Question

what is Dales vasomotor reversal response and clinical toxicity of beta receptor antagonist drugs

Answer 1

VASOMOTOR REVERSAL OF DALES: This concept was first discovered by SIR HH DALE and it is seen with ADRENALINE drugs.

WE HAVE TO KEEP IN MIND THAT:

* alpha1 acts on blood vessels which cause vasoconstriction and thus increase blood pressure.

* beta2 present in blood vessel cause vasodilation and thus fall in blood pressure.

Normally adrenaline in lower concentraion works on beta receptors whereas in higher concentration works on all receptors of vessels. If we give adrenaline intravenously in higher concentration and rapidly then it will act on alpha1 and beta 2 receptor but after some time alpha1 receptor action will predominant the beta2 action therefore rise in blood pressure will be seen.

After rapid metabolism in body the concentration of adrenaline is decreased and as we know that at lower level adrenaline acts on beta2 receptors therefore there will be falls in BP. This phenomenon is known as BIPHASIC RESPONSE.

In the next step we give the nonselective aplha blocker which blocks the action of alpha receptor and there will be no action of alpha1 in blood vessels.

In third step again if we administer adrenaline then there will be only action of beta2 receptors so the BP will fall.

This response or phenomenon called DALES VASOMOTOR REVERSAL RESPONSE.

CLINICAL TOXICITY OF BETA RECEPTOR ANTAGONIST DRUG:

Beta receptor antagonist drugs are also known as beta-blockers. Examples are propranolol, atenolol, etc. These are used to reduce blood pressure.

SIDE EFFECTS can be: fatigue, nausea, vomiting, depression, cold hands and feet, weight gain, arrhythmias, bradycardia, orthostatic hypotension, blurred vision, pulmonary edema, etc.

* Never give beta-blockers to the patient with ASTHMA as it triggers the ASTHMATIC ATTACK.

* As beta-blockers have no serious side effects, therefore, it rarely cause any death due to toxicity. But it is important for diabetic patients with beta-blocker therapy to check blood sugar level as it can block the signs of low sugar level such as "rapid heart rate".

* If toxicity or overdose occurs then the signs could be: bradycardia, severe dizziness, fainting, severe drowsiness, bluish fingernails or palms, seizures, and dyspnea. Notify the physician immediately.

*Hypotension can be treated by Trendelenburg position, and iv fluids.

* Vasopressor may be used and glucagon has been used to treat bradycardia and hypotension.

* Advise patient to check the pulse regularly if it is less than 50 beats per minute then notify the doctor and hold the dose. Notify if any of the above symptoms seen. never miss the dose or double the dose without prescription.