An enzyme-replacement injection for hypophosphatasia
Asfotase alfa
An enzyme-replacement injection used to treat hypophosphatasia, a rare inherited condition that affects how bones and teeth form.
What is Asfotase alfa?
Asfotase alfa is a specialist enzyme-replacement medicine used to treat hypophosphatasia, a rare inherited condition in which a missing enzyme means bones and teeth do not form and harden properly. It works by replacing that enzyme so the body can mineralise bone normally. It is given as an injection under the skin, several times a week, under specialist care. The most common problem is a reaction where the injection is given, and the team also keeps an eye out for calcium building up in places such as the eyes or kidneys.
Education and reference only. This is a plain-language guide to Asfotase alfa — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Asfotase alfa is an enzyme-replacement therapy used in hypophosphatasia, a rare inherited condition in which the body lacks enough of an enzyme (alkaline phosphatase) needed to harden bone and teeth. Without it, bones can be soft, weak or poorly formed, and there can be problems with breathing, growth and the teeth, especially when the condition starts in babies and children. Asfotase alfa is a manufactured copy of the missing enzyme, given as a regular injection under the skin. It is started and supervised by a specialist team and is a long-term treatment.
How it works
In hypophosphatasia, a shortage of the enzyme alkaline phosphatase means a substance that should be cleared away builds up and blocks bone from mineralising, so bone stays soft and weak. Asfotase alfa replaces that missing enzyme activity, helping the body clear the build-up and lay down healthy, hardened bone. Because the enzyme only works while it is present in the body, it is given regularly, several times a week, to keep its effect going. Over time this can improve how bones form and, in severely affected children, how they breathe, move and grow.
Company & origin
Originated / developed by: Specialist manufacturer.
A specialist enzyme-replacement medicine used in the UK to treat hypophosphatasia, a rare inherited bone condition.
Practical use
How to take Asfotase alfa
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Have it as an injection under the skin, usually several times a week, as your specialist team has trained you.
- Rotate the injection site each time to reduce skin reactions and lumps.
- Watch for reactions where the injection is given, which are common and usually settle on their own.
- Seek urgent help for any signs of a serious allergic reaction, such as difficulty breathing, swelling of the face or feeling faint.
- Do not stop treatment without specialist advice, as the benefits depend on keeping it going, and attend your eye and kidney checks.
Weighing it up
Advantages & disadvantages of Asfotase alfa
Advantages
- Replaces the missing enzyme that causes hypophosphatasia, helping bones form and harden.
- Can improve breathing, movement and growth in severely affected babies and children.
- Can be given at home under the skin after training, fitting around daily life.
Disadvantages
- Needs regular injections under the skin several times a week, for the long term.
- Very commonly causes reactions where the injection is given.
- Calcium can build up in places such as the eyes or kidneys, so monitoring is needed.
Practical use
Good to know
The most important practical point is that asfotase alfa is given as an injection under the skin several times a week, usually at home after training, and injection sites are rotated to reduce reactions. Reactions where the injection is given — redness, swelling, itching, lumps or skin colour changes — are very common and usually settle, but more serious allergic or anaphylactoid reactions can happen and need urgent attention. A specific safety concern is that calcium can build up in places it should not, such as the eyes or kidneys, so the specialist team arranges eye checks and kidney monitoring. It is a long-term treatment that should not be stopped without specialist advice, as the benefits depend on continuing it. The team will also watch growth, bone health and calcium levels over time.
Who should not take it / use with caution
- People who have had a serious allergic reaction to asfotase alfa should not use it.
- It is used with care, and with monitoring, in pregnancy under specialist guidance.
- It should only be used under specialist supervision, with regular eye and kidney monitoring.
Monitoring
- Eye checks and kidney monitoring to watch for calcium building up where it should not.
- Reviewing bone health, growth and how the condition is responding over time.
- Watching for injection-site and allergic-type reactions.
Side effects
- Reactions where the injection is given, such as redness, swelling, itching, lumps or skin colour changes.
- More general reactions soon after a dose, such as fever, chills, flushing or feeling unwell.
- Less commonly, calcium building up in the eyes or kidneys, which monitoring is designed to catch.
- Rarely, serious allergic or anaphylactoid reactions, which need urgent medical attention.
Key interactions
- It can affect certain laboratory blood tests that measure enzyme activity, so labs should know you are taking it.
- There are few well-established routine medicine interactions, but tell your team about everything you take.
- Other medicines or supplements affecting calcium should be reviewed by the specialist team.
Available as: A solution for injection under the skin.
Answers
Asfotase alfa: frequently asked questions
What is asfotase alfa used for?
It is used to treat hypophosphatasia, a rare inherited condition in which a missing enzyme means bones and teeth do not form and harden properly, by replacing that enzyme.
How is it given?
It is given as an injection under the skin several times a week, usually at home after your specialist team has trained you, rotating the injection site each time.
Why do I need eye and kidney checks?
Calcium can sometimes build up in places such as the eyes or kidneys, so the specialist team arranges regular eye and kidney monitoring to catch this early.
Why does the injection site react?
Reactions where the injection is given, such as redness, swelling or lumps, are very common and usually settle; rotating sites helps reduce them.
Can I stop it once my bones improve?
No. It is a long-term treatment whose benefits depend on continuing it, so only change or stop it on specialist advice.
Authoritative sources
- BNF
- NICE CKS
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