Injectable lipid emulsion (ILE), previously referred to as intravenous fat emulsion, serves as an important source of energy and essential fatty acids in patients receiving parenteral nutrition (PN). Until recently, the only available emulsions for use in the US were products containing 100% soybean oil (SO-based), which comprises long-chain triglycerides. In 2016, the US Food and Drug Administration approved a four-oil lipid emulsion product marketed as Smoflipid by Fresenius Kabi. This product contains 30% soybean oil, 30% medium-chain triglycerides, 25% olive oil, and 15% fish oil, available as a 20% emulsion. The phytosterol content is less in this emulsion compared with SO-based ILE. Smoflipid is contraindicated in patients with known hypersensitivity to soybean, fish, egg, or peanut proteins.1
Smoflipid is indicated in the US for use in adults with a usual daily dose of 1-2 grams/kg per day, not to exceed 2.5 grams/kg per day. The emulsion may be administered intravenously into a central or peripheral vein, using a 1.2 micron filter for administration.1
The introduction of the first successful ILE in the 1960s was a major breakthrough in PN, as this SO-based ILE not only assisted in the prevention of essential fatty acid deficiency, its use allowed another source of energy to offset excessive intake of parenteral dextrose.2 In 1984, a second-generation ILE, a 50:50 mixture of SO and medium chain triglycerides, was introduced in Europe; this product is not available in the US. The 1990s saw the introduction of an ILE consisting of 80% olive oil and 20% SO. This third-generation product is not currently marketed in the US. The fourth-generation ILEs, including Smoflipid, include fish oil alone or in combination with one or more additional oils.2
Concerns with SO-Based Emulsion
SO-based ILEs have proven to be an effective modality to deliver calories and reduce the carbohydrate load from dextrose. SO-based ILE is calorically dense and prevents essential fatty acid deficiency from occurring in patients receiving PN. The high content of omega-6 polyunsaturated acids in SO-based ILE has been a concern in clinical practice,3 especially in the critically ill population, as the omega-6 pathway is known to produce pro-inflammatory leukotrienes and prostanoids.2
SO-based ILE infused at a rapid rate has been shown to impair the phagocytic activity of the reticuloendothelial system, which may lead to higher rates of bacterial infection and reduced long-term survival.4 The 2016 Society of Critical Care Medicine and the American Society for Parenteral and Enteral Nutrition (ASPEN) Guidelines for the Provision of Nutrition Support in the Adult Critically Ill Patient suggest withholding or limiting the use of SO-based ILE during the first week of initiating PN.5 The evidence supporting this recommendation was rated as very low, and this was the only recommendation in the guidelines not meeting an 80% or higher level of agreement.6 It is important to note that early elimination of SO-based ILE is largely based on one prospective study. This research was conducted more than 20 years ago, and there have since been changes in standards of care in critical care.6
A New ILE in the US Market
Smoflipid, new to the US market, is composed of a four-oil blend and may offer advantages over SO-based ILE in patients with elevated liver function tests and in the critically ill population. In 2013, a randomized, controlled, double-blind, prospective, 28-day study in patients with intestinal failure showed improvement in alanine transaminase, aspartate transaminase, and total bilirubin.7 These improvements were statistically significant and provide the basis for consideration of Smoflipid in patients receiving PN for an extended period. It should be noted that this study contained only 73 patients total (34 in the Smoflipid arm and 39 in the SO-based group).7
In 2017, a meta-analysis of randomized, controlled trials was published observing outcomes with perioperative ILEs containing omega-3 fatty acids (fish oil-containing) versus non-fish oil containing.8 Data from 19 randomized, controlled trials with a total of 1167 patients were analyzed. The meta-analysis concluded that fish oil-containing ILE was associated with reduced infectious morbidity and a significant reduction in hospital length of stay.8
The majority of trials comparing fish oil-containing ILE with traditional SO-based ILE have short durations, and they do not evaluate the potential for development of essential fatty acid deficiency (EFAD) in patients who are on long-term PN. This concern is due to the lower ratio of n-6 polyunsaturated acids within the fish oil-containing ILEs (Smoflipid). EFAD manifests as a linoleic acid deficiency with an increase in mead acid levels; mead acid is produced when there is a lack of essential fatty acids. Patients with EFAD show clinical symptoms of dry, scaly rash; impaired wound healing; and immune dysfunction. However, clinical trials have shown that the diagnostic criteria for EFAD does not rise to the threshold for EFAD if ILE is delivered in 1 g/kg/day. This could be due to the higher content of arachidonic acid in the fish oil component of Smoflipid.9-11
The ASPEN position paper, Clinical Role for Intravenous Fat Emulsion (published in 2012 before the introduction of alternative ILEs in the US), concluded that these ILEs are safe and effective sources of energy and essential fatty acids. These products may have potential biochemical and/or clinical benefits.2 Alternative ILE products, such as Smoflipid, have the potential to benefit patients requiring long-term PN and those with inflammatory conditions. Further research is needed to verify these benefits. Benefit may be seen in the critically ill population and in patients receiving home PN.
Phil Ayers, PharmD, BCNSP, FASHP, is a clinical specialist in nutrition support and chief of clinical pharmacy services in the department of pharmacy at Baptist Health Systems in Jackson, Mississippi. He serves as secretary-treasurer for the board of directors of ASPEN and is the current president of the Mississippi Pharmacists Association.
Jenny Anderson, MS, RD, LD, CNSC, is a registered dietitian at Baptist Health Systems in Jackson. She completed her undergraduate degree in nutrition and dietetics at the University of Southern Mississippi and obtained her Master’s Degree from the University of Alabama.
Carman Dixon, PharmD, is a clinical pharmacy specialist at Mississippi Baptist Medical Center in Jackson. He is the lead pharmacist for the Pharmacokinetics Service in addition to serving on the Medication Safety and Pharmacy and Therapeutics Committees. He is a past-president of the Mississippi Society of Health-System Pharmacists and is the current education chairman for the Mississippi Pharmacist Association.
Mays, PharmD, CNSC, is a clinical pharmacy specialist in nutrition support at the University of Mississippi Medical Center in Jackson. He is a clinical assistant professor at the University of Mississippi School of Pharmacy. Andrew serves as president-elect for the Mississippi Society of Health-System Pharmacists and president of the Mississippi Society for Parenteral and Enteral Nutrition.
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