Tolerability and well-being with metoprolol in a controlled release (CR/ZOK) formulation: a review article.

Extensive research and clinical usage of metoprolol have shown the compound to be safe and well tolerated if the contraindications are taken into consideration. However, as with other beta-blockers, unwanted effects may occur during treatment. Although usually mild, these side effects may be of considerable clinical importance, especially since once initiated, therapy is often life-long. Results of previous studies have indicated that some of these symptoms are associated with high plasma concentrations of the drug. Theoretically, side effects may thus be reduced by administration of metoprolol in a controlled-release formulation (CR/ZOK) which yields relatively low plasma concentrations over approximately 24 hours. Using clinically relevant doses, metoprolol CR/ZOK affects beta 2-adrenoceptor-mediated functions (e.g., broncho-dilatation in asthmatics) less than tablets do. In addition, less leg fatigue during exercise has been reported. The clinical studies published so far indicate that metoprolol CR/ZOK is as well tolerated as or better tolerated than, conventional metoprolol tablets. Furthermore, metoprolol CR/ZOK is tolerated equally or better than atenolol in terms of CNS-related symptoms.