Drug-nutrient interactions Flashcards
What mechanisms does drug/nutrient interactions affect?
Absorption
Distribution
Metabolism
Excretion
What is the rate limiting step for most solid-dose formulations?
Disintegration and dissolution
What is the rate limiting step for liquid medications in solution?
Blood perfusion of the intestines
How can blood perfusion of the intestines be decreased?
Dx states
Edema
Surgery
Sepsis
What factors can alter medication absorption?
Presence of other drugs Gastric emptying rate Route of administration Location of the distal tip of the enteral tube Presence of food
How can we enhance absorption
Use liquid medications to bypass dissolution step. Administer liquid medications or pulverized tablets with adequate fluid.
Administer additional free water flushes in conjunction with scheduled medications.
How does administering liquid medications or pulverized tablets with adequate fluid enhance absorption?
Expands stomach and enhances gastric emptying
If we need to enhance absorption and the medication is a tablet, what should we do?
Pulverize it
What factors may inhibit itraconazole absorption?
Placement of distal tip of enteral tube.
Tablets require acidic environment for dissolution (poor absorption with post pyloric administration).
Liquid form already dissolved (Amenable to post pyloric administration)
What factors may inhibit Cipro absorption?
Main site of absorption is upper part of intestinal tract.
Mixed results with absorption via feeding tubes
Treatment failure seen when administered via jejunostomy tube.
Which medications are better taken on an empty stomach?
PCNs
Tetracyclines
Rifampin
How do we adjust feedings for medications better taken on empty stomachs?
Hold feeds 30-60 minutes before medication administration.
Hold feeds 30 minutes after medication administration.
Re-adjust feeding schedule to ensure patient receives 24-hr nutritional needs
What GI intolerances may inhibit absorption during tube feedings?
Nausea Vomiting Diarrhea Cramping Increased gastric residuals
What medications decrease gastric transit time?
Prokinetic agents:
Metoclopramide
Erythromycin
What medications delay gastric emptying or decrease GI motility?
Anticholinergics
Al-containing antacids
Narcotics
What are some anticholinergics
Antihistamines
Tricyclic antidepressants
Phenothiazines
Medications for Parkinson’s disease
How do anticholinergics work?
Cause smooth muscle relaxation and inhibit gastric motility
How do aluminum-containing antacids inhibit absorption?
Delay gastric emptying
How do narcotics inhibit absorption?
Interfere with normal peristalsis and delay gastric emptying
What factors affect distribution?
Protein binding
Solubility and tissue distribution
How does protein binding affect distribution?
May increase half-life of drug
Decreases hepatic metabolism
How does solubility and tissue distribution affect distribution?
Hydrophilic substances principally distributed within fluid compartments of the body
What factors affect Metabolism?
CYP450 enzyme system
Inducers of CYP1A2
How does CYP3A4 affect metabolism?
Involved in metabolism of most currently marketed drugs
What other isoenzymes are commonly associated with drug metabolism?
CYP1A2
CYP2C9
CYP2D6
What are some nutritional inducers of CYP1A2?
Broccoli
Brussel sprouts
Charcoal-broiled meats
How do nutritional inducers of CYP1A2 affect metabolism?
May decrease bioavailability and effectiveness of some drugs.
May lead to toxicity of other drugs.
How does grapefruit juice affect metabolism?
Inhibits CYP1A2 and CYP3A4
How does cranberry juice affect metabolism?
Inhibits CYP2C9
Warfarin metabolism
Results in increased INR and bleeding
What is enterohepatic cycling?
Drugs may be reabsorbed back into the bloodstream and return to the liver by the enterohepatic circulation. The drug then undergoes further metabolism or is secreted back into the bile.
What drugs undergo enterohepatic cycling?
Macrolides
Ceftriaxone
Nafcillin
Doxycycline
What is the major elimination pathway for most water-soluble drugs and metabolites?
Urinary (renal)
What method of excretion is mediated by protein transporters?
Gastrointestinal (bile)
How do drugs enter the duodenum?
Via the common bile duct
What are the five types of enteral incompatibilities?
Physical Pharmaceutical Physiologic Pharmacologic Pharmacokinetic
What is physical incompatibility?
Chemical instability that occurs when two susceptible substances are mixed together
What is the result of physical incompatibility?
Results in a physical change between two substances
What are precipitates that are formed from physical incompatibility?
Curdling
Focculation
Altered enteral formulation consistency
Viscosity
How does pharmaceutical incompatibility alter the drug?
It interferes with:
Efficacy
Potency
Tolerance
What medication forms are not amenable to feeding tube administration?
Enteric coated
Sustained release
Sublingual
What is the result of physiologic incompatibility?
Result of non-pharmacologic action incurred by the medication or by the suspending medium
What types of medications does physiologic incompatibility typically occur with?
High osmolality liquid medications.
Sorbitol containing medications.
What do patients typically experience with physiologic incompatibility?
Nausea Bloating Increased gastric residuals Cramping Diarrhea
What is the result of pharmacologic incompatibility?
When a medication alters tolerance of the EN or PN regimen because of its MOA
What does pharmacologic incompatibility generally lead to?
A greater than expected pharmacologic effect of medication (prokinetic agents).
Unintended side effects of medications.
How does pharmacokinetic incompatibility affect nutrition regimens?
EN or PN regimen alters the bioavailability, absorption, distribution, metabolism, and/or elimination of a medication
What are some common medications that alter pharmacokinetic compatibility?
Phenytoin
Warfarin
Cipro
Meds that should be taken on an empty stomach
How should medications be administered via enteral feeding tubes?
IR formulations: Oral tablets Hard gelatin capsules Soft gelatin capsules Liquid formulations
What should you do before and after each medication is administered via a feeding tube?
Flush the tube with water
How are solid tablets administered via a feeding tube?
Crushed to a fine powder
Mix with water before administration
How are hard gelatin capsules administered via a feeding tube?
Open and mix thoroughly with water
How are soft gelatin capsules administered via a feeding tube?
Empty by creating a pin-hole in one end of the capsule
Squeeze contents out and mix with water
What is the preferred administration via enteral tubes?
Liquid medications
Why are liquid medications preferred via enteral tubes?
Better absorption.
Decreased potential for enteral tube occlusion.
Potential for producing adverse effects.
Where can sorbitol be found?
In all liquids except tunctures and emulsions
What are the advantages of hyperosmolar liquids?
Stomach more tolerant.
How should administration of hyperosmolar liquids be adjusted?
More diluent if administered in small intestines vs stomach
What are advantages of suspensions?
Present few incompatibility concerns.
Does not contain sorbitol,
May be hyperosmolar.
Antibiotics often available in suspension
What are some granular-type medications?
Psyllium hydrophilic mucilloid
Cholestyramine resin
What is the use of cholestyramine resin?
May be added to control diarrhea.
Can be added as hypercholesterolemia agent.
When should granular-type medications not be used?
With small-bore feeding tubes
Why are enteric coated medications not recommended for administration via tube?
May induce a pharmaceutical incompatibility.
Therapeutic equivalent or alternative administration should be considered.
What is the purpose of enteric coating?
Protects the stomach lining
Protect from destruction of acidic environment
Why are SL or buccal medications not recommended for administration via tube?
Placed under cheek or tongue and absorbed into systemic circulation.
Why are sustained-release tablets or capsules not recommended for administration via tube?
High peaks and low troughs.
Capsules containing beads can lead to occlusion.
Dissolving in water or saline can affect integrity of beads.
Why are syrups not recommended for administration via tube?
Physical incompatibility.
pH less than or equal to 4 denatures protein in enteral formulation.
Be aware of protein source of EN.
Physical incompatibilities cannot be avoided by diluting the syrup.
What type of drugs cause drug-nutrient interactions?
PPIs
Phenytoin
Warfarin
How are PPI capsules containing enteric coated beads administered to avoid drug-nutrient interactions
Mix with acidic juice (orange or apple).
Dissolve beads in 8.4% sodium bicarbonate solution
How are enterc coated PPI tablets administered to avoid drug-nutrient interactions?
Dissolve tablets in 4.2% sodium bicarbonate solution
What are some strategies to maintain therapeutic phenytoin levels?
Hold tube feeding 2 hours before and after phenytoin dose.
Dilute phenytoin with 30-60mL water before administration.
Monitor blood levels more frequently when changing from established parenteral dose to suspension form.
What type of feedings are considered with warfarin to avoid drug-nutrient interactions?
Bolus or cyclic feedings
What influences compatibility of PN infusions?
Exposure time between nutrients
Additives present
What source is a great reference for parenteral incompatibility?
Trissel’s Handbook on Injectable Drugs
Is admixing PN with medications advised?
No
What two medications are safe to add to PN?
Insulin and famotidine
What line should PN be administered by?
Via dedicated line at all times
What lines should never be used for PN?
Y sites
