18th January 2024

Drug monitoring

In order to minimise the risk of the above adverse effects, DMARD therapy requires screening before initiation as well as monitoring during therapy.

Baseline assessment before initiating any DMARD should include height, weight, BP and blood tests (FBC, U&Es, LFTs). Any comorbidities should also be noted as this may influence DMARD choice- this should include screening for occult viral infections. Anti-Pneumococcal and Influenza vaccines are also advised.

Standard blood monitoring schedule when starting or adding a new DMARD

• Check FBC, U&Es, LFTs and albumin every 2 weeks until on stable dose for 6 weeks
• Once on a stable dose, check  FBC, U&Es, LFTs and albumin every month for 3 months
• After this, check  FBC, U&Es, LFTs and albumin at least every 12 weeks

In patients at higher risk of toxicity, blood monitoring should be more frequent. In addition, certain drugs require specific considerations:

• Methotrexate- all patients should be co-prescribed at least 5mg once weekly dose of folic acid supplementation.
• Azathioprine- measure a baseline thiopurine methyltransferase (TPMT)
• Hydroxychloroquine- baseline ophthalmic examination within 1 year of starting therapy

Table 1: Summary of standard blood monitoring schedule for common DMARDs. Adapted from: Ledingham J, Gullick N, Irving K, Gorodkin R, Aris M, Burke J et al. BSR and BHPR guideline for the prescription and monitoring of non-biologic disease-modifying anti-rheumatic drugs. Rheumatology. 2017;56(6):865-868.BSR and BHPR guideline for the prescription and monitoring of non-biologic disease-modifying anti-rheumatic drugs | Rheumatology | Oxford Academic (oup.com)

Other considerations when prescribing and monitoring DMARDs

Prescribing DMARDs in patients with co-morbidities requires some specific considerations. Caution is required, particularly in patients with pre-existing lung disease (particularly with drugs known to cause pneumonitis) and deranged liver function tests. In patients who have chronic viral hepatitis, anti-viral therapy should be initiated before commencing immunosuppressive DMARDs. In patients with chronic kidney disease, dose reduction and increased frequency of blood monitoring may be required.

In the perioperative period, DMARD therapy does not usually need to be stopped, but each case should be assessed on an individual basis. In the case of serious infections, many of the DMARDs, including methotrexate, leflunomide,  and sulfasalazine, should be paused while the patient recovers from the infection.