A previous study provided supporting data for the concept that anti-human immunodeficiency virus (HIV) drugs, as represented
by aurintricarboxylic acid (ATA), can be released from a calcium–alginate complex through the action of citrate derived from
seminal fluid (1). This approach is especially attractive because the highest concentration of the anti-HIV drug would be
released only during insemination and would, theoretically, be most effective for protecting women against infection from
HIV-positive sexual partners. While the intended route of application is intravaginal, it is possible that intrarectal administration
could potentially provide chemoprophylaxis for men and women.
This approach may be a useful adjunct to condoms and anti-HIV drugs in gels. The initial study provided dissolution data for
a single concentration of citrate and aurintricarboxylic acid in a range of calcium–alginate formulations, where both calcium
chloride and sodium alginate were used in equivalent concentrations (from 0.5–2.0% w/v). The purpose of the present study
was to investigate the effect of variables (i.e., calcium and alginate) in the formulation and to investigate citrate as the
most important physiological factor for dissolution. Although ATA was used in the previous study, the focus on calcium and
alginate as variables is more important when considering other anti-HIV drugs (2–5).
Calcium–alginate gels may be formed readily into various sizes and shapes from dry, ultrathin films that rapidly release drug
upon simple hydration (i.e., immediately after intravaginal and intrarectal application) to suppositories with sustained-release
characteristics (6). The present study also investigates the ability of cellulose to enhance viscosity in the formulation
without interfering with the ionic interactions between calcium, alginate, and citrate.
Calcium chloride, sodium citrate, microgranular α-cellulose, and aurintricarboxylic acid (sodium salt) were obtained from
Sigma-Aldrich (St. Louis, MO). Sodium alginate as Protanal LF 200 was obtained from Protan (Portsmouth, NH). The first formulation
trial examined the effect of citrate on dissolution. In this trial, two different formulations were evaluated. At a fixed
concentration of ATA in alginate, where each mL of alginate (i.e., 0.5 and 2.0% w/v) contained 1 mg of ATA, the ATA was immobilized
in calcium alginate with equal (w/v) concentrations of calcium chloride and sodium alginate. Beads of calcium–alginate ATA
complex (~25 μL/bead) were produced by dropwise addition of the ATA–alginate mixture into aqueous solutions of calcium chloride.
The beads were stored in water at 4 °C until tested. For citrate dissolution testing, 1 mL of sodium citrate (66 or 132 mM
at pH 8.0) was added to five calcium–alginate ATA beads placed in each well of a 24-well Corning Costar 3473 microtiter plate
(Corning, Corning, NY) and incubated at 23 °C.
The time necessary for total dissolution of the beads was gauged by visual inspection. The microtiter plates were mixed by
an MS-3 digital mixer (IKA, Staufen, Germany) at 500 rpm. Procedures for the second formulation trial (for testing the effect
of calcium in the formulation) were identical, except that beads were produced by adding 0.5 and 2.0% alginate solutions to
0.5, 1.0, and 2.0% (w/v) calcium-chloride solutions. A single concentration of citrate was used for dissolution testing (i.e.,
132 mM). For fabrication of suppositories without ATA, 1 g of cellulose was thoroughly mixed with 20 mL of 2% (w/v) alginate
solution to prepare a cellulose–alginate suspension. The suspension (2 mL) was loaded into a 10-cc syringe (No. 305482, BD,
Franklin Lakes, NJ) from which the end was removed at the 1-mL index mark, yielding an open bore. The suspension was extruded
from the syringe directly into 100 mL of 2% (w/v) calcium-chloride solution (at 23 °C) and stirred by oscillation for 20 min
in an orbital mixer (Belly Button, Stovall, Greensboro, NC).
The suppositories contained approximately 2 mL each and were stored in distilled water at 4 °C until tested. For dissolution
testing, each suppository was placed into one well of a six-well, Corning Costar 3471 microtiter plate (Corning) and incubated
at 23 °C. Each well contained 5 mL of sodium citrate at a concentration of 132 mM. The microtiter plates were mixed with an
MS-3 digital mixer at 250 rpm. The time necessary for total dissolution of the suppositories was gauged by visual inspection.