Doxazosin

Registered South African indications:

• Hypertension - mild to moderate
• Treatment of symptoms in benign prostatic hyperplasia (BPH) and for reduced urinary flow associated with BPH

Registered South African contraindications

Immediate release tablet

• Hypersensitivity to the active ingredient or any of its excipients
• Hypersensitivity to quinazolines
• Pregnancy
• Breastfeeding
• Patients with a history of orthostatic hypotension
• Patients with benign prostatic hyperplasia and concomitant congestion of upper urinary tract, chronic urinary tract infection of bladder stones
• As monotherapy in patients either overflow bladder or anuria or without progressive renal insufficiency

Extended release tablet

• Hypersensitivity to the active ingredient or any of its excipients
• Hypersensitivity to quinazolines
• Pregnancy
• Breastfeeding
• Patients with a history of gastrointestinal obstruction, oesophageal obstruction, or any degree of decreased lumen diameter of the gastrointestinal tract

• Hepatic impairment
• Pulmonary oedema due to aortic or mitral stenosis
• High output cardiac failure
• Pulmonary embolism  
• Pericardial effusion
• Left ventricular failure
• Eye (cataract) surgery
• Carcinoma of the prostate
• Priapism
• Surgical resection
• May impair ability to drive and operate machinery

Forms avail. in SA and covered in this monograph: tab, fct, extended release tab (XR tab)

South African registered indications and dosages

Hypertension - mild to moderate

• Oral (tab): Initial: 1mg, once dly; Titrate by doubling the dose at intervals of 7-14 days depending on the individual patient's urodynamics and BPH symptomatology; Usual recommended dose: 2-4mg, once dly; Max: 8mg/24hrs
• Oral (XR tab): Initial: 4mg, once dly in the morning with food; Depending on patient’s symptomatic response and tolerability, increase to: 8mg, once dly; Max: 8mg/24hrs

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In patients not adequately controlled on a single antihypertensive medicine, doxazosin extended release tablet may be used in combination with a thiazide diuretic or a beta-adrenoceptor blocking medicine

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Treatment of symptoms in benign prostatic hyperplasia (BPH) and for reduced urinary flow associated with BPH

• Oral (tab): Initial: 1mg, once dly; Titrate by doubling the dose at intervals of 7-14 days depending on the individual patient's urodynamics and BPH symptomatology; Usual recommended dose: 2-4mg, once dly; Max: 8mg/24hrs
• Oral (XR tab): 4mg, once dly; Depending on the individual patient's urodynamics and BPH symptomatology, titrate at an interval of 3-4 weeks to: 8mg, once dly; Max: 8mg/24hrs

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May be used in BPH patients who are either hypertensive or normotensive

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Method of administration
For oral use. Doxazosin extended release tablets should be taken with food. The tablets should be swallowed whole with a sufficient amount of liquid and must not be chewed, divided, cut, or crushed
In extended release tablets, the medicine is contained within a non-absorbable shell that has been specially designed to slowly release the medicine. When this process is completed, the empty tablet is eliminated from the body. Advise patient's that they should not be concerned if they occasionally observe the empty tablet in the stools

Not established for use in children

Pregnancy

South African recommendations

• Contraindicated
• Safety in pregnancy has not yet been established

Breastfeeding

South African recommendations

• Contraindicated
• Safety in breastfeeding has not yet been established

Fertility

South African recommendations

• Fertility in males: Studies in rats after oral administration of doxazosin base showed reduced fertility in males, which was reversible after two weeks of treatment termination at doxazosin base exposure of 13-fold above the human exposure (AUC) at the MHRD of 8mg doxazosin extended release tablets. There have been no reports of any effects of doxazosin on male fertility in humans

• No dose adjustment recommended

• Caution; no dose adjustment recommended

• No dose adjustment recommended

Central Nervous System Disorders 

• Somnolence
• Dizziness
• Headache
• Stroke
• Hypoasthesia
• Syncope
• Tremor
• Agitation
• Depression
• Anxiety
• Insomnia
• Nervousness
• Parasthesia
• Asthenia
• Fatigue
• Malaise

Cardiovascular Disorders 

• Palpitations
• Tachycardia
• Angina pectoris
• Myocardial infarction
• Hypotension
• Postural hypotension
• Bradycardia
• Cardiac arrhythmias

Respiratory Disorders 

• Bronchitis
• Cough
• Respiratory tract infection
• Dyspnoea
• Rhinitis
• Epistaxis
• Bronchospasm
• Chest pain

Gastrointestinal Disorders 

• Abdominal pain
• Dyspepsia
• Dry mouth
• Nausea and vomiting
• Constipation
• Flatulence
• Gastroenteritis
• Diarrhoea

Hepatobiliary Disorders 

• Abnormal hepatic function tests
• Cholestasis
• Jaundice
• Hepatitis

Genitourinary Disorders 

• Cystitis
• Urinary incontinence  
• Urinary tract infection
• Dysuria
• Micturition frequency
• Haematuria
• Polyuria
• Increased diuresis
• Nocturia
• Impotence
• Gynaecomastia
• Priapism
• Retrograde ejaculation

Endocrine and Metabolic Disorders

• Gout
• Increased appetite
• Anorexia
• Peripheral oedema
• Weight gain

Musculoskeletal Disorders 

• Back pain
• Myalgia
• Arthralgia
• Muscle cramps
• Muscle weakness

Skin and Subcutaneous Tissue Disorders 

• Pruritus
• Skin rash
• Urticaria
• Alopecia
• Purpura
• Flushing

Immune, Blood and Lymphatic System Disorders 

• Allergic reaction
• Leukopaenia
• Thrombocytopaenia
• Facial oedema
• Influenza-like symptoms

Sensory Disorders 

• Blurred vision
• Vertigo
• Tinnitus
• Introperative floppy iris syndrome

• Phosphodiesterase-5-inhibitors
• Sildenafil
• Tadalafil
• Vardenafil
• Other alpha blockers
• Antihypertensives
• Strong CYP3A4 inhibitors
• Clarithromycin
• Indinavir
• Itraconazole
• Ketoconazole
• Nefazodone
• Nelfinavir
• Ritonavir
• Saquinavir
• Telithromycin
• Voriconazole

None routine

Information to be given to the patient

• Doxazosin is surrounded by an inert, non-absorbable shell that has been specifically designed to control the release of the drug over a prolonged period
• Patients should be advised for this reason that doxazosin tablets should be swallowed whole, and should not be chewn, divided or crushed
• After transit through the gastrointestinal tract, the empty tablet shell is excreted
• Patients should be advised that they should not be concerned if they occasionally observe remains in their stools that look like a tablet

Postural hypotension/syncope

• 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
• It is prudent medical practice to monitor blood pressure on initiation of therapy to minimise the potential for postural effects
• When instituing therapy, 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

Doxazosin is a potent and selective post-junctional alpha-1 adrenoreceptor antagonist that decreases blood pressure through reduction in systemic vascular resistance. This effect is thought to result from selective blockade of the alpha-1-adrenoreceptors located in the vasculature.

Tablet 1mg

• Adco-Doxazosin (Adcock)
• Cardugen (Mylan)

Tablet 2mg

• Adco-Doxazosin (Adcock)

Tablet 4mg

• Adco-Doxazosin (Adcock)
• Cardugen (Mylan)
• Cardura XL 4mg (Pfizer) originator
• Carzin XI (Pharma Dynamics)
• Urodoxa (Aurobindo)

Tablet 8mg

• Cardura XL 8mg (Pfizer) originator