Lecture 7 - Drug absorption and disease Flashcards
what is enteral feeding?
some patients may not be Abel to take their medication orally and have dysphagia which may be caused by;
Parkinsons disease, stroke, MS, MND
Partial intestinal failure eg IBD, short bowel syndrome
Psychological problems eg severe depression or anorexia nervosa
what are the various enteral feeding routes?
Nasogastric tube through nose and into stomach
Gastrostomy tube inserted directly into the stomach through the abdominal wall.
Jejunostomy tube is inserted through the abdomen but goes further into the jejunum
Nasojejunal tube (NJ tube): This tube is inserted through the nose and extends into the jejunum.
Nasoduodenal tube: This tube is inserted through the nose into the duodenum
Peripheral Parenteral Nutrition (PPN): This method involves delivering nutrients through a vein in the arm
Total Parenteral Nutrition (TPN): TPN is delivered directly into a large vein, usually in the chest.
summarise how a tablet is ingested in absorption
Disintegration: The tablet breaks down into smaller particles.
Dispersion of particles: These smaller particles spread out within the gastrointestinal (GI) tract.
Dissolution: The particles dissolve in the GI fluids to form a solution of the active ingredient.
The active ingredient, represented as RCOOH (a carboxylic acid group attached to a drug molecule), is in equilibrium with its ionized form (RCOO^-) in the aqueous solution within the GI tract.
The non-ionized form (RCOOH) is more lipid-soluble, allowing it to cross the lipid-rich GI membrane into the body’s systemic circulation.
The ionized form (RCOO^-), being less lipid-soluble, does not readily cross the membrane.
describe the process of drug absorption form the GIT
Once the drug molecules have crossed the GIT membrane, they enter the bloodstream in an aqueous environment again. From there, they are transported throughout the body to exert their therapeutic effects.
partitioning of molecules is when the drug meocuels distribute themselves between the GIT lipid membrane and the aqueous extracellaulr fluid before entering the bloodstream. this determines how much of the drug absorbed into systemic circulation
what is the issue with omeprazole and enteral feeding
omeprazole (LOZEC MUPS) has no absorption and medication is rendered useless
what are drug based issues with enteral feeding?
careful monitoring of the patient is required. issues are;
Binding of drugs to tube
Eg carbamazepine, diazepam or phenytoin
Direct interaction of drug and feed causing reduced drug absorption
Eg carbamazepine, ciprofloxacin, phenytoin and other highly bound protein drugs…
Direct interaction of drug and feed causing tube blockage
Eg acidic solutions (chlorphenamine, promethazine)
Drug administration on an empty stomach
Eg penicillin ketoconazole, tetracyclines
Drug-drug interactions
give an example of a drug unsuitable for administration via enteral feeding tube
it is recommended that phenytoin should never be administered via enteral feeding tube. absorption is extra,ely unpredictable. only use if there is no suitable alternative route or drug eg IV phenytoin
