Liraglutide (GLP-1 receptor agonist) differs from sitagliptin (DPP-4 inhibitor) in its degree of GLP-1 receptor activation. Liraglutide achieves supraphysiological GLP-1 effects because:

• A Liraglutide inhibits DPP-4 and also stimulates GLP-1 secretion from L-cells
• B Liraglutide crosses the blood-brain barrier achieving higher CNS GLP-1 concentrations
• C Liraglutide has a longer half-life due to albumin conjugation increasing receptor occupancy time
• D Liraglutide is a full receptor agonist while sitagliptin only prevents endogenous GLP-1 degradation ✓

Explanation

Sitagliptin inhibits DPP-4 (dipeptidyl peptidase-4), preventing degradation of endogenous GLP-1 released from intestinal L-cells, raising GLP-1 levels 2-3 fold (physiological range). Liraglutide is an exogenous GLP-1 receptor agonist that directly activates GLP-1R at pharmacological (supraphysiological) concentrations, achieving greater HbA1c lowering, weight reduction, and cardiovascular/renal benefits. Liraglutide's long half-life (~13 h) does result from fatty acid conjugation enabling albumin binding that resists DPP-4 degradation.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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