Zoledronic Acid Infusion (Aclasta): What to Expect, Side Effects and How Long It Lasts

Zoledronic acid (zoledronate, brand name Aclasta) is an osteoporosis medicine given as a 5mg drip into a vein once a year. It belongs to the bisphosphonate family, slows the breakdown of bone and is usually given in a hospital day unit. Most people have it for about three years before a formal review, and the main thing to be ready for is a short, flu-like reaction after the first dose.

What is zoledronic acid?

Zoledronic acid is a bisphosphonate, the same family of bone-protecting medicines as alendronic acid and risedronate, but given as a yearly infusion rather than a tablet. The Royal Osteoporosis Society (ROS) describes zoledronate (brand name Aclasta) as a drug treatment for osteoporosis given as an intravenous infusion, or "drip", once a year Royal Osteoporosis Society.

Like other bisphosphonates, it works by slowing the cells that break bone down, which helps the bone you have stay stronger and lowers your chance of breaking a bone. The names "zoledronic acid", "zoledronate" and "Aclasta" all refer to the same medicine. (A higher-strength version is also used in some cancer care; this article covers the yearly 5mg osteoporosis dose only.)

Who is offered a zoledronic acid infusion?

In the UK, zoledronic acid is licensed for women after the menopause and adult men with osteoporosis who are at increased risk of fracture, including people who have recently broken a hip after a minor fall. The official product information also lists osteoporosis linked to long-term steroid tablets, and Paget's disease of bone emc, Aclasta SmPC.

According to the ROS, it is usually a second-line option, or used when tablets are unsuitable, and it is often given after a recent hip fracture. Doctors occasionally offer it to younger women. It may not suit you if you have low blood calcium, severe kidney problems, or are pregnant or breastfeeding Royal Osteoporosis Society. The product information sets a clear kidney limit: it must not be given if your creatinine clearance (a measure of kidney function) is below 35 ml/min.

After a hip fracture operation, the recommendation is to give the infusion at least two weeks after the hip has been repaired emc, Aclasta SmPC. For the wider picture of how doctors choose between treatments, see our guide to osteoporosis treatment in the UK and how to prevent a hip fracture.

What checks do you need before the infusion?

Before each infusion you will normally have a blood test to check your kidneys, calcium and vitamin D, because the drip is not safe if your kidneys are struggling or your calcium is low. The ROS explains that if your calcium or vitamin D levels are very low, your doctor may delay treatment until they have improved, and may advise calcium and vitamin D supplements Royal Osteoporosis Society.

The product information says low calcium must be treated with enough calcium and vitamin D before starting, that people must be "appropriately hydrated" before the dose, and that kidney function should be calculated before each dose emc, Aclasta SmPC. Hydration matters most for older people and anyone taking water tablets (diuretics). Our guide to vitamin D for bone health explains why levels matter so much for bone medicines.

What happens on the day of a bone infusion?

On the day, a nurse puts a small cannula into a vein in your arm and the 5mg dose runs in through a drip over at least 15 minutes. The infusion is most often given in a hospital, although some GP surgeries also give it Royal Osteoporosis Society.

A typical visit looks like this:

• Before: drink one or two glasses of water, as the ROS advises, and take your usual medicines unless you have been told otherwise.
• Checks: a nurse confirms your recent blood results and asks about dental work, eye problems and any new medicines.
• The drip: you sit in a chair for the infusion. It should not be rushed; the minimum time is 15 minutes.
• After: drink another glass or two of water and go home the same day. The ROS suggests not planning anything strenuous for the next few days in case you feel flu-ish.

What are the side effects of zoledronic acid?

The most common side effect is a short-lived, flu-like reaction (fever, chills, aching muscles or joints and headache) in the first few days after the first infusion. The ROS says this affects up to 3 in 10 people after the first dose, is much less common after later doses and usually settles within a couple of days. Paracetamol or ibuprofen may help Royal Osteoporosis Society.

The product information reports that most of these post-infusion symptoms appear within three days, that fever was reported in 17.1% of people after the first infusion, and that the overall rate of reported side effects fell sharply with the second and third infusions emc, Aclasta SmPC.

Other side effects listed by the ROS include:

• Bone, joint or muscle pain: fewer than 1 in 10 people.
• Irregular heartbeat (atrial fibrillation): uncommon. Tell your doctor if you have it or are at risk.
• Eye inflammation: fewer than 1 in 100. Contact your doctor promptly if you get a painful red eye or blurred vision.
• Atypical thigh bone fracture: fewer than 1 in 1,000, usually after many years of use. Report any new pain in the thigh, hip or groin.
• Osteonecrosis of the jaw (ONJ): fewer than 1 in 1,000, usually after major dental work.

What dental advice is there for zoledronic acid?

See your dentist before starting if you can, keep up good oral hygiene, and have routine dental check-ups throughout treatment. The product information recommends a dental examination with preventive dentistry for people with risk factors before treatment, encourages all patients to keep up good oral hygiene and routine check-ups, and advises that invasive dental procedures should be done with caution and not close to the time of an infusion emc, Aclasta SmPC.

Always tell your dentist you are having zoledronic acid. Osteonecrosis of the jaw is rare, but it is far easier to prevent than to treat. Our article on alendronic acid side effects covers the jaw and thigh-bone risks shared by all bisphosphonates in more detail.

How long does zoledronic acid last, and how many years will I have it?

One infusion protects your bones for a full year, and UK guidance says to plan for at least three yearly infusions before reviewing whether to continue. The National Osteoporosis Guideline Group (NOGG) makes a strong recommendation to plan intravenous zoledronate for at least three years. It advises longer treatment, for at least six years, for people at higher risk: for example, those aged 70 or over when they started, people with a previous hip or spine fracture, those taking 7.5mg or more of prednisolone a day, and anyone who breaks a bone during the first three years NOGG.

Because zoledronate stays in bone, the ROS says it may keep helping for about two to three years after the last dose. At the review your doctor may advise carrying on, a planned treatment pause of a year or two, switching drug or stopping Royal Osteoporosis Society. If you pause, NOGG recommends a fresh fracture risk assessment three years after stopping zoledronate to decide whether to restart. Breaking a bone while on treatment does not necessarily mean the medicine has failed, but tell your GP.

Is a zoledronic acid infusion better than tablets?

Neither is better for everyone. The yearly drip suits people who cannot take tablets correctly or get stomach problems with them, while tablets avoid the hospital or clinic visit. Here is how the options compare:

	Zoledronic acid infusion	Bisphosphonate tablets
How often	Once a year	Daily, weekly or monthly
How it is taken	Drip in hospital or clinic, at least 15 minutes	Empty stomach, plain water, stay upright for 30 to 60 minutes
Stomach and gullet irritation	Avoided	Possible
Typical first review	After about 3 years	After about 5 years

Weekly alendronic acid or risedronate tablets are often tried first. Ibandronic acid offers a monthly tablet or a three-monthly injection. If bisphosphonates are not suitable, doctors may consider denosumab (Prolia), and people with very severe osteoporosis may be offered a bone-building drug such as teriparatide or romosozumab first.

How do you know the treatment is working?

Your doctor judges progress mainly through your fracture risk, any new fractures and, sometimes, a repeat DXA scan at review. Bone density changes slowly, so scans are spaced out. Alongside NHS care, some people choose a radiation-free bone health assessment with Screen My Bones to keep an eye on their bones between appointments. It uses REMS ultrasound, which does not replace a DXA scan for diagnosis or NHS treatment decisions, but can be repeated without radiation for monitoring.

Whatever you use, keep taking calcium and vitamin D if advised, stay active with weight-bearing exercise, and do not change or stop your treatment without speaking to your GP or specialist.

---

This article is part of our bone health series. It is general information, not a substitute for advice from your own doctor or pharmacist.