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Doxazosin
Overview
What is Doxazosin?
Doxazosin mesylate is a quinazoline compound that is a selective inhibitor of the alpha 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 molecular formula for doxazosin mesylate is CHNO • CHOS 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 Tablets, USP for oral administration, contain 1 mg, 2 mg, 4 mg or 8 mg of doxazosin as doxazosin mesylate. In addition, each tablet also contains the following inactive ingredients: anhydrous lactose, colloidal silicon, magnesium stearate, microcrystalline cellulose, sodium lauryl sulfate and sodium starch glycolate. The 2 mg tablets also contain D&C Red No. 30 Aluminum Lake, the 4 mg tablets contain FD&C Blue No. 2 Aluminum Lake, and the 8 mg tablets contain D&C Red No. 30 Aluminum Lake and FD&C Blue No. 2 Aluminum Lake.
What does Doxazosin look like?
What are the available doses of Doxazosin?
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What should I talk to my health care provider before I take Doxazosin?
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How should I use Doxazosin?
Doxazosin tablets are indicated for the treatment of both the urinary outflow obstruction and obstructive and irritative symptoms associated with BPH: obstructive symptoms (hesitation, intermittency, dribbling, weak urinary stream, incomplete emptying of the bladder) and irritative symptoms (nocturia, daytime frequency, urgency, burning). Doxazosin may be used in all BPH patients whether hypertensive or normotensive. In patients with hypertension and BPH, both conditions were effectively treated with doxazosin monotherapy. Doxazosin provides rapid improvement in symptoms and urinary flow rate in 66 to 71% of patients. Sustained improvements with doxazosin were seen in patients treated for up to 14 weeks in double-blind studies and up to 2 years in open-label studies.
DOSAGE MUST BE INDIVIDUALIZED.
What interacts with Doxazosin?
Doxazosin tablets are contraindicated in patients with a known sensitivity to quinazolines (e.g., prazosin, terazosin), doxazosin, or any of the inert ingredients.
What are the warnings of Doxazosin?
Syncope and "First-dose" Effect
Doxazosin, like other alpha-adrenergic blocking agents, can cause marked hypotension, especially in the upright position, with syncope and other postural symptoms such as dizziness. Marked orthostatic effects are most common with the first dose but can also occur when there is a dosage increase, or if therapy is interrupted for more than a few days. To decrease the likelihood of excessive hypotension and syncope, it is essential that treatment be initiated with the 1 mg dose. The 2, 4, and 8 mg tablets are not for initial therapy. Dosage should then be adjusted slowly (see section) with evaluations and increases in dose every two weeks to the recommended dose. Additional antihypertensive agents should be added with caution.
Patients being titrated with doxazosin should be cautioned to avoid situations where injury could result should syncope occur, during both the day and night.
In an early investigational study of the safety and tolerance of increasing daily doses of doxazosin in normotensives beginning at 1 mg/day, only 2 of 6 subjects could tolerate more than 2 mg/day without experiencing symptomatic postural hypotension. In another study of 24 healthy normotensive male subjects receiving initial doses of 2 mg/day of doxazosin, seven (29%) of the subjects experienced symptomatic postural hypotension between 0.5 and 6 hours after the first dose necessitating termination of the study. In this study, 2 of the normotensive subjects experienced syncope. Subsequent trials in hypertensive patients always began doxazosin dosing at 1 mg/day resulting in a 4% incidence of postural side effects at 1 mg/day with no cases of syncope.
In multiple dose clinical trials in hypertension involving over 1,500 hypertensive patients with dose titration every one to two weeks, syncope was reported in 0.7% of patients. None of these events occurred at the starting dose of 1 mg and 1.2% (8/664) occurred at 16 mg/day.
In placebo-controlled, clinical trials in BPH, 3 out of 665 patients (0.5%) taking doxazosin reported syncope. Two of the patients were taking 1 mg doxazosin, while one patient was taking 2 mg doxazosin when syncope occurred. In the open-label, long-term extension follow-up of approximately 450 BPH patients, there were 3 reports of syncope (0.7%). One patient was taking 2 mg, one patient was taking 8 mg and one patient was taking 12 mg when syncope occurred. In a clinical pharmacology study, one subject receiving 2 mg experienced syncope.
If syncope occurs, the patient should be placed in a recumbent position and treated supportively as necessary.
Priapism
Rarely (probably less frequently than once in every several thousand patients), alpha antagonists, including doxazosin, have been associated with priapism (painful penile erection, sustained for hours and unrelieved by sexual intercourse or masturbation). Because this condition can lead to permanent impotence if not promptly treated, patients must be advised about the seriousness of the condition (see ).
What are the precautions of Doxazosin?
General
Prostate 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 alpha 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 alpha 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 alpha 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
(See )
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 alpha 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 alpha 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 alpha 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 alpha 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 ).
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/mm range over periods of 20 and 40 weeks. One BPH patient had a decrease from WBC count of 4800/mm to 2700/mm 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. 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 C 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 C 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 (C) in dogs 14 times the C exposure in humans receiving a 12 mg/day therapeutic dose] and in Wistar rats at doses of 100 mg/kg/day (C exposures 15 times human C 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.
Pregnancy
Teratogenic Effects
Pregnancy 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 C 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-C]-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.
What are the side effects of Doxazosin?
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.
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): 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%); dysuria (0.5% vs. 1.3%), and 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.
| 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% |
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.
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. angina pectoris, myocardial infarction, cerebrovascular accident; pallor; thirst, gout, hypokalemia; lymphadenopathy, purpura; breast pain; alopecia, dry skin, eczema; paresis, tremor, twitching, confusion, migraine, impaired concentration; paroniria, amnesia, emotional lability, abnormal thinking, depersonalization; parosmia, earache, taste perversion, photophobia, abnormal lacrimation; increased appetite, anorexia, fecal incontinence, gastroenteritis; bronchospasm, sinusitis, coughing, pharyngitis; renal calculus; 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 ).
In post-marketing experience the following additional adverse reactions have been reported: priapism; hypoesthesia; gynecomastia; vomiting; allergic reaction; bradycardia; leukopenia, thrombocytopenia; hepatitis, hepatitis cholestatic; bronchospasm aggravated; urticaria; Intraoperative Floppy Iris syndrome (see ); hematuria, micturition disorder, micturition frequency, nocturia.
| 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% |
What should I look out for while using Doxazosin?
Doxazosin tablets are contraindicated in patients with a known sensitivity to quinazolines (e.g., prazosin, terazosin), doxazosin, or any of the inert ingredients.
What might happen if I take too much Doxazosin?
Experience with doxazosin overdosage is limited. Two adolescents who each intentionally ingested 40 mg doxazosin with diclofenac or acetaminophen, were treated with gastric lavage with activated charcoal and made full recoveries. A two-year-old child who accidentally ingested 4 mg doxazosin 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 and was reported to have been drowsy. A 32-year-old female with chronic renal failure, epilepsy and depression intentionally ingested 60 mg doxazosin (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, alcohol and flurazepam developed hypotension which responded to fluid therapy.
The oral LD 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.
How should I store and handle Doxazosin?
Store at 20° to 25ºC (68° to 77°F).[See USP Controlled Room Temperature]Dispense in a tight container as defined in the USP.Store at 20° to 25ºC (68° to 77°F).[See USP Controlled Room Temperature]Dispense in a tight container as defined in the USP.Store at 20° to 25ºC (68° to 77°F).[See USP Controlled Room Temperature]Dispense in a tight container as defined in the USP.Doxazosin Tablets, USP are available as tablets for oral administration. Each tablet contains doxazosin mesylate equivalent to 1 mg, 2 mg, 4 mg or 8 mg of doxazosin.They are supplied by as follows:Doxazosin Tablets, USP are available as tablets for oral administration. Each tablet contains doxazosin mesylate equivalent to 1 mg, 2 mg, 4 mg or 8 mg of doxazosin.They are supplied by as follows:
Clinical Information
Chemical Structure
No Image foundClinical Pharmacology
Non-Clinical Toxicology
Doxazosin tablets are contraindicated in patients with a known sensitivity to quinazolines (e.g., prazosin, terazosin), doxazosin, or any of the inert ingredients.Most (98%) of plasma doxazosin is protein bound. 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 C 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.
Reference
This information is obtained from the National Institute of Health's Standard Packaging Label drug database.
"https://dailymed.nlm.nih.gov/dailymed/"
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