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Last reviewed on RxList: 2/7/2018
Strensiq Side Effects Center

Last reviewed on RxList 2/7/2018

Strensiq (asfotase alfa) injection is a tissue nonspecific alkaline phosphatase indicated for the treatment of patients with perinatal/infantile-and juvenile-onset hypophosphatasia (HPP). Common side effects of Strensiq include:

  • injection site reactions (redness, discoloration, pain, tenderness, itching, swelling, bruising, or a hard lump),
  • body fat redistribution (lipodystrophy),
  • calcification of soft tissues, and
  • allergic reactions (difficulty breathing, nausea, puffy eyes, dizziness, vomiting, fever, headache, flushing, irritability, chills, skin redness, rash, itching, and changes in the sense of taste).

The recommended dosage regimen of Strensiq is 2 mg/kg administered subcutaneously three times per week, or 1 mg/kg administered six times per week. Strensiq may interact with other drugs. Tell your doctor all medications and supplements you use. Tell your doctor if you are pregnant before using Strensiq. It is unknown if it would affect a fetus. It is unknown if Strensiq passes into breast milk. Consult your doctor before breastfeeding.

Our Strensiq (asfotase alfa) injection Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


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Strensiq Professional Information


The following adverse reactions are described below and elsewhere in the labeling:

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

The data described below reflect exposure to STRENSIQ in 99 patients with perinatal/infantile-or juvenile-onset HPP (age 1 day to 58 years) treated with STRENSIQ, most for more than 2 years (range 1 day to 312 weeks [78 months]): 51 patients received at least 96 weeks (24 months) of treatment and 39 patients received 168 weeks (42 months) or more of treatment.

Common Adverse Reactions

Overall, the most common adverse reactions reported were injection site reactions (63%). Other common adverse reactions included lipodystrophy (28%), ectopic calcifications (14%), and hypersensitivity reactions (12%).

Table 4 summarizes the adverse reactions that occurred at a rate of at least 10% in clinical trials following subcutaneous injection of STRENSIQ, by patient population and STRENSIQ dosage regimen.

The frequency of injection site reactions, lipodystrophy and ectopic calcification were higher in patients with juvenile-onset HPP as compared to perinatal/infantile-onset HPP patients.

The majority of injection site reactions resolved within a week. Two patients experienced injection site reactions that led to reductions of their STRENSIQ dose. One patient switched from six times per week dosing to 3 times per week dosing as a result of injection site reactions. One other patient experienced a severe injection site reaction of injection site discoloration and withdrew from the trial.

Table 4: Adverse Reactions Reported in at Least 10% of Patients with Perinatal/Infantile-or Juvenile-onset HPP Enrolled in STRENSIQ Clinical Trials

Adverse Reaction Category or Term Perinatal/ Infantile-onset HPP Juvenile-onset HPP
(N=20) n (%)
STRENSIQ less than or equal to 6 mg/kg per week
(N=66) n (%)
STRENSIQ more than 6 mg/kg/weeka
(N=13) n (%)
(N=79) n (%)
Injection site reactions 38 (58) 6 (46) 44 (56) 18 (90)
  Erythema 29 (44) 3 (23) 32 (41) 15 (75)
  Discoloration/ Hypopigmentation 11 (17) 1 (8) 12 (15) 8 (40)
  Pain/ Tenderness 10 (15) 1 (8) 11 (14) 8 (40)
  Pruritus/ Itching 10 (15) 0 (0) 10 (13) 7 (35)
  Swelling 8 (12) 0 (0) 8 (10) 6 (30)
  Induration 9 (14) 1 (8) 10 (13) 3 (15)
  Macule 4 (6) 0 (0) 4 (5) 7 (35)
  Reaction, not otherwise specified 6 (9) 1 (8) 7 (9) 4 (20)
  Bruising 6 (9) 0 (0) 6 (8) 4 (20)
  Nodule 2 (3) 0 (0) 2 (3) 2 (10)
  Other injection site reactionsb 10 (15) 3 (23) 13 (17) 4 (20)
Ectopic calcifications 3 (5) 0 (0) 3 (4) 11 (55)
Lipodystrophy 12 (18) 2 (15) 14 (18) 14 (70)
  Injection site atrophy 4 (6) 2 (15) 6 (8) 8 (40)
  Injection site hypertrophy 5 (8) 0 (0) 5 (6) 6 (30)
  Other lipodystrophyc 4 (6) 0 (0) 4 (5) 1 (5)
Hypersensitivity reactions 7 (11) 3 (23) 10 (13) 2 (10)
  Vomiting/emesis 2 (3) 2 (15) 4 (5) 2 (10)
  Other hypersensitivity reactionsd 6 (9) 2 (15) 8 (10) 2 (10)
a Adverse reactions are from the combined period of 6 mg/kg and above (i.e. total drug exposure regardless of starting dose and intermediary doses as long as the patient reached doses > 6 mg/kg).
b Other injection site reactions include injection site rash, inflammation, papule, hemorrhage, hematoma, urticaria, warmth, calcification, mass, scar and cellulitis.
c Other lipodystrophy includes lipohypertrophy.
d Other hypersensitivity reactions include erythema/redness, pyrexia/fever, irritability, nausea, pain, rigor/chills, hypoesthesia oral, headache, flushing, and anaphylaxis.

Less Common Adverse Reactions

Adverse reactions that occurred at rates less than 1% included:


As with all therapeutic proteins, there is potential for immunogenicity. During clinical trials, anti-drug antibodies have been detected in patients receiving treatment with STRENSIQ using an electrochemiluminescent (ECL) immunoassay. Antibody positive samples were tested to determine the presence of neutralizing antibodies based on in vitro inhibition of the catalytic activity of STRENSIQ. Among 98 patients with hypophosphatasia (HPP) enrolled in the clinical trials and who had post-baseline antibody data, 76 (78%) tested positive for anti-drug antibodies at some time point after receiving STRENSIQ treatment. Among those 76 patients, 34 (45%) also showed the presence of neutralizing antibodies. No correlation was observed between the anti-drug antibody titer and neutralizing antibody (% inhibition) values. Formation of anti-drug antibody resulted in a reduced systemic exposure of asfotase alfa. [see CLINICAL PHARMACOLOGY].

The detection of antibody formation is dependent on the sensitivity and specificity of the assay. Additionally, the observed incidence of antibody (including neutralizing antibody) positivity in an assay may be influenced by several factors including assay methodology, sample handling, timing of sample collection, concomitant medications, and underlying disease. For these reasons, comparison of the incidence of the antibodies to STRENSIQ with the incidence of antibodies to other products may be misleading.

Read the entire FDA prescribing information for Strensiq (Asfotase Alfa for Subcutaneous Administration)


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© Strensiq Patient Information is supplied by Cerner Multum, Inc. and Strensiq Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

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