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.
Carduran (Pfizer)
2 mg and 4 mg tablets
Indication: mild to moderate hypertension
Doxazosin is an alpha1adrenergic receptor blocker which has been approved for the treatment of mild to moderate hypertension. The drug is similar to prazosin, but has a longer duration of action, with a half life in excess of 20 hours. It can therefore be taken once a day.
The drug is well absorbed from the gut but then undergoes first pass metabolism. Doxazosin has its maximum effect on blood pressure after 2-6 hours. Prescribers are therefore advised to check the adequacy of blood pressure control 24 hours after an oral dose.
Most of the drug is bound to plasma proteins and is extensively metabolised.
Alpha1adrenergic receptor blockers do not affect the lipid profile in the same way as other antihypertensives. Treatment may result in reduced cholesterol concentrations. This theoretical advantage should be balanced against the unknown long term effects. Regular ophthalmoscopic examinations of patients taking doxazosin have been advised on account of optic disc changes seen in animal studies.
Prazosin has been associated with postural hypotension and dizziness, which is particularly prominent after the first dose. It is not yet known if these risks will be significantly less with doxazosin than with prazosin.
