Intralipid 10%: physicochemical characterization

Capillary electrokinetic chromatography for studying interactions between β-blockers and Intralipid emulsion

Toxicity of β-blockers is one of the most common causes of poison-induced cardiogenic shock throughout the world. Therefore, methodologies for in vivo removal of the drugs from the body have been under investigation. Intralipid emulsion (ILE) is a common commercial lipid emulsion used for parenteral nutrition, but it has also been administered to patients suffering from drug toxicities. In this work, a set of β-blockers of different hydrophobicity's (log KD values ranging from 0.16 to 3.8) were investigated. The relative strength of the interactions between these compounds and the ILE was quantitatively assessed by means of binding constants and adsorption constants of the formed β-blocker-ILE complexes. The binding constants were determined by capillary electrokinetic chromatography and the adsorption constants were calculated based on different adsorption isotherms. Expectedly, the binding constants were strongly related to the log KD values of the β-blockers. The binding and adsorption constants also show that less hydrophobic β-blockers interact with ILE, suggesting that this emulsion could be useful for capturing such compounds in cases of their overdoses. Thus, the use of ILE for treatment of toxicities caused by a larger range of β-blockers is worth further investigation.

Hospital Production of Sterile 2% Propofol Nanoemulsion: Proof of Concept

In the context of essential drug shortages, this article reports a proof of concept for the hospital preparation of a 2% propofol injectable nanoemulsion. Two processes for propofol were assessed: mixing propofol with the commercial Intralipid® 20% emulsion and a “de novo” process performed using separate raw materials (i.e., oil, water, and surfactant) and optimized for droplet size reduction with a high-pressure homogenizer. A propofol HPLC-UV stability-indicating method was developed for process validation and short-term stability. In addition, free propofol in the aqueous phase was quantified by dialysis. To envision routine production, sterility and endotoxin tests were validated. Only the “de novo” process using high-pressure homogenization gave satisfactory physical results similar to commercialized Diprivan® 2%. Both terminal heat sterilization processes (121 °C, 15 min and 0.22 µm filtration) were validated, but an additional pH adjustment was required prior to heat sterilization. The propofol nanoemulsion was monodisperse with a 160 nm mean droplet size, and no droplets were larger than 5µm. We confirmed that free propofol in the aqueous phase of the emulsion was similar to Diprivan 2%, and the chemical stability of propofol was validated. In conclusion, the proof of concept for the in-house 2% propofol nanoemulsion preparation was successfully demonstrated, opening the field for the possible production of the nanoemulsion in hospital pharmacies.

Predicting the efficacy of opioid sequestration by intravenous lipid emulsion using biologically relevant in vitro models of drug distribution

Intravenous lipid emulsions (ILE), among other uses, are utilized in the treatment of poisonings caused by lipophilic substances. The body of evidence regarding the benefits of this treatment is growing but information about opioids-ILE interaction is still very scarce. In this work, the impact of ILE on the distribution of buprenorphine, fentanyl and butorphanol used in various concentrations (100-500 ng/ml) was investigated. Two different in vitro models were used: disposition of the drugs in plasma after ultracentrifugation and distribution into the simulated biophase (cell monolayer of 3T3 fibroblasts or J774.E macrophages). We confirmed the ability of ILE to sequester the three drugs of interest which results in their decrease in the aqueous part of the plasma by 34.2-38.2%, 11.7-28.5% and 6.0-15.5% for buprenorphine, fentanyl and butorphanol, respectively. Moreover, ILE affected the drug distribution to the biophase in vitro, however, in this case the drug concentration in cells decreased by 97.3 ± 3.1%, 28.6 ± 5.4% and 13.0 ± 7.5% for buprenorphine, fentanyl and butorphanol, respectively. The two models revealed notable differences in ILE's potential for drug sequestration, especially for buprenorphine. Similar, but not as pronounced tendencies were observed for the two other drugs. These discrepancies may result from the difference in protein abundance and resulting drug-protein binding in both systems. Nevertheless, the results obtained with both in vitro models correlated well with the partition coefficient (logP) values for these drugs.

Lipemia in the Plasma Sample Affects Fentanyl Measurements by Means of HPLC-MS2 after Liquid-Liquid Extraction

Examination of fentanyl levels is frequently performed in certain scientific evaluations and forensic toxicology. It often involves the collection of very variable blood samples, including lipemic plasma or serum. To date, many works have reported the methods for fentanyl detection, but none of them have provided information about the impact on the assay performance caused by an excessive amount of lipids. This aspect may be, however, very important for highly lipophilic drugs like fentanyl. To address this issue, we developed the liquid chromatography method with mass spectrometry detection and utilized it to investigate the impact of lipids presence in rabbit plasma on the analytical method performance and validation. The validation procedure, conducted for normal plasma and lipemic plasma separately, resulted in good selectivity, sensitivity and linearity. The limits of detection and quantification were comparable between the two matrices, being slightly lower in normal plasma (0.005 and 0.015 µg/L) than in lipemic plasma (0.008 and 0.020 µg/L). Liquid–liquid extraction provided a low matrix effect regardless of the lipid levels in the samples (<10%), but pronounced differences were found in the recovery and accuracy. In the normal plasma, this parameter was stable and high (around 100%), but in the lipemic matrix, much more variable and less efficient results were obtained. Nevertheless, this difference had no impact on repeatability and reproducibility. In the present work, we provided reliable, convenient and sensitive method for fentanyl detection in the normal and lipemic rabbit plasma. However, construction of two separate validation curves was necessary to provide adequate results since the liquid-liquid extraction was utilized. Therefore, special attention should be paid during fentanyl quantification that involves lipemic plasma samples purified by this technique.

Coexistence of oil droplets and lipid vesicles in propofol drug products

Propofol is intravenously administered oil-in-water emulsion stabilized by egg lecithin phospholipids indicated for the induction and maintenance of general anesthesia or sedation. It is generally assumed to be structurally homogenous as characterized by commonly used dynamic light scattering technique and laser diffraction. However, the excessive amount of egg lecithin phospholipids added to the propofol formulation may, presumably, give rise to additional formation of lipid vesicles (i.e., vesicular structures consisting of a phospholipid bilayer). In this study, we investigate the use of high-resolution cryogenic transmission electron microscopy (cryo-TEM) in morphological characterization of four commercially available propofol drug products. The TEM result, for the first time, reveals that all propofol drug products contain lipid vesicles and oil droplet-lipid vesicle aggregated structures, in addition to oil droplets. Statistical analysis shows the size and ratio of the lipid vesicles varies across four different products. To evaluate the impact of such morphological differences on active pharmaceutical ingredient (API)'s distribution, we separate the lipid vesicle phase from other constituents via ultracentrifuge fractionation and determine the amount of propofol (2,6-diisopropylphenol) using high performance liquid chromatography (HPLC). The results indicate that a nearly negligible amount of API (i.e., NMT 0.25% of labeled content) is present in the lipid vesicles and is thus primarily distributed in the oil phase. As oil droplets are the primary drug carriers and their globule size are similar, the findings of various lipid vesicle composition and sizes among different propofol products do not affect their clinical outcomes.

Physical Characterization of Halofantrine-Encapsulated Fat Nanoemulsions

We report the colloidal characterization of halofantrine (Hf)-laden soybean oil fat emulsions. Hf increased the zeta potential, at all pH values, of the fat emulsions. Concomitant with this, the isoelectric point (i.e.p.) of the emulsion increased to higher pH values. The emulsion was destabilized by a small amount of Hf; interestingly, however, this was ameliorated by increasing the amount of Hf. The particle size and polydispersity of the fat emulsion reflected this with a small Hf concentration resulting in a significant increase in both particle size and polydispersity, but less so as the Hf concentration was increased. Emulsions lost stability as the pH approached the i.e.p. and this effect was greatest for the small Hf concentration emulsions. Cryogenic transmission electron microscopy showed the presence of beading or string-like behavior leading to gross distortions of the spherical shape for highly unstable emulsions. We conclude that to maintain good stability for Hf-laden soybean oil emulsions, the pH of the emulsion should be kept away from its i.e.p, and also that the drug concentration should be maintained at a relatively high value.

Phospholipids at the interface: current trends and challenges

Phospholipids are one of the major structural elements of biological membranes. Due to their amphiphilic character, they can adopt various molecular assemblies when dispersed in water, such as bilayer vesicles or micelles, which give them unique interfacial properties and render them very attractive in terms of foam or emulsion stabilization. This article aims at reviewing the properties of phospholipids at the air/water and oil/water interfaces, as well as the recent advances in using these natural components as stabilizers, alone or in combination with other compounds such as proteins. A discussion regarding the challenges and opportunities offered by phospholipids-stabilized structure concludes the review.

An innovative method for determining lipemia interference in blood specimens

BACKGROUND

Lipemia interference in blood samples is usually determined by adding exogenous substances that cause turbidity or by using ultracentrifugation to clarify the sample. However, there are a number of problems associated with these methods, which make it difficult to ascertain with certainty that lipemia is the cause of interference. We assessed a novel method for evaluating lipemia interference.

METHODS

Lipemic and non-lipemic serum samples, with similar HDL cholesterol concentrations, were mixed in various proportions (5 concentrations) and assayed for HDL and triglycerides. Thus, matched HDL samples with increasing triglycerides concentrations were tested. We then calculated the percent recovery for HDL for each mixture.

RESULTS

Six matched sets of samples had HDL recoveries ranging from 95.9% to 101.1% (n=6 sets, 5 concentrations per set, total of 30 concentrations), with HDL concentrations ranging from 0.78 to 2.16 mmol/l. Triglycerides concentrations in these samples ranged from 1.06 to 9.78 mmol/l for the 30 concentrations.

CONCLUSIONS

We determined that there was no triglycerides interference on the HDL method performed on the Hitachi S40 Clinical Analyzer up to a triglycerides concentration of 9.78 mmol/l. This matching method is simple to perform and proved useful in evaluating interference due to lipemia.

Degradation kinetics of hydrolytically susceptible drugs in O/W emulsions—Effects of interfacial area and lecithin

To investigate the influence of the interfacial area and the emulsifier lecithin on the degradation rate of drugs prone to hydrolysis in parenteral lipid O/W emulsions we measured the degradation kinetics of phenyl salicylate in systems consisting of Miglyol as oil, buffered and isotonized aqueous phase and lecithin as emulsifier. Two-layer oil over water systems and emulsions of different oil droplet diameters and emulsifier contents were tested and a kinetic model was developed to interpret the results. The measurements showed a complex influence of interfacial area and liposomal concentration on the hydrolysis of phenyl salicylate. The interface between oil and water does not act as a diffusion barrier for phenyl salicylate, neither without nor with an interfacial layer of emulsifier. However, the presence of the layer and the formation of liposomes by the emulsifier lead to an overall acceleration of the hydrolysis. Three effects, partially counteracting each other, could be distinguished: the increase of phenyl salicylate concentration in the aqueous phase with increasing emulsifier concentration, the acceleration of hydrolysis with increasing interfacial area and the protection from hydrolysis by incorporation of phenyl salicylate into the emulsifier liposomes.

Partitioning of parabens between phases of submicron emulsions stabilized with egg lecithin

Partitioning of methyl and propyl parabens (methyl and propyl hydroxybenzoate, paraben M and P) between the major phases in the parenteral submicron emulsions was studied. The investigated emulsions contained 10% or 20% soya-bean oil, 1.2% or 2.4% egg lecithin, 0.18% or 0.36% paraben M and 0.02% or 0.04% paraben P. The aqueous phase was obtained by ultracentrifugation, and subsequently, it was subjected to ultrafiltration, which procedure allowed to distinguish between the fractions of free preservatives (Fw) and incorporated in the liposomal or micellar region (Flm). The fractions present in the oily phase and in the interface were calculated. Depending on the formulation, Fw was 17-31% and 2.3-6.0% for paraben M and P, respectively. The Flm values were in a very narrow range, i.e. 3.0-6.0% for both preservatives. Substantial accumulation, i.e. 38-58% was found in the interface and the partitioning into this region was related to the oil/lecithin ratio rather than to lipophilicity of the preservative.

Partition of antimicrobial additives in an intravenous emulsion and their effect on emulsion physical stability

A number of antimicrobial agents are potentially applicable to the preservation of small-volume parenteral emulsions. However, the physical stability of these emulsions is of paramount importance in ensuring their safety, and it is possible that antimicrobial additives could reduce the emulsion stability by a number of mechanisms. We have studied the effects of several antimicrobial agents on the physical stability of Diprivan, an intravenous anaesthetic emulsion. A particular problem is that many antimicrobial additives require an acidic pH in order to be effective (e.g. sodium benzoate, sodium metabisulphite) and the emulsion surface potential is insufficient to stabilize the emulsion to coalescence under these conditions. In addition several antimicrobial agents (e.g. methyl paraben and benzoic acid) partition into the oil phase of the emulsion, requiring the use of increased concentrations to remain effective. We describe an assay technique to quantify the oil partition, liposomal partition, and droplet surface adsorption of the additives. This illustrates that significantly more additive is partitioned out of the water phase than might be predicted from simple oil/water partition experiments.