Prazosin

MAXDOSE DELIBERATELY LEFT BLANK. The only numeric ceiling in the SPC (20 mg daily in divided doses) sits under the Hypertension heading and is the hypertension ceiling. This page leads on Raynaud's phenomenon, for which the SPC gives no maximum and a usual maintenance of only 1 mg or 2 mg twice daily — roughly 2 to 4 mg a day. Surfacing 20 mg/day as this page's maximum would present a 5- to 10-fold overshoot as if it were a Raynaud's target, so the ceiling has been left inside the dose text where it is labelled with the indication it belongs to. FIRST-DOSE HYPOTENSION: a very small percentage of patients may respond in an abrupt and exaggerated manner to the initial dose. Postural hypotension evidenced by dizziness and weakness, or rarely loss of consciousness, has been reported particularly at the commencement of therapy — hence the 500 microgram starting dose given in the evening. §4.4 was cut at the source-fetch limit part-way through this sentence, so the full first-dose precaution text was not retrieved and must be read from the SPC. OTHER INDICATIONS IN THE SAME SPC, RECORDED BUT NOT PART OF THIS PAGE'S PRIMARY DOSE: congestive cardiac failure — recommended starting dose 500 micrograms two, three or four times daily, increasing to 4 mg in divided doses, adjusted to clinical response with careful monitoring of cardiopulmonary signs and symptoms and, when indicated, haemodynamic studies; dosage may be adjusted as often as every two to three days under close medical supervision, and in severely ill decompensated patients rapid adjustment over one to two days may be indicated and is best done where haemodynamic monitoring is available; therapeutic dosages in clinical studies ranged from 4 mg to 20 mg daily in divided doses, with a usual daily maintenance dosage of 4 mg to 20 mg in divided doses. Benign prostatic hyperplasia — 500 micrograms twice daily for 3 to 7 days with the initial dose in the evening, then adjusted to clinical response; usual maintenance 2 mg twice daily, which should not be exceeded unless the patient also requires prazosin as antihypertensive therapy, and such patients should be treated only under the supervision of the practitioner responsible for their hypertension. PATIENTS ALREADY ON OTHER ANTIHYPERTENSIVE THERAPY WITH INADEQUATE CONTROL: reduce the other drug to a maintenance level and initiate prazosin at 500 micrograms in the evening, then continue with 500 micrograms twice or three times daily, increasing gradually according to response; there is evidence that adding prazosin to an ACE inhibitor, beta-adrenergic antagonist or calcium antagonist may produce a substantial reduction in blood pressure, so the low initial dosage regimen is recommended. ELDERLY: the elderly may be more susceptible to hypotension, so initiate therapy with the lowest possible dose. PAEDIATRIC: the SPC states prazosin is not recommended for the treatment of children under the age of 12 years since safe conditions for its use have not been established, and it gives no paediatric dose. Direct any under-18 use to a specialist and to current prescribing references.