Somatostatin

Somatostatin is produced in hypothalamic neurons, pancreatic delta cells and gut endocrine cells, and circulates as a 14-residue and a 28-residue form. It binds all five somatostatin receptor subtypes with roughly equal affinity, all of which are Gi-coupled and inhibitory. Physiologically it brakes growth hormone and TSH release from the pituitary, insulin and glucagon from the islets, and gastrin, secretin, VIP and pancreatic enzyme release from the gut, while reducing splanchnic arterial flow and portal pressure. That last effect is the reason it is still infused in acute variceal haemorrhage in Europe. Its half-life of a couple of minutes makes any use outside a continuous drip impossible, which is exactly the problem the analogue class was built to solve.

Targets: SSTR1, SSTR2, SSTR3, SSTR4, SSTR5, Splanchnic blood flow

• · Some centres double the infusion to 500 mcg per hour in ongoing bleeding. This is an inpatient drug only.

Work out your exact syringe units →

• commonNausea and abdominal cramping— Worse with rapid bolus administration.
• commonHyperglycaemia then rebound hypoglycaemia— Insulin and glucagon are both suppressed; glucose must be watched during and after infusion.
• uncommonBradycardia and flushing— Usually with the initial bolus.

• Pregnancy and breastfeeding
• Not suitable for outpatient or self-administered use in any form

• redundantoctreotide — Octreotide is the long-acting stand-in for exactly this molecule.
• synergyterlipressin — Both lower portal pressure in variceal bleeding, though guidelines generally pick one vasoactive agent.

• · Continuous blood glucose during infusion
• · Heart rate and blood pressure
• · Haemoglobin and evidence of ongoing bleeding

Prescription hospital product in parts of Europe and Asia; not marketed in the US.

• Baveno VII consensus on portal hypertension, vasoactive drug recommendations (guideline)
• Reichlin 1983 NEJM, two-part review of somatostatin physiology (review)

Somatostatin is the reference molecule for the whole class and understanding it explains why every analogue looks the way it does. It binds all five SSTR subtypes at comparable low-nanomolar affinity: the Signifor label's comparison table gives SRIF-14 IC50 values of 0.93 nM at SSTR1, 0.15 at SSTR2, 0.56 at SSTR3, 1.5 at SSTR4 and 0.29 at SSTR5. All five are Gi/Go-coupled, so the signalling is uniformly inhibitory: adenylate cyclase down, inward-rectifier potassium channels open, voltage-gated calcium channels closed, and in several subtypes recruitment of the phosphatases SHP-1 and SHP-2. Because every subtype is inhibitory and the ligand hits all of them, somatostatin is a universal brake rather than a targeted drug, which is why it suppresses GH, TSH, insulin, glucagon, gastrin, secretin, VIP, motilin and pancreatic enzymes at once. The reason it survives in European practice for variceal bleeding is a different property: it constricts the splanchnic arterial bed and cuts portal venous inflow, partly directly and partly by inhibiting the vasodilator peptides, notably glucagon, that keep the splanchnic circulation dilated in cirrhosis. Portal pressure falls within minutes and recovers within minutes of stopping. The pharmacophore every analogue copies is the Phe7-Trp8-Lys9-Thr10 segment on the beta-turn; the rest of the ring exists to hold that turn in shape.

The main clinical error is treating somatostatin as though it were a long-acting analogue. It is not; the effect ends within minutes of the infusion stopping, so any interruption for a line change, transfer or procedure is a period of unprotected portal pressure. The second is failing to anticipate the post-infusion glucose dip. The third is pushing the rate in ongoing bleeding when the real problem is that the varices need mechanical control. Outside hospital there is nothing sensible to say about this molecule: anyone who has bought a vial labelled somatostatin for self-administration has bought a compound with a two-minute half-life that does nothing useful outside a continuous drip.

1. 250 mcgHour 0 — 250 mcg slow intravenous bolus at the start of treatment for acute variceal bleeding.
2. 250 mcgHours 0 to 120 — 250 mcg per hour by continuous infusion for 2 to 5 days alongside band ligation and antibiotic prophylaxis.
3. 500 mcgIf bleeding continues — Some centres double the infusion to 500 mcg per hour. There is no titration to a target level; the escalation is protocol-driven and binary.

• SSTR1 — IC50 0.93 +/- 0.12 nM (Signifor LAR label comparison table)

  Inhibitory Gi coupling with antiproliferative signalling and inhibition of GH release.

• SSTR2 — IC50 0.15 +/- 0.02 nM

  The dominant secretory brake: GH, glucagon, gastrin and serotonin release all fall.

• SSTR3 — IC50 0.56 +/- 0.17 nM

  Inhibitory signalling with a documented pro-apoptotic arm.

• SSTR4 — IC50 1.5 +/- 0.4 nM

  The subtype essentially no clinical analogue reaches; its human roles remain poorly defined.

• SSTR5 — IC50 0.29 +/- 0.04 nM

  Insulin and incretin suppression, plus ACTH suppression in corticotroph tissue.

• Splanchnic arteriolar tone

  Reduced splanchnic inflow and portal pressure within minutes of starting an infusion, which is the basis for use in acute variceal haemorrhage.

Portal pressure and secretory suppression begin within one to two minutes of the bolus and are fully established within about five. Everything reverses in a similar timeframe when the infusion stops. There is no accumulation, no loading and no steady state to reach in any meaningful sense.

In variceal bleeding, somatostatin is one of three interchangeable vasoactive options alongside terlipressin and octreotide, and guidelines pick one rather than combining them. What it genuinely combines with is endoscopic band ligation, prophylactic antibiotics, which independently reduce mortality, and restrictive transfusion. Adding a second vasoactive agent buys ischaemia, not haemostasis. In an outpatient or enhancement context there is no stack to discuss, because there is no outpatient use of this molecule at all.

Against octreotide: octreotide is the long-acting stand-in built specifically to solve this molecule's half-life problem, and in the US it fills the variceal bleeding role entirely because somatostatin was never marketed there. Against terlipressin: terlipressin is a prodrug with a slow-release profile that can be given as intermittent boluses rather than a continuous drip, which is operationally easier, and it carries the stronger mortality signal in meta-analysis; somatostatin is gentler on the systemic circulation and causes far less ischaemia. Against the analogues as a class: native somatostatin is the only one that hits all five receptor subtypes at once, which makes it a better physiological probe and a worse drug.

Not applicable. This is an inpatient intravenous product used for a defined 2 to 5 day episode, priced per vial within a hospital formulary, and it is not marketed in the US at all.

• ?The somatostatin-14 sequence given is the standard published sequence and I am confident in it, but I did not resolve it against a primary source in this session, so verified is false.
• ?Volume of distribution, protein binding and quantitative clearance for native somatostatin are not well characterised in any source I resolved.
• ?Meta-analysed mortality data comparing somatostatin, octreotide and terlipressin in variceal bleeding exist, but I did not verify a specific reference this session.
• ?The Baveno VII citation is included as further reading only; I did not confirm its identifiers.

• Baveno VII consensus workshop: personalized care in portal hypertension de Franchis R, et al., Baveno VII Faculty, Journal of Hepatology, 2022

  Further reading, not verified in this session. The Baveno consensus statements are where the vasoactive drug recommendations for variceal bleeding, treating somatostatin, terlipressin and octreotide as interchangeable first-line options, are actually set.

• SIGNIFOR LAR (pasireotide) for injectable suspension - FDA prescribing information Recordati Rare Diseases, DailyMed

  Carries the SSTR1-5 binding table for native somatostatin-14 quoted above, which is the cleanest sourced set of affinity numbers for the parent molecule.