Pharmacology: Agonists, Antagonists, and GI Medications

Agonists and Antagonists

• Agonists activate receptors, mimicking natural chemicals/hormones
• Antagonists block receptors, preventing natural chemical effects

Contraindications

• Drugs should not be used in certain situations

Proton Pump Inhibitors (PPIs)

• Drugs ending in "-prazole" (e.g., Pantoprazole, Omeprazole, Dexlansoprazole)
• Suppress gastric acid production
• Drug of choice for GERD (Gastroesophageal Reflux Disease)
• Used with antibiotics to treat H. Pylori
• Taken once daily, 30 minutes to 1 hour before meals

Histamine 2 Receptor Antagonists (H2RAs)

• Drugs ending in "-tidine" (e.g., Cimetidine, Famotidine, Ramotidine, Nizatridine)
• Cause a strong secretion of gastric acid
• Do not block histamine on gastric acid-producing cells
• Caution in renal impairment

Antacids

• Alkaline compounds neutralizing stomach acid, like Mylanta and Maalox.
• Magnesium, Aluminum, and Calcium compounds
• PRN (as needed) for acute management
• Can be taken 1-3 hours after meals, or at bedtime, for acid reduction
• Caution in renal failure

Milk of Magnesia

• Causes diarrhea

Aluminum Hydroxide

• Increased sodium, constipation
• Hypophosphatemia (low phosphorus in blood)
• Binds with certain drugs

Calcium Carbonate

• Constipation, can make constipation worse
• Belching and flatulence
• May contribute to milk-alkali syndrome (high calcium levels)

Maalox

• Alkaline compounds; combines Magnesium, Aluminum and Calcium
• PRN for acute management, for example after meals

Antiflatulents: Simethicone

• Antifoaming agent; reduces gas bubbles
• Does not prevent gas, only makes it easier to expel

Cytoprotective Agents: Sucralfate

• No significant adverse effects
• Lowers absorption of other drugs (take at least 2 hours apart)
• Prevents ulcers caused by NSAIDs (like ibuprofen)

Cytoprotective Agents: Cytotec

• Lowers gastric acid secretion, increases bicarbonate, and maintains blood flow.
• Associated with diarrhea, abdominal pain, spotting
• Pregnancy risk category X

Antibiotics

• Used for bacterial enteritis

Phenothiazines

• CNS depressing properties; associated with antipsychotic medication.
• Photosensitivity, blurred vision, urinary retention, dry mouth, confusion

Phenothiazines: Drugs

• BBW (Black Box Warning): Children under 2 can experience respiratory depression and subcutaneous tissue injury.

Antihistamines

• Prevent histamine from widespread tissue effects
• Side effects can include CNS depression

Antihistamine Drugs

• Hydroxyzine, meclizine

Serotonin Receptor Antagonists: Ondansetron

• Commonly used antiemetic agent, used for emesis with chemo
• Relatively safe for all age groups

Substance P/ Neuronkinin I Antagonists: Aprepitant

• Effective for nausea and vomiting with chemotherapy
• More selective than other receptors
• Taken for a full 2-3 days to see full effects

Bulk Forming Laxatives: Psyllium

• Soft, formed stool; should be taken with a full glass of water
• 1 hour before or 2 hours after meals
• Lower cholesterol, increase bulk, and lubricate fecal matter
• Effects in 6-8 hours

Lubricant Laxatives: Mineral Oil

• Lower absorption of fat-soluble vitamins, pneumonia possible
• Not a true laxative, rather low surface tension of fecal matter

Surfactant Laxatives: Docusate

• Docusate sodium and Docusate calcium are prototype
• Takes 1-3 days to take effect, taken with full glass of water
• Do not precipitate laxative effect, more to assist in stool passage through bowel

Cathartics

• Rapid/strong bowel evacuation, better than laxatives
• Irritate bowels
• Increases water secretion into lumen
• Creates a semifluid stool within 6-12 hours
• Ex: Bisacodyl (prototype)

Stimulant Cathartics

• Increase secretion/increase bowel movement; often taken when other treatments aren't working or are less appropriate.
• Take on an empty stomach to avoid interactions with milk
• Ex: Glycerin, Senna, Castor oil

Saline Cathartics (Osmotic Laxatives)

• Draw water into the intestinal lumen to soften stool
• Potential for fluid/electrolyte imbalance (e.g. increased magnesium/sodium, etc)
• Caution is necessary with issues that cause build up of magnesium/sodium/etc.
• Ex: Magnesium salts, Sodium salt

Saline Cathartics: Polyethylene glycol (PEG-ES)

• Cleanses the bowel prior to procedures
• Not recommended for more than 2 weeks, due to possible unpleasant adverse effects
• Nonabsorbic Compound

Opioid Antidiarrheal Agents

• Diphenoxylate with Atropine (for diarrhea)
• Loperamide (Low-per-a-mide)

Adjuvant Andtidiarrheal Agents

• Cholinergic drugs inhibit acetylcholinesterase, impacting production of acetylcholine
• Increased acetylcholine causes enhanced parasympathetic effects (SLUDGE/DUMBELLS)

Cholinergic drugs/Acetylcholinesterase inhibitors

• Drugs like Donepezil treat conditions like Alzheimer's disease
• Memantine, but not cholingeric, is a treatment for Alzheimers, too
• Pyridostigmine is used to treat myasthenia gravis

Migraines/Headaches: NSAIDs

• Naproxen
• Ornaproxin sodium
• Sumatriptan (often combined with Naproxen)

Migraines/Headaches: Triptans

• Sumatriptan

Migraines/Headaches: Ergot Alkaloids

• Estradiol can help prevent declining estrogen from affecting migraines

Migraines/Headaches: Anti-emetic Chlorpromazine HCL

Overview of agonists, antagonists, contraindications, proton pump inhibitors (PPIs), H2RAs, and antacids. Includes drug mechanisms, uses, and cautions for gastrointestinal conditions like GERD and H. pylori. Focus on how these drugs affect gastric acid production.