Rectal Absorption Time for Systemic Effects
Rectal absorption timing is drug- and formulation-dependent. (pmc.ncbi.nlm.nih.gov)
Systemic absorption after rectal administration commonly begins within minutes and reaches peak plasma concentrations within about 1 to 2 hours for some rectal liquid/solution formulations. (journals.sagepub.com)
Typical Time Course Parameters
- Onset of measurable absorption: minutes to roughly 1 hour, depending on the drug and formulation. (pmc.ncbi.nlm.nih.gov)
- Time to peak concentration (Tmax): about 1 to 2 hours has been reported for rectally administered phenytoin solution. (journals.sagepub.com)
- Late absorption and exposure attainment: longer rectal retention time can materially affect overall absorption exposure; modeling work for a rectal midazolam gel formulation indicated retention longer than 3 hours to reach >80% of modeled pharmacokinetic/pharmacodynamic effects. (sciencedirect.com)
Factors That Determine Absorption Timing
- Rectal retention time: increased retention time increases exposure from rectal formulations. (sciencedirect.com)
- Formulation and physicochemical properties: dissolution, disintegration, and drug properties affect absorption rate from rectal dosage forms. (pmc.ncbi.nlm.nih.gov)
- Rectal physiology: the rectal wall is thin and has rich blood supply, supporting relatively prompt absorption once drug contacts the mucosa. (merckmanuals.com)