Alpha 1 receptor antagonists

Question 1

Action of phenoxybenzamine

Answer 1

Phenoxybenzamine covalently binds with and irreversibly inactivates alpha receptors- long duration

Question 2

What are the uses of phenoxybenzamine?

Answer 2

As it has a vasodilator action it is used for control of blood pressure and autonomic symptoms in phaeocromocytoma, prior to or during surgery for the condition.

Question 3

Why does phenoxybenzamine have side effects?

Answer 3

The drug has non-specific actions related to effects on other receptors, including muscarinic, histamine and 5-HT receptors. These underpin its many side effects.

Question 4

Action of phentolamine

Answer 4

Phentolamine is a competitive reversible antagonist of A receptors with a much shorter duration of action.

Question 5

What are the uses of phentolamine?

Answer 5

As it has a vasodilator action it is used for control of blood pressure and autonomic symptoms in phaeocromocytoma, prior to or during surgery for the condition.

Question 6

Cause of phaeocromocytoma

Answer 6

Development is linked to hypoxia, conditions that may cause hypoxia include severe hypertension, congenital heart disease, drugs, withdrawal from drugs or a familial disorder

Question 7

What is the presentation of phaeocromocytoma?

Answer 7

Presentation: increased blood pressure due to raised levels of noradrenaline and adrenaline, may be resistant to conventional medicines, sweating, abdominal pain, rapid heart rate, irritability and anxiety, episodic and sudden onset of severe headaches

Question 8

Diagnosis of phaeocromocytoma

Answer 8

Diagnosis: MRI, PET imaging, lab tests to assess hormone levels, blood plasma and urine test for catecholamine and metanephrine levels

Question 9

What is the treatment of phaeocromocytoma?

Answer 9

Treatment: surgical removal of the tumour is usually the main method of treatment, in cancerous PCC radiotherapy and chemotherapy may be required after surgery, steroids until the adrenal glands restart normal function

Question 10

Selective A1 receptor antagonists

Answer 10

Prazosin, doxazosin and terazosin are antihypertensive agents, used alone or in combination with other hypertensive drugs, not recommended for first line treatment according to the ACD guidelines.

Question 11

Give a use of selective A1 receptor antagonists

Answer 11

All of these drugs can be used to relax the smooth muscle of the bladder and the prostate capsule. They are therefore used for treatment of urinary retention and symptomatic treatment of benign prostatic hyperplasia.