Effects of food on drug therapy

Question 1

drug absorption

Answer 1

• The presence of food & nutrients in the stomach/intestine can alter absorption of a drug
  – Often ↓/interferes with absorption

Question 2

for some medications, bioavailability is _ when taken with food

Answer 2

greater

Question 3

bioavailability

Answer 3

fraction of an administered drug that reaches systemic circulation
– If administered by IV, bioavailability is 100%
– Oral administration is associated with lower bioavailability

Question 4

delayed gastric emptying:

Answer 4

Rate of gastric emptying is influenced by the presence of food in the stomach & the type of meal or food ingested
– High-fibre or high-fat meals can delay gastric emptying

Question 5

chelation

Answer 5

• Occurs between certain medications & divalent or trivalent cations
  – e.g., Fe, Ca, Mg, Zn, Al
• Can lead to reduced drug absorption
  – Most commonly seen with tetracycline and fluoroquinolone antibiotics (e.g., ciprofloxacin, cephalosporin)
• Optimally, will stop non-critical supplements for the duration of the antibiotic prescription

Question 6

pH of the GI tract:

Answer 6

• Situations resulting in changes to the gastric (stomach) pH can reduce drug absorption

Question 7

many meds treating _ aim to reduce the pH of the stomach

Answer 7

GERD

– e.g., antacids, H2-receptor antagonists (e.g., Pepcid) or proton-pump inhibitors

Question 8

Physical incompatibilities between enteral feed and medications include

leads to…

Answer 8

– Granulation
– gel formation
– Separation of the enteral product

this leads to:
- clogged feeding tubes
- interrruption of delivery of nutrition to the patient

Question 9

*Drug formulations that CAN cause granulation and gel formation include:

Answer 9

– Ciprofloxacin suspension (Cipro),
– Chlorpromazine (thorazine) concentrate,
– ferrous sulfate elixir,
– Guaifenesin (Robitussin), and
– Metoclopramide (Reglan) syrup

Question 10

albumin

Answer 10

• Albumin is the most important drug -binding protein in the blood
• Patients with albumin levels <30 g/L have ↑ risk of adverse drug effects
  – A lower dose of highly protein-bound drugs (e.g., warfarin; phenytoin) is recommended for patients with low albumin levels

Question 11

enzyme systems in the _ and _ are responsible for much of the drug metabolizing activity in the body

Answer 11

liver & intestinal tract

Question 12

food can inhibit or increase metabolism of medication by

Answer 12

enhancing the activity of these enzyme systems

– e.g., consumption of grapefruit & related citrus fruits inhibits the cytochrome P-450 3A4 enzyme system responsible for oxidative metabolism of many oral medications

Question 13

Occasionally there is competition between food & drugs for metabolizing enzymes in the

Answer 13

liver

– When this is the case, more of the drug is likely to be circulated, which can lead to a toxic effect