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Pharmacology: Pharmacodynamics: Doxazosin is a selective, long-acting α1-adrenoceptor antagonist.
It reduces blood pressure by preventing the contraction of the smooth muscles in peripheral vascular walls, thus reducing the total peripheral vascular resistance. Blood pressure reduction in the standing position is similar to that in the sitting position. Patients with hypertension who take ordinary Kamiren tablets may replace them with Kamiren XL modified-release tablets. The efficacy and safety of treatment do not change. The effects on heart function are insignificant and transient. Resistance to doxazosin does not develop even after prolonged treatment.
Doxazosin reduces total cholesterol, LDL-cholesterol, triglyceride fats and produces an increase in blood HDL-cholesterol, therefore it has a protective effect against the development of atherosclerosis and coronary heart disease. Doxazosin is suitable for patients with non-insulin-dependent diabetes mellitus because it has a neutral or even positive effect on blood sugar and insulin. It inhibits platelet aggregation. After prolonged administration, left ventricular mass is reduced. Doxazosin is a safe drug in patients with renal impairment, chronic obstructive pulmonary disease, peripheral arterial angiopathy and gout.
A doxazosin dose is effective for more than 24 hours. The full effect will be seen after several weeks of regular use. If the effect is unsatisfactory, the patients may be concurrently treated with other antihypertensives: beta-blockers, diuretics, calcium channel antagonists or angiotensin-converting enzyme inhibitors.
Doxazosin prevents contraction of the smooth muscles of the upper part of the urethra and prostatic muscles, which encircle and compress the urethra. Due to muscle relaxation, micturition is facilitated, which considerably relieves the bothersome symptoms seen in benign prostatic hyperplasia. A beneficial effect on these symptoms is already seen within the first two weeks of treatment and increases with further treatment. Compared to the ordinary doxazosin tablets, the modified-release tablets have improved ratio between the efficacy and safety.
The effect of the drug on normal blood pressure is negligible.
The existing sexual dysfunction may improve.
Pharmacokinetics: Kamiren XL modified-release tablets are well absorbed after oral administration. Doxazosin gradually achieves maximum plasma concentrations in 8 to 9 hours. The maximum plasma concentrations of modified-release tablets are only one third of the concentrations of the standard tablets while the lowest concentrations are similar in both forms of the drug. Therefore the plasma profile of doxazosin is more uniform and the ratio between the maximum and minimum plasma concentrations twice lower in this form of the drug compared to the standard tablets.
In the blood, doxazosin is almost completely bound to plasma proteins. It is metabolized in the liver and subsequently excreted in the feces, mostly as metabolites. Less than 5% of an administered dose remains unchanged. The elimination half-life is 22 hours.
The pharmacokinetic properties of doxazosin in the elderly and patients with renal impairment do not differ significantly from those in young patients with normal renal function.
In patients with hepatic impairment, doxazosin is excreted more slowly and the plasma concentrations and AUC are considerably increased.
