plasma protein binding of ceftriaxone

1. The plasma protein binding characteristics of ceftriaxone, a new cephalosporin antibiotic, were determined in human, baboon, rabbit, dog and rat plasma.

2. The protein binding of ceftriaxone was similar and concentration-dependent in human, baboon, rabbit and rat plasma, being highly bound (90-95%) at low concentrations (<100μg/ml) but considerably less bound (approx. 60%) at high concentrations (> 400 μg/ml). Binding in dog plasma was also concentration-dependent but much lower (approx. 25%) at lower concentrations (30 μg/ml) and virtually unbound (2%) at high concentrations (1 mg/ml) over a similar concentration range.

3. Binding of ceftriaxone to human plasma involved two sites: a high affinity-low capacity (saturable) site and a low affinity-high capacity site. Binding to dog plasma apparently was at a single, high affinity-low capacity site.

4. The pharmacokinetics of ceftriaxone in an animal species with binding characteristics similar to man (baboon), appear to be non-linear when based on total drug concentration and linear when based on the free drug concentration. In the dog, pharmacokinetic parameters did not change appreciably if calculated from total or free drug concentrations, due to the low protein binding.     

Free concentration and protein binding of ceftriaxone]

Ceftriaxone (CTRX) was administered in dose of 1 g 30 minutes intravenous drip infusion to 5 healthy volunteers. Cefpiramide (CPM) and cefotetan (CTT) were administered as control antibiotics. The serum concentrations of total and free drugs, using ultrafiltration, were assayed by bioassay and HPLC. Protein binding rates and pharmacokinetic parameters were calculated. Free concentration of antibiotics were following orders in each sampling time: CTRX greater than CTT greater than CPM. Mean free concentrations of CTRX at 0 hour and at 8 hours after intravenous drip infusion was more than 20 micrograms/ml and more than 2 micrograms/ml. Even at 24 hours after intravenous drip infusion free concentrations of CTRX were detectable. Mean half life in beta phase by HPLC was following orders: CTRX (7.5 hours) greater than CPM (5.4 hours) greater than CTT (4.7 hours). Mean protein binding rates were following orders: CPM (98%) greater than CTT (94%) greater than CTRX (92%). Conclusions: Characteristic of CTRX is high free drug concentration and long half life.     

Protein binding of ceftriaxone: comparison of three techniques of determination and the effect of 2-hydroxybenzoylglycine, a drug-binding inhibitor in uremia

Ceftriaxone is a third-generation cephalosporin exhibiting a long half-life and a concentration-dependent protein binding. This study compared three techniques of protein binding determination (equilibrium dialysis chamber, ultrafiltration cones (Centriflo), and ultrafiltration (Centrifree micro-partition system) on human plasma and serum at ceftriaxone concentrations achieved clinically. A second objective was to determine the effect of 2-hydroxybenzoylglycine (HBG) on the protein binding of ceftriaxone. High performance liquid chromatography (HPLC) and liquid scintillation counting assays were used. Equilibrium dialysis was rotated for 12 h. The supplier's recommendations were followed for ultrafiltration techniques. The plasma protein binding of ceftriaxone, as determined by equilibrium dialysis and assayed by HPLC, decreased from 98.6 to 73.5% for drug concentrations varying from 25 to 400 micrograms/ml. Somewhat lower values were obtained with Centrifree, the binding fell from 92.1 to 73.5% for the same concentration range. Serum protein binding was similar to results obtained with plasma samples. Centriflo cones yielded more inconsistent results. A significant difference was seen between the three techniques (p less than 0.0001, three-way analysis of variance). The addition of HBG, a compound that inhibits drug binding in uremia, resulted in ceftriaxone binding defects similar to those seen in uremic serum. Although equilibrium dialysis remains a classic method of protein binding determination, Centrifree appears to be a better system.     

Effect of probenecid on the elimination and protein binding of ceftriaxone

Summary The kinetics and binding parameters of ceftriaxone have been characterized in eight normal subjects who received, in sequence, 1.0 g ceftriaxone and 1.0 g ceftriaxone together with 250 and 500 mg probenecid q.i.d.Probenecid increased the total systemic clearance (CL _S ^T ) from 0.244 to 0.312 ml/min/kg, whereas the terminal half-life (t _1/2() ^T ) fell from 8.1 to 6.5 h. In contrast, the renal clearance of free ceftriaxone (CL _R ^F ) was decreased from 2.09 to 1.67 ml/min/kg, confirming a small but significant contribution of tubular secretion to the renal elimination of ceftriaxone.The final value of CL _R ^F was attained with the lower dose probenecid, whereas the non-renal clearance of free ceftriaxone (CL _NR ^F ) fell progressively from 2.78 to 1.90 ml/min/kg with the increasing probenecid dose. The total decrease in the systemic clearance of free ceftriaxone (CL _S ^F ) after the higher dose of probenecid was about 30% (4.87 to 3.57 ml/min/kg).As a consequence of a decreased affinity constant (K_A), the average free fraction in plasma (f) was increased by 54% after the low dose and by 74% after the high dose of probenecid.The protein binding interaction between probenecid and ceftriaxone appears to be unique. The results are of limited clinical consequence for ceftriaxone but they emphasise the importance of evaluating the kinetics of the free drug when examining interactions involving probenecid.Abbreviations AUC^T, AUC^F plasma AUC of total and free (unbound) drug - CL _S ^T , CL _S ^F clearance: total systemic, free systemic - CL _O ^T , CL _R ^F total oral, free renal - CL _NR ^F free non-renal - V _Z ^T V _SS ^T apparent volume of distribution: terminal phase, total drug; corrected steady-state, total drug [14] - f average free fraction of drug in plasma - f_e fraction of dose excreted unchanged in urine - t _1/2() ^T terminal t_1/2: total drug - t _1/2() ^F free drug - K_A affinity constant - nP capacity constant - C _av ^ss steady-state concentration in plasma during multiple dosing - C_B bound concentration - C_F free (unbound) concentration     

Factors affecting ceftriaxone plasma protein binding during open heart surgery

Factors most likely contributing to reduced ceftriaxone plasma protein binding in patients undergoing open heart surgery (OHS) were examined. Binding was determined by equilibrium dialysis. It was found that ceftriaxone does not bind significantly to red blood cells, alpha 1-acid glycoprotein, or to protamine, and that the pH of serum did not significantly affect binding. Albumin is the major protein to bind ceftriaxone, and binding decreases with lower albumin concentrations due to fewer binding sites. The binding of ceftriaxone was not affected by the in vitro addition of heparin or methylprednisolone, but high concentrations of methylprednisolone hemisuccinate increased the free fraction of ceftriaxone. Increased concentrations of free fatty acids (FFA) were demonstrated in several patients undergoing OHS. The in vitro addition of palmitic, stearic, linoleic, and oleic acids in high concentrations decreased the binding of ceftriaxone. Ceftriaxone binding in patient samples correlated with the molar ratio of FFA to albumin, but not to either individually. The dual effect of increased FFA and decreased albumin concentrations in OHS patients appears responsible for most of the observed binding alterations.     

Effect of caffeine on ceftriaxone disposition and plasma protein binding in the rat

Previous studies have shown that caffeine can affect drug kinetics by altering drug binding to plasma protein, drug absorption, or drug distribution. In this study, the effect of caffeine on the in vivo protein binding and the disposition of ceftriaxone (a highly protein-bound cephalosporin) were investigated in the rat. Ceftriaxone 100 mg/kg and caffeine 20 mg/kg were i.v. injected via the tail vein and ceftriaxone in plasma, plasma filtrate, urine, feces, and tissues (brain, heart, kidney, liver, gut, lung, and muscle) was assayed by HPLC with UV detection. The fraction of free ceftriaxone in plasma ranged from 5.6 to 32.8% of total ceftriaxone (3-347 micrograms/ml) without caffeine and showed no alteration by caffeine. The total amount of ceftriaxone excreted in urine and feces was increased significantly (p less than 0.05) from 13.1 +/- 1.8 mg (mean +/- SD, 54.6% of total) to 15.3 +/- 1.1 mg (63.8% of total) by caffeine coadministration. The terminal half-life of ceftriaxone in plasma was shortened from 59 to 47 min, and the area under the plasma drug concentration-time curve (AUC) was reduced from 612 to 516 micrograms hr/ml. Although the peak drug concentrations and the times of peak concentration of ceftriaxone in tissues were not altered by caffeine administration, the elimination of ceftriaxone was increased, as indicated by generally shorter half-lives (decreases ranged from 17.5% in liver to 34.2% in brain) and lower AUC values (from 9.0% in heart to 54.5% in brain). These results suggest that caffeine does not alter the protein binding of ceftriaxone, but enhances the elimination of ceftriaxone in the rat.     

Effect of caffeine on ceftriaxone disposition and plasma protein binding in the rat

Previous studies have shown that caffeine can affect drug kinetics by altering drug binding to plasma protein, drug absorption, or drug distribution. In this study, the effect of caffeine on the in vivoprotein binding and the disposition of ceftriaxone (a highly protein-bound cephalosporin) were investigated in the rat. Ceftriaxone 100mg/kg and caffeine 20mg/kg were i.v. injected via the tail vein and ceftriaxone in plasma, plasma filtrate, urine, feces, and tissues (brain, heart, kidney, liver, gut, lung, and muscle) was assayed by HPLC with UV detection. The fraction of free ceftriaxone in plasma ranged from 5.6 to 32.8% of total ceftriaxone (3–347 g/ml) without caffeine and showed no alteration by caffeine. The total amount of ceftriaxone excreted in urine and feces was increased significantly (p<0.05)from 13.1±1.8mg (mean±SD, 54.6% of total) to 15.3 ±1.1 mg (63.8% of total) by caffeine coadministration. The terminal half-life of ceftriaxone in plasma was shortened from 59 to 47 min, and the area under the plasma drug concentration-time curve (AUC)was reduced from 612 to 516 g hr/ml Although the peak drug concentrations and the times of peak concentration of ceftriaxone in tissues were not altered by caffeine administration, the elimination of ceftriaxone was increased, as indicated by generally shorter half-lives (decreases ranged from 17.5% in liver to 34.2% in brain) and lower AUCvalues (from 9.0% in heart to 54.5% in brain). These results suggest that caffeine does not alter the protein binding of ceftriaxone, but enhances the elimination of ceftriaxone in the rat.This study was supported in part by a grant from Chong Kun Dang Co., Korea.     

Protein binding predictions in infants

Plasma binding protein levels are lower in the newborn than in the adult and gradually increase with age. At birth, human serum albumin (HSA) concentrations are close to adult levels (75%–80%), while alpha 1-acid glycoprotein (AAG) is initially half the adult concentration. As a result, the extent of drug binding to HSA is closer to that of the adult than are those drugs bound largely to AAG. A model that incorporates the fraction unbound in adults and the ratio of the binding protein concentration between infants and adults successfully predicted the fraction unbound in infants and children.     

Protein binding of nifedipine

The protein binding of nifedipine in concentrations up to 1200 ng ml-1 has been measured in serum, pure human albumin solution and pure human alpha 1-acid glycoprotein (AAG) solutions by ultrafiltration. The drug was extensively bound in serum from four healthy volunteers with a mean (+/- s.d.) fraction bound of 0.992 +/- 0.008. In albumin solution (40 g litre-1) the mean (+/- s.d.) fraction bound 0.970 +/- 0.012, was not significantly different (P greater than 0.05) from that in serum, suggesting that albumin is the major, but not necessarily the only, binding protein for nifedipine in serum. The binding of nifedipine in solutions of AAG was proportional to the AAG concentration and ranged from 0.514 +/- 0.059 to 0.755 +/- 0.035 in solutions containing 50 and 150 mg % AAG, respectively. Binding of nifedipine in all protein solutions was linear.     

Protein binding of propisomide

This paper describes the protein binding of propisomide to human serum and isolated proteins using equilibrium dialysis. The drug is exclusively bound to alpha1-acid glycoprotein with high affinity. The binding is saturable even at low concentrations of the drug. Thus, the fraction unbound varied from 0.05 to 0.60 with decreasing serum concentration. The major metabolite of the drug or other drugs with affinity for alpha1-acid glycoprotein can displace propisomide from its binding site only when present in serum at high levels. Two ultrafiltration techniques are compared to equilibrium dialysis for the determination of serum protein binding of propisomide. Ultrafiltration does not give reliable results. Equilibrium dialysis is retained as an accurate method for the determination of the fraction unbound of propisomide.     

Protein binding of flucloxacillin in neonates

The isoxazolyl penicillins, including flucloxacillin, have the highest levels of plasma protein binding among the semisynthetic penicillins. Because only the free fraction of the penicillin is pharmacologically active, it would be useful to measure both protein-bound and free flucloxacillin to determine its protein binding. Until now, flucloxacillin protein binding in newborn infants has been investigated in only two studies with relatively small populations. In the present study, flucloxacillin protein binding was investigated in 56 (preterm) infants aged 3 to 87 days (gestational age, 25-41 weeks). Surplus plasma samples from routine gentamicin assays of each infant were collected and combined to obtain a sufficiently large sample for analysis. Free flucloxacillin was separated from protein-bound flucloxacillin using ultrafiltration. Reversed-phase high-performance liquid chromatography with ultraviolet detection was used to measure free flucloxacillin concentrations in ultrafiltrate and total flucloxacillin concentrations in pooled plasma. Flucloxacillin protein binding was 74.5% +/- 13.1% (mean +/- standard deviation) with a high variability among the infants (34.3% to 89.7%). High Pearson correlations were found between protein binding and the covariates-plasma albumin concentration (r = 0.804, P < 0.001, n = 18) and plasma creatinine concentration (r = -0.601, P < 0.001, n = 45). Statistically significant but less striking correlations were found between protein binding and gestational age, postconceptional age, body weight, and triglyceride concentration. Because of the high variability of protein binding among infants, it is difficult to devise a flucloxacillin dosage regimen effective for all infants. Individualized dosing, based on free flucloxacillin concentrations, might help to optimize treatment of late-onset neonatal sepsis, but practical obstacles will probably prevent analysis of free flucloxacillin concentrations in newborn infants on a routine basis.     

Effect of caffeine on the plasma protein binding and the disposition of ceftriaxone

The effects of caffeine on the in-vitro protein binding and the pharmacokinetics of ceftriaxone (a highly protein bound cephalosporin) were investigated. Caffeine failed to decrease in-vitro protein binding of ceftriaxone. Rabbit plasma concentrations of ceftriaxone (30 mg kg-1 i.v.) were elevated significantly (P less than 0.05 at 0.3, 0.6 and 1 h after injection) when caffeine 5 or 10 mg kg-1 i.v. was co-administered compared with ceftriaxone given alone. Caffeine increased the volume of distribution of the central compartment (V1) for ceftriaxone significantly from 49 +/- 38 ml kg-1 (mean +/- s.d., n = 6) to 97 +/- 33 ml kg-1 (caffeine 5 mg kg-1, P less than 0.05), and 94 +/- 8 ml kg-1 (caffeine 10 mg kg-1, P less than 0.05) and decreased the volume of distribution of the peripheral compartment (V2) from 145 +/- 106 ml kg-1 (mean +/- s.d., n = 6) to 31 +/- 18 ml kg-1 (caffeine 5 mg kg-1, P less than 0.5) and 36 +/- 31 ml kg-1 (caffeine 10 mg kg-1, P less than 0.1). The rate of transfer of ceftriaxone to the peripheral compartment (k12) was also decreased significantly (P less than 0.05) after caffeine. The elevated plasma concentration of ceftriaxone, increased V1 value and the decreased V2 and k12 values are probably the result of caffeine altering the distribution of ceftriaxone to the central and the peripheral compartments.