Ondansetron Oral Dissolve Tab vs. Oral Solution in Children Presenting to the Emergency Department with Gastroenteritis.

BACKGROUND: Ondansetron is often used in the emergency department (ED) to promote oral rehydration in children with acute gastroenteritis (AGE), yet medication solutions administered orally may be poorly tolerated in this population. OBJECTIVES: We compared the tolerability of ondansetron oral dissolve tab (ODT) to oral solution (OS) in children presenting to the ED with AGE. METHODS: Using alternate-day controlled clinical trial design, children aged 3 months to 10 years received either ondansetron ODT or OS. Our primary outcome was early vomiting (within 15 min of drug administration). The secondary outcome was intravenous (i.v.) fluid administration. RESULTS: There were 462/534 eligible children who met study criteria. Demographics, severity, and duration of illness were similar between groups. Using intention-to-treat analysis, early vomiting occurred in 8/209 ODT vs. 19/253 OS children (3.8% vs. 7.5%; odds ratio [OR] 0.49; 95% confidence interval [CI] 0.18-1.21). Using as-treated analysis, 6/222 (2.7%) children receiving ODT experienced early vomiting, compared with 21/221 (9.5%) of the OS group (OR 0.26; 95% CI 0.09-0.70). The proportion of children discharged without i.v. fluids was not different (intention-to-treat: ODT = 91.4% (191/209), OS = 94.1% (238/253), OR 1.49, 95% CI 0.69-3.28; as-treated: ODT = 92.3% (205/222), OS = 93.2% (206/221), OR 0.88, 95% CI 0.40-1.93). CONCLUSIONS: Using a conservative intention-to-treat analysis, we found that children presenting to an ED with AGE did not have statistically less early vomiting with ondansetron ODT as compared with OS. However, our as-treated analysis demonstrates that children receiving ondansetron ODT experienced early vomiting approximately one-third as often as those receiving OS. The rate of i.v. fluid administration was no different between groups regardless of the type of analysis used.

A conformationally mobile cysteine residue (Cys-561) modulates Na+ and H+ activation of human CNT3.

In humans, the SLC28 concentrative nucleoside transporter (CNT) protein family is represented by three Na+-coupled members; human CNT1 (hCNT1) and hCNT2 are pyrimidine and purine nucleoside-selective, respectively, whereas hCNT3 transports both purine and pyrimidine nucleosides and nucleoside drugs. Belonging to a phylogenetic CNT subfamily distinct from hCNT1/2, hCNT3 also mediates H+/nucleoside cotransport. Using heterologous expression in Xenopus oocytes, we have characterized a cysteineless version of hCNT3 (hCNT3C-). Processed normally to the cell surface, hCNT3C- exhibited hCNT3-like transport properties, but displayed a decrease in apparent affinity specific for Na+ and not H+. Site-directed mutagenesis experiments in wild-type and hCNT3C- backgrounds identified intramembranous Cys-561 as the residue responsible for this altered Na+-binding phenotype. Alanine at this position restored Na+ binding affinity, whereas substitution with larger neutral amino acids (threonine, valine, and isoleucine) abolished hCNT3 H+-dependent nucleoside transport activity. Independent of these findings, we have established that Cys-561 is located in a mobile region of the hCNT3 translocation pore adjacent to the nucleoside binding pocket and that access of p-chloromercuribenzene sulfonate to this residue reports a specific H+-induced conformational state of the protein ( Slugoski, M. D., Ng, A. M. L., Yao, S. Y. M., Smith, K. M., Lin, C. C., Zhang, J., Karpinski, E., Cass, C. E., Baldwin, S. A., and Young, J. D. (2008) J. Biol. Chem. 283, 8496-8507 ). The present investigation validates hCNT3C- as a template for substituted cysteine accessibility method studies of CNTs and reveals a pivotal functional role for Cys-561 in Na+- as well as H+-coupled modes of hCNT3 nucleoside transport.