CARDURA® XL (doxazosin mesylate extended release
tablets) contains doxazosin mesylate which is a quinazoline compound with
the chemical name 1-(4-amino-6,7-dimethoxy-2-quinazolinyl)-4-(1,4- benzodioxan-2-ylcarbonyl)
piperazine methanesulfonate. The empirical formula for doxazosin mesylate
is
C23H25N5O5
• CH4O3S
and the molecular weight is 547.6. It has the following structure:
CARDURA XL is an extended release tablet for oral use and is designed
to deliver 4 or 8 mg of doxazosin as the free base. Each 4 and 8 mg tablet
contains 5.1 and 10.2 mg doxazosin mesylate (includes a 5% overage) to provide
4 and 8 mg doxazosin as a free base, respectively. The inactive ingredients
for CARDURA XL are: polyethylene oxide, sodium chloride, hypromellose, red
ferric oxide, titanium dioxide, magnesium stearate, cellulose acetate, Macrogol®,
pharmaceutical glaze and black iron oxide.
CARDURA XL System Components and Performance
CARDURA XL is similar in appearance to a conventional tablet. It consists,
however, of an osmotically active drug core surrounded by a semipermeable
membrane. The core itself is divided into two layers: an "active" layer
containing the drug, and a "push" layer containing pharmacologically inert
(but osmotically active) components. The membrane surrounding the tablet
is permeable to water but not to drug or osmotic excipients. As water from
the gastrointestinal tract enters the tablet, pressure increases in the
osmotic layer and "pushes" against the drug layer, resulting in the release
of drug through a small, laser-drilled orifice in the membrane on the drug
side of the tablet.
CARDURA XL utilizes GITS (Gastrointestinal Therapeutic System) which
is designed to provide a controlled rate of delivery of doxazosin into the
gastrointestinal lumen which is independent of pH or gastrointestinal (GI)
motility. The function of CARDURA XL depends upon the existence of an osmotic
gradient between the contents of the bi-layer core and fluid in the GI tract.
Drug delivery is essentially constant as long as the osmotic gradient remains
constant, and then gradually falls to zero. The biologically inert components
of the tablet remain intact during GI transit and are eliminated in the
feces as an insoluble shell.