- quote -


Thanks. I hope the board excuses me for asking (almost) the same question
twice.

Since the last time, I have read the paper by Fiscell on "Efficiency of
Installation Methodsfor Prostaglandin Medications", 2006 J of Ocular Pharm.
He discusses drop volume from the Xalatan bottle. First off, (as he point
out) the eye can receive (approx) 30 microLiters in the "palpebral fissure"
or the space between the lids. The tear volume is 7 to 10 microLiters. So
20 to 23 microLiters is available for the medication.

Xalatan has a prescribed dose of 1.5 microGrams. This results in 83.3
drops per bottle or 30 microLiters per drop.

So with this (very assumed) drop volume, 20-23 microLiters of the drop is
installed and the rest overflows. Into the nasal duct, or essentially
one-third of the drop is wasted.

As the paper points out, by holding the Xalatan bottle vertically, at 45
degrees, and horizontally, one gets 94.3, 88.4, 67.1 drops per bottle. A
40% variation from high drop volume to low.

With these variations in drop volume, and the admonition of not to double
drop, and that half a drop might be ok, just exactly what is really the
prescribed medication goal that is desired? Are we talking about a certain
microGram input (plus or minus a certain tolerance)? Or a certain amount of
the 0.005% solution into the eye? Or what?

As the paper points out, the guy holding the bottle better be instructed
to hold it correctly.

Don W.

On 5/18/08 12:35 PM, in article 1y%Xj.5760$r82.2313[at]nlpi069.nbdc.sbc.com,
"Don W" <dwilgus[at]prodigy.net> wrote:

- quote -

chronically. "Double-dropping" tends to get the excess squeezed out onto the
skin where it causes this (dark rings under the eyes). To help prevent this,
even with one drop, it is a good idea to wash the eyelids skin off after
instilling the drop. (It also sometimes causes darkening and growth of
eyelashes, but rinsing off will not prevent this. Now, if they could just
figure out how to package this for people who want this eyelash effect ...)

Some of the excess does go into the tear ducts as mentioned.

On a different note, it is to be dosed only once a day. More frequent use
may recuce its pressure-lowering effects. Xalatan works by causing a type of
inflammation of the sclera, causing scleral outflow. Too much inflammation
reduces this effect.

When using Xalatin, the directions say that one should not "double drop".
That this tends to minimize the effectiveness of the medication. Really
don't understand this. If one puts in too much, the overflow goes down the
nasal duct. And it is the percent solution that stays in the eye along with
the initial tear volume that determines how much medication the eye gets.

Does dropping in the second drop produce a tearing reaction that dilutes
the concentration of the entire 2 drop volume? Seems like that is what is
happening.

Don W.