Julio asked
Hello, I have multiple concerns about starting methotrexate for my RA. My biggest concern is the photosensitivity, especially since I live in Florida. Is it known how long after taking your weekly dose that you can safely go outside in the sun? Thank you so much!
Answer
You are correct that methotrexate is associated with photosensitivity, like many other medications. Drug-induced photosensitivity may present in a variety of ways. Most reactions are generally classified as either phototoxic or photoallergic. Photoallergic reactions are relatively rare, immunological response, which are not dose-related as the allergy develops after multiple days of continuous exposure. It occurs when light causes a drug to act as a hapten (a molecule that elicits an immune response), triggering a hypersensitivity response. Methotrexate is overwhelming associated with phototoxic reactions however.
Phototoxic reactions are chemically-induced reactions when the drug absorbs UVA light and causes cellular damage. This reaction can be seen with initial exposure to a drug, is probably dose-related (higher dosages equals higher incidence). It usually has rapid onset and manifests as what looks like an exaggerated sunburn. This reaction will be seen only on skin areas exposed to the sun. In terms of managing this photosensitivity, your approach will be based more on avoidance and protection from the sun versus timing out when you dose your medication. Now, it must be said that photosensitivity only appears to affect around 1-5% of patients so there is a good chance you will not be affected. The incidence of photosensitivity also appears to be relatively small in patients taking weekly doses of methotrexate vs. daily.
Weekly oral treatment with low doses of methotrexate (MTX) is often the therapy-of-choice for patients with rheumatoid arthritis (RA). There are several reasons for this including good disease control, convenient dosing and low toxicity. Even when taken weekly, over time, your body reaches a sort of maintenance drug level in the body and the weekly dose is commonly known as a maintenance methotrexate dose. Usually after 4-8 doses (4-8 weeks), there is very little change in drug concentrations in the body, so it doesn't much matter how long after dosing you expose yourself to the sun. Honestly, if you DO experience any sort of sun reactions, your best bet is to minimize sun exposure. Use of UVA-protective sunscreens and physical barriers such as clothing provide the best light protection.
You want to be sure that your sunscreen has UVA coverage. Ingredients that have UVA coverage include: avobenzone, dioxybenzone, oxybenzone, titanium dioxide, zinc oxide.
An acute attack may be managed in a number of different ways based on severity. A mild reaction may be handled similarly to a sunburn, with skin protectants and topical or systemic analgesics (e.g. acetaminophen or ibuprofen) You may also benefit from application of cooling creams or gels. If you have blisters that are broken, antibacterial creams may be necessary to prevent infection.
