Epinephrine in local anesthetics?

on 20.1.09 with 0 comments

CASE: your pt is taking prazosin (Minipres) (vasodilator, alpha-1 blocker) for HTN and propranolol (Inderal) (beta-blocker) to control a cardiac arrhythmia. These conditions are well controlled and he appears medically stable.

Epinephrine works via alpha-1, so it is attenuated. If you had to inject epinephrine as an emergency (1:1000) for tx of anaphylactic shock, propranolol blocks beta-1 in the heart so the epinephrine will be blocked or markedly attenuated… so we’ve basically pharmacologically denervated this patient; alpha and beta receptors are blocked.

Epinephrine contained in lidocaine had little effects on carotid and cerebral dynamics; so you’re not altering blood flow to the brain when you’re using epinephrine. But, if you put norepinephrine in your lidocaine it increased the BP, decreased the heart rate, and decreased carotid blood flow. Clearly, this is another reason we don’t use norepinephrine in local anesthetic.

--even at 1:80,000 epinephrine does not affect carotid and cerebral blood flow, so don’t be afraid to use the lidocaine with epi.

Although there are some guidelines for use of epinephrine in dentistry, that doesn’t necessarily mean that it is contraindicated in those instances. For example, a patient taking levothyroxin as thyroid replacement therapy for hypothyroidism, to restore their T3/T4 so that they are euthyroid, is not contraindicated for epinephrine. Although epi does accentuate the effects of thyroxin, and thyroxin does accentuate the cardiovascular effects of epi, if the patient is taking just the right amount of L-thyroxin to be euthyroid (normal), there will be no adverse effects of epinephrine. However, the risk lies in the circumstance where the patient is not well controlled, and is in the hyperthyroid range—in this instance epinephrine is contraindicated. That is why you always check to make sure that the patient is well controlled.

Category: Pharmacology Notes



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