The following adverse reactions have been identified during post-approval use of doxazosin mesylate. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.
In post-marketing experience, the following additional adverse reactions have been reported:
Blood and Lymphatic System Disorders: leukopenia, thrombocytopenia;
Immune System Disorders: allergic reaction;
Nervous System Disorders: hypoesthesia;
Eye Disorders: Intraoperative Floppy Iris Syndrome [see Warnings and Precautions (5.4)] ;
Cardiac Disorders: bradycardia;
Respiratory, Thoracic and Mediastinal Disorders: bronchospasm aggravated;
Gastrointestinal Disorders: vomiting;
Hepatobiliary Disorders: cholestasis, hepatitis cholestatic;
Skin and Subcutaneous Tissue Disorders: urticaria;
Musculoskeletal and Connective Tissue Disorders: muscle cramps, muscle weakness;
Renal and Urinary Disorders: hematuria, micturition disorder, micturition frequency, nocturia;
Reproductive System and Breast Disorders: gynecomastia, priapism.
In vitro studies suggest that doxazosin is a substrate of CYP 3A4. Strong CYP3A inhibitors may increase exposure to doxazosin. Monitor blood pressure and for symptoms of hypotension when doxazosin mesylate is used concomitantly with strong CYP3A inhibitors [see Clinical Pharmacology (12.3)].
Concomitant administration of doxazosin mesylate with a phosphodiesterase-5 (PDE-5) inhibitor can result in additive blood pressure lowering effects and symptomatic hypotension. Monitor blood pressure and for symptoms of hypotension [see Warnings and Precautions (5.1)].
The limited available data with doxazosin mesylate in pregnant women are not sufficient to inform a drug-associated risk for major birth defects and miscarriage. However, untreated hypertension during pregnancy can result in increased maternal risks [see Clinical Considerations]. In animal reproduction studies, no adverse developmental effects were observed when doxazosin was orally administered to pregnant rabbits and rats during the period of organogenesis at doses of up to 41 and 20 mg/kg, respectively (exposures in rabbits and rats were 10 and 4 times, respectively, the human AUC exposures with a 12 mg/day therapeutic dose). A dosage regimen of 82 mg/kg/day in the rabbit was associated with reduced fetal survival [see Data].
The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2-4% and 15-20%, respectively.
Disease-associated maternal and/or embryo/fetal risk
Hypertension in pregnancy increases the maternal risk for pre-eclampsia, gestational diabetes, premature delivery, and delivery complications (e.g., need for cesarean section, and post-partum hemorrhage). Hypertension increases the fetal risk for intrauterine growth restriction and intrauterine death.
Radioactivity was found to cross the placenta following oral administration of labelled doxazosin to pregnant rats. Studies in pregnant rabbits and rats at daily oral doses of up to 41 and 20 mg/kg, respectively (plasma drug concentrations of 10 and 4 times, respectively, the human AUC exposures with a 12 mg/day therapeutic dose), have revealed no evidence of adverse developmental effects. A dosage regimen of 82 mg/kg/day in the rabbit was associated with reduced fetal survival. In peri- and postnatal studies in rats, postnatal development at maternal doses of 40 or 50 mg/kg/day of doxazosin (about 8 times human AUC exposure with a 12 mg/day therapeutic dose) was delayed, as evidenced by slower body weight gain and slightly later appearance of anatomical features and reflexes.
There is limited information on the presence of doxazosin mesylate in human milk [see Data]. There is no information on the effects of doxazosin mesylate on the breastfeed infant or the effects on milk production.
A single case study reports that doxazosin mesylate is present in human milk, which resulted in an infant dose of less than 1% of the maternal weight-adjusted dosage and a milk/plasma ratio of 0.1. However, these data are insufficient to confirm the presence of doxazosin mesylate in human milk.
The safety and effectiveness of doxazosin mesylate have not been established in children.
Benign Prostatic Hyperplasia (BPH)
The safety and effectiveness profile of doxazosin mesylate was similar in the elderly (age ≥ 65 years) and younger (age < 65 years) patients.
Hypertension Clinical studies of doxazosin mesylate did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients.
In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal or cardiac function, and of concomitant disease or other drug therapy.
Doxazosin mesylate is extensively metabolized in the liver. Hepatic impairment is expected to increase exposure to doxazosin. Use of doxazosin mesylate in patients with severe hepatic impairment (Child-Pugh Class C) is not recommended. Monitor blood pressure and for symptoms of hypotension in patients with lesser degrees of hepatic impairment (Child-Pugh Class A and B) [see Clinical Pharmacology (12.3)].
Experience with doxazosin mesylate overdosage is limited. Two adolescents, who each intentionally ingested 40 mg doxazosin mesylate tablets with diclofenac or acetaminophen, were treated with gastric lavage with activated charcoal and made full recoveries. A two-year-old child who accidently ingested 4 mg doxazosin mesylate was treated with gastric lavage and remained normotensive during the five-hour emergency room observation period. A six-month-old child accidentally received a crushed 1 mg tablet of doxazosin mesylate and was reported to have been drowsy. A 32-year-old female with chronic renal failure, epilepsy, and depression intentionally ingested 60 mg doxazosin mesylate (blood level = 0.9 mcg/mL; normal values in hypertensives = 0.02 mcg/mL); death was attributed to a grand mal seizure resulting from hypotension. A 39-year-old female who ingested 70 mg doxazosin mesylate, alcohol, and Dalmane® (flurazepam) developed hypotension which responded to fluid therapy.
The oral LD50 of doxazosin is greater than 1000 mg/kg in mice and rats. The most likely manifestation of overdosage would be hypotension, for which the usual treatment would be intravenous infusion of fluid. As doxazosin is highly protein bound, dialysis would not be indicated.
Doxazosin mesylate is a quinazoline compound that is a selective inhibitor of the alpha1 subtype of alpha-adrenergic receptors. The chemical name of doxazosin mesylate is 1-(4-amino-6,7-dimethoxy-2-quinazolinyl)-4-(1,4 benzodioxan-2-ylcarbonyl) piperazine methanesulfonate. The empirical formula for doxazosin mesylate is C23 H25 N5 O5 • CH4 O3 S and the molecular weight is 547.6. It has the following structure:
Doxazosin mesylate is freely soluble in dimethylsulfoxide, soluble in dimethylformamide, slightly soluble in methanol, ethanol, and water (0.8% at 25°C), and very slightly soluble in acetone and methylene chloride. Doxazosin mesylate is available as colored tablets for oral use and contains 1 mg (white), 2 mg (yellow), 4 mg (orange) and 8 mg (green) of doxazosin as the free base.
The inactive ingredients for all tablets are: microcrystalline cellulose, NF; lactose, NF; sodium starch glycolate, NF; magnesium stearate, NF and sodium lauryl sulfate, NF. The 2 mg tablet contains D&C yellow #10 Aluminum Lake and FD&C yellow #6 Aluminum Lake; the 4 mg tablet contains FD&C yellow #6 Aluminum Lake; the 8 mg tablet contains FD&C blue #2 Aluminum Lake and D&C yellow #10 Aluminum Lake.
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