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One tablet can contain 0.5 or 1 mg of active substance – prazosin.
The drug is characterized by antihypertensive and vasodilating effect.
Pharmacodynamics and pharmacokinetics
The mechanism of action of the drug is based on the ability of prazosin to block postsynaptic α1-adrenergic receptors and interfere with vasoconstrictive effects of sympathetic innervation, as well as catecholamines.
Prazosin as an α-adrenergic blocking drug has both an expanding effect both on the arteries and veins, a little more on voluminous venous vessels, which leads to a decrease in the venous influx to the heart and facilitating the work of the heart muscle due to a decrease in peripheral resistance. Thus, both pre- and post-loading on the myocardium decreases: a decrease in the end-diastolic pressure along the way of peripheral veins widening and a decrease in the inflow to the right atrium, and a decrease in the pressure in the aorta are observed.
The peak of the hypotensive effect as a result of taking a single dose comes on the 1-4th hour and can last up to 10 hours. In addition, it is possible to develop both early (3-5 days) and late (by 12 months) tolerance, which requires an increase in dosage.
Absorption of prazosin is from the gastrointestinal tract, with bioavailability of 50-85%. It binds to plasma proteins by 95%, then is metabolized in the liver along the way of detachment of the methyl group, conjugation to form 4 active metabolites, having 25% pharmacological activity.
Indications for use
The use of the drug is appropriate for hypertension and congestive heart failure.
☞ hypersensitivity to prazosin and other inactive components;
☞ constrictive pericarditis (squeezing);
☞ cardiac tamponade, heart defects, characterized by reduced pressure ☞☞☞ when filling the left ventricle;
☞ pregnancy or lactation;
☞ children’s age (up to 12 years).
Against the background of therapy, Prazozin can develop:
☛ severe hypotension;
☛ an increase in diuresis;
☛ manifestations of allergic reactions;
☛ dizziness, headaches, a feeling of fatigue, nausea, dry mouth, darkness in the eyes.
Long-term treatment can lead to edema of the lower extremities.
Prazosin, instructions for use (Method and dosage)
Take the tablets orally for 0.5-1 mg several times a day (2-3 times, regardless of diet), gradually increasing the dose after 3 days.
The recommended maintenance dose may vary between 3-20 mg per day (in divided form).
The phenomenon of the first dose
The use of the drug should begin with a small dose before bedtime in the amount of 0.5-1 mg. After this, the patient is recommended bed rest, since postural hypotension may develop until fainting, collapse and other reactions associated with the phenomenon of the first dose. The greatest manifestation of these reactions, if previously treated with diuretics.
Admission of overdose of the drug can lead to a marked decrease in blood pressure (BP). In this case, it is recommended to take a horizontal position and raise your legs.
☛ Prazosin and Nifedipine are incompatible;
☛ the hypotonic effect of Prazosin is increased under the action of diuretics, ☛ sympatholytics, β-adrenoblockers, increasing the risk of a strong decrease in blood pressure;
☛ with Digoxin, a significant increase in its concentration in the blood plasma;
☛ Indomethacin may decrease the efficacy of Prazosin;
☛ simultaneous application with clonidine leads to a change in the antihypertensive effect of the latter.
Should be stored in places protected from moisture and light rays, at temperatures below +25 ° C, out of children’s reach.
The drug should not be used after 3 years from the date of release.