Toprol XL and Betaloc CR are interchangeable
Toprol XL is an extended-release tablet containing metoprolol succinate. When it was formulated, the drug metoprolol was already available on the market as immediate release Lopressor. Lopressor contains a different salt of the drug, metoprolol tartrate. These two salts do not have the exact same size, or molecular weight. 100 mg of metoprolol tartrate corresponds to 95 mg of metoprolol succinate.
In order to simplify the conversion of existing Lopressor patients to Toprol-XL, the Toprol XL manufacturers (Astra Zeneca) in the United States decided to label their formulation in terms of metoprolol tartrate (Lopressor) equivalents, rather than simply indicating the amount of metoprolol succinate the tablets actually contain. Therefore, a tablet of Toprol XL which contains 95 mg of metoprolol succinate is labelled in the US as Toprol XL 100 mg (as it is equivalent to 100 mg of metoprolol tartrate, or Lopressor).
Toprol-XL is marketed in New Zealand by the same manufacturer, Astra Zeneca, under the brand name of Betaloc CR. Unlike in the US, in New Zealand the labelled tablet strength actually reflects the amount of metoprolol succinate the tablets contain, and not its metoprolol tartrate equivalent.
Therefore, Toprol XL 100 mg is the same as Betaloc CR 95 mg in New Zealand. The other drug strengths compare as follows: Toprol XL 50 mg converts to Betaloc XL 47.5 mg, Toprol XL 25 mg to Betaloc CR 23.75 mg and Toprol XL 200 mg to Betaloc CR 190 mg.
In summary, Betaloc CR in New Zealand is the same brand name formulation of metoprolol succinate as Toprol XL in the US. The apparent and confusing difference in their labelled strengths is not due to an actual difference in drug content but rather a result of the labelling equivalency to metoprolol tartrate accepted in the US.
To verify the US labelling of Toprol XL, visit this page.
TOPROL-XL, metoprolol succinate, is a beta1-selective (cardioselective) adrenoceptor blocking agent, for oral administration, available as extended-release tablets. TOPROL-XL has been formulated to provide a controlled and predictable release of metoprolol for once-daily administration. The tablets comprise a multiple unit system containing metoprolol succinate in a multitude of controlled release pellets. Each pellet acts as a separate drug delivery unit and is designed to deliver metoprolol continuously over the dosage interval. The tablets contain 23.75, 47.5, 95 and 190 mg of metoprolol succinate equivalent to 25, 50, 100 and 200 mg of metoprolol tartrate, USP, respectively.