Genryzon Prescribing Guide

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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.

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## 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)

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## 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

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## 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.

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## 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

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## 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.

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## 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.

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## 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**

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## 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)

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## 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.