BMA Concise Guide to Medicine & Drugs

Doxazosin

Brand names Cardura, Cardura XL, Doxadura, Slocinx XL

Used in the following combined preparations None

QUICK REFERENCE

Drug group Vasodilator, antihypertensive drug, and drug for urinary disorders

Overdose danger rating Medium

Dependence rating Low

Prescription needed Yes

Available as generic Yes

GENERAL INFORMATION

Doxazosin is an antihypertensive vasodilator drug that relieves hypertension (high blood pressure) by relaxing the muscles in the blood vessel walls. It may be administered together with other antihypertensive drugs, including beta blockers, since its effects on blood pressure are increased when it is combined with most other antihypertensives.

Doxazosin can also be given to patients with an enlarged prostate gland. It relaxes the muscles around the prostate gland and bladder exit, making bladder emptying easier. However, this effect may cause incontinence when the drug is used in women. Dizziness and fainting may occur with doxazosin. Typically, this occurs on standing and may improve with continued use but it may limit the drug’s use, especially in elderly people.

INFORMATION FOR USERS

Your drug prescription is tailored for you. Do not alter dosage without checking with your doctor.

How taken/used Tablets, MR tablets.

Frequency and timing of doses 1–2 x daily.

Adult dosage range Hypertension 1mg (starting dose for tablets), increased gradually as necessary up to 16mg; or 4mg (starting dose for MR tablets) increased as necessary to 8mg. Enlarged prostate 1mg (starting dose), increased gradually at 1–2-week intervals up to 8mg.

Onset of effect Within 2 hours.

Duration of action 24 hours.

Diet advice None.

Storage Keep in original container at room temperature out of the reach of children.

Missed dose If you forget to take a tablet, skip that dose completely but carry on as normal the following day.

Stopping the drug Do not stop taking the drug without consulting your doctor; stopping the drug may lead to a rise in blood pressure.

Exceeding the dose An occasional unintentional extra dose is unlikely to be a cause for concern. Larger overdoses may cause dizziness or fainting. Notify your doctor.

POSSIBLE ADVERSE EFFECTS

Nausea, weakness, drowsiness, and swollen ankles are common adverse effects of doxazosin. However, the main problem is that it may cause dizziness or fainting when you stand up. It may also cause a stuffy or runny nose and sleep disturbances. Consult your doctor if any of these symptoms are severe, if you develop a rash, or if you are a woman and the drug causes incontinence. Consult your doctor urgently if you experience palpitations or chest pain.

INTERACTIONS

General note Any drugs that can reduce blood pressure are likely to increase the blood-pressure-lowering effect of doxazosin. These include diuretics, beta blockers, ACE inhibitors, calcium channel blockers, nitrates, some antipsychotics and antidepressants, and drugs for erectile dysfunction.

SPECIAL PRECAUTIONS

Be sure to tell your doctor if:

· You have long-term liver problems.

· You have heart problems.

· You have problems with urinary incontinence.

· You have had an allergic reaction to doxazosin in the past.

· You are due to have cataract surgery or another operation.

· You are taking other medicines.

Pregnancy Safety in pregnancy not established. Discuss with your doctor.

Breast-feeding Safety not established. The drug passes into the breast milk. Discuss with your doctor.

Infants and children Not recommended.

Over 60 Reduced dose may be necessary. Take extra care when standing up until you have learned how the drug affects you.

Driving and hazardous work Avoid such activities until you have learned how doxazosin affects you because the drug can cause drowsiness, dizziness, and fainting.

Alcohol Avoid excessive amounts. Alcohol may increase some of the adverse effects of this drug, such as dizziness, drowsiness, and fainting.

Surgery and general anaesthetics A general anaesthetic may increase the low blood pressure effect of doxazosin.

PROLONGED USE

No known problems.