About

Sarah Ho is the CVM Director of Student Engagement at the College of Veterinary Medicine at NC State University. Her role involves overseeing student development and engagement initiatives, fostering a supportive and collaborative campus community, and promoting student success and well-being. She is actively involved in creating opportunities for students to enrich their academic experience through extracurricular activities, study abroad programs, research projects, and community building. Her focus is on supporting the next generation of veterinary professionals by ensuring they have a comprehensive and enriching educational environment.

Research topics

• Pharmacology
• Medicine
• Biology
• Biotechnology
• Physical therapy
• Risk analysis (engineering)
• Environmental health
• Toxicology
• Business
• Management
• Marketing
• Statistics
• Internal medicine
• Mathematics
• Food science
• Bioinformatics
• Computational biology
• Microbiology

Selected publications

• Avoiding drug residues: a multivariate approach to estimating withdrawal intervals in edible tissues of goats following extra label administration of flunixin meglumine

  Frontiers in Veterinary Science · 2026-05-07

  articleOpen accessSenior author

  Introduction Flunixin meglumine is a non-steroidal anti-inflammatory drug (NSAID) commonly used extra-label in goats, necessitating the determination of an extended withdrawal interval (WDI) to minimize the risk of violative residues at slaughter. Current U.S. Food and Drug Administration (FDA) guidance estimates WDIs using univariate ordinary least squares (OLS) regression applied to concentrations at or above the limit of detection (LOD), defining the WDI as the time at which the upper bound of the 95% confidence interval for the 99% quantile falls below a specified tolerance. However, residue concentrations measured across multiple tissues from the same animal may be correlated, and excluding observations below the LOD may distort estimates by removing information from the terminal depletion phase. Materials and methods We propose a multivariate linear regression (MvLR) framework that jointly models inter-tissue dependence while accommodating left-censored observations. Regression parameters are estimated using OLS and generalized least squares (GLS) under the uncensored MvLR model, and via an expectation conditional-maximization (ECM) algorithm under a censored MvLR formulation. Withdrawal intervals are computed using the multivariate t-distribution to obtain the upper limit of the 95% confidence interval for the 99% quantile across tissues. The methods are illustrated using tissue-residue data from 20 Boer goats administered flunixin meglumine at 2.2 mg/kg, with five animals euthanized at each of four post-treatment time points (24, 48, 72, and 96 h) and are further evaluated in a simulation study. Results The simulation results indicate that the ECM-based censored MvLR approach yields stable parameter estimation and reliable WDI inference in the presence of censoring. Applying this framework to the goat residue data suggests that a withdrawal interval of at least 10 days is recommended to ensure that residues across all tissues fall below conservative safety thresholds. Discussion These findings suggest that a multivariate censored modeling framework can improve WDI estimation by accounting for inter-tissue correlation and incorporating observations below the LOD, addressing key limitations of current univariate FDA-style approaches.

  PublisherDOI

• Evaluating the Effect of Acetylsalicylic Acid in Turkey Poults Experimentally Infected with Coccidia

  Avian Diseases · 2026-03-05

  article

  Acetylsalicylic acid (ASA), originally trademarked as Aspirin, is a common nonsteroidal anti-inflammatory drug (NSAID) used in human and veterinary medicine to mitigate pain and pyrexia caused by inflammatory processes. There is limited information on the effectiveness of ASA in turkey production. The objective of this study was to investigate the effect of ASA on turkey poults with induced coccidial enteritis. Two experimental trials were conducted. In both trials, the turkeys were divided into four groups: no coccidia + no ASA; no coccidia + ASA (NA); coccidia + no ASA (CN); and coccidia + ASA (CA). In both trials, turkeys in groups CN and CA were given 100× the dose of a commercial turkey coccida vaccine. Starting 48 hr postinoculation and for 7 days, the turkeys from groups NA and CA were given ASA (50 mg/kg per day). For Trial 1, ASA was given via oral gavage twice daily, whereas in Trial 2 (T2), ASA was in the drinking water. Poult weights and cloacal temperatures were recorded daily. Blood was collected daily from two randomly selected birds from each group for biochemical analysis and to assess the serum salicylic acid and nitric oxide (NO) levels. At the end of the trials, tissues were examined histologically, and immune gene expression was evaluated. Coccidia infection was the factor that had most significant influence on the majority of measured parameters. ASA had minimal to no effect on reducing clinical signs, minimizing weight loss, or controlling body temperature. These findings may be due to the rapid elimination of the drug or because sick birds did not consume sufficient ASA. In T2, it was estimated that the CA group poults consumed 31 mg/kg of ASA or less per day. Although the drinking water concentration was calculated to match the total daily intake (50 mg/kg per day), ASA's rapid metabolism meant that continuous low-level ingestion might not have reached the therapeutic plasma threshold achieved by two to three daily bolus doses. Because ASA is rapidly metabolized, a higher total daily dose may be required when provided in drinking water to maintain effective serum concentrations compared with bolus administration. Although the serum NO and tissue gene expression analysis showed that coccidia infection predominantly induces an inflammatory response, the anti-inflammatory effect of ASA administered to birds in the NA or CA groups were nil to minimal. This study highlights the complexity of ASA's effects on turkeys.

  PublisherDOI

• Withdrawal interval estimations of oxytetracycline and chlortetracycline in swine using physiologically based pharmacokinetic models: a global trade perspective

  Toxicological Sciences · 2026-04-01

  article

  Violative drug residues in animal-derived food are a global food safety concern. Physiologically based pharmacokinetic (PBPK) modeling is a valuable tool for predicting drug residues in edible tissues and determining withdrawal intervals (WDIs). This study aimed to develop a PBPK model for oxytetracycline (OTC) and chlortetracycline (CTC) in swine to determine WDIs based on different regulatory requirements of different countries. The models were calibrated and evaluated with the pharmacokinetic data after oral administration via feed and drinking water collected from the Food Animal Residue Avoidance Databank (FARAD). The models can accurately capture the observed kinetics in plasma and edible tissues (liver, muscle, kidney, and fat), and most of the model predictions were within a 3-fold factor of observed data (87.9% for OTC and 88.9% for CTC). WDIs of OTC and CTC were determined using the population PBPK models based on maximum residue limits (MRLs) from 13 countries or regions under the label dosage regimens. The models were converted to a web-based PBPK dashboard. The models are a useful tool for predicting tissue residues and estimating WDIs based on different MRLs across countries, thereby supporting food safety assessment and international trade of meat products derived from swine treated with OTC and CTC.

  PublisherDOI

• Pharmacokinetics of a Single Subcutaneous Extended‐Release Buprenorphine (Ethiqa <scp>XR</scp> ) in Healthy Beagles

  Journal of Veterinary Pharmacology and Therapeutics · 2026-05-20

  articleOpen access

  This study evaluated the pharmacokinetics of an extended-release buprenorphine formulation (Ethiqa XR) in dogs and explored potential sex differences. Twelve healthy intact beagles (6 males and 6 females) received a single subcutaneous injection of Ethiqa XR (0.2 mg/kg). Blood samples were collected up to 168 h post-administration, and plasma buprenorphine concentrations were measured using liquid chromatography-tandem mass spectrometry. Vital signs, sedation, and nausea scores were recorded. Therapeutic plasma concentrations were sustained for approximately 60-90 h in both sexes, depending on the therapeutic threshold used (0.6 or 1.0 ng/mL). Although no significant differences in pharmacokinetics were detected, drug exposure and elimination were greater in females: median peak plasma buprenorphine concentrations (male: 1.6 ng/mL, female: 2.9 ng/mL); median terminal half-life (male: 36.6 h, female: 24.7 h); area under the curve (AUC 0-12 h) (male: 12.8 h*ng/mL, female: 16.9 h*ng/mL); AUC (0-96 h) (male: 94.4 h*ng/mL, female: 137.7 h*ng/mL). Time to maximum concentrations were 24 h in both sexes. Higher buprenorphine concentrations were associated with decreased body temperature and heart rate in both sexes and positively correlated with nausea and sedation scores, but only in females. Ethiqa XR administration resulted in therapeutic plasma concentrations up to 90 h, suggesting it may be an alternative option for post-operative pain control.

  PublisherDOI

• Pharmacokinetics of Ampicillin Trihydrate in Plasma, Interstitial, and Peritoneal Fluid Following Intraperitoneal or Intramuscular Administration in Steers at the Beginning of a Standing Flank Laparotomy

  Journal of Veterinary Pharmacology and Therapeutics · 2025-09-04

  articleOpen access

  Prophylactic and perioperative use of antibiotics is common prior to abdominal surgery in cattle for minimizing the risk of postoperative infections. Yet, there is little information on drug concentrations at sites of potential infections following surgical procedures. The objective of this study was to compare the concentrations in the plasma, peritoneal fluid, and interstitial fluid of ampicillin trihydrate in cattle. In a randomized design, ampicillin trihydrate, a β-lactam antibiotic, was administered to 12 healthy Holstein-Friesian steers intraoperatively via intraperitoneal (IP; n = 6) or intramuscular (IM; n = 6) injection in the cervical neck muscles at 11 mg/kg for both groups. For IP administration, ampicillin trihydrate was deposited into the abdominal cavity following an incision in the right paralumbar fossa. Steers in the IM group were administered ampicillin prior to surgical closure. Peritoneal fluid and interstitial fluid were collected using ultrafiltration probes. IP administration achieved higher concentrations in peritoneal fluid as compared to IM administration. Maximum plasma concentrations were significantly higher following IP administration (3.11 ± 2.5 μg/mL; p < 0.004) compared to the IM group (0.05 ± 10.9 μg/mL). Despite high peritoneal fluid concentrations of ampicillin, the variability in critical pharmacokinetic parameters following IP administration raises concerns about its therapeutic reliability. The correlation between intraperitoneal drug concentrations and clinical efficacy warrants further investigation.

  PublisherOA PDFDOI

• Investigating the Pharmacokinetics and Efficacy of Intramammary Ceftiofur Hydrochloride in Prevention of Udder Inflammation in Non‐Lactating Dairy Heifers

  Journal of Veterinary Pharmacology and Therapeutics · 2025-04-21 · 1 citations

  articleOpen accessSenior authorCorresponding

  Mastitis is the most burdensome concern for the dairy cattle industry. Antimicrobials are often prophylactically administered to dairy cows at dry-off to reduce the risk of intramammary infection during the dry period and subsequent lactation. Mastitis incidence has increased in dairy heifers after calving, leading to extralabel drug use of various dry cow products, including intramammary ceftiofur hydrochloride. However, the pharmacokinetics and efficacy of this application have yet to be studied. This study aimed to compare the pharmacokinetics and efficacy following no treatment, a non-antimicrobial teat sealant, or a single dose of intramammary ceftiofur given at 21 or 14 days before expected calving. We hypothesized that milk collected following dosing would contain drug residues below the FDA tolerance of 100 ng/mL by calving, and heifers within the ceftiofur treatment groups would have lower somatic cell counts (SCCs) than heifers in the teat sealant and nontreatment control groups. Following treatment or no treatment of 24 prepartum heifers, milk samples were collected until 21 days after calving. Somatic cell counts and ceftiofur concentrations were assessed utilizing a cell counter and UPLC/MS detection, respectively. Ceftiofur administration did not significantly reduce SCCs compared to other groups by days 7, 14, or 21. For heifers treated 14 and 21 days prior to calving, milk had a maximum ceftiofur concentration of 8.14 ± 6.24 and 4.20 ± 5.07 ng/mL 48 h into lactation, respectively. The minimal ceftiofur concentrations in milk collected from these heifers indicate that administration of ceftiofur 14 or 21 days before calving is unlikely to lead to violative residues. However, it is essential that regional regulations regarding the use of ceftiofur are adhered to.

  PublisherOA PDFDOI

• Pharmacokinetics and withdrawal interval calculations for meat and milk of intravenously administered compounded methylene blue in healthy cattle

  American Journal of Veterinary Research · 2025-11-18

  articleOpen accessSenior author

  Objective: To characterize the pharmacokinetics in blood and plasma and determine residue profiles of IV-administered methylene blue (MB) to support withdrawal interval (WDI) recommendations. Methods: This was a prospective, nonrandomized pharmacokinetic and residue study using noncompartmental analysis. The study took place from May 2023 through December 2023. Eight Holstein-cross cattle (4 steers, 2 heifers, 2 cows; ages, 5.4 to 6 months for steers and heifers and approx 5.5 years for cows; mean weights, 198 to 495 kg) were housed individually with controlled diet and water access. Animals received 6 mg/kg of compounded 2.5% MB IV. Blood and plasma samples were collected for 72 hours. Milk samples were collected twice daily. At 3 and 6 days after dose, tissue samples were collected after euthanasia. Drug concentrations were measured via UPLC-MS-MS assay. Withdrawal interval estimates used modified FDA tolerance limits and European Medicines Agency time-to-safe-concentration methods. Results: MB was rapidly eliminated, with plasma concentrations below the limit of quantification by 12 hours and blood by 24 hours. No residues were detected in any tissues at sampling times. Milk concentrations were detected at approximately 12 hours (0.084 ± 0.04 µg/mL). Milk WDI estimates were 89 hours and approximately 5 days based on the modified FDA and European Medicines Agency approaches, respectively. Conclusions: IV MB at 6 mg/kg in cattle was well tolerated, eliminated rapidly, and produced no tissue residues at 3 or 6 days. Clinical Relevance: Data suggest that compounded MB at this dose and route as an emergency antidote poses no food safety concerns provided WDIs of 5 days for milk and 6 days for meat are recommended to producers.

  PublisherDOI

• Pharmacokinetics of a single dose of flunixin transdermal formulation in American bullfrogs (Lithobates catesbeianus)

  American Journal of Veterinary Research · 2025-03-10

  articleOpen access

  Objective: To determine the pharmacokinetics of a single dose of flunixin transdermal formulation in American bullfrogs (Lithobates catesbeianus). Methods: Clinically healthy, purpose-bred adult bullfrogs housed at the North Carolina State University College of Veterinary Medicine were enrolled in a sparse-sampling population study. Frogs were administered 3.3 mg/kg transdermal flunixin meglumine (Banamine Transdermal; Merck Animal Health) on the dorsum via micropipette under manual restraint in July of 2022. Frogs were maintained in individual containers out of water for 4 hours and randomly assigned to 2 of the following venipuncture time points: 1, 2, 4, 8, 12, or 24 hours, with 7 frogs sampled per time point. Blood was collected from the popliteal sinus. Ultra performance liquid chromatography-tandem mass spectrometry was used to determine plasma flunixin concentrations. Data were analyzed using noncompartmental analysis. Results: Flunixin was detected in all samples collected from 21 bullfrogs (9 males and 12 females). A mean peak plasma concentration of 2.39 µg/mL was reached between 1 and 2 hours. The elimination half-life was 15.0 hours. Plasma concentrations were similar across individuals at 1, 2, and 4 hours (range at 1 and 2 hours, 2.32 to 2.55 µg/mL) but were variable at 8, 12, and 24 hours (range at 24 hours, 0.16 to 1.79 µg/mL). Mucus and/or epithelial loss was noted at the drug application site in 18 of 21 frogs. No additional clinical signs or mortality occurred. Conclusions: Transdermal flunixin was systemically absorbed, and plasma concentrations exceeded established therapeutic ranges in other species. Most frogs developed mild cutaneous lesions. Clinical Relevance: Transdermal flunixin was detected in plasma for 24 hours; however, variability in plasma concentrations over time and topical side effects may limit its use.

  PublisherOA PDFDOI

• Pharmacokinetics of Intravenous and Transdermal Flunixin Meglumine in Wool and Hair Sheep ( <i>Ovis aries</i> )

  Journal of Veterinary Pharmacology and Therapeutics · 2025-08-01

  articleOpen access

  The objective of the study was to evaluate the pharmacokinetics of flunixin meglumine of intravenous (IV) and transdermal (TD) flunixin meglumine administration on different coat types (wool vs. hair) in 12 healthy sheep. Polled dorset (wool) sheep (n = 6) and katahdin (hair) sheep (n = 6) received 2.2 mg/kg IV and 3.3 mg/kg TD with a 10-day washout period between treatments. Plasma samples were obtained for 96 h following both IV and TD administration, respectively. Flunixin concentrations were quantified by use of high-performance liquid chromatography with mass spectrometry, and PK parameters were derived using different modeling techniques. A population non-linear mixed effect model showed that coat type has a significant effect on the absorption rate following TD administration. The mean bioavailability of TD flunixin was not significantly different (48.76% ± 17.49% and 36.61% ± 4.33%; p = 0.093) in wool and hair sheep, respectively. Maximum plasma concentrations following TD administration were higher in wool sheep (1.57 μg/mL; range, 0.6-3.41 μg/mL) compared to hair sheep (0.57 μg/mL; range, 0.36-0.83 μg/mL). The PK results provide further support for clinical studies to examine the efficacy of TD flunixin in different breeds of sheep.

  PublisherOA PDFDOI

• Applications of PBPK Models to Predict Tissue Residues and Extralabel Withdrawal Times of Drugs in Food Animals: Perspectives from the Food Animal Residue Avoidance Databank (FARAD) Program

  The AAPS Journal · 2025-10-06 · 2 citations

  reviewOpen access

  Physiologically based pharmacokinetic (PBPK) models are commonly used in human drug discovery and development and human health risk assessment of environmental chemicals. One emerging application of PBPK models is to predict tissue residues and withdrawal times of drugs in food animals, which is important for human food safety assessment of animal-derived food products, such as meat, milk, and eggs. This review summarizes existing guidelines to establish the regulatory agency approved label withdrawal period and available pharmacometric methods to predict extralabel withdrawal times, with a focus on PBPK modeling. We conducted a comprehensive literature search on existing PBPK models in food animals. Two hundred thirteen PBPK models in different food animal species (e.g., cattle, swine, sheep, goats, and chickens) from 113 publications were identified. The general procedure to build a PBPK model for a drug in food animals to predict withdrawal times is summarized. Differences in PBPK modeling between humans and food animals and between different food animal species are discussed. Novel uses of PBPK models to predict extralabel withdrawal times are illustrated with recent case studies from the Food Animal Residue Avoidance Databank (FARAD). Recent advances and challenges in PBPK modeling in food animals are discussed, followed by our future perspectives on how to develop more robust PBPK models for food animals to address the safety assessment of animal-derived food products.

  PublisherOA PDFDOI

Recent grants

• NIH Grant R01OH003669

  NIH · $2.3M · 2015

Frequent coauthors

• Jim E. Riviere

  Kansas State University

  154 shared

• Lisa A. Tell

  University of California, Davis

  43 shared

• Arthur L. Craigmill

  42 shared

• Geoffrey Smith

  35 shared

• C. McCombie

  Association for Regional and International Underground Storage

  25 shared

• F Secre- Tary

  UCL Australia

  25 shared

• John Evans

  25 shared

• Richmond Gordon

  Stellenbosch University

  25 shared

Labs

• CVM Pharmacology LabPI