Patients who may benefit from feeding tube delivery of nutritional supplements include those with abnormal esophageal or stomach peristalsis, altered anatomy secondary to surgery, depressed consciousness, or impaired digestive capacity. The enteral route is considered to be the superior route of administration of nutritional supplements.

Mechanism of Action and Drug Effects

The enteral formula groups provide the basic building blocks for anabolism. Different combinations and amounts of these nutrients are used based on the individual patient’s anabolic needs. Enteral nutrition supplies complete dietary needs through the gastrointestinal tract by the normal oral route or by feeding tube.

Indications

Contraindications

The usual contraindication to nutritional supplements of any kind is known allergy to a specific product or genetic disease that renders a patient unable to metabolize certain types of nutrients.

Adverse Effects

The most common adverse effect of nutritional supplements is gastrointestinal intolerance, manifesting as diarrhea. Infant nutritional formulations are most commonly associated with allergies and digestive intolerance. The other nutritional supplements are commonly associated with osmotic diarrhea. Rapid feeding or bolus doses can result in dumping syndrome, which produces intestinal disturbances. In addition, tube feeding places the patient at significant risk for aspiration pneumonia. This is especially true in patients in whom mental status, gag reflexes, and general mobility are compromised.

Interactions

Various nutrients can interact with drugs to produce significant food-drug interactions. With some exceptions, food usually delays the absorption of drugs when administered simultaneously. High gastric acid content or prolonged emptying time can result in decreased effects of certain antibiotics (cephalosporins, erythromycin, and penicillins). An increased absorption rate resulting in increased therapeutic effects can be seen when corticosteroids or vitamins A and D are given with nutritional supplements. The antibiotic effects of tetracyclines and quinolones are decreased when they are given with nutritional supplements as a result of chemical inactivation. These drugs must be given at least 2 hours before or after tube feedings.

Tube feedings can also reduce the absorption of phenytoin, which may result in seizures. It is recommended that tube feedings be held for at least 2 hours before and after the administration of phenytoin. This can be problematic, because the patient may not receive adequate nutrition due to withholding of feedings. This issue is somewhat controversial, and some suggest that the interaction is more theoretical than actual. Thus, some institutions have decided to ignore this possible interaction and to monitor phenytoin levels and patient status, rather than holding the tube feedings, whereas others continue to hold the tube feedings. Often the patient requires intravenous phenytoin when continuous tube feedings are necessary.

Dosages

Because nutrient requirements vary greatly, dosages are individualized according to patient needs.

Elemental Formulations

Elemental formulations are enteral supplements that contain dipeptides, tripeptides, or crystalline amino acids. Minimal digestion is required with elemental formulations. These supplements are indicated for patients with pancreatitis, partial bowel obstruction, irritable bowel disease, radiation enteritis, bowel fistulas, and short bowel syndrome. They are contraindicated in patients who have had hypersensitivity reactions to them. Elemental formulation supplements are available without a prescription and have no pregnancy category.

Polymeric Formulations

Polymeric formulations are enteral supplements that contain complex nutrients derived from proteins, carbohydrates, and fat. The polymeric formulations are some of the most commonly used enteral formulations because they most closely resemble normal dietary intake. They are preferred over elemental formulations in patients who have fully functional gastrointestinal tracts and have no specialized nutrient needs. Polymeric formulations are less hyperosmolar than elemental formulations and therefore cause fewer gastrointestinal problems. They are contraindicated in patients who have had hypersensitivity reactions to them. They are available without a prescription and have no pregnancy category classification.

Modular Formulations

Altered Amino Acid Formulations

Amin-Aid is one of the many amino acid formulation nutritional supplements available. Many of the nutritional supplements in this category are also listed as modular formulations because they can be used as both single-nutrient formulas and as nutritional formulations for patients with genetic errors of metabolism. Specialized amino acid formulations are used most commonly in patients who have metabolic disorders such as phenylketonuria, homocystinuria, and maple syrup urine disease. They are also used to supply nutritional support to patients with illnesses such as renal impairment, eclampsia, heart failure, or liver failure.

Parenteral Nutrition

Parenteral nutritional supplementation (intravenous administration) is the preferred method for patients who are unable to tolerate and/or maintain adequate enteral or oral intake. Instead of administration of partially digested nutrients into the gastrointestinal tract (as in enteral nutrition), vitamins, minerals, amino acids, dextrose, and lipids are administered intravenously directly into the circulatory system. This effectively bypasses the entire gastrointestinal system, which eliminates the need for absorption, metabolism, and excretion. Parenteral nutrition is also called total parenteral nutrition (TPN) or hyperalimentation.

TPN can supply all of the calories, carbohydrates, amino acids, fats, trace elements, vitamins, and minerals needed for growth, weight gain, wound healing, convalescence, immunocompetence, and other health-sustaining functions.