The pharmacology of methotrexate

Ectopic pregnancy (EP) is a major cause of maternal morbidity and mortality. The treatment of this condition is primarily surgical, but medical management in selected cases is safe, effective, cost-effective and eliminates the morbidity of surgery. Methotrexate (MTX) is a folate antagonist that can be used for non-oncologic purposes including the treatment of EP. The dose and duration of MTX therapy for EP is much lower than that used in oncology cases, thus reducing side effects and increasing safety. MTX selectively acts on rapidly dividing cells, such as trophoblast cells which comprise the implantation site of the early gestation. The two most common methods of administering MTX to patients with EP are im. administration of a single-dose, based on body surface area and calculated by the equation 50 mg/m(2) (without the need for leucovorin rescue), or the multiple-dose regimen of 1 mg/kg of MTX, alternating with 0.1 mg/kg of leucovorin rescue. Both methods have a similar side effect profile, resulting in the rare occurrence of nausea, vomiting, stomatitis, elevated liver function tests, anorexia and diarrhoea. The two methods yield success rates similar to those of conservative surgical therapy with similar future fertility. The potential single- and multi-dose methods have never been directly compared, but it appears that the success of multiple dosing is more effective. As the efficacy of MTX therapy is not 100%, women must be followed clinically until there is compete resolution of human Chorionic Gonadotropin (hCG) titres from their serum.