Relistor - methylnaltrexone bromide

What is Relistor?

Relistor is a medicine that contains the active substance methylnaltrexone bromide. It is available in solution for injection containing 12 mg of methylnaltrexone bromide in 0.6 ml.

What is Relistor used for?

Relistor is used to treat constipation induced by opioids (painkillers linked to morphine) in severely ill adult patients receiving palliative care (treatment of symptoms of a disease not aimed at its resolution) if the response to normal laxatives is not sufficient.

The medicine can only be obtained with a prescription.

How is Relistor used?

Relistor is given by injection under the skin once every two days. The dose depends on the patient's weight and should be reduced in the presence of severe kidney problems. The medicine is not recommended for patients with severe kidney problems undergoing dialysis or severe liver problems. The patient can inject alone after proper training.

How does Relistor work?

Opioids relieve pain by binding to "opioid receptors" in the brain and spinal cord. These receptors are also found in the intestine. When opioids bind to receptors in the intestine, intestinal motility decreases and this causes constipation.

The active substance in Relistor, methylnaltrexone bromide, is an antagonist of mu opioid receptors. This means that it blocks a particular type of opioid receptor, the "mu opioid receptor". Methylnaltrexone bromide is derived from naltrexone, a known substance used to block the action of opioids. Compared to naltrexone, methylnaltrexone bromide has a lower ability to penetrate the brain; this means that it blocks the opioid mu receptors in the intestine but not in the brain. By blocking these receptors, Relistor reduces opioid-induced constipation without interfering with their pain-relieving action.

How has Relistor been studied?

The effects of Relistor were first tested in experimental models before being studied in humans.

Relistor has been the subject of two main studies involving a total of 288 patients with advanced disease and constipation caused by opioids. Both studies compared the efficacy of Relistor with that of a placebo (a dummy treatment) in stimulating evacuation. The main measure of effectiveness in both studies was the number of patients who evacuated within four hours of the first administration. The second study also examined the number of patients who evacuated at least twice in the four hours following the first four administrations.

What benefit has Relistor shown during the studies?

Relistor was more effective than placebo in stimulating evacuation. In the two studies considered together, 55% of the patients who took Relistor evacuated within four hours of the first injection (91 out of 165), compared with 15% of placebo-treated patients (18 out of 123).

In the second study, 52% of patients taking Relistor evacuated at least twice in the four hours following the first four administrations (32 out of 62), compared to 8% of placebo-treated patients (6 out of 71).

What is the risk associated with Relistor?

The most common side effects associated with Relistor (ie seen in more than 1 patient in 10) are abdominal pain (stomach ache), nausea, flatulence (intestinal air) and diarrhea. For the full list of all side effects reported with Relistor, see the Package Leaflet.

Relistor should not be used in patients who may be hypersensitive (allergic) to methylnaltrexone bromide or any of the other ingredients. It should also not be used in patients with intestinal blockage or other conditions that require urgent bowel surgery.

Why has Relistor been approved?

The Committee for Medicinal Products for Human Use (CHMP) decided that Relistor's benefits are greater than its risks for the treatment of opioid-induced constipation in patients with advanced disease who are treated with palliative care if the response to standard laxative therapy is not sufficient. The committee recommended that Relistor be given marketing authorization.