| name | genryzon-prescribing-guide |
| description | Bedside prescribing reference for Genryzon (somatrogon, Pfizer India) — the once-weekly long-acting growth hormone for paediatric growth hormone deficiency. Use when a clinician asks how to start Genryzon, how to dose somatrogon in a child, how to switch a child from daily growth hormone to weekly somatrogon, how to inject the Genryzon pen, missed-dose rule for somatrogon, when to stop somatrogon, or needs a monograph-level prescribing decision for a paediatric GHD patient. Applies to children and adolescents ≥3 years of age. Grounded in the Pfizer India Product Monograph (Genryzon LPD, 2022 — PfLEET 2022-0081166). |
Genryzon (Somatrogon) Prescribing Guide
Once-weekly long-acting recombinant human growth hormone for paediatric GHD. Initiated and monitored by a paediatric endocrinologist.
Step 1 — Confirm the patient qualifies
Genryzon is indicated when ALL of these are true:
- Child or adolescent ≥3 years of age
- Confirmed growth disturbance due to insufficient growth hormone secretion (paediatric GHD) by an endocrinologist
- Open epiphyses (do not use for growth if plates are closed)
Do NOT use if any of:
- Active tumour (intracranial tumour must be inactive AND antitumour therapy complete before starting)
- Acute critical illness — post open-heart surgery, abdominal surgery, multiple trauma, acute respiratory failure
- Prader-Willi syndrome without confirmed GHD (sudden death reports in PWS + severe obesity / airway obstruction / sleep apnoea / respiratory infection)
- Hypersensitivity to somatrogon or excipients (m-cresol, poloxamer 188, L-histidine, sodium chloride, citric acid, trisodium citrate)
- Child <3 years — safety/efficacy not established
- Pregnancy, or renal/hepatic impairment (no data)
Step 2 — Pretreatment work-up (do BEFORE first dose)
- Thyroid function — treat any pre-existing hypothyroidism first (hypothyroidism blunts the GH response)
- Adrenal function — GH may unmask central hypoadrenalism; if on glucocorticoid replacement, plan to review dose after starting
- Glucose tolerance — baseline FPG ± HbA1c; GH reduces insulin sensitivity
- Fundoscopy — baseline, for later comparison if benign intracranial hypertension is suspected
- Tumour clearance — confirm intracranial tumour inactive; antitumour therapy complete
- Auxology + bone age — baseline height, weight, height velocity, bone age
Step 3 — Prescribe the starting dose
Standard dose: 0.66 mg/kg body weight, subcutaneous, ONCE WEEKLY.
Choose pen strength by body weight:
| Body weight (weekly dose 0.66 mg/kg) | Pen to use | Increment |
|---|
| Up to ~18 kg (dose ≤12 mg) | 24 mg / 1.2 mL pen (0.2–12 mg range) | 0.2 mg |
| ~18–45 kg (dose 12–30 mg) | 60 mg / 1.2 mL pen (0.5–30 mg range) | 0.5 mg |
| >45 kg (dose >30 mg) | 60 mg pen — split into TWO injections at DIFFERENT sites | 0.5 mg |
Round the calculated dose to the nearest available increment.
Step 4 — Administer
- Route: subcutaneous only
- Sites: abdomen · thighs · buttocks · upper arms — rotate at every dose
- Caregiver required for injections into upper arms and buttocks
- Timing: same day each week, any time of day
- If >1 injection needed to deliver the full dose (i.e. >30 mg) → each injection at a different site
- Train patient + caregiver in pen technique before self-administration
Step 5 — Handle switches and calendar changes
Switching from daily GH → weekly somatrogon:
Start weekly somatrogon at 0.66 mg/kg/week on the day AFTER the last daily injection.
Missed dose:
- Within 3 days of the scheduled dose → give ASAP, then resume the usual weekly schedule
- More than 3 days late → skip that dose, give the next dose on the regularly scheduled day
Changing the weekly dosing day:
Allowed, provided at least 3 days between two consecutive doses. Then continue weekly on the new day.
Step 6 — Monitor and titrate
Follow-up interval: every 6–12 months (more frequent during puberty). At each visit:
- Auxology: height, weight, growth velocity
- Biochemistry: serum IGF-1 (see rule below), TSH, free T4, fasting glucose, HbA1c if diabetic risk
- Pubertal status (Tanner stage)
- Bone age (annually or as indicated)
- Fundoscopy if suspicious symptoms
IGF-1 titration rule (critical — commonly done wrong):
- Always draw the IGF-1 sample 4 days after the prior weekly dose — otherwise the level is unrepresentative
- Target: IGF-1 SDS between −2 and +2 (aim close to 0)
- If IGF-1 SDS is >2 above the mean for age and sex → REDUCE the somatrogon dose by 15%
- More than one 15% reduction may be needed — reassess after each
Female patients on oral estrogen: oral estrogen ↓ IGF-1 response to GH → a higher somatrogon dose may be needed to hit target IGF-1. Re-check IGF-1 if oral estrogen is started or stopped.
Step 7 — When to STOP treatment
Discontinue Genryzon when ANY of the following:
- Evidence of epiphyseal closure
- Achievement of final or near-final height — annualised height velocity <2 cm/year
- Bone age >14 years in girls OR >16 years in boys
Guardrails
- Do not start until the pretreatment work-up (Step 2) is complete — starting somatrogon in an untreated hypothyroid child wastes therapy; starting in unrecognised central hypoadrenalism risks adrenal crisis when glucocorticoid replacement is unmasked
- IGF-1 timing matters — 4 days post-dose. A sample taken 1 or 6 days post-dose misleads titration
- Split doses >30 mg into two injections at different sites — do not deliver as a single injection
- Watch for these red flags during treatment and act on them:
- Severe abdominal pain → pancreatitis workup
- Limp or hip/knee pain → slipped capital femoral epiphysis
- Papilloedema, persistent headache, vision changes → benign intracranial hypertension → temporarily hold somatrogon, fundoscopy
- Injection-site myalgia or disproportionate pain → myositis (m-cresol excipient); switch to a metacresol-free GH
- New or recurrent neoplasm — especially childhood cancer survivors with prior cranial radiation (meningioma risk)
- Progression of scoliosis
- Glucocorticoids — concurrent glucocorticoid can inhibit growth response; ACTH-deficient children on replacement need their glucocorticoid dose reviewed. Somatrogon may also unmask previously undiagnosed central hypoadrenalism
- Diabetes — GH ↓ insulin sensitivity. Patients on insulin or OADs may need dose ↑ after starting; monitor glucose more closely
- Thyroxine — GH ↑ T4→T3 conversion, may unmask hypothyroidism; check TFTs at each review and replace if indicated
- CYP3A4 substrates (sex steroids, corticosteroids, anticonvulsants, ciclosporin) — somatrogon may ↑ their clearance and lower their levels
- Do NOT use in Prader-Willi syndrome unless the child also has documented GHD — sudden death has been reported in PWS on GH with severe obesity, airway obstruction, sleep apnoea, or respiratory infection
- Note the batch number in the patient record (biological product traceability)
Source
Pfizer Products India Pvt. Ltd. GENRYZON® (Somatrogon) Solution for Injection in Pre-filled Pen — Prescribing Information (India). LPD version 2022-0081166 (PfLEET 2022-0081166). 40 pages.
