A nurse is teaching a client who is starting to take methotrexate to treat rheumatoid arthritis. Which of the following instructions should the nurse include in the teaching?

A. Methotrexate is an immunosuppressant and antimetabolite that is primarily excreted through the kidneys. It can cause nephrotoxicity and crystal formation in the renal tubules if not adequately cleared. Encouraging the client to drink at least 2 liters of water daily helps promote renal perfusion, enhance drug excretion, and reduce the risk of kidney damage. This is an essential safety instruction, especially for long-term therapy. B. Methotrexate for rheumatoid arthritis is administered once weekly, not daily. Taking it daily can lead to severe toxicity, including bone marrow suppression, increased risk of infection, hepatotoxicity, and gastrointestinal ulceration. This makes daily dosing a dangerous and common medication error. C. Avoiding foods high in vitamin K is relevant for clients taking anticoagulants such as Warfarin, not methotrexate. Methotrexate does not interact with vitamin K in this way. Instead, clients are often prescribed folic acid supplements to reduce adverse effects like stomatitis and bone marrow suppression. D. Methotrexate can cause stomatitis and oral mucositis due to its effect on rapidly dividing cells. Alcohol-based mouthwashes can irritate and dry the oral mucosa, worsening discomfort and increasing the risk of ulceration. Clients should use non-alcohol-based rinses such as saline or baking soda solutions instead.