Prediction of pesticide acute toxicity using two-dimensional chemical descriptors and target species classification.

Previous modelling of the median lethal dose (oral rat LD50) has indicated that local class-based models yield better correlations than global models. We evaluated the hypothesis that dividing the dataset by pesticidal mechanisms would improve prediction accuracy. A linear discriminant analysis (LDA) based-approach was utilized to assign indicators such as the pesticide target species, mode of action, or target species - mode of action combination. LDA models were able to predict these indicators with about 87% accuracy. Toxicity is predicted utilizing the QSAR model fit to chemicals with that indicator. Toxicity was also predicted using a global hierarchical clustering (HC) approach which divides data set into clusters based on molecular similarity. At a comparable prediction coverage (~94%), the global HC method yielded slightly higher prediction accuracy (r2 = 0.50) than the LDA method (r2 ~ 0.47). A single model fit to the entire training set yielded the poorest results (r2 = 0.38), indicating that there is an advantage to clustering the dataset to predict acute toxicity. Finally, this study shows that whilst dividing the training set into subsets (i.e. clusters) improves prediction accuracy, it may not matter which method (expert based or purely machine learning) is used to divide the dataset into subsets.

Prediction of in vitro and in vivo oestrogen receptor activity using hierarchical clustering.

In this study, hierarchical clustering classification models were developed to predict in vitro and in vivo oestrogen receptor (ER) activity. Classification models were developed for binding, agonist, and antagonist in vitro ER activity and for mouse in vivo uterotrophic ER binding. In vitro classification models yielded balanced accuracies ranging from 0.65 to 0.85 for the external prediction set. In vivo ER classification models yielded balanced accuracies ranging from 0.72 to 0.83. If used as additional biological descriptors for in vivo models, in vitro scores were found to increase the prediction accuracy of in vivo ER models. If in vitro activity was used directly as a surrogate for in vivo activity, the results were poor (balanced accuracy ranged from 0.49 to 0.72). Under-sampling negative compounds in the training set was found to increase the coverage (fraction of chemicals which can be predicted) and increase prediction sensitivity.

Comparison of global and mode of action-based models for aquatic toxicity.

The ability to estimate aquatic toxicity is a critical need for ecological risk assessment and chemical regulation. The consensus in the literature is that mode of action (MOA) based toxicity models yield the most toxicologically meaningful and, theoretically, the most accurate results. In this study, a two-step prediction methodology was developed to estimate acute aquatic toxicity from molecular structure. In the first step, one-against-the-rest linear discriminant analysis (LDA) models were used to predict the MOA. The LDA models were able to predict the MOA with 85.8-88.8% accuracy for broad and specific MOAs, respectively. In the second step, a multiple linear regression (MLR) model corresponding to the predicted MOA was used to predict the acute aquatic toxicity value. The MOA-based approach was found to yield similar external prediction accuracy (r(2) = 0.529-0.632) to a single global MLR model (r(2) = 0.551-0.562) fit to the entire training set. Overall, the global hierarchical clustering approach yielded a higher combination of accuracy and prediction coverage (r(2) = 0.572, coverage = 99.3%) than the other approaches. Utilizing multiple two-dimensional chemical descriptors in MLR models yielded comparable results to using only the octanol-water partition coefficient (log K(ow)).

MOAtox: A comprehensive mode of action and acute aquatic toxicity database for predictive model development.

The mode of toxic action (MOA) has been recognized as a key determinant of chemical toxicity and as an alternative to chemical class-based predictive toxicity modeling. However, the development of quantitative structure activity relationship (QSAR) and other models has been limited by the availability of comprehensive high quality MOA and toxicity databases. The current study developed a dataset of MOA assignments for 1213 chemicals that included a diversity of metals, pesticides, and other organic compounds that encompassed six broad and 31 specific MOAs. MOA assignments were made using a combination of high confidence approaches that included international consensus classifications, QSAR predictions, and weight of evidence professional judgment based on an assessment of structure and literature information. A toxicity database of 674 acute values linked to chemical MOA was developed for fish and invertebrates. Additionally, species-specific measured or high confidence estimated acute values were developed for the four aquatic species with the most reported toxicity values: rainbow trout (Oncorhynchus mykiss), fathead minnow (Pimephales promelas), bluegill (Lepomis macrochirus), and the cladoceran (Daphnia magna). Measured acute toxicity values met strict standardization and quality assurance requirements. Toxicity values for chemicals with missing species-specific data were estimated using established interspecies correlation models and procedures (Web-ICE; http://epa.gov/ceampubl/fchain/webice/), with the highest confidence values selected. The resulting dataset of MOA assignments and paired toxicity values are provided in spreadsheet format as a comprehensive standardized dataset available for predictive aquatic toxicology model development.

HLA-DRB1*0102 is associated with TINU syndrome and bilateral, sudden-onset anterior uveitis but not with interstitial nephritis alone.

BACKGROUND: Tubulointerstitial nephritis and uveitis (TINU) syndrome is a rare form of uveitis. Previously, the authors had demonstrated a strong association of human leukocyte antigen (HLA) DRB1*0102 with TINU. Here, the authors performed HLA analysis on subjects with isolated bilateral sudden-onset uveitis (as in the TINU subtype) or with isolated tubulointerstitial nephritis (TIN). METHODS: Patients with sudden onset, anterior, bilateral uveitis not fulfilling a diagnosis of TINU were identified. Pathology reports were reviewed to identify subjects with biopsy-proven TIN. Molecular typing of the HLA-DRB1 gene was performed by the Luminex technology-based sequence-specific oligonucleotide (SSO) hybridisation method (One Lambda, Canoga Park, California). HLA-DRB1 allele frequencies were compared with normal published controls (http://www.ncbi.nlm.nih.gov/projects/gv/mhc/ihwg.cgi dbMHC Europe cohort) and the published TINU cohort (n=18). RESULTS: The authors included 28 subjects with uveitis and 14 with TIN. There was a significantly higher frequency of DRB1*0102 in the isolated uveitis cohort versus in normal controls (10.7% vs 0.6%, respectively, p<0.0001; RR 14.3 (6.9-29.8)). None of the nephritis patients showed this HLA subtype. Another association with HLA-DRB1*08 was seen in the isolated uveitis cohort with an allele frequency of 10.7% versus 2.7% in normal controls (p=0.0019; RR 4.0 (1.8-9.0)). In contrast, the HLA-DRB1*08 was not different from controls in the TINU cohort (allele frequency 2.8%, p=not significant). CONCLUSION: The incidence of HLA-DRB1*0102 is increased in sudden-onset bilateral anterior uveitis, as seen in patients with TINU. The same allele does not appear to occur in increased frequency in patients with isolated TIN. HLA DRB1*0102 might predispose to this subset of uveitis.

Gender and laterality affect recurrences of acute anterior uveitis.

AIM: Acute anterior uveitis (AAU) associated with HLA-B27 or axial spondyloarthritis (axial SpA) is primarily unilateral and recurrent. We tested the hypotheses that disease laterality and gender affected recurrences of AAU. METHODS: We studied 207 AAU subjects who were either HLA-B27 positive or had a verified history of axial SpA with documentation of the first uveitis episode. We recorded gender, laterality, duration, and time between episodes. RESULTS: Of 207 subjects, 126 (60.9%) had axial spondyloarthritis. Of the 179 with known HLA-B27 status, 174 (97.2%) were HLA-B27 positive. The initial episode of AAU occurred slightly more often in the right eye, 109 (52.6%), than in the left, 91 (44.0%) or bilaterally, 7 (3.4%), but the difference between right and left was not significant (p=0.23). Interestingly, 69.4% of subsequent episodes occurred in the same eye affected previously (95% CI 59.3%, 78.3%, p=0.0001). In subjects with recurrent AAU, the probability of being disease-free for one year was 38.9% (95% CI 29.1%, 52.0%) using Kaplan-Meier estimates. Univariate analyses showed that male gender (p=0.03) and AAU which recurred in the same eye (p=0.04) was associated with a shorter time interval between episodes. Multivariate analysis by the Cox proportional hazards model showed similar results. CONCLUSIONS: The initial episode of unilateral AAU associated with HLA-B27 or axial SpA randomly affects either eye. Subsequent episodes occur more often in the same eye previously affected. Male gender and history of unilateral AAU in the same eye are associated with a shortened time interval between relapses.

Predictive models for carcinogenicity and mutagenicity: frameworks, state-of-the-art, and perspectives.

Mutagenicity and carcinogenicity are endpoints of major environmental and regulatory concern. These endpoints are also important targets for development of alternative methods for screening and prediction due to the large number of chemicals of potential concern and the tremendous cost (in time, money, animals) of rodent carcinogenicity bioassays. Both mutagenicity and carcinogenicity involve complex, cellular processes that are only partially understood. Advances in technologies and generation of new data will permit a much deeper understanding. In silico methods for predicting mutagenicity and rodent carcinogenicity based on chemical structural features, along with current mutagenicity and carcinogenicity data sets, have performed well for local prediction (i.e., within specific chemical classes), but are less successful for global prediction (i.e., for a broad range of chemicals). The predictivity of in silico methods can be improved by improving the quality of the data base and endpoints used for modelling. In particular, in vitro assays for clastogenicity need to be improved to reduce false positives (relative to rodent carcinogenicity) and to detect compounds that do not interact directly with DNA or have epigenetic activities. New assays emerging to complement or replace some of the standard assays include Vitotox, GreenScreenGC, and RadarScreen. The needs of industry and regulators to assess thousands of compounds necessitate the development of high-throughput assays combined with innovative data-mining and in silico methods. Various initiatives in this regard have begun, including CAESAR, OSIRIS, CHEMOMENTUM, CHEMPREDICT, OpenTox, EPAA, and ToxCast. In silico methods can be used for priority setting, mechanistic studies, and to estimate potency. Ultimately, such efforts should lead to improvements in application of in silico methods for predicting carcinogenicity to assist industry and regulators and to enhance protection of public health.

Activation of nucleotide oligomerization domain 2 exacerbates a murine model of proteoglycan-induced arthritis.

In addition to its role in innate immunity, nucleotide oligomerization domain 2 (NOD2) has been shown to play a suppressive role in models of colitis. Notably, mutations in NOD2 cause the inherited granulomatous disease of the joints called Blau syndrome, thereby linking NOD2 with joint disease as well. However, the role of NOD2 in joint inflammation has not been clarified. We demonstrate here that NOD2 is functional within the mouse joint and promotes inflammation, as locally or systemically administered muramyl dipeptide (MDP; the NOD2 agonist) resulted in significant joint inflammation that was abolished in NOD2-deficient mice. We then sought to investigate the role of NOD2 in a mouse model of inflammatory arthritis dependent on adaptive immunity using TCR-transgenic mice whose T cells recognized the dominant epitope of proteoglycan (PG). Mice immunized with PG in the presence of MDP developed a more severe inflammatory arthritis and histopathology within the joints. Antigen-specific activation of splenocytes was enhanced by MDP with respect to IFN-gamma production, which would be consistent with the Th1-mediated disease in vivo. Intriguingly, NOD2 deficiency did not alter the PG-induced arthritis, indicating that NOD2 does not play an essential role in this model of joint disease when it is not activated by MDP. In conclusion, we demonstrate that in a model of inflammatory arthritis dependent on T and B cell priming, NOD2 activation potentiates disease. However, the absence of NOD2 does not alter the course of inflammatory arthritis, in contrast to models of intestinal inflammation.

Activation of NOD2 in vivo induces IL-1beta production in the eye via caspase-1 but results in ocular inflammation independently of IL-1 signaling.

Nucleotide-binding and oligomerization domain 2 (NOD2) belongs to the emerging Nod-like receptor (NLR) family considered important in innate immunity. Mutations in NOD2 cause Blau syndrome, an inherited inflammation of eye, joints, and skin. Mutations in a homologous region of another NLR member, NALP3, cause autoinflammation, wherein IL-1beta plays a critical role. Here, we tested the hypothesis that IL-1beta is a downstream mediator of NOD2-dependent ocular inflammation. We used a mouse model of NOD2-dependent ocular inflammation induced by muramyl dipeptide (MDP), the minimal bacterial motif sensed by NOD2. We report that MDP-induced ocular inflammation generates IL-1beta and IL-18 within the eye in a NOD2- and caspase-1-dependent manner. Surprisingly, two critical measures of ocular inflammation, leukocyte rolling and leukocyte intravascular adherence, appear to be completely independent of IL-1 signaling effects, as caspase-1 and IL-1R1-deficient mice still developed ocular inflammation in response to MDP. In contrast to the eye, a diminished neutrophil response was observed in an in vivo model of MDP-induced peritonitis in caspase-1-deficient mice, suggesting that IL-1beta is not essential in NOD2-dependent ocular inflammation, but it is involved, in part, in systemic inflammation triggered by NOD2 activation. This disparity may be influenced by IL-1R antagonist (IL-1Ra), as we observed differential IL-1Ra levels in the eye versus plasma at baseline levels and in response to MDP treatment. This report reveals a new in vivo function of NOD2 within the eye yet importantly, distinguishes NOD2-dependent from NALP3-dependent inflammation, as ocular inflammation in mice occurred independently of IL-1beta.

Anterior uveitis accompanies joint disease in a murine model resembling ankylosing spondylitis.

BACKGROUND: Uveitis is often associated with a systemic inflammatory disease such as ankylosing spondylitis. Our understanding of the eye's susceptibility to immune-mediated uveitis as in the apparent absence of infection has been limited by a relative lack of experimental models. Here we sought to assess whether ocular inflammation occurs in a previously described murine model of proteoglycan-induced spondylitis, wherein mice develop progressive spondylitis, sacroiliitis and peripheral arthritis--features common to the clinical presentations of ankylosing spondylitis. METHODS: Using intravital microscopy we examined the ocular inflammatory response after the onset of arthritis in mice that overexpressed the T cell receptor (TCR) specific for a dominant arthritogenic epitope of cartilage proteoglycan [TCR-Tg (transgenic) mice] or BALB/c controls. RESULTS: Immunized TCR-Tg mice showed a significant increase in the number of rolling and adhering cells within the iris vasculature compared to adjuvant control mice. Cellular infiltration within the iris tissue, as assessed by intravital microscopy and histology, was also increased. Our initial temporal analysis has revealed that immunized TCR-Tg mice show a significant increase in intravascular inflammation by 2 weeks after immunization, but it diminishes at 4 weeks after immunization. CONCLUSIONS: Although these data are preliminary, this model has the potential to clarify the mechanisms accounting for the coexistence of eye and sacroiliac inflammation as occurs in patients with ankylosing spondylitis.

Cloning, sequencing and expression analysis of the mouse NOD2/CARD15 gene.

BACKGROUND: Mutations in the human NOD2/CARD15 gene have been associated with Crohn's disease and Blau syndrome. The objective of the present study was to clone the murine form of NOD2 and characterize its tissue distribution, function and response to inflammatory stimuli. METHODS: Murine NOD2 was isolated using anchored polymerize chain reaction (PCR). Sequence analysis confirmed the identification of full-length cDNA representing the murine NOD2 gene. Using this sequence to search a Mus musculus supercontig database, NOD2 genomic DNA was identified. NOD2 was transfected into human embryonic kidney (HEK) cells and nuclear factor kappa B (NF-kappaB) activation was measured using a reporter assay. Tissue distribution and changes in transcription in mouse monocytes in response to inflammatory stimuli was determined by real time PCR. RESULTS: The NOD2 gene spans 39 KB and contains 12 coding exons on chromosome 8. Expression of mouse NOD2 into HEK cells resulted in NF-kappaB activation. NOD2 was found to be expressed in all mouse tissues analyzed except skin, with highest levels in lung, thymus and spleen. NOD2 mRNA levels increased greater than two-fold in a monocyte cell line in response to lipopolysaccharide, lipoteichoic acid, interferon-g and tumor necrosis factor-alpha. CONCLUSIONS: Common structural and functional features between human and mouse NOD2 were identified. This should allow for development of relevant animal models to evaluate the role of NOD2 in chronic inflammatory disorders.

Intraocular in vivo imaging of activated T-lymphocytes expressing green-fluorescent protein after stimulation with endotoxin.

BACKGROUND: Intravital microscopy allows imaging of specific cell populations in vivo. The value of this technique is well established, but would be enhanced if one could distinguish functional states of cells in vivo. Interleukin-2 (IL-2) is expressed upon stimulation of T-cells and is a commonly used marker for T-cell activation. This study tests the use of enhanced green fluorescent protein (GFP) as a reporter gene for interleukin-2 (IL-2) expression in vivo. METHODS: Characterization of mice that have the GFP gene under the control of IL-2 regulatory sequences has previously been published. Uveitis was induced by injection of E. coli endotoxin into the vitreous of these IL-2/GFPki transgenic mice. Four hours later, 3 microg of recombinant mouse IL-2 was injected into the anterior chambers of one group of mice. In vivo imaging of infiltrating cells in the iris stroma was performed with fluorescence microscopy at 6, 24, 48, and 72 h after endotoxin injection. The absolute number of fluorescent cells per mm2 was evaluated. RESULTS: Eyes with endotoxin-induced uveitis had cells that expressed GFP and were identifiable by intravital microscopy. The fluorescent cells were exclusively seen in the subset of cells that had infiltrated the iris stroma or arrested along the vascular endothelium. The number of GFP-positive infiltrating cells in the iris increased from undetectable at baseline to 0.5 cells/mm2 at 6 h and 1.3 cells/mm2 at 72 h. The animals that received endotoxin as well as IL-2 tended to have more GFP-positive cells at the 48-h and 72-h time points, but these differences were not statistically significant CONCLUSIONS: GFP is commonly used as a reporter gene for in vitro expression assays. The results presented here document that transgenic mice with GFP under the control of IL-2 regulatory elements can be used with intravital microscopy for in vivo expression assays that allow detection of activated T-cells at multiple time points within the same animal. This provides a novel method for temporal and spatial studies on the state of cell activation in inflammatory responses.

Prediction of the acute toxicity (96-h LC50) of organic compounds to the fathead minnow (Pimephales promelas) using a group contribution method.

A group contribution method has been developed to correlate the acute toxicity (96-h LC50) to the fathead minnow (Pimephales promelas) for 397 organic chemicals. Multilinear regression and computational neural networks (CNNs) were used for model building. The models were able to achieve a fairly good correlation of the data (r2 > 0.9). The linear model, which included four specific interaction terms, provided a rapid means of predicting the toxicity of a compound. The CNN model was able to yield virtually the same predictions with or without the four interaction terms that were included in the multilinear model.

Inefficient assembly and intracellular accumulation of antibodies with mutations in V(H) CDR2.

We previously described secretion defects in four mutants of the murine anti-phosphocholine Ab, T15. The mutant heavy (H) chains had amino acid replacements in the V(H) complementarity-determining region 2 (HCDR2) and were expressed at normal intracellular levels. Here, the intracellular fate of the secretion-defective mutant heavy chains was investigated. Metabolic labeling demonstrated that the T15 wild-type Ab was secreted within a 4-h chase. In contrast, the mutant H chains accumulated with intracellular t(1/2) values ranging from 10 to 24 h. The mutant H chains were associated with increased levels of the molecular chaperones BiP and GRP94, and remained endoglycosidase H sensitive, suggesting retention in the endoplasmic reticulum. Assembly of the mutant H chains with T15 light (L) chain was arrested at the H2 and H2L intermediate stages of the T15 wild-type pathway (H2 --> H2L --> H2L2). Even though some assembly with L chain occurred, it was not as a secretion-competent H2L2 Ig moiety. The T15 L chains coexpressed with mutant H chains were degraded efficiently except for a minor L chain population with a long t(1/2) that was apparently protected at the H2L stage. To our knowledge, this is the first study demonstrating that intracellular half-lives of Ig H and L chains can be influenced by somatic mutations in HCDR2.

Comparison of cuffed and uncuffed endotracheal tubes in young children during general anesthesia.

BACKGROUND: Uncuffed endotracheal tubes are routinely used in young children. This study tests a formula for selecting appropriately sized cuffed endotracheal tubes and compares the use of cuffed versus uncuffed endotracheal tubes for patients whose lungs are mechanically ventilated during anesthesia. METHODS: Full-term newborns and children (n = 488) through 8 yr of age who required general anesthesia and tracheal intubation were assigned randomly to receive either a cuffed tube sized by a new formula [size(mm internal diameter) = (age/4) + 3], or an uncuffed tube sized by the modified Cole's formula [size(mm internal diameter) = (age/4) + 4]. The number of intubations required to achieve an appropriately sized tube, the need to use more than 21.min-1 fresh gas flow, the concentration of nitrous oxide in the operating room, and the incidence of croup were compared. RESULTS: Cuffed tubes selected by our formula were appropriate for 99% of patients. Uncuffed tubes selected by Cole's formula were appropriate for 77% of patients (P < 0.001). The lungs of patients with cuffed tubes were adequately ventilated with 2 1.min-1 fresh gas flow, whereas 11% of those with uncuffed tubes needed greater fresh gas flow (P < 0.001). Ambient nitrous oxide concentration exceeded 25 parts per million in 37% of cases with uncuffed tubes and in 0% of cases with cuffed tubes (P < 0.001). Three patients in each group were treated for croup symptoms (1.2% cuffed; 1.3% uncuffed). CONCLUSIONS: Our formula for cuffed tube selection is appropriate for young children. Advantages of cuffed endotracheal tubes include avoidance of repeated laryngoscopy, use of low fresh gas flow, and reduction of the concentration of anesthetics detectable in the operating room. We conclude that cuffed endotracheal tubes may be used routinely during controlled ventilation in full-term newborns and children during anesthesia.

Deletion in HCDR3 rescues T15 antibody mutants from a secretion defect caused by mutations in HCDR2.

We recently described mutants of the murine anti-phosphocholine Ab T15, with changes in heavy chain complementarity determining region 2 (HCDR2) that caused loss of secretion. Surprisingly, the T15 HCDR2 mutations did not alter secretion when placed into the related anti-phosphocholine Ab D16, which differs from T15 only in HCDR3 and light (L) chain. Here, we exploit the differences between these two Abs to assess the basis of the secretion defect. The T15 L chain is not secreted in the absence of heavy (H) chain. In contrast, D16 L chain is secreted in the absence of H chain, as are most L chains. We co-expressed the T15 wild-type (wt) and mutant H chains with the D16 L chain, as well as with another secreted L chain, J558L. The mutant H chains were not secreted when expressed with either heterologous L chain. These results establish that the T15 L chain is not uniquely associated with the defect. The T15 and D16 Abs also differ in HCDR3 length in that D16 lacks four amino acid residues (Ser99, Ser100, Tyr100a, Trp100b) present in T15. We deleted these four residues from T15 wt and mutant H chains. Secretion of T15 wt was unaffected by the deletion, but shortening HCDR3 restored secretion in the HCDR2 mutants regardless of L chain association. Together these data demonstrate that both the HCDR2 and HCDR3 domains contain structural information that may affect the secretion competence of Abs.

Binding of phenylphosphocholine-carrier conjugates to the combining site of antibodies maintains a conformation of the hapten.

The structural basis of the binding of phenylphosphocholine haptens to antibodies was studied. This was done by preparing antibodies and testing binding to conjugates of phenylphosphocholine. The choice of haptens was made in order to evaluate the contribution of the carrier to binding, and its effect on hapten conformation in the active site. Thus, phosphocholine (PC) was diazophenyl-linked to tyrosine or histidine as single amino acid carriers and to tripeptides or octapeptides containing tyrosine or histidine as central amino acids to which PC was attached. Relative affinity was assessed by inhibition enzyme-linked immunosorbent assay (ELISA) and binding constants were determined by fluorescence quenching. Fluorinated haptens were used to determine the kinetics of binding using 19F nuclear magnetic resonance. The transferred nuclear Overhauser effect was used to characterize conformation of the bound hapten. We had previously shown that nitrophenylphosphocholine unlinked to carrier is bound in the active site as a bent structure [Bruderer, U., Peyton, D. H., Barbar, E., Fellman, J. H., & Rittenberg, M. B. (1992) Biochemistry 31, 584-589]. We show here that this same bent conformation is retained in the active site regardless of the neighboring carrier or the conformation of the hapten in the unbound conjugate. The presence of the carrier residues in the bound state does, however, influence affinity.

Posttonsillectomy vomiting. Ondansetron or metoclopramide during paediatric tonsillectomy: are two doses better than one?

This randomized, double blinded, placebo controlled, prospective study compared the anti-emetic efficacy of one preoperative dose of metoclopramide 0.25 mg.kg-1 intravenously or ondansetron 0.15 mg.kg-1 intravenously with two doses of the same drugs (second dose administered one h postoperatively) in 200 preadolescent children undergoing tonsillectomy with either isoflurane or propofol anaesthesia. The incidence of posttonsillectomy vomiting was significantly reduced (P < 0.005) by two doses of either metoclopramide or ondansetron (18% and 8%, respectively) compared with placebo (50%). No difference in posttonsillectomy vomiting exists between the children who received isoflurane and those who received a propofol infusion. Our results suggest that two doses of metoclopramide 0.25 mg.kg-1 intravenously, like two doses of ondansetron 0.15 mg.kg-1, are effective in reducing vomiting after tonsillectomy in children who have received either isoflurane or propofol anaesthesia.