Final answer:
The exact rate-limiting step in the metabolism of 5-fluorouracil (5-FU) isn't mentioned; however, in drug metabolism, such a step usually corresponds to the slowest step in the pathway, which greatly affects drug efficacy and toxicity.
Step-by-step explanation:
The rate-limiting step in the metabolism of 5-fluorouracil (5-FU) is not explicitly provided in the supplied reference material. However, in general pharmacology and biochemistry, a rate-limiting step is often referred to as the slowest step in a metabolic pathway or chemical reaction. For 5-FU, a key step in its metabolic pathway involves the conversion to its active nucleotide form, which inhibits DNA synthesis.
Although the specific rate-limiting step in 5-FU metabolism isn't stated, it's important to recognize that rate-limiting steps can significantly influence the efficacy and toxicity of a drug. For similar drugs like gemcitabine and floxuridine, prodrug activation and subsequent metabolism are critical for their anticancer effects.