Somatotropin
Bovine somatotropin (bST), Porcine somatotropin (pST), Recombinant human growth hormone (rhGH)
Also known as: Posilac · Humatrope · Nutropin · Genotropin · Norditropin · rbST · Human growth hormone · rhGH · Somatropin
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Growth hormone replacement | 0.3-0.7 IU/kg weekly divided into 3-5 doses | SC/IM | divided into 3-5 doses weekly | Continue for at least 6 weeks to evaluate response | 🌍 EU |
- Growth hormone replacement: IM injection is painful. Monitor IGF-1.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Growth hormone replacement | 0.3-0.7 IU/kg weekly divided into 3-5 doses | SC/IM | divided into 3-5 doses weekly | Continue for at least 6 weeks to evaluate response | 🌍 EU |
- Growth hormone replacement: IM injection is painful. Monitor IGF-1.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Somatotropin, commonly known as growth hormone (GH), is a peptide hormone produced by the anterior pituitary gland. In veterinary medicine, recombinant bovine somatotropin (rbST) has historically been used to increase milk production in dairy cattle, while porcine somatotropin is utilized to improve feed efficiency and muscle growth in swine.
In small animal medicine (dogs and cats), human recombinant somatotropin is occasionally used off-label to treat pituitary dwarfism (growth hormone deficiency).
Clinical Pearl: Due to species-specific differences in amino acid sequences, human GH can induce neutralizing antibody formation in dogs and cats, which may limit its long-term efficacy. Porcine GH is highly homologous to canine GH and is the preferred therapeutic option if it can be sourced.
Mechanism of action
Somatotropin binds to specific cell surface receptors in target tissues (liver, bone, muscle, adipose).
- Direct effects: Stimulates lipolysis and inhibits glucose uptake, leading to increased blood glucose levels (diabetogenic effect).
- Indirect effects: Mediated primarily through the stimulation of Insulin-like Growth Factor-1 (IGF-1) production in the liver.
GH → Liver → IGF-1 release → Binds to IGF receptors → Promotes cellular proliferation, linear bone growth (at open epiphyseal plates), and protein synthesis.
Safety & warnings
Contraindications
- Closed epiphyseal plates (if seeking linear growth)
- Neoplasia (may stimulate tumor growth)
- Diabetes mellitus
- Hypersensitivity to the drug or formulation components
- Patients with closed epiphyses (unless treating specific adult-onset deficiencies)
- Known hypersensitivity
- Active neoplasia
Adverse effects
- Insulin resistance / Diabetes mellitus
- Acromegaly (with prolonged use)
- Antibody formation (when using human GH in pets)
- Diabetogenic effect (hyperglycemia/diabetes mellitus)
- Local injection site reactions
- Antibody formation (reducing long-term efficacy)
Precautions
Important: Monitor blood glucose closely, as somatotropin is highly diabetogenic. Use with extreme caution in patients with a history of pancreatitis or those at risk for diabetes mellitus. In small animals, monitor for signs of acromegaly (broadening of facial features, increased interdental spaces, organomegaly) during prolonged therapy. GH therapy can also unmask underlying hypothyroidism.
Drug interactions
May antagonize the growth-promoting effects of somatotropin.
Somatotropin induces insulin resistance, potentially requiring significant adjustments in insulin dosage for diabetic patients.
Monitoring
- Serum IGF-1 levels
- Blood glucose and urine glucose
- Thyroid panel (TSH/T4)
- Growth rate and body weight
- Physical signs of acromegaly
- Growth rate/body weight
- Injection site reactions
Pharmacokinetics
Half-life
Absorption
Well absorbed after subcutaneous (SC) or intramuscular (IM) injection.
Distribution
Localizes to highly perfused organs, particularly the liver and kidneys.
Metabolism
Undergoes hepatic and renal degradation.
Elimination
Cleared rapidly from circulation, but biological effects (mediated via IGF-1) are prolonged.
Overdose
Acute overdose is unlikely to cause severe clinical signs other than transient hypoglycemia followed by hyperglycemia. Chronic overdosage leads to acromegaly and diabetes mellitus.
Available products
Formulations
- Injectable solution
- Lyophilized powder for injection
- Injectable: 2-16 IU vials for reconstitution
Veterinary
- Posilac (recombinant bovine somatotropin)
Human-labeled
- Humatrope
- Nutropin
- Genotropin
- Saizen
- Norditropin
Regulatory status
Human authorized products used off-label under the cascade.
POM. Human authorized products used off-label under the cascade.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store in the refrigerator (2-8°C). Do not freeze. Reconstituted solutions should be used within the timeframe specified by the manufacturer (usually 14-21 days) and handled gently to prevent protein denaturation.
Client information
Somatotropin is given by injection under the skin.
- Consistency is key: Administer the medication exactly as directed by your veterinarian to maintain steady hormone levels.
- Monitor for increased thirst or urination: This drug can increase blood sugar levels and potentially lead to diabetes. Contact your vet if you notice your pet drinking or urinating more than usual.
- Storage: Keep the medication refrigerated. Do not shake the vial vigorously, as this can damage the fragile hormone proteins. Gently roll the vial to mix if instructed.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.