Par Pharmaceutical Companies, Inc has begun shipping metoprolol succinate extended release 100 mg and 200 mg tablets. As previously announced, in November 2006 Par entered into a supply and distribution agreement with AstraZeneca in the US to distribute metoprolol succinate extended release tablets, which is substitutable for AstraZeneca's Toprol-XL extended release tablets. Par began shipping 25 mg tablets of generic Toprol-XL at that time.

Toprol-XL is a beta-1-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.

Combined moving annual total US sales of Toprol-XL in 100 mg and 200 mg tablets were $778 million, according to IMS Health data released in March.

Metoprolol succinate extended release is indicated for the treatment of hypertension, alone or in combination with other antihypertensives; the long-term treatment of angina pectoris; and the treatment of stable, symptomatic (NYHA Class II or III) heart failure of ischemic, hypertensive, or cardiomyopathic origin. It was studied in patients already receiving ACE inhibitors, diuretics, and, in the majority of cases, digitalis.

Metoprolol succinate extended release is contraindicated in severe bradycardia, heart block of greater than first degree, cardiogenic shock, decompensated cardiac failure, sick sinus syndrome (unless permanent pacemaker is in place), and in patients who are hypersensitive to any component of this product.

In clinical trials of patients with hypertension and angina pectoris, the most common adverse events reported with immediate release metoprolol tartrate are tiredness (10 per cent), dizziness (10 per cent), depression (5 per cent), diarrhoea (5 per cent), pruritus or rash (5 per cent), shortness of breath (3 per cent), and bradycardia (3 per cent).