AuthorisedTherapeutic use (Phase IV)Interventional

ACTOR – AUC Control of Tacrolimus in Organ Recipients

When you have a kidney transplant, you need medicine to stop your body from rejecting the new organ. Prograf (tacrolimus) is one of the main medicines used for this. However, getting the dose just right can be tricky. Too little medicine may lead to rejection, while too much can cause unwanted side effects. The ACTOR study is testing better ways to measure how much tacrolimus stays in your blood over a 12-hour period. Participants take their regular Prograf capsules and have several blood tests throughout the day to track medicine levels. Researchers will also study gut bacteria to see if they change how the body breaks down the medicine. The aim is to help doctors personalise doses in the future, making treatments safer and more effective for people with a kidney transplant.

At a glance

Status

Authorised

Phase

Therapeutic use (Phase IV)

Sponsor

Oslo Universitetssykehus HF

Enrolment target

Start

02 Sep 2026

Kidney transplantation

What is this study about?

A kidney transplant can be life-changing, but the immune system naturally sees the new kidney as foreign and tries to fight it. To protect the new organ, patients must take immunosuppressant medicines every day. One of the most widely used treatments is a medicine called tacrolimus, often sold under the brand name Prograf.

Tacrolimus is very effective, but it requires careful balancing. Everyone absorbs and clears the medicine at different speeds. If the levels in your blood drop too low, your immune system could reject your kidney. If the levels climb too high, the medicine can cause side effects or harm the kidneys. At the moment, doctors usually check medicine levels with a single blood test taken just before the next dose, but this does not always show the full picture of how the drug works throughout the day.

The ACTOR clinical trial investigates a more detailed way to measure medicine levels over a full 12-hour cycle. By taking small blood samples at set times, doctors can map out the exact rise and fall of the medicine in the bloodstream. The study also looks at whether the natural bacteria living in your gut affect how your body absorbs the drug.

By taking part, you help researchers find out whether simpler, fewer blood tests can give the same accurate information as multiple tests. The ultimate goal is to create simpler, tailored treatment plans that protect transplanted kidneys and keep patients healthier for longer.

Key takeaways

The ACTOR study tests better ways to track tacrolimus (Prograf) levels in kidney transplant patients.
It aims to make anti-rejection medicine dosing safer, more accurate, and more personal.
Participation involves taking your usual medicine and having blood samples taken over 12 hours.
Researchers will also explore whether gut bacteria affect how the medicine is absorbed.
Taking part is voluntary and will not disrupt your routine NHS transplant care.

Who may be eligible?

This trial is open to adults aged 18 and over who have had a kidney transplant and are taking or due to take the anti-rejection medicine Prograf (tacrolimus).

Both men and women can join. Because the study focuses on how tacrolimus behaves in the body, participants must be able to attend the clinic for scheduled blood tests over a set period.

Your transplant team will check your general health and medical history to make sure taking part is safe for you. If you have other serious medical conditions or are taking medicines that interfere with how tacrolimus is absorbed, you may not be able to join.

Could this study suit you?

Answer these quick questions to see if you may be eligible. This is a guide only — the research team makes the final call.

You are aged 18 or older.
You have received a kidney transplant.
You are currently taking or prescribed Prograf (tacrolimus).
You are able to stay at the clinic for blood tests over a 12-hour period.
You are willing to provide blood and stool samples for research.

Answer every question to see your result.

What does participation involve?

Taking part involves visiting the clinic for a monitoring day where your blood levels are checked over 12 hours. You will take your standard Prograf 1 mg capsules as prescribed. During the visit, a small tube (cannula) may be placed in your arm so staff can take several small blood samples without needing to prick your skin each time.

You may also be asked to provide a stool sample so researchers can study your gut bacteria. The team will monitor your blood pressure, kidney function, and general wellbeing. Most of the intensive testing happens over one or two key visits, with routine follow-up appointments linked to your normal NHS transplant care.

Potential risks and benefits

Taking part may not directly change your health outcomes, but you will receive very close monitoring of your transplant and medicine levels. The results could help doctors improve dosing for future kidney transplant recipients. The main risks are minor discomfort or bruising from blood tests and the time commitment needed for clinic visits. As with all NHS-approved research, your participation is completely voluntary. You can choose to leave the study at any time without giving a reason, and your regular medical care will not be affected in any way.

Locations (1)

Some site locations are approximate. We're improving this — please verify with the trial team before travelling.

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Unverified
Norway

Common questions

What is Prograf?

Prograf is a brand name for tacrolimus, a standard medicine taken daily by transplant patients to stop the immune system from rejecting a new kidney.

Why do researchers need multiple blood samples?

Medicine levels rise and fall after you swallow a capsule. Multiple small samples show the complete journey of the drug in your body over 12 hours, giving a much clearer picture than a single test.

Will taking part change my normal treatment?

No, Prograf is already an approved, standard medicine for kidney transplants. The study looks at how your body handles the medicine rather than testing an unproven drug.

Why are researchers looking at gut bacteria?

The friendly bacteria in your digestive system can affect how well medicines are absorbed into your bloodstream. Learning more about this could help doctors pick the best dose for you.

Can I leave the study if I change my mind?

Yes. You can leave the study at any time. Your decision will not alter your normal NHS care or your relationship with your transplant team.