Beta 2 Receptor Agonists Overview

Medications that bind to β2 receptors in the airway, leading to smooth muscle relaxation and bronchodilation.

β2 agonists stimulate the cyclic AMP pathway, which promotes relaxation of smooth muscles in the airways.

β2 agonists can cause tachycardia (fast heart rate) and tremors due to their effect on β1 receptors.

These medications provide rapid relief for bronchospasm and last for 4-6 hours.

These medications provide long-term control of asthma symptoms and last for 12 hours.

These medications provide even longer-lasting control of asthma symptoms and last for 24 hours.

These medications block muscarinic cholinergic receptors, preventing acetylcholine from constricting airway muscles.

Inhaled anticholinergics decrease cyclic GMP levels, reducing the contractility of airway smooth muscles.

These medications provide rapid relief for bronchospasm and last for 4-6 hours.

These medications provide long-term control of asthma symptoms and last for 12-24 hours.

These medications inhibit phosphodiesterases, leading to an increase in cyclic AMP and relaxation of airway smooth muscles.

These medications reduce inflammation in the airways by inhibiting IgE and mast cell activity.

These medications block the effects of leukotrienes, inflammatory mediators that contribute to asthma symptoms.

These medications block the action of histamine, reducing allergic reactions.

Medications that help to thin and loosen mucus in the respiratory tract, making it easier to cough up.

Common side effects include gastrointestinal upset such as nausea, vomiting, and diarrhea.

Diuretics are widely used to treat high blood pressure (HTN) and heart failure (HF) because they help reduce fluid retention.

Diuretics reduce cardiac output by decreasing plasma volume, initially reducing peripheral resistance and blood pressure.

There are several classes of diuretics, each acting on different parts of the kidney to increase urine production.

Diuretics can cause electrolyte imbalances like hypokalemia (low potassium), hypercalcemia (high calcium), and hyponatremia (low sodium).

Decreased fluid volume due to diuretic use can lead to low blood pressure (hypotension).

Loop diuretics inhibit sodium reabsorption in the ascending loop of Henle, resulting in increased potassium excretion and powerful diuresis.

Thiazide diuretics work in the distal renal tubule, also increasing potassium excretion, but with longer duration and less diuresis.

Aldosterone antagonist diuretics block aldosterone's effect in the distal tubule, preventing sodium reabsorption and potassium loss.

Common loop diuretics include furosemide and bumetanide.

Thiazide diuretics include chlorthalidone, hydrochlorothiazide, indapamide, metolazone.

Examples of aldosterone antagonists are spironolactone, triamterene, amiloride, eplerenone.

Laxative abuse can lead to electrolyte imbalances, fluid loss, and other complications.

Stimulant laxatives like bisacodyl and senna increase intestinal motility by stimulating nerve activity.

Diphenoxylate and difenoxin are antidiarrheal medications that should be avoided in children, especially those with Down syndrome due to their potential for serious side effects.

Antidiarrheals, like diphenoxylate and difenoxin, should not be used for intestinal infections as they can worsen the condition.

Eluxadoline is a medication for chronic diarrhea in IBS, but should be avoided in patients with a history of biliary disorders, pancreatitis, severe liver impairment, or heavy alcohol use.

Alosetron is a medication for females with diarrhea-predominant IBS that doesn't respond to other therapies. It selectively blocks the 5-HT3 receptor, decreasing intestinal motility and secretions.

Antihistamines like dimenhydrinate, diphenhydramine, hydroxyzine, and meclizine are most effective for motion sickness nausea and vomiting by slowing neuronal communication in the vestibulocerebellar areas.

Antihistamines can cause anticholinergic effects, especially in older adults. In children they may cause agitation instead of sedation.

Phenothiazines like prochlorperazine, perphenazine, and promethazine are used to prevent and treat nausea and vomiting by blocking dopamine receptors in the chemoreceptor trigger zone.

Phenothiazines can cause extrapyramidal symptoms (EPS) like muscle spasms, tremors, and rigidity, especially in children.

Cannabinoids like dronabinol are used to treat nausea and vomiting due to chemotherapy, especially when other treatments fail. They also stimulate appetite.

Cannabinoids can cause THC-like effects like euphoria, sensory changes, impaired concentration, memory problems, and seizures.

5-HT3 receptor antagonists like palonosetron, ondansetron, dolasetron, and granisetron are used to prevent chemotherapy-induced nausea and vomiting by blocking serotonin receptors.

Anticholinergics like scopolamine are used to prevent nausea and vomiting due to motion sickness by blocking acetylcholine receptors in the parasympathetic nervous system, decreasing salivation and GI motility.

Substance P/neurokinin 1 (NK1) receptor antagonists like aprepitant are used to prevent chemotherapy-induced nausea and vomiting by blocking NK1 receptors as an adjunct therapy with 5-HT3 antagonists and dexamethasone.

Trimethobenzamide is used to treat nausea and vomiting by blocking dopamine-2 receptors in the chemoreceptor trigger zone.

Study gastrointestinal pharmacology by first understanding the normal biology and physiology of the GI system, then the pathophysiology of diseases and conditions, and finally the therapeutic options for these conditions.

These drugs block the histamine-2 receptors on gastric parietal cells, reducing the production of hydrochloric acid (HCl) and increasing the pH of gastric juices towards alkalinity.

H2RAs have varying effects on gastric secretions volume, hydrogen ion concentration, gastric emptying speed, LES pressure, and postprandial/fasting serum gastrin levels.

Potential side effects include antiandrogenic effects (gynecomastia, erectile dysfunction), cardiac rhythm/conduction issues, CNS alterations, hematologic changes, GI issues, vitamin B12 deficiency, immune-related effects, and fever.

H2RAs do NOT block histamine-1 receptors, meaning they are not anticholinergic.

Use of H2RAs during pregnancy and lactation is not well-studied, so they should be avoided unless the benefit outweighs the risk.

Metoclopramide is used for lower tiers of GERD therapy, primarily for gastroparesis, due to potential serious side effects (EPS). It has prokinetic properties, but does NOT heal esophageal lesions.

Bethanechol is another drug for lower tiers of GERD therapy, primarily for gastroparesis. It also has prokinetic properties, but does NOT heal esophageal lesions.

Antacids improve LES tone and increase gastric pH, contributing to GERD treatment.

PUD therapy aims to eradicate H. pylori, reduce/eliminate symptoms, heal ulcer lesions, prevent complications like bleeding/perforation/carcinoma, and prevent recurrence.

Proton pump inhibitors (PPIs) are the primary antisecretory medications used for PUD, as they are far more effective than H2RAs at suppressing gastric acid.

GERD therapy aims to prevent or decrease symptoms, heal esophagitis or any erosive esophageal lesions, prevent complications including life-threatening ones like esophageal carcinoma, and prevent recurrent symptoms.

Non-pharmacologic GERD management includes avoiding trigger foods and drinks, not overeating, avoiding bending over and strenuous exercise after meals, elevating the head of the bed, weight loss, and smoking cessation.

Antacids are used as needed for frequent or non-frequent GERD symptoms, as adjunctive therapy for PUD, hypersecretory states, hyperphosphatemia, and calcium deficiency.

Antacids neutralize hydrochloric acid (HCl) by forming salt and water, inhibiting pepsin's proteolytic activity, improving lower esophageal sphincter (LES) tone, and slowing gastric motility (aluminum-based antacids).

Aluminum- and calcium-based antacids can cause constipation, while magnesium-based antacids can lead to diarrhea.

Antacids should not be used as monotherapy for significant disease or frequent symptoms, should not be used if the cause of gastrointestinal symptoms is unclear, should not be used in patients with hypercalcemia or a history of renal stones (calcium-based), and should not be used in patients with renal failure (magnesium- or aluminum-based).

Proton pump inhibitors (PPIs) are highly effective in suppressing gastric acid secretion and are considered the preferred treatment for most patients with frequent GERD symptoms or serious complications like esophagitis.

PPIs block the H+/K+-ATPase enzyme system in parietal cells, preventing the secretion of hydrogen ions needed to form hydrochloric acid (HCl).

PPIs are generally well-tolerated in the short term but can cause GI symptoms, dizziness, drowsiness, acute interstitial nephritis, and long-term effects such as nutrient deficiencies, increased risk of hip fracture, CKD/AKI, infections, and potential associations with gastric cancer, dementia, and overall mortality.

PPIs are contraindicated in patients with a history of hypersensitivity, should be used cautiously in patients with hepatic dysfunction and older adults, should be avoided during pregnancy unless absolutely necessary, should be used cautiously during lactation, and require ongoing lifestyle modifications for optimal results.

Histamine-2 receptor antagonists (H2RAs) are used to treat GERD, with or without erosive esophagitis, PUD, and hypersecretory states, but PPIs are generally preferred.

Drugs that improve lower esophageal sphincter (LES) tone are used in conjunction with acid-suppressing medications to enhance symptom relief.

Prokinetic agents are reserved for patients who continue to experience GERD symptoms despite maximal acid suppression therapy and lifestyle modifications.

Cytoprotective agents, which protect the gastric mucosa, are typically used in PUD and not typically in GERD.