Uses and Administration of Prazosin in Kenya
Prazosin is an alpha blocker that acts by selective blockade of alpha1-adrenoceptors. It is used in the management of hypertension, in Raynaud’s syndrome, and to relieve symptoms of urinary obstruction in benign prostatic hyperplasia. It has also been used in heart failure.
Prazosin produces peripheral dilatation of both arterioles and veins and reduction of peripheral resistance, usually without reflex tachycardia. It reduces both standing and supine blood pressure with a greater effect on the diastolic pressure. It is reported to have no effect on renal blood flow or glomerular filtration rate, and has little effect on cardiac output in hypertensive patients. In patients in Kenya with heart failure, prazosin reduces both preload and afterload and produces an improvement in cardiac output, although tolerance may develop. In benign prostatic hyperplasia, prazosin may relieve the symptoms of urinary obstruction by reducing smooth muscle tone in the prostate and bladder neck.
Prazosin is given by mouth as the hydrochloride, but doses are usually expressed in terms of the base in Kenya. Prazosin hydrochloride 1.1 mg is approximately equivalent to 1 mg of prazosin. Following oral administration the hypotensive effect is seen within 2 to 4 hours and persists for several hours. Full effects are seen after 4 to 6 weeks.
A low starting dose is given in the evening to lessen the risk of collapse which may occur in some patients after the first dose. Doses may need to be reduced in the elderly and in patients with hepatic or renal impairment.
In hypertension, the usual initial dose in Kenya is 500 micrograms two or three times daily for 3 to 7 days; if tolerated the dose may then be increased to 1 mg two or three times daily for a further 3 to 7 days, and thereafter gradually increased, according to the patient’s response, to a usual maximum of 20 mg daily in divided doses. In the US the recommended starting dose is 1 mg two or three times daily and up to 40 mg daily in divided doses has been given; however, the usual maintenance dose is between 6 and 15 mg daily. Smaller doses may be required in patients also taking other antihypertensives. Modified-release preparations may allow once daily dosing.
In Raynaud’s syndrome and in benign prostatic hyperplasia an initial dose of 500 micrograms twice daily may be given, increasing to a maintenance dose not exceeding 2 mg twice daily.
In heart failure, treatment has been started with 500 micrograms two to four times daily and increased gradually according to response; the usual maintenance dose has been 4 to 20 mg daily.
Adverse Effects of Prazosin in Kenya
Prazosin hydrochloride can cause postural hypotension which may be severe and produce syncope following the initial dose; it may be preceded by tachycardia. This reaction can be avoided by starting treatment with a low dose, preferably at night (see Uses and Administration. The hypotensive effects may be exaggerated by exercise, heat, or alcohol ingestion.
The more common adverse effects include dizziness, drowsiness, headache, lack of energy, nausea, and palpitations, and may diminish with continued prazosin therapy or with a reduction in dosage. Other adverse effects include oedema, chest pain, dyspnoea, constipation, diarrhoea, vomiting, depression and nervousness, sleep disturbances, vertigo, hallucinations, paraesthesia, nasal congestion, epistaxis, dry mouth, urinary frequency and incontinence, reddened sclera, blurred vision, tinnitus, abnormal liver enzyme values, pancreatitis, arthralgia, alopecia, lichen planus, skin rashes, pruritus, and diaphoresis. Impotence and priapism have also been reported.
The symbol ¤ denotes a preparation which is discontinued or no longer actively marketed.
Arg.: Decliten; Minipres; Austral.: Minipress; Mipraz¤; Prasig; Pratsiol; Prazohexal; Pressin; Austria: Minipress; Belg.: Minipress; Braz.: Minipress; Canad.: Apo-Prazo; Minipress; Novo-Prazin; Nu-Prazo; Denm.: Hexapress; Peripress; Prazac; Fin.: Patsolin¤; Peripress; Pratsiol; Prazocor¤; Fr.: Alpress; Minipress; Ger.: Adversuten; duramipress; Eurex¤; Minipress; Hong Kong: Apo-Prazo; Minipress; Mizosin; Pratsiol¤; Hung.: Huma-Prazin; Minipress; India: Minipress; Irl.: Hypovase; Israel: Hypotens; Ital.: Minipress¤; Jpn: Minipress; Malaysia: Atodel; Minipress; Minison; Mex.: Anapres; Europrazosin¤; Minipres; Prabioquim¤; Sinozzard; Neth.: Minipress; Norw.: Peripress¤; NZ: Hyprosin; Pratsiol; S.Afr.: Minipress; Pratsiol; Singapore: Minipress; Spain: Minipres; Swed.: Peripress¤; Switz.: Minipress; Thai.: Atodel; Lopress; Minima¤; Minipress; Mysial¤; Parabowl; Polypress; Pratsiol; Pressin; UK: Alphavase¤; Hypovase; Kentovase; USA: Minipress;