ABSTRACT
This is a prospective study to determine whether a maternal orally administered azo
dye, phenazopyridine hydrochloride, would cross into amniotic fluid, and thus be of
potential aid in the diagnosis of rupture of the membranes. Based on anecdotal experience,
we hypothesized that this compound would cross the placenta and be excreted in the
fetal urine, causing discoloration of the amniotic fluid. Ten patients with uncomplicated
pregnancies undergoing elective amniocentesis for obstetric indications received an
oral dose of 400 mg of phenazopyridine hydrochloride 4 hours prior to the procedure.
Amniotic fluid was also available from five control patients who did not receive phenazopyridine
hydrochloride. The typical orange-to-red discoloration of the urine was seen in all
study patients, indicating ingestion of the dye. None of the ten patients had evidence
of the azo dye in their amniotic fluid by visual inspection or by spectrophotometric
absorbance. After the amniotic fluid samples were acidified, the presence of the azo
dye was visually demonstrable, and spectrophotometry confirmed measurable concentrations
(mean ± SE: 13.08 ± 0.72 μg/ml). We conclude that although phenazopyridine hydrochloride
does cross the placenta into the fetal compartment, its presence causes a visual and
spectrophotometric change in the color of amniotic fluid only when the normal basic
pH of amniotic fluid is acidified.
