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Active ingredient: Doxazosin - Brands, Medical Use, Clinical Data

Brands, Medical Use, Clinical Data

Drug Category

  • Vasodilator Agents
  • Antihypertensive Agents
  • Anticholesteremic Agents
  • Alpha-adrenergic Blocking Agents

Dosage Forms

  • Tablet (oral)

Brands / Synonyms

Alfadil; Cardenalin; Cardular; Cardura; Cardura XL; Cardura-1; Cardura-2; Cardura-4; Carduran; Diblocin; Doxazosin mesylate; Normothen; Supressin

Indications

For treatment and management of Hypertension and urinary obstruction symptoms of BPH.

Pharmacology

Doxazosin is an alpha-adrenergic blocking agent used to treat hypertension and benign prostatic hyperplasia. Accordingly, Doxazosin is a selective inhibitor of the alpha1 subtype of alpha adrenergic receptors. In the human prostate, Doxazosin antagonizes phenylephrine (alpha1 agonist)-induced contractions, in vitro, and binds with high affinity to the alpha1c adrenoceptor, which is thought to be the predominant functional type in the prostate. Studies in normal human subjects have shown that Doxazosin competitively antagonized the pressor effects of phenylephrine (an alpha1 agonist) and the systolic pressor effect of norepinephrine. The antihypertensive effect of Doxazosin results from a decrease in systemic vascular resistance and the parent compound Doxazosin is primarily responsible for the antihypertensive activity.

Mechanism of Action

Doxazosin acts by inhibiting the postsynaptic alpha(1)-adrenoceptors on vascular smooth muscle. This inhibits the vasoconstrictor effect of circulating and locally released catecholamines (epinephrine and norepinephrine), resulting in peripheral vasodilation.

Absorption

65%

Toxicity

Symptoms of overdose include hypotension. Oral LD50 is greater than 1000 mg/kg in mice and rats.

Biotrnasformation / Drug Metabolism

Hepatic.

Contraindications

Doxazosin mesylate is contraindicated in patients with a known sensitivity to quinazolines (e.g., prazosin, terazosin) or any of the inert ingredients.

Drug Interactions

Most (98%) of plasma doxazosin is protein bound. In vitro data in human plasma indicate that doxazosin mesylate has no effect on protein binding of digoxin, warfarin, phenytoin or indomethacin. There is no information on the effect of other highly plasma protein bound drugs on doxazosin binding. Doxazosin mesylate has been administered without any evidence of an adverse drug interaction to patients receiving thiazide diuretics, beta-blocking agents, and nonsteroidal anti-inflammatory drugs. In a placebo-controlled trial in normal volunteers, the administration of a single 1 mg dose of doxazosin on day 1 of a four-day regimen of oral cimetidine (400 mg twice daily) resulted in a 10% increase in mean AUC of doxazosin (p=0.006), and a slight but not statistically significant increase in mean Cmax and mean half-life of doxazosin. The clinical significance of this increase in doxazosin AUC is unknown.

In clinical trials, doxazosin mesylate tablets have been administered to patients on a variety of concomitant medications; while no formal interaction studies have been conducted, no interactions were observed. Doxazosin mesylate tablets have been used with the following drugs or drug classes:

1. Analgesic/anti-inflammatory (e.g., acetaminophen, aspirin, codeine and codeine combinations, ibuprofen, indomethacin).

2. Antibiotics (e.g., erythromycin, trimethoprim and sulfamethoxazole, amoxicillin).

3. Antihistamines (e.g., chlorpheniramine).

4. Cardiovascular agents (e.g., atenolol, hydrochlorothiazide, propranolol).

5. Corticosteroids.

6. Gastrointestinal agents (e.g., antacids).

7. Hypoglycemics and endocrine drugs.

8. Sedatives and tranquilizers (e.g., diazepam).

9. Cold and flu remedies.

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