Bioequivalence and Bioavailability Forum

Hi Pravin17,

❝ Please explain me that how it is possible that half life is early or less that its Tmax. For one drug half life is 5hrs and Tmax is 13hrs. Please explain how it is?

Tmax (and Cmax) reflect how quickly the drug becomes absorbed. The half-life reflects how quickly it gets out of the blood once it is already absorbed.
Elimination is done by processes that are completely different from processes relating to absorption so you shouldn't expect too much relation. To make it all more confusing all molecules known to science display a marked lack of social skills. In fact I'd go as far as calling them egocentric: Those absorbed generally agree to being eliminated from the body without waiting for all the unabsorbed colleagues to become absorbed.

And SODF with a Tmax of 13 hrs. could also be a formulation phenomenon. MR?

Hi Pravin,

❝ Dear Sir,

      ▲▲ Not interested in opinions of female members of the Forum?

❝ Please explain me that how it is possible that half life is early or less that its Tmax. For one drug half life is 5hrs and Tmax is 13hrs.

Absorption is independent from distribution/elimination. What we “see” in the very late part of the pro­file reflects the slowest rate-constant of the drug’s PK (not necessarily elimination). Your example is typical for a controlled release formulation. Once we cross the Rubicon of flip-flop PK (k_a ≤ k_el) what you call “half life” likely describes absorption – not elimination.