(dox ay' zoe sin)
P : Caution when used during pregnancy
L : Caution when used during lactation
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Doxazosin is indicated for the treatment of hypertension and can be used as the sole agent to control blood pressure in the majority of patients. In patients inadequately controlled on single antihypertensive therapy, Doxazosin may be used in combination with a thiazide diuretic, beta-adrenoceptor blocking agent, calcium antagonist or an angiotensin-converting enzyme inhibitor.
Benign prostatic hyperplasia: Doxazosin is indicated for the treatment of urinary outflow obstruction and symptoms associated with benign prostatic hyperplasia (BPH). Doxazosin may be used in BPH patients who are either hypertensive or normotensive.
Dosage & Administration
Doxazosin may be administered in the morning or the evening.
Hypertension: Doxazosin is used in a once daily regimen: the initial dose is 1mg, to minimise the potential for postural hypotension and/or syncope. Dosage may then be increased to 2mg after an additional one or two weeks of therapy and thereafter, if necessary to 4mg. The majority of patients who respond to Doxazosin will do so at a dose of 4mg or less. Dosage can be further increased if necessary to 8mg or the maximum recommended dose of 16mg.
Benign prostatic hyperplasia: The recommended initial dosage of Doxazosin is 1mg given once daily to minimise the potential for postural hypotension and/or syncope (see section 4.4). Depending on the individual patient's urodynamics and BPH symptomatology dosage may then be increased to 2mg and thereafter to 4mg and up to the maximum recommended dose of 8mg. The recommended titration interval is 1-2 weeks. The usual recommended dose is 2-4mg daily.
Children: The safety and efficacy of Doxazosin in children have not been established.
Elderly: Normal adult dosage.
Patients with renal impairment: Since there is no change in pharmacokinetics in patients with impaired renal function, the usual adult dose of Doxazosin is recommended.
Doxazosin is not dialysable.
Patients with hepatic impairment: There are only limited data in patients with liver impairment and on the effect of drugs known to influence hepatic metabolism (e.g. cimetidine). As with any drug wholly metabolised by the liver, Doxazosin should be administered with caution to patients with evidence of impaired liver function
Should overdosage lead to hypotension, the patient should be immediately placed in a supine, head down position. Other supportive measures may be appropriate in individual cases.
If this measure is inadequate, shock should first be treated with volume expanders. If necessary, vasopressor should then be used. Renal function should be monitored and supported as needed.
Since Doxazosin is highly protein bound, dialysis is not indicated.
Doxazosin is contraindicated in:
1) Patients with a known hypersensitivity to quinazolines (e.g. prazosin, terazosin, doxazosin), or any of the excipients
2) Patients with a history of orthostatic hypotension
3) Patients with benign prostatic hyperplasia and concomitant congestion of the upper urinary tract, chronic urinary tract infection or bladder stones.
4) During lactation (for the hypertension indication only, see section 4.6: Fertility, pregnancy and lactation)
5) Patients with hypotension (for benign prostatic hyperplasia indication only)
Doxazosin is contraindicated as monotherapy in patients with either overflow bladder or anuria with or without progressive renal insufficiency.
Initiation of Therapy - In relation with the alpha-blocking properties of doxazosin, patients may experience postural hypotension evidenced by dizziness and weakness, or rarely loss of consciousness (syncope), particularly with the commencement of therapy (see section 4.2: Posology and method of administration). Therefore, it is prudent medical practice to monitor blood pressure on initiation of therapy to minimise the potential for postural effects.
When instituting therapy with any effective alpha-blocker, the patient should be advised how to avoid symptoms resulting from postural hypotension and what measures to take should they develop. The patient should be cautioned to avoid situations where injury could result, should dizziness or weakness occur during the initiation of Doxazosin therapy.
Use in patients with Acute Cardiac Conditions:
As with any other vasodilatory anti-hypertensive agent it is prudent medical practice to advise caution when administering doxazosin to patients with the following acute cardiac conditions:
- pulmonary oedema due to aortic or mitral stenosis
- high-output cardiac failure
- right-sided heart failure due to pulmonary embolism or pericardial effusion
- left ventricular heart failure with low filling pressure.
Use in Hepatically Impaired patients:
As with any drug wholly metabolised by the liver, Doxazosin should be administered with particular caution to patients with evidence of impaired hepatic function (see section 4.2: Posology and method of administration). Since there is no clinical experience in patients with severe hepatic impairment use in these patients is not recommended.
Use with PDE-5 Inhibitors:
Concomitant administration of doxazosin with phosphodiesterase-5-inhibitors (eg sildenafil, tadalafil, and vardenafil) should be done with caution as both drugs have vasodilating effects and may lead to symptomatic hypotension in some patients. To reduce the risk of orthostatic hypotension it is recommended to initiate the treatment with phosphodiesterase-5-inhibitors only if the patient is hemodynamically stabilized on alpha-blocker therapy. Furthermore, it is recommended to initiate phosphodiesterase-5-inhibitor treatment with the lowest possible dose and to respect a 6-hour time interval from intake of doxazosin. No studies have been conducted with doxazosin prolonged release formulations.
Use in patients undergoing cataract surgery:
The 'Intraoperative Floppy Iris Syndrome' (IFIS, a variant of small pupil syndrome) has been observed during cataract surgery in some patients on or previously treated with tamsulosin. Isolated reports have also been received with other alpha-1 blockers and the possibility of a class effect cannot be excluded. As IFIS may lead to increased procedural complications during the cataract operation current or past use of alpha-1 blockers should be made known to the ophthalmic surgeon in advance of surgery.
Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medicine.
Chest pain, fatigue, headache, influenza-like symptoms, pain, hypotension, palpitation, abdominal pain, diarrhoea, nausea, oedema, dizziness, dry mouth, somnolence, dyspnoea, respiratory disorders, vision abnormalities, impotence, urinary tract infection, increased sweating, anxiety, insomnia. Vertigo, orthostatic hypotension, arrhythmia, hypotension, arthralgia/arthritis, muscle weakness, myalgia, kinetic disorders, ataxia, hypertonia, muscle cramps, flushing, tinnitus, sexual dysfunction, rhinitis, epistaxis, polyuria, urinary incontinence, fatigue/malaise, face oedema.
Decreased hypotensive effect with NSAIDs. Increased hypotensive effect with alpha-blockers, diuretics, ACE inhibitors, calcium-channel blockers.
Pregnancy Category (US FDA)
Use during pregnancy: As there are no adequate and well-controlled studies in pregnant women, the safety of Doxazosin during pregnancy has not yet been established. Accordingly, during pregnancy, Doxazosin should be used only when, in the opinion of the physician, the potential benefit outweighs the potential risk. Although no teratogenic effects were seen in animal testing, reduced foetal survival was observed in animals at extremely high doses. These doses were approximately 300 times the maximum recommended human dose.
Use during lactation:
Doxazosin is contraindicated during lactation as animal studies have shown that doxazosin accumulates in milk of lactating rats, and there is no information about the excretion of the drug into the milk of lactating women. The clinical safety of Doxazosin during lactation has not been established, consequently Doxazosin is contra-indicated in nursing mothers.
Use during breast-feeding: Alternatively, mothers should stop breast-feeding when treatment with doxazosin is necessary
Mechanism of Action
Doxazosin is a potent and selective post-junctional alpha-1-adrenoceptor antagonist. This action results in a decrease in systemic blood pressure. Doxazosin is appropriate for oral administration in a once daily regimen in patients with essential hypertension.
Doxazosin has been shown to be free of adverse metabolic effects and is suitable for use in patients with coexistent diabetes mellitus, gout and insulin resistance.
Doxazosin is suitable for use in patients with co-existent asthma, left ventricular hypertrophy and in elderly patients. Treatment with Doxazosin has been shown to result in regression of left ventricular hypertrophy, inhibition of platelet aggregation and enhanced activity of tissue plasminogen activator. Additionally, Doxazosin improves insulin sensitivity in patients with impairment.
Doxazosin, in addition to its antihypertensive effect, has in long term studies produced a modest reduction in plasma total cholesterol, LDL-cholesterol and triglyceride concentrations and therefore may be of particular benefit to hypertensive patients with concomitant hyperlipidaemia.
Administration of Doxazosin to patients with symptomatic BPH results in a significant improvement in urodynamics and symptoms. The effect in BPH is thought to result from selective blockade of the alpha-adrenoceptors located in the muscular stroma and capsule of the prostate, and in the bladder neck.
Absorption: Following oral administration in humans (young male adults or the elderly of either sex), doxazosin is well absorbed and approximately two thirds of the dose is bioavailable.
Biotransformation/Elimination: Approximately 98% of doxazosin is protein-bound in plasma.
Doxazosin is extensively metabolised in man and in the animal species tested, with the faeces being the predominant route of excretion.
The mean plasma elimination half-life is 22 hours thus making the drug suitable for once daily administration.
After oral administration of Doxazosin the plasma concentrations of the metabolites are low. The most active (6' hydroxy) metabolite is present in man at one fortieth of the plasma concentration of the parent compound, which suggests that the antihypertensive activity is in the main due to doxazosin.
There are only limited data in patients with liver impairment and on the effects of drugs known to influence hepatic metabolism (e.g. cimetidine). In a clinical study in 12 subjects with moderate hepatic impairment, single dose administration of doxazosin resulted in an increase in AUC of 43% and a decrease in apparent oral clearance of 40%. As with any drug wholly metabolised by the liver, Doxazosin should be administered with caution to patients with impaired liver function.
C02CA04 - doxazosin; Belongs to the class of alpha-adrenoreceptor antagonists, peripherally-acting antiadrenergic agents. Used in the treatment of hypertension.
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Why Doxazosin is prescribed?
Doxazosin is used in men to treat the symptoms of an enlarged prostate, which include difficulty urinating, painful urination, and urinary frequency and urgency. Doxazosin is also used alone or in combination with other medications to treat high blood pressure. Doxazosin is in a class of medications called alpha-blockers. It relieves the symptoms of BPH by relaxing the muscles of the bladder and prostate. It lowers blood pressure by relaxing the blood vessels so that blood can flow more easily through the body.
How should Doxazosin be used?
Doxazosin comes as a tablet and an extended-release tablet to take by mouth. The doxazosin tablet is usually taken with or without food once a day in the morning or in the evening. The doxazosin extended-release tablet is usually taken once a day with breakfast. To help you remember to take doxazosin, take it around the same time every day. Follow the directions on your prescription label carefully, and ask your Doctor to explain any part you do not understand. Take doxazosin exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.
Swallow the extended-release tablets whole; do not split, chew, or crush them.
Your doctor will start you on a low dose of doxazosin and gradually increase your dose, not more than once every 1 to 2 weeks. If you stop taking doxazosin for a few days or longer, consult your doctor. Your doctor will have to start you again on the lowest dose of doxazosin and gradually increase your dose.
Doxazosin controls high blood pressure and the symptoms of BPH but does not cure them. It may take a few weeks before you feel the full benefit of doxazosin. Continue to take doxazosin even if you feel well. Do not stop taking doxazosin without talking to your doctor.
Other uses for Doxazosin
This medication may be prescribed for other uses; ask your Doctor for more information.
What Special Precautions to follow?
Before taking doxazosin,
- inform your Doctor if you are allergic to doxazosin, prazosin, terazosin, or any other medications.
- inform your Doctor what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: antihistamines; clarithromycin; ipratropium; itraconazole; ketoconazole; medications for erectile dysfunction such as sildenafil, tadalafil, or vardenafil; medications for high blood pressure; medications for HIV/AIDS including atazanavir, indinavir, nelfinavir, ritonavir, or saquinavir; medications for irritable bowel disease, motion sickness, Parkinson's disease, ulcers, or urinary problems; nefazodone; telithromycin; and voriconazole. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
- inform your doctor if you have angina; low blood pressure; or if you have or have ever had prostate cancer or liver disease. If you are taking the extended-release tablet, tell you doctor if you have constipation, short bowel syndrome, or narrowing or a blockage of the intestines.
- inform your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while taking doxazosin, consult your doctor.
- talk to your doctor about the risks and benefits of taking doxazosin if you are 65 years of age or older. Older adults should not usually take doxazosin because it is not as safe as other medications that can be used to treat the same conditions.
- if you are having surgery, including dental surgery, tell the doctor or dentist that you are taking doxazosin. If you need to have eye surgery at any time during or after your treatment, be sure to inform your doctor that you are taking or have taken doxazosin.
- you should know that doxazosin may make you drowsy or dizzy. Do not drive a car, operate machinery, or perform dangerous tasks for 24 hours after the first time you take doxazosin or after your dose is increased.
- you should know that doxazosin may cause dizziness, lightheadedness, and fainting when you get up too quickly from a lying position. This is more common when you first start taking doxazosin, when your dose is increased, or if your treatment has been stopped for more than a few days. To avoid this problem, get out of bed slowly, resting your feet on the floor for a few minutes before standing up. If you experience these symptoms, sit or lie down. If these symptoms do not improve, consult your doctor.
What special dietary instructions to follow?
Follow your doctor's directions for your meals, including advice for a reduced salt diet.
What to do if I forget a dose?
Take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one. Check with your doctor if you have missed two or more doses.
What side effects can this medication cause?
Doxazosin may cause side effects. Tell your doctor if any of these symptoms or those listed in the SPECIAL PRECAUTIONS section are severe or do not go away:
- swelling of the hands, feet, ankles, or lower legs
- shortness of breath
- weight gain
- muscle or joint pain or weakness
- abnormal vision
- runny nose
- decreased sexual ability
- rapid, pounding, or irregular heartbeat
- chest pain
- shortness of breath
- painful erection of the penis that lasts for hours
Some side effects can be serious. If you experience any of these symptoms, consult your doctor immediately:
Doxazosin may cause other side effects. Consult your doctor if you have any unusual problems while taking this medication.
What Storage conditions are needed for this medicine?
Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture. Throw away any medication that is outdated or no longer needed. Talk to your Doctor about the proper disposal of your medication.
In case of emergency/overdose
In case of overdose, consult your Doctor. If the victim has collapsed or is not breathing, consult local medical emergency services.
Symptoms of overdose may include:
What other information should I know?
If you are taking doxazosin extended-release tablets, you may notice something that looks like a tablet in your stool. This is just the empty tablet shell, and this does not mean that you did not get your complete dose of medication.
Keep all appointments with your doctor. If you are taking doxazosin to control high blood pressure, your blood pressure should be checked regularly to determine your response to doxazosin.
Do not let anyone else take your medication.
It is important for you to keep a written list of all of the prescription and nonprescription medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.
This information is provided for reference only and not a replacement for and should only be used in conjunction with full consultation with a registered medical practitioner. It may not contain all the available information you require and cannot substitute professional medical care, nor does it take into account all individual circumstances. Although great effort has been made to ensure content accuracy, mph-bd shall not be held responsible or liable for any claims or damages arising from the use or misuse of the information contained herein, its contents or omissions, or otherwise.