IMDUR

What it is

IMDUR contains isosorbide mononitrate. IMDUR modified release tablets are available in strengths of 60 mg or 120 mg. Isosorbide mononitrate is an active metabolite of isosorbide dinitrate that reduces the workload of the heart by producing venous and arterial dilatation.

Approved indications

— Prophylactic treatment of angina pectoris.

Dosing overview

The initial dose is one 60 mg IMDUR tablet taken once daily, and the dose may be increased to 120 mg once daily. IMDUR should not be administered twice daily. If headache occurs, the initial dose may be reduced to half a 60 mg tablet daily until the headache disappears. Patients with severe renal impairment may require dosage reduction to half a tablet given once daily. IMDUR should not be chewed or crushed, and should be swallowed whole with half a glass of fluid.

Key safety warnings

There is a risk of developing tolerance to haemodynamic and antianginal effects if higher doses (more than 120 mg per day) and/or more frequent doses (such as twice daily) of IMDUR are administered. IMDUR should be administered once a day to ensure intervals with low nitrate concentrations are achieved each day, reducing the risk of tolerance development. Severe hypotension, particularly with upright posture, may occur with even small doses of isosorbide mononitrate. Hypotension and lightheadedness on standing may be more frequent in patients who have consumed alcohol. The drug should be used with caution in patients who may be volume depleted or who are already hypotensive. IMDUR are not recommended for the management of acute attacks of angina pectoris. The benefits of isosorbide mononitrate in patients with acute myocardial infarction or congestive cardiac failure have not been established. Because the effects of isosorbide mononitrate are difficult to terminate rapidly, the medicine is not recommended in these settings. Abrupt withdrawal of IMDUR is not recommended because of the possibility of severe exacerbation of anginal symptoms. Patients may develop dizziness when first using IMDUR and should be advised to determine how they react before they drive or operate machinery.

Contraindications

Known hypersensitivity to nitrates or to any of the components in IMDUR. Shock (including cardiogenic shock), hypotension, obstructive hypertrophic cardiomyopathy and pericarditis. Phosphodiesterase type 5 inhibitors (such as sildenafil, tadalafil and vardenafil) must not be given concomitantly with IMDUR.

PBS listing

IMDUR 60 mg sustained release tablets are listed on the PBS with 2 items; the listing includes both restricted and unrestricted restrictions, with an ex-manufacturer price of A$6.64. IMDUR 120 mg sustained release tablets are listed on the PBS with 2 items; the listing includes both restricted and unrestricted restrictions, with an ex-manufacturer price of A$9.94.

Regulatory history

IMDUR 60 mg modified release tablets were first registered on the ARTG on 8 December 1993. IMDUR 120 mg modified release tablets were first registered on the ARTG on 23 February 1998.