Methotrexate

MTX is the most commonly used rheumatology drug and is the starter drug for nearly all patients with rheumatoid arthritis. It was originally a cancer drug but used in lower doses in rheumatology. It is oral, injectable or injectable solution can be taken orally. 

Dose range is 10-25 mg. 

• Nausea
• Oral ulcers
• Hair loss
• Diarrhea
• "the blahs"
• headache
• Liver enzyme elevation/liver disease
• Lung disease

Lung/Interstitial pneumonitis

7x more likely on MTX. Low-dose MTX may induce pulmonary AEs, such as cough and dyspnea. Hypersensitivity pneumonitis due to LD-MTX is believed to be relatively rare and is characterized by fever, shortness of breath, eosinophilia, and interstitial lung abnormalities on chest imaging; some cases progress to permanent lung damage. Prior studies suggest that pneumonitis occurs in 0.1% to 1% of patients using LD-MTX. However, systemic rheumatic diseases may have pulmonary manifestations, such as interstitial lung disease, that are unrelated to LD-MTX and pose a challenge for determining causality. In addition, LD-MTX may increase risk for infection because of its immunosuppressive effects. [1]
In a study of nearly 5000 patients by Solomon et al ,6 patients (0.3%) in the LD-MTX group and 1 (0.04%) in the placebo group had possible pneumonitis (HR, 6.94 [CI, 0.85 to 56.0]; exact test P = 0.044); no cases could be considered probable or definite because too little information was provided. The cases in the LD-MTX group occurred between 2 and 27 months after randomization. All participants were men, none reported any history of tobacco use, and 2 died. In addition, when considering any pulmonary AE, there was an increased risk with LD-MTX (HR, 1.42 [CI, 1.14 to 1.77]). Finally, the risk for any infectious AE, pulmonary or otherwise, was elevated (HR, 1.15 [CI, 1.01 to 1.30]). [1]