The deference in efficacy of Metoprolol for ischemic
and Carvedilol for non ischemic heart failure appears to come Patho-physiology
of heart failure in these conditions, Beta -1 receptor density is higher in patients
of ischemic heart failure as compared to non-ischemic heart failure, so Metoprolol
succinate a selective Beta-1 receptor blocker has a edge in treating heart
failure due to ischemia.
Infracted myocardium is denervated so nor-epinephrine
released is less as compared to non-ischemic myocardium; Carvedilol a non
selective blocker; beta-1, beta-2 and alpha blocker reduces myocardial non-epinephrine
levels, has an edge in treating non-ischemic heart failure.
In COMET trial Metoprolol tarterate was used, which is
a short acting drug, with higher peaks and lower troughs, the higher peak
concentrations lead to surges of maximal beta-receptor blockade and loss of
selectivity, and the lower troughs lead to loss of beta-1 blockade and
potential rebound. These fluctuvations may be reason of lesser efficacy of Metoprolol
in ischemic heart failure in COMET study.
