GLP-1 Receptor AgonistsComplete Pharmacist & NAPLEX Guide
Master everything about GLP-1 drugs: Ozempic, Wegovy, Mounjaro, Zepbound, and the new oral Foundayo. Mechanism of action, dosing, side effects, counseling points, and NAPLEX high-yield facts.
Mechanism of Action
GLP-1 (glucagon-like peptide-1) receptor agonists are incretin mimetics that work through multiple mechanisms:
Glucose-Dependent Insulin Secretion
Stimulate pancreatic beta cells to release insulin ONLY when blood glucose is elevated. This glucose-dependent action reduces hypoglycemia risk compared to sulfonylureas.
Glucagon Suppression
Suppress glucagon release from alpha cells, reducing hepatic glucose output. This effect is also glucose-dependent.
Delayed Gastric Emptying
Slow gastric emptying, leading to prolonged satiety and reduced postprandial glucose spikes. This contributes to weight loss effects.
Central Appetite Suppression
Act on hypothalamic GLP-1 receptors to reduce appetite and food intake. This is the primary mechanism for weight loss.
NAPLEX Pearl:
Tirzepatide (Mounjaro/Zepbound) is a dual GIP/GLP-1 agonist, providing additional glucose-dependent insulin secretion through GIP receptors. This dual mechanism may explain its superior efficacy in clinical trials.
GLP-1 Drug Comparison Chart
| Brand Name | Generic | Indication | Route | Frequency | Starting Dose | Maintenance |
|---|---|---|---|---|---|---|
| Ozempic | semaglutide | Type 2 Diabetes | Subcutaneous injection | Once weekly | 0.25 mg | 0.5-2 mg |
| Wegovy | semaglutide | Chronic weight management | Subcutaneous injection | Once weekly | 0.25 mg | 2.4 mg |
| Mounjaro | tirzepatide | Type 2 Diabetes | Subcutaneous injection | Once weekly | 2.5 mg | 5-15 mg |
| Zepbound | tirzepatide | Chronic weight management | Subcutaneous injection | Once weekly | 2.5 mg | 5-15 mg |
| FoundayoNEW | orforglipron | Chronic weight management | Oral | Once daily | 0.8 mg | 5.5-17.2 mg |
| Rybelsus | semaglutide | Type 2 Diabetes | Oral | Once daily | 3 mg | 7-14 mg |
Side Effects & Safety
Boxed Warning: Thyroid C-Cell Tumors
All GLP-1 agonists carry a boxed warning for thyroid C-cell tumors based on rodent studies. Contraindicated in patients with personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).
Common Side Effects
- • Nausea - Most common, usually transient (30-40%)
- • Vomiting - Often improves with dose titration
- • Diarrhea - May occur in early treatment
- • Constipation - Due to delayed gastric emptying
- • Abdominal pain - Usually mild to moderate
Serious Adverse Events
- • Pancreatitis - Discontinue if suspected
- • Gallbladder disease - Risk with rapid weight loss
- • Acute kidney injury - Often due to dehydration
- • Hypoglycemia - Risk with sulfonylureas/insulin
- • Diabetic retinopathy - Monitor with rapid A1c drop
Patient Counseling Points
For Injectable GLP-1s (Ozempic, Wegovy, Mounjaro, Zepbound)
- 1. Inject once weekly on the same day each week. Can be any time of day, with or without food.
- 2. Rotate injection sites (abdomen, thigh, upper arm). Never inject into same exact spot.
- 3. Store unused pens in refrigerator. After first use, can store at room temperature up to 56 days.
- 4. If a dose is missed by more than 5 days, skip it and take the next dose on the regular day.
For Oral Rybelsus
- 1. Take first thing in the morning on an empty stomach.
- 2. Swallow whole with no more than 4 ounces of plain water only.
- 3. Wait at least 30 minutes before eating, drinking, or taking other medications.
- 4. Do not crush, chew, or split tablets.
NEWFor Oral Foundayo (orforglipron)
- 1. No food or water restrictions - can take any time of day!
- 2. Take once daily at approximately the same time each day.
- 3. Dose titration over several months (0.8 mg to 2.5 mg to 5.5 mg to higher if needed).
- 4. Key advantage over Rybelsus: more convenient dosing without timing restrictions.
NAPLEX High-Yield Facts
Must Know for the Exam
- • GLP-1 agonists have glucose-dependent insulin release
- • All have boxed warning for thyroid C-cell tumors
- • Contraindicated in MTC or MEN2
- • Semaglutide/tirzepatide reduce cardiovascular events
- • Injectable forms are dosed once weekly
Common Exam Questions
- • Rybelsus: 30 min before food, 4 oz water max
- • Major side effects: GI symptoms, pancreatitis
- • Reduce sulfonylurea/insulin dose when adding GLP-1
- • Tirzepatide is a dual GIP/GLP-1 agonist
- • A1C reduction: typically 1.0-1.8%
Practice Question Preview
A patient on Ozempic reports severe abdominal pain radiating to the back. Which action is most appropriate?
Frequently Asked Questions
What is the difference between Ozempic and Wegovy?
Both contain semaglutide, but Ozempic is FDA-approved for type 2 diabetes (max dose 2 mg/week), while Wegovy is approved for chronic weight management (higher dose of 2.4 mg/week).
Can GLP-1 agonists be used with insulin?
Yes, but insulin doses often need to be reduced by 20-50% to prevent hypoglycemia. GLP-1 agonists should NOT be combined with DPP-4 inhibitors.
What makes Foundayo different from Rybelsus?
Foundayo can be taken any time of day without food or water restrictions. Rybelsus must be taken on an empty stomach with limited water and 30-minute wait.
Are compounded GLP-1 medications safe?
The FDA and manufacturers warn against compounded GLP-1s due to concerns about purity, sterility, and accurate dosing.
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