GI Pharm

Question 1

Calcium carbonate

Answer 1

= Tums
A type of antacid
Caution using antacids with meds that chelate

May cause constipation or flatulence
~10% of Ca++ absorbed into blood

Question 2

Magnesium hydroxide

Answer 2

A type of antacid
May cause diarrhea
~20% Mg absorbed into blood

Question 3

Major interactions with antacids

Answer 3

Lily of the valley
Strophanthus
(Both to calcium)

Question 4

Histamine(2)-receptor antagonists

H2RA

Answer 4

Selective, competitive blocking of basolateral side of receptors of parietal cells

Duration = longer than other antacids - 4-10hrs tf less dosage

Can be taken preventatively

Famotidine, ranitidine, cimetidine, nizatidine

Question 5

H2RA adverse drug reactions

Answer 5

Anti-androgenic (reversible gynecomastia & rarely impotence)
Arrythmias 
Headache
Dizziness
GI

Question 6

Major H2RA interactions

Answer 6

Caffeine

St. John’s wort

Question 7

Proton Pump Inhibitors

Answer 7

Selective, IRREVERSIBLE, H/K/ATPase inhibition (on luminal side of parietal cells)

Become more effective with repeat dosing
Duration = 24 hours

Very susceptible to acid in the stomach (they are broken down very easily)
When taken with food, the bioavailability is cut in half
70-90% when taken with just water

Omeprazole, esomeprazole, lansoprazole, pantoprazole, rabeprazole

Question 8

Adverse drug rxns of PPIs

Answer 8

Mg depletion
Osteoporosis
C. Diff infx
Community acquired pneumonia 
HA
Dizziness
GI

Question 9

Major interactions with PPIs

Answer 9

Grapefruit

St. John’s wort

Question 10

Simethicone = Gas-X

Answer 10

Mechanism = inert silicone polymer = defoaming agent. —> reduces surface tension of gas bubbles

Not absorbed

Interactions = decreases the levels of thyroid products i.e. levothyroxyine

Question 11

Activated charcoal - “Charcoal Plus” brand

Answer 11

= charcoal with simethicone

Highly absorptive

Unknown efficacy and safety

May impact absorption of medications

Question 12

Alpha Galactosidase

Beano, Gaz Away

Answer 12

Mechanisms: mold-derived enzymes cleave oligosaccharides before reaching colonic bacteria
- recommended for gas prevention in high fiber diets

Fda safe and effective

Avoid with DM and galactosemia

No interactions known

Question 13

Laxatives

Answer 13

Potential overuse/abuse
Leads to dependence
Rectal laxatives exist esp when concern for intestinal obstruction
May cause electrolyte disturbance

Question 14

Senna drugs

Senokot, Ex-Lax

Answer 14

Anthraquinone
Stimulates peristaltic activity
Stimulant laxative
Cramps, nausea, vomiting = ADR
Also, melanosis coli

Question 15

Stimulant Lax

Bisacodyl

Answer 15

Stimulate peristalsis
Irritating SM of intestine
Cramps, diarrhea, n/v = ADR
Electrolyte disturbance

Jalap (ele/fluid depletion), Oleander (causes K depletion which may lead to cardiac glycoside toxicity)

Question 16

Osmotic (electrolyte) laxative

Answer 16

Polyethylene glycol, mg citrate

PEG = water retention in stool & inc stool freq
May cause urticaria
Max = 17g/day

MgCitrate = 30% of Mg absorbed, water retention in stool
May cause flatulence
No certain Max

Both may cause cramps, diarrhea
Both should be used for less than 1 week
Both OTC

Question 17

Stool softeners

Answer 17

Docusate (colace)
OTC

Comes in sodium and calcium formulations
Oral or rectal administration
Mechanism: reduces surface tension of the oil-water interface of the stool… this enhances the incorporation of water and fat into stool.
Helps with secretion of water and electrolytes from mucosa into bowel
It is absorbed and excreted into bile, then cleared from system

ADR - the liquid formulation may irritate the throat

Less of concern with bowel obstruction (but not tx for the bowel obstruction)

Avoid using in combo with mineral oil
(Can increase bioavailability of various oral agents)

Question 18

Loperamide (Immodium)

Answer 18

Anti-diarrheal
Opiate-like
Potential for abuse

Onset in less than an hour

Decreases GI motility by effects on circular and longitudinal muscles… reduced GI secretions produced by opiod receptor binding effects in intestinal mucosa

Poorly absorbed
ADR: dizziness, cramps, nausea, toxic megacolon and rashes (rare)

Interactions = henbane (additive anticholinergic effects), scopolamine (“”), St. John’s wort (induction of PgP)

Question 19

Diphenoxylate and Atropine (lomotil)

Answer 19

Opioid like antidiarrheal

Opioid receptor agonist (stim Mu receptors) which inhibits excessive GI motility and GI propulsion. 
Extensively absorbed (hydrolyzed to active diphenoxylic acid)

Controlled substance **
OTC versions contain subtherapeutic atropine to discourage abuse

Interactions = henbane and scopolamine [additive anticholinergic effects]