Clinical medicine profile
Prazosin
Therapeutic agent (verify pharmacological class)
- Route
- See product SmPC
- Schedule
- POM
- ATC
- Not assigned
- PPB status
- registered
Safety essentials
The information most likely to change a prescribing or dispensing decision.
Contraindications
- CONTRAINDICATIONS Prazosin hydrochloride capsules are contraindicated in patients with known sensitivity to quinazolines, prazosin, or any of the inert ingredients.
Precautions
- WARNINGS As with all alpha-blockers, prazosin hydrochloride may cause syncope with sudden loss of consciousness.
- In most cases, this is believed to be due to an excessive postural hypotensive effect, although occasionally the syncopal episode has been preceded by a bout of severe tachycardia with heart rates of 120 to 160 beats per minute.
- Syncopal episodes have usually occurred within 30 to 90 minutes of the initial dose of the drug
- occasionally, they have been reported in association with rapid dosage increases or the introduction of another antihypertensive drug into the regimen of a patient taking high doses of prazosin hydrochloride.
- The incidence of syncopal episodes is approximately 1% in patients given an initial dose of 2 mg or greater.
- Clinical trials conducted during the investigational phase of this drug suggest that syncopal episodes can be minimized by limiting the initial dose of the drug to 1 mg, by subsequently increasing the dosage slowly, and by introducing any additional antihypertensive drugs into the patient’s regimen with caution (see DOSAGE AND ADMINISTRATION ) .
- Hypotension may develop in patients given prazosin hydrochloride who are also receiving a beta-blocker such as propranolol.
- If syncope occurs, the patient should be placed in the recumbent position and treated supportively as necessary.
- This adverse effect is self-limiting and in most cases does not recur after the initial period of therapy or during subsequent dose titration.
- Patients should always be started on the 1 mg capsules of prazosin hydrochloride.
- The 2 mg and 5 mg capsules are not indicated for initial therapy.
- More common than loss of consciousness are the symptoms often associated with lowering of the blood pressure, namely, dizziness and lightheadedness.
Dosing matrix
Population and organ-function guidance, shown together for faster comparison.
DOSAGE AND ADMINISTRATION The dose of prazosin hydrochloride capsules should be adjusted according to the patient’s individual blood pressure response. The following is a guide to its administration: Initial Dose 1 mg two or three times a day (see WARNINGS. ) Maintenance Dose Dosage may be slowly increased to a total daily dose of 20 mg given in divided doses. The therapeutic dosages most commonly employed have ranged from 6 mg to 15 mg daily given in divided doses. Doses higher than 20 mg usually do not increase efficacy, however a few patients may benefit from further increases up to a daily dose of 40 mg given in divided doses. After initial titration some patients can be maintained adequately on a twice daily dosage regimen. Use With Other Drugs When adding a diuretic or other antihypertensive agent, the dose of prazosin hydrochloride capsules should be reduced to 1 mg or 2 mg three times a day and retitration then carried out. Concomitant administration of prazosin hydrochloride capsules with a PDE-5 inhibitor can result in additive blood pressure lowering effects and symptomatic hypotension; therefore, PDE-5 inhibitor therapy should be initiated at the lowest dose in patients taking prazosin hydrochloride capsules.
See label paediatric section if present; otherwise use paediatric formulary — do not extrapolate adult doses.
Review renal impairment dosing; many agents need CrCl/eGFR adjustment.
- CrCl 0–120: Confirm renal dosing in product SmPC / primary label.
Review hepatic impairment dosing; monitor LFTs if agent is hepatically cleared or hepatotoxic.
Use, effects & interactions
Indications
- INDICATIONS AND USAGE Prazosin hydrochloride capsules are indicated for the treatment of hypertension, to lower blood pressure.
- Lowering blood pressure reduces the risk of fatal and nonfatal cardiovascular events, primarily strokes and myocardial infarctions.
- These benefits have been seen in controlled trials of antihypertensive drugs from a wide variety of pharmacologic classes, including this drug.
- Control of high blood pressure should be part of comprehensive cardiovascular risk management, including, as appropriate, lipid control, diabetes management, antithrombotic therapy, smoking cessation, exercise, and limited sodium intake.
- Many patients will require more than one drug to achieve blood pressure goals.
- For specific advice on goals and management, see published guidelines, such as those of the National High Blood Pressure Education Program’s Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC).
- Numerous antihypertensive drugs, from a variety of pharmacologic classes and with different mechanisms of action, have been shown in randomized controlled trials to reduce cardiovascular morbidity and mortality, and it can be concluded that it is blood pressure reduction, and not some other pharmacologic property of the drugs, that is largely responsible for those benefits.
- The largest and most consistent cardiovascular outcome benefit has been a reduction in the risk of stroke, but reductions in myocardial infarction and cardiovascular mortality also have been seen regularly.
- Elevated systolic or diastolic pressure causes increased cardiovascular risk, and the absolute risk increase per mmHg is greater at higher blood pressures, so that even modest reductions of severe hypertension can provide substantial benefit.
- Relative risk reduction from blood pressure reduction is similar across populations with varying absolute risk, so the absolute benefit is greater in patients who are at higher risk independent of their hypertension (for example, patients with diabetes or hyperlipidemia), and such patients would be expected to benefit from more aggressive treatment to a lower blood pressure goal.
- Some antihypertensive drugs have smaller blood pressure effects (as monotherapy) in black patients, and many antihypertensive drugs have additional approved indications and effects (e.g., on angina, heart failure, or diabetic kidney disease).
- These considerations may guide selection of therapy.
Adverse effects
- ADVERSE REACTIONS Clinical trials were conducted on more than 900 patients.
- During these trials and subsequent marketing experience, the most frequent reactions associated with prazosin hydrochloride therapy are: dizziness 10.3%, headache 7.8%, drowsiness 7.6%, lack of energy 6.9%, weakness 6.5%, palpitations 5.3%, and nausea 4.9%.
- In most instances, side effects have disappeared with continued therapy or have been tolerated with no decrease in dose of drug.
- Less frequent adverse reactions which are reported to occur in 1 to 4% of patients are: Gastrointestinal: vomiting, diarrhea, constipation.
- Cardiovascular: edema, orthostatic hypotension, dyspnea, syncope.
- Central Nervous System: vertigo, depression, nervousness.
- Dermatologic: rash.
- Genitourinary: urinary frequency.
- EENT: blurred vision, reddened sclera, epistaxis, dry mouth, nasal congestion.
- In addition, fewer than 1% of patients have reported the following (in some instances, exact causal relationships have not been established): Gastrointestinal: abdominal discomfort and/or pain, liver function abnormalities, pancreatitis.
- Cardiovascular: tachycardia.
- Central Nervous System: paresthesia, hallucinations.
- Dermatologic: pruritus, alopecia, lichen planus.
- Genitourinary: incontinence, impotence, priapism.
Drug interactions
Open multi-drug checker ↗- Professional use: confirm indication, dose, duration, monitoring and patient counselling points against current Kenya STG / EML and the product SmPC.
- Document allergy status and key interactions.
Mechanism & disposition
Alpha-adrenoceptor blocking agents Mechanism is agent-specific.
Read complete mechanism
Alpha-adrenoceptor blocking agents Mechanism is agent-specific. At receptor, enzyme, ion channel, transporter or microbial target level, the drug alters a physiological or pathological pathway to produce its therapeutic effect. Confirm precise molecular mechanism in current SmPC / pharmacology reference for this INN before high-stakes decisions.
Product-specific
Product-specific
See product SmPC
relative to the drug in a 20% alcoholic solution is 90%, resulting in peak levels approximately 65% of that of the drug in solution. Animal studies indicate that prazosin hydrochloride is extensively metabolized, primarily by demethylation and conjugation, and excreted mainly via...
in man. In clinical studies in which lipid profiles were followed, there were generally no adverse changes noted between pre-and post-treatment lipid levels.
of two to three hours. The drug is highly bound to plasma protein. Bioavailability studies have demonstrated that the total
Pregnancy, lactation & diet
Usage in Pregnancy: Pregnancy Category C. Prazosin hydrochloride has been shown to be associated with decreased litter size at birth, 1, 4, and 21 days of age in rats when given doses more than 225 times the usual maximum recommended human dose. No evidence of drug-related external, visceral, or skeletal fetal abnormalities were observed. No drug-related external, visceral, or skeletal abnormalities were observed in fetuses of pregnant rabbits and pregnant monkeys at doses more than 225 times and 12 times the usual maximum recommended human dose, respectively. The use of prazosin and a beta-blocker for the control of severe hypertension in 44 pregnant women revealed no drug-related fetal abnormalities or adverse effects. Therapy with prazosin was continued for as long as 14 weeks. 1 Prazosin has also been used alone or in combination with other hypotensive agents in severe hypertension of pregnancy by other investigators. No fetal or neonatal abnormalities have been reported with the use of prazosin. 2 There are no adequate and well controlled studies which establish the safety of prazosin hydrochloride in pregnant women. Prazosin hydrochloride should be used during pregnancy only if the potential benefit justifies the potential risk to the mother and fetus.
Nursing Mothers: Prazosin hydrochloride has been shown to be excreted in small amounts in human milk. Caution should be exercised when Prazosin hydrochloride is administered to a nursing woman. Usage in Children: Safety and effectiveness in children have not been established.
Brands & loaded prices
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Sources & review state
Decision support only. Confirm patient-specific decisions against the current product SmPC, Kenya STG/EML, and professional judgement.