Fluorouracil Dosing Guide: Simple Tips for Safe Use
If you’ve been prescribed fluorouracil (5‑FU), you probably have a lot of questions about how much to take and when. The good news is the dosing isn’t mysterious – it follows clear patterns that doctors adjust for your weight, cancer type, and how you’re feeling.
First, know that fluorouracil comes in three main forms: an IV infusion, an oral tablet, and a topical cream. Each one has its own schedule, so never mix them up. Your doctor will tell you which version you need, but here’s a quick snapshot.
Typical IV and Oral Schedules
For most solid tumors, the IV dose is calculated as milligrams per square meter of body surface area (mg/m²). A common plan is 400‑600 mg/m² given over 5‑minutes, repeated every two weeks. Some doctors spread the dose over several days – for example, 1,200 mg/m² split into 300 mg/m² each day for four days.
When you take 5‑FU orally, the dose is usually expressed in milligrams per kilogram (mg/kg). A typical regimen is 300‑400 mg/kg per day for two weeks, followed by a two‑week break. This “two‑on, two‑off” cycle helps your body recover from side effects.
Topical Fluorouracil: How Much to Apply
Topical 5‑FU treats skin lesions like actinic keratosis. The cream is usually 5% strength, and you’ll apply a thin layer once or twice daily. Most dermatologists tell patients to use it for 2‑4 weeks, then stop and let the skin heal. If redness or irritation gets too strong, cut back to once a day or skip a day.
Remember, the amount you spread matters. Roughly a nickel‑size pea‑sized dab per lesion is enough – don’t slather it on like a moisturizer.
Now, let’s talk about dose tweaks. If you develop mouth sores, diarrhea, or low blood counts, your oncologist may lower the dose by 25‑50% or extend the rest period. The goal is to stay effective while keeping side effects manageable.
What about missed doses? For IV, you’ll need to reschedule with the infusion center – don’t just skip it. For oral pills, take the missed dose as soon as you remember, unless it’s almost time for the next one; then just skip it and continue on schedule. Never double up.
Hydration is key, especially with IV 5‑FU. Drink plenty of water before and after the infusion to help your kidneys clear the drug. Some clinics also give you a vitamin B‑complex supplement to reduce hand‑foot syndrome, a common side effect.
Lastly, keep a simple log. Write down the date, time, and amount of each dose, plus any side effects you notice. This log helps your doctor spot patterns and adjust the plan faster.
Fluorouracil can be a powerful tool against cancer when you follow the dosing rules and stay in touch with your care team. Stick to the schedule, watch for symptoms, and don’t hesitate to call your doctor if anything feels off. With the right approach, you’ll get the most benefit and the fewest problems.
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