A 26-year-old woman presents with a 2-week history of right iliac fossa pain, vaginal spotting and mild dizziness. Her last menstrual period was 7 weeks ago. Urine pregnancy test is positive. Transvaginal ultrasound shows no intrauterine pregnancy and a right adnexal mass suspicious for ectopic pregnancy. She is haemodynamically stable. What is the most appropriate management?