D. K. F. Meijer

Pharmacokinetics of biliary excretion in man. VI. Indocyanine green

SummaryThe pharmacokinetics of Indocyanine Green (ICG) has been studied in 15 patients given 0.5, 1.0 and 2.0 mg · kg−1. The plasma disappearance and biliary excretion rate were measured in patients with tightly fitting catheters under slight negative pressure in order to achieve complete collection of bile. Recovery of unchanged ICG in bile over 18 h after the i.v. injection was 80% of the dose in all three dose groups.Plasma disappearance in all 3 groups was biphasic, showing an initial phase with a t1/2 of 3–4 min and a secondary phase with a dose-dependent apparent t1/2 of 67.6, 72.5 and 88.7 min, respectively. After 0.5 and 1.0 mg · kg−1 the biliary excretion rate curves showed an ascending phase with a mean t1/2 of 5 min and a descending phase with a mean t1/2 of 72 min. It was inferred that the secondary component of the plasma-decay mainly reflected the biliary excretion rate. After 2.0 mg · kg−1 in some patients the biliary excretion curve showed features of saturation; the t1/2 of the descending phase ranged from 73 to 440 min, and the time of maximal excretion was increased from 1.3 to 2.7 h after injection, whilst the mean maximal excretion rate was in the same range as the excretion rate after the 1.0 mg · kg−1 dose. The non-linear pharmacokinetics was only moderately reflected in the measured plasma disappearance patterns. Two compartment analysis of the plasma levels indicated a clearance of 230–260 ml · min−1, whereas the clearance conventionally calculated from the initial t1/2 was 475 ml · min−1. The volume of the central compartment in 70 kg patients was 2.31, which is about the plasma volume. The fictive volume of distribution in the liver (V2) was 70–90 l, indicating marked hepatic storage of ICG. This was probably due to the very low liver-to-plasma transport rate (k21) of 0.006–0.10 min−1. Thus, the biliary excretion of ICG can be quantified by 2-compartment pharmacokinetic analysis of plasma disappearance curves, including a secondary phase. The latter, slow component was apparent at very low plasma levels due to the marked hepatic storage, and it was also influenced by retention of small amounts of impurities or degradation products. Improved detectability of this phase cannot simply be obtained by increasing the dose, since at doses exceeding 1.0 mg · kg−1 non-linear elimination may complicate the pharmacokinetic analysis.

Preparation and characterization of conjugates of (modified) human serum albumin and liposomes: drug carriers with an intrinsic anti-HIV activity

Human serum albumin (HSA) derivatized with cis-aconitic anhydride (Aco-HSA) that was earlier shown to inhibit replication of human immunodeficiency virus type 1 (HIV-1), was covalently coupled to conventional liposomes, consisting of phosphatidylcholine, cholesterol and maleimido-4-(p-phenylbutyryl)phosphatidylethanolamine, using the heterobifunctional reagent N-succinimidyl-S-acetylthioacetate (SATA). The amount of HSA that could be coupled to the liposomes depended on derivatization of the HSA and ranged from 64.2 +/- microgram HSA/micromol total lipid for native HSA to 29.5 +/- 2.7 microgram HSA/micromol total lipid for HSA in which 53 of the epsilon amino groups of lysine were derivatized with cis-aconitic anhydride (Aco53-HSA). Incorporation of 3.8 mol% of total lipid of a poly(ethylene glycol) derivative of phosphatidylethanolamine (PEG-PE) in the liposomes resulted in a lower coupling efficiency of Aco-HSA. The elimination and distribution of the liposomal conjugates in rats in vivo was largely dependent on the modification of the HSA coupled to the liposomes. With native HSA-liposomes, more than 70% of the conjugate was still found in the blood plasma 30 min after i.v. injection in rats, while at this time Aco-HSA-liposomes were completely cleared from the circulation. The rapid clearance of conventional Aco-HSA-liposomes was due to a rapid uptake into the liver and could be considerably decreased by incorporating PEG-PE in the liposomal bilayer. After 3 h 60% of Aco-HSA-PEG-liposome conjugates were found in the blood. In an in vitro anti-HIV-1 assay, the 50% inhibitory concentrations (IC50) for Aco39-HSA-liposomes and Aco53-HSA-liposomes expressed as protein weight, were 2.87 microgram/ml and 0.154 microgram/ml, respectively. When PEG-PE was incorporated, the Aco53-HSA-liposomes retained anti HIV-1 activity (IC50:3.13 microgram/ml). The possibility to modulate the residence time in the bloodstream of Aco-HSA-liposomes and the potent anti-HIV-1 activity of these conjugates, may allow the development of an intrinsically active drug carrier system. By incorporating anti HIV-1 drugs such as AZT into such liposomes a drug delivery system can be designed that might act simultaneously on the virus/cell binding by virtue of the coupled Aco-HSA and on the RNA/DNA transcription of the HIV-1 replication cycle through the nucleoside analogue.

Low Molecular Weight Proteins as Carriers for Renal Drug Targeting: Naproxen–Lysozyme

AbstractLow molecular weight proteins (LMWPs), such as lysozyme, may be suitable carriers to target drugs to the kidney. In this study the antiinflammatory drug naproxen was covalently bound to lysozyme (1:1). Pharmacokinetics of the conjugate, naproxen–lysozyme (nap-LYSO), were compared to that of an equimolar mixture of uncoupled naproxen with lysozyme in freely moving rats. Similar plasma kinetics and organ distribution for native lysozyme and the drug conjugate were observed (Clp = 1.2 and 1.1 ml/min; n

Distribution of quaternary ammonium compounds between particulate and soluble constituents of rat liver, in relation to their transport from plasma into bile

t_{1/2,beta }

The role of the liver in clearance of glycoproteins from the general circulation, with special reference to intestinal alkaline phosphatase.

n = 85 and 75 min, respectively). In case of the uncoupled naproxen–lysozyme mixture, a monoexponential plasma disappearance of naproxen with a n

POTENTIALS AND LIMITATIONS OF THE LOW-MOLECULAR-WEIGHT PROTEIN LYSOZYME AS A CARRIER FOR RENAL DRUG TARGETING

t_{1/2}