Comparison of the pharmacokinetics of an ondansetron solution (8 mg) when administered intravenously, orally, to the colon, and to the rectum

Current Updates in Rectal Infusion of Fluids and Medications

Purpose of Review

Rectal infusion is a feasible alternative for the immediate administration of medication and fluids when intravenous access is delayed, contraindicated, or unnecessary. Advances in medical device technology have made rectal infusion more practical and easier for medical care providers, and more comfortable for patients. This paper briefly reviews the history of therapeutic rectal infusion, including recent improvements in technology and the existing evidence for the use of this technique.

Recent Findings

While ultrasound-guided peripheral intravenous (PIV) access techniques and other alternatives to landmark-based PIV catheter insertion have recently improved the ability of providers to overcome challenges related to difficult vascular access (DVA), these challenges are increasingly affecting patient outcomes, emergency department throughput, and the cost of medical care. In recent years, waves of parenteral drug, fluid, and supply shortages have affected hospitals. Concurrently, advances in rectal infusion technology have made rectal infusion easier, more comfortable, and more cost-effective than many parenteral options.

Summary

The infusion of resuscitative fluids and medications via the rectal route has previously fallen out of favor due to concurrent improvements in IV access devices. However, this technique demonstrates the potential for a reemergence considering the current challenges facing healthcare providers and systems. Improvements in rectal infusion devices, coupled with an aging population, increased incidence of DVA, shortages in parenteral drugs, fluids, supplies and skilled staff, and the need for care improvements in the post-acute setting have contributed to a greater need for easy, safe and effective alternatives to IV infusion.

Plasma and cerebrospinal fluid pharmacokinetics of ondansetron in humans

AIMS

Changes in serotonergic sensory modulation associated with overexpression of 5-HT3 receptors in the central nervous system (CNS) have been implicated in the pathophysiology of neuropathic pain after peripheral nerve damage. 5-HT3 receptor antagonists such as ondansetron can potentially alleviate neuropathic pain, but have limited effectiveness, due potentially to limited CNS access. However, there is currently limited information on CNS disposition of systemically-administered 5-HT3 receptor antagonists. This study evaluated the cerebrospinal fluid (CSF) disposition of ondansetron, as a surrogate of CNS penetration.

METHODS

Fifteen patients were given a single 16 mg intravenous 15 minute infusion of ondansetron, followed by serial blood and a single CSF sampling. Population pharmacokinetic (PK) modelling was implemented to describe the average and individual plasma and CSF profiles of ondansetron. A two-compartmental model was used to capture ondansetron plasma PK with a single CSF compartment to describe distribution to the CNS.

RESULTS

The individual model-estimated CSF to plasma partition coefficients of ondansetron were between 0.09 and 0.20. These values were mirrored in the calculated CSF penetration ratios, ranging from 0.08 to 0.26.

CONCLUSIONS

After intravenous administration, CSF concentrations of ondansetron were approximately 7-fold lower than those observed in the plasma. A model could be developed to describe individual CSF concentration-time profiles of ondansetron based on a single CSF data point. The low CSF penetration of ondansetron may explain its limited analgesic effectiveness, and affords an opportunity to explore enhancing its CNS penetration for targeting conditions such as neuropathic pain.

Assessing the impacts on fetal dosimetry of the modelling of the placental transfers of xenobiotics in a pregnancy physiologically based pharmacokinetic model

The developmental origin of health and diseases theory supports the critical role of the fetal exposure to children's health. We developed a physiologically based pharmacokinetic model for human pregnancy (pPBPK) to simulate the maternal and fetal dosimetry throughout pregnancy. Four models of the placental exchanges of chemicals were assessed on ten chemicals for which maternal and fetal data were available. These models were calibrated using non-animal methods: in vitro (InV) or ex vivo (ExV) data, a semi-empirical relationship (SE), or the limitation by the placental perfusion (PL). They did not impact the maternal pharmacokinetics but provided different profiles in the fetus. The PL and InV models performed well even if the PL model overpredicted the fetal exposure for some substances. The SE and ExV models showed the lowest global performance and the SE model a tendency to underprediction. The comparison of the profiles showed that the PL model predicted an increase in the fetal exposure with the pregnancy age, whereas the ExV model predicted a decrease. For the SE and InV models, a small decrease was predicted during the second trimester. All models but the ExV one, presented the highest fetal exposure at the end of the third trimester. Global sensitivity analyses highlighted the predominant influence of the placental transfers on the fetal exposure, as well as the metabolic clearance and the fraction unbound. Finally, the four transfer models could be considered depending on the framework of the use of the pPBPK model and the availability of data or resources to inform their parametrization.

Ondansetron pharmacokinetics in pregnant women and neonates: towards a new treatment for neonatal abstinence syndrome

Ondansetron is the drug of choice to prevent nausea in women undergoing cesarean surgery and can be used to prevent neonatal abstinence syndrome (NAS). The pharmacokinetics of ondansetron have not been characterized in pregnant women or in newborns. A nonlinear mixed-effects modeling approach was used to analyze plasma samples obtained from 20 nonpregnant and 40 pregnant women following a single administration of 4 or 8 mg ondansetron, from umbilical cord blood at delivery, and from neonates after birth. The analysis indicates that: ondansetron disposition is not affected by pregnancy (P > 0.05), but influenced by dose (P < 0.05), and is characterized by rapid transplacental transfer and longer elimination half-life in neonates compared to their mother. A dosing regimen for prevention of NAS was designed based on the model. The regimen involves IV administration of 4 mg to the mothers shortly before cord clamping, or oral administration of 0.07 mg/kg (or equivalently 0.04 mg/kg IV) to neonates.

Tolerability and pharmacokinetic properties of ondansetron administered subcutaneously with recombinant human hyaluronidase in minipigs and healthy volunteers

BACKGROUND

Subcutaneous ondansetron facilitated by recombinant human hyaluronidase PH20 (rHuPH20) is an alternative for treating nausea/vomiting in patients who cannot receive ondansetron by other routes of administration.

OBJECTIVE

Based on preclinical results in minipigs, a Phase I study was designed to assess the tolerability and pharmacokinetic properties of subcutaneous ondansetron + rHuPH20 compared with intramuscular, intravenous, or oral ondansetron monotherapy in healthy volunteers.

METHODS

In a crossover design, 3 minipigs were dosed with subcutaneous ondansetron 0.08 mg/kg + rHuPH20, or as intramuscular or intravenous monotherapy, for the evaluation of plasma ondansetron concentrations and local tolerability. In a randomized, open-label, 4-way crossover study, subjects received a randomized sequence of SC ondansetron 4 mg + rHuPH20, or ondansetron monotherapy IM (4 mg), IV (4 mg), or PO (8 mg), over 4 daily visits. Study participants included healthy volunteers aged 19 to 65 years with adequate venous access in both upper extremities and no history of QT-interval prolongation. Primary tolerability end points (administration-site observations, systemic adverse events [AEs], and subject-assessed pain) were assessed, and pharmacokinetic parameters (AUC, Cmax, Tmax, t½) were computed to compare relative rate and extent of systemic exposure. Results were described using summary statistics, and bioequivalence was determined with a linear mixed-effects model.

RESULTS

In the preclinical study, no adverse events or significant local reactions were observed. The Cmax (45.8 ng/mL at 0.08 hour) with subcutaneous administration + rHuPH20 was 83% greater and was achieved 68% faster than with intramuscular administration (Cmax = 25 ng/mL at 0.25 hour). In the clinical study, a total of 12 subjects (7 women, 5 men; white majority; mean age, 44.8) were randomized. The majority of AEs were at the injection site, mild in severity, and transient. After subcutaneous administration of ondansetron + rHuPH20, geometric mean Cmax was 35% higher than with intramuscular ondansetron, 43% lower than with intravenous ondansetron, and 126% higher than with oral ondansetron (corrected for dose). Bioequivalence tests demonstrated that systemic exposure after subcutaneous administration was similar to that after intramuscular or intravenous administration and significantly greater than that after oral administration.

CONCLUSIONS

Subcutaneous ondansetron + rHuPH20 was generally well-tolerated. Subcutaneous dosing resulted in an extent of systemic exposure similar to that with intramuscular or intravenous dosing and greater than that with oral administration, and may be an option for clinical administration of ondansetron. ClinicalTrials.gov identifier: NCT01572012.

Ondansetron-loaded biodegradable microspheres as a nasal sustained delivery system: in vitro/in vivo studies

The aim of this study was to prepare ondansetron-loaded biodegradable microspheres as a nasal delivery system. Microspheres were prepared with emulsification/spray-drying technique using poly(d,l-lactide) (PLA) and two different types of poly(d,l-lactide-co-glycolide) (PLGA). The effect of the type of organic solvent (dichloromethane (DCM) or a mixture of DCM and ethyl acetate) on the microsphere characteristics was also examined. The prepared microspheres were evaluated with respect to the morphological properties, particle size, zeta potential, drug loading efficiency, and in vitro drug release. The mean particle size (d(50)) of microsphere formulations was ranged from 11.67-25.54 μm, indicating suitable particle size for nasal administration. All microspheres had low drug loading efficiency in the range of 12.28-21.04%. The results indicated that particle size of microspheres were affected by both type of polymer and organic solvent, however drug loading efficiency of microspheres were affected by only the type of organic solvent used. All microspheres were negatively charged due to the polymers (PLA or PLGA) used. A prolonged in vitro drug release profile was observed for 96 h. Based on in vitro data, the selected microsphere formulation has been applied via nasal route to rats in vivo. Following nasal administration of ondansetron-loaded microsphere to rats, ondansetron plasma levels were within a range of 30-48 ng/mL during 96 h, indicating a sustained drug delivery pattern and relatively a constant plasma drug concentration level. The results suggested that biodegradable microspheres prepared with emulsification/spray-drying technique could be considered to deliver ondansetron via nasal route to obtain a prolonged release.

Colonic treatments and targets: issues and opportunities

The colon provides a plethora of therapeutic opportunities. There are multiple disease targets, drug molecules, and colon-specific delivery systems to be explored. Clinical studies highlight the potential for systemic delivery via the colon, and the emerging data on the levels of cell membrane transporters and metabolic enzymes along the gut could prove advantageous for this. Often efflux transporters and metabolic enzyme levels are lower in the colon, suggesting a potential for improved bioavailability of drug substrates at this site. The locoregional distribution of multiple metabolic enzymes (including cytochromes), efflux transporters (including P-glycoprotein and breast cancer resistance proteins), and influx transporters (including the solute carrier family) along the intestine is summarized. Local delivery to the colonic mucosa remains a valuable therapeutic option. New therapies that target inflammatory mediators could improve the treatment of inflammatory bowel disease, and old and new anticancer molecules could, when delivered topically, prove to be beneficial adjuncts to the current systemic or surgical treatments. New issues such as pharmacogenomics, chronotherapeutics, and the delivery of prebiotics and probiotics are also discussed in this review. Targeting drugs to the colon utilizes various strategies, each with their advantages and flaws. The most promising systems are considered in the light of the physiological data which influence their in vivo behavior.

Toward an increased understanding of the barriers to colonic drug absorption in humans: implications for early controlled release candidate assessment

The purpose of this study was to increase the understanding of in vivo colonic drug absorption in humans by summarizing and evaluating all regional in vivo human absorption data with focus on the interpretation of the colonic absorption data in relation to intestinal permeability and solubility. In addition, the usefulness of the Biopharmaceutics Classification System (BCS) in early assessment of the in vivo colonic absorption potential of controlled release drug candidates was investigated. Clinical regional absorption data (Cmax, Tmax, and AUC) of 42 drugs were collected from journal articles, abstracts, and internal reports, and the relative bioavailability in the colon (Frel(colon)) was obtained directly or calculated. Bioavailability, fraction dose absorbed, and information if the compounds were substrates for P-glycoprotein (P-gp) or cytochrome P450 3A (CYP3A) were also obtained. The BCS I drugs were well absorbed in the colon (Frel(colon) > 70%), although some drugs had lower values due to bacterial degradation in the colon. The low permeability drugs (BCS III/IV) had a lower degree of absorption in the colon (Frel(colon) < 50%). There was a clear correlation between in vitro Caco-2 permeability and Frel(colon), and atenolol and metoprolol may function as permeability markers for low and high colonic absorption, respectively. No obvious effect of P-gp on the colonic absorption of the drugs in this study was detected. There was insufficient data available to fully assess the impact of low solubility and slow dissolution rate. The estimated in vivo fractions dissolved of the only two compounds administered to the colon as both a solution and as solid particles were 55% and 92%, respectively. In conclusion, permeability and solubility are important barriers to colonic absorption in humans, and in vitro testing of these properties is recommended in early assessment of colonic absorption potential.

Bioequivalence assay between orally disintegrating and conventional tablet formulations in healthy volunteers

The purpose of this study was to evaluate bioequivalence of two commercial 8 mg tablet formulations of ondansetrona available in the Brazilian market. In this study, a simple, rapid, sensitive and selective liquid chromatography-tandem mass spectrometry method is described for the determination of ondansetron in human plasma samples. The method was validated over a concentration range of 2.5-60 ng/ml and used in a bioequivalence trial between orally disintegrating and conventional tablet ondansetron formulations, to assess its usefulness in this kind of study. Vonau flash (Biolab Sanus Farmacêutica, Brazil, as test formulations) and Zofran (GlaxoSmithKline, Brazil, as reference formulation) were evaluated following a single 8 mg dose to 23 healthy volunteers of both genders. The dose was administered after an overnight fast according to a two-way crossover design. Bioequivalence between the products was determinated by calculating 90% confidence interval (90% CI) for the ratio of C(max), AUC(0-t) and AUC(0-infinity) values for the test and reference products, using logarithmically transformed data. The 90% confidence interval for the ratio of C(max) (87.5-103.8%), AUC(0-t) (89.3-107.2%) and AUC(0-infinity) (89.7-106.0%) values for the test and reference products is within the 80-125% interval, proposed by FDA, EMEA and ANVISA. It was concluded that two ondansetron formulations are bioequivalent in their rate and extent of absorption.

Novel approach to improve permeation of ondansetron across shed snake skin as a model membrane

The purpose of this study was to investigate the feasibility of transdermal drug delivery of ondansetron, an antagonist of the 5-HT3 receptor, used for the treatment of chemotherapy-induced emesis. The permeability of ondansetron from an aqueous suspension through shed snake skin as a model membrane was very low and in order to improve it, several enhancers were tested. Ethanol increased the flux at a concentration of 40% or more. The solubility of ondansetron also increased as the ethanol concentration increased. The permeability coefficient increased after pretreatment of the shed snake skin with Azone, oleic acid or lauryl alcohol. Further improvement of the permeability was observed when ethanol was combined with other enhancers and was maximum for the combination of ethanol and oleic acid. Oleic acid dramatically increased the partition of ondansetron to n-hexane and shed snake skin. Oleic acid may enhance the permeation of ondansetron in two ways: by a direct effect on the stratum corneum or via counterion formation of an ion-pair. The maximum flux obtained from the combination of ethanol and other enhancers seems to be high enough to obtain a therapeutic effect.

Comparison of zafirlukast (Accolate) absorption after oral and colonic administration in humans

PURPOSE

This study characterized the gastrointestinal (GI) absorption of zafirlukast after oral and colonic administration in humans.

METHODS

Five healthy subjects received zafirlukast solution (40 mg) orally and via an oroenteric tube into the colon in a randomized, crossover fashion. Two additional subjects were dosed into the distal ileum. Serial blood samples were obtained and plasma concentrations were quantitated by HPLC.

RESULTS

Mean +/- SD pharmacokinetic parameters after oral vs. colonic administration were: AUC infinity of 2076 +/- 548 vs. 602 +/- 373 ng x h/mL, respectively, and Cmax of 697 +/- 314 vs. 194 +/- 316 ng/mL, respectively. Mean colon:oral AUCalpha and Cmax were 0.29 and 0.30, respectively. Median tmax values were 2.0 and 1.35 hr after oral and colonic administration. First-order absorption rate constants (Ka and Kac) were estimated from a two-compartment model with first-order elimination. Kac:Ka was <0.5 in 4 of the 5 subjects dosed in the colon.

CONCLUSIONS

Zafirlukast was absorbed at multiple sites in the GI tract. The rate and extent of zafirlukast absorption was less after colonic than oral administration. Zafirlukast was significantly absorbed in the distal ileum. This study demonstrated that gamma scintigraphy, digital radiography, and fluoroscopy can be used to track the movement and confirm the location of the oroenteric tube in the GI tract.

Mucoadhesive suppositories of ramosetron hydrochloride utilizing Carbopol

Suppositories are the preferable dosage form for patients at home or experiencing nausea. Serotonin (5-HT(3))-receptor antagonists are used to treat vomiting in intravenous or oral administration but not suppository form. Ramosetron hydrochloride (RAM) is a new 5-HT(3) antagonist which effectively inhibits vomiting, and we prepared RAM suppositories using Witepsol((R)) H-15 (H-15) containing Carbopol((R)) 934P (CP). The viscosity of suppository base and RAM release properties from suppositories were examined. Plasma RAM concentrations after administration of suppositories to rabbits were estimated and irritation of rectal tissues were observed. Antiemetic effects of suppositories were studied using ferrets. The base viscosity increased with addition of CP. Suppositories containing CP exhibited better absorption in rabbits compared to H-15 suppositories, correlated with release behavior. Suppositories containing 2% CP had 2.5 times larger AUC(0-24 h) than H-15 suppositories, and the MRT was prolonged by 5.8 h compared with i.v. administration. 10% CP suppositories administered to rabbits for 5 days did not irritate the tissues. Antiemetic studies indicated that 2% CP suppository of RAM might have the same effect as i.v. administration. These results suggest that RAM suppositories containing CP are safe and useful in once-a-day dosage form for treatment of chemotherapy-induced nausea.

Design of a new multiparticulate system for potential site-specific and controlled drug delivery to the colonic region

A multiparticulate dosage form consisting of a hydrophobic core coated with a pH-dependent polymer is proposed for colonic specific delivery of drugs. Different approaches for colon-specific drug delivery have been studied over the last decade, including prodrugs, polymeric coating using pH-sensitive or bacterial degradable polymers and matrices. In this work, we present a new multiparticulate system to deliver active molecules to the colonic region, which combines pH-dependent and controlled drug release properties. This system was constituted by drug loaded cellulose acetate butyrate (CAB) microspheres coated by an enteric polymer (Eudragit(R) S). Both, CAB cores and pH-sensitive microcapsules, were prepared by the emulsion-solvent evaporation technique in an oily phase. Ondansetron (OS) and budesonide (BDS), two interesting drugs with a potentially new application for the local treatment of intestinal disorders, were efficiently microencapsulated in CAB microspheres at different polymer concentrations (6 and 8%). These hydrophobic cores (about 60 and 110 micrometer in size, respectively) were then microencapsulated with Eudragit(R) S, resulting in multinucleated structures, except in the case of BDS-CAB microspheres prepared at 8% CAB concentration, in which more mononucleated microcapsules were obtained. The in vitro drug release studies of pH-sensitive microcapsules containing the hydrophobic cores showed that no drug was released below pH 7. After that, CAB microspheres efficiently controlled the release of BDS, the release behavior being affected by the different polymer concentration used in their preparation. However, OS-CAB microspheres did not maintain their controlled-release properties once the enteric polymer dissolved. The extraction of the drug by the Eudragit(R) solvent during the second microencapsulation process was in this case the cause for the failure of the controlling release mechanism.

Clinical pharmacokinetics of ondansetron. A review

5-HT3 receptors are ubiquitous in the enteric, sympathetic, parasympathetic and sensory nervous systems and in the central nervous system (CNS) (Kilpatrick et al 1990). In man 5-HT3 receptors are mainly situated on enterochromaffin cells in the gastrointestinal mucosa, which are innervated by vagal afferents (Reynolds et al 1989), and the area postrema of the brain stem, which forms the chemoreceptor trigger zone. Ondansetron is a selective antagonist at 5-HT3 receptors. It is 100 times more potent than metoclopramide at this site (Tyers 1992). It shows limited binding to other receptors and has a wide therapeutic window. Ondansetron is a useful antiemetic which probably has both central and peripheral actions in patients undergoing radiotherapy, cytotoxic chemotherapy or general anaesthesia (Naylor & Rudd 1992). This paper reviews the pharmacokinetics of ondansetron in health and disease to provide information for clinicians; it might alter prescribing and alert them to possible drug interactions.

Preoperative oral ondansetron for pediatric tonsillectomy

This prospective, randomized, double-blind, placebo-controlled study evaluated the antiemetic efficacy of preoperative oral ondansetron, 0.075 mg/kg or 0.15 mg/kg, in 136 preadolescent children premedicated with midazolam 0.5 mg/kg per os and dexamethasone 0.1 mg/kg intravenously prior to undergoing tonsillectomy with isoflurane anesthesia. The incidence of vomiting during the 24 h after tonsillectomy was significantly reduced (P < 0.04) by ondansetron 0.15 mg/kg compared with placebo and ondansetron 0.075 mg/kg (15%, 38%, and 36%, respectively). There was a significant reduction (P < 0.03) in the mean number of vomiting episodes per patient during the 24 h immediately after tonsillectomy in the ondansetron 0.15 mg/kg group compared with the placebo and ondansetron 0.075 mg/kg study groups (0.2 +/- 0.6, 0.8 +/- 1.3, and 0.8 +/- 1.3, respectively). The need for antiemetic rescue therapy (ondansetron 0.15 mg/kg intravenously after three episodes of emesis prior to discharge) was significantly greater in children who received placebo compared with the ondansetron 0.15 mg/kg study group (13% vs 0%, P < 0.05). We conclude that ondansetron 0.15 mg/kg, administered orally prior to tonsillectomy, is associated with reduced postoperative vomiting in preadolescent children. In addition, the preoperative oral administration of ondansetron 0.075 mg/kg is no more effective than placebo in preventing posttonsillectomy vomiting in preadolescent children.