ADVERSE REACTIONS

Benign Prostatic Hyperplasia

The incidence of adverse events has been ascertained from worldwide clinical trials in 965 BPH patients. The incidence rates presented below (Table 3) are based on combined data from seven placebo-controlled trials involving once daily administration of doxazosin in doses of 1 to 16 mg in hypertensives and 0.5 to 8 mg in normotensives. The adverse events when the incidence in the doxazosin group was at least 1% are summarized in Table 3. No significant difference in the incidence of adverse events compared to placebo was seen except for dizziness, fatigue, hypotension, edema and dyspnea. Dizziness and dyspnea appeared to be dose-related.

TABLE 3 ADVERSE REACTIONS DURING PLACEBO-CONTROLLED STUDIES

BENIGN PROSTATIC HYPERPLASIA
Body System	DOXAZOSIN (N=665)	PLACEBO (N=300)
BODY AS A WHOLE
Back pain	1.8%	2.0%
Chest Pain	1.2%	0.7%
Fatigue	8.0%*	1.7%
Headache	9.9%	9.0%
Influenza-like symptoms	1.1%	1.0%
Pain	2.0%	1.0%
CARDIOVASCULAR SYSTEM
Hypotension	1.7%*	0.0%
Palpitation	1.2%	0.3%
DIGESTIVE SYSTEM
Abdominal Pain	2.4%	2.0%
Diarrhea	2.3%	2.0%
Dyspepsia	1.7%	1.7%
Nausea	1.5%	0.7%
METABOLIC AND NUTRITIONAL DISORDERS
Edema	2.7%*	0.7%
NERVOUS SYSTEM
Dizziness†	15.6%*	9.0%
Mouth Dry	1.4%	0.3%
Somnolence	3.0%	1.0%
RESPIRATORY SYSTEM
Dyspnea	2.6%*	0.3%
Respiratory Disorder	1.1%	0.7%
SPECIAL SENSES
Vision Abnormal	1.4%	0.7%
UROGENITAL SYSTEM
Impotence	1.1%	1.0%
Urinary Tract Infection	1.4%	2.3%
SKIN & APPENDAGES
Sweating Increased	1.1%	1.0%
PSYCHIATRIC DISORDERS
Anxiety	1.1%	0.3%
Insomnia	1.2%	0.3%

*p < 0.05 for treatment differences†Includes vertigo

In these placebo-controlled studies of 665 doxazosin patients, treated for a mean of 85 days, additional adverse reactions have been reported. These are less than 1% and not distinguishable from those that occurred in the placebo group. Adverse reactions with an incidence of less than 1% but of clinical interest are (doxazosin vs. placebo): Cardiovascular System: angina pectoris (0.6% vs. 0.7%), postural hypotension (0.3% vs. 0.3%), syncope (0.5% vs. 0.0%), tachycardia (0.9% vs. 0.0%); Urogenital System: dysuria (0.5% vs. 1.3%), and Psychiatric Disorders: libido decreased (0.8% vs. 0.3%). The safety profile in patients treated for up to three years was similar to that in the placebo-controlled studies.

The majority of adverse experiences with doxazosin were mild.

Hypertension

Doxazosin mesylate has been administered to approximately 4,000 hypertensive patients, of whom 1,679 were included in the hypertension clinical development program. In that program, minor adverse effects were frequent, but led to discontinuation of treatment in only 7% of patients. In placebo-controlled studies adverse effects occurred in 49% and 40% of patients in the doxazosin and placebo groups, respectively, and led to discontinuation in 2% of patients in each group. The major reasons for discontinuation were postural effects (2%), edema, malaise/fatigue, and some heart rate disturbance, each about 0.7%.

In controlled hypertension clinical trials directly comparing doxazosin to placebo there was no significant difference in the incidence of side effects, except for dizziness (including postural), weight gain, somnolence and fatigue/malaise. Postural effects and edema appeared to be dose related. The prevalence rates presented below are based on combined data from placebo- controlled studies involving once daily administration of doxazosin at doses ranging from 1 to 16 mg. Table 4 summarizes those adverse experiences (possibly/probably related) reported for patients in these hypertension studies where the prevalence rate in the doxazosin group was at least 0.5% or where the reaction is of particular interest.

TABLE 4 ADVERSE REACTIONS DURING PLACEBO-CONTROLLED STUDIES

	HYPERTENSION
	DOXAZOSIN (N=339)	PLACEBO (N=336)
CARDIOVASCULAR SYSTEM
Dizziness	19%	9%
Vertigo	2%	1%
Postural Hypotension	0.3%	0%
Edema	4%	3%
Palpitation	2%	3%
Arrhythmia	1%	0%
Hypotension	1%	0%
Tachycardia	0.3%	1%
Peripheral Ischemia	0.3%	0%
SKIN & APPENDAGES
Rash	1%	1%
Pruritus	1%	1%
MUSCULOSKELETAL SYSTEM
Arthralgia/Arthritis	1%	0%
Muscle Weakness	1%	0%
Myalgia	1%	0%
CENTRAL & PERIPHERAL N.S.
Headache	14%	16%
Paresthesia	1%	1%
Kinetic Disorders	1%	0%
Ataxia	1%	0%
Hypertonia	1%	0%
Muscle Cramps	1%	0%
AUTONOMIC
Mouth Dry	2%	2%
Flushing	1%	0%
SPECIAL SENSES
Vision Abnormal	2%	1%
Conjunctivitis/Eye Pain	1%	1%
Tinnitus	1%	0.3%
PSYCHIATRIC
Somnolence	5%	1%
Nervousness	2%	2%
Depression	1%	1%
Insomnia	1%	1%
Sexual Dysfunction	2%	1%
GASTROINTESTINAL
Nausea	3%	4%
Diarrhea	2%	3%
Constipation	1%	1%
Dyspepsia	1%	1%
Flatulence	1%	1%
Abdominal Pain	0%	2%
Vomiting	0%	1%
RESPIRATORY
Rhinitis	3%	1%
Dyspnea	1%	1%
Epistaxis	1%	0%
URINARY
Polyuria	2%	0%
Urinary Incontinence	1%	0%
Micturition Frequency	0%	2%
GENERAL
Fatigue/Malaise	12%	6%
Chest Pain	2%	2%
Asthenia	1%	1%
Face Edema	1%	0%
Pain	2%	2%

Additional adverse reactions have been reported, but these are, in general, not distinguishable from symptoms that might have occurred in the absence of exposure to doxazosin. The following adverse reactions occurred with a frequency of between 0.5% and 1%: syncope, hypoesthesia, increased sweating, agitation, increased weight. The following additional adverse reactions were reported by < 0.5% of 3,960 patients who received doxazosin in controlled or open, short- or long-term clinical studies, including international studies. Cardiovascular System: angina pectoris, myocardial infarction, cerebrovascular accident; Autonomic Nervous System: pallor; Metabolic: thirst, gout, hypokalemia; Hematopoietic: lymphadenopathy, purpura; Reproductive System: breast pain; Skin Disorders: alopecia, dry skin, eczema; Central Nervous System: paresis, tremor, twitching, confusion, migraine, impaired concentration; Psychiatric: paroniria, amnesia, emotional lability, abnormal thinking, depersonalization; Special Senses: parosmia, earache, taste perversion, photophobia, abnormal lacrimation; Gastrointestinal System: increased appetite, anorexia, fecal incontinence, gastroenteritis; Respiratory System: bronchospasm, sinusitis, coughing, pharyngitis; Urinary System: renal calculus; General Body System: hot flushes, back pain, infection, fever/rigors, decreased weight, influenza-like symptoms.

Doxazosin has not been associated with any clinically significant changes in routine biochemical tests. No clinically relevant adverse effects were noted on serum potassium, serum glucose, uric acid, blood urea nitrogen, creatinine or liver function tests. Doxazosin has been associated with decreases in white blood cell counts (see PRECAUTIONS).

In post-marketing experience the following additional adverse reactions have been reported: Autonomic Nervous System: priapism; Central Nervous System: hypoesthesia; Endocrine System: gynecomastia; Gastrointestinal System: vomiting; General Body System: allergic reaction; Heart Rate/Rhythm: bradycardia; Hematopoietic: leukopenia, thrombocytopenia; Liver/Biliary System: hepatitis, hepatitis cholestatic; Respiratory System: bronchospasm aggravated; Skin Disorders: urticaria; Special Senses: Intraoperative Floppy Iris syndrome (see PRECAUTIONS: General: Cataract Surgery); Urinary System: hematuria, micturition disorder, micturition frequency, nocturia.

1 mg, 2 mg, 4 mg and 8 mg1

Rx only

1** (Each****tablet contains doxazosin mesylate equivalent to 1 mg, 2 mg, 4 mg or 8 mg of doxazosin)**

PRECAUTIONS

GeneralProstate Cancer

Carcinoma of the prostate causes many of the symptoms associated with BPH and the two disorders frequently co-exist. Carcinoma of the prostate should therefore be ruled out prior to commencing therapy with doxazosin.

Cataract Surgery

Intraoperative Floppy Iris Syndrome (IFIS) has been observed during cataract surgery in some patients on or previously treated with alpha1 blockers. This variant of small pupil syndrome is characterized by the combination of a flaccid iris that billows in response to intraoperative irrigation currents, progressive intraoperative miosis despite preoperative dilation with standard mydriatic drugs, and potential prolapse of the iris toward the phacoemulsification incisions. The patient's surgeon should be prepared for possible modifications to their surgical technique, such as the utilization of iris hooks, iris dilator rings, or viscoelastic substances. There does not appear to be a benefit of stopping alpha1 blocker therapy prior to cataract surgery.

Orthostatic Hypotension

While syncope is the most severe orthostatic effect of doxazosin, other symptoms of lowered blood pressure, such as dizziness, lightheadedness, or vertigo can occur, especially at initiation of therapy or at the time of dose increases.

Hypertension

These symptoms were common in clinical trials in hypertension, occurring in up to 23% of all patients treated and causing discontinuation of therapy in about 2%.

In placebo-controlled titration trials in hypertension, orthostatic effects were minimized by beginning therapy at 1 mg per day and titrating every two weeks to 2, 4, or 8 mg per day. There was an increased frequency of orthostatic effects in patients given 8 mg or more, 10%, compared to 5% at 1 to 4 mg and 3% in the placebo group.

Benign Prostatic Hyperplasia

In placebo-controlled trials in BPH, the incidence of orthostatic hypotension with doxazosin was 0.3% and did not increase with increasing dosage (to 8 mg/day). The incidence of discontinuations due to hypotensive or orthostatic symptoms was 3.3% with doxazosin and 1% with placebo. The titration interval in these studies was one to two weeks.

Patients in occupations in which orthostatic hypotension could be dangerous should be treated with particular caution. As alpha1 antagonists can cause orthostatic effects, it is important to evaluate standing blood pressure two minutes after standing and patients should be advised to exercise care when arising from a supine or sitting position.

If hypotension occurs, the patient should be placed in the supine position and, if this measure is inadequate, volume expansion with intravenous fluids or vasopressor therapy may be used. A transient hypotensive response is not a contraindication to further doses of doxazosin.

Information for Patients

(SeePatient Leaflet)

Patients should be made aware of the possibility of syncopal and orthostatic symptoms, especially at the initiation of therapy, and urged to avoid driving or hazardous tasks for 24 hours after the first dose, after a dosage increase, and after interruption of therapy when treatment is resumed. They should be cautioned to avoid situations where injury could result should syncope occur during initiation of doxazosin therapy. They should also be advised of the need to sit or lie down when symptoms of lowered blood pressure occur, although these symptoms are not always orthostatic, and to be careful when rising from a sitting or lying position. If dizziness, lightheadedness, or palpitations are bothersome they should be reported to the physician, so that dose adjustment can be considered. Patients should also be told that drowsiness or somnolence can occur with doxazosin or any selective alpha1 adrenoceptor antagonist, requiring caution in people who must drive or operate heavy machinery.

Patients should be advised about the possibility of priapism as a result of treatment with alpha1 antagonists. Patients should know that this adverse event is very rare. If they experience priapism, it should be brought to immediate medical attention for if not treated promptly it can lead to permanent erectile dysfunction (impotence).

Drug/Laboratory Test Interactions

Doxazosin does not affect the plasma concentration of prostate specific antigen in patients treated for up to 3 years. Both doxazosin, an alpha1 inhibitor, and finasteride, a 5-alpha reductase inhibitor, are highly protein bound and hepatically metabolized. There is no definitive controlled clinical experience on the concomitant use of alpha1 inhibitors and 5-alpha reductase inhibitors at this time.

Impaired Liver Function

Doxazosin should be administered with caution to patients with evidence of impaired hepatic function or to patients receiving drugs known to influence hepatic metabolism (see CLINICAL PHARMACOLOGY).

Leukopenia/Neutropenia

Analysis of hematologic data from hypertensive patients receiving doxazosin in controlled hypertension clinical trials showed that the mean WBC (N = 474) and mean neutrophil counts (N = 419) were decreased by 2.4% and 1%, respectively, compared to placebo, a phenomenon seen with other alpha blocking drugs. In BPH patients the incidence of clinically significant WBC abnormalities was 0.4% (2/459) with doxazosin and 0% (0/147) with placebo, with no statistically significant difference between the two treatment groups. A search through a data base of 2,400 hypertensive patients and 665 BPH patients revealed 4 hypertensives in which drug-related neutropenia could not be ruled out and one BPH patient in which drug-related leukopenia could not be ruled out. Two hypertensives had a single low value on the last day of treatment. Two hypertensives had stable, non-progressive neutrophil counts in the 1000/mm3 range over periods of 20 and 40 weeks. One BPH patient had a decrease from WBC count of 4800/mm3 to 2700/mm3 at the end of the study; there was no evidence of clinical impairment. In cases where follow-up was available the WBCs and neutrophil counts returned to normal after discontinuation of doxazosin. No patients became symptomatic as a result of the low WBC or neutrophil counts.

Drug Interactions

Most (98%) of plasma doxazosin is protein bound. In vitro data in human plasma indicate that doxazosin 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 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 4-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 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 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.

Cardiac Toxicity in Animals

An increased incidence of myocardial necrosis or fibrosis was displayed by Sprague-Dawley rats after 6 months of dietary administration at concentrations calculated to provide 80 mg doxazosin/kg/day and after 12 months of dietary administration at concentrations calculated to provide 40 mg doxazosin/kg/day (AUC exposure in rats 8 times the human AUC exposure with a 12 mg/day therapeutic dose). Myocardial fibrosis was observed in both rats and mice treated in the same manner with 40 mg doxazosin/kg/day for 18 months (exposure 8 times human AUC exposure in rats and somewhat equivalent to human Cmax exposure in mice). No cardiotoxicity was observed at lower doses (up to 10 or 20 mg/kg/day, depending on the study) in either species. These lesions were not observed after 12 months of oral dosing in dogs at maximum doses of 20 mg/kg/day [maximum plasma concentrations (Cmax) in dogs 14 times the Cmax exposure in humans receiving a 12 mg/day therapeutic dose] and in Wistar rats at doses of 100 mg/kg/day (Cmax exposures 15 times human Cmax exposure with a 12 mg/day therapeutic dose). There is no evidence that similar lesions occur in humans.

Carcinogenesis, Mutagenesis, Impairment of Fertility

Chronic dietary administration (up to 24 months) of doxazosin mesylate at maximally tolerated doses of 40 mg/kg/day in rats and 120 mg/kg/day in mice revealed no evidence of carcinogenic potential. The highest doses evaluated in the rat and mouse studies are associated with AUCs (a measure of systemic exposure) that are 8 times and 4 times, respectively, the human AUC at a dose of 16 mg/day.

Mutagenicity studies revealed no drug- or metabolite-related effects at either chromosomal or subchromosomal levels.

Studies in rats showed reduced fertility in males treated with doxazosin at oral doses of 20 (but not 5 or 10) mg/kg/day, about 4 times the AUC exposures obtained with a 12 mg/day human dose. This effect was reversible within two weeks of drug withdrawal. There have been no reports of any effects of doxazosin on male fertility in humans.

PregnancyTeratogenic EffectsPregnancy Category C

Studies in pregnant rabbits and rats at daily oral doses of up to 41 and 20 mg/kg, respectively (plasma drug concentrations 10 and 4 times human Cmax and AUC exposures with a 12 mg/day therapeutic dose), have revealed no evidence of harm to the fetus. A dosage regimen of 82 mg/kg/day in the rabbit was associated with reduced fetal survival. There are no adequate and well- controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, doxazosin should be used during pregnancy only if clearly needed.

Radioactivity was found to cross the placenta following oral administration of labeled doxazosin to pregnant rats.

Nonteratogenic Effects

In peri-postnatal studies in rats, postnatal development at maternal doses of 40 or 50 mg/kg/day of doxazosin (8 times human AUC exposure with a 12 mg/day therapeutic dose) was delayed as evidenced by slower body weight gain and a slightly later appearance of anatomical features and reflexes.

Nursing Mothers

Studies in lactating rats given a single oral dose of 1 mg/kg of [2-14C]-doxazosin indicate that doxazosin accumulates in rat breast milk with a maximum concentration about 20 times greater than the maternal plasma concentration. It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when doxazosin is administered to a nursing mother.

Pediatric Use

The safety and effectiveness of doxazosin as an antihypertensive agent have not been established in pediatric patients.

Geriatric Use

The safety and effectiveness profile of doxazosin in BPH was similar in the elderly (age > 65 years) and younger (age < 65 years) patients.

Clinical studies of doxazosin 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.