Pharmacokinetics of methylphenidate in preschoolers with attention-deficit/hyperactivity disorder

OBJECTIVE

The aim of this study was to compare the pharmacokinetics of immediate-release methylphenidate (MPH) in preschool and school-aged children with attention-deficit/hyperactivity disorder (ADHD).

METHODS

Preschool children 4-5 years (n = 14) and school-aged children 6-8 years (n = 9) with diagnoses of ADHD were titrated to an effective dose of MPH based on parent, teacher, and clinician ratings in a protocol specified by the Preschoolers with ADHD Treatment Study (PATS) and then attended a laboratory school where the single morning dose of immediate release MPH was administered. Blood samples for measurement of MPH concentrations were obtained predose, and at 1, 2, 4, and 6 hours postdose. A nonlinear model was used to derive three pharmacokinetic (PK) values for analysis: Peak plasma concentration (C(max)), half-life (t(1/2)), and clearance (CL).

RESULTS

The two groups did not differ in the mean mg dose of MPH (p = 0.33), or in the weight-adjusted mg/kg dose (p = 0.20). Dose-normalized C(max) was significantly higher (p = 0.003), and clearance was significantly slower (p = 0.0002) in preschool than in school-aged children.

CONCLUSIONS

In this sample, age significantly affected absorption and metabolism of MPH, so that preschool children had greater exposure than school-aged children to the same weight-adjusted dose. These data suggest additional studies should be performed to characterize age-related differences in PK properties of MPH that may inform practitioners about dosing strategies based on the age and size of children being treated.

Approaches to the development of medications for the treatment of methamphetamine dependence

BACKGROUND

Methamphetamine abuse has become an increasing problem in both the United States and globally with concomitant increases in adverse medical, social and environmental sequelae. Behavioral therapies have been used with some success to treat methamphetamine abusers and dependent individuals, but are not universally efficacious. Methamphetamine has a rich pharmacology that theoretically provides many opportunities for potential pharmacotherapeutic intervention. Nevertheless, there are no approved medications with an indication for treating methamphetamine abusers or addicts at this time.

AIM

To describe briefly how methamphetamine functions and affects function in brain and report how basic researchers and clinicians are attempting to exploit and exploiting this knowledge to discover and develop effective pharmacotherapies.

RESULTS

Scientifically based approaches to medications development by evaluating medications that limit brain exposure to methamphetamine; modulate methamphetamine effects at vesicular monoamine transporter-2 (VMAT-2); or affect dopaminergic, serotonergic, GABAergic, and/or glutamatergic brain pathways that participate in methamphetamine's reinforcing effects are presented.

CONCLUSION

The evidence supports the rationale that pharmacotherapies to decrease methamphetamine use, or reduce craving during abstinence may be developed from altering the pharmacokinetics and pharmacodynamics of methamphetamine or its effects on appetitive systems in the brain.

[Khat--a new drug of abuse in Norway]

BACKGROUND

The stimulating drug, Khat, is a drug of abuse that has become known in Norway due to increased immigration from East-Africa, especially Somalia.

METHOD

Review of recent literature.

RESULTS

Khat is present in leaves from the tree Catha Edulis and is taken by chewing the leaves. The biologically active compounds are cathinone, cathine and norephedrine. Analysis of cathinone in urine can be performed at the Norwegian Institute of Public Health. The effects of khat are similar to, but weaker than those of amphetamine. Khat stimulates the central nervous system causing increased alertness, euphoria and occasionally psychosis, and increases activity in the peripheral sympathetic nervous system leading to palpitations, increased blood pressure, large pupils and red eyes. Tannin in khat damages teeth and causes constipation. With increased use of khat in the society it is important for the clinician to have some knowledge of the effects of khat.

Methylphenidate controlled-delivery capsules (EquasymXL, Metadate CD): a review of its use in the treatment of children and adolescents with attention-deficit hyperactivity disorder

Controlled-delivery methylphenidate (methylphenidate CD) [EquasymXL, Metadate CD], an oral stimulant, is approved in the US and EU to treat children aged>or=6 years who have been diagnosed with attention-deficit hyperactivity disorder (ADHD). Once-daily methylphenidate CD is generally well tolerated and effective in the treatment of children and adolescents with ADHD. Methylphenidate CD resulted in superior control of ADHD symptoms compared with osmotic release oral system (OROS) methylphenidate over a time period corresponding to that of an average school day in a laboratory classroom. In 3-week clinical trials conducted in a community setting, methylphenidate CD was superior to placebo and noninferior to methylphenidate immediate-release (IR) in the treatment of children and adolescents with ADHD. Thus, methylphenidate CD should be considered an important primary treatment on its own or in addition to behavioral and psychosocial interventions, for when a reduction in ADHD symptoms is required during the school day in preference to the evening.

Smokable ("ice", "crystal meth") and non smokable amphetamine-type stimulants: clinical pharmacological and epidemiological issues, with special reference to the UK

"Ice", "crystal meth", is the smokable form of methamphetamine hydrochloride. This paper will comment on the pharmacological, epidemiological, clinical and social issues related to smoking the drug as opposed to either its injection or ingestion. Furthermore, some data related to amphetamines/methamphetamines consumption, request for treatment, seizures, related offences and deaths in the UK (1990-2002) will be offered here. Peak rates, for most indicators, were reached at the end of the '90s, to fall down in the following years. The only indicator which seemed not to show any declining rates is number of deaths, but this may be related to a more general increase in stimulant death rates recently observed in the UK. It is argued that methamphetamines, and particularly "crystal meth", could reach the same prevalence levels of use in the UK as it is already in the US but recent reclassification of the drug to Class A in the UK could help to better control this emerging issue.

Effect of caffeine on quinidine transport to the central nervous system in rats

We studied the effect of caffeine on the transport of quinidine through the blood-brain barrier (BBB) to the central nervous system (CNS) in rats. The anesthetized animals received quinidine in the form of a retrograde intra-arterial bolus injection (15 s) into the right axillary artery 30 min after receiving a subcutaneous injection of caffeine (test group) or physiological solution (control group). Rats were decapitated at 30, 60, 90, 120, and 240 s after quinidine administration. Blood samples were taken from the left jugular vein. Upon washing, the brain, was divided into the brainstem, cerebellum, and cerebral hemispheres to determine the quinidine content in each section, using a standard spectrofluorimetric method. Quninidine attained maximal concentrations in the CNS with a latency compared with that in blood; the CNS values were higher. Quinidine kinetics showed two compartments in the CNS, one consisting of the brainstem and cerebellum, in which quinidine concentrations were higher, and the other the cerebral hemispheres. Caffeine caused a significant deceleration of quinidine transition through the BBB to the CNS.

The Pharmacokinetic Properties of Methamphetamine in Rats with Previous Repeated Exposure to Methamphetamine: The Differences between Long-Evans and Wistar Rats

Repeated treatment with methamphetamine (METH) causes long-term behavioral changes, so-called behavioral sensitization (BS), in humans as well as experimental animals. However, there are no reports as to whether repeated METH treatment can establish BS in stress-sensitive Long-Evans (LE) rats. Thus, we investigated the effect of repeated METH treatment (5 mg/kg x 5 days) on the establishment of BS in LE rats. Wistar (WIS) rats were used as a reference. In LE rats, repeated METH treatment failed to cause BS although it did enhance METH-induced hyperlocomotion in WIS rats. The levels of METH in brain dialysate and the ratio of the area under the concentration-time curve area in plasma to that in brain dialysate was increased in repeated METH-treated WIS rats as reported previously, but not in repeated METH-treated LE rats. METH increases plasma corticosterone (CORT) in both strains. However, the intensity of increment of CORT by repeated METH was lower in LE rats than that in WIS rats. Repeated METH treatment decreased the expression of METH-transposable and CORT-sensitive transporter, organic cation transporter 3 (OCT3), in the brain of WIS rats. However, the intensity of the decrement of OCT3 with repeated METH treatment was similar between both strains. Taken together, these results suggest that the lack of establishment of BS in LE rats might have been caused by the unchanged brain penetration of METH after repeated METH administration, and that the differential CORT response to METH is an important strain difference.

Persistence of tolerance to methamphetamine-induced monoamine deficits

Methamphetamine is a highly addictive and potent stimulant, the use of which has increased significantly in recent years. In addition to the severe behavioral and societal consequences associated with methamphetamine abuse, methamphetamine can cause persistent damage to monoaminergic nerve terminals in rats, as measured by either monoamine concentrations or activity of the rate limiting synthetic enzymes, tyrosine hydroxylase and tryptophan hydroxylase. Repeated, sub-neurotoxic doses of methamphetamine, however, can cause rats to become resistant to the neurotoxic effects of multiple high-dose administrations of methamphetamine; a phenomenon known as tolerance. This study investigates the persistence of tolerance evoked by pretreatment with escalating-dose administrations of methamphetamine. Rats were pretreated over several days with low, escalating doses of methamphetamine, followed by high-dose methamphetamine challenge after variable recovery periods. Results revealed that tolerance to monoaminergic deficits persisted for at least one week, but was completely eliminated by 31 days. There were no differences in the distribution of methamphetamine or its major metabolite, amphetamine, between methamphetamine-pretreated animals and saline-pretreated animals 2 h after the final methamphetamine challenge injection, and there were no regional differences in methamphetamine concentrations between the frontal cortex, hippocampus or striatum. We also observed that while methamphetamine pretreatment attenuated the hyperthermia caused by the high-dose methamphetamine challenge, significant reductions in methamphetamine-induced hyperthermia were not required for the development of tolerance with this regimen.

Escalating dose pretreatment induces pharmacodynamic and not pharmacokinetic tolerance to a subsequent high-dose methamphetamine binge

A major feature of human methamphetamine (METH) abuse is the gradual dose escalation that precedes high-dose exposure. The period of escalating doses (EDs) is likely associated with development of tolerance to aspects of METH's pharmacologic and toxic effects but the relative contributions of pharmacokinetic and pharmacodynamic factors have not been well defined. In our prior studies in rats, we showed that pretreatment with an ED-METH regimen (0.1-4.0 mg/kg over 14 days) attenuated the toxicity of a subsequently administered high-dose METH binge (4 x 6 mg/kg at 2 h interval) that itself produced behavioral stereotypy, increases in core temperature, and decreases in DA system phenotypic markers in caudate-putamen (CP). Using those ED-METH and binge protocols in the present studies, pharmacokinetic and pharmacodynamic parameters that may have contributed to the apparent neuroprotection afforded by ED-METH were assessed. The ED-METH regimen itself reduced [(3)H]WIN35,428 (WIN) binding to the dopamine transporter (DAT) by 15% in CP, but did not affect DA content. During the METH binge, ED-METH pretreated animals showed attenuated increases in core temperature while concurrent microdialysis studies in CP showed a reduced DA response despite unaltered extracellular levels of METH. At 1 h after the binge, concentrations of METH and its metabolite amphetamine in brain and plasma were unaffected by the ED-METH. The results show that ED-METH pretreatment produces reductions in DAT binding and the DA response during a subsequent METH binge by altering pharmacodynamic and not pharmacokinetic parameters.

Human pharmacology of the methamphetamine stereoisomers

OBJECTIVE

To help predict the consequences of precursor regulation, we compared the pharmacokinetics and pharmacodynamics of the methamphetamine (INN, metamfetamine) stereoisomers.

METHODS

In this study 12 methamphetamine abusers received intravenous d-methamphetamine (0.25 and 0.5 mg/kg), l-methamphetamine (0.25 and 0.5 mg/kg), racemic methamphetamine (0.5 mg/kg), or placebo with the use of a 6-session, double-blind, placebo-controlled, balanced crossover design. Pharmacokinetic measures (including area under the plasma concentration-time curve [AUC], elimination half-life, systemic clearance, apparent volume of distribution during the elimination phase, and apparent bioavailability) and pharmacodynamic measures (including heart rate, blood pressure, respiratory rate, and visual analog scale ratings for "intoxication," "good drug effect," and "drug liking") were obtained.

RESULTS

Pharmacokinetic parameters for the individual enantiomers given separately were similar, with dose-proportional increases in AUC and maximum plasma concentration. After racemate administration, the AUC for d-methamphetamine was 30% smaller than that for l-methamphetamine (P = .0085). The elimination half-lives were longer for l-methamphetamine (13.3-15.0 hours) than for d-methamphetamine (10.2-10.7 hours) (P < .0001). Compared with placebo, d-methamphetamine (0.25 mg/kg, 0.5 mg/kg, and racemic) increased the heart rate (P < .0001), blood pressure (P < .0001), and respiratory rate (P < .05), and this increase lasted for 6 hours. The peak heart rate changes after racemic methamphetamine and 0.5 mg/kg d- and l-methamphetamine were similar (18.7 +/- 23.4 beats/min, 13.5 +/- 18.5 beats/min, and 10.7 +/- 10.2 beats/min, respectively), but racemic methamphetamine and 0.5 mg/kg d-methamphetamine increased systolic blood pressure more than 0.5 mg/kg l-methamphetamine (33.4 +/- 17.8 beats/min and 34.5 +/- 18.9 beats/min, respectively, versus 19.5 +/- 11.3 beats/min; P < .01). l-Methamphetamine, 0.5 mg/kg, was psychoactive, producing peak intoxication (46.0 +/- 35.3 versus 30.3 +/- 24.9) and drug liking (47.7 +/- 35.1 versus 28.6 +/- 24.8) ratings similar to 0.5 mg/kg d-methamphetamine, but the effects of l-methamphetamine dissipated more quickly (approximately 3 hours versus 6 hours). The effects of 0.25 mg/kg l-methamphetamine were similar to those of placebo. Racemic methamphetamine was similar to d-methamphetamine with regard to most pharmacodynamic measures.

CONCLUSION

The pharmacokinetics of the methamphetamine enantiomers are similar, but there are substantial pharmacodynamic differences between the isomers. At high doses, l-methamphetamine intoxication is similar to that of d-methamphetamine, but the psychodynamic effects are shorter-lived and less desired by abusers. Racemic and d-methamphetamine have similar effects and would be expected to have comparable abuse liabilities.

Dexmethylphenidate extended release: in attention-deficit hyperactivity disorder

Dexmethylphenidate extended release (XR) is an orally administered, bimodal release, capsule formulation of the active d-enantiomer of methylphenidate (MPH), which inhibits dopamine and norepinephrine (noradrenaline) reuptake to increase their concentration in the extraneuronal space. A single dose of dexmethylphenidate XR mimics the pharmacokinetic profile of two doses of dexmethylphenidate immediate-release formulation administered 4 hours apart, albeit with less fluctuation in plasma concentration. Once-daily dexmethylphenidate XR was more effective than placebo in reducing attention-deficit hyperactivity disorder (ADHD) symptom scores in children, adolescents and adults with ADHD in four randomised, double-blind, placebo-controlled trials of up to 7 weeks' duration. In crossover trials in children (aged 6-12 years), dexmethylphenidate XR 20 mg/day reduced mean ADHD symptom scores 1 hour after administration (by 43% in one trial) and was significantly better than placebo for up to 12 hours. Dexmethylphenidate XR 5-30 mg/day reduced mean ADHD symptom scores by 49%, while scores declined by 16% with placebo in a 7-week trial in children and adolescents (aged 6-17 years). Dexmethylphenidate XR 20, 30 or 40 mg/day reduced ADHD symptom scores by 36-46% versus a 21% reduction with placebo in a 5-week trial in adults (aged 18-60 years). Dexmethylphenidate XR was generally well tolerated in children, adolescents and adults with ADHD, with an adverse-event profile typical of MPH.

Effect of Repeated Cocaine Administration on Detection Times in Oral Fluid and Urine

Detection times reported for single-dose studies may not predict detection times following repeated cocaine dosing. Although repeated cocaine administration can result in drug accumulation and extended excretion time, there is a paucity of data from controlled dosing studies with repeated drug administration. We compared detection times for cocaine and benzoylecgonine (BZE) in oral fluid and BZE in urine following single and repeated cocaine dosing. Two groups of cocaine-experienced subjects participated in these studies. The single-dose group received cocaine by intravenous, intranasal, and smoked administration. The repeated dose group received daily escalating oral cocaine doses culminating in a total of 1,250-2,000 mg. Oral fluid and urine specimens following the last dosing were analyzed by gas chromatography-mass spectrometry. Detection times were determined as the time to the last positive specimen. The effect of repeated dosing was to extend oral fluid detection times for cocaine approximately fourfold and BZE detection times sevenfold, whereas urine BZE detection times were extended twofold. Because cocaine abusers frequently self-administer higher and repeated doses, we conclude that the short detection times observed in single-dose studies underestimate the utility of oral fluid for detection of cocaine abuse in realistic settings.

Advances in psychotropic formulations

BACKGROUND

Successful pharmacotherapy is dependent on several factors. While efficacy is obviously important, other factors that are often overlooked include the availability of optimal dosage forms, treatment compliance and reduction in side effects. A number of innovative delivery systems have been developed to address suboptimal therapy outcomes by enhancing drug delivery, assuring efficacy of treatment, reducing side effects, and improving compliance.

OBJECTIVE

The purpose of this review is to discuss the advances in formulations for various psychotropic agents that have been developed for the treatment of psychiatric illnesses such as depression, attention deficit hyperactivity disorder, schizophrenia and other psychotic disorders.

METHODS

Information was identified via a MEDLINE and EMBASE search of data published between 2002 and 2005 with keywords 'psychotropic', 'atypical antipsychotic', 'antidepressant' or 'anxiolytic' in combination with 'new/novel/advanced formulation/delivery/technology', or 'controlled release/extended release', or 'fast-acting/fast-dissolving/orodispensible', or 'intramuscular/inject'.

RESULTS

In antidepressant therapy, formulations that allow extended release for once-daily and even once-weekly administration, orally disintegrating tablets, and transdermal systems have all been introduced. Long-acting central nervous system stimulants for the treatment of attention deficit hyperactivity disorder eliminate the need for multiple dosing. A number of new formulations of atypical antipsychotic agents have become available, offering important alternatives in certain patient groups. These include rapid-acting intramuscular injections, liquid formulations, and fast-dissolving tablets, all of which are useful options in the acute treatment setting as well as for geriatric and/or pediatric populations. Furthermore, formulations that deliver sustained levels of medications, including a long-acting antipsychotic and a new extended-release oral formulation, are important new developments that may improve compliance and offer efficacy and safety benefits in long-term management.

CONCLUSIONS

New formulations of psychotropics can offer advantages over older formulations in terms of convenience, side-effect profiles, efficacy, and/or a fast onset of action. Treatment-related factors can help to enhance patient's satisfaction with treatment and compliance, thereby improving patient prognosis and outcomes in both acute and outpatient management.

Effect of overuse of the antimigraine combination of indomethacin, prochlorperazine and caffeine (IPC) on the disposition of its components in chronic headache patients

BACKGROUND

The combination of indomethacin, prochlorperazine and caffeine (IPC) is one of the most utilized formulations for the treatment of migraine attacks in Italy. Several patients suffering from chronic headache overuse this symptomatic medication in the attempt to control their headache.

OBJECTIVE

To verify whether overuse of IPC combination by chronic headache patients is associated with modified disposition of its components.

METHODS

We studied indomethacin, prochlorperazine, and caffeine disposition in 34 female subjects suffering from primary headaches, subdivided into four groups: eight migraine patients occasionally using IPC combination suppositories-group 1; nine patients with chronic headache and probable medication-overuse headache, daily taking one or more suppositories of the IPC combination-group 2; 11 migraine patients occasionally using "mild" suppositories of the IPC combination-group 3; six migraine patients occasionally taking tablets of the IPC combination-group 4. The IPC combination habitually used was administered to each patient. Blood samples were taken at baseline and at fixed intervals up to 6h after administration. Plasma levels of indomethacin and prochlorperazine were assayed by high-pressure liquid chromatographic (HPLC) method; caffeine levels were assayed by enzyme multiplied immunoassay test (EMIT). Pharmacokinetic parameters were calculated by means of a computer software (P K Solutions 2.0. Summit Research Services, Montrose, CO, USA).

RESULTS

Half-life of indomethacin was longer, and clearance lower, in group 2 than in the other groups; AUC of indomethacin in group 2 was twice that in group 1 (P<0.05, Newman-Keuls' test). Peak concentrations and AUC(0-->infinity) of caffeine were significantly higher in group 2 than in the other groups (P<0.05, Newman-Keuls' test). We could not define prochlorperazine disposition because it was not detectable in the majority of blood samples.

CONCLUSION

Overuse of IPC combination in chronic headache patients is associated with increased plasma levels of indomethacin and caffeine, and with delayed elimination of indomethacin; the high and sustained concentrations of these drugs may cause rebound headache, organ damages, and perpetuate medication-overuse headache.

Methylphenidate blood levels and therapeutic response in children with attention-deficit hyperactivity disorder: I. Effects of different dosing regimens

BACKGROUND AND PURPOSE

Methylphenidate (MPH) is a drug of choice for treating attention-deficit/hyperactivity disorder (ADHD), although its use has been complicated by its short duration of action. The development of ideal long-acting preparations requires detailed understanding of the pharmacokinetic and pharmacodynamic consequences of complex dosing regimens. The purpose of this study was to ascertain if administration paradigms that produce stable or rising MPH levels alter the rate with which MPH is absorbed, and to determine how effectively long-acting administration paradigms compare with thrice daily administration of immediate-release MPH.

METHOD

Forty-eight boys diagnosed with ADHD (mean age 10.6 +/- 1.1 year) participated in this double-blind, parallel group study to evaluate the pharmacokinetics and efficacy and of 1 mg/kg/day MPH administered in five different paradigms and placebo. Objective measures of activity and attention (McLean Motion Attention Test; M-MAT) and plasma measures of d- and l-MPH were obtained hourly during the course of a 12-hour laboratory session.

RESULTS

The rate of absorption and elimination of d-MPH was dependent on the pattern of administration, particularly on the initial bolus concentration. This suggests that d-MPH may act on the gastrointestinal system to slow absorption of additional d-MPH. There were significant differences among regimens on time course and degree of therapeutic response. Pulsatile administration produced greater improvement than escalating levels.

Efficacy and safety of dexmethylphenidate extended-release capsules in children with attention-deficit/hyperactivity disorder

OBJECTIVE

The efficacy and safety of dexmethylphenidate extended release (d-MPH-ER) was compared to placebo in pediatric patients with attention-deficit/hyperactivity disorder (ADHD).

METHOD

This multicenter, randomized, double-blind, placebo-controlled, parallel-group, two-phase study included 97 patients (ages 6-17 years) with DSM-IV-defined ADHD. The study was carried out between 2001 and 2003. After a 2-week evaluation phase, patients were randomized to d-MPH-ER or placebo for 7 weeks. Flexible d-MPH-ER dosing (30 mg/day) was permitted for 5 weeks, then patients remained on their optimal dose during the last 2 study weeks. The primary efficacy measure was change from baseline to final rating in Conners ADHD/DSM-IV Scale-Teacher version (CADS-T) total subscale score. Secondary efficacy variables included changes from baseline to final visit in CADS-T Inattentive and Hyperactive-Impulsive subscale scores, CADS-P DSM-IV total subscale score and Inattentive and Hyperactive-Impulsive subscale scores, Clinical Global Impressions-Improvement (CGI-I) and CGI-Severity (CGI-S) scale scores, and Child Health Questionnaire Parent Form 50 scores.

RESULTS

d-MPH-ER improved CADS-T total scores significantly compared with placebo (p <.001), and 67.3% of d-MPH-ER patients were rated much improved or very much improved on CGI-I at final visit versus 13.3% of placebo patients (p <.001). More patients taking d-MPH-ER (49.1%) than placebo (25.5%) spontaneously reported adverse events suspected as drug related.

CONCLUSIONS

Once-daily d-MPH-ER was more effective than placebo in the treatment of ADHD in children and adolescents.

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.

Dietary caffeine intake does not affect methotrexate efficacy in patients with rheumatoid arthritis

OBJECTIVE

Methylxanthines, like caffeine, have been thought to reverse the antiinflammatory effects of methotrexate (MTX) in rheumatoid arthritis (RA). We investigated whether patients with RA taking MTX with a higher dietary caffeine intake have a worse clinical response to MTX than those with a lower intake.

METHODS

Patients with RA enrolled in a prospective cohort study and currently taking MTX were divided equally into low, moderate, and high caffeine consumers. MTX clinical response was defined by the Disease Activity Score (DAS)28, Multidimensional Health Assessment Questionnaire (MDHAQ) score, and duration of morning stiffness. Regression models were used to study the relationship between caffeine intake and MTX response adjusting for age, sex, and other relevant variables at study enrollment.

RESULTS

Two hundred and sixty-four patients with RA taking MTX had an average caffeine intake of 211.7 mg and average MTX dose of 16.0 mg/wk. The low caffeine group comprised 87 patients, the moderate 86, and the high 91. In 3 multivariate models, there was no statistical difference in MTX efficacy between groups, as measured by DAS28 score, MDHAQ score, and duration of morning stiffness at study enrollment. Moderate and high caffeine group had higher DAS28 scores, physician's global assessment, and swollen joint counts, but differences were not significant.

CONCLUSION

Caffeine intake among patients taking high doses of MTX for RA did not affect MTX efficacy and RA disease activity over time.

Fluvoxamine impairs single-dose caffeine clearance without altering caffeine pharmacodynamics

BACKGROUND

Coadministration of fluvoxamine impairs the clearance of caffeine and prolongs its elimination half-life, which is attributable to inhibition of CYP1A2 by fluvoxamine. The clinical importance of this interaction is not established.

AIM

To evaluate the effects of fluvoxamine on the kinetics and dynamics of single doses of caffeine.

METHODS

Seven healthy subjects received single 250 mg doses of caffeine (or matching placebo) together with fluvoxamine (four doses of 100 mg over 2 days) or with matching placebo in a double-blind, four-way crossover study. For 24 h after caffeine or placebo administration, plasma caffeine and fluvoxamine concentrations were determined. Psychomotor performance, sedation, and electroencephalographic (EEG) "beta" frequency activity were also assessed.

RESULTS

Fluvoxamine significantly reduced apparent oral clearance of caffeine (105 vs. 9.1 mL min(-1), P < 0.01; mean difference: 95.7 mL min(-1), 95% CI: 54.9-135.6), and prolonged its elimination half-life (4.9 vs. 56 h, P < 0.01; mean difference: 51 h, 95% CI: 26-76). Caffeine produced CNS-stimulating effects compared with placebo. However, psychomotor performance, alertness, or EEG effects attributable to caffeine were not augmented by coadministration of fluvoxamine.

CONCLUSIONS

Fluvoxamine greatly impaired caffeine clearance, but without detectable changes in caffeine pharmacodynamics. However, this study does not rule out possible adverse effects due to extensive accumulation of caffeine with daily ingestion in fluvoxamine-treated individuals.

Contribution of drug doses and conditioning periods to psychomotor stimulant sensitization

RATIONALE

Repeated intermittent administration of psychostimulant drugs such as amphetamine and cocaine can cause sensitization (reverse tolerance) to the locomotor-stimulating actions in rats. Sensitization to the stimulant effects of these drugs might contribute to the development and maintenance of addictive behaviors (e.g. compulsive drug use).

OBJECTIVES

Studies were designed to systematically examine how testing conditions affect the development and expression of locomotor sensitization to cocaine and amphetamine.

METHODS

Rats were treated once daily with intraperitoneal (i.p.) administration of amphetamine (0.5-2.0 mg/kg) or cocaine (5.0-20 mg/kg) and placed in activity chambers for 30, 60, or 120 min. All amphetamine-preexposed rats were challenged with 0.5 mg/kg amphetamine, and all cocaine-preexposed rats were challenged with 5.0 mg/kg cocaine for 120-minute activity tests 2 weeks after the final injection.

RESULTS

Rats treated repeatedly with 2.0 mg/kg amphetamine and tested for 60 min in activity chambers or 20 mg/kg cocaine and tested for 30 min in activity chambers were most active in response to the drug challenge. These time points coincide with the maximal behavioral effects of each drug, as measured after the first injection. In contrast, rats treated with 2.0 mg/kg amphetamine and tested for 30 min or 20 mg/kg cocaine and tested for 120 min were least active in response to the drug challenge.

CONCLUSIONS

Repeated association of the peak behavioral effects of high doses of amphetamine or cocaine with the drug-paired environment produces maximal expression of sensitized locomotor responses. Certain testing conditions appear to disrupt sensitization to these same doses of the drugs.

Modafinil: is it ready for prime time?

Psychostimulants have been used to treat many symptoms associated with advanced cancer. The primary role of psychostimulants in such cases is the treatment of symptoms such as cancer-related fatigue, opioid-induced sedation, depression, and cognitive dysfunction associated with malignancies. These uses for psychostimulants came after approval for treatment of disorders such as attention deficit disorder. Modafinil, a new psychostimulant, is following a similar path after its approval for use in attention deficit disorder in 1998. Modafinil has been used to treat fatigue associated with neurodegenerative disorders such as multiple sclerosis and amyotrophic lateral sclerosis. It is now being increasingly used for cancer-related symptoms targeted by psychostimulants. Preliminary evidence from literature review suggests that modafinil is efficacious in improving opioid-induced sedation, cancer-related fatigue, and depression. There is no evidence to support its use in the treatment of cognitive dysfunction related to cancer or to support its having analgesic properties. Well-designed, randomized, controlled clinical trials are still needed to further elucidate the precise role of this drug in the care of patients with cancer. Specifically, large placebo-controlled trials with modafinil must be conducted in patients with cancer, with specific attention paid to pain control, depression, cognitive function, and adverse effects.

Subjective, behavioral, and physiological effects of acute caffeine in light, nondependent caffeine users

RATIONALE

Caffeine produces mild psychostimulant effects that are thought to underlie its widespread use. However, the direct effects of caffeine are difficult to evaluate in regular users of caffeine because of tolerance and withdrawal. Indeed, some researchers hypothesize that the psychostimulant effects of caffeine are due largely to the reversal of withdrawal and question whether there are direct effects of caffeine consumption upon mood, alertness, or mental performance in nondependent individuals.

OBJECTIVE

This study investigated the physiological, subjective, and behavioral effects of 0, 50, 150, and 450 mg caffeine in 102 light, nondependent caffeine users.

METHODS

Using a within-subjects design, subjects participated in four experimental sessions, in which they received each of the four drug conditions in random order under double blind conditions. Participants completed subjective effects questionnaires and vital signs were measured before and at repeated time points after drug administration. Forty minutes after the capsules were ingested, subjects completed behavioral tasks that included tests of sustained attention, short-term memory, psychomotor performance, and behavioral inhibition.

RESULTS

Caffeine significantly increased blood pressure, and produced feelings of arousal, positive mood, and high. Caffeine increased the number of hits and decreased reaction times in a vigilance task, but impaired performance on a memory task.

CONCLUSION

We confirm that acute doses of caffeine, at levels typically found in a cup of coffee, produce stimulant-like subjective effects and enhance performance in light, nondependent caffeine users. These findings support the idea that the drug has psychoactive effects even in the absence of withdrawal.

Modafinil: new indications for wake promotion

In January 2004, the wake-promoting agent, modafinil, was approved in the US for the treatment of excessive sleepiness (ES) associated with obstructive sleep apnoea/hypopnoea syndrome (OSAHS) and shift-work sleep disorder (SWSD), representing an expansion of its labelling from the initial indication for ES associated with narcolepsy. A total of five randomised, placebo-controlled studies in these three disorders showed statistically significant benefits on various objective measures and subjective estimates of ES, including the Multiple Sleep Latency Test, Maintenance of Wakefulness Test, Epworth Sleepiness Scale and Karolinska Sleepiness Scale. Significant improvement was also seen in overall clinical condition (on the Clinical Global Impression of Change) and measures of sustained attention and reaction time (on the Psychomotor Vigilance Task). The clinical efficacy of modafinil, combined with improved safety over CNS stimulants, has made it the most prescribed medication for the treatment of ES associated with narcolepsy. Modafinil is the only medication approved for ES associated with OSAHS and SWSD (for OSAHS, it is indicated as an adjunct to standard treatments for the under-lying obstruction). Unlike many other medications used for ES, modafinil is not known to be abused. The most common adverse event reported in clinical studies was headaches; most were transient and mild-to-moderate in severity. Modafinil also has the potential for interactions with other drugs metabolised via cytochrome P450 enzyme pathways. Potential obstacles to the use of modafinil include an under-recognition of ES and its consequences. Increased education, both of the public and the medical community, should improve the recognition and therapy of ES.