1. Clinical Overview
Octreotide acetate is a synthetic octapeptide analogue of the natural hormone somatostatin. It mimics the pharmacological actions of somatostatin but with a significantly longer duration of action. It is a potent inhibitor of growth hormone (GH), glucagon, insulin, and various gastrointestinal (GI) hormones. In the Indian market, it is a critical drug for managing acromegaly, carcinoid syndrome, and GI bleeding from varices.
| Onset | Duration | Bioavailability |
|---|---|---|
| Subcutaneous: Within 30 minutes. Intravenous: Immediate. | Subcutaneous: 8-12 hours. Long-acting depot (LAR): Approximately 28 days. | Subcutaneous: Approximately 100%. Intramuscular (LAR): Approximately 60-63%. |
2. Mechanism of Action
Octreotide is a potent, long-acting synthetic octapeptide that mimics the physiological effects of the endogenous hormone somatostatin. It binds with high affinity to somatostatin receptors (predominantly subtypes 2 and 5). This binding inhibits the secretion of numerous hormones and bioactive substances, including growth hormone (GH), thyroid-stimulating hormone (TSH), insulin, glucagon, gastrin, vasoactive intestinal peptide (VIP), secretin, motilin, and pancreatic polypeptide. It also reduces splanchnic blood flow and intestinal fluid secretion.
3. Indications & Uses
- Acromegaly: Long-term maintenance therapy after adequate response to initial treatment with subcutaneous octreotide.
- Carcinoid Syndrome: For symptomatic treatment of patients with metastatic carcinoid tumors to suppress or inhibit the associated severe diarrhea and flushing episodes.
- Vasoactive Intestinal Peptide (VIP) secreting tumors (VIPomas): For the treatment of profuse watery diarrhea.
4. Dosage & Administration
Adult Dosage: Acromegaly: Initial: 50 mcg SC TID. Titrate based on GH/IGF-1 levels. Maintenance: 100-200 mcg SC TID. Max: 1500 mcg/day. For transition to LAR: After stable SC dose, give LAR 20 mg IM every 4 weeks. Carcinoid/VIPoma: Initial: 100-200 mcg SC BID-TID. Range: 150-750 mcg/day. Max: 1500 mcg/day.
Administration: Subcutaneous injection: Rotate injection sites (thigh, abdomen, buttocks). Administer between meals to minimize GI side effects. For LAR formulation: Deep IM gluteal injection, alternate buttocks every 4 weeks. Reconstitute LAR suspension strictly as per manufacturer's instructions.
5. Side Effects
Common side effects may include:
- Injection site pain, redness, or swelling.
- Nausea, abdominal pain, diarrhea, flatulence.
- Headache, dizziness.
- Hyperglycemia or hypoglycemia.
- Constipation.
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 glycemic control; can cause both hypo- and hyperglycemia. Frequent glucose monitoring required. | Major |
| Beta-blockers (e.g., Propranolol) | Additive effect on heart rate; may cause severe bradycardia. | Moderate |
| Calcium channel blockers (e.g., Verapamil) | Additive effect on heart rate; monitor. | Moderate |
| Drugs metabolized by CYP3A4 (e.g., Midazolam) | Potential for altered metabolism; monitor. | Moderate |
7. Patient Counselling
- DO rotate injection sites with each dose to prevent skin reactions.
- DO monitor your blood sugar regularly if you have diabetes.
- DO report severe abdominal pain, yellowing of skin/eyes (jaundice), or pale stools immediately.
- DO keep your doctor's appointments for ultrasound monitoring of gallbladder.
- DONT change the dose or stop the medicine without consulting your doctor.
- DONT drive if you feel dizzy or fatigued after the injection.
8. Toxicology & Storage
Overdose: Hypoglycemia followed by hyperglycemia, lethargy, weakness, dizziness, nausea, abdominal cramps, diarrhea, malabsorption, weight loss, flushing, bradycardia, arrhythmias, and cardiac arrest.
Storage: Store unopened vials/ampoules in a refrigerator at 2°C to 8°C. Protect from light. Do not freeze. After opening or dilution, use immediately. For Sandostatin LAR, after reconstitution, use within 1 hour. Keep out of reach of children.