Development and validation of a high-performance liquid chromatography-tandem mass spectrometry assay for the quantification of Dexamphetamine in human plasma

Dexamphetamine is registered for the treatment of attention deficit hyperactivity disorder and narcolepsy. Current research has highlighted the possible application of dexamphetamine in the treatment of cocaine addiction. To support clinical pharmacologic trials a new simple, fast, and sensitive assay for the quantification of dexamphetamine in human plasma using liquid chromatography tandem mass spectrometry (LC-MS/MS) was developed. Additionally, it is the first reported LC-MS assay with these advantages to be fully validated according to current US FDA and EMA guidelines. Human plasma samples were collected on an outpatient basis and stored at nominally -20°C. The analyte and the internal standard (stable isotopically labeled dexamphetamine) were extracted using double liquid-liquid extraction (plasma-organic and organic-water) combined with snap-freezing. The aqueous extract was filtered and 2μL was injected on a C18-column with isocratic elution and analyzed with triple quadrupole mass spectrometry in positive ion mode. The validated concentration range was from 2.5-250ng/mL and the calibration model was linear. A weighting factor of 1 over the squared concentration was applied and correlation coefficients of 0.997 or better were obtained. At all concentrations the bias was within ±15% of the nominal concentrations and imprecision was ≤15%. All results were within the acceptance criteria of the latest US FDA guidance and EMA guidelines on method validation. In conclusion, the developed method to quantify dexamphetamine in human plasma was fit to support a clinical study with slow-release dexamphetamine.

Multiple daily-dose pharmacokinetics of lisdexamfetamine dimesylate in healthy adult volunteers

OBJECTIVE

To evaluate the pharmacokinetics of lisdexamfetamine dimesylate (LDX; Vyvanse) in fasting healthy adult volunteers.

BACKGROUND

LDX is the first pro-drug stimulant and is indicated for the treatment of attention-deficit/hyperactivity disorder. LDX was developed with the goal of providing an extended effect that is consistent throughout the day, with a reduced potential for abuse, overdose toxicity, and drug tampering.

METHODS

This was an open-label, multipledose phase 1 study. LDX 70 mg/d was administered in the morning to 12 subjects for 7 days. Twenty blood samples were drawn during the study. Descriptive statistics were used for pharmacokinetic parameters.

RESULTS

Based on C(min), steady-state d-amphetamine concentration (20.6 ng/mL) was reached by day 5, whereas LDX was undetectable, and 95% of the d-amphetamine was eliminated within 48 hours following the final dose on day 7. At steady state, d-amphetamine achieved a mean +/- standard deviation C(max) of 90.1 +/- 29.6 ng/mL, with a median T(max) of 3.0 hours. The AUC(0-inf) for d-amphetamine was 1453 +/- 645.7 ng.h/mL. Complete elimination of the pro-drug occurred approximately 6 hours following the final dose on day 7. Adverse events were mild to moderate and similar to other oral amphetamines.

CONCLUSIONS

This study describes the steady-state pharmacokinetics of LDX, a new pro-drug stimulant. Possible study limitations include an open-label design and a small sample size.

Development and validation of a liquid chromatography/tandem mass spectrometry assay for the simultaneous determination of d-amphetamine and diphenhydramine in beagle dog plasma and its application to a pharmacokinetic study

A new drug, quick-acting anti-motion capsule (QAAMC) composed of d-amphetamine sulfate, dimenhydrinate and ginger extraction has been studied for anti-motion-sickness use. We have developed a sensitive, specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the quantitative determination of d-amphetamine and diphenhydramine, the main effective components of the QAAMC, using pseudoephedrine as the internal standard. The analytes and internal standard were isolated from 200 microL plasma samples by a simple liquid-liquid extraction (LLE). Reverse-phase HPLC separation was accomplished on a Zorbax SB-C18 column (100 mm x 3.0 mm, 3.5 microm) with a mobile phase composed of methanol-water-formic acid (65:35:0.5, v/v/v) at a flow rate of 0.2 mL/min. The method had a chromatographic total run time of 5 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 136.0-->91.0 (D-amphetamine), 256.0-->167.0 (diphenhydramine) and 166.1-->148.0 (IS) used for quantitation. The method was sensitive with a lower limit of quantitation (LLOQ) of 0.5 ng/mL for d-amphetamine and 1 ng/mL for diphenhydramine, with good linearity in the range 0.5-200 ng/mL for D-amphetamine and 1-500 ng/mL for diphenhydramine (r(2)> or =0.9990). All the validation data, such as accuracy, precision, and inter-day repeatability, were within the required limits. The method was successfully applied to pharmacokinetic study of the QAAMC in beagle dogs.

The role of the polymorphic efflux transporter P-glycoprotein on the brain accumulation of d-methylphenidate and d-amphetamine

The psychostimulant medications methylphenidate (MPH) and amphetamine (AMP), available in various ratios or enantiopure formulations of their respective active dextrorotary isomers, constitute the majority of agents used in the treatment of attention-deficit/hyperactivity disorder (ADHD). Substantial interindividual variability occurs in their pharmacokinetics and tolerability. Little is known regarding the potential role of drug transporters such as P-glycoprotein (P-gp) in psychostimulant pharmacokinetics and response. Therefore, experiments were carried out in P-gp knockout (KO) mice versus wild-type (WT) mice after intraperitoneal dosing (2.5 mg/kg) of d-MPH or (3.0 mg/kg) of d-AMP. After the administration of each psychostimulant, locomotor activity was assessed at 30-min intervals for 2 h. Total brain-to-plasma drug concentration ratios were determined at 10-, 30-, and 80-min postdosing time-points. The results showed no statistically supported genotypic difference in d-AMP-induced locomotor activity stimulation or in brain-to-plasma ratio of d-AMP. As for d-MPH, the P-gp KO mice had 33% higher brain concentrations (p < 0.05) and 67.5% higher brain-to-plasma ratios (p < 0.01) than WT controls at the 10-min postdosing timepoint. However, in spite of elevated brain concentrations, d-MPH-induced locomotor activity increase was attenuated for P-gp compared with that for WT mice. These data indicate that P-gp has no apparent effect on the pharmacokinetics and pharmacodynamics of d-AMP. In addition, d-MPH is a relatively weak P-gp substrate, and its entry into the brain may be limited by P-gp. Furthermore, the mechanism by which d-MPH-induced locomotor activity was attenuated in P-gp KO mice remains to be elucidated.

Single- and multiple-dose pharmacokinetics of an oral mixed amphetamine salts extended-release formulation in adults

OBJECTIVES

Assess the bioavailability of mixed amphetamine salts extended-release (MAS XR) 30-mg capsules and the dose proportionality of pharmacokinetic measures for MAS XR 20, 40, and 60 mg.

METHODS

Study A, an open-label single-period study, and Study B, a randomized, open-label, three-way crossover study, were conducted in healthy adults in a clinical research unit. In Study A, 20 subjects received a single MAS XR 30-mg capsule by mouth daily for 7 days. In Study B, 12 subjects received single oral doses of MAS XR 20, 40, and 60 mg separated by 7-14-day washout periods.

FINDINGS

Plasma dextroamphetamine (d-amphetamine) and levoamphetamine (l-amphetamine) concentrations were measured using a validated LC-MS/MS method. In Study A, a 3:1 ratio of d-amphetamine to l-amphetamine was observed for AUC0-inf and Cmax. Tmax was 4.2 and 4.3 hours for d-amphetamine to l-amphetamine, respectively. In Study B, for d- and l-amphetamine, statistically significant differences were observed for AUC0-t, AUC0-inf, and Cmax between all doses; there was a linear relationship between pharmacokinetic variables and dose and Tmax was similar for each isomer (range: 4.5-5.3 hours) with all given MAS XR doses.

CONCLUSION

The extent of exposure as assessed by mean AUC0-24 and Cmax reflected the 3:1 ratio of d-amphetamine to l-amphetamine in MAS XR 30-mg capsules. The pharmacokinetic profiles of MAS XR 20, 40, and 60 mg are dose proportional for the isomers.

An evaluation of the sensitivity of the standardised field sobriety tests to detect the presence of amphetamine

RATIONALE

The Standardised Field Sobriety Tests (SFSTs), designed and validated to assess impairment associated with alcohol intoxication, are currently being employed by the Victoria Police (Australia) for the identification of driving impairment associated with drugs other than alcohol.

OBJECTIVES

The aim of this study was to evaluate whether the SFSTs are a sensitive measure for identifying the presence of dexamphetamine and methamphetamine.

METHODS

Three studies each employed a repeated-measures, counterbalanced, double-blind placebo-controlled design. In each study, 20 healthy volunteers completed two treatment conditions: either 0.42 mg/kg d,l-dexamphetamine and placebo, 0.42 mg/kg d,l-methamphetamine and placebo, or 0.42 mg/kg d-methamphetamine and placebo. Performance was assessed using the SFSTs, consisting of the Horizontal Gaze Nystagmus test, the Walk and Turn test, and the One Leg Stand test. Blood and saliva samples were obtained before and immediately after the administration of the SFSTs (120 and 170 min post drug administration).

RESULTS

At 120 and 170 min post drug administration, d,l-dexamphetamine blood levels were 83.16 and 98.42 ng/ml, respectively; d,l-methamphetamine levels were 90 and 95 ng/ml, respectively; and d-methamphetamine blood levels were 72 and 67 ng/ml, respectively. None of the three amphetamine doses impaired performance on the SFSTs. Using the SFSTs, the presence of dexamphetamine was identified in 5% of cases, d-methamphetamine in 5%, and d,l-methamphetamine in 0% of cases.

CONCLUSIONS

Under these conditions, the SFSTs are not a sensitive measure for detecting the presence of low levels of amphetamine.

Decreasing amphetamine-induced dopamine release by acute phenylalanine/tyrosine depletion: A PET/[11C]raclopride study in healthy men

Acute phenylalanine/tyrosine depletion (APTD) has been proposed as a new method to decrease catecholamine neurotransmission safely, rapidly, and transiently. Validation studies in animals are encouraging, but direct evidence in human brain is lacking. In the present study, we tested the hypothesis that APTD would reduce stimulated dopamine (DA) release, as assessed by positron emission tomography (PET) and changes in [(11)C]raclopride binding potential (BP), a measure of DA D2/D3 receptor availability. Eight healthy men received two PET scans, both following d-amphetamine, 0.3 mg/kg, p.o., an oral dose known to decrease [(11)C]raclopride BP in ventral striatum. On the morning before each scan, subjects ingested, in counter-balanced order, an amino-acid mixture deficient in the catecholamine precursors, phenylalanine, and tyrosine, or a nutritionally balanced mixture. Brain parametric images were generated by calculating [(11)C]raclopride BP at each voxel. BP values were extracted from the t-map (threshold: t=4.2, equivalent to p<0.05, Bonferroni corrected) and a priori identified regions of interest from each individual's coregistered magnetic resonance images. Both receptor parametric mapping and region of interest analyses indicated that [(11)C]raclopride binding was significantly different on the two test days in the ventral striatum (peak t=6.31; x=-25, y=-8, and z=0.1). In the t-map defined cluster, [(11)C]raclopride BP values were 11.8+/-11.9% higher during the APTD session (p<0.05). The reduction in d-amphetamine-induced DA release exhibited a linear association with the reduction in plasma tyrosine levels (r=-0.82, p<0.05). Together, the results provide the first direct evidence that APTD decreases stimulated DA release in human brain. APTD may be a suitable new tool for human neuropsychopharmacology research.

Relationship of plasma amphetamine levels to physiological, subjective, cognitive and biochemical measures in healthy volunteers

Acute administration of the stimulant dextro-amphetamine produces multiple physiological, subjective cognitive and biochemical changes. These effects are similar to those seen in mania, and may be a useful model for mania. The aim of the present study was more fully to determine the multiple effects of dextro-amphetamine and to relate these to changes in plasma levels of the drug. In a double-blind, placebo-controlled crossover study in 25 healthy volunteers (ages 18-45), the effects of 25 mg of oral dextro-amphetamine were examined. Physiological, subjective, cognitive changes, concentrations of amino acids and metabolites of biogenic amines period were related to changes in plasma amphetamine concentrations over 500 min. Peak concentrations of dextro-amphetamine occurred at 2.5-3.5 h post-administration and levels decreased to 75% of peak value after 500 min. The results from the present study indicate that the subjective psychological, cognitive and blood pressure changes frequently did not mirror the time course of plasma levels of the drug. Thus, there was no clear-cut relationship between plasma levels and effects. In addition, dextro-amphetamine caused no significant changes in amino acids or amino metabolite concentrations. In conclusion, while dextro-amphetamine administration definitely causes several changes which are seen in mania, there remain some physiological and metabolic differences between these two conditions.

Steady-state pharmacokinetics and tolerability of modafinil administered alone or in combination with dextroamphetamine in healthy volunteers

The potential for a drug-drug interaction between modafinil and dextroamphetamine, each at steady state, was investigated in an open-label, randomized, single-period studyin 32 healthy male and female volunteers. All subjects received modafinil orally once daily for 28 days (200 mg on Days 1-7; 400 mg on Days 8-28). On Days 22 to 28, half of the subjects also received dextroamphetamine (20 mg) orally 7 hours after modafinil. Samples for pharmacokinetic (PK) profiling were obtained on Days 21 and 28. The mean changes in PK parameters for modafinil and its two circulating metabolites between the two groups were not statistically significantly different, except Cmax for modafinil acid. Adverse events obtained in the two groups were similar and mild or moderate in nature. The results indicate that administration of low-dose dextroamphetamine in this dosing regimen does not alter the steady-state pharmacokinetics of modafinil. The combination has a similar tolerability profile as modafinil alone.

Laboratory validation study of drug evaluation and classification program: alprazolam, d-amphetamine, codeine, and marijuana

The Drug Evaluation and Classification (DEC) program is used by police agencies to identify drivers impaired because of drug use and to determine the class(es) of drug causing the impairment. The primary goal of this study was to determine the validity of the DEC evaluation in predicting whether research volunteers were administered alprazolam, d-amphetamine, codeine, or marijuana. A secondary goal was to determine the accuracy of Drug Recognition Examiners (DREs) in detecting if subjects were dosed with these drugs. Community volunteers (n = 48) were administered alprazolam (0, 1, 2 mg), d-amphetamine (0, 12.5, 25 mg), codeine (0, 60, 120 mg), or marijuana (0, 3.58% THC) in a double-blind, randomized, between-subject design. A single drug dose or placebo was administered at each experimental session, and blood samples were obtained before and after dosing. With the exception of marijuana, plasma drug concentration was at or near maximum during the DEC evaluation. The ability of the DEC evaluation to predict the intake of alprazolam, d-amphetamine, codeine, or marijuana was optimal when using 2-7 variables from the evaluation. DREs' decisions of impairment were consistent with the administration of any active drug in 76% of cases, and their drug class decisions were consistent with toxicology in 32% of cases, according to standards of the International Association of Chiefs of Police. These findings suggest that the DEC evaluation can be used to predict accurately acute administration of alprazolam, d-amphetamine, codeine, and marijuana and that predictions of drug use may be improved by focusing on a subset of variables.

Pharmacokinetic and pharmacodynamic analysis of the actions of D-amphetamine and D-methamphetamine on the dopamine terminal

To establish whether the actions of D-amphetamine (Amp) and D-methamphetamine (MeAmp) on the striatal dopamine system were equipotent, pharmacokinetic profiles of each drug were applied to an analysis of their respective induced dopamine efflux profiles. Amp or MeAmp (1 and 5 mg/kg i.v.) was administered to chloral hydrate-anesthetized rats; plasma and brain kinetics were then assessed from 5 to 60 min. Dose-dependent increases in Amp and MeAmp plasma levels resulted in proportional increases in striatum levels that were equivalent for both drugs; elimination rates also were similar and were characterized by a first-order decay process. After MeAmp administration, low levels of brain MeAmp metabolites were detected throughout the 1-hr time period; relative to MeAmp, Amp and p-hydroxy-MeAmp levels were less than 10 and 1%, respectively. The drug-induced dopamine efflux profiles in the striatum were characterized by microdialysis; Amp and MeAmp (1, 2.5 and 5 mg/kg i.v.) effected equivalent, dose-dependent increases in extracellular dopamine levels. For both drugs at 5- and 10-min postinjection, increases in drug striatum levels preceded increases in dopamine efflux. In contrast, from the time of the peak dopamine responses observed at 10 to 20 min until the end of the study at 90 min, changes in striatal drug levels were correlated with extracellular dopamine levels; this correlation was similar for both drugs. These results indicate that Amp and MeAmp pharmacokinetics and their subsequent dopamine responses in the striatum are equivalent. The pharmacokinetic analysis can be extended to the interpretation of other comparative studies that assess effects of Amp and MeAmp.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of d-amphetamine in biological samples using high-performance liquid chromatography after precolumn derivatization with o-phthaldialdehyde and 3-mercaptopropionic acid

An HPLC method is described for the determination of amphetamine using fluorometric detection after derivatization with o-phthaldialdehyde and 3-mercaptopropionic acid. This procedure is more sensitive (detection limit 370 fmol in microdialysate buffer standards, 1.5 pmol in extracted plasma and tissue samples) than most of the previous methods described for the determination of amphetamine with HPLC-fluorescence detection. Due to the stability of the derivative it is also suitable for autosampling after manual derivatization. Investigators currently using o-phthaldialdehyde derivatization and fluorometric detection for amino acid determination should be able to rapidly implement this method.

The amphetamine challenge test correlates with affective lability in healthy volunteers

The personality dimension of mood lability may be reflected in the mood response to the amphetamine challenge test. To test this hypothesis, the investigators acutely administered oral dextroamphetamine or placebo in a double-blind fashion to 11 normal control subjects who were free of any psychiatric disorders. Increased scores on interview and self-report measures of mood change during the challenge test, particularly increases in depression and anxiety, positively correlated with scores on the Affective Lability Scale, a measure of the lifetime personality trait of mood lability. These findings suggest that a dysphoric response to amphetamine is a marker for affective lability and that it may be useful to study this trait in patients with personality disorders.

The prolactin response to d- and l-fenfluramine and to d-amphetamine in human subjects

Twelve normal male volunteers took part in a double-blind placebo-controlled study to measure the effects of d- and l-fenfluramine singly and in combination with d-amphetamine on plasma prolactin levels. Both isomers of fenfluramine were found to differ significantly in their effects from d-amphetamine, and from placebo, causing prolactin levels to rise. d-Fenfluramine produced the greatest change. There were minor differences between the level of activity of the two drugs when given in conjunction with d-amphetamine. d-Amphetamine produced a non-significant reduction in prolactin secretion. The neurochemical basis for the experimental findings reported is considered, with special reference to the use of d-fenfluramine as a specific serotonergic probe.

Abolition of latent inhibition by a single 5 mg dose of d-amphetamine in man

The performance of healthy volunteer subjects on an auditory latent inhibition (LI) paradigm was assessed following administration of a single oral dose of d-amphetamine or placebo. It was predicted that a low (5 mg), but not a high (10 mg), dose of d-amphetamine would disrupt LI. The prediction was supported with left ear presentation of the preexposed stimulus only. When the preexposed stimulus was presented to the right ear the predicted pattern of findings was not obtained. It is concluded that the dopaminergic system is involved in the mediation of LI in man and it is speculated that the interaction between amphetamine dose and ear of presentation of the preexposed stimulus may reflect normally occurring dopaminergic hemisphere asymmetry.

The effect of amphetamine on regional cerebral blood flow during cognitive activation in schizophrenia

To explore the role of monoamines on cerebral function during specific prefrontal cognitive activation, we conducted a double-blind placebo-controlled crossover study of the effects of 0.25 mg/kg oral dextroamphetamine on regional cerebral blood flow (rCBF) as determined by 133Xe dynamic single-photon emission-computed tomography (SPECT) during performance of the Wisconsin Card Sorting Test (WCST) and a sensorimotor control task. Ten patients with chronic schizophrenia who had been stabilized for at least 6 weeks on 0.4 mg/kg haloperidol participated. Amphetamine produced a modest, nonsignificant, task-independent, global reduction in rCBF. However, the effect of amphetamine on task-dependent activation of rCBF (i.e., WCST minus control task) was striking. Whereas on placebo no significant activation of rCBF was seen during the WCST compared with the control task, on amphetamine significant activation of the left dorsolateral prefrontal cortex (DLPFC) occurred (p = 0.0006). Both the mean number of correct responses and the mean conceptual level increased (p less than 0.05) with amphetamine relative to placebo. In addition, with amphetamine, but not with placebo, a significant correlation (p = -0.71; p less than 0.05) emerged between activation of DLPFC rCBF and performance of the WCST task. These findings are consistent with animal models in which mesocortical catecholaminergic activity modulates and enhances the signal-to-noise ratio of evoked cortical activity.

Pharmacokinetic consequences of spaceflight

Spaceflight induces a wide range of physiological and biochemical changes, including disruption of gastrointestinal (GI) function, fluid and electrolyte balance, circulatory dynamics, and organ blood flow, as well as hormonal and metabolic perturbations. Any of these changes can influence the pharmacokinetics and pharmacodynamics of in-flight medication. That spaceflight may alter bioavailability was proposed when drugs prescribed to alleviate space motion sickness (SMS) had little therapeutic effect. Characterization of the pharmacokinetic and/or pharmacodynamic behavior of operationally critical medications is crucial for their effective use in flight; as a first step, we sought to determine whether drugs administered in space actually reach the site of action at concentrations sufficient to elicit the therapeutic response.

Dextroamphetamine-induced arousal in human subjects as a model for mania

Because of the practical difficulties which arise in studying manic patients, a reproducible model for mania using human subjects would be a valuable adjunct to research in this condition. Dextroamphetamine, given as a single oral 20 mg dose, fulfils the criteria for such a model in that there are very close similarities between the changes which occur after dextroamphetamine and those which have been observed in mania in terms of subjective experience, physiological and endocrine changes, and response to pharmacological agents.

Psychostimulant plasma concentration and learning performance

Six normal adults were administered an oral dose of 0.25 mg/kg of dextroamphetamine, and their learning performance on a paired-associate task and drug blood level were measured at hourly intervals for 5 hours postdrug intake. Dextroamphetamine plasma concentration peaked at 2 to 3 hours following the oral dose, and learning errors were lowest during the same period. A self-report measure of mood also yielded findings consistent with peak plasma concentration. Similar findings obtained with hyperactive children treated with methylphenidate (Ritalin) lead the authors to conclude that the paired-associate learning task may be useful as an indicator of psychostimulant plasma levels, as a predictor of clinical response after an acute dose, and as a highly controlled task for studying psychostimulant drug effects on learning.

Studies in the mechanism of phenylethylamine uptake by rabbit erythrocytes

The mechanism of phenylethylamine (PEA) uptake by in vitro rabbit erythrocyte preparations involve both a larger component of passive diffusion and an Na+-dependent facilitated transport system. This is reflected by the fast rate and lack of saturation of PEA erythrocyte uptake, and by the decrease in PEA tissue/medium ratio when the amine was incubated in an Na+-free medium or in the presence of ouabain. Results obtained after the addition of iodoacetamide or by the use of glucose-free medium suggest the Na+-K+ gradient as the driving force responsible for operation of the carrier mechanism. Preliminary results indicate that amphetamine PEA share a similar mechanism for their uptake by rabbit erythrocytes. At the levels normally present in rabbit blood (c. 1 X 10(-8)M), about one-third of the PEA is found in the serum and only a very small portion of it (less than 1%) is present as the "biologically active" non-ionized amine. Most of the remaining phenylethylamine is bound to plasma protein or inside the erythrocytes.

Computer analyzed EEG in amphetamine-responsive hyperactive children

Electroencephalographic (EEG) frequency analysis and evoked potentials (EPs) of 27 hyperactive children were examined to determine which, if any, of these electrophysiological parameters might be useful for the selection of those children likely to respond to stimulant medication. The children were treated with placebo, d-amphetamine, and l-amphetamine in double-blind fashion and in random order. EEGs for frequency analysis, visual EPs, and auditory EPs were obtained before and during treatment. Off medication, hyperactive responders to amphetamine had higher predominant beta frequency and shorter latencies of some EP waves than did nonresponders. Although the findings reported here would not select all responders, they would allow the exclusion of most nonresponders.

Kinetic studies on the entry of d-amphetamine into the central nervous system: I. Cerebrospinal fluid

After intravenous administration to rats, d-amphetamine undergoes a rapid distributive phase (k approximately 0.99.min-1) during which the drug is lost from plasma. The rate of entry into the cerebrospinal fluid (CSF) is also rapid (k approximately 0.58.min-1), suggesting that the drug moves directly from plasma to CSF. Entry of drug into CSF is mainly by diffusion. Neither active transport associated with CSF formation nor active transport independent of CSF formation is quantitatively important. After intracerebroventricular injection, d-amphetamine disappears from CSF relatively slowly (k approximately 0.063.min-1). Egress of drug is mainly by diffusion (k approximately 0.044.min-1), although active transport associated with bulk absorption does play a measurable role (k approximately 0.019.min-1). At steady state, the concentration of free drug in plasma and in CSF is equivalent.

Effect of anorexic drugs on food intake and the micro-structure of eating in human subjects

Human volunteer subjects of normal weight received oral doses of (+)amphetamine (10 mg) or (+/-)fenfluramine (30 mg and 60 mg) together with a placebo control according to a within-subjects design. The effects of these treatments were monitored by measuring food intake in a test meal, subjective ratings of hunger motivation and the micro-structure of eating behaviour abstracted from videotaped recordings of the test meal. Various measures of the rate of feeding were computed from these recordings. Amphetamine and fenfluramine (60 mg) showed generally similar effects on food intake and on the subjective experience of hunger, but displayed differing actions on the fine structure of eating. Amphetamine increased latency to initiation of eating and increased the rate of food ingestion, whilst fenfluramine slowed the local rate of eating and eliminated the characteristic decline in the rate of feeding across the course of a meal. These findings display certain resemblance to the results of animal experiments involving similar pharmacological manipulations and emphasise the importance of measuring rate of feeding in animal and human studies. The results of this study suggest that the micro-analysis of feeding behaviour not only provides a tool for understanding systems involved in the modulation of food consumption but also reveals information which may be helpful for the use of drugs in the treatment of obesity.

Comparison of radioimmunoassay and gas chromatographic mass spectrometric assay for d-amphetamine

Quantification of low levels of psychotropic drugs (10(-7) to 10(-9) g ml-1) in small volumes of plasma requires sensitive and accurate methods. Validation of these methods is best achieved by comparing results obtained using several techniques. In this study, amphetamine levels in plasma were measured using gas chromatography mass spectrometry and radioimmunoassay. Correlation of the results obtained by the two methods was found to be positive and high (R = 0.9822). The average coefficient of variation between assays for gas chromatography mass spectrometry was 5.8% and for radioimmunoassay was 12.3%, while the average coefficient of variation within assays for gas chromatography mass spectrometry was 4.9% and for radioimmunoassay 6.9%. Although gas chromatography mass spectrometry was 1.9 times more sensitive than radioimmunoassay, for most purposes, the convenience of the radioimmunoassay method outweights the technical superiority of gas chromatography mass spectrometry.

Plasma levels of d-amphetamine in hyperactive children. Serial behavior and motor responses

Amphetamine has been clearly documented to be an efficacious treatment for hyperactive children. The pharmacokinetics of amphetamine have been studied in adults, but not in children. Sixteen male children who scored greater than 2SD from norms on Factors I and IV of Conner's Teacher Rating Scale and who were not excluded for reasons to do with medical or psychiatric conditions, intelligence, or age, had a plasma d-amphetamine apparent elimination half-life of 6.8 +/- 0.5h. Peak plasma level occurred between 3 and 4h (62.7 +/- 3.8 and 65.9 +/- 3.6 ng/ml, respectively). Six of these children had a repeat study and there were no significant differences within subject in apparent elimination half-lives and attained peak blood levels. The variation in plasma levels was greater during absorption than during elimination. Both behavioral and motor activity responses as analyzed by differences between amphetamine and placebo days (by paired t-tests) indicate significant responses between hours 1--4; however, these responses do not correlate with plasma amphetamine levels; they occur during the absorption phase. The decreased response to later similar plasma levels of d-amphetamine may be related to depletion of catecholamine stores, to replacement by a 'false neurotransmitter' metabolite of amphetamine, or to alteration in receptor sensitivity.

Tachyphylaxis to d-amphetamine: a reexamination of the phenomenon

Single or multiple injections of d-amphetamine (10(-3)--10(0) mg/kg) were administered to rats, after which steady-state blood levels of drug were determined. After single injections of d-amphetamine, there was a linear relationship between amount of administered drug and steady-state blood level of drug. After multiple injections of d-amphetamine, steady-state blood levels of drug conformed to the equation D = Doe--kappaepsilont. An attempt was made to relate steady-state blood levels of drug to steady-state responses (e.g., increase in blood pressure or heart rate). At steady-state, amphetamine-induced pressor responses were too small to be analyzed, but tachycardic responses were easily analyzed. It was found that steady-state heart rate responses were dose related to steady-state blood levels of drug. This was true regardless of whether d-amphetamine was administered once or repeatedly. The data indicate that, when tested in rats at sub-toxic doses, d-amphetamine does not evoke tachyphylaxis in relation to heart rate responses which are measured under steady-state conditions.

Kinetics, salivary excretion of amphetamine isomers, and effect of urinary pH

Amphetamine was administered to healthy subjects as the racemic mixture and as (+)- and (-)-isomers under conditions of urine acidification and alkalinization. Plasma and saliva concentration of each isomer was measured and the kinetics of the individual isomers were determined. (+)-amphetamine was eliminated more rapidly than the (-)-isomer. The difference in half-life between isomers was maximal under basic urinary pH conditions. Saliva amphetamine levels were higher than plasma levels and in the postabsorptive phase were predictably proportional to plasma drug levels.

Time-action and behavioral effects of amphetamine, ethanol, and acetylmethadol

As time increased between drug administration and the start of experimental sessions, effects of drugs on food-maintained responding in rhesus monkeys increased to a maximum and then decreased. d-Amphetamine, ethanol, and alpha-l-acetylmethadol (LAAM) generally decreased high response rates in one component of a chain schedule, while very low response rates in another component were increased reliably only by ethanol. The time of peak LAAM and ethanol concentrations in blood or plasma corresponded with or overlapped the time of maximal behavioral effect, while the time of maximal behavioral effect with d-amphetamine occurred somewhat prior to the time of peak plasma-amphetamine concentration. With d-amphetamine and perhaps with ethanol, effects on operant responding were greater after 30-min pretreatment intervals than after six-hr pretreatment intervals despite higher plasma or blood concentrations at six hours than at 30 min.

Amphetamines, growth hormone and narcolepsy

1 Plasma amphetamine and growth hormone levels have been measured in eight normal and twenty-six narcoleptic subjects following a single dose of (+)-amphetamine (20 mg) or (-)-amphetamine (20 mg) by mouth. 2 Peak plasma levels and the shape of the plasma amphetamine-time curve were similar with both isomers in normal and narcoleptic subjects. 3 In most normal subjects both (+)-and (-)-amphetamine (20 mg) caused an increase in the plasma concentration of growth hormone. The two isomers were approximately equipotent in this respect. Neither (+)- nor (-)-amphetamine (20 mg) caused an increase in plasma growth hormone concentration in narcoleptics. 4 Following amphetamine (30 mg), two of six narcoleptic subjects had an increase in plasma growth hormone concentration. 5 Levodopa (250 mg) with (-)-alpha-methyldopa hydrazine 25 mg (Sinemet) by mouth, caused a rise in plasma growth hormone concentration in most normal subjects. The magnitude of the Sinemet-induced rise in plasma growth hormone concentration in narcoleptics was less than in normal subjects.

Effects of dopaminergic agonists and antagonists of feeding in intact and 6-hydroxydopamine-treated rats

The effects on food intake of treatments which alter central dopaminergic function were examined in rats. Doses of d-amphetamine that increased the conversion of 3H-tyrosine to 3H-dopamine in the brain were found to decrease food intake, an effect that was reduced by the systemic administration of the dopaminergic antagonists alpha-methyltyrosine, haloperidol or spiroperidol. The dopaminergic agonists, apomorphine, dopa, cocaine and methylphenidated, also reduced feeding and these effects were attenuated by low doses of spiroperidol. In larger doses, spiroperidol itself decreased feeding, and this effect was potentiated by alpha-methyltyrosine. The ability of dopaminergic agonists and antagonists to inhibit food intake was also observed in rats treated with 6-hhyroxydopamine so as to produce a selective 83% depletion of dopamine. In these animals, d-amphetamine was found to be less effective as an anorexic agent, whereas dopa, apomorphine, alpha-methyltyrosine and spiroperidol each was more effective in reducing food intake. These alterations in sensitivity may reflect neurochemical changes which occur at residual dopaminergic synapses after subtotal lesions of dopaminergic neurons. We conclude that both increases and decreases in central dopaminergic activity can reduce feeding and propose that some intermediate rate of dopamine release provides an optimal level of neuronal activity for feeding by the hungry animal.

Radioimmunoassay of amphetamines in rat parotid saliva

Amphetamines, a commonly abused class of drugs, have been detected in various biological specimens, in particular, urine and blood. However, little information is available concerning the detection of these drugs in saliva. This investigation, utilizing the rat salivary secretions, has been attempted to establish the ability of amphetamines to be secreted in saliva and to determine the feasibility of using radioimmunoassay (RIA) for drug detection in saliva. The results of this investigation showed that (1) d-amphetamine and methamphetamine decreased salivary flow, (2) after d-amphetamine RIA tests were demonstrated in both saliva and plasma for a period of fifty minutes, and (3) positive RIA reactions were obtained by the following metamphetamine metabolites: amphetamine, 4-hydroxynorephedrine and 4-hydroxyamphetamine. Methamphetamine and 4-hydroxy-N-methylamphetamine were found to be non-reactive in the radioimmunoassay procedure. The results indicate that saliva could be radioimmunoassayed for the detection of amphetamine or amphetamine derivatives after the administration of either d-amphetamine and methamphetamine.

Specificity of an antibody directed against d-methamphetamine. Studies with rigid and nonrigid analogs

The specificity of an antibody directed against d-(S)-methamphetamine (MA) was determined by competitive binding assay with more than 50 compounds-metabolites, homologs, and analogs of amphetamine. The antibody appears to be specific both for the side chain and the aromatic ring of d-(S)-amphetamine (A). The basic requirements for a compound to be bound to the antibody are (a) an aromatic ring, (b) a basic nitrogen, and (c) a two-carbon chain between the aromatic ring and the nitrogen. A transoid conformation for the phenethylamine skeleton is preferred. The interaction of the antibody with compounds differing from MA or A in side-chain substitutions was directly proportional to the closeness of their structure to MA and/or A. The antibody exhibited greatly reduced affinity for ring-substituted analogs of A; the p-hydroxy metabolite of A did not bind to the antibody. A radioimmunoassay of A is described; it was utilized to study the disposition of A in dogs.

Comparison of the time course of the anorectic effect of fenfluramine and amphetamine with drug levels in blood

Time courses of the suppressive effects on food intake of (+)-amphetamine and (plus or minus)-fenfluramine in deprived rats were found to be different. Amphetamine displayed a potent initial action which rapidly decayed, and this behavioural effect was consistent with the measured blood concentration of amphetamine which showed a peak at 1 h followed by rapid clearance. For fenfluramine, the initial suppression of eating was maintained over several hours and was, for the first hour, related to the blood concentration of fenfluramine but later to an active metabolite, norfenfluramine. The study shows how drug-induced changes in feeding behaviour fluctuate over time and illustrate how single measures of food intake may overlook information about the effectiveness of anorectic drugs.

Kinetics and metabolism of amphetamine in the brain of rats of different ages

The kinetics and tissue distribution of amphetamine and its metabolites p-hydroxyamphetamine (p-PH-A) and p-hydroxynorephedrine (p-OH-NE) were investigated in young adult (3-4 months) and old (20-25 months) male rats, after i.p. injection of 5 mg/kg tritium labelled D-amphetamine. The concentrations of these drugs were determined in plasma, cerebral cortex, brainstem and hypothalamus, by thin layer chromatography. 1. From 60 min up to 4 hrs after injection of amphetamine the concentration of amphetamine in plasma and brain tissue of old rats was significantly (P less than 0.05 higher than in young adult animals. In both age groups the levels of amphetamine in cerebral cortex greater than brain stem greater than hypothalamus. 2. The blood-brain barrier is permutle to p-OH-A; 10 to 20 min afer i.v. injection of 10 muCi/kg of p-OH-A (10 mCi/m mole) the ratio of brain/blood plasma was found to be 1:3. The half life of p-OH-A in blood plasma was almost identical after injection of amphetamine and p-OH-A (90 min and 98 min respectively). 3. The levels of p-OH-NE in different brain areas were significantly lower (P less than 0.05) in old animals than in young adult rats 4 hrs after application of amphetamine. This metabolite of amphetamine shows a higher concentration in the hypothalamus earlier than in other brain regions.