Alfadil (Doxazosin)
Alpha-1 adrenergic blocker for essential hypertension — extended-release tablets
Alfadil is an alpha-1 adrenergic blocker containing the active ingredient doxazosin mesilate. It is prescribed for the treatment of essential hypertension (high blood pressure not caused by an identifiable condition). Available as extended-release tablets in 4 mg and 8 mg strengths, Alfadil provides 24-hour blood pressure control with once-daily dosing. This guide covers uses, dosage, interactions, side effects, and important safety information based on international clinical guidelines.
Quick Facts: Alfadil
Key Takeaways
- Alfadil (doxazosin) is an alpha-1 adrenergic blocker that lowers blood pressure by relaxing blood vessels, allowing blood to flow more easily.
- The extended-release tablets must be swallowed whole — never crushed, chewed, or split — and provide 24-hour blood pressure control with once-daily dosing.
- Dizziness and lightheadedness may occur, especially at the start of treatment; avoid driving or operating machinery until you know how Alfadil affects you.
- Inform your eye surgeon before cataract surgery if you are taking or have previously taken Alfadil, as it may cause intraoperative floppy iris syndrome (IFIS).
- Do not stop taking Alfadil abruptly without medical supervision, as this may cause a rebound increase in blood pressure.
What Is Alfadil and What Is It Used For?
Alfadil belongs to a class of medications known as alpha-adrenergic blocking agents, commonly referred to as alpha-blockers. The active substance, doxazosin mesilate, selectively targets alpha-1 adrenergic receptors found on the smooth muscle cells of blood vessels. By blocking these receptors, Alfadil causes the blood vessels to dilate (widen), which reduces the resistance that the heart must work against when pumping blood. This action results in a measurable decrease in both systolic and diastolic blood pressure.
The primary indication for Alfadil is essential hypertension, which is high blood pressure that is not caused by an identifiable underlying medical condition such as kidney disease or hormonal disorders. Essential hypertension accounts for approximately 90–95% of all hypertension cases globally, according to the World Health Organization (WHO). Uncontrolled hypertension is a major risk factor for cardiovascular events, including heart attack, stroke, heart failure, and chronic kidney disease.
One of the notable advantages of doxazosin therapy is its favorable effect on blood lipid profiles. Clinical studies have demonstrated that doxazosin produces a moderate increase in the ratio of high-density lipoprotein (HDL) cholesterol to total cholesterol. This is clinically significant because many patients with hypertension also have dyslipidemia, and a treatment that addresses both conditions simultaneously offers additional cardiovascular benefit.
Alfadil is formulated as an extended-release tablet, which uses a controlled-release mechanism to deliver doxazosin slowly and steadily over a 24-hour period. The tablet shell, which is not dissolved by digestion and may be visible in the stool, is designed to allow the medication to be released through a small opening in one side of the tablet. This formulation allows for once-daily dosing, which is convenient for patients and promotes better medication adherence. The extended-release formulation also helps minimize the peak-to-trough blood pressure fluctuations that can occur with immediate-release formulations.
Alfadil may be used as monotherapy (the sole antihypertensive agent) to control blood pressure. In patients whose blood pressure is not adequately controlled with Alfadil alone, it can be used in combination with other antihypertensive medications, including thiazide diuretics, beta-blockers, calcium channel blockers, or ACE inhibitors, in accordance with current clinical guidelines from the European Society of Cardiology (ESC) and the American Heart Association (AHA).
What Should You Know Before Taking Alfadil?
Contraindications
Alfadil must not be taken in the following circumstances:
- Allergy to doxazosin or other quinazolines: If you are allergic to doxazosin, other quinazoline derivatives (such as prazosin or terazosin), or any of the inactive ingredients in the formulation. Signs of an allergic reaction include rash, itching, swelling, severe dizziness, and difficulty breathing.
- Gastrointestinal obstruction or narrowing: If you have or have previously had a blockage in the gastrointestinal tract or a narrowing of the digestive system. Because Alfadil is an extended-release tablet that releases its active ingredient as it passes through the digestive system, any obstruction could interfere with drug absorption and potentially worsen the blockage.
- Orthostatic hypotension: If you have a history of dizziness or fainting when rising from a lying or sitting position due to low blood pressure. Alpha-blockers can exacerbate orthostatic hypotension, which may increase the risk of falls and injury.
- Benign prostatic hyperplasia with upper urinary tract complications: If you have an enlarged prostate together with upper urinary tract obstruction, chronic urinary tract infection, or bladder stones. These conditions require alternative treatment strategies.
Warnings and Precautions
Several important safety considerations apply when using Alfadil. You should discuss these with your prescribing physician before starting treatment.
Alfadil extended-release tablets must be swallowed whole. They must not be chewed, split, or crushed. Damaging the tablet shell can destroy the controlled-release mechanism and lead to an excessively rapid release of the drug, potentially causing a dangerous drop in blood pressure.
First-dose effect and orthostatic hypotension: Dizziness, weakness, and in rare cases fainting (syncope) may occur, particularly at the beginning of treatment. This phenomenon, known as the “first-dose effect,” results from a sudden drop in blood pressure when moving from a supine to an upright position. Patients should be especially careful during the initial dosing period to avoid situations where dizziness could cause injury, such as climbing ladders or operating heavy equipment. If dizziness or faintness occurs, lie down immediately — symptoms typically resolve quickly. Blood pressure should be monitored regularly at the start of treatment.
Heart failure and pulmonary edema: Patients with severe heart problems, particularly congestive heart failure or pulmonary edema (fluid in the lungs), should use Alfadil with caution and under close medical supervision. Alpha-blockers can affect cardiac hemodynamics and may worsen heart failure in susceptible patients. Regular monitoring is essential, especially during the initiation phase of therapy.
Liver disease: Alfadil should be used with caution in patients with liver impairment due to limited clinical data on the use of doxazosin in this population. The liver plays a key role in metabolizing doxazosin, and impaired hepatic function may lead to elevated drug levels in the blood, increasing the risk of adverse effects. Use of Alfadil is not recommended in patients with severe liver disease.
Cataract surgery (Intraoperative Floppy Iris Syndrome): If you are scheduled for eye surgery, particularly cataract surgery, it is critical to inform your ophthalmologist that you are currently taking or have previously taken Alfadil. Alpha-blockers, including doxazosin, have been associated with a condition known as Intraoperative Floppy Iris Syndrome (IFIS), which can lead to complications during surgery. If the eye surgeon is aware beforehand, appropriate surgical modifications can be made to minimize risk.
Priapism: In very rare cases, alpha-blockers can cause priapism — a prolonged, painful erection that does not resolve on its own. If this occurs, seek emergency medical attention immediately. Untreated priapism can cause permanent damage to the erectile tissue.
Pregnancy and Breastfeeding
If you are pregnant, think you may be pregnant, are planning a pregnancy, or are breastfeeding, consult your doctor before taking Alfadil.
Pregnancy: There is insufficient clinical experience with doxazosin in pregnant women. Alfadil should only be used during pregnancy if clearly indicated by a physician and after a careful risk-benefit assessment. Animal reproductive studies alone cannot fully predict human response, and the potential risks to the developing fetus are not well characterized.
Breastfeeding: Small amounts of doxazosin, the active substance in Alfadil, may be excreted into breast milk. Nursing mothers should not take Alfadil unless their physician has determined that the benefit outweighs the potential risk to the infant. If breastfeeding is necessary, the physician may recommend an alternative antihypertensive medication with better-established safety data during lactation.
Children and Adolescents
Alfadil is not recommended for use in children or adolescents under 18 years of age. The safety and efficacy of doxazosin have not been established in pediatric populations. If a child or adolescent requires antihypertensive treatment, alternative medications with established pediatric dosing should be used.
Driving and Operating Machinery
The ability to drive and operate machinery may be impaired, particularly at the beginning of treatment or when the dose is increased. Doxazosin can cause dizziness, drowsiness, and blurred vision, all of which can affect reaction time and attention. Do not drive or operate machinery until you are certain that you can do so safely. Discuss with your doctor if you need to drive regularly.
Alfadil contains less than 1 mmol sodium (23 mg) per tablet, making it essentially sodium-free. This is relevant for patients on a sodium-restricted diet for cardiovascular health reasons.
How Does Alfadil Interact with Other Drugs?
Drug interactions occur when one medication affects the way another medication works in the body. Because Alfadil lowers blood pressure, the most clinically significant interactions involve other drugs that also lower blood pressure or that affect how doxazosin is metabolized in the liver. Always inform your healthcare provider about all medications you are taking, including prescription drugs, over-the-counter medicines, herbal supplements, and vitamins.
Major Interactions
PDE-5 inhibitors (sildenafil, tadalafil, vardenafil): Both Alfadil and PDE-5 inhibitors used for erectile dysfunction have blood pressure-lowering effects. When taken together, an additive hypotensive effect can occur, potentially causing symptomatic orthostatic hypotension (dizziness, lightheadedness, or fainting when standing up). To reduce this risk, you should be stabilized on your alpha-blocker therapy before starting a PDE-5 inhibitor. You should also begin with the lowest available dose of the PDE-5 inhibitor and take it at least 6 hours apart from your dose of Alfadil.
Other antihypertensive agents: Using Alfadil in combination with other blood pressure-lowering medications (such as ACE inhibitors, angiotensin receptor blockers, beta-blockers, calcium channel blockers, or diuretics) can produce an additive blood pressure-lowering effect. While this may be therapeutically beneficial under medical supervision, it also increases the risk of hypotension. Blood pressure should be monitored carefully when adding or adjusting doses of concomitant antihypertensive therapy.
Moderate Interactions
CYP3A4 inhibitors: Doxazosin is primarily metabolized by the CYP3A4 enzyme system in the liver. Drugs that inhibit this enzyme can increase blood levels of doxazosin, potentially intensifying its effects and side effects. Important CYP3A4 inhibitors include:
- Antibiotics and antifungals: Clarithromycin, telithromycin, itraconazole, ketoconazole, voriconazole
- HIV protease inhibitors: Ritonavir, indinavir, nelfinavir, saquinavir
- Antidepressants: Nefazodone
If you must take any of these medications concurrently with Alfadil, your doctor may need to adjust your dose of Alfadil or monitor your blood pressure more frequently.
| Drug / Drug Class | Type | Effect | Clinical Advice |
|---|---|---|---|
| PDE-5 inhibitors (sildenafil, tadalafil, vardenafil) | Major | Additive blood pressure reduction; risk of symptomatic hypotension | Stabilize on alpha-blocker first; start PDE-5 inhibitor at lowest dose; take at least 6 hours apart |
| Other antihypertensives (ACE inhibitors, ARBs, beta-blockers, CCBs, diuretics) | Major | Enhanced blood pressure lowering; increased hypotension risk | Monitor blood pressure regularly; dose adjustments may be needed |
| Clarithromycin, telithromycin | Moderate | Increased doxazosin levels via CYP3A4 inhibition | Monitor for enhanced hypotensive effect; consider dose reduction |
| Itraconazole, ketoconazole, voriconazole | Moderate | Increased doxazosin levels via CYP3A4 inhibition | Monitor for enhanced hypotensive effect; consider dose reduction |
| HIV protease inhibitors (ritonavir, indinavir, nelfinavir, saquinavir) | Moderate | Increased doxazosin levels via CYP3A4 inhibition | Use with caution; monitor blood pressure closely |
| Nefazodone | Moderate | Increased doxazosin levels via CYP3A4 inhibition | Monitor for hypotension; consider alternative antidepressant |
Alfadil can be taken with or without food. There are no known clinically significant food-drug interactions. However, grapefruit juice may theoretically increase doxazosin levels through CYP3A4 inhibition; it is prudent to discuss this with your doctor if you regularly consume grapefruit products.
What Is the Correct Dosage of Alfadil?
Always take Alfadil exactly as your doctor has prescribed. Do not change the dose or stop taking the medication without consulting your healthcare provider. The dosage regimen is designed to gradually achieve optimal blood pressure control while minimizing the risk of side effects.
Adults
Standard Adult Dosing
Starting dose: 4 mg once daily (one 4 mg tablet).
Dose adjustment: It may take up to 4 weeks for the full antihypertensive effect of Alfadil to become apparent. If blood pressure is not adequately controlled after 4 weeks, the dose may be increased to 8 mg once daily (two 4 mg tablets or one 8 mg tablet), depending on your individual response.
Maximum dose: 8 mg daily.
Administration: Swallow the tablet whole with a sufficient amount of liquid (a glass of water is recommended). Do not chew, split, or crush the tablet.
Elderly Patients
Elderly Dosing
The standard adult dose is recommended for elderly patients. No dose adjustment is generally required based on age alone. However, elderly patients may be more susceptible to orthostatic hypotension and should be monitored more closely, particularly at the start of treatment or when doses are increased.
Patients with Kidney Disease
Renal Impairment Dosing
The standard adult dose can be used in patients with kidney disease. Doxazosin is primarily metabolized by the liver, and renal impairment does not significantly affect its clearance. No dose adjustment is necessary based on kidney function alone.
Patients with Liver Disease
Hepatic Impairment Dosing
Due to insufficient clinical data, Alfadil is not recommended for patients with severe liver disease. Doxazosin is primarily metabolized in the liver via CYP3A4, and impaired hepatic function may lead to increased drug levels and a heightened risk of adverse effects. Patients with mild to moderate liver impairment should use Alfadil with caution under close medical supervision.
| Patient Group | Starting Dose | Maximum Dose | Notes |
|---|---|---|---|
| Adults | 4 mg once daily | 8 mg once daily | Increase after 4 weeks if needed |
| Elderly | 4 mg once daily | 8 mg once daily | Standard dose; monitor closely for orthostatic hypotension |
| Kidney impairment | 4 mg once daily | 8 mg once daily | No dose adjustment needed |
| Mild-moderate liver impairment | 4 mg once daily | As tolerated | Use with caution; close monitoring required |
| Severe liver impairment | Not recommended | Not recommended | Insufficient safety data |
| Children (<18 years) | Not recommended | Not recommended | Safety and efficacy not established |
Missed Dose
If you miss a dose of Alfadil or take less than the prescribed amount, skip the missed dose entirely and take the next dose at your usual time. Do not take a double dose to make up for a forgotten dose. Doubling up can cause an excessive drop in blood pressure, leading to dizziness, weakness, or fainting.
Overdose
A significant overdose of Alfadil may cause a severe and sustained drop in blood pressure. Symptoms may include pronounced dizziness, rapid heart rate (tachycardia), and flushing. If an overdose is suspected, contact your doctor or emergency services immediately. Lie down with your legs elevated to help maintain blood flow to vital organs. Because doxazosin is highly protein-bound, dialysis is not effective in removing it from the body. Treatment is primarily supportive, with intravenous fluid replacement and vasopressors if necessary.
Stopping Treatment
Do not stop taking Alfadil without consulting your doctor. Abruptly discontinuing antihypertensive therapy can cause a rebound increase in blood pressure, which may increase the risk of cardiovascular events. If treatment with Alfadil needs to be stopped, your doctor will typically reduce the dose gradually and may start an alternative antihypertensive agent to ensure continuous blood pressure control.
The active ingredient in Alfadil is enclosed within a shell that is designed to control drug release over an extended period. This shell is not digested and passes through the gastrointestinal tract intact. It is normal to occasionally see a tablet-like residue in your stool — this is the empty shell and does not mean the medication was not absorbed.
What Are the Side Effects of Alfadil?
Like all medicines, Alfadil can cause side effects, although not everyone experiences them. The following side effects are categorized by frequency based on clinical trial data and post-marketing surveillance reports. Most side effects are mild to moderate in severity and tend to occur most frequently at the beginning of treatment or when the dose is increased.
Common
May affect up to 1 in 10 patients
- Respiratory tract infections, urinary tract infections
- Dizziness, headache, drowsiness, vertigo
- Palpitations, tachycardia (rapid heartbeat)
- Low blood pressure, orthostatic hypotension
- Bronchitis, cough, shortness of breath (dyspnea), runny nose (rhinitis)
- Abdominal pain, indigestion (dyspepsia), dry mouth, nausea
- Itching (pruritus)
- Back pain, muscle pain (myalgia)
- Cystitis, urinary incontinence
- Fatigue, chest pain, flu-like symptoms, peripheral edema (swelling in arms/legs)
Uncommon
May affect up to 1 in 100 patients
- Allergic reactions, gout, increased or decreased appetite
- Anxiety, depression, insomnia
- Cerebrovascular disturbances, reduced touch sensation (hypoesthesia), fainting (syncope), tremor
- Tinnitus (ringing in the ears)
- Angina pectoris, myocardial infarction (heart attack)
- Nosebleeds (epistaxis)
- Constipation, diarrhea, flatulence, vomiting, gastroenteritis
- Skin rash
- Joint pain (arthralgia), difficulty urinating, blood in urine, increased urinary frequency
- Erectile dysfunction, pain, abnormal liver function tests, weight gain
Rare
May affect up to 1 in 1,000 patients
- Gastrointestinal obstruction
Very Rare
May affect up to 1 in 10,000 patients
- Low white blood cell count (leukopenia), low platelet count (thrombocytopenia)
- Agitation, nervousness
- Positional dizziness, tingling (paresthesia), blurred vision
- Slow heart rate (bradycardia), irregular heartbeat (arrhythmia)
- Flushing, bronchospasm
- Cholestasis (bile flow blockage), hepatitis (liver inflammation), jaundice
- Hair loss (alopecia), purpura (skin bleeding), urticaria (hives)
- Muscle cramps, muscle weakness
- Urination disorders, nocturia (increased nighttime urination), increased urine volume
- Gynecomastia (breast enlargement in men), malaise
Frequency Not Known
Cannot be estimated from available data
- Retrograde ejaculation (dry ejaculation in men)
- Intraoperative floppy iris syndrome (IFIS) — complications during cataract surgery
Priapism: A persistent, painful erection lasting more than 4 hours requires immediate medical attention. This is a very rare but serious side effect of alpha-blockers. Untreated priapism can lead to permanent erectile damage.
If you experience any side effects, including any not listed above, talk to your doctor or pharmacist. You can also report suspected side effects to your national medicines regulatory agency to help ensure the continued safe use of this medication.
How Should You Store Alfadil?
Proper storage of medications is essential to maintain their effectiveness and safety. Follow these storage guidelines for Alfadil:
- Temperature: Store at or below 30°C (86°F). Do not freeze.
- Moisture protection: Keep the tablets in their original packaging (blister pack or HDPE bottle) to protect against moisture, which can degrade the controlled-release mechanism.
- Light: No special light protection is required, but it is good practice to store medications away from direct sunlight.
- Child safety: Keep this medication out of the sight and reach of children.
- Expiry date: Do not use Alfadil after the expiry date printed on the carton and blister. The expiry date refers to the last day of that month.
- Disposal: Do not dispose of unused medications via household waste or wastewater. Return unused tablets to a pharmacy for proper disposal to protect the environment.
What Does Alfadil Contain?
Active ingredient: Doxazosin mesilate. Each 4 mg extended-release tablet contains 4.85 mg doxazosin mesilate, which is equivalent to 4.0 mg of doxazosin (the active moiety). Each 8 mg tablet contains 9.70 mg doxazosin mesilate, equivalent to 8.0 mg of doxazosin.
Inactive ingredients (excipients): Macrogol (polyethylene glycol), hypromellose, red iron oxide (E172), magnesium stearate, sodium chloride, cellulose acetate, titanium dioxide (E171), shellac, and black iron oxide (E172).
Appearance: Alfadil extended-release tablets are round, biconvex, white film-coated tablets. The 4 mg tablets have “CXL 4” printed on one side, and the 8 mg tablets have “CXL 8” printed on one side. The active substance is released slowly through a small hole on one side of the tablet.
Available pack sizes: Alfadil is available in blister packs of 7, 10, 14, 20, 28, 30, 50, 56, 98, and 100 tablets. Hospital packs of 140 and 300 tablets are also available. HDPE bottles with child-resistant closures and desiccant, containing 30 or 100 tablets, are available in some markets. Not all pack sizes may be marketed in every country.
Frequently Asked Questions About Alfadil
Alfadil (doxazosin) is an alpha-1 adrenergic blocker primarily used to treat essential hypertension (high blood pressure). It works by selectively blocking alpha-1 receptors in blood vessel walls, causing the vessels to relax and widen, which reduces the resistance against which the heart pumps and lowers blood pressure. Alfadil is available as extended-release tablets in 4 mg and 8 mg strengths and provides 24-hour blood pressure control with a single daily dose.
No. Alfadil extended-release tablets must always be swallowed whole with a glass of water. Crushing, chewing, or splitting the tablets would destroy the controlled-release mechanism, causing the entire dose of doxazosin to be released at once. This could lead to a dangerously rapid drop in blood pressure. It is normal to see an empty tablet shell in your stool — this means the medication has been properly released and absorbed.
Dizziness is one of the most common side effects of Alfadil, particularly at the beginning of treatment. If you experience dizziness or lightheadedness, lie down immediately and elevate your legs — the symptoms should resolve within a few minutes. Avoid standing up too quickly from a sitting or lying position. Your blood pressure should be checked regularly at the start of treatment. If dizziness persists or is severe, contact your doctor, who may need to adjust your dose.
Alfadil and PDE-5 inhibitors (such as sildenafil/Viagra, tadalafil/Cialis, and vardenafil/Levitra) both lower blood pressure. Taking them together can cause an excessive drop in blood pressure, leading to dizziness, lightheadedness, or fainting. To minimize this risk, you should be stabilized on Alfadil before starting a PDE-5 inhibitor, begin with the lowest dose, and take the two medications at least 6 hours apart. Always consult your doctor before combining these medications.
Yes, this is very important. If you are scheduled for cataract surgery, you must tell your ophthalmologist that you are taking or have previously taken Alfadil. Alpha-blockers such as doxazosin can cause Intraoperative Floppy Iris Syndrome (IFIS), a condition that can complicate the surgical procedure. If your surgeon knows in advance, they can take the appropriate precautions to ensure a safe operation.
There is limited clinical data on the use of doxazosin during pregnancy. Alfadil should only be used during pregnancy when the potential benefits clearly outweigh the risks, and only under direct medical supervision. Small amounts of doxazosin may pass into breast milk, so breastfeeding while taking Alfadil is generally not recommended unless your doctor has specifically advised it. If you are pregnant, planning to become pregnant, or breastfeeding, discuss your options with your healthcare provider.
References
- Williams B, Mancia G, Spiering W, et al. 2018 ESC/ESH Guidelines for the management of arterial hypertension. European Heart Journal. 2018;39(33):3021-3104. doi:10.1093/eurheartj/ehy339
- Whelton PK, Carey RM, Aronow WS, et al. 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults. Journal of the American College of Cardiology. 2018;71(19):e127-e248. doi:10.1016/j.jacc.2017.11.006
- European Medicines Agency (EMA). Doxazosin — Summary of Product Characteristics. ema.europa.eu
- World Health Organization (WHO). Hypertension Fact Sheet. who.int/hypertension
- British National Formulary (BNF). Doxazosin monograph. National Institute for Health and Care Excellence (NICE). bnf.nice.org.uk
- ALLHAT Officers and Coordinators. Major outcomes in high-risk hypertensive patients randomized to angiotensin-converting enzyme inhibitor or calcium channel blocker vs diuretic: The ALLHAT trial. JAMA. 2002;288(23):2981-2997. doi:10.1001/jama.288.23.2981
- Chang DF, Campbell JR. Intraoperative floppy iris syndrome associated with tamsulosin. Journal of Cataract & Refractive Surgery. 2005;31(4):664-673. doi:10.1016/j.jcrs.2005.02.027
- Mancia G, Kreutz R, Brunström M, et al. 2023 ESH Guidelines for the management of arterial hypertension. Journal of Hypertension. 2023;41(12):1874-2071. doi:10.1097/HJH.0000000000003480
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