Seloken® (metoprolol) was first introduced in the mid 1970s as an immediate release, β1 -selective beta-blocker. Like other immediate release drugs, the plasma concentration overshoots the optimal therapeutic range (within 2 hours post dosing for Seloken ), later falling below this range (within 6-8 hours) ;17 . As the dose-response curve of metoprolol approaches a plateau in the range 200-300 nmol/L, higher plasma concentrations deliver little additional β1 blockade. However, at higher plasma concentrations β1 -selectivitiy decreases and blockade of β2 receptors increases, thereby contributing to unwanted adverse effects.
An immediate release beta-blocker will produce plasma concentrations of active substance that initially exceed and later fall short of the optimal therpeutic range 17 .
The controlled release/extended release formulation of Seloken - Seloken ZOK (metoprolol CR/XL) - avoids the undesirable effects of plasma peaks and troughs by delivering metoprolol at a predetermined, and near-constant rate over the 24-hour dosage period.
Benefits of the Seloken® ZOK formulation
- Once-daily dosage
- More even plasma concentration of metoprolol over the 24-hour dosage period than immediate release tablets 2,18,19
- More even blockade of β1-receptors over the 24 hour dosage period than conventional, immediate release tablets 2,20
- Reduced risk of peak plasma concentration-related side effects, including impaired lung function, leg and general fatigue, and metabolic disturbances 3-6
