Terazosin

Terazosin is a selective alpha 1 blocker with a long duration, used for hypertension and benign prostatic hyperplasia. It resembles doxazosin and prazosin in its effects and hazards. It is stocked in few East African markets, where doxazosin or tamsulosin are usual.

Classification. Selective post synaptic alpha 1 blocker; quinazoline.

Mechanism. Blocks alpha 1 receptors on arterial and venous smooth muscle and on the prostate and bladder neck, lowering vascular resistance and urinary outlet resistance.

Pharmacodynamics. Blood pressure falls within 1 hour, peaks at 2 to 3 hours, with effect lasting 24 hours. Orthostatic hypotension is greatest after the first dose.

Pharmacokinetics. Oral bioavailability about 90% and little first pass metabolism; peak at 1 hour; half life about 12 hours; mainly faecal excretion with some renal.

Hypertension, adult (add on).

• Start 1 mg at bedtime.

• Double the dose weekly as tolerated, to 2 mg, 5 mg and 10 mg.

• Usual maintenance 1 to 5 mg once daily (up to 10 mg); maximum 20 mg daily, though doses over 20 mg do not add benefit.

Benign prostatic hyperplasia, adult.

• Start 1 mg at bedtime.

• Increase to 2 mg, 5 mg, then 10 mg once daily after 1 to 2 weeks at each step.

• Usual maintenance 5 to 10 mg once daily; maximum 20 mg daily.

• Assess the symptom response at 4 to 6 weeks.

Restarting. If therapy is interrupted for several days, restart at 1 mg.

Children. Not established.

Contraindications. Hypersensitivity to quinazolines; micturition syncope.

Warnings. First dose syncope; orthostatic hypotension; priapism; intraoperative floppy iris syndrome; fluid retention; caution in cardiac failure and severe liver impairment. Can cause a fall in haemoglobin, haematocrit and albumin through haemodilution.

Adverse effects. Dizziness, weakness, headache, palpitations, nasal congestion, peripheral oedema, blurred vision, somnolence, nausea.

Interactions. Phosphodiesterase 5 inhibitors: hypotension; start at the lowest dose. Other antihypertensives add hypotension. Alcohol worsens orthostatic effects.

Special groups.

• Pregnancy: limited data; avoid unless essential.

• Breastfeeding: limited data; avoid.

• Older adults: bedtime dosing and slow titration.

• Kidney impairment: no adjustment; not removed by dialysis.

• Liver impairment: use with caution.

Formulations. Tablets 1 mg, 2 mg, 5 mg and 10 mg; capsules 1 mg to 10 mg in some markets.

Administration. Oral once daily at bedtime. Warn about dizziness on standing.

Baseline. Sitting and standing blood pressure, prostate assessment, eye history.

Monitoring. Pressure at 2 to 3 hours after the first dose and each increase; urinary symptoms score at 4 to 6 weeks; oedema and weight.

Stopping. No taper needed.

Common prescribing errors. Starting above 1 mg; assuming equivalence in milligram terms with doxazosin or tamsulosin; omitting the eye warning.