Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Dextromethorphan and guaifenesin are the main active components in over-the-counter cough medications. Prenatal exposure to dextromethorphan has been shown to be teratogenic in animal models. Data from human studies for either dextromethorphan or guaifenesin are limited and inconclusive. We used data from the population-based National Birth Defects Prevention Study (NBDPS) to examine associations between maternal periconceptional (one month before through three months after conception) use of cough medications containing dextromethorphan, with or without guaifenesin, and isolated neural tube defects (NTDs). We also used NBDPS data to explore associations between such exposures and other isolated major birth defects, as well as associations between maternal periconceptional use of cough medications containing guaifenesin alone and isolated major birth defects. Enrolled cases comprised 19,538 live births, still births, and elective terminations with isolated major birth defects, and enrolled controls comprised 10,200 live births without defects delivered from October 1997 through December 2009. Telephone interview reports of pregnancy exposures, including periconceptional use of cough medications, were obtained from mothers of case and control infants. Two approaches were used to build multivariable models: backward model selection and comparing the change in odds ratios (ORs) by adding each covariable individually into the main effect models. Adjusted ORs (aORs) and 95% confidence intervals (CIs) for maternal periconceptional exposure of cough medications containing dextromethorphan, with or without guaifenesin, or guaifenesin alone, respectively, and 22 types of birth defects were estimated using multivariable logistic regression analysis. Applying our first multivariable model building approach, we observed that maternal periconceptional use of dextromethorphan, with or without guaifenesin, was marginally significantly associated with an increased risk of all NTDs combined (aOR=1.7, 95%CI=1.0-2.9), or spina bifida alone (aOR=1.9, 95%CI=1.0-3.5). Applying our second model-building approach confirmed the associations with all NTDs combined and spina bifida alone (aOR==1.9, 95% CI=1.2-3.0 and aOR=2.1, 95% CI=1.2-3.8; respectively). For other isolated birth defects, a positive, marginally significant association was observed for maternal periconceptional use of dextromethorphan, with or without guaifenesin, and cleft lip with or without cleft palate (aOR=1.3, 95%CI=1.0-1.7) applying our first model building approach. Our second model-building approach produced significant associations between such exposure and gastroschisis (aOR=1.8, 95%CI=1.2-2.8). With regard to maternal periconceptional use of cough medications containing guaifenesin alone, we observed marginally significant associations with all NTDs combined (aOR=1.9, 95%CI=1.1-3.5), spina bifida alone (aOR=2.3, 95%CI=1.1-4.4), or anorectal atresia (aOR=1.9, 95%CI=1.0-3.6) applying our first model-building approach. Applying our second model-building approach did not suggest significant associations between such exposure and birth defects. Our findings suggest that maternal periconceptional use of cough medications containing dextromethorphan or guaifenesin may produce selected major structural birth defects in offspring. These findings provide important evidence to better understand the safety of these cough medications and informs about the potential of this modifiable exposure to cause isolated birth defects. Additional population-based research is necessary to validate these positive associations between cough medications and selected isolated birth defects identified in our study.

The physical stability of guaifenesin in melt-extruded acrylic matrix tablets was investigated. The initial study found that recrystallization was caused by guaifenesin supersaturation in Eudragit[Trademark] L100-55, and that the instability was confined to tablet surfaces. Drug release was not affected by crystal growth as guaifenesin is very water soluble. The addition of a polymer in which guaifenesin showed a higher solubility to the matrix blend decreased recrystallization on storage as supersaturation levels dropped. The second investigation identified heterogeneous nucleation as an additional factor in guaifenesin recrystallization. A quantitative assay showed that talc in matrix tablets accelerated the onset and extent of the recrystallization due to a nucleating effect on guaifenesin. Storage under elevated humidity conditions promoted recrystallization as well, but crystal growth was not correlated with water uptake, which implied a nucleating effect of moisture on guaifenesin. The third study investigated the effect of aqueous film-coating of the matrix tablets to stabilize amorphous guaifenesin using either hypromellose or ethylcellulose as coating polymers. The selection of the coating polymer influenced crystal morphology, and was a major factor in delaying the onset of crystallization, ranging from 1-3 weeks (ethylcellulose film-coatings) to 3-6 months (hypromellose film-coatings). Higher weight gains retarded recrystallization. Factors promoting drug and polymer diffusion, such as long curing times and elevated temperatures during both curing and storage, incomplete film coalescence and high core drug concentrations all resulted in an earlier onset of crystallization. The effects of single-screw extrusion (SSE) and twin-screw extrusion (TSE) of diltiazem hydrochloride and guaifenesin-containing blends in Eudragit[Trademark] L100-55 on drug morphology and dispersion were studied in the fourth project. Guaifenesin solubilized diltiazem hydrochloride, and plasticized Eudragit[Trademark] L100-55. Extrusion temperature influenced the drug morphology in single-screw extrudates, while TSE rendered all formulations amorphous due to higher dispersive mixing capabilities. Drug distribution improved with extrusion temperature and by TSE over SSE. Homogeneous matrices showed the slowest drug release at pH 1.0. Recrystallization was inversely correlated to drug distribution. In conclusion, the physical stability of guaifenesin in hot melt-extruded acrylic matrix tablets was shown to be affected by formulation, processing and post-processing factors. / text