Pharmacy Focus: The Evolution of Fat Emulsions

Intravenous fat emulsions (IVFEs) are suspensions of oil in an aqueous medium manufactured to provide a dense source of energy in parenteral nutrition. IVFEs have the potential to prevent essential fatty acid deficiency (EFAD) in critically ill patients, but unfortunately the lipid constituent has also been associated with the development of liver disease, fat overload syndrome, and worsening respiratory function.1

Many ingredients are common to all IVFEs, but the oil sources and their percentages makes them different from one another. IVFEs currently contain egg yolk phospholipid (i.e. lecithin) as an emulsifying agent, and differ in their percentages of soybean oil, medium-chain triglycerides (MCTs - i.e. coconut oil), olive oil, and fish oil (EPA, DHA). The oil used dictates how IVFEs are metabolized, and each oil provides unique beneficial and detrimental properties. A soybean-based fat emulsion has been the predominant IVFE available to American practitioners since its approval in 1972. Newer preparations on the market in the US, such as SMOFlipid, are combining oil sources, including soybean, MCTs, olive oil and fish oil.2

​Each emulsion has inflammatory characteristics based on the different oil sources and predominant fatty acids used in production. Since 1960, emulsions have evolved from being solely made with soybean oil to being combined with MCTs, olive oil, and more recently, fish oil. This evolution of IVFEs has yielded less pro-inflammatory emulsions, with fish oil being the least pro-inflammatory of them all. Fish oil emulsions are also rich in the antioxidant alpha-tocopherol (Vitamin E), which is added to prevent the oxidation of its fatty acids. The addition of fish oil to lipid emulsions has demonstrable effects on cell membranes and inflammatory processes.

There are many complications associated with intravenous fat emulsions. The ideal IVFE would reverse or prevent EFAD without leading to those complications. Although the ideal emulsion has yet to be developed, alternatives are being tested and adopted by practitioners. Research is bringing us closer to finding the optimal product for critically ill patients.
 
References:
1. Anez-Bustillos L, Dao DT, Baker MA, Fell GL, Puder M, Gura KM. Intravenous Fat Emulsion Formulations for the Adult and Pediatric Patient: Understanding the Differences. Nutrition in Clinical Practice. 2016;31(5):596-609. doi:10.1177/0884533616662996.
2. Smoflipid: Lipid Injectable Emulsion, USP 20%. Smoflipid: Lipid Injectable Emulsion, USP 20%. http://smoflipid.com/smoflipid-composition.html. Accessed November 23, 2016.