Define Effect of feeding method on drug availability?

The form in which a drug is administered or enters the body can influence its absorption, metabolism or excretion. This becomes more pronounced among critically ill patients who cannot consume drugs orally and are on enteral food support. If the drug has to be administered though the enteral feeding tube it needs to be either crushed or dissolved in a solvent. Crushing oral preparations to pass down the tube may alter their absorption time/activity.

Some of the drugs cannot be added to the food infusion as it may alter their stability. Several drugs are available only in the form of tablets or capsules, dissolving these in feed, water, alcohol or sorbitol may not always be feasible. Drug such as cimetidine, aluminium hydroxide, metaclorpromide are physically incompatible with enteral foods. Certain drugs like phenytoin form complexes with calcium and protein thereby resulting in markedly reduced absorption of this medication. Such drugs need to given only by stopping enteral feed infusions for 1-2 hours. Patients on total parenteral nutrition generally have a separate tube (catheter) for infusion of drugs. Toxicity/over dosage of drugs is frequently observed in case of certain drugs administered directly into the blood.