None reported

Pheochromocytoma Pre-operative hypertension Radial artery vasospasm

Peripheral vascular disorders Pulmonary hypertension

Adjunct to the short term management of urinary retention due to neurogenic bladder

Short-term treatment of BPH in patients awaiting surgery.

 Agents for Pheochromocytoma includes- Phenotolame, Phenoxybenzene HCL, Metryrosine , 

Nasal congestion, miosis, postural hypotension, with dizziness and compensatory tachycycardia or hypotension and inhibition of ejuculation may occur. They may vary according to degree of adrenergic blockade and tend to to decrease as therapy continues. GI irritation, drowsiness, and fatigue also occur Sedation, fatigue Pregnancy and lactation

Conditions where a small fall in blood pressure may be undesirable Pregnancy, lactation, cerbrovascular incidents and in the recovery period following myocardial infraction.

Special precautions:

Administer with caution to patients with marked cerbral or coronary arteriosclerosis or renal damage, tachycardia or hypotension. Adrenergic blocking effects may aggrevate respiratory infections. Pregnancy and lactation

Concomittant therapy- Phenoxybenzamine-induced alpha-adrenergic blockage leaves beta-adrenergic receptors unopposed. Compound that stimulate both types of receptors (ie. ephinephrine) may produce an exaggerated hypotensive responses and tachycardia.

Carcinogenesis/ Mutagenesis- Phenoxybenzamine has shown in vitro mutagenic activity in the Ames test and in mouse lymphoma assay. In animals repeated intraperitonal phenoxybenzamine resulted in peritonal sacrcomas, chronic oral dosing produced malignant GI tumors. Clinical significance is not established. Nevertheless, consider these results in determing benefit -to cost ratio.

Indications:

Phecochromocytoma

Dosage:

Individualise dosage. Slowly increase small initial doses umtil the desired eFfect is obtained or side efects become troublesome Initially 10mg twice daily. Increase dosage every other day until optimal dosage is obtained as judged by blood pressure control. Usual dosage range is 20 to 40mg 2 or 3 times daily.

Overdosage- Symptoms

Symptoms may include postural hypotension, resulting in dizziness, or fainting, tachycardia particularly postural, vomiting, lethargy, shock. These are largely due to block of the sympathetic nervous system and of the circulating epinephrine

Treatment

1. Discontinue the drug

2. Trteat circulatory failure, if present

3. In mild overdosage, recumbent position with legs elevated usally restores cerbral circulation

4.In more severe cases institute measures to combat shock effect

5. Usual pressor agents are not efective.

6. Do not use epinephrine.

7. The patient may have to kept flat for 24 hours or more as the drugs effect isprolonged.

8. Leg bandages and an abdominal binder may shorten disability period.

9. May use epinephrine IV to combat severe hypotension, it primarily stimulates alpha receptors

10. Although phenoxybenzamine is an alpha-blocker sufficient norephinephrine will overcome this effect.

 Missed dose-

 1. If you miss a dose of this medicine, take it as soon as possible.

2. However, if it is almost time for next dose, skip the missed dose and go back to your regular dosing schedule.

3. Do not double doses.

=================================================================================== Agents for Pheochromocytoma includes- Phenotolame, Phenoxybenzene HCL, Metryrosine , ================================================================================== Pharmacology: An irreversible alpha-adrenergic receptor ( both pre and postsynaptic ) blocking agent which can produce and maintain ( chemical sympathectomy ). It increases blood flow to skin, mucosa, and abdominal viscera, and lowers supine and standing blood pressures. It has no effect on the parasympathetic system Phenoxybenzamine hydrochloride is a long acting adrenergic alpha-receptor blocking agent. Following oral administration the drug has a gradual onset over several hours and persists for 3 to 4 days following a single dose. It has no effect on the parasympathetic system. Phenoxybenzene is effective as a pre-operative preparation for phenochromocytoma. Phenoxybenzamine prevents alpha-adrenoreceptor mediated spasm of the human radial artery than papaverine. It is also harmful to the endothelium. Pharmacokinetics: Absorption from GI tract is incomplete (20 % to 30% ). Phenoxybenzamine is incompletely and variably absorbed from the GI tract. The maximum effect is attained approx. 1 hour after intervenous dose. The prolonged action of the drug is probably due to formation of a stable covalent bond beween an intermediate of phenoxybenzamine and the receptor. It is highly lipid souble and may accumulate in fat following administration of large doses It has a half-life of approx 24 hours. It is dealkylated to form N-phenoxylsopropyl-benzyl-amine. It is metabolised in the liver and excreted in urine and bile. Small amounts of the drug remain in the body for upto one week.

None reported

Contra-indicated for use during pregnancy and lactation.