What could happen if i take 240mg of lasix (furosemide) all at once?

Lasix (furosemide): This is a large dose which we would use only in unusual circumstance. The effect would depend on the patient's physiology. In an otherwise normal patient a large diuresis could be expected and possibly side effects such as ringing in the ears or hearing loss. In someone for whom the dose was appropriate we'd expect less diuresis and perhaps less in side effects. The answer is not simple