The enteral route is any method of delivering medication or nutrition through the gastrointestinal (GI) tract. This includes swallowing a pill, placing a tablet under your tongue, and receiving liquid nutrition through a feeding tube that ends in your stomach or intestine. The word “enteral” comes from the Greek word for intestine, but the term covers the entire digestive system from mouth to rectum.
Routes That Count as Enteral
Most people think “enteral” just means swallowing something, but the category is broader than that. There are four main enteral routes, and they differ in where the drug enters the body and how quickly it reaches the bloodstream.
- Oral: Swallowing a tablet, capsule, or liquid. The drug travels to the stomach, then the small intestine, where most absorption happens. This is the slowest enteral route because the drug has to survive stomach acid and pass through the liver before reaching the rest of the body.
- Sublingual: Placing a drug under the tongue. The thin, blood-vessel-rich tissue there absorbs the drug directly into the bloodstream, bypassing the liver entirely. Onset times can rival injections, with some medications reaching peak blood levels in about 30 minutes.
- Buccal: Tucking a drug between the cheek and gum. Similar to sublingual, this route skips liver metabolism, but absorption is slower. It works well for medications that benefit from a more extended release.
- Rectal: Administering medication through the rectum. The highly vascular rectal lining absorbs drugs quickly, and this route partially bypasses the liver. It’s useful when a patient is vomiting or unable to swallow.
Why the Liver Matters: First-Pass Metabolism
The biggest difference between swallowing a drug and placing it under your tongue comes down to what the liver does. When you swallow a medication, it’s absorbed in the small intestine and carried directly to the liver through a dedicated blood vessel before it ever reaches the rest of your body. The liver breaks down a significant portion of the drug during this trip, a process called first-pass metabolism. This means a smaller amount of the active drug actually makes it into your bloodstream.
Sublingual, buccal, and rectal routes partially or completely avoid this liver detour. That’s why a blood pressure medication like captopril can lower blood pressure faster when dissolved under the tongue: the oral version takes one to two hours to hit its peak effect because it has to travel through the gut and liver, while the sublingual version reaches peak concentration in roughly 30 minutes. The drug itself is the same; the route changes how much of it survives the journey.
Enteral Feeding Tubes
When someone can’t eat or swallow safely, nutrition can still be delivered enterally through a feeding tube. The type of tube depends on how long it’s needed.
For short-term use (less than four to six weeks), tubes are inserted through the nose. A nasogastric (NG) tube runs from the nose to the stomach. A nasoduodenal tube reaches the first section of the small intestine, and a nasojejunal tube extends to the second section. These are placed at the bedside without surgery, though blind insertion carries a small risk of mispositioning: between 0.5% and 16% of nasal tubes end up in the airway or chest cavity rather than the GI tract, which is why placement is confirmed before feeding begins.
For longer-term use (more than four to six weeks), tubes are placed through the abdominal wall directly into the stomach or intestine. A gastrostomy tube (G-tube) goes into the stomach. A jejunostomy tube (J-tube) goes into the second part of the small intestine. A combination tube (GJ-tube) enters the stomach and passes through into the jejunum. These require a minor procedure to place but are more stable and comfortable for ongoing use.
Complications of Tube Feeding
Enteral feeding is generally safer and less expensive than intravenous (parenteral) nutrition, but it comes with its own set of problems. Diarrhea is the most common GI complication, affecting about 30% of patients on hospital wards and up to 80% of patients in intensive care. Nausea and vomiting affect 20% to 30% of patients, particularly right after tube feeding starts.
The causes of diarrhea during tube feeding are often not the formula itself. Antibiotics and other medications given alongside the feeding are frequent culprits. Antibiotics can promote the growth of harmful bacteria like C. difficile, and certain ingredients in liquid medications, such as sorbitol, can trigger profuse diarrhea on their own.
Aspiration, where stomach contents flow backward into the lungs, is the most serious risk. It’s more common when patients are fed through a nasogastric tube while lying flat, and in people with impaired consciousness, weak cough reflexes, or conditions like stroke or dementia. Elevating the head of the bed during and after feeding is one of the simplest ways to reduce this risk.
When Enteral Delivery Can’t Be Used
There are situations where delivering anything through the GI tract is unsafe. A complete bowel obstruction is the clearest example: if nothing can pass through the intestine, putting food or medication in from above will only make things worse. Active bleeding in the GI tract is another absolute contraindication, as is a condition called ileus, where the intestine stops moving (sometimes seen after major trauma or with infections in the abdominal cavity).
Patients with severely reduced blood flow to the intestine also cannot receive enteral nutrition safely. Feeding an intestine that isn’t getting enough blood supply can worsen the damage, leading to tissue death and dangerous bacterial overgrowth. In all of these cases, nutrition is delivered intravenously until the gut can function again.
Enteral vs. Parenteral: Why the Gut Route Is Preferred
Parenteral nutrition, delivered directly into the bloodstream through an IV, bypasses the GI tract entirely. It’s a lifeline when the gut isn’t working, but it carries higher risks and costs. Bloodstream fungal infections occur in about 4% of patients receiving IV nutrition. The financial cost of parenteral solutions is also significantly higher than enteral formulas.
Using the gut, even partially, helps maintain the health of the intestinal lining and supports the immune system that lives there. This is why clinical teams generally try to start enteral feeding as early as safely possible and reserve parenteral nutrition for patients whose GI tract truly cannot handle the job. In many cases, a combination of both routes bridges the gap until full enteral feeding becomes tolerable.
Giving Medications Through a Feeding Tube
Feeding tubes aren’t just for nutrition. They’re also used to deliver medications when a patient can’t swallow pills. This requires some care to avoid clogging the tube or interfering with how the drug works. Tubes are typically flushed with 30 mL of water before and after each medication to keep them clear, using a 60 mL syringe. Medications need to be in liquid form or crushed and dissolved. Not all medications can be crushed safely: extended-release tablets, enteric-coated pills, and certain other formulations can become dangerous or ineffective if their structure is broken.