Tirzaepatide mechanism of action

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tirzepatide

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tirzepatide prescribing information mechanism of action GIP GLP-1 receptor agonist FDA

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Tirzepatide is a once-weekly dual incretin receptor agonist. It activates both:

GIP receptors - glucose-dependent insulinotropic polypeptide receptors
GLP-1 receptors - glucagon-like peptide-1 receptors

Main actions

Pancreatic beta cells: increases insulin secretion, but mainly when blood glucose is elevated.
Pancreatic alpha cells: suppresses inappropriate glucagon release, also in a glucose-dependent manner. This reduces hepatic glucose output.
Stomach and gut: GLP-1 receptor activation slows gastric emptying, particularly early in therapy, reducing the post-meal glucose rise.
Brain/appetite pathways: reduces hunger, food intake, and caloric intake, contributing to substantial weight loss. GLP-1 has a recognized role in appetite regulation; GIP may add to this effect.
Long duration: its fatty-acid side chain promotes albumin binding, protects it from rapid clearance, and gives an approximately 5-day half-life, allowing weekly administration.

So, in simplified form:

Tirzepatide lowers glucose by increasing glucose-appropriate insulin and decreasing glucose-appropriate glucagon, while reducing appetite and slowing gastric emptying.

Because these insulin and glucagon effects are glucose-dependent, tirzepatide by itself has a relatively low intrinsic risk of hypoglycemia. Hypoglycemia risk rises when it is combined with insulin or an insulin secretagogue such as a sulfonylurea.

The FDA describes tirzepatide as selectively activating both receptors and enhancing first- and second-phase insulin secretion while lowering glucagon in a glucose-dependent fashion in the current prescribing information. It is structurally a GIP-based modified peptide with a fatty-diacid moiety for prolonged action.

Katzung's Basic and Clinical Pharmacology, 16th Edition, p. 1190
A recent Cochrane review of tirzepatide in adults with obesity is indexed as PMID 41161687.

Inherited thrombophilias

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inherited thrombophilia testing

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ASH 2023 thrombophilia testing guideline inherited thrombophilia recommendations

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https://ashpublications.org/bloodadvances/article/7/22/7101/…

Inherited thrombophilias

Inherited thrombophilia refers to germline abnormalities that increase a person's tendency to develop venous thromboembolism (VTE), chiefly deep-vein thrombosis (DVT) and pulmonary embolism (PE). Thrombosis usually results from the inherited risk interacting with acquired factors such as surgery, immobility, estrogen exposure, pregnancy, obesity, trauma, cancer, and age.

Major inherited thrombophilias

Disorder	Core mechanism	Usual risk category
Factor V Leiden (FVL)	Factor V is resistant to cleavage/inactivation by activated protein C, so thrombin generation persists	Common, low-to-moderate risk if heterozygous; higher risk if homozygous
Prothrombin G20210A mutation	Raises circulating prothrombin, promoting thrombin formation	Common, low-to-moderate risk
Antithrombin deficiency	Loss of inhibition of thrombin and factor Xa	Uncommon, high risk
Protein C deficiency	Reduced activated protein C anticoagulant activity	Uncommon, high risk
Protein S deficiency	Reduced cofactor activity for activated protein C	Uncommon, high risk

Factor V Leiden

Factor V Leiden is the most common inherited thrombophilia in people of Northern European ancestry. The F5 c.1691G>A variant produces the Arg506Gln substitution. It removes a major activated-protein-C cleavage site, so factor Va is inactivated much more slowly and coagulation is favored. Heterozygotes have roughly a 5 to 10-fold relative increase in venous-thrombosis risk, and homozygotes have a greater risk. It is primarily associated with venous, not arterial, thrombosis.
Tietz Textbook of Laboratory Medicine, 7th Edition, pp. 2738-2739.

Important clinical points

These conditions predispose predominantly to VTE, not routine arterial events such as myocardial infarction or ischemic stroke.
A mutation does not mean a clot will inevitably occur. Absolute risk depends strongly on family history, genotype, prior VTE, and acquired triggers.
Risk increases substantially with combined estrogen contraception, pregnancy/postpartum state, surgery, immobilization, and malignancy.
“High-risk thrombophilia” usually means antithrombin, protein C, or protein S deficiency, or homozygous/combined FVL and prothrombin variants.
Antiphospholipid syndrome is acquired, not inherited. It may be investigated in an appropriate thrombosis work-up but should not be grouped with inherited thrombophilias.

Testing

A typical inherited thrombophilia panel includes:

Factor V Leiden mutation
Prothrombin G20210A mutation
Antithrombin activity
Protein C activity
Free protein S antigen or activity

Testing is not routinely useful for everyone with VTE. It is generally not recommended after VTE clearly provoked by major surgery, trauma, or prolonged immobilization. It may be considered when the outcome would change management, for example in selected young patients with unprovoked or unusual-site VTE, recurrent VTE, or a strong family history of high-risk thrombophilia.
Tietz Textbook of Laboratory Medicine, 7th Edition, p. 3136.

Testing protein C, protein S, and antithrombin during an acute clot, pregnancy, liver disease, or anticoagulant therapy can produce misleading results. Genetic tests for FVL and prothrombin G20210A are unaffected by anticoagulation, but functional assays often need careful timing and specialist interpretation.

Current ASH testing guidance recommends against general-population screening before combined oral contraceptives, and limits testing to specific scenarios where results are likely to affect decisions. A 2024 systematic review of VTE risk in hereditary thrombophilia is indexed as PMID 39167180.

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