- Drugs List
- Therapeutic Indications
- Precautions and Warnings
- Pregnancy and Lactation
- Side Effects
Oral formulations containing phenoxybenzamine hydrochloride
Hypertension - due to phaeochromocytoma
Starting dose: 10mg daily. Increase by 10mg daily until control of hypertensive episodes is achieved, or postural hypotension occurs.
Maintenance dose: Usually 1mg/kg to 2mg/kg daily in two divided doses.
When tumours are secreting an appreciable amount of adrenaline as well as noradrenaline, concurrent beta-adrenergic blockade may be necessary to control tachycardia and arrhythmias.
Use with caution.
10mg daily should be sufficient.
Hypertension in phaeochromocytoma (unlicensed)
0.5mg/kg to 1mg/kg twice daily. Titrate according to response.
Within 1 month of a myocardial infarction
Precautions and Warnings
Children 1 month to 18 years
Congestive cardiac failure
Glucose-galactose malabsorption syndrome
Ischaemic heart disease
Severe cardiac disorder
Advise patient dizziness may affect ability to drive or operate machinery
Staff & patient: Risk of contact sensitisation,avoid contamination of hands
Advise patient that postural hypotension may occur
Potentially mutagenic and carcinogenic
Phenoxybenzamine has been shown to be carcinogenic and mutagenic in animal and bacterial models and so should only be used after very careful consideration of the risks in patients in which alternative treatment is inappropriate.
Pregnancy and Lactation
Use phenoxybenzamine with caution during pregnancy.
The manufacturer states that there is little evidence for the safety of phenoxybenzamine use during pregnancy and thus should not be used unless considered essential.
Schaefer (2015) suggests that phenoxybenzamine can be used during pregnancy. If phenoxybenzamine is used during the first trimester, a follow-up sonography should be offered to verify normal development of the foetus.
Maternal alpha-blockade may reduce or eliminate the adverse effect of hypertension on placental perfusion and subsequently reduce the risk of poor foetal health. No adverse effects have been reported in the limited data available (Briggs, 2015).
The use of all medication in pregnancy should be avoided whenever possible; particularly in the first trimester. Non-drug treatments should also be considered. When essential, a medication with the best safety record over time should be chosen, employing the lowest effective dose for the shortest possible time. Polypharmacy should be avoided. Teratogens taken in the pre-embryonic period, often quoted as lasting until 14 to 17 days post-conception, are believed to have an all-or-nothing effect. Where drugs have a short half-life, and when the date of conception is certain, this may allow women to be reassured where drug exposure has occurred within this time frame. Further advice may be available from the UK National Teratology Information Service (NTIS) and through ToxBase, available via password on the internet ( www.toxbase.org ) or if this is unavailable at the backup site ( www.toxbasebackup.org ).
Use phenoxybenzamine with caution during breastfeeding.
Schaefer (2015) suggests that phenoxybenzamine should not be used during breastfeeding. If the mother is taking phenoxybenzamine, the infant should not be weaned but a change is therapy is recommended.
The molecular weight of the drug (about 340) is low enough such that excretion of the drug into breast milk should be expected. Potential adverse effects on the infant are unknown (Briggs, 2015).
Neonates, infants born prematurely, those with low birth weight, those with an unstable gastrointestinal function or who have serious illnesses may require special consideration. For any infant, if a drug is prescribed to the nursing mother, it should be at the lowest practical dose and for the shortest time. When drug administration is unavoidable and breastfeeding is to continue, minimisation of exposure of the infant to the drug may sometimes be achieved by timing the maternal doses to just after a feeding episode. Infants exposed to drugs via breast milk should be monitored for unusual signs or symptoms. Interactions between the drug received by the infant from the mother's milk and medication prescribed for the infant should also be considered, for example, when the drug given to the infant may prevent metabolism of the drug received via breast milk.
Specialist advice is available from the UK Drugs in Lactation Advisory Service at https://www.midlandsmedicines.nhs.uk/content.asp?section=6&subsection=17&pageIdx=1
Failure of ejaculation
It is strongly recommended that the UK National Poisons Information Service be consulted on cases of suspected or actual overdose where there is doubt over the degree of risk or about appropriate management.
The following number will direct the caller to the relevant local centre (0844) 892 0111
Information may be obtained if you have access to ToxBase the primary clinical toxicology database of the National Poisons Information Service. This is available via password on the internet ( www.toxbase.org ) or if this is unavailable at the backup site ( www.toxbasebackup.org ).
Last Full Review Date: January 2017
Drugs During Pregnancy and Lactation: Treatment Options and Risk Assessment, 3rd edition (2015) ed. Schaefer, C., Peters, P. and Miller, R. Elsevier, London.
Drugs in Pregnancy and Lactation: A Reference Guide to Fetal and Neonatal Risk, 10th edition (2015) ed. Briggs, G., Freeman, R. Wolters Kluwer Health, Philadelphia.
Summary of Product Characteristics: Phenoxybenzamine 10mg Capsules. Concordia International. Revised November 2015.
NICE Evidence Services Available at: www.nice.org.uk Last accessed: 13 September 2017
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Medscape UK | Univadis prescription drug monographs & interactions are based on FDB Multilex Content
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