Methylnaltrexone for Opioid Induced Constipation

Inclusion Criteria: * Age ≥ 18 years * Receiving palliative care * Life expectancy ≥ 2 weeks * Able to give informed consent * Receiving opioid treatment with either morphine sulphate, oxycodone or fentanyl * Opioid treatment, both * On a regular schedule (not just as needed or rescue doses) for the control of pain or dyspnea for at least 2 weeks before the first dose of methylnaltrexone, and * On a stable opioid regimen for at least 3 days before the first dose of methylnaltrexone. This is defined as no dose reduction of ≥ 50%, dose increases are permitted. If rescue medication is prescribed of a different type of opioid than the regular dosed opioid, the rescue medication should be switched to the same type as the regular dosed opioid for at least 3 days before the first dose of methylnaltrexone. * Has diagnosis of constipation, defined as either * \< 3 bowel movements during the previous week by history and no clinically notable laxation\* in the 24 hours before the first dose of methylnaltrexone, or * No clinically notable laxation\* in the 48 hours before the first dose of methylnaltrexone. * Constipation is defined as opioid induced, determined by investigator * On stable laxative regimen for ≥ 3 days before the first dose of methylnaltrexone. This is defined as at least one type of laxative in an adequate dosing regimen, (e.g. macrogol 2 packets daily, magnesium(hydr)oxide 500 mg three times daily, bisacodyl 10 mg daily or sennoside A+B 10 ml daily) or at least two types of laxatives in a suboptimal dose with patient characteristics hampering optimal treatment. * If the subject is a woman with presumed child bearing potential; negative urine pregnancy test at screening * Surgically sterile or agrees to use a medically acceptable method of birth control or practice sexual abstinence for the duration of the methylnaltrexone treatment and the following 15 days. \~ * including laxation after rescue laxative or enema \~ not necessary for postmenopausal women Exclusion Criteria: * Previous treatment with methylnaltrexone * Known or suspected mechanical gastrointestinal obstruction * Presence of an other cause of bowel dysfunction that is considered to be a major contribution to the constipation according to investigator * Presence of a peritoneal catheter for intraperitoneal chemotherapy or dialysis * Clinically relevant active diverticular disease * History of bowel surgery within 10 days before first dose of methylnaltrexone * Fecal ostomy * Use of vinca alkaloids within previous 4 months * Body weight \<38 kg * Renal failure defined as EGFR \<30 ml/min per 1.73m2 or requires dialysis. * Known or suspected allergy to methylnaltrexone or similar compounds (e.g. naltrexone or naloxone) * Participation in a study with investigational products within 30 days before first dose of methylnaltrexone. * Pregnant or nursing * Clinically important abnormalities that may interfere with participation or compliance to the study, determined by investigator Additional exclusion criteria for the immunologic and angiogenic analysis part of the study: * Chemotherapy or treatment with tyrosine kinase inhibitor during 4 weeks before inclusion or treatment scheduled during participation in this study. * Treatment with high dose corticosteroids during 2 weeks before inclusion in this study. This is defined as the equivalent of 30 mg of prednisone per day for ≥ 2 consecutive days.