Evidence of a flip-flop phenomenon in acamprosate pharmacokinetics: anin vivo study in rats

Pharmacokinetics of robenacoxib following single intravenous, subcutaneous and oral administrations in Baladi goats (Capra hircus)

The purpose of this study was to assess the pharmacokinetics of robenacoxib (RX), a COX-2 selective non-steroidal anti-inflammatory drug, in goats after single intravenous (IV), subcutaneous (SC) and oral (PO) administrations. 5-month-old healthy female goats (n = 8) were used. The animals were subjected to a three-phase, two-dose (2 mg/kg IV, 4 mg/kg SC, PO) unblinded, parallel study design, with a four-month washout period between the IV and SC treatment, and a one-week period between the SC and PO treatment. Blood was drawn from the jugular vein in heparinized vacutainer tubes at 0, 0.085 (for IV only), 0.25, 0.5, 0.75, 1, 1.5, 2, 4, 6, 8, 10 and 24 h. Plasma RX concentrations were measured using HPLC coupled to a UV multiple wavelength detector, and the data were pharmacokinetically analysed using ThothPro™ 4.3 software in a non-compartmental approach. Following IV administration, terminal elimination half-life, volume of distribution and total clearance were 0.32 h, 0.24 L/kg and 0.52 L/h/kg, respectively. For SC and PO, the mean peak plasma concentrations were 2.34 and 3.34 μg/mL at 1.50 and 0.50 h, respectively. The t1/2λz was significantly different between the IV and the extravascular (EV) administrations (0.32 h IV vs 1.37 h SC and 1.63 h PO), suggesting the occurrence of a flip-flop phenomenon. The significant difference in Vd values between IV (0.24 L/kg) and EV (0.95 L/kg SC and 1.71 L/kg; corrected for F %) routes might have also triggered the t1/2λz difference. The absolute average SC and PO bioavailability were high (98% and 91%, respectively). In conclusion, the IV administration of RX might not be suitable for goats, due to its short t1/2λz. The EV routes, however, appear to be convenient for the drug's occasional use.

Disposition kinetics of robenacoxib following intravenous and oral administration in geese (Anser anser domesticus)

Robenacoxib (RX) is a veterinary cyclooxygenase-2 selective inhibitor drug. It has never been tested on birds and is only labelled for use in cats and dogs. The purpose of this study was to assess its pharmacokinetics in geese after single intravenous (IV) and oral (PO) administrations. Four-month healthy female geese (n = 8) were used. Geese were subjected to a two-phase, single-dose (2 mg/kg IV, 4 mg/kg PO), open, longitudinal study design with a four-month washout period between the IV and the PO phases. Blood was collected from the left wing vein to heparinized tubes at 0, 0.085 (for IV only), 0.25, 0.5, 0.75, 1, 1.5, 2, 4, 6, 8, 10, and 24 h. Plasma RX concentrations were measured using HPLC coupled to an UV detector, and the data were pharmacokinetically analysed using ThothPro™ 4.3 software in a non-compartmental approach. Following IV administration, terminal elimination half-life, volume of distribution, and total clearance were 0.35 h, 0.34 L/kg, and 0.68 L/h/kg, respectively. For the PO route, the mean peak plasma concentration was 6.78 μg/mL at 0.50 h. The t1/2λz was very short and significantly different between the IV and PO administrations (0.35 h IV vs. 0.99 h PO), suggesting the occurrence of a flip-flop phenomenon. The Cl values corrected for the F% were significantly different between IV and PO administrations. It might have been a consequence of the longitudinal study design and the altered physiological and environmental conditions after a 4-month washout period. The absolute oral F% computed with the AUC method surpassed 150%, but after normalizing it to t1/2λz, it was 46%. In conclusion, the administration of RX might not be suitable for geese, due to its short t1/2λz.

Pharmacokinetics of three formulations of vitacoxib in horses

The pharmacokinetic properties of three formulations of vitacoxib were investigated in horses. To describe plasma concentrations and characterize the pharmacokinetics, 6 healthy adult Chinese Mongolian horses were administered a single dose of 0.1 mg/kg bodyweight intravenous (i.v.), oral paste, or oral tablet vitacoxib in a 3-way, randomized, parallel design. Blood samples were collected prior to and at various times up to 72 hr postadministration. Plasma vitacoxib concentrations were quantified using UPLC-MS/MS, and pharmacokinetic parameters were calculated using noncompartmental analysis. No complications resulting from the vitacoxib administration were noted on subsequent administrations, and all procedures were tolerated well by the horses throughout the study. The elimination half-life (T_1/2λz ) was 4.24 ± 1.98 hr (i.v.), 8.77 ± 0.91 hr (oral paste), and 8.12 ± 4.24 hr (oral tablet), respectively. Maximum plasma concentration (C_max ) was 28.61 ± 9.29 ng/ml (oral paste) and 19.64 ± 9.26 ng/ml (oral tablet), respectively. Area under the concentration-versus-time curve (AUC_last ) was 336 ± 229 ng hr/ml (i.v.), 221 ± 94 ng hr/ml (oral paste), and 203 ± 139 ng hr/ml, respectively. The results showed statistically significant differences between the 2 oral vitacoxib groups in T_max value. T_1/2λz (hr), AUC_last (ng hr/ml), and MRT (hr) were significantly different between i.v. and oral groups. The longer half-life observed following oral administration was consistent with the flip-flop phenomenon.

High body clearance and low oral bioavailability of alantolactone, isolated from Inula helenium, in rats: extensive hepatic metabolism and low stability in gastrointestinal fluids

Alantolactone (ALA) is a major bioactive sesquiterpene lactone present in the roots of Inula helenium L. (Asteraceae) which has been used widely in traditional medicine against various diseases such as asthma, cancer and tuberculosis. The pharmacologic activities of alantolactone have been well characterized, yet information on the physicochemical and pharmacokinetic properties of alantolactone and their mechanistic elucidation are still limited. Thus, this study aims to investigate the oral absorption and disposition of alantolactone and their relevant mechanisms. Log P values of alantolactone ranged from 1.52 to 1.84, and alantolactone was unstable in biological samples such as plasma, urine, bile, rat liver microsomes (RLM) and simulated gastrointestinal fluids. The metabolic rate of alantolactone was markedly higher in rat liver homogenates than in the other tissue homogenates. A saturable and concentration-dependent metabolic rate profile of alantolactone was observed in RLM, and rat cytochrome P450 (CYP) 1 A, 2C, 2D and 3 A subfamilies were significantly involved in its hepatic metabolism. Based on the well-stirred model, the hepatic extraction ratio (HER) was estimated to be 0.890-0.933, classifying alantolactone as a drug with high HER. Moreover, high total body clearance (111 ± 41 ml/min/kg) and low oral bioavailability (0.323%) of alantolactone were observed in rats. Taken together, the present study demonstrates that the extensive hepatic metabolism, at least partially mediated by CYP, is primarily responsible for the high total body clearance of alantolactone, and that the low oral bioavailability of alantolactone could be attributed to its low stability in gastrointestinal fluids and a hepatic first-pass effect in rats. Copyright © 2016 John Wiley & Sons, Ltd.

Predicting pharmacokinetic profile of therapeutic antibodies after iv injection from only the data after sc injection in cynomolgus monkey

1. The number of developed therapeutic monoclonal antibodies (mAbs) has increased in this decade. This study aims to predict their pharmacokinetic profiles after intravenous (iv) injection using only the data taken after subcutaneous (sc) injection in cynomolgus monkey. 2. Two-compartment model parameters, Q, V_c and V_p, were collected from the published data after iv injection in cynomolgus monkey for 21 mAbs (Group A). Bioavailability after sc injection (F), CL and serum/plasma concentration after iv injection of other published 19 mAbs (Group B) were predicted using the estimated geometric means of Q, V_c and V_p in Group A and the serum/plasma concentration after sc injection in Group B. 3. F and CL of 18 out of 19 mAbs in Group B were successfully predicted within 30% difference of observed value. Moreover, most of the observed serum/plasma concentrations after iv injection of mAbs in Group B were successfully predicted within 2-fold difference. Our approach suggests that iv injection might not be required to evaluate absorption of mAbs after sc injection in cynomolgus monkey. Therefore, our approach might reduce the time and cost of drug development, reduce the burden on resources, and also contribute to animal welfare.

Pharmacokinetics of Inhaled Rifampicin Porous Particles for Tuberculosis Treatment: Insight into Rifampicin Absorption from the Lungs of Guinea Pigs

Tuberculosis (TB) is a life-threatening infection that requires a lengthy treatment process that is often associated with adverse effects. Pulmonary delivery of anti-TB drugs has the potential to increase efficacy of treatment by increasing drug concentrations at the lungs, the primary site of infection. The aim of the present study is to evaluate the disposition of rifampicin (RIF) after its pulmonary administration as porous particles (PPs) to guinea pigs and contrast it to that after oral administration. RIF microparticles were prepared by spray drying a solution of RIF and L-leucine (9:1), and the resulting particles were characterized for their physicochemical properties. Animals received RIF either as intravenous solution (iv), as oral suspension of micronized RIF (ORS) and RIF-PPs (ORPP), or by insufflation of the PPs (IRPP). Plasma samples were collected at preselected time points, and bronchoalveolar lavage (BAL) was performed at the end of the study. RIF concentrations in biological samples were analyzed by HPLC. Plasma concentration versus time data was analyzed by compartmental and noncompartmental methods. RIF PPs were thin walled porous particles with mass median aerodynamic diameter (MMAD) of 4.8±0.1 μm, GSD=1.29±0.03, and fine particle fraction below 5.8 μm of 52.9±2.0%. RIF content in the resulting particles was 91.8±0.1%. Plasma concentration vs time profiles revealed that the terminal slope of the iv group was different from that of the oral or pulmonary groups, indicating the possibility of flip-flop kinetics. RIF from IRPP appeared to be absorbed faster than that of ORPP or ORS as evidenced by higher RIF plasma concentrations up until 2 h. Notably, similar AUC (when corrected by dose), similar CL, λ, and half-life were obtained after oral administration of RIF at 40 mg/kg and pulmonary administration of RIF at 20 mg/kg. However, RIF in the IRPP group had a shorter Tmax and higher bioavailability than orally dosed groups. In addition, RIF concentrations in the BAL of animals in the IRPP group were 3-4-fold larger than those in the orally dosed groups. The disposition in ORS and ORPP were best described by a model with two sequential compartments, whereas the disposition of IRPP was best described by a two parallel compartment model. The advantages of delivering RIF by the pulmonary route are demonstrated in the present study. These include achieving higher RIF concentrations in the lungs and similar systemic levels after pulmonary delivery of one-half of the oral nominal dose. This is expected to result in a more effective treatment of pulmonary TB, as shown previously in published efficacy studies.

Few Drugs Display Flip-Flop Pharmacokinetics and These Are Primarily Associated with Classes 3 and 4 of the BDDCS

This study was conducted to determine the number of drugs exhibiting flip-flop pharmacokinetics following oral (p.o.) dosing from immediate-release dosage forms and if they exhibit a common characteristic that may be predicted based on BDDCS classification. The literature was searched for drugs displaying flip-flop kinetics (i.e., absorption half-life larger than elimination half-life) in mammals in PubMed, via internet search engines and reviewing drug pharmacokinetic data. Twenty two drugs were identified as displaying flip-flop kinetics in humans (13 drugs), rat (nine drugs), monkey (three drugs), horse (two drugs), and/or rabbit (two drugs). Nineteen of the 22 drugs exhibiting flip-flop kinetics were BDDCS Classes 3 and 4. One of the three exceptions, meclofenamic acid (Class 2), was identified in the horse; however, it would not exhibit flip-flop kinetics in humans where the p.o. dosing terminal half-life is 1.4 h. The second, carvedilol, can be explained based on solubility issues, but the third sapropterin dihydrochloride (nominally Class 1) requires further consideration. The few drugs displaying p.o. flip-flop kinetics in humans are predominantly BDDCS Classes 3 and 4. New molecular entities predicted to be BDDCS Classes 3 and 4 could be liable to exhibit flip-flop kinetics when the elimination half life is short and should be suspected to be substrates for intestinal transporters.

The development of acamprosate as a treatment against alcohol relapse

INTRODUCTION

Globally, alcohol abuse and dependence are significant contributors to chronic disease and injury and are responsible for nearly 4% of all deaths annually. Acamprosate (Campral), one of only three pharmacological treatments approved for the treatment of alcohol dependence, has shown mixed efficacy in clinical trials in maintaining abstinence of detoxified alcoholics since studies began in the 1980s. Yielding inconsistent results, these studies have prompted skepticism.

AREAS COVERED

Herein, the authors review the preclinical studies which have assessed the efficacy of acamprosate in various animal models of alcohol dependence and discuss the disparate findings from the major clinical trials. Moreover, the authors discuss the major limitations of these preclinical and clinical studies and offer explanations for the often-contradictory findings. The article also looks at the importance of the calcium moiety that accompanies the salt form of acamprosate and its relevance to its activity.

EXPERT OPINION

The recent discovery that large doses of calcium largely duplicate the effects of acamprosate in animal models has introduced a serious challenge to the widely held functional association between this drug and the glutamate neurotransmission system. Future research on acamprosate or newer pharmacotherapeutics should consider assessing plasma and/or brain levels of calcium as a correlate or mediating factor in anti-relapse efficacy. Further, preclinical research on acamprosate has thus far lacked animal models of chemical dependence on alcohol, and the testing of rodents with histories of alcohol intoxication and withdrawal is suggested.

The clinical pharmacology of acamprosate

Acamprosate is one of the few medications licensed for prevention of relapse in alcohol dependence, and over time it has proved to be significantly, if moderately, effective, safe and tolerable. Its use is now being extended into other addictions and neurodevelopmental disorders. The mechanism of action of acamprosate has been less clear, but in the decade or more that has elapsed since its licensing, a body of translational evidence has accumulated, in which preclinical findings are replicated in clinical populations. Acamprosate modulates N-methyl-d-aspartic acid receptor transmission and may have indirect effects on γ-aminobutyric acid type A receptor transmission. It is known to decrease brain glutamate and increase β-endorphins in rodents and man. Acamprosate diminishes reinstatement in ethanolized rodents and promotes abstinence in humans. Although acamprosate has been called an anticraving drug, its subjective effects are subtle and relate to diminished arousal, anxiety and insomnia, which parallel preclinical findings of decreased withdrawal symptoms in animals treated with acamprosate. Further understanding of the pharmacology of acamprosate will allow appropriate targeting of therapy in individuals with alcohol dependence and extension of its use to other addictions.

Antileishmanial activity of a series of N²,N⁴-disubstituted quinazoline-2,4-diamines

A series of N(2),N(4)-disubstituted quinazoline-2,4-diamines has been synthesized and tested against Leishmania donovani and L. amazonensis intracellular amastigotes. A structure-activity and structure-property relationship study was conducted in part using the Topliss operational scheme to identify new lead compounds. This study led to the identification of quinazolines with EC50 values in the single digit micromolar or high nanomolar range in addition to favorable physicochemical properties. Quinazoline 23 also displayed efficacy in a murine model of visceral leishmaniasis, reducing liver parasitemia by 37% when given by the intraperitoneal route at 15 mg kg(-1) day(-1) for 5 consecutive days. Their antileishmanial efficacy, ease of synthesis, and favorable physicochemical properties make the N(2),N(4)-disubstituted quinazoline-2,4-diamine compound series a suitable platform for future development of antileishmanial agents.

Flip-flop pharmacokinetics--delivering a reversal of disposition: challenges and opportunities during drug development

Flip-flop pharmacokinetics is a phenomenon often encountered with extravascularly administered drugs. Occurrence of flip-flop spans preclinical to human studies. The purpose of this article is to analyze both the pharmacokinetic interpretation errors and opportunities underlying the presence of flip-flop pharmacokinetics during drug development. Flip-flop occurs when the rate of absorption is slower than the rate of elimination. If it is not recognized, it can create difficulties in the acquisition and interpretation of pharmacokinetic parameters. When flip-flop is expected or discovered, a longer duration of sampling may be necessary in order to avoid overestimation of fraction of dose absorbed. Common culprits of flip-flop disposition are modified dosage formulations; however, formulation characteristics such as the drug chemical entities themselves or the incorporated excipients can also cause the phenomenon. Yet another contributing factor is the physiological makeup of the extravascular site of administration. In this article, these causes of flip-flop pharmacokinetics are discussed with incorporation of relevant examples and the implications for drug development outlined.

Acamprosate modulates experimental autoimmune encephalomyelitis

OBJECTIVE

This pilot study aimed to determine the efficacy of acamprosate (N-acetyl homotaurine) in reducing the pathological features of experimental autoimmune encephalomyelitis (EAE) which is an animal model for multiple sclerosis (MS).

BACKGROUND

The amino acid taurine has multiple biological activities including immunomodulation and neuromodulation. The synthetic acetylated taurine derivative, acamprosate, which crosses the blood-brain barrier more readily compared to taurine, is currently being used for the prevention of alcohol withdrawal symptoms associated with enhanced glutamatergic receptor function and GABA receptor hypofunction.

METHODS

EAE was induced in C57BL/6 female mice with myelin oligodendrocyte glyocoprotein, amino acid 35-55. Mice were treated with 20, 100 and 500 mg/kg acamprosate for 21 days.

RESULTS

Neurological scores at disease peak were reduced by 21, 64 and 9% in the 20, 100 and 500 mg/kg groups, respectively. Neurological improvement in the 100 mg/kg group correlated with a reduction in numbers of inflammatory lesions and the extent of CNS demyelination. Blood TNF-α levels were significantly reduced in the 500 mg/kg group.

DISCUSSION

Acamprosate and other taurine analogs have a potential for future MS therapy.

Investigation of the relationship between in vitro and in vivo release behaviors of acamprosate from enteric-coated tablets

Acamprosate calcium is a highly soluble drug with low permeability that is used to maintain abstinence in alcohol-dependent patients. The aim of this study was to investigate the relationship between in vitro and in vivo behaviors of acamprosate from enteric-coated tablets. The in vitro release behavior of acamprosate tablets in pH 6.8 buffer solution was determined in three dissolution conditions, 50 and 150 rpm (paddle method) and 180 rpm (basket method). The results of this in vitro experiment indicated that acamprosate tablets hardly disintegrated, and drug dissolution was retarded despite the extremely hydrophilic nature of the drug. A single dose (333 mgx2 tablets) of each formulation was orally administered to four beagle dogs under fasting conditions, and the pharmacokinetic parameters were calculated. The mean AUC0-48, Cmax, Tlag and Tmax for the two types of tablets ranged from 41.5-53.6 microg.h/mL, 4.3-4.5 microg/mL, 2.0-2.5 h and 3.8-4.0 h, respectively. In conclusion, it is suggested that retarded drug release from the tablets and the low drug permeability may result in poor absorption and erratic bioavailability of this drug in humans.

A microdialysis study of extracellular levels of acamprosate and naltrexone in the rat brain following acute and repeated administration

Acamprosate and naltrexone are widely used in the treatment of alcoholism. However, numerous studies in rodents have shown differential effects of these compounds on alcohol consumption and/or relapse-like behavior following acute versus repeated administration. In order to determine if these differential behavioral effects could be attributable to changes in extracellular levels of these compounds, we used in vivo microdialysis to monitor extracellular levels of acamprosate and naltrexone in the rat medial prefrontal cortex following acute and repeated intraperitoneal administration. For acute treatment, animals received a single administration of acamprosate (100 or 300 mg/kg) or naltrexone (1 or 3 mg/kg). For repeated treatment, animals received once daily treatment with saline, acamprosate (300 mg/kg) or naltrexone (3 mg/kg) for 10 days before a subsequent challenge with the compound according to their respective pretreatment group. Dialysate levels of acamprosate and naltrexone were analyzed by liquid chromatography-tandem mass spectrometry and high performance liquid chromatography, respectively. Following acute administration, peak dialysate concentrations of each compound were dose-dependent, observed within 1 hour of administration, and were found to be in the low micromolar range for acamprosate and in the low to mid-nanomolar range for naltrexone. Pretreatment with acamprosate, but not naltrexone, for 10 days resulted in higher dialysate concentrations of the compound relative to saline-pretreated controls. Thus, repeated administration of acamprosate, but not naltrexone, results in augmented extracellular levels of the compound in the brain relative to saline-pretreated controls, which may explain the need for repeated administration of acamprosate in order to observe effects on alcohol consumption and/or relapse.

Stereoselective pharmacokinetics of ketorolac in calves after a single intravenous and oral dose

The purpose of this study was to establish the stereospecific pharmacokinetics of ketorolac (KT) in calves following a single 2 mg/kg intravenous (i.v.) and a single 8 mg/kg oral dose. Plasma concentrations were determined using a stereoselective HPLC assay. Pharmacokinetic parameters for both the stereoisomers were estimated by model-independent methods. Following an i.v. dose, the plasma concentration profiles of the stereoisomers were similar with half-lives of 5.9 +/- 5.1 h for R-KT and 6.0 +/- 4.9 h for S-KT. Clearance values for R- and S-KT after an i.v. dose were 0.0470 +/- 0.0370 and 0.0480 +/- 0.0370 L/h/kg respectively. After an oral dose, the terminal half-lives were longer than following i.v. administration with values of 14.77 +/- 3.08 and 14.55 +/- 2.95 h for R-KT and S-KT respectively. The average oral bioavailability was 86.5 +/- 20.6% for R-KT and 86.7 +/- 20.3% for S-KT. The results indicate that the stereoisomers of KT have similar pharmacokinetic profiles in calves. Although, unlike humans, bioinversion between KT stereoisomers appears minimal in calves, studies with individual isomers are needed before any firm conclusions can be drawn about this lack of KT bioinversion.