Azathioprine

About Azathioprine

Azathioprine, an immunosuppressant, is converted in the body to 6-mercaptopurine and then to thioguanine nucleotides, which act partly by being built into the DNA of dividing cells. The label covers prevention of rejection after a kidney transplant, alongside other treatment, and active rheumatoid arthritis. After a transplant it usually starts at 3 to 5 mg per kg once a day from the day of the operation and is lowered to 1 to 3 mg per kg for maintenance. For rheumatoid arthritis it starts at about 1 mg per kg (50 to 100 mg) a day as one dose or two; after six to eight weeks the dose can rise in steps four weeks apart, to at most 2.5 mg per kg a day. A response usually takes six to eight weeks, and arthritis that has not improved after 12 weeks can be considered unresponsive.

The boxed warning says long-term immunosuppression with azathioprine raises the risk of cancer, including lymphoma after transplant and hepatosplenic T-cell lymphoma, an aggressive lymphoma whose reported cases have been fatal, mostly in adolescent and young adult males treated for inflammatory bowel disease (a use the FDA has not approved), some also on a TNF blocker. Skin cancer is a particular risk, so sunlight and ultraviolet light are limited with protective clothing and a high-protection sunscreen. It can cause severe drops in white cells, red cells and platelets, serious infections including progressive multifocal leukoencephalopathy (a brain infection), and a stomach reaction with severe nausea and vomiting. It must not be used by anyone allergic to it, for rheumatoid arthritis in pregnancy, or for rheumatoid arthritis after alkylating drugs such as cyclophosphamide, chlorambucil or melphalan. Nausea and vomiting are common and often ease with divided doses or doses taken after meals.

Before starting, the prescriber may test for TPMT and NUDT15 deficiency, inherited enzyme differences that raise the risk of severe, life-threatening drops in blood counts at usual doses: people with deficiency are usually offered another treatment, and those with partial deficiency take a lower dose, but testing never replaces blood counts. A complete blood count with platelets is checked weekly in the first month, twice a month in the second and third months, then monthly or more often after dose changes. With allopurinol the azathioprine dose is cut to about a third or a quarter, and febuxostat is not recommended with it. It can harm an unborn baby, breastfeeding is not recommended, and the label calls for proper handling and disposal of the tablets.

Taking Azathioprine

How to take it

Once or twice a day as prescribed; dividing the dose or taking it after meals can ease nausea. Keep every blood test appointment, and report fever, signs of infection, or unusual bleeding or bruising. Only the prescriber changes the dose.

If you miss a dose

Take it as soon as you remember, unless it is almost time for the next dose; then skip the missed dose. Do not take two doses at once.

Storage

At room temperature in a dry place, protected from light and tightly closed, out of reach of children. Ask the pharmacy how to dispose of unused tablets.

Interactions to know about

With allopurinol the dose must be much lower, and febuxostat is not recommended with it. ACE inhibitors, trimethoprim-sulfamethoxazole and ribavirin can deepen drops in blood counts, aminosalicylates such as mesalamine and sulfasalazine call for caution, and it can weaken the effect of warfarin. Avoid live vaccines while taking it.

This summarizes the official prescribing information. Your prescriber’s and pharmacist’s instructions, and the leaflet that comes with your medicine, take priority.

Why the cash price for Azathioprine differs from pharmacy to pharmacy

Generic 50 mg azathioprine is an old medicine with several makers, so a quote is mostly the pharmacy’s markup and dispensing fee, and the spread between pharmacies comes from how each prices a routine generic. A prescription that names Imuran and blocks substitution is priced as a brand.

Azasan’s 75 and 100 mg tablets are a branded generic: a prescription for them is quoted on what the pharmacy pays for that product, and a pharmacy that does not stock them may order them in. A daily dose written as whole 50 mg tablets is quoted as the generic instead.

Ways to pay less for Azathioprine without insurance

• Ask for generic azathioprine, ask whether it is on the pharmacy’s flat-price generic list, and compare more than one pharmacy.
• If your daily dose can be made of whole 50 mg tablets (100 or 150 mg, for example), ask the pharmacy to quote that against Azasan, and ask the prescriber which to write.
• Ask for a ninety-day supply once your dose and blood counts are stable.
• Upload the prescription to Script Unlock so licensed pharmacies can quote their cash price. You pay the pharmacy directly.

Questions to ask your pharmacist about Azathioprine

1. 1.Has my TPMT or NUDT15 status been checked, and does my dose reflect it?
2. 2.Is it safe with my allopurinol or febuxostat for gout?
3. 3.When are my blood counts due, and which signs of infection or bleeding mean I should call?
4. 4.Which vaccines should I avoid while I take it?

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