Genryzon Prescribing Guide

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:

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.