GI Pharmacology - Constipation, Diarrhea, IBS, Antiemetics, and IBD

Comprehensive vocabulary flashcards covering GI pharmacology including laxatives, antidiarrheals, IBS treatments, antiemetics, hemorrhoid therapies, and medications for Inflammatory Bowel Disease (IBD).

Constipation

Defined as infrequent stools, meaning fewer than $3$ bowel movements per week; patients may also complain of hard stools, straining, and incomplete evacuation.

Diarrhea

Defined as more than $2-3$ liquid bowel movements per day.

Emollient Laxatives (Stool Softeners)

A class of medications, such as Docusate (Colace), that act as surfactants to increase the amount of water and fat incorporated into stool; used for patients who must avoid straining.

Saline Laxatives

Agents like Polyethylene glycol (Miralax) and Magnesium citrate that draw fluid into the intestine via osmosis to stimulate peristalsis; effect time varies from $1-6$ hours for Milk of Magnesia to $1-3$ days for Miralax.

Bulk Laxatives

Medications such as Psyllium (Metamucil) and Methylcellulose (Citrucel) that increase water absorption in the intestine to promote peristalsis; they are safe for children but contraindicated in fecal impaction.

Stimulant Laxatives

Agents like Bisacodyl (Dulcolax) and Senna that stimulate the colonic intramural neuronal plexus to alter water secretion and increase contractions; they carry an increased risk for perforation if used with bowel obstruction.

Glycerin Laxatives

Local colon osmotic irritants, such as Bisacodyl suppositories (Fleet), that provide instant fecal lubrication; they must be retained in the rectum for $5-15$ minutes.

Lactulose Syrup

A hyperosmotic laxative degraded to $NH_4^+$ (ammonium) in the gut to draw in water; requires caution in diabetic patients due to its galactose content.

Bismuth subsalicylate (Pepto-Bismol)

An antidiarrheal with antibacterial and antiviral properties; the salicylate component provides antisecretory effects by inhibiting the cyclooxygenase enzyme.

Loperamide (Imodium)

An antidiarrheal that acts on mu-opioid receptors of the myenteric plexus to slow motility, inhibit peristalsis, and increase anal sphincter tone.

Diphenoxylate/atropine (Lomotil)

A controlled substance antidiarrheal containing a synthetic opioid agonist; atropine is added to discourage abuse by causing unpleasant anticholinergic effects at high doses.

Irritable Bowel Syndrome (IBS)

A chronic functional disorder involving abdominal pain, cramping, and changes in bowel habits, which may present as constipation (IBS-C), diarrhea (IBS-D), or a mixture.

Low FODMAP Diet

A dietary approach for IBS management that involves avoiding gas-producing foods such as garlic, beans, onions, and gluten-based breads.

Lubiprostone (Amitiza)

A secretagogue and prostaglandin $E$ analog that activates $CLC-2$ chloride channels in intestinal epithelial cells to increase fluid secretion and motility.

Linaclotide (Linzess) & Plecanatide (Trulance)

Guanylate cyclase-C ($GC-C$) agonists that increase extracellular $cGMP$ to decrease visceral pain and increase intestinal fluid secretion; they carry a Black Box Warning for death due to dehydration in children.

Tenapanor (Ibsrela)

An ion channel blocker that inhibits sodium/hydrogen exchanger $3$ ($NHE3$), reducing sodium absorption to increase water secretion into the intestinal lumen.

Rifaximin (Xifaxan)

A nonabsorbable antibiotic that binds to the $\beta$-subunit of bacterial RNA polymerase to block transcription; used for IBS-D and traveler's diarrhea caused by $E. coli$.

Antispasmodics (Dicyclomine & Hyoscyamine)

Medications that antagonize acetylcholine receptors at parasympathetic sites in smooth muscle to cause relaxation in patients with IBS-D.

Eluxadoline (Viberzi)

A controlled substance for IBS-D that stimulates mu-opioid and kappa-opioid receptors while antagonizing delta opioid receptors; contraindicated in patients with gallbladder disease.

Alosetron (Lotronex)

A $5-HT3$ receptor antagonist indicated only for women with severe chronic IBS-D who failed other treatments; carries risks of severe constipation and ischemic colitis.

Selective Serotonin Reuptake Inhibitors (SSRIs) in IBS

Antidepressants like Citalopram and Sertraline used to help with IBS pain and stress-induced symptoms by increasing serotonin levels in the gut.

Promethazine (Phenergan)

An antiemetic that acts as an $H1$ histamine and alpha-adrenergic receptor antagonist; it has a Black Box Warning for respiratory depression in children under $2$ years old.

Ondansetron (Zofran)

A selective $5HT3$ receptor antagonist antiemetic that blocks serotonin in the brain and vagal neurons; side effects include $QT$ interval prolongation.

Metoclopramide (Reglan)

A dopamine receptor blocker that enhances motility and gastric emptying; it carries a Black Box Warning for Tardive Dyskinesia ($TD$).

Internal Hemorrhoids

Swollen veins in the anal canal that originate from above the dentate line; typically present with painless bleeding.

External Hemorrhoids

Swollen veins in the anal canal that originate from below the dentate line.

Local Anesthetics (Rectal)

Agents like Dibucaine $1.00\%$ and Pramoxine $1.00\%$ that inactivate sodium channels in neuronal membranes to provide short-term numbness for hemorrhoid symptoms.

Vasoactive Agents (Hemorrhoids)

Medications such as Nitroglycerine ointment (manages sphincter spasms) and Phenylephrine (Preparation H) which provides vasoconstriction to shrink vessels.

Crohn's Disease

A form of Inflammatory Bowel Disease characterized by patchy, transmural inflammation that can occur throughout the small and large bowel; symptoms include diarrhea, weight loss, and malnutrition.

Ulcerative Colitis

A form of Inflammatory Bowel Disease characterized by continuous and uniform inflammation in the large bowel; bloody stool and stool urgency are common symptoms.

5-Aminosalicylic Acid Derivatives (5-ASA)

Inflammatory Bowel Disease medications like Mesalamine and Sulfasalazine that block cyclooxygenase and inhibit prostaglandin production.

JAK Inhibitors (Tofacitinib)

Medications that inhibit Janus-associated kinases ($JAK$) $1$, $2$, and $3$ to disrupt cytokine signaling; carries a Black Box Warning for serious infections, malignancies, and thrombosis.

TNF-Inhibitors

Biologic therapies like Infliximab (Remicade) and Adalimumab (Humira) that use antibodies to target dysregulated Tumor Necrosis Factor in Inflammatory Bowel Disease.

Alpha 4 Integrin Inhibitors

Monoclonal antibodies such as Natalizumab (Tysabri) that inhibit memory T-lymphocyte migration into inflamed GI tissue; associated with the rare risk of Progressive Multifocal Leukoencephalopathy ($PML$).

Anti-IL 12/23 Agents (Ustekinumab)

Biologic agents that block the $p40$ subunit shared by $IL-12$ and $IL-23$ to interrupt the inflammatory cascade in the bowel.