Octreotide

Drug Information: Octreotide

Octreotide is a synthetic octapeptide that mimics the actions of the natural hormone somatostatin. It is more potent than somatostatin in inhibiting growth hormone, glucagon, and insulin secretion. Octreotide is used to treat acromegaly, carcinoid syndrome, and other conditions where hormone overproduction is a problem, as well as for management of variceal bleeding.

Category

Hormones – Other endocrine medications

Mechanism of Action

Octreotide is a somatostatin analog that mimics the effects of natural somatostatin, but with a longer half-life and enhanced potency. Somatostatin is a peptide hormone that inhibits the secretion of various hormones, including growth hormone (GH), insulin, glucagon, gastrin, vasoactive intestinal peptide (VIP), secretin, motilin, and pancreatic polypeptide.

Octreotide exerts its effects by binding to somatostatin receptors (SSTRs), which are G protein-coupled receptors located on the surface of various cells, including those in the pituitary gland, pancreas, and gastrointestinal tract. There are five subtypes of SSTRs (SSTR1-5), and octreotide has a high affinity for SSTR2 and SSTR5.

By binding to SSTRs, octreotide inhibits adenylate cyclase, reducing the intracellular concentration of cyclic AMP (cAMP). This, in turn, leads to the inhibition of hormone release. Specifically, in acromegaly, octreotide suppresses GH secretion by pituitary somatotroph cells. In carcinoid syndrome and other neuroendocrine tumors, it inhibits the release of serotonin, substance P, and other vasoactive substances, thereby reducing symptoms like flushing and diarrhea. In the context of variceal bleeding, octreotide reduces splanchnic blood flow and portal pressure, which helps to control bleeding.

Clinical Uses

Octreotide has a variety of clinical applications due to its somatostatin-like effects. One of its primary uses is in the treatment of **acromegaly**, a condition caused by excessive growth hormone secretion, often due to a pituitary tumor. Octreotide helps to normalize GH and IGF-1 levels, reducing the symptoms of acromegaly.

It is also used to manage **carcinoid syndrome**, which results from the overproduction of hormones by carcinoid tumors. Octreotide can alleviate symptoms such as flushing, diarrhea, and wheezing by inhibiting the release of serotonin and other vasoactive substances. Furthermore, it’s utilized in treating other **neuroendocrine tumors** that secrete hormones like VIP (vasoactive intestinal peptide).

In the context of **variceal bleeding**, particularly esophageal varices secondary to portal hypertension in liver cirrhosis, octreotide is administered to reduce splanchnic blood flow and portal venous pressure, thereby helping to control acute bleeding episodes. It acts by causing vasoconstriction in the mesenteric arterioles, which decreases portal blood flow.

Other uses include managing **diarrhea** associated with short bowel syndrome and controlling **pancreatic fistula** output. Off-label uses have also been explored for conditions like dumping syndrome and certain types of refractory diarrhea.

Dosage

**Adults:**

* **Acromegaly:** Initially, 50 mcg subcutaneously (SC) three times daily. Dosage is then adjusted based on GH and IGF-1 levels, typically ranging from 100 mcg to 500 mcg SC three times daily.
* **Carcinoid Syndrome/VIPomas:** 100-600 mcg/day in 2-4 divided doses subcutaneously.
* **Variceal Bleeding:** Bolus IV injection of 50 mcg followed by continuous IV infusion of 50 mcg/hour for 2-5 days.

**Pediatrics:**
Dosage is determined by the physician based on the child’s weight and condition.
* **Neuroendocrine Tumors:** 1-10 mcg/kg/day divided every 6-12 hours subcutaneously.
* The long-acting formulation (octreotide LAR) is not typically used in children.
**Route of administration:** Subcutaneous injection or intravenous injection/infusion. The long-acting release (LAR) formulation is given via intramuscular injection every 28 days after initial titration.

Indications

* Acromegaly
* Carcinoid syndrome (and other neuroendocrine tumors)
* Variceal bleeding
* VIPomas
* Diarrhea related to short bowel syndrome
* Pancreatic fistula

Contraindications

* Hypersensitivity to octreotide or any of its excipients.
* Caution is advised in patients with gallbladder disease, as octreotide can inhibit gallbladder contractility and may lead to gallstone formation.
* Use with caution in patients with diabetes, as octreotide can affect glucose regulation. Dosage adjustments of insulin or oral hypoglycemic agents may be necessary.
* Octreotide should be used with caution in patients with cardiac disorders, as it can cause bradycardia.

FAQ

**Q: What is Octreotide used for?**
A: Octreotide is used to treat conditions where the body produces too much of certain hormones. These include acromegaly (excess growth hormone), carcinoid syndrome (hormones from carcinoid tumors), and VIPomas (tumors producing vasoactive intestinal peptide). It’s also used to manage variceal bleeding.

**Q: How is Octreotide administered?**
A: Octreotide can be administered subcutaneously (injection under the skin) or intravenously (into a vein). There is also a long-acting release (LAR) formulation that is given as an intramuscular injection every 28 days.

**Q: What are the common side effects of Octreotide?**
A: Common side effects include nausea, diarrhea, abdominal pain, injection site reactions, and gallstone formation. It can also affect blood sugar levels and cause bradycardia (slow heart rate).

**Q: Can Octreotide be used during pregnancy?**
A: Octreotide should be used during pregnancy only if clearly needed and the potential benefit justifies the potential risk to the fetus. It is important to discuss this with your doctor.

**Q: Does Octreotide cure Acromegaly?**
A: Octreotide helps manage Acromegaly by lowering growth hormone levels, but it is not necessarily a cure. In some cases, surgery or radiation therapy may be needed in addition to octreotide treatment.

**Q: How does Octreotide help with variceal bleeding?**
A: Octreotide reduces blood flow to the intestines and decreases portal vein pressure, helping to control bleeding from esophageal varices.

**Q: What should I do if I miss a dose of Octreotide?**
A: If you miss a dose, take it as soon as you remember. However, if it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not double the dose to catch up.

**Q: Will Octreotide interact with other medications?**
A: Octreotide can interact with several medications, including insulin, oral hypoglycemic agents, beta-blockers, and bromocriptine. It is important to inform your doctor about all the medications you are taking.