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PEBC: Theme of the Week: Marketed Prodrugs and Their Metabolites

Drug manufacturers can use variety of methods to create new yet familiar products to maximize return on investment. Once a drug is discovered, its prodrugs or metabolites may be considered for development. These can have benefits such as improved absorption, metabolism, delivery and patient response.

Here are some medications which are related through their metabolism.

--------------- 1) Codeine and morphine: For pain relief, codeine is metabolized by CYP2D6 into its active metabolite morphine. Due to genetic CYP2D6 variability, patients with poor metabolism cannot convert codeine into active morphine for pain relief. The workaround is to give morphine tablets. This is also a safer option in pregnancy and children as the response to morphine is predictable and controlled with less risk of overdose.

2) Risperidone and paliperidone: For the treatment of psychosis, risperidone is also metabolized by CYP2D6 through 9-hydroxylation into its active metabolite paliperidone.

3) Valacyclovir and acyclovir: For viral infections, valacyclovir is an esterified version of acyclovir, which has improved bioavailability and penetration. In the body, it is then converted into the active metabolite acyclovir.

4) Capecitabine and fluorouracil: Capecitabine is a prodrug which is converted into fluorouracil in the body to treat certain cancers. Interestingly enough, capecitabine is an oral tablet, whereas fluorouracil is an intravenous medication.

5) Leflunomide and teriflunomide: Interestingly, leflunomide is converted into teriflunomide by a ring opening process. However, each one has a different indication: leflunomide is indicated for rheumatoid arthritis, whereas teriflunomide is indicated for multiple sclerosis.

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