Hilary Jones...Drummer

 

"...the character of the nurse is as important as the knowledge she possesses." ~Jarvis, 1996

 

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"Nursing is an art: and if it is to be made an art, it requires an exclusive devotion as hard a preparation, as any painter's or sculptor's work; for what is the having to do with dead canvas or dead marble, compared with having to do with the living body, the temple of God's spirit? It is one of the Fine Arts: I had almost said, the finest of Fine Arts." Florence Nightingale.
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Online music for your listening pleasure.

Dosage

basic drug?

acid drug?

pH

pKa

ionized (%)

Example

1)  The pH of the stomach is 2.5.  The pKa of sodium pentothal is 7.4 and it is acidic.  If a patient is given sodium pentothal orally instead of IV, will it put the patient to sleep?  See the example below:

Doesn't work, just an example

None of the sodium pentothal is ionized in the stomach.  Therefore the patient would absorb 100% of this medication and it would put him to sleep.

 

 

 

2)  A basic drug with a pKa of 7.8 is a known teratogen.  If given IV to a pregnant woman whose blood pH is 7.4, will this drug cross the placenta and effect the baby?  See the example below:

In this example, 72% of the drug is ionized which means 28% of the drug is unionized and will pass through the placenta to effect the baby.

Basics on Ionization

Ionized = water soluble = poor absorption through stomach, BBB, and placenta.

Non-ionized = lipid soluble = absorbed well (cell membranes are composed of lipids)

For example, sodium (Na+) and chloride (Cl-) are both ionized.  Cells must provide a channel for these ions to enter an otherwise impenetrable lipid membrane.

 

Formula

Percent Ionized Formula

 where x = -1 if acid drug or 1 if basic drug

 

Basic Rules

pKa is defined as the pH were a drug exists as 50% ionized and 50% unionized

 

If pKa - pH = 0, then 50% of drug is ionized and 50% is unionized

 

An acid in an acid solution will not ionize
An acid in a basic solution will ionize
A base in a basic solution will not ionize
A base in an acid solution will ionize

 

If pKa - pH = 0.5, then the solution is 75% ionized/ 25% unionized or
75% unionized/ 25% ionized

 

If pKa - pH > 1 then the solution is 99-100% ionized or 99-100% unionized*

Slight discrepancy between this statement and formula used for calculator.  Formula used indicates solutions would be 90-100% ionized or unionized.  These rules were taken from my Nursing 605 course.  My chemistry background is weak and I'm unable to verify the formula used.  Other than this, the formula follows the basic rules.

Formula provided by Mark Earll

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