Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.
Toprol-XL (AstraZeneca)
23.75 mg, 47.5 mg, 95 mg and 190 mg controlled-release tablets
Approved indication: chronic heart failure
Australian Medicines Handbook section 6.4.3
Beta blockers used to be contraindicated in heart failure, but they can benefit some patients with chronic stable heart failure.1 A placebo-controlled study of 3991 patients who were already on optimum therapy, such as a diuretic and an ACE inhibitor, found that metoprolol significantly reduced deaths. After a year the mortality rate was 7.2%in the metoprolol group and 11% in the placebo group.2
The preparation used in the clinical trial was an extended-release formulation. This contained metoprolol succinate as opposed tometoprolol tartrate which is used in the treatment of angina and hypertension.
The two salts of metoprolol have been compared in a haemodynamic study. This found that both salts had similar effects.3The extended-release formulation is given once a day. Its peak plasma concentrations are only 25% or 50% of those of the conventional formulation, but they produce comparable beta blockade over 24 hours.
When the extended-release tablets are prescribed for heart failure, the dose must be slowly increased over several weeks. If the heart failure gets worse during this titration metoprolol succinate may need to be discontinued.
