steriods and prodrugs

Question 1

definition of prodrugs and example

Answer 1

Compounds that are pharmacologically inert but can be converted by an enzyme or chemical action to an active form of the drug, at or near their target site.
e.g Levodopa - treat parkinsons: Dopamine is too polar to cross the BBB but there is a transport system for amino acids, such as levodopa. Once it enters the brain it is decarboxylated to dopamine

Question 2

What are the uses of prodrugs?

Answer 2

Increase solubility (lipid or water)
Improve taste
Increase stability (biological and chemical)
Reduce toxicity
Modify the time of duration of action
Deliver drugs to specific site in the body
Alleviate pain when administered by injection

Question 3

What are the two main classes of prodrugs?

Answer 3

Bioprecursor prodrugs
- Molecules that already contain
the embryo of the active
species within their structure
- Rely on metabolic or chemical
modification
- Can involve one step, or a
series of steps (oxidation or
reduction)
Carrier prodrugs
- Combination of active drug
and carrier species
- Example: lipophilic carrier
transport drug across
membranes
- The link between the carrier
and active species must be a
group that is easily
metabolised e.g. ester or
amide

Question 4

Criteria that all prodrugs should follow

Answer 4

• The prodrug should be less
  toxic than the drug
• The prodrug should be
  significantly less active (or
  inactive) than the parent drug
• The rate of formation of the
  active form from the prodrug
  should be rapid enough to
  maintain the drug’s
  concentration within the
  therapeutic window
• The metabolites from the
  prodrug should be non-toxic
• The prodrug should improve
  bioavailability if administered
  orally
• The prodrug should be site
  specific

Question 5

Facts about steroids

Answer 5

They all share a common tetracyclic structure but have different functional groups and substituents
The stereochemistry of the three 6-membered rings in fully saturated steroids is identical in all mammalian steroids (chair conformation)
Only 1 stereoisomer occurs naturally for any particular steroids despite having multiple stereocentres