Prescribing guide
Strensiq (asfotase alfa)Weight-based dosing, vial selection, supervised initiation, monitoring and prior authorization for hypophosphatasiaFor prescribers and their offices treating hypophosphatasia (HPP): what the pharmacy needs before it ships, what the prior authorization wants documented, the titration and the monitoring the label requires.
Dispensing gate
No REMS; boxed warning for anaphylaxis, so initiate under healthcare provider supervision; confirm perinatal/infantile- or juvenile-onset HPP, record current weight, obtain baseline eye exam and renal ultrasound, and fax the Rx form to PANTHERx Rare, the exclusive preferred specialty pharmacy.
Example PA threshold
Cigna example, effective September 15, 2026: ALPL variants, low baseline ALP or elevated PLP, PPi or urinary PEA; current or past HPP manifestations or a parent or sibling with HPP; onset before 18; geneticist, endocrinologist, metabolic or HPP specialist.
Monitoring
Eye exam and renal ultrasound at baseline and periodically; weight for dose recalculation; growth, respiratory status and radiographs for response; anti-drug antibody testing via Alexion if HPP worsens after an initial response; serum ALP is uninterpretable on treatment.
Support line
Alexion OneSource, 1-888-765-4747, Monday to Friday 8:30am to 8pm ET, enrollment fax 1-800-420-5150; PANTHERx Rare 1-844-787-6747, fax 1-844-787-2527; CoPay Program as little as $0 for commercial plans with a variable annual maximum; no published bridge or free-drug program.
Give your patient their plan
A one-page handout for starting Strensiq, in plain language: what the first fill waits on, the first dates, who will call and the symptoms to report, with blank lines for the start date and your office's number. The link opens the patient's full first 90 days page, where their dates become calendar entries.
trialfriend.com/p/strensiqBefore the first fill: REMS, labs and enrollment
The steps that the pharmacy, the REMS or the drugmaker's program will wait on, in the order they usually need to happen. A first fill of a specialty drug most often stalls on one of these rather than on the plan.
| Step | What it requires | Source |
|---|---|---|
| Confirm the indication | Perinatal/infantile- or juvenile-onset HPP. No contraindications. Pediatric safety and effectiveness are established from 4 open-label trials in 89 pediatric patients. | FDA label |
| Weigh the patient | Round to the nearest kilogram. Weekly dose (mg) = weight (kg) × dose (mg/kg/week); volume = dose ÷ 40mg/mL or 100mg/mL, rounded to the nearest hundredth of a mL. The Rx form asks for current weight and its date. | FDA label |
| Choose the vial | 18mg/0.45mL, 28mg/0.7mL and 40mg/mL at 40mg/mL; 80mg/0.8mL at 100mg/mL only for patients 40kg or more. The Rx form says to check both concentration boxes for patients over 40kg; PANTHERx selects vial strengths. | Prescription form |
| Baseline assessments | Ophthalmologic examination and renal ultrasound before treatment. | FDA label |
| Complete the Rx form | ICD-10 E83.3, E83.31 or E83.39; ALP and PLP or PEA with lab copies; onset and current signs and symptoms; regimen 2mg/kg 3 times a week, 1mg/kg 6 times a week or other; 28-day supply, refills ×11 or other; wet signature, no stamps. Fax to PANTHERx Rare at 1-844-787-2527 with both sides of all insurance cards. | Prescription form |
| Enroll in OneSource | A separate enrollment form, by Adobe eSign, email to OneSource@Alexion.com or fax to 1-800-420-5150. Interpreters are available. | OneSource enrollment |
| Prior authorization | PANTHERx Rare runs the benefits investigation, relays PA requirements, tracks status, ships on approval and can coordinate a denial response. Field Reimbursement Managers give case-specific help only when the patient is enrolled in OneSource. | Access guide |
| PA packet | Alexion's guide lists onset before 18 for adults, low ALP and an elevated PLP or PEA as common criteria, and suggests at least 2 recent ALP values more than 30 days apart; some plans add a specialist, genetic testing, renal and eye exams, radiographs or functional tests. | PA criteria guide |
| Supervised first dose | Initiate under healthcare provider supervision with appropriate monitoring and support measures; train the caregiver on preparation, site rotation and anaphylaxis signs. | FDA label |
Prior authorization criteria and what to document
One public policy as the example: Cigna, September 15, 2026. Approval a year at a time, with the same criteria at each review. Cigna's policy IP0308 took effect September 15, 2026 after an August 2026 review with no criteria changes, and it cites the July 2024 Strensiq label. That matches the current label's text, so the policy does not predate it. Other plans set their own rules, and this one is an example. The federal employee plan, for example, asks for eye and kidney checks and improvement in growth and X-rays after the first year.
| Element | What the policy asks | In the chart | Source |
|---|---|---|---|
| Diagnosis | One of: pathogenic ALPL variants; low baseline serum ALP; or an elevated TNSALP substrate (serum PLP, serum or urinary PPi, urinary PEA), each with documentation | Genetic report or dated lab reports; Alexion notes PPi testing is not commercially available | Cigna policy |
| Clinical picture | Current or past manifestations such as skeletal abnormalities, premature tooth loss, muscle weakness, poor feeding, failure to thrive, respiratory problems or vitamin B6-dependent seizures; or a parent or sibling with HPP | Chart notes, radiographs, dental history | Cigna policy |
| Age at onset | Disease onset before 18 years of age | History documenting first signs, especially for adults with juvenile-onset HPP | Cigna policy |
| Prescriber | Geneticist, endocrinologist, metabolic disorder sub-specialist or a physician who specializes in HPP, prescribing or consulting | Specialty on the request or the consult note | Cigna policy |
| Other plans | FEP Blue 5.30.015 (effective April 1, 2025): baseline and periodic eye exams and renal ultrasound; agreement to assess growth and radiographs at 1 year and stop without improvement; renewal for 2 years requires documented improvement | Eye and renal reports; dated growth and X-ray comparisons | FEP Blue policy |
| Letter of medical necessity | Alexion's template covers signs and symptoms, labs, radiographs and genetic testing, the treatment plan and an optional request for expedited review | Use with the Rx form or for an appeal | Sample LMN |
Strensiq dosing and titration
| When | Label | Source |
|---|---|---|
| Perinatal/infantile-onset | 6mg/kg/week: 2mg/kg 3 times a week or 1mg/kg 6 times a week; may increase for lack of efficacy (no improvement in respiratory status, growth or radiographs) to 3mg/kg 3 times a week, 9mg/kg/week. | FDA label |
| Juvenile-onset | 6mg/kg/week: 2mg/kg 3 times a week or 1mg/kg 6 times a week. Table 3 (3mg/kg) is recommended only for perinatal/infantile onset. | FDA label |
| Table 1 examples, 2mg/kg 3×/week | 3kg 6mg 0.15mL (18mg vial); 10kg 20mg 0.5mL (28mg vial); 20kg 40mg 1mL (40mg vial); 25kg 50mg 1.25mL (two 28mg vials); 40kg 80mg 0.8mL (80mg vial); 60kg 120mg 1.2mL (two 80mg vials). | FDA label |
| Table 2 examples, 1mg/kg 6×/week | 3kg 3mg 0.08mL; 10kg 10mg 0.25mL (18mg vial); 20kg 20mg 0.5mL (28mg vial); 40kg 40mg 1mL (40mg vial); 50kg 50mg 0.5mL (80mg vial); 100kg 100mg 1mL (two 80mg vials). | FDA label |
| Table 3 examples, 3mg/kg 3×/week | 3kg 9mg 0.23mL (18mg vial); 7kg 21mg 0.53mL (28mg vial); 10kg 30mg 0.75mL (40mg vial); 15kg 45mg 1.13mL (two 28mg vials); 25kg 75mg 1.88mL (two 40mg vials). | FDA label |
| Administration | Subcutaneous only; volumes over 1mL split equally between 2 syringes at 2 sites. 1mL syringes, ½ inch 25 to 29 gauge needles, larger bore to withdraw and smaller to inject. Rotate abdomen, thigh, deltoid or buttocks; the IFU says not the buttocks in infants. Avoid red, inflamed or swollen areas. | FDA label |
| Handling | Out of the refrigerator 15 to 30 minutes before injection, no other warming; administer within 3 hours. Single-dose vials; discard unused product. Do not freeze or shake. | FDA label |
| Supply | Cartons of 1 or 12 single-dose vials per strength; store at 2°C to 8°C (36°F to 46°F) in the original carton, protected from light. A 12-vial carton covers 4 weeks of single-vial doses at 3 times a week. | FDA label |
| Days' supply | The Rx form writes a 28-day supply with refills ×11 or other; PANTHERx dispenses needles and syringes. | Prescription form |
| Missed dose | The label gives no missed-dose instruction. | FDA label |
Monitoring the Strensiq label requires
| When | What | What the label says to do with it | Source |
|---|---|---|---|
| First dose | Supervised initiation for hypersensitivity | Anaphylaxis signs included difficulty breathing, choking sensation, nausea, periorbital edema and dizziness; discontinue and give epinephrine for a severe reaction | FDA label |
| Baseline and periodically | Ophthalmologic examination and renal ultrasound | Ectopic calcification (conjunctival, corneal, nephrocalcinosis, nephrolithiasis) reported in 14%; 55% in juvenile-onset patients; causality versus disease unclear | FDA label |
| Each injection | Injection site and lipodystrophy | Injection site reactions 63% overall, 90% juvenile-onset, most resolved within a week; lipodystrophy 28% after several months; rotate sites | FDA label |
| Ongoing | Weight, growth, respiratory status and radiographs | Dose follows weight; lack of improvement in respiratory status, growth or radiographs is the label's basis for escalation in perinatal/infantile onset | FDA label |
| Loss of response | Recurrent or worsening HPP symptoms, laboratory or imaging biomarkers after an initial response | 89% developed anti-drug antibodies and 57% of those neutralizing antibodies; no marketed assay, so contact Alexion Medical Information at 1-888-765-4747 or medinfo@alexion.com; close follow-up | FDA label |
| Laboratory | Serum ALP and ALP-conjugated assays | Elevated ALP is expected and unreliable for decisions; ALP-conjugated immunoassays may give erroneous results, so tell the lab and use another platform | FDA label |
| Registry | HPP Registry, voluntary long-term follow-up | Encourage participation; www.hppregistry.com | FDA label |
Strensiq drug interactions and contraindications
| Label category | Agents and what the label says | Source |
|---|---|---|
| Laboratory tests using ALP | Analytical interference with ALP-conjugated test systems for hormones, bacterial antigens and antibodies; use assays without ALP-conjugate technology | FDA label |
| Serum alkaline phosphatase | Expected to be high from circulating asfotase alfa; do not rely on it for clinical decisions | FDA label |
| Drug-drug interactions | The label lists no drug-drug interactions; section 7 covers only laboratory interference | FDA label |
| Pregnancy and lactation | No human data; no embryofetal effects in rats and rabbits at up to 21 and 24 times human exposure; no data on milk | FDA label |
| Vitamin B6 | Decreased vitamin B6 was reported at under 1%, and 1 juvenile-onset patient had a dose reduction for low vitamin B6 levels | FDA label |
Why a first fill stalls, and the fix
- The prescription went to another pharmacyAlexion's prescription form goes to PANTHERx Rare, which Alexion calls the exclusive preferred specialty pharmacy for Strensiq. The office resends it there, which is a routing fix rather than a denial.
- The plan says the labs are missingAlexion's guide to common plan criteria lists low ALP and a raised PLP or PEA. It suggests sending at least 2 recent ALP results taken more than 30 days apart.
- The plan says HPP began too lateCigna's policy, effective September 15, 2026, requires that the disease began before age 18. Adults with childhood-onset HPP need records showing when symptoms began.
- The prescriber is not a specialistCigna asks for a geneticist, an endocrinologist, a metabolic specialist or an HPP specialist to prescribe or consult. A consult note from one of them can meet this.
- The appeal was deniedAlexion's access guide lists a resubmission, a peer-to-peer review or a formal appeal. Alexion offers prescribers a sample appeal letter and a letter of medical necessity template.
- A copay you cannot payThe CoPay Program can bring eligible commercial plans to as little as $0, up to a yearly maximum that may vary. Medicare, Medicaid, TRICARE, VA and other government plans are excluded, and OneSource can point to outside help.
Alexion OneSource
- A free support program with a dedicated Case Manager who answers questions about HPP and Strensiq
- Help understanding insurance coverage for Strensiq and with financial concerns or gaps in coverage
- Support preparing for injections and help avoiding treatment gaps during insurance changes, travel or other life events OneSource team
- A CoPay Program for commercial insurance, as little as $0 up to a yearly maximum, not valid with Medicare, Medicaid, TRICARE, VA or other government plans CoPay terms
- For people with Medicare, Medicaid or other government plans, connection to third-party resources that may help with costs OneSource financial help
- Interpreters for families whose preferred language is not English OneSource enrollment
Questions prescribers' offices ask about Strensiq
What is the Strensiq dose for perinatal/infantile- and juvenile-onset HPP?
6mg/kg per week subcutaneously, as 2mg/kg 3 times a week or 1mg/kg 6 times a week, per sections 2.2 and 2.3 of the current label (highlights revised 7/2024, DailyMed version December 12, 2025). For perinatal/infantile-onset HPP only, the dose may be increased for lack of efficacy up to 9mg/kg per week as 3mg/kg 3 times a week. Injection site reactions may limit tolerability of the 6-times-weekly regimen.
When can the 80mg/0.8mL vial be used?
Only in patients 40kg or more, per section 2.4 of the current label (revised 7/2024). The 100mg/mL formulation gives about 25% lower systemic exposure than the 40mg/mL vials at the same dose (section 12.3), which may not be adequate in pediatric patients under 40kg.
What does the boxed warning require at initiation?
Initiation under the supervision of a healthcare provider with appropriate medical monitoring and support measures, per the boxed warning and section 2.1 added in July 2024. Anaphylaxis has occurred within minutes of injection and more than 1 year after initiation; discontinue and give epinephrine for a severe reaction, and weigh rechallenge case by case.
What monitoring does the Strensiq label recommend?
Ophthalmologic examination and renal ultrasound at baseline and periodically, per section 5.3 of the current label (revised 7/2024). Do not rely on serum ALP, which is elevated by circulating drug (section 7.1); if HPP worsens after an initial response, consider anti-drug antibody testing through Alexion Medical Information at 1-888-765-4747 (section 5.4).
What do insurers ask for to approve Strensiq?
The Cigna policy IP0308, effective September 15, 2026, asks for ALPL variants, low baseline ALP or an elevated substrate, clinical manifestations or a family history, onset before age 18, and a geneticist, endocrinologist, metabolic or HPP specialist, with approval for 1 year. It cites the July 2024 label.
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Sources
- STRENSIQ- asfotase alfa solution, prescribing information, Patient Information and Instructions for Use, highlights revised 7/2024, DailyMed version 18, Alexion Pharmaceuticals, via DailyMed, 2025-12-12.
- Drugs@FDA application record, BLA125513, STRENSIQ (asfotase alfa), submissions and approval dates, FDA, via openFDA, 2026-11-10.
- Alexion OneSource™ | STRENSIQ | About OneSource, Alexion Pharmaceuticals, 2026-11-10.
- Alexion OneSource™ | STRENSIQ | Fill Out a Start Form, Alexion Pharmaceuticals, 2026-11-10.
- Alexion OneSource™ | STRENSIQ | Financial Assistance, Alexion Pharmaceuticals, 2026-11-10.
- Alexion OneSource™ | STRENSIQ | Meet The Team, Alexion Pharmaceuticals, 2026-11-10.
- Alexion OneSource™ CoPay Program Terms and Conditions, US/ALL/1223 V1 12/2024, Alexion Pharmaceuticals, 2026-11-10.
- Alexion Access Navigator | Strensiq, Alexion Pharmaceuticals, 2026-11-10.
- STRENSIQ® (asfotase alfa) Prescription (Rx) Form for the Treatment of Pediatric-Onset Hypophosphatasia (HPP), US/STQ-H/0574 V1 07/2024, Alexion Pharmaceuticals, 2026-11-10.
- How to Access STRENSIQ, access and reimbursement guide, US/STQ-H/0475 V3 07/2024, Alexion Pharmaceuticals, 2026-11-10.
- A Guide to Common Prior Authorization (PA) Criteria for STRENSIQ® (asfotase alfa), US/STQ-H/0724 V1 07/2025, Alexion Pharmaceuticals, 2026-11-10.
- Sample Letter of Medical Necessity for STRENSIQ® (asfotase alfa), US/STQ-H/0196 V6 11/2025, Alexion Pharmaceuticals, 2026-11-10.
- Drug Coverage Policy IP0308, Enzyme Replacement Therapy, Strensiq, Cigna, 2026-09-15.
- Strensiq (asfotase alfa), pharmacy policy 5.30.015, Blue Cross and Blue Shield Federal Employee Program, 2025-04-01.
A reference drawn from the December 12, 2025 label, the drugmaker's published program and one public insurer policy shown as an example, checked on November 10, 2026. Labels and policies change; the label on DailyMed and the plan's current policy govern. Trial Friend is not a medical provider. It reports what these documents say and does not judge whether a drug is safe or right for any patient; that is the prescriber's decision. Not a substitute for the prescribing information.