A new formulation of selegiline: improved bioavailability and selectivity for MAO-B inhibition.

Seven randomised comparative studies were conducted in healthy volunteers to compare the pharmacokinetic and pharmacodynamic profiles of selegiline hydrochloride in a new formulation designed for buccal absorption "Zydis Selegiline" (1.25-10 mg) with conventional selegiline hydrochloride tablets "conventional selegiline tablets" (10 mg). A total of 156 healthy volunteers participated in these studies. Plasma concentrations of selegiline and its primary metabolites, N-desmethylselegiline (DMS), l-amphetamine (AMT), and l-methamphetamine (MET) were measured using Gas Chromatography Mass Spectrometry (GCMS) and gas liquid chromatography (GLC) assays. Inhibition of monoamine-oxidase type B (MAO-B) and monoamine oxidase type A (MAO-A) activity was determined by measurement of as beta-phenylethylamine (PEA) by GCMS and 5-hydroxyindoleacetic acid (5-HIAA) by High Performance Liquid Chromatography (HPLC) assays. Almost a third (2.96 mg) of a 10 mg selegiline dose in Zydis Selegiline was absorbed pre-gastrically (predominantly buccally) within 1 minute. Mean [SD] area-under-the curve (AUC(0- infinity)) values following Zydis Selegiline 10 mg (5.85 [7.31] ng.h/mL) were approximately five times higher than those following conventional selegiline tablets 10 mg (1.16 [1.05] ng.h/mL). In contrast, plasma concentrations of metabolites were significantly ( p<0.001) lower following Zydis Selegiline 10 mg than following conventional selegiline tablets 10 mg. Plasma concentrations of selegiline and its metabolites increased in a dose-dependent manner over the dose-range Zydis Selegiline 1.25-5 mg. Bioavailability was determined using AUC and peak plasma concentrations (C(max)). The C(max) of selegiline was similar following administration of Zydis Selegiline 1.25 mg (1.52 ng/mL) or conventional selegiline tablets 10 mg (1.14 mg/mL). The range of values for AUC(0- infinity) and C(max) following Zydis Selegiline 1.25 mg were entirely contained within the range following conventional selegiline tablets 10 mg, with a much higher variability of plasma selegiline concentrations occurring after conventional selegiline tablets than after Zydis Selegiline. As expected, peak plasma concentrations for DMS, AMT and MET were consistently lower after Zydis Selegiline 1.25 mg (1.19, 0.34, 0.93 ng/ml, respectively) than after conventional selegiline tablets 10 mg (18.37, 3.60, 12.92 ng/ml, respectively). A significant (r=0.0001) correlation between daily PEA excretion (a measure of brain MAO-B inhibition) and the log-transformed AUC((0-t)) for selegiline was demonstrated. Mean daily PEA excretion was similar following Zydis Selegiline 1.25 mg and conventional selegiline tablets 10 mg (13.0 microg versus 17.6 microg). In contrast, there was no correlation between PEA excretion and selegiline metabolites, indicating that selegiline metabolites do not significantly inhibit MAO-B. Urinary excretion of 5-HIAA (used as a marker for MAO-A inhibition) was unrelated to plasma concentrations of selegiline or DMS following single or repeat dosing of Zydis Selegiline 1.25 mg or conventional selegiline tablets 10 mg. However, comparison of treatment groups revealed a significantly lower excretion of 5-HIAA in the conventional selegiline tablets 10 mg group than in the Zydis Selegiline 1.25 mg group after repeated administration over 13 days. In summary, by reducing the opportunity for first-pass metabolism, the absorption of selegiline from Zydis Selegiline was more efficient and less variable than from conventional selegiline tablets. Compared with conventional selegiline tablets 10 mg, Zydis Selegiline 1.25 mg yielded similar plasma concentrations of selegiline and degree of MAO-B inhibition, but markedly reduced concentrations of the principal metabolites. Thus, the lower but equally MAO-B inhibitory dose of selegiline in Zydis Selegiline 1.25 mg, which is associated with lower concentrations of potentially harmful metabolites, could offer a safer and more predictable treatment in the management of patients with Parkinson's disease.

A new low-dose formulation of selegiline: clinical efficacy, patient preference and selectivity for MAO-B inhibition.

Three studies were performed using a fast dissolving formulation of selegiline hydrochloride designed for buccal absorption "Zydis Selegiline". The aim of the first study was to compare the therapeutic efficacy of Zydis Selegiline (1.25 mg or 10 mg) with conventional selegiline hydrochloride tablets "conventional selegiline tablets" (10 mg) in patients with Parkinson's disease (PD) who were previously treated with conventional selegiline tablets as an adjunct to levodopa/dopamine agonist therapy. Patients were observed for 4 weeks to ensure that they were stable. Stable patients (n=197) were then randomised to continue with conventional selegiline tablets 10 mg (n=68), or to treatment with Zydis Selegiline 1.25 mg (n=64) or Zydis Selegiline 10 mg (n=62) for 12 weeks in this randomised, parallel group study. A further aim was to establish the acceptability of Zydis Selegiline compared with conventional selegiline tablets. Patient preference for Zydis Selegiline was also evaluated in a second study, a single-dose, randomised, two-way crossover study conducted in patients with PD (n=148). Patients were stratified by the presence or absence of swallowing and salivation problems and were randomised to either Zydis Selegiline 5 mg or a placebo fast-dissolving formulation. In a third study, the degree of potentiation of the tyramine pressor effect following Zydis Selegiline was compared with that following conventional selegiline tablets in healthy volunteers. A total of 24 healthy volunteers were randomised to receive Zydis Selegiline 1.25 mg or conventional selegiline tablets 10 mg for 14-16 days in an open-label, randomised parallel group study. Both Zydis Selegiline (1.25 mg and 10 mg) treatments were shown to be therapeutically equivalent to conventional selegiline tablets 10 mg based on comparison of mean total Unified Parkinson's Disease Rating Scale (UPDRS) scores. Therapeutic equivalence was defined a priori as the 90% confidence interval (CI) for the difference in total UPDRS scores between groups to lie entirely within the range +/-5. The difference (90% CI) in mean adjusted total UPDRS between Zydis Selegiline 1.25 mg and conventional selegiline tablets 10 mg was -2.50 (-4.84, -0.17), and for Zydis Selegiline 10 mg and conventional selegiline tablets 10 mg, 0.04 (-2.30, 2.38). For the motor subscores of the UPDRS, differences between adjusted means (90% CI) compared with the conventional selegiline tablets group were: Zydis Selegiline 1.25 mg, -2.14 (-3.94, -0.33) and Zydis Selegiline 10 mg, -0.90 (-2.70, +0.91). Patients who switched from conventional selegiline tablets to Zydis Selegiline 1.25 mg showed a slight improvement in UPDRS scores following 12 weeks of treatment (standard error of difference 1.039; p=0.01). In the single-dose crossover study, most (61%) patients liked Zydis Selegiline 5 mg; a significantly greater proportion than the null hypothesis of 50% (p<0.002). However, only 62 patients (46%) indicated that they liked the taste of Zydis Selegiline. Nevertheless, the proportion of patients who preferred Zydis Selegiline (65%) to their usual medication was significantly greater than the null hypothesis of 50% (p<0.001). Similar findings were demonstrated in the 12-week study where a higher proportion of patients who received up to 3 months of treatment indicated a preference for either Zydis Selegiline 1.25 mg (90%) or Zydis Selegiline 10 mg (86%) over conventional selegiline tablets 10 mg. More than 90% of patients found Zydis Selegiline easy to take, with 61% rating it as extremely easy. Most (81%) patients taking Zydis Selegiline 1.25 mg liked the taste compared with 45% taking Zydis Selegiline 5 mg (in the previous study). Zydis Selegiline did not potentiate the tyramine effect: a pressor effect was elicited after 400 mg tyramine both before and after 14 days of treatment with Zydis Selegiline 1.25 mg. In contrast, after 14 days treatment with conventional selegiline tablets 10 mg, the threshold dose required to elicit the tyramine pressor response was significantly (p<0.0001) reduced from 400 mg to 200 mg. In summary, Zydis Selegiline at doses of 1.25 mg and 10 mg was therapeutically equivalent to conventional selegiline tablets 10 mg. The Zydis Selegiline formulation was well-liked by all patients, with most preferring Zydis Selegiline 1.25 mg to their usual selegiline tablet. Furthermore, Zydis Selegiline was well tolerated and, unlike conventional selegiline tablets, appeared to retain specificity for inhibition of monoamine oxidase type B (MAO-B), since it did not potentiate the pressor response to tyramine.

A European multicentre study to evaluate the tolerability of apomorphine sublingual administered in a forced dose-escalation regimen in patients with erectile dysfunction.

OBJECTIVE: To determine the risk-benefit ratio of a forced dose-escalation regimen (2 to 3 to 4 mg) in a European clinical study evaluating apomorphine sublingual (SL) in treating erectile dysfunction (ED), by evaluating the overall tolerability and efficacy of the regimen compared with placebo in patients with ED, and evaluating efficacy by assessing the proportion of successful attempts resulting in sexual intercourse. PATIENTS AND METHODS: This randomized, double-blind, two-arm, parallel-group study was conducted in 507 patients enrolled at 34 European sites. After a 1-2 week screening period, patients were treated for 8 weeks with either placebo or apomorphine SL administered as a forced dose-escalation regimen. Heterosexual men (aged 18-70 years) were eligible for participation in the study if they were in stable health, a stable relationship of > or = 6 months duration, had a history of erectile inability, and were diagnosed with ED (successful in fewer than half of attempts to attain and maintain an erection firm enough for intercourse during the 30 days before screening). Patients provided information (recorded on diary cards and reviewed at each study visit) about the frequency and success in achieving erections and of sexual intercourse attempts during both the screening and treatment periods. The dosing regimen required patients to take one tablet of apomorphine SL (2 mg for 2 weeks, then 3 mg for 2 weeks and finally 4 mg for the remaining 4 weeks) or placebo 15-25 min before intercourse, and intercourse was to be attempted at least twice a week. Safety data were collected throughout the 8-week study period, and included recording adverse events, vital signs and changes in laboratory test values for standard haematology and biochemistry variables. The primary efficacy variable was the proportion of successful attempts, defined as an erection rigid enough for sexual intercourse, occurring after dosing (successful intercourse rate). The proportion of erections achieved was a secondary efficacy variable. RESULTS: Of the 507 patients, 254 received apomorphine SL and 253 received placebo; 87% of patients in both groups completed the 8-week treatment period. Of the patients receiving apomorphine SL, 24% had hypertension, 11% had coronary artery disease, 10% had diabetes, and 5.5% had benign prostatic hypertrophy; 62.6% of treated patients received concomitant medications for these maladies. The treatment groups were balanced for demographic and baseline variables, including comorbidity factors. Treatment-emergent adverse events, reported by > 5% of patients in the treated group, were nausea (9.8%), dizziness (7.1%) and headache (6.7%), compared with 0.4%, 2.4% and 4.0%, respectively, in the placebo group. Sixty-six patients withdrew from the study, 16 because of study drug-related adverse events (12 from the apomorphine and four from the placebo group). Six patients (three in each group) reported a total of nine serious treatment-emergent adverse events, all of which resolved by the end of the study. In the intention-to-treat population, the proportion of successful attempts at sexual intercourse and of erections were statistically greater in the apomorphine than in the placebo group (P = 0.001 and 0.021, respectively); analysis of the per-protocol population results confirmed this significant difference. CONCLUSION: This European study supports the safety and tolerability of apomorphine SL despite the forced escalation to a 4-mg dose (exceeding the approved 2-3 mg dose). Adverse effects were not treatment-limiting. These results further support the clinically significant efficacy of apomorphine SL for treating ED at all doses used. The risk/benefit ratio supports apomorphine SL as a safe and effective alternative in managing ED.

Identification of ligands selective for central I2-imidazoline binding sites.

Using radioligand binding techniques, several compounds selective for mammalian brain imidazoline 2 receptors have been identified. In rabbit brain membranes, a series of 6 and/or 7 aromatic-substituted derivatives of the alpha 2-adrenoceptor antagonist idazoxan were found to show moderate affinity for I2 receptors over alpha 2-adrenoceptors, in particular 6,7-dichloroidazoxan, which was 41 fold selective in favour of I2 receptors. Modification of the benzodioxan ring of idazoxan could also result in affinity and selectivity, which was moderate (2.7 nM, 161 fold) in the case of the 1,3-benzodioxan isomer of idazoxan (2-(1,3-benzodioxanyl)-2-imidazoline), and high (1.3 nM, 2873 fold) in the case of 2-(2-benzofuranyl-2-imidazoline) (2-BFI). Analogues of 2-BFI with halogenic substitutions of the aromatic ring were also found to retain high affinity and moderate to high selectivity for I2-sites. In particular, the 7-chloro (Ki 2.8 nM, 2192 fold) and the 4,6-dibromo (Ki 6.1 nM, 361 fold) analogues of 2-BFI. These new ligands should prove invaluable for investigating the pharmacology and physiology of I2 receptors.

Suramin: a selective inhibitor of purinergic neurotransmission in the rat isolated vas deferens.

The effects of the putative P2 purinoceptor antagonist suramin on contractile responses of the rat isolated vas deferens to electrical field stimulation and exogenously applied drugs (alpha,beta-methylene ATP and noradrenaline) were investigated. Suramin was devoid of agonist activity in the rat vas deferens. The response of the vas deferens to single pulse field stimulation was characteristically biphasic with a large first component peaking between 260-300 ms after the stimulus followed by a second smaller component peaking at about 650 ms post-stimulus. Suramin (100 nM-1 mM) selectively impaired the first, purinergic phase of the response to single pulse field stimulation but was without effect on the second, noradrenergic component. The response of the vas deferens to trains of electrical field stimuli (10 Hz for 10 s) was also biphasic. Suramin (1 microM-1 mM) reduced the first (less than 1 s) phase of the response by 30%, the second (greater than 5 s) plateau phase by 50% and inhibited the intermediate (2-4 s) phase by 80%. Dose-contact periods of 20 or 30 min respectively were sufficient to achieve equilibration of the inhibitory effects of suramin against the responses to single pulse field stimulation or trains of pulses. Following 30 min incubation with 1 mM suramin, the remaining first and second phase components of the response to trains of pulses were impaired and subsequently abolished by the alpha 1-adrenoceptor antagonist WB4101 establishing their noradrenergic origin. Suramin (300 microM) abolished responses of the vas deferens to alpha,beta-methylene ATP but was without effect on those to noradrenaline. Suramin (30 microM) induced a rightward shift in the concentration-response relationship to alpha,beta-methylene ATP that was associated with a significant 40% increase in the maximum response, but did not modify responses to noradrenaline. The inhibitory effects of suramin (3-300 microM) on responses of the vas deferens to approximate EC50 concentrations of alpha,beta-methylene ATP were reversible on repeated washout for 40-60 min. These results reveal suramin to be a useful pharmacological tool for the study of purinergic neurotransmission in rodent vasa deferentia.

Characterization and autoradiographical localization of non-adrenoceptor idazoxan binding sites in the rat brain.

1. In rat whole brain homogenates, saturation analysis revealed that both [3H]-idazoxan and [3H]-RX821002, a selective alpha 2-adrenoceptor ligand, bound with high affinity to an apparent single population of sites. However, the Bmax for [3H]-idazoxan was significantly (P less than 0.01) greater than that for [3H]-RX821002. 2. In competition studies, (-)-adrenaline displaced 3 nM [3H]-idazoxan binding with an affinity consistent with [3H]-idazoxan labelling alpha 2-adrenoceptors. However, this displacement was incomplete since 23.68 +/- 1.11% of specific [3H]-idazoxan binding remained in the presence of an excess concentration (100 microM) of (-)-adrenaline. In contrast, unlabelled idazoxan promoted a complete displacement of [3H]-idazoxan binding with a Hill slope close to unity and an affinity comparable with its KD determined in saturation studies. 3. Displacement of [3H]-idazoxan binding by the alpha 2-adrenoceptor antagonists yohimbine, RX821002 (2-(2-methoxy-1,4-benzodioxan-2-yl)-2-imidazoline) and RX811059 (2-(2-ethoxy-1,4-benzodioxan-2-yl)-2-imidazoline) was more complex, with Hill slopes considerably less than unity, and best described by a two-site model of interaction comprising a high and low affinity component. The proportion of sites with high affinity for each antagonist was similar (60-80%). 4. The rank order of antagonist potency for the high affinity component in each displacement curve (RX821002 greater than RX811059 greater than yohimbine) is similar to that determined against the binding of [3H]-RX821002 to rat brain, suggesting that these components reflect the inhibition of [3H]-idazoxan binding to alpha 2-adrenoceptors.The remaining component in each displacement curve exhibiting low affinity towards these antagonists is attributable to the displacement of [3H]-idazoxin from a non-adrenoceptor idazoxan binding site (NAIBS) since a comparable amount of [3H]-idazoxan binding was not displaced by an excess concentration of (-)-adrenaline.5. The displacement of [3H]-idazoxan binding by RX801023 (6-fluoro-(2-(1,4-benzodioxan-2-yl)-2-imidazoline) was also best described by a model assuming a two site interaction with 20.07 +/- 3.11% of the sites labelled displaying high affinity for RX801023. The Ki of RX801023 for the remainder of the sites labelled was similar to its Ki versus [3H]-RX821002, indicating that this drug displays improved affinity and NAIBS/z2-adrenoceptor selectivity compared with idazoxan.6. In autoradiographical studies, the distribution of 5 nM [3H]-idazoxan binding to sections of rat whole brain was consistent with that reported from previous studies and resembled the distribution ofM2-adrenoceptors. However, when sections of brain were coincubated with concentrations of alpha2-adrenoceptor agonists or antagonists predicted to saturate alpha2-adrenoceptors, there remained distinct areas of binding corresponding to discrete brain nuclei. This remaining binding was however displaced by unlabelled idazoxan (3 microM) or RX801023 (3 microM) indicative of the labelling of NAIBS.7. Quantitative autoradiography of NAIBS revealed several brain nuclei which contained higher densities of these sites than alpha2-adrenoceptors, notably the area postrema, interpeduncular nucleus,arcuate nucleus, ependyma and pineal gland.

Neurotransmitter feedback is not important in modulating the noradrenergic component of responses of rat vas deferens to twin pulse electrical field stimulation.

1. Drug effects on the full time-course of tension responses of the rat vas deferens to challenges of twin pulse field stimulation (TPFS) were examined. A microprocessor-controlled system was used to regulate stimulus delivery, on-line data collection and subsequent data analysis. 2. The second, noradrenergic phase of the response to the second stimulus of TPFS was missing when the interpulse interval was set at 3 s but was progressively restored as the interpulse interval was extended to 120 s. 3. With a 3 s interpulse interval, the missing second phase of the response to the second stimulus was not restored by the selective alpha 2-adrenoceptor antagonists yohimbine, imiloxan or idazoxan, indicative that alpha 2-adrenoceptor-mediated feedback inhibition of noradrenaline release is not the predominant mechanism modulating this response component. 4. Incubation with the P1-purinoceptor antagonist 8-phenyl-theophylline also failed to restore the missing noradrenergic component in the response to the second stimulus of TPFS. 5. Nevertheless, both responses to TPFS were impaired by the selective alpha 2-adrenoceptor agonist clonidine and by the P1-purinoceptor agonist 2-chloroadenosine, indicating the presence of functional presynaptic receptors of both types. These agonist-induced inhibitory effects were readily reversed by those antagonists which had failed to restore the missing noradrenergic component in the second response to TPFS.

Separation of putative alpha 1A- and alpha 1B-adrenoceptor mediated components in the tension response of the rat vas deferens to electrical field stimulation.

1. The effects of the putative alpha 1B-adrenoceptor antagonist, chloroethylchlonidine (CEC), on tension responses of the rat isolated whole vas deferens to single and multiple pulses of electrical field stimulation have been evaluated by use of a microcomputer system which enables the averaging of like-responses throughout their time course. 2. CEC (10(-7) to 3 x 10(-6) M) selectively and in a concentration-dependent manner blocked the noradrenergic component of the response to a single field stimulus in the absence or presence of nifedipine (10(-5) M, which blocked the purinergic but not the noradrenergic component of the response). The concentration-response curve of the vas to exogenously-applied noradrenaline (NA) was unaffected by CEC (10(-6) M) but was flattened by nifedipine (10(-5) M). 3. The tension response to 10 Hz trains of pulses was biphasic, with an early (less than 2 s) and a plateau (greater than 4 s) phase. We deduce from our pharmacological analysis that the early phase contains a putative alpha 1B-adrenoceptor component (susceptible to CEC or prazosin but not to nifedipine) and a P2-purinoceptor component (susceptible to suramin or nifedipine) whereas the plateau phase contains an alpha 1A-adrenoceptor component (susceptible to prazosin or nifedipine but not to CEC) and a P2-purinoceptor component (susceptible to suramin or nifedipine). 4. We suggest that the putative alpha 1B-adrenoceptors may be functionally confined to the synaptic region whereas the putative alpha 1A-adrenoceptors are excluded from this region. Trains of pulses would allow NA to accumulate and spill out beyond the synaptic region to reach and activate the putative alphalA-adrenoceptors.