Although d -amphetamine is a competitive substrate for DAT rather than a classical reuptake inhibitor, these same principles apply to its pharmacological action. Thus, the rate and magnitude of neuronal dopamine release produced by amphetamine is absolutely dependent on the rate and concentration of drug that reaches DAT sites in the brain Heal et al.
There has been little research conducted in humans on this kinetic course using brain imaging, but it seems likely that the same rules apply. Consistent with the findings in microdialysis experiments, d -amphetamine has greater potency than l- amphetamine to evoke stimulant-like subjective effects in rats Schechter, and behavioural activation in primates Scraggs and Ridley, Both amphetamine isomers have been shown to serve as positive reinforcers in animals i. The same is true for human subjects Smith and Davis, ; Van Kammen and Murphy, , with the d -isomer once again being two to threefold more potent than the l -isomer Risner, ; Smith and Davis, ; Van Kammen and Murphy, ; Yokel and Pickens, As indicated above, it is the combination of the rapid rate of increase and magnitude of effect that accounts for the powerful stimulant effects of amphetamine.
Although l- amphetamine is the less potent of the two isomers, its pharmacological efficacy should not be underestimated. Cheetham et al. In contrast, the maximum increases in dopamine efflux achieved by classical dopamine reuptake inhibitors e. The importance of the rate of increase of synaptic dopamine concentrations to the induction of stimulation and euphoria is exemplified by the observation that bupropion and GBR were not experienced as stimulant or euphoriant by normal volunteers Hamilton et al.
In those bupropion and GBR trials where d -amphetamine was employed as the positive control, its stimulant, energising and reinforcing effects were unequivocally recognised by normal subjects and recreational drug users Hamilton et al. In previous reviews, we have extensively described the efficacy and safety of stimulant and non-stimulant drugs used in the management of ADHD and compared the relative merits of each Heal et al.
This analysis has revealed that the stimulants, including amphetamine, are still accepted to be the most efficacious drugs available. On the other hand, the innovations in formulation technology and drug delivery systems have made significant strides forward in improving the clinical management of ADHD. All of the stimulants have biological half-lives that require at least twice-daily dosing to deliver efficacy over 12—14 h.
ADHD is characterised by inattention, distractibility, working memory deficits and impulsivity, and as such, subjects with this disorder are particularly unsuited to compliance with rigid dosing schedules. Examples of once-daily amphetamine medications include MES-amphetamine XR and the d- amphetamine prodrug, lisdexamfetamine. As briefly discussed earlier in the review, lisdexamfetamine is the first amphetamine prodrug to have been approved for use in treating ADHD.
This profile is consistent with lisdexamfetamine being pharmacologically inactive. Although there is no definitive information on the subject, the large molecular size and polar characteristics of lisdexamfetamine predict that the parent molecule is unlikely to cross the blood—brain barrier.
In vitro experiments revealed that the metabolism of lisdexamfetamine to d -amphetamine occurs in red blood cells by rate-limited enzymatic hydrolysis Pennick, Lack of affinity of lisdexamfetamine for a portfolio of abuse-related molecular targets. The locomotor activity of the rats was also simultaneously monitored.
After administration of equivalent doses of lisdexamfetamine and IR d- amphetamine 1. These observations are entirely consistent with the postulated rate-limited enzymatic conversion of lisdexamfetamine to d- amphetamine.
This difference in PK characteristics had a profound impact on the pharmacological effects of these two compounds in rats Figure 5. Lisdexamfetamine produced a gradual and sustained increase in striatal dopamine efflux, whereas the increase produced by IR d- amphetamine was faster in onset, reaching a peak at 30 min, and it subsequently declined more rapidly Figure 5.
In the case of lisdexamfetamine, the more gradual and sustained increase in dopamine efflux was associated with a much smaller and visibly delayed locomotor response. Using the hysteresis analysis in a more conventional way to explore the relationship between the plasma concentration of d- amphetamine and the functional response, there was a clear difference between the two compounds with an anticlockwise hysteresis for lisdexamfetamine and no hysteresis for IR d- amphetamine Rowley et al.
The anticlockwise hysteresis shows that the functional effect of lisdexamfetamine was greater as the plasma concentration of d- amphetamine was falling, whilst the lack of hysteresis with IR d- amphetamine demonstrates that as soon as the plasma concentration of the drug starts to decline, so does its pharmacological effect.
The clinical importance of these findings will be discussed in the following section. The efficacy of lisdexamfetamine has been demonstrated in a number of randomised, double-blind, placebo-controlled clinical trials in ADHD in children, adolescents Biederman et al.
Since lisdexamfetamine has been the subject of several reviews Dew and Kollins, ; Heal et al. Biederman et al. Following a 3-week, open-label run-in period where the dose of MES-amphetamine XR was optimised to 10, 20 or 30 mg once a day, subjects were then randomised into a 3-way double-blind, placebo-controlled crossover trial. They received their optimal dose of MES-amphetamine XR, an equivalent dose of lisdexamfetamine in terms of d- amphetamine base, or placebo.
On the primary and secondary efficacy variables of behaviour, attention and problem solving, lisdexamfetamine delivered equivalent or better efficacy than MES-amphetamine XR with both drugs being maximally effective at 2 h post-dose Biederman et al. However, on the problem-solving endpoints, it was also evident that lisdexamfetamine maintained its maximum effect for at least 12 h, whereas the effect of MES-amphetamine XR showed a clear decline after 6—8 h Biederman et al.
An exceptionally long duration of effect of lisdexamfetamine was observed by Wigal et al. A post-hoc analysis of the data also showed that the sex and age of the subjects had no significant influence on the efficacy of lisdexamfetamine Wigal et al. These observations fit well with the PD profile of lisdexamfetamine in the microdialysis experiments.
Another way to produce a more gentle increase of brain dopamine is to bind d -amphetamine to a support. Another factor that almost certainly contributes to the consistently high level of therapeutic efficacy observed with lisdexamfetamine treatment is the very low inter- and intra-subject variability in the plasma concentration of d -amphetamine observed after administration of the prodrug compared with traditionally formulated stimulants, including beaded and osmotic-release formulations.
Once again, the reproducible pharmacokinetics of its active metabolite, d -amphetamine, are probably due to the rate-limited, enzymatic cleavage of the precursor molecule that occurs primarily in red blood cells Ermer et al. In two earlier published studies, Jasinski and Krishnan compared the subjective effects of lisdexamfetamine and IR d -amphetamine in drug-experienced human volunteers when these compounds were administered intravenously Jasinski and Krishnan, a and orally Jasinski and Krishnan, b.
In the trial where they compared these compounds after oral administration, IR d -amphetamine 40 mg However, the peak effect of the higher dose of lisdexamfetamine was even more delayed, at 4. Both compounds yielded equivalent AUC h values, but compared with the equivalent dose of IR d -amphetamine, the C max for plasma d- amphetamine was threefold smaller for lisdexamfetamine and the t max was threefold greater Jasinski and Krishnan, b.
From these results, it can be concluded that although in terms of d- amphetamine base equivalents lisdexamfetamine is clearly less potent than IR d -amphetamine, it does nonetheless produce d -amphetamine-like subjective effects in man. Although increasing the dose of lisdexamfetamine enhanced its efficacy, it also progressively delayed its time of peak effect.
Furthermore, switching to the intravenous route for lisdexamfetamine appeared to have relatively little influence on the abuse potential of the prodrug. To explore this possibility further, we performed a post-hoc analysis on the data in the original clinical study reports Jasinski, , NRP A02; Jasinski, , NRP A03 to compare pharmacodynamics and pharmacokinetics of lisdexamfetamine when given by the clinical route oral versus one of those favoured by recreational abusers intravenous.
This topic is of particular importance because lisdexamfetamine has very high aqueous solubility, making the prodrug very easy to extract. This result shows that the subjective effects of lisdexamfetamine were not enhanced when the drug was given intravenously. Blood pressure measurements are useful objective measures of the PD effects of sympathomimetic drugs. Compared with placebo, 50 mg lisdexamfetamine significantly increased the peak systolic blood pressure when administered both orally and intravenously and diastolic blood pressure when given orally Figure 6.
What is also evident from the data in Figure 6 is that the magnitude of increases in systolic and diastolic blood pressures was not statistically different after oral or intravenous administration of lisdexamfetamine. A comparison of the pharmacodynamics and pharmacokinetics of orally versus intravenously administered 50 mg lisdexamfetamine.
A comparison of the mean peak increases in systolic and diastolic blood pressure produced by intravenous versus oral administration of 50 mg lisdexamfetamine. Means are adjusted for differences between the treatment groups at baseline. SEM was calculated from the residuals of the statistical model. There were no significant differences between the peak increases in systolic and diastolic blood pressure evoked by 50 mg lisdexamfetamine administered intravenously and orally. The PK parameters for plasma d- amphetamine observed after oral versus intravenous administration of lisdexamfetamine 50 mg are also summarised in Table 4.
The AUC 0-infinity shows that the overall drug exposure was identical irrespective of the route of administration. Importantly, intravenous injection of lisdexamfetamine did not either significantly increase the C max of d- amphetamine, nor did it significantly reduce its t max. Although the AUC These findings strengthen the view that the unusual mechanism for metabolic conversion of lisdexamfetamine to d- amphetamine has important implications for its liability for recreational abuse.
The subjective effects of a 50 mg dose of lisdexamfetamine were identical in magnitude when the prodrug was administered orally or by intravenous injection, demonstrating that intravenous injection did not enhance the pharmacological potency of lisdexamfetamine in the CNS.
The increases in systolic and diastolic blood pressures after oral or by intravenous administration of lisdexamfetamine were also identical, confirming by objective and quantifiable physiological measures that the intravenous injection route did not enhance its pharmacological potency.
These results are complemented by those of Ermer et al. Although the findings do not demonstrate that lisdexamfetamine lacks any potential for recreational abuse, they do indicate that its attractiveness to abusers will be reduced compared with IR d -amphetamine.
Based on these data, the likelihood that lisdexamfetamine will be widely abused by the intravenous or nasal route is very low.
It is now just over a hundred years since amphetamine was first discovered. In that period amphetamine has transformed from a drug that was widely available without prescription for the treatment of a broad range of disorders to being highly restricted Controlled Drugs that, in Europe at least, have all but disappeared from the formularies in many countries. The very clear links between molecular structure and pharmacological mode of action and, in turn, efficacy and safety in humans, makes amphetamine a textbook example of translational validity.
Amphetamine ranks alongside methylphenidate as the most effective drugs available for the management of ADHD, and the advances that have been made in developing genuine once-daily medications have addressed some of the problems of therapeutic coverage, whilst at the same time reducing the risk of diversion and recreational abuse. The authors wish to state that the material presented in this review reflect only their views and not necessarily those of the Shire Pharmaceuticals.
Conflict of interest: The authors declare that there are no conflict of interest. Funding: Part of this research was funded by Shire Pharmaceuticals. National Center for Biotechnology Information , U. Journal of Psychopharmacology Oxford, England. J Psychopharmacol. Author information Copyright and License information Disclaimer. Email: ku. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article has been cited by other articles in PMC. Abstract Amphetamine was discovered over years ago. Keywords: Abuse liability, amphetamine, attention deficit hyperactivity disorder ADHD , drug formulations, lisdexamfetamine, microdialysis. Open in a separate window. Figure 1. Table 1. Amphetamines — past and present. IR: immediate release; XR: extended release.
A clinical perspective on the use of amphetamine in the treatment of ADHD ADHD is arguably the most under-diagnosed and treated of all psychiatric disorders, especially in adults Kooij et al. The pharmacology of amphetamine The chemical structure, particularly the 3-dimensional 3-D structure of amphetamine, is critical in determining the pharmacological effects that underpin its considerable therapeutic benefits and also its liability for recreational abuse.
Figure 2. Actions comprising the pharmacological mechanism of amphetamine. Figure 3. Table 2. Figure 4. Figure 5. Clinical implications The primary action of amphetamine is to increase synaptic concentrations of monoamine neurotransmitters, thereby indirectly enhancing noradrenergic, dopaminergic neurotransmission in the CNS.
But in contrast to the effective measures employed against precursor smuggling, controls on chemicals used to make precursors are far more lax; some aren't even controlled at all. So, given the profitability of the trade in amphetamines, it has become cost-effective for drug gangs to become their own chemical companies.
The rise in worldwide pre-precursor production has inspired stricter controls on the chemicals. Large seizures of pre-precursors have taken place in Belgium, Poland, and the Netherlands over the last three years, with some seizures netting over one ton of the chemicals. Despite these successes, the effectiveness of pre-precursor controls is limited. As the chemicals become ever more fundamental, and concurrently serve many legitimate uses in commercial and industrial products, regulation will be increasingly difficult.
Having to monitor an expanding array of drugs and substances makes it more likely that law enforcement will let some slip through the gaps. The use of pre-precursors in amphetamine production is a relatively new trend, and traditional methods of of trafficking still dominate.
But as pressure from law enforcement increases and the cost of smuggling or diverting precursors rises, more groups may be pushed to produce precursors themselves, creating a boom in the illicit pre-precursor market.
And get our latest investigations on organized crime and corruption delivered straight to your inbox. We use cookies to improve your experience by storing data about your preferences, your device or your browsing session. Beginning in the s, abuse of amphetamine skyrocketed as illegal methamphetamine production took off. This period also saw a surge in prescriptions of amphetamine drugs for treating attention deficit disorders.
Abuse and medical use of amphetamines has continued to increase over the past decade. S Food and Drug Administration banned the sale of any supplement containing ephedrine, which had become a common supplement for athletes. The ban stemmed from a rise in the number of health issues related to the drug and several deaths of people looking to increase endurance and lose weight with ephedrine supplements, according to Harvard Health Publishing. In the U. However, it's difficult to accurately track methamphetamine use, because the drug is manufactured and distributed illegally.
Additionally, the majority of methamphetamines come from outside the U. In Portland, Oregon, more than people died from methamphetamine use in ; that was three times more than just 10 years earlier, the Times reported.
Portland was just one such example of a location that inundated by methamphetamine use. While the physical changes amphetamines cause in the brain are permanent, several therapeutic treatment programs that can help people overcome their addiction. The most-successful treatments include addiction education, family counseling, cognitive behavior therapy and peer-support groups. This article is for informational purposes only and is not meant to offer medical advice. Live Science.
Rachel Ross.
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