Moxonidine

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.

Physiotens (Solvay)
0.2 and 0.4 mg tablets
Approved indication: hypertension
Australian Medicines Handbook section 6.4.8

Centrally-acting antihypertensive drugs such as methyldopa and clonidine are no longer widely used to control blood pressure. Their usefulness is limited by their adverse effects. Moxonidine has been developed as a more tolerable centrally-acting drug.

The imidazoline receptors are found in the brainstem and in the kidney. Stimulation of these receptors by an agonist, such as moxonidine, reduces sympathetic activity, lowering peripheral vascular resistance, and thereby reducing blood pressure.

The tablet formulation of moxonidine is well absorbed with a bioavailability of 88%. Most of the dose is excreted unchanged in the urine. Although the half-life is only around 2.2 hours, blood pressure can be controlled by a single daily dose.

Placebo-controlled trials show that moxonidine works better than placebo and that the effect on blood pressure is similar to enalapril. Other studies have shown no statistical difference between moxonidine and hydrochlorothiazide, atenolol and nifedipine.¹

Moxonidine has been available in the UK since 1996. Analysis of prescribing data from 409 general practitioners shows that moxonidine is not extensively used. It seems to be prescribed when several other treatments have failed to control hypertension. Out of 71 775 people with hypertension only 830 took moxonidine and 80% of these patients were taking it with at least one other antihypertensive.²

Although moxonidine may cause fewer adverse effects than clonidine, dry mouth and somnolence can still occur. Approximately 5% of the patients withdrew from clinical trials because of adverse events. Although the trials were short, rebound hypertension does not appear to be a major problem when moxonidine is stopped. Rebound hypertension may occur if the patient stops a beta blocker at the same time. Patients ceasing this combination should therefore withdraw the beta blocker first.

A trial of moxonidine in patients with heart failure had to be stopped because of increased mortality compared to treatment with placebo.³ Moxonidine is therefore contraindicated in any degree of heart failure. It is also contraindicated in patients with bradycardia, heart block or renal impairment and in people more than 75 years old. Caution is required if a patient has a history of unstable angina, severe coronary artery disease or angioneurotic oedema.

manufacturer did not respond to request for data

The Transparency Score () is explained in New drugs: transparency', Vol 37 No 1, Aust Prescr 2014;37:27.