Methotrexate vs Tazarotene

This drug is taken once a week. Taking it every day can cause fatal bone marrow failure. Pick one day of the week, write it down, and keep to it.

Test dose: A single small dose, often 2.5 mg to 5 mg, with blood counts checked about a week later before going further. A safety check, not the treatment dose.

Starting dose: Commonly 7.5 mg to 15 mg once weekly, adjusted for age, weight, kidney function and other illnesses. Lower in older people and in reduced kidney function.

Going up: Small steps, usually 2.5 mg to 5 mg every few weeks with blood tests in between, until the psoriasis responds or side effects set the ceiling.

Usual dose: Most people settle between 15 mg and 25 mg once weekly. Above about 15 mg tablet absorption gets unreliable, a common point to switch to the injection.

Folic acid alongside it: It reduces nausea, mouth ulcers and blood count problems. Usually a daily dose on the days you are not taking methotrexate, or one larger weekly dose on a different day. It does not stop the drug working.

Total course: No fixed course. It continues as long as it works and blood tests stay normal, which for some people is years.

Once a week, on the same day every week. Choose a day you will remember and write it somewhere visible. Some people take the whole dose at once; some split it into two portions about twelve hours apart on the same day to reduce nausea. Do not spread it across different days unless you were told to.

Take tablets with water, and with food if they upset your stomach. An evening dose means the tiredness and mild nausea happen while you are asleep.

Folic acid goes on the other days, as prescribed. It is not a substitute for a missed methotrexate dose.

With the weekly injection, keep to the same day and rotate the site.

Take it as soon as you remember if it is within about two days of your usual day. If longer, skip it and take the next on your usual day. Never take two weekly doses close together to catch up, and never take a daily dose to make up for a missed week.

If you have taken more than one weekly dose, or taken it several days in a row, contact a doctor or a poison center straight away. Do not wait to see how you feel. This overdose is treatable caught early and dangerous when it is not.

Methotrexate is watched by blood test, and the schedule is not optional. The problems it causes are silent until they are advanced.

Before starting: Full blood count, liver tests, kidney function, and a pregnancy test where relevant. Hepatitis B, hepatitis C, HIV and tuberculosis screening is standard, because the drug damps the immune system. A chest x-ray if there is any history of lung disease.

Early on: Blood counts and liver tests within a week or two of starting, and again after each dose increase. This is when a sudden drop in blood counts would show.

Once stable: Full blood count, liver tests and kidney function every one to three months, depending on the dose and what else you take, for as long as you are on the drug.

The liver over the long term: Years of methotrexate can scar the liver, and the risk rises with total lifetime dose, heavy alcohol use, obesity, diabetes and fatty liver disease. Biopsy used to be the check; most clinics now use a blood marker of scarring and a scan of liver stiffness.

The lungs: A rare but serious lung inflammation can occur. A new dry cough, breathlessness or fever means being seen, not waiting for the next appointment.

What to report between tests: Mouth ulcers, unexplained bruising or bleeding, sore throat or fever, dark urine, yellowing of the eyes or skin, severe nausea, any new cough or breathlessness.

First doseTaking it: Once a week, not daily, with folic acid on the other days. Nausea, tiredness or mouth soreness in the day or two after each dose is common early on; folic acid usually blunts it.

Weeks 1 to 2Settling in: Nothing visible in the skin yet.

Weeks 4 to 8Working: Plaques thin and spread less, thickness and scale first. Joint pain from psoriatic arthritis often improves in the same window, one reason it is chosen over a skin-only treatment.

About 3 monthsJudge it here: Substantial improvement is the realistic target.

Beyond 3 monthsLong term: Where it suits, the result holds while the dose continues, with regular blood tests. Some stay on it for years.

Many monthsNails: Nail psoriasis can improve, but slowly. Nails always lag behind the skin.

Generic methotrexate tablets are among the least expensive systemic treatments in dermatology. Folic acid is cheap too.

The weekly auto-injector pens cost considerably more, and coverage usually requires showing that tablets caused nausea or did not work well enough. Plain injectable vials are cheaper than the pens.

The real cost is the monitoring, repeated blood tests and periodically a liver scan or blood marker. Usually covered, but they are appointments and not optional.

Insurers frequently require a trial of methotrexate before approving a biologic, one reason it is still so often the first systemic drug tried.