Enteral route

O Parenteral nutrition (PN), also called total parenteral nutrition (TPN), is the intravenous administration of fluids, macronutrients, electrolytes, vitamins, and trace elements for the purpose of weight maintenance or gain, to preserve or replete lean body mass and visceral proteins, and to support anabolism and nitrogen balance when the oral/enteral route is not feasible or adequate. 

Parenteral nutrition can be a lifesaving therapy in patients with intestinal failure, but the oral or enteral route is preferred when providing nutrition support ( when the gut works, use it ). Compared with PN, enteral nutrition generally is associated with fewer infectious complications (e.g., pneumonia, intraabdominal abscess, and catheter-related infections) and potentially improved outcomes.1-3 However, if used in appropriate patients (i.e., patients with questionable intestinal function or when the intestine cannot be used), PN can be used safely and effectively and may improve nutrient delivery.4 Indications for PN are listed in Table 97-1.1... 

The goal is to transition the patient to enteral or oral nutrition and taper off PN as soon as feasible clinically. When initiating enteral or oral nutrition, monitor the patient for glucose, fluid, and electrolyte abnormalities. Perform calorie counts to determine the adequacy of nutrition via the oral or enteral route. When the patient is tolerating more than 50% of total estimated daily calorie and protein requirements via the oral or enteral route, wean PN by about 50%. PN can be stopped once the patient is tolerating more than 75% of total estimated daily calorie and protein requirements via the oral or enteral route, assuming that intestinal absorption is maintained. 

Enteral routes technically include any that will put a material directly into the GI tract, but the use of enteral routes other than oral (such as rectal) is rare in toxicology. Though there are a number of variations of technique and peculiarities of animal response that are specific to different animal species, there is also a great deal of commonality across species in methods, considerations, and mechanisms. 

Chemicals that are metabolized rapidly by the liver cannot be given for systemic effect by the enteral route because the portal circulation carries them directly to the liver. For example, lidocaine, a drug of value in controlling cardiac arrhythmias, is absorbed well from the gut, but is completely inactivated in a single passage through the liver. 

Most patients who cannot feed normally can be fed either by infusion of a nutrient solution into a vein (the parenteral route) or by a tube into the stomach or the jejunum (the enteral route). These solutions deliver all the essential nutrients. Indeed, many patients who cannot eat normally live productive lives while being nourished exclusively by one or both of these routes. 

The statins, lovastatin (L), simvastatin (S), pravastatin (P), fluvastatin (F), cerivastatin, and atorvastatin, inhibit HMG CoA reductase. The active group of L, S, P, and F (or their metabolites) resembles that of the physiological substrate of the enzyme (A). L and S are lactones that are rapidly absorbed by the enteral route, subjected to extensive first-pass extraction in the liver, and there hydrolyzed into active metabolites. P and F represent the active form and, as acids, are actively transported by a specific anion carrier that moves bile acids from blood into liver and also mediates the selective hepatic uptake of the mycotoxin, amanitin (A), Atorvastatin has the longest duration of action. 

Diphenolmethane derivatives (p. 177) were developed from phenolphthalein, an accidentally discovered laxative, use of which had been noted to result in rare but severe allergic reactions. Bisac-odyl and sodium picosulfate are converted by gut bacteria into the active colon-irritant principle. Given by the enteral route, bisacodyl is subject to hydrolysis of acetyl residues, absorption, conjugation in liver to glucuronic acid (or also to sulfate, p. 38), and biliary secretion into the duodenum. Oral administration is followed after approx. 6 to 8 h by discharge of soft formed stooL When given by suppository, bisacodyl produces its effect within 1 h. 

Routes of administration are either enteral or parenteral. The former term denotes all routes pertaining to the alimentary canal. Therefore, sublingual, oral, and rectal are enteral routes of administration. All other routes, such as intravenous, intramuscular, subcutaneous, dermal, vaginal, and intraperitoneal, are parenteral routes. 

The pharmacokinetic phase of drug action includes the Absorption, Distribution, Metabolism and Elimination (ADME) of the drug. Many of the factors that influence drug action apply to all aspects of the pharmacokinetic phase. Solubility (see Section 3.3), for example, is an important factor in the absorption, distribution and elimination of a drug. Furthermore, the rate of drug dissolution, that is, the rate at which a solid drug dissolves in the aqueous medium, controls its activity when a solid drug is administered by enteral routes (see Section 2.6) as a solid or suspension. 

Distinguish between parenteral and enteral routes of administration. 

This relationship holds true regardless of the way in which a single dose of the drug is administered. However, for enteral routes the dose is the amount... 

The oral route is, of course, the principal enteral route of drug administration. However, two other examples are worthy of note. First, the sublingual route (beneath the tongue) provides relatively good absorption because of its rich capillary bed it is routinely used for the administration of nitroglycerin tablets in the treatment of... 

The portal venous system carries blood from the gastrointestinal tract (GIT) to the liver. This blood carries any nutrients, drugs or toxins that have been absorbed via the enteral route. The liver s handling of drugs and toxins is discussed later in this chapter. 

Enteral routes of drug absorption are from the stomach and the small and large intestine. Substances absorbed from these areas enter the splanchnic circulation and pass through the liver before entering the systemic circulation. 

Enteral routes Buccal or sublingual (SL) Rapid absorption from lipid-soluble drugs No first-pass effects Some drug may be swallowed Not for most drugs or drugs with high doses... 

Enteral route, in which food is administered by mouth or a feeding tube that is fed directly into the stomach or small intestine. 

Rehydration and maintenance of water and electrolytes are primary treatment goals until the diarrheal episode ends. If the patient is volume depleted, rehydration should be directed at replacing water and electrolytes to normal body composition. Then water and electrolyte composition are maintained by replacing losses. Many patients will not develop volume depletion and therefore will only require maintenance fluid and electrolyte therapy. Parenteral and enteral routes may be used for supplying water and electrolytes. If vomiting and dehydration are not severe, enteral feeding is the less costly and preferred method. In the United States, many commercial oral rehydration preparations are available (Table 36-3). 

Little information is available concerning alterations in vitamin requirements in ARF. Reduced plasma concentrations of vitamin A, ascorbate, vitamin D, and vitamin E have been reported in patients with ARF, whereas vitamin K concentrations are relatively increased. Losses of vitamins via dialysis also must be considered. Traditional HD clears several water-soluble vitamins such as folic acid, vitamins C and B12, and pyridoxine, but not the highly protein-bound vitamins A and D. The clinical significance of these findings in ARF is unknown. Currently, it seems prudent to administer vitamins at least daily in doses recommended by the Nutrition Advisory Group of the American Medical Association for patients receiving PN (see Chap. 137)." Administration of ascorbic acid should be restricted to under 200 mg/day to avoid secondary oxalosis which may worsen renal function." If the enteral route is used for nutritional support, vitamin administration should at least meet the recommended daily allowances (RDAs). 

Protein typically is well tolerated as a caloric source in SBS patients. For those SBS patients on EN it is controversial what molecular form of the macronutrient maximizes protein absorption. In the past, EN often was initiated with elemental products that contained free amino acids as the protein source because the efficiency of protein uptake was perceived to be better. However, total protein absorption is faster and more complete with dipeptide and tripeptide formulations. It appears that the absorption of free amino acids by the enteral route is a saturable process, whereas the absorption of small peptides is not. These more complex protein sources also may stimulate intestinal adaptation. ... 

When oral feedings are not adequate, the enteral route is preferred for nutritional support in pulmonary patients who have a functional gut and can meet their needs through this route. In acute respiratory failure PN is often recommended when the GI tract is not usable, or as a supplement to EN if sufficient energy intake is otherwise not possible. ... 

The ongoing assessment involves careful observation of tlie patient every 2 to 4 hours for adverse drug reactions when the antifungal diaig is given by the oral or jiar-enteral route. Wlien tliese dru are applied topically to tlie skin, tlie nurse inspects the area at tlie time of each application for localized skin reactions. When tliese dm are administered vaginally, tlie nurse questions tlie patient r arding any discomfort or otlier sensations... 

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