Enteral Administration
Introduction
An enteral feeding tube (EFT) provides a means of maintaining nutritional intake when oral intake is inadequate or when there is restricted access to the gastrointestinal tract, e.g. owing to obstruction. It is also increasingly being used as a route for drug administration.
Types of Feeding Tubes
The type of feeding tube used will vary depending on the intended duration of feeding and the part of the GI tract the feed needs to be delivered to.
- Nasoenteric tubes are used for short- to medium-term feeding (days to weeks), whereas
- Ostomy tubes are used for long-term feeding (months to years)
Enteral Feeding Tubes
The external diameter of the feeding tube is measured in French unit (Fr) where 1 Fr = 0.33 mm.
- Small bore tubes may be between 5-12 French.
- Large bore tubes are those which measure more than 14 French.
Enteral feeding tubes are made up of polyvinyl chloride (PVC), polyurethane (PUR), silicone or latex.
- Silicone and latex tubes are softer and more flexible than polyurethane tubes and therefore require thicker walls to prevent stretching and collapsing. As a result of the differences in rigidity, a silicone or latex tube of the same French size as a polyurethane tube will have a smaller internal diameter.
In recent years there has been a trend towards decreasing the size of feeding tubes used for reasons of patient comfort and acceptability.
Drug Considerations
Several issues have to be considered before drug being administered through enteral tube.
- The enteral feeding tube type
- Size of lumen and length of tube
- Narrow tubes and long tubes are more likely to become blocked. Correct choice of formulation and effective flushing are essential to prevent blockage.
- Tube location in the GI tract
- Medication expected to act locally in the stomach, such as antacids or sucralfate would be ineffective if given through a tube terminating in the intestine.
- Effects of food on drug absorption
- The presence of some components in the feed formulation (e.g. calcium, iron) might bind with the drug, therefore result in changing of the molecular size or solubility thus reduce the absorption.
- High-protein diet will result in decreased absorption of methyldopa and levodopa.
NOTE: The use of a nasogastric tube is suitable for enteral feeding for up to 6 weeks. Polyurethane or silicone feeding tubes are unaffected by gastric acid and can therefore remain in the stomach for a longer period than PVC tubes, which can only be used for up to 2 weeks.
General Recommendations
To prevent feeding tube occlusions, use size 8Fr–12Fr for NG tubes (adults) and 10Fr or above for gastrostomy/jejunostomy tubes.
Small syringes create high intraluminal pressures and may damage the tube. To reduce the risk of rupturing the fabric of the enteral feeding tube, the largest functional syringe size should be used; 30-50 ml syringes are recommended. In clinical practice this tends to be a 50 ml syringe.
Feeding tubes should be flushed (e.g., 15-30 ml of water) before and after administration of medication via the tube to prevent tube blockage (in the case of fluid-restricted patients, revise the flush volumes to meet the patient's prescribed fluid restriction, air flushes may be used to replace water flushes).
When several medications are to be given at the same time, all medications should be administered separately and the tube flushed with at least 5 ml of water after each dose.
The patient should be nursed semi-recumbent (sitting up) at an angle of 30 degrees or greater to reduce reflux of the medication and flushes. This promotes gravity-assisted progression of the fluid.
When deciding which medication formulation is appropriate for administration via an enteral feeding tube, many factors need to be taken into consideration.
- Solutions or soluble tablets are the formulation of choice. Do not crush tablets or open capsules unless an alternative formulation or drug is unavailable.
- When medicines are crushed, the person does not receive the entire dose. Some of the dose will be left in the crushing device and in the medicine cup. The amount lost depends on which crushing device is used and how the medicine is given. If the device is not rinsed twice (and the rinses given with the dose), an average of 24% of the dose can be lost.
- It is not necessarily correct to assume that a liquid is preferable to a tablet; unwanted side-effects of the excipients of a liquid formulation must be borne in mind. For example, sorbitol can cause diarrhoea (particularly in doses above 7.5 g per day in adults and doses greater than 0.5 g/kg in children).
- Almost all liquid medicines must be diluted before giving into an enteral feeding tube. Usually 30 ml for adults or a volume that is at least equal to the dose is required.
- Many liquids have a high osmolarity and can cause diarrhoea and cramping.
- Some liquids are thick enough to block the tube if they are not diluted enough to pass easily through the tube.
- The stability of or bioavailability of the medicine may be reduced if it is diluted. Always measure the dose first, then dilute it and give the dose straight away.
- Examples: Abacavir, Amoxicillin with Clavulanic Acid, Azithromycin, Carbamazepine, Frusemide, Phenytoin and Sodium Valproate.
- The needs of the patient or carers must also be considered; it may not be practical for the patient to carry several bottles of liquid medication with them on a daily basis.
- If the tablet is effervescent, first disperse it in water in a medicine cup (usually volume of 10-20 ml of water, but best consult medicine monograph) then draw up into an oral dispenser or enteral syringe. This allows effervescing gases to escape.
Medications that Should Not Be Altered
Crushing tablets and opening capsules should only be considered as a last resort, because of potential dosing inaccuracies, occupational exposure and increased dose preparation time.
There are few types of medicines that should not be altered.
NOTE: Useful references on whether a drug can be administered by enteral feeding tube or not is discussed in a separate post.
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