1. Clinical Overview
Octreotide acetate is a long-acting synthetic octapeptide analogue of the natural hormone somatostatin. It mimics somatostatin's pharmacological actions but with a significantly longer duration of effect. It is a potent inhibitor of growth hormone, glucagon, and insulin secretion, and reduces splanchnic blood flow and gastrointestinal (GI) secretion and motility. The 10mg strength is typically used for long-term maintenance therapy via deep subcutaneous or intramuscular injection.
| Onset | Duration | Bioavailability |
|---|---|---|
| Rapid suppression of growth hormone and other peptides occurs within 30-60 minutes of subcutaneous injection. The depot formulation (long-acting release) provides therapeutic levels after an initial lag. | Subcutaneous injection: 8-12 hours. Long-acting release (LAR) intramuscular injection: Approximately 28-30 days. | Subcutaneous: ~100%. Intramuscular (LAR): The microsphere formulation provides sustained release, with bioavailability comparable to subcutaneous administration over the monthly period. |
2. Mechanism of Action
Octreotide is a potent, long-acting somatostatin analogue. It binds with high affinity to somatostatin receptors (primarily subtypes 2 and 5), mimicking the inhibitory actions of endogenous somatostatin. This leads to suppression of secretion from various endocrine and exocrine glands, inhibition of intestinal motility, reduction of splanchnic blood flow, and modulation of cell proliferation.
3. Indications & Uses
- Acromegaly: Long-term maintenance therapy after adequate response to subcutaneous octreotide.
- Symptomatic treatment of Gastroenteropancreatic Neuroendocrine Tumors (GEP-NETs) including carcinoid tumors (to control symptoms like flushing and diarrhea).
- Thyrotropin-Secreting Pituitary Adenomas (TSHomas): To control TSH hypersecretion.
4. Dosage & Administration
Adult Dosage: Acromegaly (LAR): Initial: 20mg IM every 4 weeks, titrated based on GH/IGF-1 levels. Max typically 30mg/4 weeks. GEP-NETs (LAR): 20mg IM every 4 weeks, may increase to 30mg. Acute Variceal Bleed: 25-50 mcg/hr IV infusion for 2-5 days. Subcutaneous: 50-200 mcg TDS, titrated.
Administration: LAR 10mg Vial: For DEEP INTRAMUSCULAR injection in the gluteal muscle ONLY. Must be reconstituted with provided diluent, shaken vigorously, and administered immediately. Do not inject intravenously or subcutaneously. Rotate injection sites. Subcutaneous 10mg/ml: For subcutaneous injection, may be self-administered after training in abdomen, thigh, or upper arm.
5. Side Effects
Common side effects may include:
- Injection site pain, redness, or nodules (LAR).
- Gastrointestinal: Nausea, abdominal pain, diarrhea, flatulence, steatorrhea.
- Biliary: Gallbladder sludge, asymptomatic gallstones.
- Glucose metabolism: Hyperglycemia or hypoglycemia.
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Cyclosporine | Octreotide may decrease cyclosporine levels; monitor levels closely. | Major |
| Bromocriptine | Octreotide increases bioavailability of bromocriptine. | Moderate |
| Insulin, Oral Hypoglycemics (e.g., Glibenclamide) | Octreotide alters glucose regulation; dose adjustment of antidiabetics often required. | Major |
| Beta-blockers (e.g., Propranolol) | Additive effect on heart rate reduction; risk of bradycardia. | Moderate |
| Calcium Channel Blockers (e.g., Verapamil) | Additive effect on heart rate reduction. | Moderate |
| Drugs metabolized by CYP3A4 (e.g., Quinidine) | Octreotide may inhibit clearance, increasing their levels. | Moderate |
| Ciprofloxacin | Octreotide reduces its absorption; administer ciprofloxacin at least 2 hours before octreotide. | Moderate |
7. Patient Counselling
- DO rotate subcutaneous injection sites daily to prevent lipodystrophy.
- DO monitor blood glucose regularly if diabetic.
- DO report severe abdominal pain, yellowing of skin/eyes, or clay-colored stools immediately.
- DON'T stop the medication abruptly without consulting your doctor.
- DON'T administer the LAR injection yourself; it must be given by a trained healthcare professional.
8. Toxicology & Storage
Overdose: Acute overdose can lead to severe hypoglycemia or hyperglycemia, lethargy, weakness, dizziness, nausea, abdominal cramps, diarrhea, bradycardia, arrhythmias, and prolonged QT interval.
Storage: Store unopened vials/ampoules at 2°C to 8°C (refrigerate). Do not freeze. Protect from light. For LAR: After reconstitution, use immediately. Do not store reconstituted suspension. For multidose vials (subcutaneous), after first use, may be stored at room temperature (below 25°C) or refrigerated for up to 2 weeks. Discard if cloudy or contains particulate matter.