Simultaneous modeling of bopindolol kinetics and dynamics

Area of Science:

• Pharmacology
• Clinical Pharmacology
• Drug Metabolism

Background:

• Bopindolol demonstrates extended beta-blocking activity (96 hours) disproportionate to its short elimination half-life (4 hours).
• Understanding the concentration-effect relationship is crucial for optimizing therapeutic outcomes with bopindolol.
• Previous studies have not fully elucidated the pharmacokinetic-pharmacodynamic profile of bopindolol, particularly after repeated dosing.

Purpose of the Study:

• To investigate the concentration-effect relationship of bopindolol after single and repeated oral doses.
• To determine if kinetic-pharmacodynamic models can predict bopindolol's effects over time.
• To explore potential mechanisms for the prolonged duration of action.

Main Methods:

• Six healthy subjects received 2-mg oral bopindolol doses, once and then daily for 13 days.
• Plasma concentrations were measured using HPLC, and beta-adrenoceptor blockade was assessed via radioreceptor assay.
• Effects were quantified by reduction in exercise-induced tachycardia (REIT) and isoproterenol dose ratio (DR-1).

Main Results:

• Only the hydrolysis product of bopindolol was measurable in plasma, with a half-life of 4-5 hours.
• Plasma concentrations and effects (REIT, DR-1) were correlated using classic effect models for up to 20 half-lives.
• Single-dose parameters accurately predicted plasma concentrations and effects for 96 hours after multiple dosing.

Conclusions:

• The prolonged beta-blocking effect of bopindolol is not due to a deep compartment, active metabolite, or irreversible receptor destruction.
• Effective receptor occupation occurs at chemically unmeasurable plasma concentrations (1-100 pmol/l), explaining the sustained effect.
• In vivo dissociation constants align with in vitro radioligand study findings, supporting the proposed mechanism.