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Alpha-1 Adrenoceptor Antagonist — Hypertension / Raynaud's / BPH Pregnancy: UK SPC §4.6, hypertension indication: 'As there are no adequate and well-controlled studies in pregnant women, the safety of Cardura during pregnancy has not yet been established. Accordingly, during pregnancy, Cardura 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.' BREAST-FEEDING: 'The excretion of doxazosin in breast milk was demonstrated to be very low (with the relative infant dose less than 1%) however human data is very limited. A risk to the newborn or infant cannot be excluded and therefore doxazosin should be used only when in the opinion of the physician, the potential benefit outweighs the potential risk.' (§4.6 states this section is not applicable to the BPH indication.)

Doxazosin

Brand names: Cardura, Doxadura

Doxazosin is a long-acting selective alpha-1 adrenoceptor antagonist used for hypertension, often as add-on therapy, and for symptomatic benign prostatic hyperplasia.

Adult dose

Dose: ADULT HYPERTENSION, ORAL IMMEDIATE-RELEASE TABLETS: start 1 mg once daily and titrate upwards. UK SPC §4.2 verbatim (Hypertension): 'Cardura 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 Cardura 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.'
Route: Oral, immediate-release Cardura tablets, for the licensed HYPERTENSION indication. §4.2: 'Method of administration: Oral administration.' SCOPE WARNING: the fetched SPC is for the IMMEDIATE-RELEASE 2 mg tablet only. It does not carry a posology for the modified-release (XL / prolonged-release) formulation the live page also mentions — §4.4 states 'No studies have been conducted with doxazosin prolonged release formulations.' The XL regimen must be taken from that product's own SPC.
Frequency: Once daily. §4.2: 'Cardura may be administered in the morning or the evening.' Titration interval for hypertension is 'one or two weeks' between increases (the SPC gives 'The recommended titration interval is 1-2 weeks' explicitly under the BPH indication). NOTE: this SPC does NOT specify bedtime dosing — the live page's 'once daily at bedtime' instruction is not supported by this source.
Max: Maximum 16 mg once daily for HYPERTENSION. UK SPC §4.2 verbatim: 'Dosage can be further increased if necessary to 8mg or the maximum recommended dose of 16mg.' DO NOT transfer this ceiling to benign prostatic hyperplasia — for BPH the SPC states a different and lower ceiling: 'up to the maximum recommended dose of 8mg' ('The maximum recommended dose for BPH is 8 mg once daily' in the US label).
Source: UK SPC (eMC) for CARDURA Tablet 2mg, §4.2. INDICATION SCOPE — the dose above is the SPC's HYPERTENSION regimen. RAYNAUD'S PHENOMENON, which this vascular page also names, is NOT an indication in this SPC and no Raynaud's posology exists in any fetched source; any such use is unlicensed and the dose must be taken from a specialist rheumatology/vascular guideline, not from this record. SECOND SPC INDICATION (different ceiling, quoted for completeness, not for the vascular page's dose): 'Benign prostatic hyperplasia: The recommended initial dosage of Cardura is 1mg given once daily to minimise the potential for postural hypotension and/or syncope. 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.' ELDERLY: 'Normal adult dosage.' FIRST-DOSE EFFECT (§4.4): 'patients may experience postural hypotension evidenced by dizziness and weakness, or rarely loss of consciousness (syncope), particularly with the commencement of therapy... it is prudent medical practice to monitor blood pressure on initiation of therapy to minimise the potential for postural effects. The patient should be cautioned to avoid situations where injury could result, should dizziness or weakness occur during the initiation of Cardura therapy.' US label §2.1 adds: 'If doxazosin tablets administration is discontinued for several days, therapy should be restarted using the initial dosing regimen.' ACUTE CARDIAC CONDITIONS (§4.4) — caution with pulmonary oedema due to aortic or mitral stenosis, high-output cardiac failure, right-sided heart failure due to pulmonary embolism or pericardial effusion, and left ventricular heart failure with low filling pressure. CATARACT SURGERY (§4.4): '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... current or past use of alpha-1 blockers should be made known to the ophthalmic surgeon in advance of surgery.' PDE-5 INHIBITORS (§4.4): co-administration 'should be done with caution as both drugs have vasodilating effects and may lead to symptomatic hypotension in some patients... 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.' Some sections of the product information we used were incomplete — check the full SPC.

Dose adjustments

Renal

UK SPC §4.2 verbatim: 'Since there is no change in pharmacokinetics in patients with impaired renal function, the usual adult dose of Cardura is recommended. Cardura is not dialysable.'

Hepatic

UK SPC §4.2 verbatim: '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, Cardura should be administered with caution to patients with evidence of impaired liver function.' §4.4 adds: 'Since there is no clinical experience in patients with severe hepatic impairment use in these patients is not recommended.' No numeric dose reduction is specified.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance or other types of quinazolines (e.g. prazosin, terazosin, doxazosin), or to any of the excipients listed in section 6.1
  • Patients with a history of orthostatic hypotension
  • Patients with benign prostatic hyperplasia and concomitant congestion of the upper urinary tract, chronic urinary tract infection or bladder stones
  • Patients with hypotension (for the benign prostatic hyperplasia indication only)
  • Contraindicated as monotherapy in patients with either overflow bladder or anuria with or without progressive renal insufficiency

Side effects

  • Common: dizziness, headache, somnolence; palpitation, tachycardia; hypotension, postural hypotension; bronchitis, cough, dyspnoea, rhinitis; abdominal pain, dyspepsia, dry mouth, nausea; pruritus; back pain, myalgia; cystitis, urinary incontinence; asthenia, chest pain, influenza-like symptoms, peripheral oedema; respiratory tract infection, urinary tract infection
  • Uncommon: gout, increased appetite, anorexia; agitation, depression, anxiety, insomnia, nervousness; cerebrovascular accident, hypoesthesia, syncope, tremor; vertigo; angina pectoris, myocardial infarction; epistaxis; constipation, flatulence, vomiting, gastroenteritis; abnormal liver function tests; skin rash, urticaria, alopecia, purpura; arthralgia; dysuria, micturition frequency, haematuria; impotence; pain, facial oedema; weight increase; allergic drug reaction
  • Rare: leukopenia, thrombocytopenia; bradycardia, cardiac arrhythmias; hot flushes; bronchospasm; cholestasis, hepatitis, jaundice; muscle cramps, muscle weakness; polyuria; gynaecomastia, priapism
  • Very rare: postural dizziness, paraesthesia; blurred vision; tinnitus; diarrhoea; increased diuresis, micturition disorder, nocturia; fatigue, malaise
  • Frequency not known: intraoperative floppy iris syndrome (see §4.4); retrograde ejaculation
  • US §6.1 cross-check, BPH trials: dizziness 15.6% (vs placebo 9%), somnolence 3% (vs 1%), hypotension 1.7% (vs 0%). 'The most commonly reported adverse reactions from clinical trials are Fatigue, malaise, hypotension, and dizziness.'

Interactions

  • PDE-5 inhibitors (e.g. sildenafil, tadalafil, vardenafil) — caution; both have vasodilating effects and may lead to symptomatic hypotension. Start the PDE-5 inhibitor only once haemodynamically stabilised on alpha-blocker therapy, at the lowest possible dose, and respect a 6-hour interval from doxazosin intake (§4.4)
  • US §7.1 cross-check: 'In vitro studies suggest that doxazosin is a substrate of CYP 3A4. Strong CYP3A inhibitors may increase exposure to doxazosin. Monitor blood pressure and for symptoms of hypotension'
  • Drugs known to influence hepatic metabolism (e.g. cimetidine) — only limited data (§4.2)
  • This interaction list may be incomplete — check the full SPC.

Monitoring

  • BLOOD PRESSURE ON INITIATION (§4.4): '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.' US §2.1 is more specific: 'Following the initial dose and with each dose increase of doxazosin tablets, monitor blood pressure for at least 6 hours following administration'
  • and for BPH 'Routinely monitor blood pressure in these patients.' PRE-OPERATIVE CHECK (§4.4): current or past alpha-1 blocker use must be disclosed to the ophthalmic surgeon before cataract surgery because of intraoperative floppy iris syndrome.
  • LIVER FUNCTION: administer with particular caution where hepatic function is impaired
  • not recommended in severe hepatic impairment (§4.2, §4.4).
  • If therapy is interrupted for several days, restart at the initial dosing regimen (US §2.1).
  • This list may be incomplete — check the full SPC.

Clinical monograph

How it works

It selectively blocks postsynaptic alpha-1 adrenoceptors on vascular smooth muscle and the prostate, producing vasodilatation and reduced bladder outflow resistance.

Prescribing in practice

  • First-dose and postural hypotension can cause collapse, so treatment is started at a low dose, ideally at bedtime, and patients warned to rise slowly.
  • It can interact additively with other antihypertensives and with phosphodiesterase-5 inhibitors to lower blood pressure.
  • Intra-operative floppy iris syndrome can complicate cataract surgery, so the ophthalmologist should be told.

Monitoring

Monitor blood pressure, including for postural drop, after initiation and dose changes, and review for dizziness, oedema and symptomatic response.

Counselling the patient

  • Take the first dose at bedtime and stand up slowly to avoid dizziness.
  • Tell your eye surgeon you take this drug before cataract surgery.
  • Report fainting, marked dizziness or ankle swelling.

Evidence & guidelines

The ALLHAT trial showed the doxazosin arm had more heart failure than a thiazide-type diuretic, which is why it is generally reserved as add-on rather than first-line antihypertensive therapy.

Reference: ALLHAT Trial; MHRA Drug Safety Update (IFIS); BSR/BHPR Raynaud's Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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