[Acetyl starch as volume substitute, a possible alternative to HES]

Effect of molecular weight and substitution on tissue uptake of hydroxyethyl starch: a meta-analysis of clinical studies

BACKGROUND

Intravenously infused hydroxyethyl starch (HES) can be found in urine, plasma and tissues. HES remaining in plasma and tissues is thought to increase the risk of clinical complications. HES solutions of lower molecular weight and substitution have been developed to increase urinary excretion and reduce plasma persistence. However, their effect on tissue uptake of HES has not been investigated in human subjects.

OBJECTIVE

Our objective was to test the hypothesis that lower molecular weight and substitution decrease tissue uptake of HES.

DATA SOURCES

Computer searches were performed of MEDLINE; EMBASE; the Cochrane Library; meeting abstract databases in surgery, anaesthesiology and intensive care; ClinicalTrials.gov; and Google. Supplementary sources were reference lists and electronic tables of journal contents. No time period or language restrictions were imposed.

STUDY SELECTION

Clinical studies were eligible for inclusion in the meta-analysis, if data were reported both for cumulative urinary excretion of HES over 24 hours after infusion and for plasma HES concentration at 24 hours.

DATA EXTRACTION

Data were extracted on 24-hour urinary excretion of HES, 24-hour HES plasma concentration, plasma volume, HES molecular weight and substitution, study design, type and demographics of subjects, indication for fluid infusion, and HES infusion regimen. Tissue uptake of HES was computed as the difference between the infused dose and the sum of urinary excretion and residual plasma HES at 24 hours.

DATA SYNTHESIS

Twenty-five clinical studies totalling 287 subjects were included. Tissue uptake of low-molecular-weight HES (≤200 kD) was 42.3% (95% confidence interval [CI] 39.6, 45.0) compared with 24.6% (CI 17.8, 31.4) for high-molecular-weight HES (p < 0.001). Similarly, tissue uptake of lower-substitution HES (≤0.5) was 42.4% (CI 39.5, 45.3) versus 26.6% (CI 19.6, 33.6) for higher-substitution HES (p < 0.001). Among the three most often investigated single HES solutions, tissue uptake of 130/0.4 (42.6%; CI 35.0, 50.2) and HES 200/0.5 (43.3%; CI 39.4, 47.2) closely coincided, whereas uptake of HES 450/0.7 (22.2%; CI 14.8, 29.6) was lower (p = 0.001 and p < 0.001, respectively).

CONCLUSIONS

This meta-analysis did not support the hypothesis that lower molecular weight and substitution decrease tissue uptake of HES. Further clinical studies of HES tissue uptake are needed.

Cationic amylose-encapsulated bovine hemoglobin as a nanosized oxygen carrier

Nanosized hemoglobin-based oxygen carriers are one of the most promising blood substitutes. In the present study, a comprehensive strategy for the preparation of nanosized cationic amylose-encapsulated hemoglobins (NCAHbs) was developed. First, cationic amylase (CA) was synthesized from amylose and quaternary ammonium salt by an etherification reaction. The structure of CA was characterized using Fourier transform infrared spectrophotometry (FTIR) and proton nuclear magnetic resonance spectrophotometry ((1)H NMR). The degree of substitution and the zeta potential were also measured. Then, the NCAHbs were prepared by electrostatic adhesion, reverse micelles and cross-linking. The UV-visible spectrophotometer was used to measure the entrapment efficiency (EE%) and drug loading efficiency (DL%) of the NCAHbs. Transmission electron microscopy and Malvern Nano-zs 90 analyzer were used to observe the size distribution and morphology of particles. Chemical structure was determined from the FTIR spectrum. A Hemox analyzer was used to measure the P(50) and Hill coefficients. A lethal hemorrhagic shock model in rats was used to evaluate the therapeutic effect of the NCAHbs. The results showed that the combined methods improved the size, stability, EE%, DL%, and oxygen-carrying capacity of the NCAHbs. The average diameter of the NCAHbs was 92.53 ± 3.64 nm, with a narrow polydispersity index of 0.027. The EE% was 80.05% ± 1.56% and DL% was 61.55% ± 1.41%. The P(50) and Hill coefficient were equal to 28.96 ± 1.33 mmHg and 2.55 ± 0.22, respectively. The size of NCAHbs remained below 200 nm for six days in PBS solution. The NCAHbs could effectively prevent lung injury from progressing to lethal hemorrhagic shock because they acted as both a volume expander and an oxygen carrier.

Pharmacokinetics of Hydroxyethyl Starch

Hydroxyethyl starch has recently become the subject of renewed interest because of the introduction of a new specification, hydroxyethyl starch 130/0.4, as well as the clinical availability of a solution using a previous hydroxyethyl starch type (hydroxyethyl starch 670/0.75) with a carrier other than 0.9% saline. Various types of hydroxyethyl starch show different pharmacokinetic behaviour. Since hydroxyethyl starch is a polydisperse solution acting as a colloid, pharmacodynamic action depends on the number of oncotically active molecules, not on the plasma concentration alone; therefore, solutions with a lower in vivo molecular weight contain more molecules at similar plasma concentrations. On the other hand, high plasma concentrations as well as high in vivo molecular weight can affect blood coagulation, especially factor VIII and von Willebrand factor. Hydroxyethyl starch types with a molar substitution >0.4 accumulate in plasma after repetitive administration, most pronounced with hetastarch (hydroxyethyl starch 670/0.75). Correspondingly, tissue storage as measured by (14)C tracer studies in animals showed significantly higher values for hydroxyethyl starch 200/0.5 compared with hydroxyethyl starch 130/0.4 (about 4-fold at the latest timepoint after the last administration), and considerably higher values for hetastarch compared with both hydroxyethyl starch 130/0.4 and 200/0.5. Hydroxyethyl starch 130/0.4 does not accumulate in plasma after single- and multiple-dose administration in contrast to all other available hydroxyethyl starch specifications. Plasma clearance of hydroxyethyl starch 130/0.4 is at least 20-fold higher than that for hetastarch, and considerably higher than for pentastarch. In patients with renal insufficiency, pharmacokinetic data are only available for hydroxyethyl starch 130/0.4. Cumulative urinary excretion, even in the presence of severe non-anuric renal failure, is higher for hydroxyethyl starch 130/0.4 than values published for older hydroxyethyl starch specifications. Hydroxyethyl starch 130/0.4 may be given to patients with severe renal impairment as long as urine flow is preserved. The pharmacodynamics with respect to the volume effect does not directly mirror pharmacokinetics in the case of hydroxyethyl starch solutions. Equivalent volume efficacy has been proven for hydroxyethyl starch 130/0.4 compared with 200/0.5. Prolonged persistence of hydroxyethyl starch in plasma and tissues can be avoided by using rapidly metabolisable hydroxyethyl starch types with molar substitution <0.5. Influence on coagulation is minimal with hydroxyethyl starch 130/0.4, and no adverse effects on kidney function have been observed even with large repetitive doses when used according to the product information.

The pharmacokinetics and tolerability of an intravenous infusion of the new hydroxyethyl starch 130/0.4 (6%, 500 mL) in mild-to-severe renal impairment

Hydroxyethyl starches (HES) are almost exclusively excreted glomerularly, in part after hydrolysis by amylase. HES 130/0.4 (Voluven; Fresenius Kabi Deutschland GmbH, Bad Homburg, Germany) was developed to improve pharmacokinetics whereas preserving the efficacy of volume effect. We studied the dependency of pharmacokinetics of HES 130/0.4 on renal function. Nineteen volunteers with stable, non-anuric renal dysfunction, ranging from almost normal creatinine clearance (CL(cr)) to severe renal impairment (mean CL(cr): 50.6 mL. min(-1). 1.73 m(-2)), were given a single infusion of 500 mL 6% HES 130/0.4 over 30 min. HES plasma concentrations were determined until 72 h, urinary excretion until 72-96 h. CL(cr) had been obtained at least twice before and twice after dosing. Standard pharmacokinetic calculations and regression analysis were performed. Area under the time concentration curve (AUC(0-inf)) clearly depended on renal function comparing subjects with CL(cr) < 50 with those with CL(cr) > or =50 (ratio 1.73). Peak concentration (C(max), 4.34 mg/mL) as well as terminal half-life (16.1 h, model independent) were not affected by renal impairment. At CL(cr) > or =30, 59% of the drug could be retrieved in urine, versus 51% at CL(cr) 15-<30. The mean molecular weight of HES in plasma was 62,704 d at 30 min, showing lower values with increased renal impairment (P = 0.04). Pre-dose amylase concentrations inversely correlated with baseline CL(cr). Residual HES plasma concentrations after 24 h were small in all subjects (< or =0.6 mg/mL). We conclude that HES 130/0.4 (500 mL 6%) can be safely administered to patients even with severe renal impairment, as long as urine flow is preserved, without plasma accumulation.

IMPLICATIONS

Dependency of the pharmacokinetics of hydroxyethyl starch 130/0.4 on renal function was studied. The area under the time concentration curve increased moderately with more severe renal dysfunction; however, small plasma concentrations were observed after 24 h. Terminal half-life and peak concentration remained unaffected by renal impairment.