Phenoxybenzamine
Clinical data | |
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Trade names | Dibenzyline |
AHFS/Drugs.com | Monograph |
MedlinePlus | a682059 |
Pregnancy category |
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Routes of administration | Oral |
ATC code | |
Pharmacokinetic data | |
Elimination half-life | 24 hours |
Identifiers | |
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JSmol) | |
Chirality | Racemic mixture |
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Phenoxybenzamine (PBZ,[1] marketed under the trade names Dibenzyline and Dibenyline) is a non-selective, irreversible alpha blocker.
Uses
It is used in the treatment of hypertension, and specifically that caused by pheochromocytoma. It has a slower onset and a longer-lasting effect compared with other alpha blockers.
It was also the first alpha blocker to be used for treatment of benign prostatic hyperplasia,[2] although it is currently seldom used for that indication due to unfavourable side effects.
It has been used in the treatment of hypoplastic left heart syndrome.[3]
It is also used in
Investigational
Phenoxybenzamine has long been known to block ejaculation without affecting semen quality or ability to achieve orgasm, which could make it an effective male contraceptive. This effect is completely reversible, and is believed to be the result of alpha-1 adrenoceptor blockade in the longitudinal muscles of the vas deferens.[4][5][6] A dose of 20 mg/day results in aspermia due to reversible paralyzing effects on the vas deferens, ampulla, and ejaculatory ducts.[7] Due to these actions, phenoxybenzamine is also useful for the treatment of premature ejaculation in men.[7]
Pharmacology
Phenoxybenzamine is used as an anti-hypertensive due to its efficacy in reducing the
As a non-selective alpha receptor antagonist, it will also affect both the postsynaptic alpha-1 and presynaptic alpha-2 receptors in the nervous system, and so reduce
Clinically, non-selective alpha antagonists block alpha receptors (but do not differentiate between alpha-1 and alpha-2). They are used as antihypertensives because they block alpha-receptor-mediated vasoconstriction. The block on alpha-2 receptors further potentiates beta-effects, increasing cardiac output.
Phenoxybenzamine has a long-lasting action, binding covalently to the alpha receptors. Its only current clinical use is in preparing patients with pheochromocytoma for surgery; its irreversible antagonism and the resultant depression in the maximum of the agonist dose-response curve are desirable in a situation where surgical manipulation of the tumour may release a large bolus of pressor amine into the circulation. Typically, phenoxybenzamine is not used in the long term, as new receptors are made to upregulate alpha stimulation. The main limiting side-effects of alpha antagonists is that the baroreceptor reflex is disrupted and thus this can cause postural hypotension.
Phenoxybenzamine also has
Stereoisomerism
Phenoxybenzamine contains a stereocenter, so there are two
Enantiomers of phenoxybenzamine | |
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(R)-Phenoxybenzamine CAS number: 71799-91-2 |
(S)-Phenoxybenzamine CAS number: 71799-90-1 |
See also
References
- ^ Bradley K. "Clinical Guideline: Phaeochromocytoma Diagnosis and Management" (PDF). University Hospitals Bristol. NHS Foundation Trust. Archived from the original (PDF) on 25 March 2023.
- PMID 88984.
- PMID 17646482.
- PMID 18382745.
- PMID 2899490.
- PMID 6430643.
- ^ ISBN 978-981-10-3694-1.
- PMID 11395517.
- PMID 8744977.
- ^ ISBN 978-0-07-148869-3.
- ISBN 978-0-08-054111-2.
- ISBN 978-0-8493-8387-8.
- ISBN 978-3-642-63389-8.
External links
- Media related to Phenoxybenzamine at Wikimedia Commons