Non-reassuring fetal status in the prolonged pregnancy: the impact of fetal weight

OBJECTIVE

To evaluate the incidence of abnormal fetal findings and Cesarean delivery for non-reassuring fetal status as a function of birth weight in the uncomplicated prolonged pregnancy.

METHODS

Seven hundred and ninety-two patients at or beyond 41 weeks' gestation were managed expectantly. Population-specific birth-weight percentiles were calculated. Fetuses were retrospectively categorized as small (birth weight < 10th percentile), average (10th percentile < or = birth weight < or = 90th percentile) or large (birth weight > 90th percentile). The incidences of abnormal antepartum fetal testing results (i.e. oligohydramnios and/or abnormal non-stress testing) and Cesarean delivery for intrapartum non-reassuring fetal status were calculated for these three birth-weight categories.

RESULTS

There was a significant inverse relationship between the incidence of abnormal fetal testing and birth-weight category (36%, 14% and 9% for small, average and large fetuses, respectively, P < 0.001). Small fetuses were more likely to require a Cesarean delivery for non-reassuring fetal status during labor than were all other fetuses (12.3% vs. 5.3%, P = 0.024).

CONCLUSIONS

The frequency of oligohydramnios and abnormal non-stress testing is inversely related to birth weight in the expectantly managed prolonged pregnancy. In addition, small fetuses born at or beyond 41 weeks' gestation have an increased rate of Cesarean delivery for intrapartum non-reassuring fetal status.

A comparison of medication errors between two storage sites

This prospective single-blinded study aimed to compare the types of medication errors and medication error rates of two medication delivery systems. The setting was a 30 bed surgical ward that was divided into two identical areas. In one area medications were stored and issued in a ward bay workstation immediately outside the patients' rooms. The alternate area used a medication trolley at the patients' bedside. Three hundred and forty opportunities for errors were observed using five nurse educators. Twenty administration errors (5.8% error rate) and two dispensing errors (0.6% error rate) were detected. A statistically significant difference was found between the two systems, where four errors occurred from the medication trolley (2.6% error rate), and fifteen errors occurred from the ward bay (9.2% error rate). These results suggest that medications were less likely to be omitted and more likely to be given on time when they were issued at the patient's bedside using the medication trolley.

Broad-spectrum cation channel inhibition by LOE 908 MS reduces infarct volume in vivo and postmortem in focal cerebral ischemia in the rat

Cation channels conduct calcium, sodium, and potassium, cations that are likely deleterious in the evolution of focal ischemic injury. Diffusion-weighted magnetic resonance imaging (DWI) is a powerful tool for evaluation of acute cerebral ischemia. We studied the effects of a novel, broad-spectrum inhibitor of several cation channels, LOE 908 MS, on acute ischemic lesion development with DWI and on cerebral infarct size using 2,3,5-triphenyltetrazolium chloride (TTC) staining postmortem. Eighteen male Sprague-Dawley rats underwent middle cerebral artery occlusion (MCAO) and were randomly and blindly assigned to either LOE 908 MS (1 mg/kg bolus 30 min after MCAO and continuous i.v. infusion of 10 mg/kg for 4 h thereafter) or vehicle. Whole-brain DWI was done before initiation of treatment and repeated every 30 min for the next 3.5 h. The animals were reperfused in the magnetic resonance imaging (MRI) scanner 90 min after MCAO. At 24 h, the animals were killed, and the brains were cut into six 2-mm-thick slices and stained with 2% TTC. Percent hemispheric lesion volume (%HLV) was calculated for each animal. Physiological parameters, body weight, and premature mortality (3 in the placebo group and 1 in the treated group) did not differ between the groups. No hypotension, abnormal behavior, or other adverse effects were seen. Pretreatment, the DWI-derived %HLV did not differ between the groups (19.8 +/- 6.2 in the control group and 17.9 +/- 7.9 in the treated group), whereas at 4 h after MCAO, it was significantly smaller in the treated group (21.8 +/- 15.4 vs 40.4 +/- 15.5, p = 0.03). Postmortem, TTC-derived %HLV was significantly attenuated in the LOE 908 MS group (21.3 +/- 11.9 vs 50.1 +/- 10.7, p = 0.0001) and the neurological scores at 24 h were significantly better among the treated rats (2.1 +/- 1.5 vs 4.0 +/- 1.0, p < 0.02). LOE 908 MS significantly improved neurological outcome and reduced infarct size without observable effects in rats as demonstrated in vivo by DWI and confirmed postmortem by TTC staining. Blocking several distinct cation channels by LOE 908 MS showed significant neuroprotection.

A glycine site antagonist ZD9379 reduces number of spreading depressions and infarct size in rats with permanent middle cerebral artery occlusion

Spreading depressions (SDs) occur in experimental focal ischemia and contribute to lesion evolution. N-methyl-D-aspartate (NMDA) antagonists inhibit SDs and reduce infarct size. The glycine site on the NMDA receptor complex offers a therapeutic target for acute focal ischemia, potentially devoid of many side effects associated with competitive and non-competitive NMDA antagonists. We evaluated the effect of the glycine antagonist, ZD9379, on SDs and brain infarction. Male Sprague-Dawley rats (n = 18) weighing 290 to 340 g undergoing permanent middle cerebral artery occlusion (MCAO) were randomly and blindly assigned to receive drug or placebo: Group 1 (pre-MCAO treatment group, n = 5) a 5 mg/kg bolus of ZD9379 over 5 minutes followed by 5 mg/kg/hour drug infusion for 4 hours beginning 30 minutes before MCAO; Group 2 (post-MCAO treatment group, n = 7) a 5 mg/kg bolus of ZD9379 30 minutes after MCAO followed by 5 mg/kg/hour drug infusion for 4 hours; and Group 3 (control group, n = 6) vehicle for 5 hours beginning 30 minutes before MCAO. SDs were monitored electrophysiologically for 4.5 hours following MCAO by continuous recording of cortical direct current (DC) potentials and electrocorticogram (ECoG). Infarct volume was measured 24 hours after MCAO by 2,3,5 triphenyltetrazolium chloride (TTC) staining. Corrected infarct volume was 90 +/- 72 mm3 (mean +/- standard deviation) in Group 1, 105 +/- 46 mm3 in Group 2, and 226 +/- 41 mm3 in Group 3 (P < .001). The corresponding numbers of SDs in the 3 groups were 8.2 +/- 5.8, 8.1 +/- 2.5, and 16.0 +/- 5.1, respectively (P < .01). When all animals (n = 18) were analyzed, infarct volumes and the number of SDs were significantly correlated (r = .68, P = .002). This study demonstrated that ZD9379 initiated before or after MCAO significantly reduced the number of SDs and infarct volume in a permanent focal ischemia model, implying that ZD9379 is neuroprotective and its neuroprotective effect may be related to inhibiting ischemia-related SDs.

Regional variations in the apparent diffusion coefficient and the intracellular distribution of water in rat brain during acute focal ischemia

BACKGROUND AND PURPOSE

The apparent diffusion coefficient of water (ADC) rapidly drops in ischemic tissue after cerebral artery occlusion. This acute drop is thought to be caused by the loss of extracellular fluid and the gain of intracellular fluid. To test the latter possibility, changes in ADC and the size of several cellular compartments were assessed in 3 regions of rat brain at the end of 90 minutes of focal cerebral ischemia.

METHODS

One middle cerebral artery was permanently occluded in 8 Sprague-Dawley rats; sham occlusions were performed in 2 other rats. ADC maps were generated 90 minutes later, and the brains were immediately perfusion fixed. Three regions of interest (ROIs) were defined on the basis of ADC range. Various neuronal, astrocytic, and capillary compartments in each ROI were quantified with light and electron microscopy.

RESULTS

At the end of 90 minutes of ischemia, mean ADC was normal in the cortex of sham-operated rats and the contralateral cortex of ischemic rats (ROI-a), 25% lower in the ipsilateral frontoparietal cortex (ROI-b), and 45% lower in the ischemic lateral caudoputamen (ROI-c). At this time, the frequency of swollen astrocytic cell bodies and volume of swollen dendrites and astrocytic processes in neuropil were ROI-a<ROI-b<ROI-c. In ROI-b and ROI-c, 40% and 60% of the neurons, respectively, were shrunken; the shrunken neurons were approximately 25% smaller in ROI-c than in ROI-b. In these areas, many capillary endothelial cells, pericytes, and perivascular foot processes were swollen.

CONCLUSIONS

The initial lowering of ADC during focal ischemia probably is the result of not only the acute loss of extracellular fluid and concomitant swelling of various cellular compartments but also concurrent neuronal shrinkage.

Cessation of secondary prophylaxis in patients with cryptococcosis

Cryptococcal disease in HIV-positive individuals is usually a consequence of advanced immunosuppression. Treatment consists of long period of induction therapy followed by long-term secondary prophylaxis, usually with fluconazole. The introduction of highly active antiretroviral therapy has resulted in improvements in immunological function such that the cessation of primary and secondary prophylaxis against several opportunistic infections has become possible. We report our experience of the cessation of secondary antifungal prophylaxis in patients responding to highly active antiretroviral therapy.

Response to HBV vaccine in relation to vaccine dose and anti-HCV positivity: a New South Wales correctional facilities' study

Currently, about two-thirds of inmates in NSW correctional facilities have a history of injection drug use, and about half have serological evidence of exposure to hepatitis C virus. The introduction of an accelerated hepatitis B vaccination program (0-1-2 months) in 1998, using a 20 microg/dose vaccine was necessitated by the need to vaccinate eligible inmates in this high-risk environment characterised by rapid client mobility. Since 1999, both 10 and 20 microg doses of vaccine were introduced. We found that sero-response rates were not significantly influenced by HCV antibody status, but were significantly lower in cohorts of inmates vaccinated with the 10 microg dose of vaccine.

Imaging of acute stroke

The utility of diagnostic imaging during the critical first few hours after stroke onset has many important applications. First and foremost, imaging technologies that can reliably detect and quantify the location of acute stroke will greatly enhance the clinician's ability to accurately diagnose individual stroke patients. Secondly, if imaging technology could provide information about the likely severity of the ischemic injury, patient prognosis and management would be enhanced. The possibility of potentially distinguishing severely injured and likely irreversible ischemic brain tissue from ischemic tissue likely not yet irreversibly injured may soon be attainable. The ability of imaging technology to reliably distinguish the status of focally ischemic brain will presumably dramatically impact upon patient management. This information, along with the data about the severity and extent of blood flow and tissue perfusion abnormalities, will help acute stroke care evolve beyond rigid time windows to individualized, pathophysiologically based treatment decisions. Not only will decisions to treat or not be made based upon imaging-derived status, but also the most appropriate type of therapy to be employed, i.e. thrombolysis, neuroprotection, therapy to reduce secondary reperfusion-related injury or combinations of these modalities. In this brief and necessarily incomplete overview of acute stroke imaging, the focus will be on new developments in CT and MRI.

Downregulation of the ERK 1 and 2 mitogen activated protein kinases using antisense oligonucleotides inhibits proliferation of porcine vascular smooth muscle cells

The current model of the arterial response to injury suggests that proliferation of vascular smooth muscle cells is a central event. Mitogen activated protein kinases are part of the final common pathway of intracellular signalling involved in cell division and thus constitute an attractive target in attempting to inhibit this proliferation. We hypothesised that antisense oligonucleotides to mitogen activated protein kinase would inhibit serum induced smooth muscle cell proliferation by downregulating the protein. Porcine vascular smooth muscle cells were cultured and an antisense oligonucleotide sequence against the ERK family of mitogen activated protein kinases (AMK1) was introduced by liposomal transfection. Sense oligonucleotides and a random sequence were used as controls. Proliferation was inhibited by AMK1 versus the sense controls, as assessed by tritiated thymidine incorporation (P<0.01). Immunoblots revealed downregulation of the target protein by AMK1 by 63% versus the sense control (P<0.05). In conclusion, antisense oligonucleotides specifically inhibited proliferation and downregulated the target protein. This is consistent with a central role for mitogen activated protein kinases in vascular smooth muscle cell proliferation in the porcine model. In addition, the data suggest a possible role for antisense oligonucleotides in the modulation of the arterial injury response.

Endothelin-1 and monocyte chemoattractant protein-1 modulation in ischemia and human brain-derived endothelial cell cultures

Brain tissue damage due to ischemia/reperfusion has been shown to be caused, in part, by activated macrophages infiltrating into the post-ischemic brain. Using the Middle Cerebral Artery Occlusion (MCAO) mouse model, this study demonstrated that, in vivo, both endothelin-1 (Et-1), a potent vasoconstrictor, and the macrophage chemokine, monocyte chemoattractant factor-1 (MCP-1) are induced in ischemia. Further studies, using human brain-derived endothelial cells (CNS-EC), showed that in vitro, Et-1 can directly stimulate MCP-1 mRNA expression and MCP-1 protein; and this Et-1-induced MCP-1 production is mediated by the ET(A) receptor. Inflammatory cytokines, tumor necrosis factor alpha and interleukin-1beta, functioned additively and synergistically, respectively, with Et-1 to increase this MCP-1 production. Partial elucidation of the signal transduction pathways involved in Et-1-induced MCP-1 production demonstrated that protein kinase C-, but not cAMP-dependent pathways are involved. These data demonstrate that Et-1, functioning as an inflammatory peptide, increased levels of MCP-1, suggesting a mechanism for chemokine regulation during ischemia/reperfusion injury.

Increases in renal epsilon-(gamma-glutamyl)-lysine crosslinks result from compartment-specific changes in tissue transglutaminase in early experimental diabetic nephropathy: pathologic implications

Diabetic nephropathy (DN) is characterized by an early, progressive expansion and sclerosis of the glomerular mesangium leading to glomerulosclerosis. This is associated with parallel fibrosis of the renal interstitium. In experimental renal scarring, the protein cross-linking enzyme, tissue transglutaminase (tTg), is up-regulated and externalized causing an increase in its crosslink product, epsilon-(gamma-glutamyl)-lysine, in the extracellular space. This potentially contributes to the extracellular matrix (ECM) accumulation central to tissue fibrosis by increasing deposition and inhibiting breakdown. We investigated if a similar mechanism may contribute to the ECM expansion characteristic of DN using the rat streptozotocin model over 120 days. Whole kidney epsilon-(gamma-glutamyl)-lysine (HPLC analysis) was significantly increased from Day 90 (+337%) and peaked at Day 120 (+650%) (p < 0.05). Immunofluorescence showed this increase to be predominantly extracellular in the peritubular interstitial space, but also in individual glomeruli. Total kidney transglutaminase (Tg) was not elevated. However, using a Tg in situ activity assay, increased Tg was detected in both the extracellular interstitial space and glomeruli by Day 60, with a maximal 53% increase at Day 120 (p < 0.05). Using a specific anti-tTg antibody, immunohistochemistry showed a similar increase in extracellular enzyme in the interstitium and glomeruli. To biochemically characterize glomerular changes, glomeruli were isolated by selective sieving. In line with whole kidney measurement, there was an increase in glomerular epsilon-(gamma-glutamyl) lysine (+361%); however, in the glomeruli this was associated with increases in Tg activity (+228%) and tTg antigen by Western blotting (+215%). Importantly, the ratio of glomerular epsilon-(gamma-glutamyl) lysine to hydroxyproline increased by 2.2-fold. In DN, changes in the kidney result in increased translocation of tTg to the extracellular environment where high Ca(2+) and low GTP levels allow its activation. In the tubulointerstitium this is independent of increased tTg production, but dependent in the glomerulus. This leads to excessive ECM cross-linking, contributing to the renal fibrosis characteristic of progressive DN.

Clenbuterol in the horse: confirmation and quantitation of serum clenbuterol by LC-MS-MS after oral and intratracheal administration

Clenbuterol is a beta2 agonist/antagonist bronchodilator, and its identification in post-race samples may lead to sanctions. The objective of this study was to develop a specific and highly sensitive serum quantitation method for clenbuterol that would allow effective regulatory control of this agent in horses. Therefore, clenbuterol-d9 was synthesized for use as an internal standard, an automated solid-phase extraction method was developed, and both were used in conjunction with a multiple reaction monitoring liquid chromatography-tandem mass spectrometry (LC-MS-MS) method to allow unequivocal identification and quantitation of clenbuterol in 2 mL of serum at concentrations as low as 10 pg/mL. Five horses were dosed with oral clenbuterol (0.8 microg/kg, BID) for 10 days, and serum was collected for 14 days thereafter. Serum clenbuterol showed mean trough concentrations of approximately 150 pg/mL. After the last dose on day 10, serum clenbuterol reached a peak of approximately 500 pg/mL and then declined with a half-life of approximately 7 h. Serum clenbuterol declined to 30 and 10 pg/mL at 48 and 72 h after dosing, respectively. By 96 h after dosing, the concentration was below 4 pg/mL, the limit of detection for this method. Compared with previous results obtained in parallel urinary experiments, the serum-based approach was more reliable and satisfactory for regulation of the use of clenbuterol. Clenbuterol (90 microg) was also administered intratracheally to five horses. Peak serum concentrations of approximately 230 pg/mL were detected 10 min after administration, dropping to approximately 50 pg/mL within 30 min and declining much more slowly thereafter. These observations suggest that intratracheal administration of clenbuterol shortly before race time can be detected with this serum test. Traditionally, equine drug testing has been dependent on urine testing because of the small volume of serum samples and the low concentrations of drugs found therein. Using LC-MS-MS testing, it is now possible to unequivocally identify and quantitate low concentrations (10 pg/mL) of drugs in serum. Based on the utility of this approach, the speed with which new tests can be developed, and the confidence with which the findings can be applied in the forensic situation, this approach offers considerable scientific and regulatory advantages over more traditional urine testing approaches.

Rocuronium: high risk for anaphylaxis?

Patients suspected of anaphylaxis during anaesthesia have been referred to the senior author's clinic since 1974 for investigation. Since release of rocuronium on to the worldwide market, concern has been expressed about its propensity to cause anaphylaxis. We identified 24 patients who met clinical and laboratory (intradermal, mast cell tryptase and morphine radioimmunoassay) criteria for anaphylaxis to rocuronium. The incidence of rocuronium allergy in New South Wales, Australia has risen in parallel with sales, while there has been an associated fall in reactions to other neuromuscular blocking drugs. Data from intradermal testing suggested that rocuronium is intermediate in its propensity to cause allergy in known relaxant reactors compared with low-risk agents (e.g. pancuronium, vecuronium) and higher-risk agents (e.g. alcuronium, succinylcholine).

Long-term follow-up of antiretroviral-naive HIV-positive patients treated with nevirapine

This article reports on the extended follow-up of 125 antiretroviral (ARV)-naive patients treated with nevirapine (NVP) in the United Kingdom. The patients have been observed for a median of 1.8 years after starting NVP (range, 4 days-2.7 years). Baseline CD4 counts and HIV RNA levels were 210 (interquartile range, 130 - 335) cells/mm3 and 4.86 (range, 4.52-5.26) log10 copies/ml, respectively. Eleven patients (9.0%) developed a rash thought to be related to NVP, of whom 4 permanently discontinued NVP. Twenty-four months after starting NVP, RNA levels had dropped by a median of 2.32 log10 copies/ml and CD4 counts increased by a median of 143 cells/mm3. In all, 96 patients had at least one viral load measured <500 copies/ml, a median of 2.8 months after starting NVP. RNA levels rebounded >500 copies/ml in 37 of these patients, on average 2 years after initial response. In conclusion, in ARV-naive patients, NVP is generally well tolerated and long-term response rates are good.

Parental medical neglect in the treatment of adolescents with anorexia nervosa

OBJECTIVE

Although childhood sexual abuse has been a frequent focus of research on eating disorders, other forms of maltreatment have been less commonly reported. Parental medical neglect is examined in this study as having serious consequences for the treatment and prognosis of patients with anorexia nervosa.

METHOD

Two case studies illustrate parental interference with treatment in which Child Protective Services (CPS) had to be involved in compliance with state law. Two adolescent females who were admitted for treatment for anorexia nervosa are presented.

RESULTS

In both cases, the parents refused to comply with the recommendations of the treatment team, placing their children's health in jeopardy. In compliance with reporting guidelines, CPS was notified in both cases.

CONCLUSIONS

Clinicians who treat minors with anorexia nervosa must consider parental compliance with treatment. Indications for the involvement of CPS are outlined. Optimally, this notification can ensure that the patient and family receive the requisite treatment.

Alterations in CD30(+) T cells in monoclonal gammopathy of undetermined significance

Monoclonal gammopathy of unknown significance (MGUS) is a monoclonal B cell expansion characterized by high levels of circulating monoclonal antibody that affects 3% of individuals over the age of 70. Although this is considered benign, a high percentage of MGUS patients develop a debilitating peripheral autoimmune neuropathy and have a significantly increased risk for progression to multiple myeloma. Here we show that the relative numbers of the CD30(+) T cell subset and levels of CD30 expression are elevated in activated lymphocytes from normal aged individuals (> or =60 years) and in MGUS patients, when compared to younger controls. PBL from MGUS patients and age-matched controls produced comparable levels of IL-6 when activated with anti-CD3 plus IL-2, and costimulation with a soluble form of CD30 ligand (sCD30L/CD8alpha) augmented anti-CD3 inducible IL-6 production similarly in both groups. However, MGUS PBL also produced measurable IL-6 when activated with sCD30L/CD8alpha alone. This capability was associated with the unique presence of CD30(+) T cells in the peripheral blood of MGUS patients. Furthermore, a higher percentage of activated MGUS T cells express CD30 when activated by incubation with idiotype-expressing autologous serum (68 +/- 13) than those activated by anti-CD3 plus IL-2 (43 +/- 7). These results indicate that quantitative alterations in CD30(+) T cells accompany aging and MGUS and that these cells may contribute to the chronic activation of B cells though the production of IL-6.

Differences between adolescents and young adults at presentation to an eating disorders program

OBJECTIVE

To describe differences between adolescents and adults in clinical presentation of eating disorders.

METHODS

Data from the charts of 622 female patients treated for an eating disorder in a division of adolescent medicine between 1980 and 1994 were coded and computerized. General categories included demographic and family factors, weight loss and weight changes, eating-related behaviors, diagnosis and severity, and treatment issues. Differences between the 438 patients who were aged 9-19 years (adolescents) and 184 patients who were aged 20-46 years (adults) were analyzed.

RESULTS

Adolescents were more likely than adults (p <.05) to have a diagnosis of "eating disorder not otherwise specified," lower global severity score, greater denial and less desire for help, weight loss > or = 3 lb/month, lower original and maximum weights, and history of fasting and elimination of junk food from their diets. Adults were more likely than adolescents (p <.05) to have >1 year of weight loss, greater total weight loss, history of binge eating and laxative use, history of diuretic and ipecac use, diagnosis of bulimia nervosa, and prior use of psychiatric medications. Adolescents and adults did not differ (p >.05) in parents' occupational level; height, weight, and percent ideal body weight at presentation; original percent ideal body weight; use of diet pills, elimination of meat and use of a low-fat diet; daily calorie intake; prior eating disorder hospitalizations; and hospitalization during the course of treatment.

CONCLUSIONS

The findings in this study document and confirm that there are important differences between adolescents and adults that must be taken into account in the evaluation and treatment of patients with eating disorders.

Employee response to major organizational redesign

A number of health care organizations are currently undergoing major organizational redesign. Despite these efforts, little is known about how these changes are affecting the employees participating in the redesign process. In response to this, a study was undertaken to determine the perceived impact of organizational redesign on nursing staff at 2 acute care hospitals that were undergoing major organizational change. Data were collected through semi-structured focus group interviews conducted on all 3 shifts (days, evenings, and nights). Findings suggest the early redesign period is highly turbulent and difficult for staff. Nurses expressed concern over changes in roles and responsibilities, disruption in work group relationships, loss of resource availability, reduction in quality of care, and alterations in physical and psychological state.

Clenbuterol in the horse: urinary concentrations determined by ELISA and GC/MS after clinical doses

Clenbuterol is a beta2 agonist/antagonist bronchodilator marketed as Ventipulmin and is the only member of this group of drugs approved by the US Food and Drug Administration (FDA) for use in horses. Clenbuterol is a class 3 drug in the Association of Racing Commissioners International (ARCI) classification system; therefore, its identification in postrace samples may lead to sanctions. Recently, the sensitivity of postrace testing for clenbuterol has been substantially increased. The objective of this study was to determine the 'detection times' for clenbuterol after administration of an oral clinical dose (0.8 g/kg, b.i.d.) of Ventipulmin syrup. Five horses received oral clenbuterol (0.8 g/kg, b.i.d.) for 10 days, and urine concentrations of clenbuterol were determined by an enhanced enzyme-linked immunoabsorbent assay (ELISA) test and gas chromatography/mass spectrometric (GC/MS) analysis by two different methods for 30 days after administration. Twenty-four hours after the last administration, urine concentrations of apparent clenbuterol, as measured by ELISA, averaged about 500 ng/mL, dropping to about 1 ng/mL by day 5 posttreatment. However, there was a later transient increase in the mean concentrations of apparent clenbuterol in urine, peaking at 7 ng/mL on day 10 postadministration. The urine samples were also analysed using mass spectral quantification of both the trimethylsilyl (TMS) and methane boronic acid (MBA) derivatives of clenbuterol. Analysis using the TMS method showed that, at 24 h after the last administration, the mean concentration of recovered clenbuterol was about 22 ng/mL. Thereafter, clenbuterol concentrations fell below the limit of detection of the TMS-method by day 5 after administration but became transiently detectable again at day 10, with a mean concentration of about 1 ng/mL. Derivatization with MBA offers significant advantages over TMS for the mass spectral detection of clenbuterol, primarily because MBA derivatization yields a high molecular weight base peak of 243 m/z, which is ideal for quantitative purposes. Therefore, mass spectral analyses of selected urine samples, including the transient peak on day 10, were repeated using MBA derivatization, and comparable results were obtained. The results show that clenbuterol was undetectable in horse urine by day 5 after administration. However, an unexpected secondary peak of clenbuterol was observed at day 10 after administration that averaged approximately 1 ng/mL. Because of this secondary peak, the detection time for clenbuterol (0.8 g/kg, b.i.d. x 10 days) is at least 11 days if the threshold for detection is set at 1 ng/mL.