Posted by ed_uk on March 15, 2005, at 9:17:14
In reply to Re: I have to go off Nardil! NO!!!!!!!!!!!!!!!!!!!!! » ace, posted by Sarah T. on March 13, 2005, at 23:51:38
Hello :-)
Epinephrine (adrenaline) is the most popular sympathomimetic vasoconstrictor in dentistry. Certain vasoconstrictors can interact dramatically with MAOIs, mainly indirecly-acting sympathomimetics such as phenlypropanolamine. Fortunately, the interaction between epinephrine and MAOIs is apparantly quite minor. Epinephrine is a directly-acting sympathoimetic. It is important to remember than directly-acting sympathomimetics have a different mechanism of action to indirectly-acting sympathomimetics. In lists of drug interactions, there has been a tendency to lump all sympathomimetics together- as if they were all the same, but they are not!! It is commonly assumed that epinephrine is dangerous, this is solely due to reports of interactions between MAOIs and other sympathomimetics which have a different mechanism of action, there haven't been any reports of serious interactions between epinephrine and MAOIs.
From Stockely's Interactions....
The pressor effects of epinephrine (adrenaline), isoprenaline (isoproterenol), norepinephrine (noradrenaline) and methoxamine may be unchanged or only moderately increased in patients taking MAOIs. The increase may be somewhat greater in those who show a significant hypotensive response to the MAOI.
Clinical evidence
(a) Effects in the absence of MAOI-induced hypotensionTwo subjects given phenelzine (Nardil) 15 mg three times daily and another given tranylcypromine (Parnate) 10 mg three times daily for 7 days showed no significant changes in their pressor responses to either epinephrine (adrenaline) or isoprenaline (isoproterenol).
Yet another study in 3 healthy subjects given tranylcypromine (Parnate) found that the effects of norepinephrine were slightly increased, while with epinephrine a two to four fold increase in the effects on heart rate and diastolic pressure took place, but a less marked increase in systolic pressure.
A patient using 1% epinephrine eye drops twice daily showed no increase in blood pressure or heart rate when treated with tranylcypromine (Parnate) 20 mg, rising to 50 mg daily.
Mechanism
These directly-acting sympathomimetic amines act directly on the receptors at the nerve endings, which innervate arterial blood vessels, so that the presence of the MAOI-induced accumulation of norepinephrine within these nerve endings would not be expected to alter the extent of direct stimulation. The enhancement seen in those patients whose blood pressure was lowered by the MAOI might possibly be due to an increased sensitivity of the receptors, which is seen if the nerves are cut, and is also seen during temporary ‘pharmacological severance’.Importance and management
The evidence is limited, but the overall picture is that some slight to moderate enhancement of the effects of norepinephrine (noradrenaline) and epinephrine (adrenaline) may occur in patients who do not show MAOI-induced hypotension. However, the authors of three of the reports cited 1,3,4 are in broad agreement that problems are unlikely to occur. One group 4 says that “it seems that the use of epinephrine, whether administered in eye drops or as a component of local anaesthesia in dental and other procedures, should not be contraindicated in patients receiving MAOIs.”The situation in patients who show a reduced blood pressure due to the use of an MAOI is less clear. One study found an increase in the pressor efforts of norepinephrine and methoxamine in hypertensive patients on pheniprazine or tranylcypromine (Parnate), whereas another 10 found no changes in the pressor effects of norepinephrine in patients on pargyline.
>The dentist had another anesthetic available, but I can't remember the name of it.Prilocaine + felypressin.........
Felypressin is a vasocontrictor which is used in dentistry. In the UK, it is available for dental use in combination with the local anesthetic prilocaine. The brand name is 'Citanest with Octapressin'.
Best regards,
Ed.
poster:ed_uk
thread:470308
URL: http://www.dr-bob.org/babble/20050312/msgs/471233.html