Pharmacokinetics and absolute bioavailability of selegiline following treatment of healthy subjects with the selegiline transdermal system (6 mg/24 h): a comparison with oral selegiline capsules.

The selegiline transdermal system is a monoamine oxidase inhibitor that was recently approved by the US Food and Drug Administration for the treatment of major depressive disorder. The current study was conducted during the selegiline transdermal system development program to characterize the single-dose pharmacokinetics and absolute bioavailability of selegiline administered by the 6-mg/24-h selegiline transdermal system in healthy volunteers. Selegiline transdermal system results were compared with those obtained after a single 10-mg oral dose of selegiline HCl. The selegiline pharmacokinetics differed greatly between the 2 routes of administration. Transdermal selegiline administration reduced metabolism and produced a high, sustained plasma selegiline concentration over the dosing period, with an absolute bioavailability of 73%. By contrast, oral dosing produced a sharp plasma selegiline peak that occurred within 1 hour and declined rapidly, with an absolute bioavailability of 4%. The data provide the basis for therapeutic advantages of the selegiline transdermal system in administering antidepressant doses of selegiline.

Simultaneous determination of selegiline and desmethylselegiline in human body fluids by headspace solid-phase microextraction and gas chromatography-mass spectrometry.

A method for the simultaneous determination of selegiline and its metabolite, desmethylselegiline, in human whole blood and urine is presented. The method, which combines a fiber-based headspace solid-phase microextraction (SPME) technique with gas chromatography-mass spectrometry (GC-MS), required optimization of various parameters (e.g., salt additives, extraction temperatures, extraction times and the extraction properties of the SPME fiber coatings). Pargyline was used as the internal standard. Extraction efficiencies for both selegiline and desmethylselegiline were 2.0-3.4% for whole blood, and 8.0-13.2% for urine. The regression equations for selegiline and desmethylselegiline extracted from whole blood were linear (r(2)=0.996 and 0.995) within the concentration ranges 0.1-10 and 0.2-20 ng/ml, respectively. For urine, the regression equations for selegiline and desmethylselegiline were linear (r(2)=0.999 and 0.998) within the concentration ranges 0.05-5.0 and 0.1-10 ng/ml, respectively. The limit of detection for selegiline and desmethylselegiline was 0.01-0.05 ng/ml for both samples. The lower and upper limits of quantification for each compound were 0.05-0.2 and 5-20 ng/ml, respectively. Intra- and inter-day coefficients of variation for selegiline and desmethylselegiline in both samples were not greater than 8.7 and 11.7%, respectively. The determination of selegiline and desmethylselegiline concentrations in Parkinson's disease patients undergoing continuous selegiline treatment is presented and is shown to validate the present methodology.

Marked effect of liver and kidney function on the pharmacokinetics of selegiline.

OBJECTIVES: The pharmacokinetics of selegiline was investigated in an open study with 4 parallel groups of 10 subjects in each. Patients with liver disease, those receiving a drug that induced hepatic enzyme activity, and those with impaired kidney function were compared with control subjects. METHODS: A single oral 20-mg dose of selegiline was administered after an overnight fast, and blood samples were collected over a period of 48 hours. Concentrations of serum selegiline and its main metabolites were determined and pharmacokinetic parameters calculated. RESULTS: The pharmacokinetic parameters of selegiline differed considerably between the patient groups and the control subjects. The area under the concentration-time curve of serum selegiline was, on average, 18-fold higher (P < .05) in patients with impaired liver function, 23-fold lower (P < .001) in patients with drug-induced liver function, and 6-fold higher (P < .05) in patients with impaired kidney function as compared with the control subjects. There was a large interindividual variation in every group. The changes in selegiline metabolite kinetics supported the changes in the kinetics of the parent compound. CONCLUSION: The elimination rate of selegiline was substantially increased in patients with drug-induced liver function and decreased in patients with impaired liver or kidney function when compared with control subjects. These results suggest that selegiline dosage adjustments may be required in patients with altered liver and kidney function.

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.

Reduced cardiovascular effects of methamphetamine following treatment with selegiline.

Selegiline is a specific MAO-B inhibitor. As MAO-B has been shown to be significantly involved in the metabolism of dopamine in certain regions of the primate brain, selegiline has been proposed for use in the treatment of drug addiction. Selegiline is also metabolized in vivo to l-methamphetamine. Therefore, when given in combination with psychostimulants such as d-methamphetamine, there is the potential for adverse effects. To study this possibility, squirrel monkeys were treated with chronic selegiline and tested with two doses of d-methamphetamine (0.1 and 1.0 mg/kg, i.v.). Following at least 7 days of treatment with once daily 0.3 mg/kg i.m. selegiline, the effects of methamphetamine on blood pressure and heart rate were no different than the effects of methamphetamine observed prior to selegiline treatment. However, following at least 10 days of treatment with 1.0 mg/kg i.m. selegiline, the effects of methamphetamine on blood pressure and heart rate were significantly reduced. Both methamphetamine and amphetamine were detected in plasma following chronic selegiline treatment. When monkeys were given an acute selegiline injection prior to methamphetamine, reduced cardiovascular effects were also seen. These results indicate that selegiline can be used safely even in combination with methamphetamine, as the cardiovascular effects of the drug combination were no greater than either drug alone, and were actually reduced at the higher selegiline dose.

Detection, quantification, metabolism, and behavioral effects of selegiline in horses.

Selegiline ([R]-[-]N,alpha-dimethyl-N-2- propynylphenethylamine or l-deprenyl), an irreversible inhibitor of monoamine oxidase, is a classic antidyskinetic and antiparkinsonian agent widely used in human medicine both as monotherapy and as an adjunct to levodopa therapy. Selegiline is classified by the Association of Racing Commissioners International (ARCI) as a class 2 agent, and is considered to have high abuse potential in racing horses. A highly sensitive LC/MS/MS quantitative analytical method has been developed for selegiline and its potential metabolites amphetamine and methamphetamine using commercially available deuterated analogs of these compounds as internal standards. After administering 40 mg of selegiline orally to two horses, relatively low (<60 ng/ml) concentrations of parent selegiline, amphetamine, and methamphetamine were recovered in urine samples. However, relatively high urinary concentrations of another selegiline metabolite were found, tentatively identified as N- desmethylselegiline. This metabolite was synthesized and found to be indistinguishable from the new metabolite recovered from horse urine, thereby confirming the chemical identity of the equine metabolite. Additionally, analysis of urine samples from four horses dosed with 50 mg of selegiline confirmed that N-desmethylselegiline is the major urinary metabolite of selegiline in horses. In related behavior studies, p.o. and i.v. administration of 30 mg of selegiline produced no significant changes in either locomotor activities or heart rates.

Quantitative analysis of selegiline and three metabolites (N-desmethylselegiline, methamphetamine, and amphetamine) in human plasma by high-performance liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry.

This report describes a sensitive and specific high-performance liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry method for the detection of subnanogram concentrations of selegiline and its three principle metabolites, N-desmethylselegiline, methamphetamine, and amphetamine, in human plasma. The assay has a dynamic range of 0.1-20 ng/mL for selegiline and N-desmethylselegiline (norselegiline) and 0.2-20 ng/mL for methamphetamine and amphetamine. The inter- and intra-assay precision and accuracy varied by less than 11% for all analytes at 0.3, 2.5, and 15 ng/mL and less than 16% at the lower limit of quantitation (0.1 ng/mL for selegiline and norselegiline; and 0.2 ng/mL for methamphetamine and amphetamine). Selegiline and its metabolites showed no significant loss in quantitative accuracy after three freeze/thaw cycles or after up to 6 h at room temperature prior to extraction. Extracted plasma samples retained quantitative accuracy after storage for at least 7 days at -20 degrees C or up to 70 h at room temperature. Methanolic stock solutions were stable for at least 6 h when kept at room temperature or at least 90 days when kept at -20 degrees C.

Effect of concomitant hormone replacement therapy containing estradiol and levonorgestrel on the pharmacokinetics of selegiline.

OBJECTIVE: The aim of this study was to investigate the effect of hormone-replacement therapy (HRT) on the pharmacokinetics of the selective monoamine oxidase B inhibitor selegiline and its primary metabolites desmethylselegiline and l-metamphetamine. METHODS: In this randomised, double-blind, cross-over trial, 12 healthy female subjects received once daily for 10 days either HRT containing 2 mg estradiol valerate and 250 microg levonorgestrel or matched placebo. On day 10, they took a single 10-mg oral dose of selegiline. The serum concentrations of selegiline, desmethylselegiline and metamphetamine were measured for 32 h. RESULTS: There was a 59% difference ( P=0.14) in the area under the serum concentration-time curve (AUC) of selegiline during the HRT compared with the placebo phase, but only a little or no concomitant reduction in the AUC of desmethylselegiline (-7%, P=0.071) or metamphetamine (2%, P=0.614) was observed. Maximum plasma concentration (C(max)) of selegiline was not changed, but a small, statistically significant, reduction in the C(max) of desmethylselegiline (-17%, P=0.03) was seen during the HRT phase. The C(max) of methamphetamine was slightly but not significantly reduced (-5%, P=0.06). The unchanged AUC ratios of desmethylselegiline/selegiline and metamphetamine/selegiline indicate that the primary metabolism of selegiline was not affected by HRT. All study treatments were well tolerated. CONCLUSION: Unlike oral contraceptives, HRT is not likely to have clinically significant pharmacokinetic interaction with selegiline.

Selegiline pharmacokinetics are unaffected by the CYP3A4 inhibitor itraconazole.

OBJECTIVE: To characterise the effects of itraconazole, a potent inhibitor of CYP3A4, on the pharmacokinetics of selegiline in healthy volunteers. METHODS: In this randomised, placebo-controlled crossover study with two phases, 12 healthy volunteers took either 200 mg itraconazole or matched placebo once daily for 4 days. On day 4, a single 10-mg oral dose of selegiline hydrochloride was administered. Serum concentrations of selegiline and its primary metabolites desmethylselegiline and l-methamphetamine were determined up to 32 h. A caffeine test was performed on day 3 of both phases, by measuring the plasma paraxanthine/caffeine concentration ratio 6 h after caffeine intake, to examine the role of CYP1A2 in selegiline pharmacokinetics. In addition, the effects of itraconazole on the metabolism of selegiline in vitro were characterised by using human liver microsomes. RESULTS: Itraconazole had no significant effects on the pharmacokinetic variables of selegiline, desmethylselegiline or l-methamphetamine, with the exception that the AUC of desmethylselegiline was increased by about 10% (P < 0.05). There was a significant correlation between the AUC(desmethylselegiline)/AUC(selegiline) ratio and the paraxanthine/caffeine ratio (r = 0.41; P < 0.05), suggesting involvement of CYP1A2 in the formation of desmethylselegiline. In experiments with human liver microsomes, itraconazole had no inhibitory effect on the formation of either desmethylselegiline or l-methamphetamine from selegiline. CONCLUSIONS: The pharmacokinetics of selegiline in healthy volunteers were unaffected by the potent CYP3A4 inhibitor itraconazole. In addition, itraconazole showed no inhibitory effect on the biotransformation of selegiline to desmethylselegiline and l-methamphetamine by human liver microsomes. These findings suggest that selegiline is not susceptible to interaction with CYP3A4 inhibitors.

Multiple-dose pharmacokinetics of selegiline and desmethylselegiline suggest saturable tissue binding.

The goal of this study was to examine the multiple-dose pharmacokinetics of selegiline and its metabolites desmethylselegiline, 1-methamphetamine, and 1-amphetamine after oral administration of selegiline HCl. Twelve healthy volunteers received 10 mg of selegiline HCl once daily for 8 days. The pharmacokinetic profiles of selegiline and the metabolites were examined from serum samples for 24 hours (i.e., the dosing interval, tau) on days 1, 4, and 8. The results indicated significant apparent accumulation of selegiline and desmethylselegiline during the 8-day period of selegiline administration. The AUC tau S of selegiline and desmethylselegiline were increased 2.7 fold (p < 0.001) and 1.5 fold (p < 0.001), respectively, from day 1 to day 8. However, the half-lives of selegiline (range, 1.5-3.5 h) and desmethylselegiline (range, 3.4-5.3 h) were found to be relatively short. Accordingly, the short half-lives of these compounds failed to predict the apparent accumulation. With both of the 1-amphetamine metabolites of selegiline, steady state was reached by day 4. We suggest that the most likely explanation for the apparent accumulation of selegiline and desmethylselegiline was the saturation of the MAO-B binding sites in tissues, although decreased first-pass metabolism of selegiline cannot be ruled out. The observed increase in selegiline and desmethylselegiline concentrations on multiple dosing is not likely to significantly increase the pharmacodynamic effect or adverse effects of selegiline compared with what has been found after a single 10-mg dose.

Pharmacokinetics of radiotracers in human plasma during positron emission tomography.

Many radiopharmaceuticals for positron emission tomography (PET) are substantially metabolized in peripheral organs. Pharmacological treatments intended to alter cerebral metabolism might also alter radiotracer metabolism, consequently altering the cerebral uptake. First-order rate constants for the metabolism of PET tracers can be calculated by a linear graphical method from the precursor and metabolite concentrations measured in plasma extracts fractionated by HPLC. We tested the effects of specific pharmacological challenges on the plasma kinetics of six tracers used for PET studies of neurotransmission. The rate of O-methylation of circulating [(18)F]fluorodopa, a tracer of dopa decarboxylase activity in brain, was unaffected by pretreatment with amantadine, an antagonist of glutamate receptors. [(11)C]Deprenyl, a tracer of monoamine oxidase activity, was rapidly metabolized to [(11)C]methamphetamine and polar metabolites in healthy volunteers. The net rate constant of this metabolism was three times higher in a group of subjects under treatment for epilepsy, consistent with induction of hepatic microsomal enzymes by antiepileptic drugs. [(11)C]Sch 23390, a ligand for dopamine D1 receptors, was rapidly metabolized to polar metabolites. The net rate constant of metabolism was unaffected by pretreatment with lorazepam. [(11)C]-(S)-Nicotine, a ligand for nicotinic receptors, was rapidly metabolized to [(11)C]-(S)-cotenine, which is less polar than the parent compound. Pretreatment with mazindol, a dopamine uptake inhibitor, was without effect on peripheral metabolism of [(11)C]-(S)-nicotine. [(11)C]WIN 35,428, a tropane derivative which labels dopamine uptake sites, was metabolized to a nonpolar metabolite, but so slowly that the rate constant of this process could not be calculated. [(11)C]Raclopride, a ligand for dopamine D2 receptors, was first metabolized to a nonpolar metabolite, which then yielded two hydrophilic metabolites. The initial metabolic step was substantially blocked by pretreatment with amphetamine, possibly indicative of competitive inhibition of microsomal oxidation. Together, these results indicate that the linear graphic method is useful for estimating the kinetics of the plasma metabolism of many widely used PET tracers. Drug-drug interactions were revealed in subjects treated with specific pharmacological agents prior to tracer administration.

Dose linearity study of selegiline pharmacokinetics after oral administration: evidence for strong drug interaction with female sex steroids.

AIMS: The purpose of this study was to characterize the dose relationship of selegline and desmethylselegiline pharmacokinetics within the selegiline dose range from 5 to 40 mg. METHODS: Eight female subjects, of whom four were using oral contraceptives, ingested a single dose of 5 mg, 10 mg, 20 mg or 40 mg of selegiline HCl in an open four-period randomized study. Concentrations of selegiline and desmethlylselegiline in serum were measured by gas chromatography for 5 h. As it became evident that the use of oral steroids had a drastic effect on selegiline concentrations, the pharmacokinetic analyses were performed separately for oral contraceptive users and those not receiving any concomitant medication. RESULTS: The total AUC and Cmax of selegiline were 10-to 20-fold higher in those subjects taking oral steroids compared with subjects with no concomitant medication; this finding was consistent and statistically significant at all the four dose levels. The dose linearity of selegiline pharmacokinetics failed to be demonstrated in both groups. The AUC and Cmax of desmethylselegiline were only moderately higher (about 1.5-fold; P=NS at each dose level) in the subjects taking oral steroids than in those not receiving concomitant medication. The AUC values of desmethylselegiline increased in a dose linear manner in subjects with no concomitant medication, but not in the oral steroid group. The metabolic ratio (AUC(desmethylselegiline)/AUC(selegiline)) was several-fold lower in the group receiving oral steroids compared with the no-concomitant-medication group (P<0.005 at all the four dose levels). CONCLUSIONS: Concomitant use of oral contraceptives caused a drastic (20-fold) increase in the oral bioavailability of selegiline. The highly significant difference in the metabolic ratio between the groups provides evidence that the mechanism of the interaction between selegiline and female sex steroids involves reduced T-demethylation of selegiline. The present results suggest that concomitant use of selegiline with exogenous female sex steroids should be avoided or the dosage of selegiline should be reduced in order to minimize the risks of selegiline related adverse drug reactions.

l-methamphetamine pharmacokinetics and pharmacodynamics for assessment of in vivo deprenyl-derived l-methamphetamine.

This study evaluated whether the caudate-putamen dopamine response that has been observed after deprenyl administration could be attributed exclusively to metabolically generated l-methamphetamine (l-MeAmp). Brain and plasma levels of deprenyl and l-MeAmp were measured after deprenyl (10 mg/kg s.c.) from 10 to 60 min in conscious rats. Peak caudate-putamen levels were observed for deprenyl (15 nmol/g) at 10 min and for l-MeAmp (3 nmol/g) at 30 min. In a parallel study, l-MeAmp metabolism was evaluated. After l-MeAmp (20 mg/kg s.c.), metabolite levels remained low relative to those of the parent compound: l-amphetamine, approximately 5 to 12%; and para-hydroxy-l-methamphetamine (OH-MeAmp), approximately 0.25%. Accordingly, l-MeAmp was considered to be the primary pharmacologically active deprenyl metabolite. A pharmacokinetic-pharmacodynamic analysis was then used to relate these pharmacokinetic data to the results of previous microdialysis studies in which increases in extracellular dopamine were measured in the caudate-putamen after l-MeAmp (3-18 mg/kg) and after deprenyl (10 mg/kg). Dopamine response-area under curve versus dose plots were generated and used to show that an administered dose of 4 mg/kg l-MeAmp would be necessary to effect a dopamine response-area under curve comparable to that observed after the deprenyl dose. However, the present pharmacokinetic results indicated that l-MeAmp brain levels after deprenyl corresponded to those that would be obtained from 0.4 mg/kg l-MeAmp (i.e., one tenth of the required dose). Collectively, these results suggest that the acute increases in extracellular dopamine observed after deprenyl are not due uniquely to metabolically generated l-MeAmp but also to other actions of deprenyl at the dopamine terminal.

CYP2D6 polymorphism is not crucial for the disposition of selegiline.

OBJECTIVE: To determine the possible impact of CYP2D6 polymorphism on the pharmacokinetics and pharmacodynamics of selegiline. METHODS: Five poor metabolizers and 8 extensive metabolizers of debrisoquin (INN, debrisoquine) were given 10 mg selegiline hydrochloride. The concentrations of selegiline and its main metabolites in serum were determined for 4 days. The pharmacodynamics were quantitated by measuring platelet monoamine oxidase type B activity for 3 weeks. In addition, the effect of selegiline and its main metabolites on the CYP2D6-catalyzed dextromethorphan O-demethylase activity and the effect of quinidine on the metabolism of selegiline were studied in human liver microsomes. RESULTS: Peak serum concentrations of selegiline were reached rapidly and ranged from 1 to 32 nmol/L. The metabolite concentrations were considerably higher and remained so for a longer period. There were no significant differences in the pharmacokinetic parameters of selegiline, desmethylselegiline, and l-amphetamine between poor metabolizers and extensive metabolizers. However, the area under the serum concentration-time curve (AUC) values of l-methamphetamine were, on average, 46% higher (P = .01) in poor metabolizers than in extensive metabolizers. No significant correlations were found between debrisoquin metabolic ratio and AUC values of selegiline or its metabolites, except for l-methamphetamine (rs = 0.90; P < .001). The maximum monoamine oxidase type B inhibition was 97% in both groups. The inhibitory potency of selegiline, desmethylselegiline, and l-methamphetamine toward dextromethorphan O-demethylase was very low (50% inhibitory concentration values from 160 to 580 mumol/L). Quinidine (< or = 100 mumol/L) did not inhibit the formation of desmethylselegiline or l-methamphetamine from selegiline. CONCLUSIONS: CYP2D6 is not important in the primary elimination of selegiline, and the biological effect of selegiline seems to be similar in poor metabolizers and extensive metabolizers of debrisoquin. The inhibitory effect of selegiline and its main metabolites on CYP2D6 activity seems to be negligible.

Pharmacokinetic evaluation of a selegiline pulsatile oral delivery system.

Selegiline is a selective, irreversible inhibitor of MAO-B, used in the treatment of Parkinson's disease, either alone or as an adjunct to L-DOPA. The sole recommended dosing regimen is 5 mg given in the morning and at noon with breakfast and lunch. A pulsatile oral dosage form was developed to mimic the conventional tablet release from two oral administrations separated by 4 h, to permit once-daily dosing and increase compliance. The pharmacokinetics of the pulsatile delivery system was studied in six healthy male volunteers. The plasma concentration-time profile from the pulsatile system of selegiline and metabolites is dissimilar to that obtained from the 5 mg bid administration of the conventional tablet and cannot be considered to be bioequivalent. The initial pulse of the delivery system is rapidly absorbed but to a lesser extent than the conventional regimen; the second pulse exhibits absorption which is delayed and prolonged. The decrease in the selegiline concentration may be due to the less absorptive surface of the lower GI tract which is available to the second pulse. Another reason could be the disparity between the in vitro and in vivo release profiles from the second pulse. Compartmental analysis indicates that the ratio of formation-absorption rate constant for the selegiline to N-desmethylselegiline pathway decreases from 1.57 +/- 1.04 for the first pulse to 0.61 +/- 0.54 for the second pulse of the pulsatile delivery system, suggesting that the upper portion of the GI tract has a greater capacity to convert selegiline to N-desmethylselegiline than the lower GI tract. The lack of in vivo and in vitro correlation is most likely due to site specific absorption/metabolism. Regimen has been previously shown to be a significant factor in estimating the extent of selegiline and metabolite exposure following oral administration. The inequivalence of dosing regimens of the same total daily dose may ultimately be linked to the saturability of gut wall metabolism. This phenomenon may preclude the development of novel delivery systems designed to mimic the recommended dosing regimen of the conventional Eldepryl tablet.

Bioequivalence evaluation of two preparations containing the highly variable compound selegiline (L-deprenyl).

Selegiline, used in the treatment of Parkinson's disease, inhibits the intracerebral degradation of dopamine and the uptake of catecholamines. Due to a high volume of distribution and also a high rate of biotransformation the concentrations of selegiline in plasma are rather low. In addition, there are indications that selegiline binds to erythrocytes. An open, randomized, 2-way cross-over study was performed in 24 healthy male volunteers to determine bioavailability and pharmacokinetic parameters of 2 oral selegiline preparations after single dose administration. Statistical tests were applied to the pharmacokinetic parameters AUCinf, AUC0-8, AUCz, Cmax and tmax. The terminal half-lives t1/2 for selegiline with geometric means of 1.69 h (n = 22) and 1.76 h (n = 21) for treatments A and B and for N-desmethyl-selegiline with geometric means of 1.98 h and 1.96 h for treatments A and B agreed very well. AUCinf of selegiline could be compared between treatments for 14 subjects only. The geometric mean ratio was 97.80% with a 90% confidence interval that ranged from 79.58%-120.17% and thus exceeded the (80%, 125%) range by a very small margin. After correction for the actual dose contained in each of the 2 preparations the geometric mean ratio was calculated to 98.39% with a 90% confidence interval that ranged from 80.06%-120.90% and thus was fully contained within the (80%, 125%) acceptance range. Treatments also agreed very well with respect to AUCinf of N-desmethyl-selegiline, the active metabolite of selegiline, with a geometric mean ratio of 96.14% with a 90% confidence interval that ranged from 92.41%-100.01% so that bioequivalence of the 2 treatments could be shown very clearly with respect to this metabolite. The AUC of N-desmethyl-selegiline in serum is about 6-fold higher than that of the parent drug. It is assessed with low variability. Thus, it is reasonable to base the judgement for or against bioequivalence primarily on the data obtained for the metabolite although "a larger acceptance range may be acceptable if inevitable and clinically acceptable" for the parent compound selegiline which certainly can be classified as a "highly variable compound".

Plasma input function determination for PET using a commercial laboratory robot.

A commercial laboratory robot system (Zymate PyTechnology II Laboratory Automation System) was interfaced to standard and custom laboratory equipment and programmed to perform rapid radiochemical assays necessary for plasma input function determination in quantitative PET studies in humans and baboons. A Zymark XP robot arm was used to carry out two assays: (1) the determination of total plasma radioactivity concentrations in a series of small-volume whole blood samples and (2) the determination of unchanged (parent) radiotracer in plasma using only solid phase extraction methods. Steady state robotic throughput for determination of total plasma radioactivity in whole blood samples (0.350 mL) is 14.3 samples/h, which includes automated centrifugation, pipetting, weighing and radioactivity counting. Robotic throughput for the assay of parent radiotracer in plasma is 4-6 samples/h depending on the radiotracer. Percents of total radioactivities present as parent radiotracers at 60 min, postinjection of 25 +/- 5.0 (N = 25), 26 +/- 6.8 (N = 68), 13 +/- 4.4 (N = 30), 32 +/- 7.2 (N = 18), 16 +/- 4.9 (N = 20), were obtained for carbon-11 labeled benztropine, raclopride, methylphenidate, SR 46349B (trans, 4-[(3Z)3-(2-dimethylamino-ethyl) oxyimino-3 (2-fluorophenyl)propen-1-yl]phenol), and cocaine respectively in baboon plasma and 84 +/- 6.4 (N = 9), 18 +/- 11 (N = 10), 74 +/- 5.7 (N = 118) and 16 +/- 3.7 (N = 18) for carbon-11 labeled benztropine, deprenyl, raclopride, and methylphenidate respectively in human plasma. The automated system has been used for more than 4 years for all plasma analyses for 7 different C-11 labeled compounds used routinely in our laboratory. The robotic radiotracer assay runs unattended and includes automated cleanup procedures that eliminates all human contact with plasma-contaminated containers.

Hair analysis for drugs of abuse. IX. Comparison of deprenyl use and methamphetamine use by hair analysis.

Deprenyl (DPN) and its metabolites, desmethyl deprenyl (desmethyl DPN), methamphetamine (MA) and amphetamine (AP), in the hair of rats and humans dosed with DPN were analyzed by selected ion monitoring of gas chromatograph-mass spectrometry (GC-MS-SIM). After intraperitoneal administration of DPN-HCl to rats (10 mg/kg/d, 10d, n = 3), the area under the concentration versus time curves (AUCs) of DPN and its metabolites in the rat plasma were compared with the concentrations of drugs in rat hair newly grown for 4 weeks. The concentrations of DPN, desmethyl DPN, MA and AP in the rat hair were 0.97 +/- 0.06, 0.68 +/- 0.02, 14.04 +/- 0.54 and 13.20 +/- 1.09 ng/mg, and the ratios of the concentrations in the hair to AUCs in their plasma were 0.05: 0.02: 0.3: 0.2, respectively. This fact suggested that the incorporation rates of DPN and desmethyl DPN into hair from blood were relatively lower than those of MA and AP. The method was applied to determination of the metabolites in scalp hair, beard and urine of humans who orally ingested DPN (15 mg/d, 5 d, n = 3). DPN (trace level), desmethyl DPN (0.17-0.29 ng/mg), MA (1.30-2.25 ng/mg) and AP (0.42-0.99 ng/mg) were detected in the scalp hair collected three weeks after the first intake, while in beard or urine these drugs were detected only for a few days.(ABSTRACT TRUNCATED AT 250 WORDS)

Gas chromatographic procedure for simultaneous determination of selegiline metabolites, amphetamine, methamphetamine and demethyl-deprenyl in pig plasma.

A sensitive assay for the simultaneous quantitative determination of amphetamine, methamphetamine and demethyl-deprenyl in pig plasma is described. NP-Gas chromatography is used to determine the extracted plasma concentrations of the three target compounds as their N-penta-fluoro-benzoyl derivatives. Quantitation is performed using 1-phenyl-2-pentylamine as internal standard. The derivatives are separated on a phenyl-methylsilicone capillary column. Quantitation limit for each target compound was 1.2 ng ml-1. Levels of amphetamine, methamphetamine and demethyl-deprenyl have been determined in plasma of pigs treated with Selegiline in different formulations and doses.