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Asfotase Alfa

Medically reviewed by Last updated on Oct 11, 2020.


(AZ fo tase AL fa)

Index Terms

  • Strensiq

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Solution, Subcutaneous [preservative free]:

Strensiq: 18 mg/0.45 mL (0.45 mL); 28 mg/0.7 mL (0.7 mL); 40 mg/mL (1 mL); 80 mg/0.8 mL (0.8 mL) [contains mouse (murine) and/or hamster protein]

Brand Names: U.S.

  • Strensiq

Pharmacologic Category

  • Enzyme


Asfotase alfa is a human recombinant tissue-nonspecific alkaline phosphatase-Fc-deca-aspartate fusion protein with enzymatic activity that promotes bone mineralization in patients with hypophosphatasia.

Onset of Action

Reduction in plasma TNSALP substrates: After 6 to 12 weeks of treatment

Time to Peak

Infants and Children ≤5 years: ~15 hours (range: 0 to 32.2 hours)

Children > 5 to 12 years: ~ 21 hours (range: 12 to 32.2 hours)

Half-Life Elimination

~5 days (based on data from 38 patients, ages undefined); in 60 patients aged 1 day to 66 years (n=45 pediatric patients): ~2.3 days

Use: Labeled Indications

Hypophosphatasia: Treatment of perinatal/infantile- and juvenile-onset hypophosphatasia (HPP)


There are no contraindications listed in the manufacturer’s labeling.

Canadian labeling: Additional contraindications (not in US labeling): Hypersensitivity to asfotase alfa or any component of the formulation.

Dosing: Adult

Hypophosphatasia (HPP): SubQ: Note: Round patient weight to the nearest kg when determining dose. Injection-site reactions may limit the tolerability of the 6 times per week regimen:

Juvenile-onset HPP: 2 mg/kg 3 times weekly or 1 mg/kg 6 times weekly.

Dosing: Pediatric

Note: Round patient weight to the nearest kg when determining dose. Do not administer the 80 mg/0.8 mL concentration vial to pediatric patients weighing <40 kg; exposure is less than what is achieved with lower concentration vials.

Perinatal/infantile-onset hypophosphatasia (HPP): Infants, Children, and Adolescents: SubQ: 6 mg/kg/week administered as either 2 mg/kg/dose 3 times weekly or 1 mg/kg/dose 6 times weekly; may titrate due to lack of efficacy (eg, no improvement in respiratory status, growth, or radiographic findings) up to 9 mg/kg/week administered as 3 mg/kg/dose 3 times weekly; in clinical trials, dose increases were considered after at least 4 weeks of therapy (Whyte 2012; Whyte 2016); maximum total weekly dose: 9 mg/kg/week. Injection-site reactions may limit the tolerability of the 6-times-per-week regimen.

Juvenile-onset hypophosphatasia (HPP): Children and Adolescents: SubQ: 6 mg/kg/week administered as either 2 mg/kg/dose 3 times weekly or 1 mg/kg/dose 6 times weekly. Injection-site reactions may limit the tolerability of the 6-times-per-week regimen.


SubQ: For subcutaneous administration only in the abdominal area, thigh, deltoid, or buttocks. Do not shake. Allow unopened vials to reach room temperature (~15 to 30 minutes) prior to administration; do not warm in microwave or hot water; administer within 3 hours upon removal from refrigerator. Rotate the injection sites to reduce the risk of lipodystrophy. Do not administer injections in areas that are reddened, inflamed, or swollen. Solution is clear, slightly opalescent or opalescent, colorless to slightly yellow; few small translucent or white particles may be present; discard vial(s) not consistent with this appearance. Administer with 1 mL syringe with 1/2 inch needle (25 to 29 gauge). Use of 2 different gauge needles is recommended; 25 gauge to withdraw medication from the vial and 29 gauge for administration. For doses >1 mL, split the volume equally between 2 syringes, and administer 2 injections using separate injection sites.


Store refrigerated at 2°C to 8°C (36°F to 46°F) in original carton and protect from light. Once removed from refrigerator, administer within 3 hours. Do not freeze or shake. Discard any unused product.

Drug Interactions

There are no known significant interactions.

Test Interactions

Asfotase alfa interferes with alkaline phosphatase (ALP)-conjugated test systems (commonly used to measure hormones, bacterial antigens, and antibodies) rendering erroneous test results. Alternative laboratory assays that do not utilize ALP-conjugate technology are recommended in patients receiving asfotase alfa.

Adverse Reactions

The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified.

Endocrine & metabolic: Ectopic calcification (includes calcification of the cornea, conjunctiva, and kidneys; 55%, juvenile-onset HPP; ≤5% perinatal/infantile-onset HPP), lipodystrophy (≤6%)

Hypersensitivity: Hypersensitivity reaction (10% to 23%)

Immunologic: Immunogenicity (positive for antidrug antibodies: 78%; neutralizing: 45%; presence of antidrug antibodies resulted in reduced systemic exposure of asfotase alfa)

Local: Erythema at injection site (juvenile-onset HPP: 75%; perinatal/infantile-onset HPP: 23% to 44%), atrophy at injection site (juvenile-onset HPP: 40%; perinatal/infantile-onset HPP: 6% to 15%), skin discoloration at injection site (including macules: Juvenile-onset HPP: 35% to 40%; perinatal/infantile-onset HPP: ≤17%), pain at injection site (juvenile-onset HPP: ≤40%; perinatal/infantile-onset HPP: ≤8% to ≤15%), tenderness at injection site (juvenile-onset HPP: ≤40%; perinatal/infantile-onset HPP: ≤15%), itching at injection site (juvenile-onset HPP: 35%; perinatal/infantile-onset HPP: ≤15%), hypertrophy at injection site (juvenile-onset HPP: 30%; perinatal/infantile-onset HPP: ≤8%), swelling at injection site (juvenile-onset HPP: 30%; perinatal/infantile-onset HPP: ≤12%), injection site reaction (≤23%; including rash, nodule, papule, inflammation, hemorrhage, hematoma, calcification, mass, scar, cellulitis, or not otherwise defined), bruising at injection site (juvenile-onset HPP: 20%; perinatal/infantile-onset HPP: ≤9%), induration at injection site (8% to 15%)

<1%, postmarketing, and/or case reports: Chronic active hepatitis, hypocalcemia, nephrolithiasis, pyridoxine deficiency


Concerns related to adverse effects:

• Antibody formation/immune-mediated effects: The presence of antibodies has been reported in 89% of treated patients in clinical trials; 57% of these patients showed the presence of neutralizing antibodies. Formation of anti-drug antibody results in a reduced systemic exposure of asfotase alfa and suggests possible immune-mediated effects resulting in disease progression (effect of antibody formation on long-term efficacy is unknown). Consider anti-asfotase alfa antibody testing in patients with progression of symptoms or worsening of disease associated laboratory and imagining biomarkers after a period of initial therapeutic response (contact Strensiq Medical Information at 1-888-765-4747 or

• Ectopic calcifications: Ectopic calcification of the eye, including the cornea and conjunctiva, and the kidneys (nephrocalcinosis, nephrolithiasis) have been reported; there is insufficient information to determine if these events were consistent with the disease (patients with hypophosphatasia are at increased risk for developing ectopic calcifications) or due to asfotase alfa. No visual changes or changes in renal function were reported resulting from the occurrence of ectopic calcifications. Eye exams and renal ultrasounds are recommended at baseline and periodically during treatment.

• Hypersensitivity reactions: Hypersensitivity reactions, including anaphylaxis, have been reported; symptoms consistent with anaphylaxis, including difficulty breathing, choking sensation, nausea, periorbital edema, and dizziness, have been reported. Reactions may occur within minutes after administration or in patients on treatment for >1 year. Other hypersensitivity reactions (eg, vomiting, fever, headache, flushing, irritability, chills, skin erythema, rash, pruritus, oral hypoesthesia) have also been reported. If a severe hypersensitivity reaction occurs, discontinue treatment and initiate appropriate medical treatment. If the decision is made to re-administer, monitor patients for a reoccurrence of signs and symptoms of a severe hypersensitivity reaction.

• Lipodystrophy: Localized lipodystrophy, including lipoatrophy and lipohypertrophy, has been reported at injection sites after several months. Ensure proper injection technique and rotate injection sites.

Other warnings/precautions:

• Elevated alkaline phosphatase: High serum alkaline phosphatase (ALP) levels are expected and reflect circulating asfotase alfa; serum ALP measurements should not be used to make clinical decisions during asfotase alfa treatment.

Monitoring Parameters

Hypersensitivity reaction; signs and symptoms of ophthalmic and renal ectopic calcifications and for changes in vision or renal function

Pregnancy Considerations

Adverse events have not been observed in animal reproduction studies.

Patient Education

What is this drug used for?

• It is used to treat a health problem that leads to bone and teeth growth that is not normal called hypophosphatasia.

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

• Injection site irritation or skin discoloration

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

• Choking

• Upset stomach

• Throwing up

• Eye or eyelid swelling

• Dizziness or passing out

• Chills

• Headache

• Flushing

• Feeling irritable

• Numbness or tingling of the mouth

• Injection site thick skin, pits, or lumps

• Vision changes

• Not able to pass urine or change in amount of urine passed

• Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.

Note: This is not a comprehensive list of all side effects. Talk to your doctor if you have questions.

Consumer Information Use and Disclaimer: This information should not be used to decide whether or not to take this medicine or any other medicine. Only the healthcare provider has the knowledge and training to decide which medicines are right for a specific patient. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a limited summary of general information about the medicine's uses from the patient education leaflet and is not intended to be comprehensive. This limited summary does NOT include all information available about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this medicine. This information is not intended to provide medical advice, diagnosis or treatment and does not replace information you receive from the healthcare provider. For a more detailed summary of information about the risks and benefits of using this medicine, please speak with your healthcare provider and review the entire patient education leaflet.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.