The putative proton-coupled organic cation antiporter is involved in uptake of triptans into human brain capillary endothelial cells

BACKGROUND

Triptans are anti-migraine drugs with a potential central site of action. However, it is not known to what extent triptans cross the blood-brain barrier (BBB). The aim of this study was therefore to determine if triptans pass the brain capillary endothelium and investigate the possible underlying mechanisms with focus on the involvement of the putative proton-coupled organic cation (H+/OC) antiporter. Additionally, we evaluated whether triptans interacted with the efflux transporter, P-glycoprotein (P-gp).

METHODS

We investigated the cellular uptake characteristics of the prototypical H+/OC antiporter substrates, pyrilamine and oxycodone, and seven different triptans in the human brain microvascular endothelial cell line, hCMEC/D3. Triptan interactions with P-gp were studied using the IPEC-J2 MDR1 cell line. Lastly, in vivo neuropharmacokinetic assessment of the unbound brain-to-plasma disposition of eletriptan was conducted in wild type and mdr1a/1b knockout mice.

RESULTS

We demonstrated that most triptans were able to inhibit uptake of the H+/OC antiporter substrate, pyrilamine, with eletriptan emerging as the strongest inhibitor. Eletriptan, almotriptan, and sumatriptan exhibited a pH-dependent uptake into hCMEC/D3 cells. Eletriptan demonstrated saturable uptake kinetics with an apparent Km of 89 ± 38 µM and a Jmax of 2.2 ± 0.7 nmol·min-1·mg protein-1 (n = 3). Bidirectional transport experiments across IPEC-J2 MDR1 monolayers showed that eletriptan is transported by P-gp, thus indicating that eletriptan is both a substrate of the H+/OC antiporter and P-gp. This was further confirmed in vivo, where the unbound brain-to-unbound plasma concentration ratio (Kp,uu) was 0.04 in wild type mice while the ratio rose to 1.32 in mdr1a/1b knockout mice.

CONCLUSIONS

We have demonstrated that the triptan family of compounds possesses affinity for the H+/OC antiporter proposing that the putative H+/OC antiporter plays a role in the BBB transport of triptans, particularly eletriptan. Our in vivo studies indicate that eletriptan is subjected to simultaneous brain uptake and efflux, possibly facilitated by the putative H+/OC antiporter and P-gp, respectively. Our findings offer novel insights into the potential central site of action involved in migraine treatment with triptans and highlight the significance of potential transporter related drug-drug interactions.

[Comparative clinical study of pharmacokinetics and bioequivalence of Relonova and Maxalt]

OBJECTIVE

Evaluation of the bioequivalence of the tested Relonova, tablets, 10 mg and Maxalt, tablets, 10 mg drugs on an empty stomach in healthy volunteers.

MATERIAL AND METHODS

The pharmacokinetic analysis population included 40 volunteers, the safety analysis population included 40 volunteers. The average age of randomized volunteers (men - 20, women - 20) was 29.3±8.9 years, height 1.71±0.09 m, body weight 70.86±11.66 kg, mean BMI 24.18±2.81 kg/m2. The method used high performance liquid chromatography with tandem mass spectrometric detection. Statistical analysis of the obtained data was performed based on the assumption of a log-normal distribution of the parameters AUC0-72 and Cmax.

RESULTS

The ratio of geometric means for the key pharmacokinetic parameters (AUC0-t, AUC0-inf and Cmax) of rizatriptan is close to 90%, CI is within the acceptable range for bioequivalent drugs (80-125%). The intrasubject variability (CVintra) for rizatriptan was 23.74% (Cmax), 10.94% (AUC0-t). The average profiles of the pharmacokinetic curves of rizatriptan when taking the test and reference drugs have similar shapes. Relonova and reference Maxalt are bioequivalent.

CONCLUSION

The results of the study make it possible to recommend Relonova for further clinical study and wide practical application.

[Does medication abuse in patients with chronic migraine influence the effectiveness of preventive treatment with topiramate?]

INTRODUCTION

Patients with chronic migraine (CM) and medication abuse are difficult to treat, and have a greater tendency towards chronification and a poorer quality of life than those with other types of headache.

AIM

To evaluate whether the presence of medication abuse lowers the effectiveness of topiramate.

PATIENTS AND METHODS

A series of patients with CM were grouped according to whether they met abuse criteria or not. They were advised to stop taking the drug that they were abusing. Treatment was adjusted to match their crises and preventive treatment with topiramate was established from the beginning. The number of days with headache and intense migraine in the previous month and at four months of treatment was evaluated.

RESULTS

In all, 262 patients with CM criteria were selected and 167 (63.7%) of them fulfilled abuse criteria. In both groups there was a significant reduction in the number of days with headache/month and number of migraine attacks/month at the fourth month of treatment with topiramate. The percentage of reduction in the number of days with headache/month in CM without abuse was 59.3 ± 36.1%, and with abuse, 48.7 ± 41.7% (p = 0.0574). The percentage of reduction in the number of days with intense migraine/month in CM without abuse was 61.2%, and with abuse, 50% (p = 0.0224). Response rate according to the number of days with headache/month in CM without abuse was 69%, and with abuse, 57%. Response rate according to the number of intense migraines/month in CM without abuse was 76.8%, and in CM with abuse, 61% (p = 0.0097).

CONCLUSIONS

Topiramate was effective in patients with CM with and without medication abuse, although effectiveness is lower in the latter case.

Zolmitriptan (Zomig®)

New triptans are being released in rapid succession with each addition demonstrating some specific pharmacokinetic properties, which may be translated into clinical advantages. Zolmitriptan (Zomig) offers a range of alternatives to migraine sufferers. The conventional tablet is consistently effective across a wide range of migraine subtypes. The orally disintegrating tablet offers an effective option for those migraineurs who are nauseated or need to take their medication earlier in the course of their migraine. Since it can be taken without fluid, the orally disintegrating tablet may be consistently used early in the migraine attack when the pain is still mild. The nasal spray aggregates all the benefits of the oral formulations and has a faster onset of action. The 5-mg dose of all three forms of zolmitriptan offers additional benefits over the 2.5-mg dose at early time points. The physician can now choose the optimum route of delivery of zolmitriptan to stop the headache, increase the likelihood of reducing disability and restore the patient to complete functionality.

Oral almotriptan: practical uses in the acute treatment of migraine

Almotriptan (Almogran, Lundbeck; Almirall Prodesfarma; Axert, Ortho-McNeil) is a novel 5-HT(1B/1D) receptor agonist (triptan) that is widely available on prescription for the acute treatment of migraine. Almotriptan has pharmacodynamic and pharmacokinetic profiles that make it suitable for use in this indication. It is a potent agonist at 5-HT(1B), (1D) and (1F) receptors, while having a low affinity for other 5-HT receptors. It is also a potent inhibitor of neurogenic inflammation. Almotriptan has a high oral bioavailability, is absorbed rapidly, has a relatively short plasma half-life and its route of elimination presents few potential problems. Placebo-controlled dose-finding studies have demonstrated that almotriptan tablets are effective and well-tolerated in the acute treatment of migraine, with a 12.5 mg dose providing the best balance between efficacy and tolerability. Large placebo-controlled studies show that the efficacy of oral almotriptan is comparable with that of the other oral triptans. In direct comparator-controlled studies, almotriptan was as effective as sumatriptan 50 and 100 mg but had a superior tolerability profile. Furthermore, the efficacy and tolerability of almotriptan is sustained in the long term following open-label administration. Meta-analyses and post hoc analyses of clinical data confirm these findings. In conclusion, almotriptan 12.5 mg is a good therapeutic choice for the symptomatic treatment of acute migraine attacks.

Pharmacokinetic Profile of Rizatriptan 10-mg Tablet and 10-mg Orally Disintegrating Tablet Administered With or Without Water in Healthy Subjects: An Open-Label, Randomized, Single-Dose, 3-Period Crossover Study

This open-label, 3-period crossover study compared the plasma concentration profiles of rizatriptan tablet, orally disintegrating tablet with water (ODTc), and ODT without water (ODTs) in 24 healthy volunteers aged 18 to 45 years. At each period, subjects received a single dose of either 10-mg rizatriptan tablet, 10-mg rizatriptan ODTs, or 10-mg rizatriptan ODTc. The authors hypothesized that ODTc has a greater geometric mean AUC(0-2h) than ODTs and that ODTc has a greater geometric mean AUC(0-1h) than tablet. A secondary end point was to compare the time of occurrence of the maximum rizatriptan plasma concentration (t(max)) of each dosing method. ODTc had a statistically significantly greater geometric mean AUC(0-2h) compared with ODTs (33.84 h x ng/mL vs 18.83 h x ng/mL; P < .001). ODTc had a slightly, but not statistically significantly, greater geometric mean AUC(0-1h) compared with rizatriptan tablet (17.07 h x ng/mL vs 13.32 h x ng/mL). The median t(max) was 0.67 hours for ODTc and tablet and 1.33 hours for ODTs. ODTc showed a slightly, but not significantly, faster rate of absorption compared with tablet. ODTs with water had a faster rate of absorption than ODTc. Future studies are needed to determine whether this pharmacokinetic difference produces differential efficacy in a clinical setting.

Bioequivalence study of 2 orodispersible formulations of zolmitriptan 5 mg in healthy volunteers

A bioequivalence study of 2 zolmitriptan (CAS 139264-17-8) orodispersible tablet formulations was carried out in 26 healthy volunteers according to an open label, randomized, 2-period, 2-sequence, crossover, single dose and fasting conditions design. The test and reference formulations were administered in 2 treatment days, separated by a washout period of 7 days. Plasma concentrations of zolmitriptan and its active metabolite (N-desmethyl-zolmitriptan) were obtained by LC/MS/MS method. Log-transformed AUCs and Cmax values were tested for bioequivalence based on the ratios of the geometric means (test/reference). Tmax was analysed nonparametrically. The 90% confidence intervals of the geometric mean values for the test/reference ratios for AUC0-t and Cmax were within the bioequivalence acceptance range of 80-125%. According to the European Guideline 1 it may be therefore concluded that test formulation of zolmitriptan 5 mg orodispersible tablet is bioequivalent to the reference formulation.

Chronic migraine: comorbidities, risk factors, and rehabilitation

Migraine is a serious illness with a spontaneous clinical evolution into a chronic form. In some episodic migraines, increase of crises frequency modifies the headache pattern in the chronic form, defined as chronic migraine (CM), with headache frequency of 15 days/month. One-year prevalence of CM includes around 2-4% of the general population. Migraine progression from episodic to chronic form is realized through a period of time involving several months or years, during which an increase of attack frequency occurs. Migraine shows a wide spectrum of comorbidities, including cardiocerebral, vascular, psychiatric, metabolic, neurologic as well as other pathologies. The single/multiple presence of such comorbidities represents a fixed factor in the process of chronicization into CM. Risk factors including medication overuse headache (MOH), obesity, and lifestyle cooperate in the evolution process to CM. MOH is the most severe complication of CM, and similarly to CM its appearance is gradual. Both CM and MOH show particular genetic background able to favor the appearance of chronicity and abuse. Rehabilitation consists of drug withdrawal procedures, re-prophylaxis through administration of innovative drugs, such as OnabotulinumtoxinA and/or topiramate, to avoid relapsing attacks, and behavioral strategies to minimize the role of risk factors. The initial relief step for drug abusers always relies in drug withdrawal. The feasible diagnostic setting for a CM tailored treatment based on the application of pharmacogenomics will allow us to predetermine the efficacy of single old and new drugs by avoiding abuse due to non-responsivity of the acute drug.

Transport characteristics of zolmitriptan in a human intestinal epithelial cell line Caco-2

The intestinal absorption characteristics and the efflux mechanisms of zolmitriptan, a new generation and highly selective 5-HT1B/1D receptor agonist used in the acute oral treatment of migraine, were investigated. A human intestinal cell line, Caco-2, was used as an in-vitro model of the intestinal mucosa to assess transepithelial transport of zolmitriptan. In the Caco-2 cells, the absorptive transport of zolmitriptan was pH dependent and the transport was enhanced at weakly alkali pH on the apical side. No concentration dependence and saturation were observed for the apical-to-basolateral and basolateral-to-apical transport of zolmitriptan at a concentration of 0.1–10 mM. The permeability ratio value was about 1.5-2.6 at a concentration of 0.1–2.0 mM. Inhibition experiments using verapamil, nifedipine and nimodipine as inhibitors were studied and indicated that P-glycoprotein participated in the transport of zolmitriptan. Inhibition of the Na+-H+ exchanger with amiloride resulted in a significant increase in absorption and a slight inhibition in secretion. This suggests that the Na+-H+ exchanger may be involved in the transport of zolmitriptan. The results indicated that the transport of zolmitriptan was mediated by both passive diffusion and active transport. A series of drug-drug interaction experiments were carried out between zolmitriptan and some drugs that may be co-administrated with zolmitriptan in the clinic. The results indicated that flunarizine, cetirizine, propranolol and atenolol potently decreased both the apical-to-basolateral and basolateral-to-apical transport rate of zolmitriptan. Cimetidine and aspirin slightly inhibited the apical-to-basolateral transport of zolmitriptan, but significantly decreased the basolateral-to-apical transport of zolmitriptan. Thus, the absorption drug-drug interactions should be considered when these drugs are co-administrated with zolmitriptan in the clinic.

Disposition and metabolism of almotriptan in rats, dogs and monkeys

Almotriptan is a new highly potent selective 5-HT1B/1D receptor agonist developed for the treatment of migraine, and the disposition of almotriptan in different animal species is now addressed in the current study. Almotriptan was well absorbed in rats (69.1%) and dogs (100%) following oral treatment. The absolute bioavailability was variable reflecting different degrees of absorption and first-pass metabolism (18.7-79.6%). The elimination half-life was short and ranged between 0.7 and 3 h. The main route of elimination of almotriptan was urine with 75.6% and 80.4% of the dose recovered over a 168-h period in rats and dogs, respectively. The gamma-aminobutyric acid metabolite formed by oxidation of the pyrrolidine ring was the main metabolite found in urine, faeces, bile, and plasma of rats and in monkey urine. By contrast, the unchanged drug, the indole acetic acid metabolite formed by oxidative deamination of the dimethylaminoethyl group, and the N-oxide metabolite were the main metabolites in dog.

[Triptans--pivotal event in migraine treatment]

Introducing serotonin 5-HT1B/1D agonists in the migraine treatment in the early 1990s had for the first time set guidelines for targeting a hypothetic physiologic source of the sequence of events in migraine, and results thus achieved were considerably better than those accomplished with earlier nonselective pharmacological approach. Triptans have revolutionized migraine management and inspired many epidemiological and public health surveys, strengthened efforts in understanding pathophysiology of migraine and initiated synthesis of many similar drugs in the triptan group, the first being sumatriptan. Triptans have risen to a therapeutic challenge posed by migraine, successfully thwarting the cycle of pain. In treating migraine sufferers, physicians can choose among seven triptans with different attributes. Each patient merits individualized approach in the treatment of migraine with triptans. Choosing the right triptan for a given patient is a matter of first matching the appropriate formulation to the patient, then deciding which agent will best meet the patient's needs. This process requires thorough understanding of the patient, careful and accurate assessment of the efficacy of previous medications used in acute care, and analysis of the individual features of the triptans being considered.

Marketed oral triptans in the acute treatment of migraine: a systematic review on efficacy and tolerability

BACKGROUND

In the current literature, there is neither a reported systematic review comparing the efficacy of triptans at 30 minutes and 1 hour after the migraine treatment, nor data related to efficacy of new marketed triptans.

OBJECTIVE

The main objective of this analysis was to compare the efficacy and tolerability of currently marketed oral, non-reencapsulated triptan formulations vs placebo in the treatment of moderate-to-severe migraine attacks.

METHODS

A systematic review of double-blind, randomized clinical trials reporting data after a single migraine attack was conducted. Efficacy results are shown using relative risk ratios with 95% confidence intervals. A sensitivity analysis was also conducted.

RESULTS

After reviewing 221 publications, 38 studies were included. All marketed triptans provided significant relief and/or absence of pain at 2 hours, and relief at 1 hour when compared with placebo. After 30 minutes, fast-dissolving sumatriptan 50 and 100 mg, sumatriptan 50 mg, and rizatriptan 10 mg showed significant relief when compared to placebo, whereas the fast-dissolving formulation of sumatriptan 100 mg was the only oral triptan that was superior to placebo in meeting the pain-free endpoint. On the other hand, fast-dissolving sumatriptan 50 and 100 mg and eletriptan 40 mg showed a lower rate of recurrence than placebo, whereas rizatriptan 10 mg was the only triptan with a recurrence rate greater than that of placebo. Adverse events associated with treatment with tablet formulations of sumatriptan and zolmitriptan were significantly more frequent than those of the placebo group. The inclusion of trials with reencapsulated triptans in the analysis introduced minor specific changes in these results.

CONCLUSION

This analysis updates the comparative data available for the 7 currently marketed oral triptans and clearly demonstrates their efficacy when compared to placebo, even with stricter endpoints, such as efficacy at 30 minutes. No triptan exhibited better tolerability than placebo. Results are diverse, depending on the triptan, which probably is a reflection of heterogeneous pharmacokinetics.

Parenteral vs. oral sumatriptan and naratriptan: plasma levels and efficacy in migraine. a comment

The clinical efficacy in migraine was compared for oral and subcutaneous sumatriptan and naratriptan. Doses of the two administration forms were chosen as resulting in comparable blood concentrations. Subcutaneous administrations of the drugs were superior for efficacy than the oral forms. This most likely due to a quicker rise in blood concentrations after subcutaneous injections.. In designing new therapies for migraine one should aim at a quick absorption of the drug, which will probably result in an increased efficacy.

Uptake and biodistribution of rizatriptan to blood and brain following different routes of administration in rats

The objective of the present study was to investigate the biodistribution profiles of rizatriptan in the blood and brain of Wistar rats after peroral, subcutaneous, intranasal and intratracheal administration with a particular view to determining the applicability of inhalation delivery to achieve rapid and high availability of the drug in both blood and the brain. Following the intratracheal administration of the drug (4.0mg/kg) to the rats, the absolute bioavailability was found to be 91.2%, significantly higher than those from intranasal or peroral routes, and T(max) in plasma and brain was attained within 2 min, significantly shorter than the T(max) of intranasal ( approximately 10 min in both plasma and brain), subcutaneous (16.7 min in plasma and 22.5 min in brain) and peroral (30.0 min in plasma and 45.0 min in brain) administration. In addition, other pharmacokinetic parameters associated with rapid onset of action including AUC(plasma/brain) and C(max), of intratracheal instillated rizatriptan appeared also to be comparable or superior to those of other delivered routes. Although AUC(brain)/AUC(plasma) ratios after intranasal delivery (43.4%) differed significantly from the ratios shown after intratracheal instillation (23.2%), the AUC(brain 0-120 min) via the latter routes was slightly but not significantly higher than that from the former routes. The results in the present study indicated that pulmonary delivery of rizatriptan may achieve maximum plasma and brain concentrations significantly more rapidly compared with intranasal, subcutaneous and peroral administration and be a promising delivery method with extremely rapid onset of action in the pain relief of migraine.

A model-based approach to treatment comparison in acute migraine

AIMS

Currently, direct comparisons between 5-HT(1B/d) receptor agonists are used to assess differences and similarities in antimigraine response. Such comparisons depend on the selected sampling time and do not allow evaluation of entire response profiles. A thorough evaluation of drug properties requires that the time course of the response be taken into account. In this investigation we show the advantages of a model-based approach to compare the efficacy of two triptans (sumatriptan vs. naratriptan).

METHODS

A Markov model was used to describe the course of a migraine attack over three clinically identified stages. Drug effects were modelled as concentration-dependent increases in transition rates and were parameterised as potency (EC(50)) and maximum effect (E(max)). Parameters were estimated using headache measurements from efficacy studies. Model estimates were then used to compare the pharmacodynamics of the two drugs in a time-independent manner.

RESULTS

Efficacy parameters could be derived, allowing for comparison between compounds. The potency ratio (EC50(suma)/EC50(nara)) for headache relief was 3.3 (0.9, 12). The ratio of maximum effects (Emax(suma)/Emax(nara)) for this endpoint was 0.74 (0.55, 0.97). To interpret these efficacy measures and explore their value for the development of antimigraine drugs, results were evaluated against the reported in vitro potency at 5-HT(1B) and 5-HT(1D) receptors.

CONCLUSIONS

Comparison of the effects of two or more drugs based on preset sampling times does not allow proper assessment of the antimigraine properties in vivo. Disease dynamics must be considered to evaluate treatment response adequately and optimise the dosing regimen in migraine.

Use of Plasma and Brain Unbound Fractions to Assess the Extent of Brain Distribution of 34 Drugs: Comparison of Unbound Concentration Ratios to in Vivo P-Glycoprotein Efflux Ratios

The P-glycoprotein (P-gp)-deficient mouse model is used to assess the influence of P-gp-mediated efflux on the central nervous system (CNS) distribution of drugs. The steady-state unbound plasma/unbound brain concentration ratio ([plasma],(u)/[brain],(u)) is an alternative method for assessing CNS distribution of drugs independent of the mechanism(s) involved. The objective of this study was to compare the degree of CNS distributional impairment determined from the in vivo P-gp efflux ratio with that determined from the [plasma],(u)/[brain],(u) ratio. CNS distribution of 34 drugs, including opioids, triptans, protease inhibitors, antihistamines, and other clinically relevant drugs with either poor CNS distribution or blood-brain barrier efflux, was studied. Plasma and brain unbound fractions were determined by equilibrium dialysis. K(p,brain) and the P-gp efflux ratio were obtained from the literature or determined experimentally. The P-gp efflux ratio and the [plasma],(u)/[brain],(u) ratio were in concurrence (<3-fold difference) for 21 of the 34 drugs. However, the [plasma],(u)/[brain],(u) ratio exceeded the P-gp efflux ratio substantially (>4-fold) for 10 of the 34 drugs, suggesting that other, non-P-gp-mediated mechanism(s) may limit the CNS distribution of these drugs. The P-gp efflux ratio exceeded the [plasma],(u)/[brain],(u) ratio by more than 3-fold for three drugs, suggesting the presence of active uptake mechanism(s). These observations indicate that when mechanisms other than P-gp affect CNS distribution (non-P-gp-mediated efflux, poor passive permeability, cerebrospinal fluid bulk flow, metabolism, or active uptake), the P-gp efflux ratio may underestimate or overestimate CNS distributional impairment. The [plasma],(u)/[brain],(u) ratio provides a simple mechanism-independent alternative for assessing the CNS distribution of drugs.

Development and validation of a selective and robust LC–MS/MS method for high-throughput quantifying rizatriptan in small plasma samples: Application to a clinical pharmacokinetic study

An analytical method based on liquid chromatography with positive ion electrospray ionization (ESI) coupled to tandem mass spectrometry detection (LC-MS/MS) was developed for the determination of a potent 5-HT(1B/1D) receptor agonist, rizatriptan in human plasma using granisetron as the internal standard. The analyte and internal standard were isolated from 100 microL plasma samples by liquid-liquid extraction (LLE) and chromatographed on a Lichrospher C18 column (4.6mm x 50mm, 5 microm) with a mobile phase consisting of acetonitrile-10mM aqueous ammonium acetate-acetic acid (50:50:0.5, v/v/v) pumped at 1.0 mL/min. The method had a chromatographic total run time of 2 min. A Varian 1200 L electrospray tandem mass spectrometer equipped with an electrospray ionization source was operated in selected reaction monitoring (SRM) mode with the precursor-to-product ion transitions m/z 270-->201 (rizatriptan) and 313.4-->138 (granisetron) used for quantitation. The assay was validated over the concentration range of 0.05-50 ng/mL and was found to have acceptable accuracy, precision, linearity, and selectivity. The mean extraction recovery from spiked plasma samples was above 98%. The intra-day accuracy of the assay was within 12% of nominal and intra-day precision was better than 13% C.V. Following a 10mg dose of the compound administered to human subjects, mean concentrations of rizatriptan ranged from 0.2 to 70.6 ng/mL in plasma samples collected up to 24h after dosing. Inter-day accuracy and precision results for quality control samples run over a 5-day period alongside clinical samples showed mean accuracies of within 12% of nominal and precision better than 9.5% C.V.

Ethanol does not significantly affect the bioavailability of almotriptan: an open, randomized, crossover, single-dose, phase I clinical trial in healthy volunteers

OBJECTIVE

A number of clinical reports have revealed a link between the use of alcohol and the onset or exacerbation of migraine headaches. This open, randomized, crossover, single-dose, phase I clinical trial evaluated the possible pharmacokinetic interactions between a single oral dose of almotriptan 12.5 mg, a 5-HT(1B/1D receptor agonist for the acute treatment of migraine, and ethanol in 16 healthy male volunteers. Tolerability and safety of this combined treatment were also assessed.

METHODS

Subjects received a crossed oral dose of almotriptan (12.5 mg) with and without concomitant alcohol intake (target plasma concentration 0.8 g/kg) in two different treatment periods. Almotriptan was administered alone, while ethanol was diluted with orange juice, which was also given to the control group. There was a washout period of 7 days between treatments. Plasma levels of almotriptan were analyzed using a sensitive and specific liquid chromatographic-tandem mass spectrometry method.

RESULTS

The 90% non-parametric confidence interval for the median t(max) of almotriptan plus ethanol compared to almotriptan alone (0.61/2.72) was outside the acceptable range (0.70 - 1.30), demonstrating that concomitant ethanol administration slightly increases the variability of absorption of almotriptan 12.5 mg. In contrast, the main bioavailability criteria parameters, C(max) and AUC, which show the rate and extent of systemic absorption, were not affected by alcohol ingestion. Therefore, it is unlikely that concomitant ethanol intake would produce clinically relevant differences in the therapeutic effect of almotriptan at the dose studied here. Tolerability of treatments was good throughout the entire study period.

CONCLUSIONS

Almotriptan 12.5 mg, with or without concomitant alcohol ingestion, showed similar plasma concentrations after a single dose in healthy volunteers with no clinically relevant drug-to-drug interactions.

Which triptan for which patient?

The triptans were developed for the acute treatment of a migraine attack and have revolutionised the treatment of this disorder since their introduction in the early 1990s. Although their mechanisms of actions are similar and based on the stimulation of specific serotonin (5-hydroxytryptamine) receptors including peripheral 1B and central and peripheral 1D subtypes, each triptan has its own distinctive pK properties that result in different profiles of efficacy and tolerability. Triptans work by decreasing neurogenic inflammation peripherally in the meninges, vasoconstriction of meningeal vessels and by modulating secondary-order neurons in the brain stem. Studies of patient attitudes towards their acute care regimens reveal that they are often unhappy with some aspect of their treatment-usually the speed of action, degree of efficacy, presence of adverse events and the need for additional doses due to frequent and/or rapid recurrence. The majority of patients, when asked in a clinical trial performed at tertiary care headache centres, are willing to try another triptan. The aim of this article is to review the pK and clinical characteristics of these acute care, migraine-specific triptan medications and discuss how their individual characteristics lead to their preferred choice in various clinical scenarios. The pK and clinical efficacy data presented are taken from older published studies in which triptans were compared to placebo or each other, but the patients were asked to wait till the headache reached moderate or severe intensity prior to taking study medication. New studies have looked at early treatment paradigms and result in better efficacy data, but are difficult to compare due to different endpoints.

Blood-brain barrier penetration of zolmitriptan--modelling of positron emission tomography data

Positron emission tomography (PET) with the drug radiolabelled allows a direct measurement of brain or other organ kinetics, information which can be essential in drug development. Usually, however, a PET-tracer is administered intravenously (i.v.), whereas the therapeutic drug is mostly given orally or by a different route to the PET-tracer. In such cases, a recalculation is needed to make the PET data representative for the alternative administration route. To investigate the blood-brain barrier penetration of a drug (zolmitriptan) using dynamic PET and by PK modelling quantify the brain concentration of the drug after the nasal administration of a therapeutic dose. [11C]Zolmitriptan at tracer dose was administered as a short i.v. infusion and the brain tissue and venous blood kinetics of [11C]zolmitriptan was measured by PET in 7 healthy volunteers. One PET study was performed before and one 30 min after the administration of 5 mg zolmitriptan as nasal spray. At each of the instances, the brain radioactivity concentration after subtraction of the vascular component was determined up to 90 min after administration and compared to venous plasma radioactivity concentration after correction for radiolabelled metabolites. Convolution methods were used to describe the relationship between arterial and venous tracer concentrations, respectively between brain and arterial tracer concentration. Finally, the impulse response functions derived from the PET studies were applied on plasma PK data to estimate the brain zolmitriptan concentration after a nasal administration of a therapeutic dose. The studies shows that the PET data on brain kinetics could well be described as the convolution of venous tracer kinetics with an impulse response including terms for arterial-to-venous plasma and arterial-to-brain impulse responses. Application of the PET derived impulse responses on the plasma PK from nasal administration demonstrated that brain PK of zolmitriptan increased with time, achieving about 0.5 mg/ml at 30 min and close to a maximum of 1.5 mg/ml after 2 hr. A significant brain concentration was observed already after 5 min. The data support the notation of a rapid brain availability of zolmitriptan after nasal administration.

Effect of food intake on the bioavailability of almotriptan, an antimigraine compound, in healthy volunteers: an open, randomized, crossover, single-dose clinical trial

This open, randomized, crossover, single-dose clinical trial evaluated the possible pharmacokinetic interaction between a single oral dose of almotriptan 25 mg, a 5-HT1B/1D receptor agonist for the acute treatment of migraine, and food intake in healthy volunteers. The influence of food intake in the rate and extent of almotriptan absorption was evaluated by bioequivalence criteria. Tolerability and safety of treatment were also assessed. 16 healthy volunteers (8 men and 8 women, aged 19-27 years) received a crossed single oral dose of almotriptan 25 mg under fasting and fed conditions, separated by a 7-day washout period. The treatment given under fasting condition was considered as reference. Plasma levels of almotriptan were analyzed using high-performance liquid chromatography (HPLC) and UV detection at 227 nm. The 90% confidence intervals (CI) for the logarithmically transformed Cmax and AUC0-infinity, values of almotriptan under fasting and fed conditions (97.8 - 124% and 102.9 - 108.2%, respectively) fell into the predetermined accepted range of 80 - 125%. No statistically significant differences in Cmax, tmax, AUC0-infinity, MRT and t1/2 were observed under fasting and fed conditions between men and women. Tolerability of treatments was good throughout the whole study period. In conclusion, administration of almotriptan 25 mg is bioequivalent under fasting and fed conditions in healthy men and women. Therefore, it is unlikely that concomitant food intake would produce clinially relevant differences in therapeutic effect with almotriptan at the dose studied here.

Preclinical neuropharmacology of naratriptan

The basic CNS neuropharmacology of naratriptan is reviewed here. Naratriptan is a second-generation triptan antimigraine drug, developed at a time when CNS activity was thought not to be relevant to its therapeutic effect in migraine. It was, however, developed to be a more lipid-soluble, more readily absorbed and less readily metabolized variant on preexisting triptans and these variations conferred on it a higher CNS profile. Naratriptan is a 5-HT(1B/1D) receptor agonist with a highly selective action on migraine pain and nausea, without significant effect on other pain or even other trigeminal pain. Probable sites of therapeutic action of naratriptan include any or all of: the cranial vasculature; the peripheral terminations of trigeminovascular sensory nerves; the first-order synapses of the trigeminovascular sensory system; the descending pain control system; and the nuclei of the thalamus. Naratriptan may prevent painful dilatation of intracranial vessels or reverse such painful dilatation. Naratriptan can prevent the release of sensory peptides and inhibit painful neurogenic vasodilatation of intracranial blood vessels. At the first order synapse of the trigeminal sensory system, naratriptan can selectively suppress neurotransmission from sensory fibers from dural and vascular tissue, while sparing transmission from other trigeminal fibers, probably through inhibition of neuropeptide transmitter release. In the periaqueductal gray matter and in the nucleus raphe magnus, naratriptan selectively activates inhibitory neurons which project to the trigeminal nucleus and spinal cord and which exert inhibitory influences on trigeminovascular sensory input. Naratriptan has also a therapeutic effect on the nausea of migraine, possibly exerting its action at the level of the nucleus tractus solitarius via the same mechanisms by which it inhibits trigeminovascular nociceptive input. The incidence of naratriptan-induced adverse effects in the CNS is low and it is not an analgesic for pain other than that of vascular headache. In patients receiving selective serotonin uptake inhibitors (SSRIs) naratriptan may cause serotonin syndrome-like behavioral side effects. The mechanism of action involved in the production of behavioral and other CNS side effects of naratriptan is unknown.

Determination of zolmitriptan in human plasma by liquid chromatography–tandem mass spectrometry method: Application to a pharmacokinetic study

A sensitive and selective liquid chromatography-tandem spectrometry method for the determination of zolmitriptan was developed and validated over the linearity range 0.05-30 ng/ml with 0.5 ml of plasma using diphenhydramine as the internal standard. Liquid-liquid extraction using a mixture of diethyl ether and dichloromethane was used to extract the drug and the internal standard from plasma. The mass spectrometer was operated under the selected reaction monitoring (SRM) mode using the atmospheric pressure chemical ionization (APCI) technique. The instrument parameters were optimized to obtain 3.0 min run time. The mobile phase consisted of acetonitrile-water-formic acid (70:30:0.5), at a flow rate of 0.5 ml/min. In positive mode, zolmitriptan produced a protonated precursor ion at m/z 288 and a corresponding product ion at m/z 58. And internal standard produced a protonated precursor ion at m/z 256 and a corresponding product ion at m/z 167. The inter- and intra-day precision (%R.S.D.) were less than 8.5% and accuracy (%error) was less than -2.5%. The method had a lower limit of quantification of 0.05 ng/ml for zolmitriptan, which offered increased sensitivity and selectivity of analysis, compared with existing methods. The method was successfully applied to a pharmacokinetic study of zolmitriptan after an oral administration of 5 mg zolmitriptan to 20 healthy volunteers.

Distribution of intranasal C-zolmitriptan assessed by positron emission tomography

Nine healthy volunteers aged 18-28 years were recruited into this open, single-centre, two-phase trial. In phase 1, two volunteers received a single dose of 11C-zolmitriptan 2.5 mg administered as a nasal spray and then underwent positron emission tomography (PET) scanning to determine the most appropriate times for scanning in phase 2. In phase 2, six volunteers received two doses and an additional volunteer one dose of 11C-zolmitriptan 2.5 mg intranasally. Volunteers underwent PET scanning over sectors covering one of the nasopharynx, lungs or abdomen, for up to 1.5 h postdose. The brain was also scanned and plasma zolmitriptan levels were measured. Almost 100% of the administered dose was detected in the nasopharynx immediately after dosing. This declined thereafter to about 50% at 20 min and to 35% at 80 min after dosing. Radioactivity appeared slowly in the upper abdomen, with 25% of given radioactivity detected at 20 min and persisting until 80 min after dosing. Minimal radioactivity was detected in the lungs. Radioactivity was detectable within brain tissue suggesting central penetration of zolmitriptan. Zolmitriptan in plasma had approached its maximum concentration by 15 min postdose. The data indicate initial absorption across the nasal mucosa contributing to an early systemic availability. 11C-Zolmitriptan administered intranasally was well tolerated.

Zolmitriptan Intranasal: A Review of the Pharmacokinetics and Clinical Efficacy

Migraine is a common disabling neurological disorder, associated with headache, nausea, and on occasions vomiting. Zolmitriptan is a widely available serotonin 5HT(1B/1D) receptor agonist with a long track record in clinical studies and in the treatment of acute migraine. A nasal formulation has been developed that has clear evidence for local absorption, resulting in plasma drug concentrations within 2 minutes of dosing, central nervous system penetration 3 minutes later, and a significant efficacy benefit versus placebo 10 to 15 minutes after dosing. Intranasal zolmitriptan offers advantages to migraineurs, particularly those seeking a more rapid onset of effect without wishing to self-inject, or those with gastrointestinal upset. The comparison of pharmacokinetic and clinical data available from different formulations of zolmitriptan contributes both to the understanding of its mode of action and the characteristics required of an acute migraine treatment if it is to meet patient needs.

Safety and Efficacy of Eletriptan in the Treatment of Acute Migraine

Eletriptan is a new selective serotonin agonist approved for the treatment of acute migraine headaches. To review the pharmacologic, pharmacodynamic, pharmacokinetic, safety, and clinical efficacy data for eletriptan, we searched the literature in PubMed/MEDLINE, EMBASE, International Pharmaceutical Abstracts, and Science Direct databases to gather all published reports from January 1996-October 2004. All English-language reports (abstract or full trial reports) about the pharmacology, pharmacokinetics, clinical efficacy, and safety of eletriptan were reviewed. Eletriptan's pharmacokinetic and pharmacodynamic parameters translate into a favorable safety and efficacy profile. The drug is rapidly absorbed when administered orally, has good bioavailability and central nervous system penetration due to its lipophilicity, and has a long half-life, which contributes to its ability to prevent recurrent headaches. Compared with other serotonin agonists, eletriptan has a longer duration of action and greater lipophilicity. Eletriptan is metabolized through the cytochrome P450 3A4 system; therefore, it does have the potential for clinically significant drug interactions. In clinical trials, eletriptan demonstrated efficacy superior to that of placebo and similar or superior efficacy to that of other serotonin agonists, with limited adverse effects. With clinical use, headache and pain-free responses and headache recurrence rates were similar to those of other serotonin agonists, but the agent is superior to ergotamine tartrate-caffeine. Based on pharmaco-economic data, eletriptan is more cost-effective than other agents in its class. Eletriptan is a safe and cost-effective option for the treatment of migraine headaches.

Eletriptan

Eletriptan (Relpax) is an orally administered, lipophilic, highly selective serotonin 5-HT(1B/1D) receptor agonist ('triptan') that is effective in the acute treatment of moderate to severe migraine attacks in adults. It has a rapid onset of action and demonstrates superiority over placebo as early as 30 minutes after the administration of a single 40 or 80 mg oral dose. The efficacy of eletriptan 20 mg was similar to that of sumatriptan 100 mg, while eletriptan 40 and 80 mg displayed greater efficacy than sumatriptan 50 or 100 mg for most endpoints. Eletriptan 40 mg was generally superior to naratriptan 2.5 mg and equivalent to almotriptan 12.5 mg, rizatriptan 10 mg and zolmitriptan 2.5 mg, while eletriptan 80 mg was superior to zolmitriptan 2.5 mg for most efficacy parameters. Eletriptan 40 and 80 mg were consistently superior to ergotamine/caffeine. Eletriptan is generally well tolerated, reduces time lost from normal activities, improves patients' health-related quality of life and appears to be at least as, if not more, cost effective than sumatriptan. Eletriptan is therefore a useful addition to the triptan family and a first-line treatment option in the acute management of migraine attacks.

Uncertainty Analysis in Pharmacokinetics and Pharmacodynamics: Application to Naratriptan

PURPOSE

The aim of the study was to predict pain relief of migraine in patients following naratriptan oral (tablet) administration by using uncertainty analysis. The analysis was based on phase I pharmacokinetic naratriptan data, sumatriptan pharmacodynamic data, and naratriptan preclinical (animal) potency information, together with general knowledge as to how migraine affects oral absorption.

METHODS

A previously developed pharmacokinetic (PK)/pharmacodynamic (PD) model for naratriptan disposition and effect was used. The uncertain parameters in the model, which were associated with absorption and scaling between first-in-class compound sumatriptan and naratriptan, were modeled using fuzzy sets theory. Global sensitivity analysis was then used to investigate the impact of each PK/PD parameter on the responses.

RESULTS

Acknowledging parametric uncertainty did not improve prediction of the probability of pain relief. Global sensitivity analysis demonstrated that predictions were heavily influenced by interindividual variability in pharmacodynamics, as the dose response relationship was relatively insensitive to the pharmacokinetics.

CONCLUSIONS

To predict the probability of pain relief following oral (tablet) administration of naratriptan, a simple dose response, instead of the PK/PD model, would have yielded very similar predictions. The naratriptan PK/PD model may be improved by either refining the PD model or better still by specifying the interindividual error by additional data collecting with an improved design.

Determination of rizatriptan in human plasma by liquid chromatographic-eletrospray tandem mass spectrometry: application to a pharmacokinetic study

A sensitive liquid chromatographic-tandem mass spectrometry(LC-MS/MS) method was developed for the determination of rizatriptan in human plasma. The analytes were extracted from plasma samples by liquid-liquid extraction, separated on a Zorbax XDB C8 column (150 x 4.6 mm i.d.) and detected by tandem mass spectrometry with an electrospray ionization interface. Zomitriptan was used as the internal standard. The method had a lower limit of quantitation of 50 pg/mL for rizatriptan, which showed more sensitivity and speed of analysis compared with reported methods. The within- and between-day precision was measured to be below 11.71% and accuracy between -5.87 and 0.86% for all quality control samples. This quantitation method was successfully applied to the evaluation of the pharmacokinetic profiles of rizatriptan after single oral administration of 5, 10 and 15 mg rizatriptan tablets to 10 healthy volunteers (five males and five females).

Pharmacokinetics of tryptamide following oral and intraperitoneal administration in rats

Tryptamide, either suspended in 1% methylcellulose or dissolved in polyethyleneglycol 400-ethanol-physiological salt solution (4:1:5) was administered po or ip at a dose 25 mg/kg to rats, and blood level of this drug was determined by HPLC method. The obtained results were used to construct the semilogarithmic plots of tryptamide concentration vs. time and pharmacokinetic parameters of tryptamide were calculated. We found that tryptamide undergoes fast absorption (t 1/2 = 4.92-17.5 min) and elimination (t 1/2 = 55.72-74.52 min), can reach C(max) values (11-13 microg/cm3) after 30 min, and gives AUC values in the range of 21.40-27.30 (microg x h/cm3).

New carrier for specific delivery of drugs to the brain

1,4-Dihydropyridines were thoroughly investigated as carriers for specific drug delivery to the brain and were found very efficient. The main problem which arises in their application in pharmaceutical preparations, is the short shelf-life time due to hydration and/or oxidation. To overcome these problems, a new carrier system is suggested. Many of 1,4-dihydropyridine-3,5-dicarboxylate derivatives are used as calcium channel blockers which are known to have long shelf-life time, and at the same time, they are safe, with no reported neurotoxicity. Since efficiency of brain specific delivery depends on the rate of oxidation of the dihydropyridine carrier, (the faster the rate, the higher the efficiency), these 3,5-dicarbonyl compounds have almost of no brain-specific delivery properties. N-alkoxycarbonylmethyl derivatives of 1,4-dihydropyridine-3,5-dicarboxylate, a new carrier system is suggested and expected to be stable enough for formulation and storage. The drug moiety will be connected to the 3,5-dicarbonyl groups in the form of esters or amides. The suggested drug-carrier once delivered and distributed in the body, will be subjected to several sequential enzymatic hydrolytic and oxidative processes. The D-carrier is designed so that, the rate of hydrolysis of the ester group at the nitrogen atom should be faster than that of the hydrolysis and release of the drug moiety. The stability and efficiency of brain specific delivery of model drugs were investigated. The in vitro and in vivo studies proved the efficiency of brain specific delivery of the carrier and at the same time its shelf life stability. The results suggest that the designed carrier is promising to be used in application of pharmaceutical formulation.

Ionic strength has a greater effect than does transmembrane electric potential difference on permeation of tryptamine and indoleacetic acid across Caco-2 cells

The effects of transmembrane electric potential difference and ionic strength on the permeation of tryptamine and indoleacetic acid across a Caco-2 cell monolayer were examined. A decrease in the transmembrane electric potential difference caused by the addition of potassium ion to the transport buffer had no effect on the permeation rate of either compound. On the other hand, an increase in ionic strength resulted in a decrease in the permeation rate of tryptamine and an increase in the permeation rate of indoleacetic acid. The changes in the permeation rate with changes in the ionic strength were correlated with the membrane surface potential monitored by 1-anilino-8-naphthalenesulfonic acid (ANS), a fluorescent probe. We tested these effects using several other cationic and anionic compounds. These effects of ionic strength were found to be common to all drugs tested. The compound that showed a relatively lower permeation rate was given relatively stronger effect. The possibility of overestimation or underestimation caused by these effects should be considered when the permeation of an ionic compound is evaluated using a cell monolayer system.

Orally bioavailable, indole-based nonpeptide GnRH receptor antagonists with high potency and functional activity

Stereospecific introduction of a methyl group to the indole-3-side chain enhanced activity in our tryptamine-derived series of GnRH receptor antagonists. Further improvements were achieved by variation of the bicyclic amino moiety of the tertiary amide and by adjustment of the tether length to a pyridine or pyridone terminus. These modifications culminated in analogue 24, which had oral activity in a rat model and acceptable oral bioavailability and half-life in dogs and monkeys.

A tryptamine analog with high affinity to the heart tissues is a potential antiarrhythmic agent

A novel tryptamine analog, 1-methyl-3-[N-(3-indolyl)ethyl]carbamoyl-1,4-dihydropyridine (T-CDS) was synthesized and converted into a stable, solid complex with 2-hydroxypropyl-beta-cyclodextrin. An aqueous solution of the complex was given intravenously to dogs and the concentration of T-CDS and its corresponding quaternary (T-Q+) forms were monitored in the blood for 50 min. The effect of the drug on vital heart parameters was monitored throughout the studies. At the end of the experiment the dogs were sacrificed and the concentration of the quaternary pyridinium form (T-Q+) was determined in the different heart tissues, as well as in the kidney, liver, lung, brain, urine and cerebrospinal fluid. The compound was found to be selectively bound to the heart muscles and showed different concentrations in different heart tissues. The T-Q+ concentrations were much higher in the heart after administration of the dihydro form (T-CDS), than after administering T-Q+ directly. The compound was found to be active on certain vital signs of the cardiovascular system and could be an effective and safe antiarrhythmic agent.

Pharmacokinetics of Rizatriptan Tablets During and Between Migraine Attacks

Gastric stasis during migraine attacks results in delayed absorption of several orally administered antimigraine agents. This study, as part of a larger trial, was conducted to examine the pharmacokinetics of rizatriptan tablets during and between migraine attacks. Participating patients met IHS criteria for migraine with or without aura, and suffered between one and eight migraines per month for the previous 6 months. In part 1 of the study, 21 patients were randomized to receive a single 5-mg tablet of rizatriptan or placebo in the migraine-free state. In part 2, the same patients were treated during migraine with rizatriptan 5-mg tablets (n=18) or placebo (n=3). Blood samples were obtained before dosing and 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, 8, and 12 hours after dosing. The plasma concentration profile (ie, AUC((0-infinity)), C(max), T(max)) of rizatriptan 5-mg tablets administered during and between migraine attacks were comparable. The median T(max) for rizatriptan between and during attacks was 1 hour, indicating rapid absorption even during a migraine attack. Rizatriptan 5 mg was well tolerated and 67% of the patients experienced headache relief 2 hours postdose.

2-[125I]iodo-5-methoxycarbonylamino-N-acetyltryptamine: a selective radioligand for the characterization of melatonin ML2 binding sites

We now describe the preparation and characterization of a novel radioligand, 2-[125I]iodo-5-methoxy-carbonylamino-N-acetyltryptamine (2-[125I]MCA-NAT), with high affinity and pharmacological selectivity for melatonin ML2 receptor sites. 2-[125I]MCA-NAT was prepared by introducing an [125I]iodine molecule on carbon 2 of 5-MCA-NAT (5-methoxycarbonylamino N-acetyltryptamine), a selective melatonin ML2 receptor ligand. The specific binding (88%) of 2-[125I]MCA-NAT (50 pM) to whole washed hamster brain membranes showed rapid kinetics of association/dissociation, and was of high affinity and saturable (Kd value = 116 +/- 14 pM; Bmax value = 15.5 +/- 1.8 fmol/mg protein, n = 3). 2-[125I]MCA-NAT showed no affinity for melatonin ML1 receptors of chicken retina. Competition curves of various melatonin analogues for 2-[125I]MCA-NAT binding to hamster brain, testes and kidney were monophasic and showed a pharmacological order of affinities (Ki values for brain, nM) identical to that of the ML2 sites [2-iodomelatonin (0.77) > 6-chloro-2-methyl-melatonin (2.56) > 6-chloromelatonin (6.8) > prazosin (21.7) > or = N-acetylserotonin (23.3 nM) > or = 5-MCA-NAT (29.5) > or = melatonin (83.9) > luzindole (1687) > serotonin (2120)]. Affinity constants for competition of melatonin analogues on [125I]MCA-NAT binding to hamster brain, testes, and kidney correlated significantly [r = 0.962, P < 0.001, n = 9; r = 0.982, P < 0.0001, n = 13; r = 0.975, P < 0.0001, n = 9, respectively) with the affinities determined on 2-[125I]iodomelatonin binding to ML2 sites (hamster brain) but not to ML1 sites (chicken retina, r = 0.33, P > 0.05, n = 16). In conclusion, 2-[125I]MCA-NAT is a specific radioligand for the identification and characterization of ML2 binding sites in brain and peripheral tissues.

Influence of biological matrix on chromatographic behavior and detection of selected acidic, neutral, and basic drugs examined by means of a standardized HPLC-DAD system

Human serum, autopsy blood, and liver samples were extracted by means of liquid-liquid extraction at acidic and at basic pH and at basic pH following acid hydrolysis. Six selected basic and six selected acidic or neutral drugs were added to the extracts. The spiked and blank samples were examined by means of reversed-phase high-performance liquid chromatography (HPLC) under standardized conditions using diode array detection. The retention index (RI) values of drugs were determined using a 1-nitroalkane scale and secondary standards. The RI values were virtually unaffected by biological matrix. On the other hand, the detection of some substances may be impaired by matrix peaks occurring regularly in biological extracts. The retention index values and UV spectra of three identified (phenethylamine, tryptamine, and indole) and nine unidentified substances were included in an HPLC database.

Identification of serotonin 5-HT4 recognition sites in the porcine caudate nucleus by radioligand binding

Specific binding for the serotonin 5-HT4 receptor (5-HT4R) radioligand [3H]GR 113808 was identified in pig caudate nucleus and characterized by serotonin subtype selective drugs. Binding was inhibited by serotonin and by synthetic indoles, benzamides and benzimidazolones known to characterize the 5-HT4R in functional tests. Rank order of potency of 5-HT4R antagonists was: GR 125487 (Ki, 0.19 nM) > GR 113808 >> SC 53606 > SDZ 205,557 > RS 235971/190 > DAU 6285 > tropisetron > DAU 6215. GR 125487 and GR 113808 were highly selective with respect to the 5-HT3 receptor (5-HT3R). Rank order of potency of 5-HT4R agonists was: SC 53116 (Ki, 21 nM) > BIMU 1 > cisapride > BIMU 8 > serotonin > renzapride > S-zacopride > metoclopramide > R-zacopride > 5-methoxytryptamine >> 5-carboxamidotryptamine. BIMU 8, renzapride, metoclopramide and the zacopride enantiomers gave shallow competition curves. The agonists were substantially less selective than the antagonists with respect to the 5-HT3R. With only two exceptions, SCH 23390 and metergoline, which bound with sub-microM affinity to the 5-HT4R, binding was not inhibited by compounds selective for other G-protein-coupled or channel-gated receptors. Highly significant correlations in affinities of compounds for 5-HT4R in caudata of pigs, guinea pigs and humans were found suggesting no difference among mammalian species.

Behavioral characterization of alpha-ethyltryptamine, a tryptamine derivative with MDMA-like properties in rats

Several reports have speculated that the tryptamine-derived drug alpha-ethyltryptamine (AET) may have effects similar to those of the amphetamine-derived drug 3,4-methylenedioxymethamphetamine (MDMA). Indeed, the US Drug Enforcement Administration has recently placed AET on the Schedule I list because of its putative similarity to MDMA. The Behavioral Pattern Monitor, which quantifies locomotor and investigatory responses of rats, was used to characterize the effects of AET in a paradigm that distinguishes between the effects of traditional hallucinogens, amphetamine-like stimulants, and MDMA-like drugs. First, a dose-response study revealed that all doses of AET tested (5, 10, 20 mg/kg) significantly increased locomotor activity. Locomotor hyperactivity is produced by MDMA or amphetamine-like stimulants, but not by classical hallucinogens, such as LSD or mescaline. Additionally, AET significantly decreased measures of investigatory behavior. Similar decreases occur with MDMA or hallucinogen administration. Second, as with MDMA, the locomotor hyperactivity induced by AET was attenuated by pretreatment (10 mg/kg) with the serotonin reuptake inhibitor fluoxetine. Thus, AET, a tryptamine-derived drug, appears to produce an MDMA-like profile of behavioral changes by virtue of releasing presynaptic serotonin.

Pharmacokinetics of tryptamide following intravenous administration in rats

Plasma and tissue levels of N-3-pyridoyl-tryptamine (tryptamide) vs. time were determined in rats following iv administration of various doses: 6.25, 12.5, 25.0 and 37.5 mg/kg. The course of changes was described by the two-compartment open model. The distribution rate constant (alpha, min-1), the elimination rate constant (beta, min-1), the body clearance (Cltot, ml/min) and its fraction absorbed (f,%) values changed depending on the dose and were respectively: 0.107-0.266, 0.0068-0.0126, 5.39-11.59 and 31.77-66.70.

Cerebral and peripheral demethylation of psychotomimetics measured by expired 14CO2

Demethylation of psychotomimetic compounds was measured by labeling each methyl and methoxy substitutent separately with 14C and injecting it into rats, intravenously and intracerebrally. Expired [14C]CO2 was measured continuously and the resultant multi-exponential curves yielded rates and integral demethylation. 5-Methoxy-N,N-dimethyltryptamine was not demethylated, eliminating one proposed metabolic pathway. 2,4,5-Trimethoxyphenalkylamines were demethylated less in the brain than peripherally, markedly so at the p-methoxy position, suggesting a possible biochemical site for endogenous induction of psychosis.

Down-regulation of tryptamine receptors following chronic administration of clorgyline

Chronic treatment with clorgyline, a type A monoamine oxidase (MAO) inhibitor (1 mg/kg/day for 11 days), reduced the number (Bmax) but not the affinity (Kd) of [3H]tryptamine binding sites in rat frontal/parietal cortical membranes. Binding was reduced for at least 36 days following the last injection. The reduction in [3H]tryptamine binding was dose-related and appeared to be maximal following a daily dose of 3 mg/kg. Chronic treatment with deprenyl, a type B MAO inhibitor (1 mg/kg/day for 11 days), did not affect [3H]tryptamine binding. Acute clorgyline administration (11 mg/kg) also had no effect. These data suggest that [3H]tryptamine binds to neurotransmitter receptors for tryptamine since mere chemical recognition sites would not be expected to be modulated by chronic drug treatment. Also, since [3H]tryptamine binding was down-regulated by a type A, but not a type B, MAO inhibitor, tryptamine may be selectively metabolized by type A MAO in vivo.

Improved delivery through biological membranes. Synthesis, distribution, and neurochemical effects of a tryptamine chemical delivery system

Enhanced central delivery of tryptamine was proposed by application of a dihydropyridine in equilibrium pyridinium salt redox system. This drug delivery method, which relies on biochemistry similar to that which occurs in the NAD+ in equilibrium NADH coenzyme system, required synthetic derivatization of tryptamine. When the resulting tryptamine chemical delivery system (TCDS) was systematically administered, it passed the blood-brain barrier intact and then oxidized. The resulting quaternary form (TQ+) accumulated in the brain of rats relative to most peripheral organs. The only organ in which a more rapid efflux was not demonstrated was the heart. Intestinal administration of the TCDS showed the ability of the system to undergo absorption and to survive the first pass through the liver. The TCDS caused central neurochemical changes consistent with central delivery of tryptamine. Possible applications of the TCDS are discussed.