A RETROSPECTIVE ANALYSIS OF LABORATORY ABNORMALITIES FOUND DURING METHOTREXATE MONITORING AND THE COST IMPLICATIONS

Background: Methotrexate (MTX) remains the first line treatment in majority of cases of inflammatory arthritis. The current British Society of Rheumatology (BSR) Guidelines suggest checking Full blood Count (FBC), ALT/AST, Albumin, Creatinine at 0,2,4,6,10,14, 18 weeks and then 12 weekly. Despite this close monitoring recommendation, MTX is generally considered a safe drug by Rheumatologists and its use has grown significantly over last two decades. Objectives: To evaluate the incidence of liver, renal and haematological toxicities during Methotrexate treatment and calculate the cost implications. Methods: 101 patients (30 males 71 females) (Age 40-89 year Mean 66.5 year) prescribed MTX were randomly selected and retrospective analysis was performed. 91 Rheumatoid arthritis, 8 Psoriatic arthritis and 2 patients had Undifferentiated Inflammatory Arthritis. 20 patients had Early Inflammatory Arthritis (<1 year) and 81 had established disease. 24 patients were on MTX for <1 year. Average dose of MTX in our cohort was 15mg once weekly (Min 7.5mg Max 25mg). All patients were on folate supplementation. Blood investigations over last 1 year were reviewed individually for all patients. Severe Liver toxicity (LS) was defined as ALT/AST >100 U/l; unexplained reduction in albumin <30 g/l and mild liver toxicity (LM) was between normal and LS values. Severe haematological toxicity (HS) was defined as WCC <3.5 × 10 /l, MCV >105 fL, Neut <1.6 × 10 /l, PLT <140 × 10 /l unexplained eosinophilia >0.5 × 10 /l and mild haematological toxicity (HM) was between normal and HS. Severe renal toxicity (RS) was defined as Creatinine increase >30% over 12 months and/or calculated GFR <60 ml/min. Mild renal toxicity (RM) was between normal and RS. Results: Over 1 year, 101 patients had total of 609 blood tests for MTX monitoring (Min 1 Max 17). FBC, Liver Function Test, Urea & Electrolytes, CRP and ESR each cost £8.54. LS was found in 4 patients, LM in 15, HM in 3 and RM in 2 patients. MTX was stopped in all 4 patients with LS. Mild toxicities (LM, HM and RM) recovered after close monitoring or reduction in dose. 5 patients with mild toxicities were on MTX for <1 year. Rest of the patients were on stable dose of MTX for >1 year. All patients with severe and mild toxicities did not have any significant comorbidities compared to rest of the patients. It was calculated that detecting one LS cost (609x8.54)/4 = £1300.2. Similarly one LM cost £346.7, one HM £1733.6 and one RM £2600.43. These costs does not include travel expenses, parking charges and time off work for appointments in phlebotomy. Conclusion: Our cohort shows that mild liver toxicity is the most commonly found abnormality during MTX monitoring and patients on stable doses still need monitoring for liver toxicity. Haematological and renal toxicities are much less common and a more relaxed monitoring schedule may be acceptable for these parameters. Regular monitoring for inflammatory markers (CRP, ESR) causes an extra cost burden. The direct cost for identifying each abnormality is considerable. REFERENCES: [1] 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 Feb 27;56(6):865-868. kew479. Disclosure of Interests: None declared DOI: 10.1136/annrheumdis-2019-eular.3790Citation: Ann Rheum Dis, volume 78, supplement 2, year 2019, page A2068Session: Public health, health services research, and health economics (Scientific Abstracts)