Pharmacokinetics of nicotine tartrate after single-dose liquid enema, oral, and intravenous administration

Comprehensive metabolic study of nicotine in equine plasma and urine using liquid chromatography/high-resolution mass spectrometry for the identification of unique biomarkers for doping control

Nicotine is classified as a stimulant, and its use is banned in horse racing and equestrian sports by the International Federation of Horseracing Authorities and the Fédération Équestre Internationale, respectively. Because nicotine is a major alkaloid of tobacco leaves, there is a potential risk that doping control samples may be contaminated by tobacco cigarettes or smoke during sample collection. In order to differentiate the genuine doping and sample contamination with tobacco leaves, it is necessary to monitor unique metabolites as biomarkers for nicotine administration and intake. However, little is known about the metabolic fate of nicotine in horses. This is the first report of comprehensive metabolism study of nicotine in horses. Using liquid chromatography/electrospray ionization high-resolution mass spectrometry, we identified a total of 17 metabolites, including one novel horse-specific metabolite (i.e., 4-hydroxy-4-(3-pyridyl)-N-methylbutanamide), in post-administration urine samples after nasoesophageal administration of nicotine to three thoroughbred mares; eight of these compounds were confirmed based on reference standards. Among these metabolites, N-hydroxymethylnorcotinine was the major urinary metabolite in equine, but it could only be tentatively identified by mass spectral interpretation due to the lack of reference material. In addition, we developed simultaneous quantification methods for the eight target analytes in plasma and urine, and applied them to post-administration samples to establish elimination profiles of nicotine and its metabolites. The quantification results revealed that trans-3'-hydroxycotinine could be quantified for the longest period in both plasma (72 h post-administration) and urine (96 h post-administration). Therefore, this metabolite is the most appropriate monitoring target for nicotine exposure for the purpose of doping control due to its long detection times and the availability of its reference material. Further, we identified trans-3'-hydroxycotinine as a unique biomarker allowing differentiation between nicotine administration and sample contamination with tobacco leaves.

Nicotine Population Pharmacokinetics in Healthy Smokers After Intravenous, Oral, Buccal and Transdermal Administration

Background

In 4 decades, numerous nicotine replacement therapy products have been developed. Population pharmacokinetic models can support exposure–response modeling and inform nicotine replacement therapy product development, but only limited model-based cross-study population pharmacokinetic analyses for nicotine replacement therapy products have been published.

Objectives

The aim of this retrospective analysis was to assess the population pharmacokinetics of nicotine across intravenous, oral, transdermal and oromucosal (mouth spray, chewing gum, lozenge and inhaler) routes and formulations in healthy smoking subjects.

Methods

Data on 930 unique subjects (46,016 observations) from 29 single- and repeated-dose studies with multiple formulations across intravenous, oral, transdermal and oromucosal routes of administration were included. Data from intravenous and extravascular routes of administration were modelled separately for run efficiency reasons. For developing extravascular models, clearance and disposition parameters and their inter-individual variabilities were fixed to the estimates for intravenously delivered nicotine. Detectable pre-dose nicotine concentrations were modelled as a hypothetical nicotine bolus into the central compartment at the start of wash-out. Modelling repeated-dose oral and buccal administrations required a time-dependent increase in clearance or decrease in bioavailability to describe the data adequately.

Results

Disposition of intravenous nicotine was best described by a three-compartment model with initial and terminal half-lives of 7 min and 4.5 h, respectively, and the absorption of single oral doses was best described with a first-order absorption rate constant of 1.55 h⁻¹. The data of buccal formulations were modelled with parallel oromucosal absorption and gastrointestinal absorption of a part of the dose that is swallowed. For transdermal nicotine, parallel zero- and first-order release from the patch and a transit-compartment absorption model best described the data. Key pharmacokinetic parameters were reliably estimated, with typical values for clearance (67 L/h for a 70-kg subject), volume of distribution (4.3 L/kg), oral bioavailability (40%) and transdermal bioavailability (76%) within expected ranges. The estimated fraction of the dose swallowed for buccal formulations ranged from 55% (gum) to 69% (lozenge).

Conclusions

Robust population pharmacokinetic models were developed for five nicotine replacement therapy product types and for intravenous and oral nicotine. These population pharmacokinetic models are used in exposure–response analyses and simulation-based nicotine replacement therapy product design.

Electronic supplementary material

The online version of this article (10.1007/s40262-020-00960-5) contains supplementary material, which is available to authorized users.

Pharmacokinetics of cotinine in rats: a potential therapeutic agent for disorders of cognitive function

BACKGROUND

Attention has been paid to cotinine (COT), one of the major metabolites of nicotine (NIC), for its pro-cognitive effects and potential therapeutic activities against Alzheimer's disease (AD) and other types of cognitive impairment. In order to facilitate pharmacological and toxicological studies on COT for its pro-cognitive activities, we conducted a pharmacokinetic (PK) study of COT in rats, providing important oral and intravenously (iv) PK information.

METHODS

In this study, plasma samples were obtained up to 48 h after COT was dosed to rats orally and iv at a dose of 3mg/kg. Plasma samples were prepared and analyzed using a sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) bioanalytical method, providing concentration profiles of COT and metabolites after oral and iv administrations.

RESULTS

The data were fitted into a one-compartment model and a two-compartment model for the oral and iv groups, respectively, providing important PK information for COT including PK profiles, half-life, clearance and bioavailability. The results suggested fast absorption, slow elimination and high bioavailability of COT in rats.

CONCLUSIONS

Several important facts about the PK properties in rats suggested COT could be a potential pro-cognitive agent. Information about the pharmacokinetics of COT in rats revealed in this study is of great importance for the future studies on COT or potential COT analogs as agents for improving cognition.

Pharmacokinetic and pharmacodynamics studies of nicotine after oral administration in mice: effects of methoxsalen, a CYP2A5/6 inhibitor

INTRODUCTION

The use of novel oral nicotine delivery devices and compositions for human consumption and for animal research studies has been increasing in the last several years.

METHODS

Studies were undertaken to examine whether the systemic administration of methoxsalen, an inhibitor of human CYP2A6 and mouse CYP2A5, would modulate nicotine pharmacokinetics and pharmacological effects (antinociception in the tail-flick, and hot-plate tests, and hypothermia) in male ICR mouse after acute oral nicotine administration.

RESULTS

Administration of intra peritoneal (ip) methoxsalen significantly increased nicotine's Cmax, prolonged the plasma half-life (fourfold decrease) of nicotine, and increased its area under the curve (AUC) compared with ip vehicle treatment. Methoxsalen pretreatment prolonged the duration of nicotine-induced antinociception and hypothermia (15mg/kg, po) for periods up to 6- and 24-hr postnicotine administration, respectively. Additionally, methoxsalen potentiated nicotine-induced antinociception and hypothermia as evidenced by leftward shifts in nicotine's dose-response curve. Furthermore, this prolongation of nicotine's effects after methoxsalen was associated with a parallel prolongation of nicotine plasma levels in mice. These data strongly suggest that variation in the rates of nicotine metabolic inactivation substantially alter pharmacological effects of nicotine given orally.

CONCLUSION

We have shown that the pharmacological effects of inhibiting nicotine's metabolism after oral administration in mice are profound. Our results suggest that inhibiting nicotine metabolism can be used to dramatically enhance nicotine's bioavailability and its resulting pharmacology, which further supports this inhibitory approach for clinical development of an oral nicotine replacement therapy.

Novel insights on the effect of nicotine in a murine colitis model

Studies showed that nicotine has a positive influence on symptoms of ulcerative colitis. In the present study, we explored the effect of nicotine treatment using different routes of administration in the dextran sodium sulfate (DSS) colitis mouse model. We also investigated the effects of cotinine, a major metabolite of nicotine, in the model. C57BL6 adult male mice were given DSS solution freely in the drinking water for seven consecutive days, and tap water was given thereafter. Disease severity, length of the colon, colon tissue histology, and inflammatory markers, including colonic myeloperoxidase activity and colonic tumor necrosis factor-α levels, were evaluated. The effect of nicotine and cotinine treatments via various different routes of administration were examined the DSS model. In addition, we measured the plasma levels of nicotine and cotinine in our treatment protocols. Administration of low, but not high, doses of oral nicotine in DSS-treated mice resulted in a significant decrease in disease severity, histologic damage scores, as well as colonic level of tumor necrosis factor-α. However, the anti-inflammatory effect of nicotine was not seen after chronic s.c. or minipump infusion of the drug. Differences in plasma levels of nicotine and cotinine do not seem to account for this lack of effect. Finally, oral cotinine alone failed to show a significant effect in the DSS model of colitis. These results highlight that dose and route of administration play a critical role in the protective effect of nicotine in the DSS mouse colitis model.

The reinforcement threshold for nicotine as a target for tobacco control

BACKGROUND

Cigarette smoking represents an enormous public health problem worldwide that leads to over 5 million deaths per year. The gradual reduction of the nicotine content of cigarettes below the threshold that is required to develop addiction is one strategy that might substantially reduce the number of addicted smokers and prevent adolescents from becoming addicted to nicotine (Benowitz and Henningfield, 1994). While the potential public health benefits of this approach are enormous, the guiding concepts and relevant empirical evidence needed to support the implementation of a nicotine reduction policy require a critical examination.

METHODS

The purpose of this paper is to briefly review the current concepts and research regarding nicotine reduction while also discussing the utility of the addictive threshold for nicotine in this approach. The accurate determination of the nicotine addiction threshold presents some conceptual challenges as there is a lack of consensus on how to best measure nicotine addiction. This difficulty can impede the progress for developing a science-based tobacco control policy. As an alternative, the nicotine reinforcement threshold is a relatively clear concept, and well-accepted methods and criteria are available to measure nicotine reinforcement.

RESULTS

However, there are many gaps in our current knowledge concerning the nicotine reinforcement threshold in humans. The threshold for nicotine reinforcement remains to be determined in controlled settings using different populations of current or potential tobacco users. In addition, the value of the nicotine reinforcement threshold in predicting tobacco use in real-world settings needs to be examined. The results of such studies will determine the potential utility of the estimated threshold for nicotine reinforcement in developing science-based tobacco control policies.

Adult mice voluntarily progress to nicotine dependence in an oral self-selection assay

Nicotine has both rewarding and aversive properties in rodents, as shown by intravenous self-administration, intracranial self-stimulation, and conditioned place preference experiments. However, high throughput models of nicotine reward have not been developed in mice. In previous two-bottle studies, mice often chose to drink less from the nicotine bottle than from the water bottle, which raises the question whether these paradigms provide a model of the reinforcing properties of oral nicotine. We hypothesized that previous two-bottle choice paradigms included factors (such as the brief duration of trials, the addition of flavorings to both bottles, water bottles located relatively close to each other, etc.) that may have obstructed the formation of a learned association between the taste of nicotine and its delayed pharmacological effects. Here we show that a paradigm designed to simplify the acquisition of a learned association resulted in nicotine consumption by various strains and sexes that diverged progressively over a period of seven weeks. The strain and sex with the highest nicotine consumption (C57BL/6J females) showed steady and statistically significant increases in nicotine consumption throughout this period. C57BL/6J females were clearly responding to the reinforcing properties of nicotine because they chose to drink over 70% of their fluids from the nicotine bottle. Moreover, they became nicotine dependent, as shown by highly significant nicotine withdrawal symptoms after the nicotine bottle was removed. The strain and sex with the lowest consumption (A/J males) showed a significant decrease in nicotine consumption, and by the end of the experiment were drinking only 24% of their fluids from the nicotine bottle.

Ulcerative colitis in smokers, non-smokers and ex-smokers

Smoking is a major environmental factor that interferes in the establishment and clinical course of ulcerative colitis (UC). Firstly, the risk of smoking status impact in the development of UC is reviewed, showing that current smoking has a protective association with UC. Similarly, being a former smoker is associated with an increased risk of UC. The concept that smoking could have a role in determining the inflammatory bowel disease phenotype is also discussed. Gender may also be considered, as current smoking delays disease onset in men but not in women. No clear conclusions can be driven from the studies trying to clarify whether childhood passive smoking or prenatal smoke exposure have an influence on the development of UC, mainly due to methodology flaws. The influence of smoking on disease course is the second aspect analysed. Some studies show a disease course more benign in smokers that in non-smokers, with lower hospitalizations rates, less flare-ups, lower use of oral steroids and even less risk of proximal extension. This is not verified by some other studies. Similarly, the rate of colectomy does not seem to be determined by the smoking status of the patient. The third issue reviewed is the use of nicotine as a therapeutic agent. The place of nicotine in the treatment of UC is unclear, although it could be useful in selected cases, particularly in recent ex-smokers with moderate but refractory attacks of UC. Finally, the effect of smoking cessation in UC patients is summarised. Given that smoking represents a major worldwide cause of death, for inpatients with UC the risks of smoking far outweigh any possible benefit. Thus, physicians should advise, encourage and assist UC patients who smoke to quit.

Fundamental reaction pathways for cytochrome P450-catalyzed 5'-hydroxylation and N-demethylation of nicotine

The reaction pathways for 5'-hydroxylation and N-demethylation of nicotine catalyzed by cytochrome P450 were investigated by performing a series of first-principle electronic structure calculations on a catalytic reaction model system. The computational results indicate that 5'-hydroxylation of nicotine occurs through a two-state stepwise process, that is, an initial hydrogen atom transfer from nicotine to Cpd I (i.e., the HAT step) followed by a recombination of the nicotine moiety with the iron-bound hydroxyl group (i.e., the rebound step) on both the high-spin (HS) quartet and low-spin (LS) doublet states. The HAT step is the rate-determining one. This finding represents the first case that exhibits genuine rebound transition state species on both the HS and the LS states for C(alpha)-H hydroxylation of amines. N-Demethylation of nicotine involves a N-methylhydroxylation to form N-(hydroxymethyl)nornicotine, followed by N-(hydroxymethyl)nornicotine decomposition to nornicotine and formaldehyde. The N-methylhydroxylation step is similar to 5'-hydroxylation, namely, a rate-determining HAT step followed by a rebound step. The decomposition process occurs on the deprotonated state of N-(hydroxymethyl)nornicotine assisted by a water molecule, and the energy barrier is significantly lower than that of the N-methylhydroxylation process. Comparison of the rate-determining free energy barriers for the two reaction pathways predicts a preponderance of 5'-hydroxylation over the N-demethylation by roughly a factor of 18:1, which is in excellent agreement with the factor of 19:1 derived from available experimental data.

Optical studies of nicotinic acetylcholine receptor subtypes in the guinea-pig enteric nervous system

Nicotinic transmission in the enteric nervous system (ENS) is extensive, but the role of individual nicotinic acetylcholine receptor (nAChR) subtypes in the functional connectivity of its plexuses has been elusive. Using monoclonal antibodies (mAbs) against neuronal alpha3-, alpha4-, alpha3/alpha5-, beta2-, beta4- and alpha7-subunits, combined with radioimmunoassays and immunocytochemistry, we demonstrate that guinea-pig enteric ganglia contain all of these nAChR-subunits with the exception of alpha4, and so, differ from mammalian brain. This information alone, however, is insufficient to establish the functional role of the identified nAChR-subtypes within the enteric networks and, ultimately, their specific contributions to gastrointestinal physiology. We have used voltage-sensitive dyes and a high-speed CCD camera, in conjunction with specific antagonists to various nAChRs, to elucidate some of the distinct contributions of the individual subtypes to the behaviour of enteric networks. In the guinea-pig, the submucous plexus has the extraordinary advantage that it is virtually two-dimensional, permitting optical recording, with single cell resolution, of the electrical activity of all of its neurones. In this plexus, the block of alpha3beta2-, alpha3beta4- and/or alpha7-nAChRs always results in a decrease in the magnitude of the synaptic response. However, the magnitude of the fast excitatory post-synaptic potentials (epsps) evoked by electrical stimulation of a neighbouring ganglion varies from cell to cell, reflecting the differential expression of subunits already observed using mAbs, as well as the strengths of the activated synaptic inputs. At the same time, we observe that submucous neurones have a substantial mecamylamine (Mec)-insensitive (non-nicotinic) component to their fast epsps, which may point to the presence of purinergic or serotonergic fast epsps in this system. In the myenteric plexus, on the other hand, the antagonist-induced changes in the evoked synaptic response vary depending upon the location of the stimulating electrode with respect to the ganglion under study. The range of activity patterns that follows sequential pharmacological elimination of individual subtypes suggests that nAChRs may be capable of regulating the activity of both excitatory and inhibitory pathways, in a manner similar to that described in the central nervous system.

Metabolism and Disposition Kinetics of Nicotine

Nicotine is of importance as the addictive chemical in tobacco, pharmacotherapy for smoking cessation, a potential medication for several diseases, and a useful probe drug for phenotyping cytochrome P450 2A6 (CYP2A6). We review current knowledge about the metabolism and disposition kinetics of nicotine, some other naturally occurring tobacco alkaloids, and nicotine analogs that are under development as potential therapeutic agents. The focus is on studies in humans, but animal data are mentioned when relevant to the interpretation of human data. The pathways of nicotine metabolism are described in detail. Absorption, distribution, metabolism, and excretion of nicotine and related compounds are reviewed. Enzymes involved in nicotine metabolism including cytochrome P450 enzymes, aldehyde oxidase, flavin-containing monooxygenase 3, amine N-methyltransferase, and UDP-glucuronosyltransferases are represented, as well as factors affecting metabolism, such as genetic variations in metabolic enzymes, effects of diet, age, gender, pregnancy, liver and kidney diseases, and racial and ethnic differences. Also effects of smoking and various inhibitors and inducers, including oral contraceptives, on nicotine metabolism are discussed. Due to the significance of the CYP2A6 enzyme in nicotine clearance, special emphasis is given to the effects and population distributions of CYP2A6 alleles and the regulation of CYP2A6 enzyme.

Human variability for metabolic pathways with limited data (CYP2A6, CYP2C9, CYP2E1, ADH, esterases, glycine and sulphate conjugation)

Human variability in the kinetics of a number of phase I (CYP2A6, CYP2C9, CYP2E1, alcohol dehydrogenase and hydrolysis) and phase II enzymes (glycine and sulphate conjugation) was analysed using probe substrates metabolised extensively (>60%) by these routes. Published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and available data on subgroups of the population (effects of ethnicity, age and disease) were abstracted using parameters relating primarily to chronic exposure [metabolic and total clearances, area under the plasma concentration time-curve (AUC)] and acute exposure (C(max)). Interindividual differences in kinetics for all these pathways were low in healthy adults ranging from 21 to 34%. Pathway-related uncertainty factors to cover the 95th, 97.5th and 99th centiles of healthy adults were derived for each metabolic route and were all below the 3.16 kinetic default uncertainty factor in healthy adults, with the possible exception of CYP2C9*3/*3 poor metabolisers (based on a very limited number of subjects). Previous analyses of other pathways have shown that neonates represent the most susceptible subgroup and this was true also for glycine conjugation for which an uncertainty factor of 29 would be required to cover 99% of this subgroup. Neonatal data were not available for any other pathway analysed.

Transport mechanisms of nicotine across the human intestinal epithelial cell line Caco-2

Ulcerative colitis is a disease more commonly seen in nonsmokers. Because nicotine was postulated to be a beneficial component of tobacco smoke for ulcerative colitis, various formulations of nicotine have been developed to improve the local bioavailability within the gastrointestinal tissue. In the present study, to characterize the disposition of nicotine in the intestines, we investigated intestinal nicotine transport using Caco-2 cells. Nicotine was predominantly transported across Caco-2 cell monolayers in a unidirectional mode, corresponding to intestinal secretion, by pH-dependent specific transport systems. The specific uptake systems appear to be distinct from organic cation transporters and the transport system for tertiary amines, in terms of its substrate specificity and the pattern of the interaction. These transport systems could play a role in the intestinal accumulation of nicotine from plasma and could also be responsible for the topical delivery of nicotine for ulcerative colitis therapy. These findings could provide useful information for the design of effective nicotine delivery.

Different pharmacokinetics of nicotine following intravenous administration of nicotine base and nicotine hydrogen tartarate in rats

Pharmacokinetics of nicotine was studied in rats following intravenous (i.v.) administration of nicotine base (NB) and nicotine hydrogen tartarate salt (NS) at a nicotine dose of 1 mg/kg. The area under the plasma concentration-time curve (AUC), mean residence time (MRT), systemic clearance (CL), distribution volume at steady state (V(ss)) and terminal plasma half-life (T(1/2,beta)) of nicotine were compared between NB and NS. Compared to NS, NB exhibited higher and sustained plasma nicotine levels, thereby yielding significantly (P<0.05) larger AUC (66.3 vs. 27.7 microg ml/min), MRT (165.7 vs. 58.3 min), T(1/2,beta) (144.2 vs. 51.4 min) and a lower CL (18.3 vs. 46.3 ml/min per kg). The V(ss) was comparable between the two compounds. The metabolic conversion to cotinine from NS was threefold larger than that from NB. The plasma protein binding and distribution to blood cells were comparable between the compounds. The apparent partition coefficient (APC) of NS decreased as a function of its concentration, while that of NB remained nearly constant. Particles of different mean sizes were observed for the 1% (w/v) aqueous solutions of NS (388.6 nm) and NB (123.8 nm). Different metabolism and/or elimination between NB and NS appear to be mainly responsible for their different pharmacokinetics.

Prolonged delivery of nicotine in rats via nasal administration of proliposomes

In order to achieve a prolonged delivery of nicotine to the systemic circulation, proliposomes containing nicotine base (NB-proliposomes) or nicotine hydrogen tartarate salt (NS-proliposomes) and a mixture of powdered nicotine hydrogen tartarate salt and sorbitol (1:9 mixture, MP) were administered intranasally to rats at a nicotine dose of 1 mg/kg. Proliposomes, lipid-sorbitol mixtures that form liposomes upon contact with water, were prepared according to previously established methods, and the mixture (MP) was prepared by mixing NS powder with sorbitol particles (105-350 micrometer in size). Nasal absorption of nicotine from these formulations was very rapid (i.e. less than 10 min was required to reach plasma peaks) and showed substantially sustained plasma nicotine levels compared to saline solutions of NB and NS, and previously reported nasal nicotine sprays. The AUC values from the proliposomes and MP were comparable to those from the saline solutions of NB and NS. However, the mean residence time (MRT) and plasma half-life (T(1/2beta)) of nicotine in the present study were much larger than those from the saline solutions. Thus, a prolonged delivery of nicotine to systemic circulation via the application of proliposomes or MP intranasally appears feasible. NB-proliposomes exhibited the best characteristics in terms of the area under the plasma concentration (AUC), MRT and T(1/2beta) of nicotine, which was followed by NS-proliposomes and MP. Retarded conversion of proliposomes and MP to liposomal emulsions and solution in the nasal cavity seems responsible, in part, for the sustained plasma nicotine concentrations, since the emulsions and solution yielded very short MRT and T(1/2beta) of nicotine. In addition, reduced metabolism to cotinine from the proliposomes and MP was apparently responsible for the sustained plasma nicotine levels. These dosage forms of nicotine appear to circumvent some of the shortcomings of transdermal patches (i.e. long T(max)) and nasal sprays (i.e. short T(1/2beta) and physicochemical instability).

An oral formulation of nicotine for release and absorption in the colon: its development and pharmacokinetics

AIMS

Ulcerative colitis is predominantly a disease of nonsmokers and transdermal nicotine has therapeutic value in active disease; however side-effects are troublesome. The aim of this study was to develop an oral formulation of nicotine which would be slowly released in the colon over 6 h, and to examine its pharmacokinetic profile in 12 healthy volunteers, with measurements of serum nicotine and cotinine, its principal metabolite.

METHODS

Nicotine was combined with a polyacrylic carbomer, Carbopol 974P which was incorporated into 13 different vehicles and their release profiles examined in vitro. The polyglycolized glyceride, Gelucire 50/13, was chosen for subsequent kinetic studies because it consistently produced a suitable release pattern which was linear. Capsules containing 3 mg nicotine, combined with carbomer in Gelucire 50/13, were coated with an acrylic resin Eudragit L; this ensured the capsule would remain intact until the ileum. On 2 separate days, 6 and 15 mg nicotine, contained in 2 and 5 capsules, respectively, were administered to 12 subjects, all nonsmokers, mean age 28 years. Serial blood measurements were taken for 36 h, serum nicotine and cotinine concentrations were measured by gas liquid chromatography.

RESULTS

There was considerable intersubject variability in the nicotine and cotinine values. Plasma nicotine levels began to rise about 4 h after ingestion of the capsules, corresponding with the oro-caecal transit time. Cmax nicotine values were 2.2 and 5 ng ml-1, obtained 7 h after the ingestion of 6 and 15 mg, respectively, of the formulation. The corresponding Cmax values for cotinine were 37 and 94.4 ng ml-1, occurring after 9-10 h. The mean for elimination half-lives in the 24 studies, including the 6 and 15 mg doses, for nicotine were 4.3+/-2.7 h and for cotinine 16.8+/-7.5 h. With 6 mg nicotine-carbomer, only 1 of 12 volunteers had possible side-effects, but with the 15 mg dose 11 out of the 12 reported adverse effects which were systemic or gastrointestinal in nature-their timing corresponded with peak serum concentrations of nicotine.

CONCLUSIONS

An oral formulation of nicotine has been developed; in the ileum and colon, this becomes available for slow linear release over 6 h and delivers high concentrations of nicotine for topical effect on the colon. 6 mg Nicotine was well tolerated, whilst 15 mg gave both systemic and gastrointestinal side-effects. High concentrations of topical nicotine in the colon are achieved with relatively low systemic bioavailablity-reflected by the Cmax and AUC values for nicotine. This, or comparable formulations, may be of therapeutic value in ulcerative colitis.

Simultaneous GC-MS determination of nicotine and cotinine in plasma for the pharmacokinetic characterization of nicotine in rats

A gas liquid chromatography/mass spectrometry assay method was developed for the simultaneous determination of nicotine and its major metabolite, cotinine, in rat plasma. Of particular interest was improving the low and variable extraction recovery for the parent drug and the metabolite. In addition, the feasibility of this assay method for pharmacokinetic studies of nicotine and cotinine after intravenous (i.v.), oral, and intraperitoneal (i.p.) administration of 1 mg kg(-1) of nicotine was tested. The low (30 and 48% for nicotine and cotinine, respectively) and variable (25 and 22% coefficient of variation for nicotine and cotinine, respectively) extraction recovery for nicotine and cotinine into dichloromethane was significantly improved by the addition of NaCl to the plasma. As a result, the recoveries for nicotine and cotinine were improved to 68 and 65%, respectively. The coefficient of variation was less than 10% in the 50-500 ng ml(-1) range and less than 16.58% at 10 ng ml(-1) for both nicotine and cotinine, indicating that the reproducibility of the assay was also improved by the extraction procedure. When injected intravenously at a dose of 1 mg kg(-1), the temporal profile of plasma concentration for nicotine followed a bi-exponential decline. Moment analysis revealed that pharmacokinetic parameters for nicotine (i.e. Cl, 46.30 ml min(-1) kg(-1); Vss, 2.77 1 kg(-1)) was similar to those reported in studies using 14C-nicotine. Absolute bioavailabilities of nicotine for i.p. and oral administration were 87.0 and 80.4%, respectively. The concentration of the metabolite increased up to 4 h to reach Cmax after i.p. and oral administrations and then declined slowly with time. These results indicate that this convenient analytical procedure is readily applicable to pharmacokinetic studies of nicotine and cotinine involving small laboratory animals with a sensitivity comparable with that reported for studies using 14C-nicotine.

Novel therapies for inflammatory bowel disease

Looking back at successes and failures in newer approaches to treating IBD, it is tempting--although still difficult--to draw conclusions about pathogenesis. When a therapy proves effective, do clinicians truly know how it works? Even with a therapy as specific as anti-TNF antibody, it is not clear if the benefit is attributable to simple binding and clearance of TNF-alpha or to binding on the cell surface and subsequent deletion of the activated macrophage. When a drug appears to be less effective than preclinical models suggest, can failures in effectiveness from delivery or dosing be differentiated? The disappointing results of clinical trials with IL-10--so at odds with the prediction of benefit from animal models--bring into question the validity of those models as well as the soundness of design of the clinical trials on which efficacy of IL-10 is judged. The variability of response even to the most narrowly targeted agents suggests that these diseases are far more heterogeneous in humans than in their murine counterparts. Clinicians are only just beginning to recognize subclinical markers of response, and it may soon be possible to predict response on the basis of genetic composition. For the moment, however, the field of pharmacogenetics is embryonic. Challenges in developing new therapeutic strategies include not only identifying novel agents, but also improving the definitions of clinical endpoints and defining efficacy at the biologic level. Only through considered evaluation of clinical evidence may clinicians determine which therapies should remain novelties and which should become an accepted part of the armamentarium.

Medical therapy for inflammatory bowel disease

CD and UC represent a spectrum of chronic IBD that present in protean ways and are accompanied by a variety of systemic sequelae. Sulfasalazine and the newer 5-aminosalicylates are important in the management of mild-to-moderate disease, whereas corticosteroids remain the primary therapy for most patients with moderate-to-severe disease (Tables 2-5). The toxicities associated with long-term steroid therapy, combined with their ineffectiveness as maintenance medications, have led to increased use of immunomodulators, such as azathioprine and 6-MP, for the treatment of steroid-dependent and steroid-resistant IBD. Infliximab is a novel therapeutic adjunct for chronically active and fistulizing CD that will herald a new era of biologic therapy for IBD. Meanwhile, CSA remains an alternative to urgent colectomy in severe UC unresponsive to corticosteroids and also for CD patients with severe disease or refractory fistulas. Finally, continued insights into the etiopathogenic pathways in IBD will provide evolving and innovative approaches until the eventual causes and cures are elucidated. In the meantime, clinicians should remain optimistic regarding current ability to reduce the morbidity and maintain the quality of life for patients suffering with these frustrating diseases.

Nicotine therapy for ulcerative colitis: a review of rationale, mechanisms, pharmacology, and clinical results

Smoking is protective against developing ulcerative colitis. Nicotine may be the cause of this protective effect. Controlled trials have demonstrated efficacy of transdermal nicotine for active ulcerative colitis. Side effects observed with transdermal nicotine include contact dermatitis, nausea, and lightheadedness. Topical administration of nicotine to the colon reduces nicotine blood concentrations and side effects, and may be of clinical benefit.

Nicotine tartrate liquid enemas for mildly to moderately active left-sided ulcerative colitis unresponsive to first-line therapy: a pilot study

BACKGROUND

Ulcerative colitis is predominantly a disease of non-smokers, and transdermal nicotine is therapeutic but often results in side-effects. Administration of nicotine as a liquid rectal enema results in less systemic nicotine absorption.

AIM

To determine the safety and clinical response of nicotine tartrate liquid enemas for active left-side ulcerative colitis in a pilot study.

METHODS

Ten non-smoking patients with mildly to moderately active left-sided ulcerative colitis unresponsive to first-line therapy were treated in an open protocol with nightly nicotine tartrate liquid enemas at a dose of 3 mg nicotine base for 1 week then 6 mg for 3 weeks. Clinical assessments were determined at baseline and 4 weeks by endoscopy, physician assessment and a patient diary of daily symptoms. Peak and trough serum nicotine and trough plasma cotinine were determined by gas chromatography/mass spectrometry and high performance liquid chromatography, respectively.

RESULTS

After 4 weeks of treatment, 5/7 patients (71%) showed clinical and sigmoidoscopic improvement (per protocol analysis). The other three patients discontinued therapy within 7 days because of inability to retain the liquid enemas. No patients showed histologic improvement. Six of the patients who completed the 4-week study had peak and trough serum nicotine concentration determined, only 1 of 6 patients had a detectable peak nicotine concentration (value 2.3 ng/mL), and all six patients had undetectable trough nicotine concentrations. The mean trough plasma cotinine concentration was 13 +/- 10 ng/mL. Transient and mild adverse events occurred in 4/10 patients (nausea, lightheadedness, tremor, sleep disturbance). Given the low or undetectable serum nicotine concentrations, these adverse events are not likely to be related to the nicotine enemas.

CONCLUSIONS

Nicotine tartrate liquid enemas administrated at a dose of 3 mg nicotine base/day for 1 week and then 6 mg/day for 3 weeks are safe and appear to result in clinical improvement in some patients with mildly to moderately active, left-sided ulcerative colitis unresponsive to first-line therapy. Placebo-controlled trials are warranted to confirm these preliminary findings.