The Drug Solubility (D/S) ratio is an in vitro measure of drug solubility that correlates with in vivo solubility. The solubility of the drug will influence the oral bioavailability.
Parameters:
(1) dose of the drug in mg
(2) aqueous solubility of the drug in mg per mL
where:
• If the aqueous solubility in not known, then it can be measured by determining the volume of water required to solubilize a test dose at body temperature (37°C).
dose/solubility ratio = D/S =
= (dose of the drug in mg) / (aqueous solubility of the drug in mg per mL)
Interpretation:
• According to the Food and Drug Administration (FDA) a D/S <= 250 indicates good in vivo solubility and dissolution will not be the rate limiting factor to the drug's absorption.
D/S Ratio
Solubility
Impact of Dissolution Rate
<= 250
good
not limiting factor to drug absorption
> 250
poor
limiting factor to drug absorption
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