CHAPTER 7 | Implications of Drug–Nutrient Interactions and Pharmacology 115
Drugs and Enteral Nutrition Interactions
Continuous enteral feeding may be an effective
method of providing nutrients to older adults who are unable to swallow or eat adequately, depend- ing on client wishes and signed advance directives. However, use of a feeding tube to administer drugs can cause problems. When liquid drug formulations are mixed with enteral feeding formulas, incompati- bilities may occur. Types of physical incompatibility include granulation, gel formation, and separation of the enteral product, frequently resulting in clogged feeding tubes and interruption of nutrition delivery. Examples of drugs that can cause granulation and gel formation are ciprofloxacin suspension, chlorprom- azine concentrate, ferrous sulfate elixir, guaifenesin, and metoclopramide syrup.69
Emulsion breakage also
commonly occurs when acidic pharmaceutical syrups are added to enteral formulas. This reaction is more common in enteral formulas with intact protein and is less common in formulas with hydrolyzed protein or free amino acids.70
Most compatibility studies of drugs and enteral
products have focused on the drug’s effect on enteral product integrity. More important is the effect of the enteral product on drug bioavailability. This area requires more research, as placement of feeding tubes in older adults is becoming more common. Bioavailability problems are common with phenytoin suspension and tube feeding. Because phenytoin has a narrow therapeutic index, phenytoin blood levels are assessed routinely, and much information exists about the reduction of phenytoin bioavailability when given with enteral feedings. Individual variability is substantial. Recommendations to separate phenytoin suspension from tube feeding formulas are common. Stopping the tube feeding before and after the phenyt- oin dose is generally suggested, but recommendations vary from 1- to 4-hour intervals. The most common recommendation is a 1- to 2-hour feeding-free inter- val, with adequate tube flushes, before and after the dose of phenytoin is administered.71 Even with separation from tube feeds, a substantial
increase in phenytoin dose may be required, and serum level monitoring is essential. Although extended- release phenytoin capsules are usually taken once daily by mouth, formulations are not interchangeable.
Phenytoin suspension requires administration twice or three times daily. This results in time periods from 4 to 12 hours per day when feeds are unable to be administered, which may not allow enough time for adequate nutritional intake.71
Chewable phenytoin
tablets may be crushed and administered via feeding tube but are more likely to clog the tube compared with phenytoin suspension. If phenytoin levels remain unstable, switching to intravenous phenytoin or fos- phenytoin may be a reasonable alternative until tol- erance of oral drug administration is reestablished.72 Information may not be readily available concerning drug and enteral product interactions. Checking with the manufacturers’ medical information department may yield more information. Box 7.9 on page 116 lists common biochemical abnormalities associated with drugs prescribed for individuals who are enterally fed.73
Medical Nutrition Therapy and Food–Drug Interactions
What should the RDN and nutrition and dietetics technicians, registered (NDTR), do with all of this information? The Joint Commission standards require that clients are educated about potential food–drug interactions and provided counseling on nutrition and modified diets.74 As part of the interdisciplinary team, the RDN (or NDTR under the supervision of the RDN) should ensure that individuals are educated about potential food–drug interactions before (prospectively) and after (retrospectively) initiating a medication to deter- mine whether an effect may be the result of a food– drug interaction. This is not solely the responsibility of any specific team member, but the RDN or NDTR often takes this role. Additionally, an interdisciplinary mechanism should be developed to alert individual clients and staff of potential food–drug interactions during meal service. Foodservice staff should be provided education and training on appropriate food substitutions to prevent food–drug interactions.74
Box
7.10 on page 117 presents information to provide to older adults when prescribed a new drug. Box 7.11 on page 117 presents steps for retro- spective medical nutrition therapy and evaluation of symptoms as possible food–drug interactions.
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