Methotrexate dosing in Children: How much ?

Methotrexate in Children with Alopecia areata

Methotrexate is sometimes used as a treatment for children with alopecia areata. Generally, topical steroids, minoxidil are used first followed sometimes by diphencyprone (DPCP) and/or anthralin as second line agents. Methotrexate in my clinic tends to be a third line agent but in some situations I will use it before DPCP and anthralin. 

Methotrexate is an immunosuppressant. It inhibits the proliferating of rapidly dividing immune system cells.  Studies of children aged 8-18 years with alopecia areata have suggested that benefit is seen in about 40 % of children who use methotrexate. 

Methotrexate Dosing in Children. 

The dose of methotrexate is discussed on a case by case basis. Generally, the dose to use depends on the child's weight. Doses in the range of 0.2 to 0.7 mg of methotrexate for every kilogram of body weight are not uncommon. The medication is only given once per week, and must never be used daily.

I generally start with 2.5 - 5 mg and slowly move upwards every week until the desired dose is obtained. For example, for a 70 pound child (31.8 kg), the dose range is 6.36 mg to 22.2 mg. I would generally start 2.5 mg in the first week and then 5 mg in the second week and then 10 mg in the third week and then 15 mg in the fourth week. One can move up faster if they wish, but this is my preference, especially in children under 10 years of age. 

Side effects of Methotrexate

Many children tolerate methotrexate well. Nausea is the most common side effect and tends to occur on the particular day of the week that the medication is taken (methotrexate is not used every day). Sometimes vomiting can occur. Other side effects include lowered blood counts, irritation of the liver, and cough from irritation of the lungs. 

I try hard to reduce nausea and especially vomiting in children taking methotrexate. Sometimes when children develop vomiting from Methotrexate then become extremely fearful of taking the medication. Administration of anti-nausea medications before taking the methotrexate can really help. About 25-30 % of children will have significant nausea with their methotrexate and 10 % will experience vomiting. 

Folic acid with Methotrexate

Folic acid is a vitamin which is prescribed every day except on the day that the child takes the methotrexate pill. The use of folic acid has been shown to reduce the chances of the child having changes in his or her blood counts and reduces the chance of the medication irritating the liver. 

Reference

Royer M, et al. Efficacy and tolerability of methotrexate in severe childhood alopecia areata. Br J Dermal 2011;165(2):407-10.