Methotrexate Dosage

The drug methotrexate is used to treat conditions such as rheumatoid arthritis and can also be used as a chemotherapy drug. Methotrexate can be taken in a number of ways, including orally, by IM, intrathecally and intravenously.

As methotrexate can be used to treat a number of different conditions, it’s important to start on the right dosage in accordance with the condition being treated. With certain conditions, a patient’s dosage can even vary according to the different stages of treatment. Starting dosages are further dependent on factors such as the medical diagnosis, the acuteness of the condition, the age of the patient, their body requirements, medications taken concurrently, and the patient’s medical history.

Starting Dose for Adults

The starting methotrexate dosage for adults usually ranges from 2.5 mg/m2 a day for mycosis fungoides to as much as 12,000mg/m2 weekly with leucovorin rescue as part of a total chemotherapeutic plan.

For acute lymphoblastic leukemia the adult dosage is 3.3mg/m2 a day at the induction stage whilst the initial dose for osteosarcoma is 12 g/m2 as a 4 hour infusion, combined with other chemotherapeutic agents. A methotrexate dosage can be increased over time if there is no initial benefit.

Dosages in Adults for Different Conditions

There are many other conditions in adults that methotrexate treats.

• In the treatment of choriocarcinoma or trophoblastic disease, a course of methotrexate is 15 to 30mg daily for 5 days.
• For rheumatoid arthritis (RA) methotrexate can be taken either as a single or divided dose. A single dose is 7.5mg weekly whilst a divided one is 2.5mg every 12 hours for 3 doses once a week.
• The dosage for psoriasis is usually 10 to 25mg a week for a single dose or a divided dose of 2.5mg every 12 hours for 3 doses once a week.

Pediatric Dosages

Children are typically started off on dosages upwards of 3mg. The pediatric methotrexate dosage for acute lymphoblastic leukemia is 100 mg/m2 over an hour followed up with a 35 hour infusion delivering 900 mg/m2 a day.

To treat meningeal leukemia, the correct dosage depends on the age of the child, with the minimum dose being 3mg initially every 2 to 5 days and the maximum being 12mg. For dermatomyositis the usual dose is 15 to 20 mg/m2 once a week. With neoplastic diseases the dosage is 7.5 to 30mg/m2 biweekly.

Although methotrexate is a useful drug, it must be handled with extreme care. Patients should always check the correct dosage with their doctor and women should avoid the medication altogether if they are pregnant, trying to get pregnant or breastfeeding.