Levoamphetamine has been used in the treatment of attention deficit hyperactivity disorder (ADHD) both alone and in combination with dextroamphetamine at different ratios.[10][12] Levoamphetamine on its own has been found to be effective in the treatment of ADHD in multiple clinical studies conducted in the 1970s.[10][12] The clinical dosages and potencies of levoamphetamine and dextroamphetamine in the treatment of ADHD have been fairly similar in these older studies.[10][12]
Available forms
Racemic amphetamine
The first patented amphetamine brand, Benzedrine, was a racemic (i.e., equal parts) mixture of the free bases or the more stable sulfate salts of both amphetamine enantiomers (levoamphetamine and dextroamphetamine) that was introduced in the United States in 1934 as an inhaler for treating nasal congestion.[2] It was later realized that the amphetamine enantiomers could treat obesity, narcolepsy, and ADHD.[2][3] Because of the greater central nervous system effect of the dextrorotatory enantiomer (i.e., dextroamphetamine), sold as Dexedrine, prescription of the Benzedrine brand fell and was eventually discontinued.[18] However, in 2012, racemic amphetamine sulfate was reintroduced as the Evekeo brand name.[3][19]
Adderall
Adderall is a 3.1:1 mixture of dextro- to levo- amphetamine base equivalent pharmaceutical that contains equal amounts (by weight) of four salts: dextroamphetamine sulfate, amphetamine sulfate, dextroamphetamine saccharate and amphetamine (D,L)-aspartate monohydrate. This result is a 76% dextroamphetamine to 24% levoamphetamine, or 3⁄4 to 1⁄4 ratio.[20][21]
Evekeo
Evekeo is an FDA-approved medication that contains racemic amphetamine sulfate (i.e., 50% levoamphetamine sulfate and 50% dextroamphetamine sulfate).[3] It is approved for the treatment of narcolepsy, ADHD, and exogenous obesity.[3] The orally disintegrating tablets are approved for the treatment of attention deficit hyperactivity disorder (ADHD) in children and adolescents aged six to 17 years of age.[22]
Other forms
Products using amphetamine base are now marketed. Dyanavel XR, a liquid suspension form became available in 2015, and contains about 24% levoamphetamine.[23]Adzenys XR, an orally dissolving tablet came to market in 2016 and contains 25% levoamphetamine.[24][25]
Levoamphetamine, similarly to dextroamphetamine, acts as a reuptake inhibitor and releasing agent of norepinephrine and dopaminein vitro.[10][14] However, there are differences in potency between the two compounds.[10][14] Levoamphetamine is either similar in potency or somewhat more potent in inducing the release of norepinephrine than dextroamphetamine, whereas dextroamphetamine is approximately 4-fold more potent in inducing the release of dopamine than levoamphetamine.[10] In addition, as a reuptake inhibitor, levoamphetamine is about 3- to 7-fold less potent than dextroamphetamine in inhibiting dopamine reuptake but is only about 2-fold less potent in inhibiting norepinephrine reuptake.[10] Dextroamphetamine is very weak as a reuptake inhibitor of serotonin, whereas levoamphetamine is essentially inactive in this regard.[10] Levoamphetamine and dextroamphetamine are both also relatively weak reversibleinhibitors of monoamine oxidase (MAO) and hence can inhibit catecholaminemetabolism.[10][35][36][37] However, this action may not occur significantly at clinical doses and may only be relevant to high doses.[35]
In rodent studies, both dextroamphetamine and levoamphetamine dose-dependently induce the release of dopamine in the striatum and norepinephrine in the prefrontal cortex.[10] Dextroamphetamine is about 3- to 5-fold more potent in increasing striatal dopamine levels as levoamphetamine in rodents in vivo, whereas the two enantiomers are about equally effective in terms of increasing prefrontal norepinephrine levels.[10] Dextroamphetamine has greater effects on dopamine levels than on norepinephrine levels, whereas levoamphetamine has relatively more balanced effects on dopamine and norepinephrine levels.[10] As with rodent studies, levoamphetamine and dextroamphetamine have been found to be similarly potent in elevating norepinephrine levels in cerebrospinal fluid in monkeys.[38][39] By an uncertain mechanism, the striatal dopamine release of dextroamphetamine in rodents appears to be prolonged by levoamphetamine when the two enantiomers are administered at a 3:1 ratio (though not at a 1:1 ratio).[10]
The catecholamine-releasing effects of levoamphetamine and dextroamphetamine in rodents have a fast onset of action, with a peak of effect after about 30 to 45minutes, are large in magnitude (e.g., 700–1,500% of baseline for dopamine and 400–450% of baseline for norepinephrine), and decline relatively rapidly after the effects reach their maximum.[10] The magnitudes of the effects of amphetamines are greater than those of classical reuptake inhibitors like atomoxetine and bupropion.[10] In addition, unlike with reuptake inhibitors, there is no dose–effectceiling in the case of amphetamines.[10] Although dextroamphetamine is more potent than levoamphetamine, both enantiomers can maximally increase striatal dopamine release by more than 5,000% of baseline.[10][40] This is in contrast to reuptake inhibitors like bupropion and vanoxerine, which have 5- to 10-fold smaller maximal impacts on dopamine levels and, in contrast to amphetamines, were not experienced as stimulating or euphoric.[10]
Dextroamphetamine has greater potency in producing stimulant-like effects in rodents and non-human primates than levoamphetamine.[10] Some rodent studies have found it to be 5- to 10-fold more potent in its stimulant-like effects than levoamphetamine.[14][41][42] Levoamphetamine is also less potent than dextroamphetamine in its anorectic effects in rodents.[14][43] Dextroamphetamine is about 4-fold more potent than levoamphetamine in motivating self-administration in monkeys and is about 2- to 3-fold more potent than levoamphetamine in terms of positive reinforcing effects in humans.[10][7][44] Potency ratios of dextroamphetamine versus levoamphetamine with single doses of 5 to 80mg in terms of psychological effects in humans including stimulation, wakefulness, activation, euphoria, reduction of hyperactivity, and exacerbation of psychosis have ranged from 1:1 to 4:1 in a variety of older clinical studies.[12][note 2][45] With very large doses, ranging from 270 to 640mg, the potency ratios of dextroamphetamine and levoamphetamine in stimulating locomotor activity and inducing amphetamine psychosis in humans have ranged from 1:1 to 2:1 in a couple studies.[12] The differences in potency and dopamine versus norepinephrine release between dextroamphetamine and levoamphetamine are suggestive of dopamine being the primary neurochemical mediator responsible for the stimulant and euphoric effects of these agents.[10]
In addition to inducing norepinephrine release in the brain, levoamphetamine and dextroamphetamine induce the release of epinephrine (adrenaline) in the peripheralsympathetic nervous system and this is related to their cardiovascular effects.[10] Although levoamphetamine is less potent than dextroamphetamine as a stimulant, it is approximately equipotent with dextroamphetamine in producing various peripheral effects, including vasoconstriction, vasopression, and other cardiovascular effects.[14]
Unlike the case of dextroamphetamine versus dextromethamphetamine, in which the latter is more effective than the former, levoamphetamine is substantially more potent as a dopamine releaser and stimulant than levomethamphetamine.[35][50] Conversely, levoamphetamine, levomethamphetamine, and dextroamphetamine are all similar in their potencies as norepinephrine releasers.[35][50]
In addition to its catecholamine-releasing activity, levoamphetamine is also an agonist of the trace amine-associated receptor 1 (TAAR1).[51][52] Levoamphetamine has also been found to act as a catecholaminergic activity enhancer (CAE), notably at much lower concentrations than its catecholamine releasing activity.[53][54][55][56] It is similarly potent to selegiline and levomethamphetamine but is more potent than dextromethamphetamine and dextroamphetamine in this action.[55] The CAE effects of such agents may be mediated by TAAR1 agonism.[57][56]
The oral bioavailability of levoamphetamine has been found to be similar to that of dextroamphetamine.[58]
The time to peak levels of levoamphetamine with immediate-release (IR) formulations of amphetamine ranges from 2.5 to 3.5hours and with extended-release (ER) formulations ranges from 5.3 to 8.2hours depending on the formulation and the study.[5][58] For comparison, the time to peak levels of dextroamphetamine with IR formulations ranges from 2.4 to 3.3hours and with ER formulations ranges from 4.0 to 8.0hours.[5][58] The peak levels of levoamphetamine are proportionally similar to those of dextroamphetamine with administration of amphetamine at varying ratios.[5] With a single oral dose of 10mg racemic amphetamine (a 1:1 ratio of enantiomers, or 5mg dextroamphetamine and 5mg levoamphetamine), peak levels of dextroamphetamine were 14.7ng/mL and peak levels of levoamphetamine were 12.0ng/mL in one study.[5]
Food does not affect the peak levels or overall exposure to levoamphetamine or dextroamphetamine with IR racemic amphetamine.[3] However, time to peak levels was delayed from 2.5hours (range 1.5–6hours) to 4.5hours (range 2.5–8.0hours).[3]
During oral selegiline therapy at a dosage of 10mg/day, circulating levels of levoamphetamine have been found to be 6 to 8ng/mL and levels of levomethamphetamine have been reported to be 9 to 14ng/mL.[7] Although levels of levoamphetamine and levomethamphetamine are relatively low at typical doses of selegiline, they could be clinically relevant and may contribute to the effects and side effects of selegiline.[7]
The plasma protein binding of levoamphetamine is 31.7%, whereas that of dextroamphetamine was 29.0% in the same study.[4]
Metabolism
Levoamphetamine and dextroamphetamine are metabolized via CYP2D6-mediated hydroxylation to produce 4-hydroxyamphetamine and additionally via oxidativedeamination.[3] There are several enzymes involved in the metabolism of amphetamine, of which CYP2D6 is one.[3] Levoamphetamine seems to be metabolized somewhat less efficiently than dextroamphetamine.[58]
The pharmacokinetics of levoamphetamine generated as a metabolite from selegiline have been found not to significantly vary in CYP2D6 poor metabolizers versus extensive metabolizers, suggesting that CYP2D6 may be minimally involved in the clinical metabolism of levoamphetamine.[17][59]
Elimination
The mean elimination half-life of levoamphetamine ranges from 11.7 to 15.2hours in different studies.[5][58][3] Its half-life is somewhat longer than that of dextroamphetamine, with a difference of about 1 to 2hours.[5][6][58] For comparison, in the same studies that reported the preceding values for levoamphetamine's half-life, the half-life of dextroamphetamine ranged from 10.0 to 12.4hours.[5][58][3]
With selegiline at an oral dose of 10mg, levoamphetamine and levomethamphetamine are eliminated in urine and recovery of levoamphetamine is 9 to 30% (or about 1–3mg) while that of levomethamphetamine is 20 to 60% (or about 2–6mg).[7]
Amphetamine, which is a racemic mixture of dextroamphetamine and levoamphetamine, was first discovered in 1887, shortly after the isolation of ephedrine.[65][60] However, it was not until 1927 that amphetamine was synthesized by Gordon Alles and was studied by him in animals and humans.[10] This led to the discovery of the stimulating effects of amphetamine in humans in 1929 after Alles injected himself with 50mg of the drug.[65][10] Levoamphetamine was first introduced in the form of racemic amphetamine (a 1:1 combination of levoamphetamine and dextroamphetamine) under the brand name Benzedrine in 1935.[10] It was indicated for the treatment of narcolepsy, mild depression, parkinsonism, and a variety of other conditions.[10] Dextroamphetamine was found to be the more potent of the two enantiomers of amphetamine and was introduced as an enantiopure drug under the brand name Dexedrine in 1937.[10] Consequent to its lower potency, levoamphetamine has received far less attention than racemic amphetamine or dextroamphetamine.[10]
Levoamphetamine was studied in the treatment of attention deficit hyperactivity disorder (ADHD) in the 1970s and was found to be clinically effective for this condition similarly to dextroamphetamine.[10] As a result, it was marketed as an enantiopure drug under the brand name Cydril for the treatment of ADHD in the 1970s.[10][15] However, it was reported in 1976 that racemic amphetamine was less effective than dextroamphetamine in treating ADHD.[10] As a result of this study, use of racemic amphetamine in the treatment of ADHD dramatically declined in favor of dextroamphetamine.[10] Enantiopure levoamphetamine was eventually discontinued and is no longer available today.[10]
Because selegiline metabolizes into levoamphetamine and levomethamphetamine, people taking selegiline can erroneously test positive for amphetamines on drug tests.[97][98]
Notes
^Synonyms and alternate spellings include: (2R)-1-phenylpropan-2-amine (IUPAC name), levamfetamine (International Nonproprietary Name [INN]), (R)-amphetamine, (−)-amphetamine, l-amphetamine, and L-amphetamine.[8][9]
^Smith & Davis (1977) reviewed 11clinical studies of dextroamphetamine and levoamphetamine including doses and potency ratios in terms of a variety of psychological and behavioral effects.[12] The summaries of these studies are in Table 1 of the paper.[12]
^ abLosacker M, Roehrich J, Hess C (October 2021). "Enantioselective determination of plasma protein binding of common amphetamine-type stimulants". J Pharm Biomed Anal. 205: 114317. doi:10.1016/j.jpba.2021.114317. PMID34419812.
^ abcdefghijklmnMarkowitz JS, Patrick KS (October 2017). "The Clinical Pharmacokinetics of Amphetamines Utilized in the Treatment of Attention-Deficit/Hyperactivity Disorder". J Child Adolesc Psychopharmacol. 27 (8): 678–689. doi:10.1089/cap.2017.0071. PMID28910145.
^ abc"L-Amphetamine". PubChem Compound. United States National Library of Medicine – National Center for Biotechnology Information. 30 December 2017. Retrieved 2 January 2018.
^"R(-)amphetamine". IUPHAR/BPS Guide to Pharmacology. International Union of Basic and Clinical Pharmacology. Retrieved 2 January 2018.
^ abcdeSilverstone T, Wells B (1980). "Clinical Psychopharmacology of Amphetamine and Related Compounds". Amphetamines and Related Stimulants: Chemical, Biological, Clinical, and Sociological Aspects. CRC Press. pp. 147–160. doi:10.1201/9780429279843-10. ISBN978-0-429-27984-3.
^ abcdefghijSmith RC, Davis JM (June 1977). "Comparative effects of d-amphetamine, l-amphetamine, and methylphenidate on mood in man". Psychopharmacology (Berl). 53 (1): 1–12. doi:10.1007/BF00426687. PMID407607.
^ abcArnold LE, Wender PH, McCloskey K, Snyder SH (December 1972). "Levoamphetamine and dextroamphetamine: comparative efficacy in the hyperkinetic syndrome. Assessment by target symptoms". Arch Gen Psychiatry. 27 (6): 816–22. doi:10.1001/archpsyc.1972.01750300078015. PMID4564954.
^ abcdeKraemer T, Maurer HH (April 2002). "Toxicokinetics of amphetamines: metabolism and toxicokinetic data of designer drugs, amphetamine, methamphetamine, and their N-alkyl derivatives". Ther Drug Monit. 24 (2): 277–89. doi:10.1097/00007691-200204000-00009. PMID11897973.
^ abcRothman RB, Vu N, Partilla JS, Roth BL, Hufeisen SJ, Compton-Toth BA, et al. (2003). "In vitro characterization of ephedrine-related stereoisomers at biogenic amine transporters and the receptorome reveals selective actions as norepinephrine transporter substrates". J. Pharmacol. Exp. Ther. 307 (1): 138–45. doi:10.1124/jpet.103.053975. PMID12954796. S2CID19015584.
^Clarke D (1980). "Amphetamine and monoamine oxidase inhibition: an old idea gains new acceptance". Trends in Pharmacological Sciences. 1 (2): 312–313. doi:10.1016/0165-6147(80)90032-2.
^Miller HH, Clarke DE (1978). "In vitro inhibition of monoamine oxidase types A and B by d- and l-amphetamine". Communications in Psychopharmacology. 2 (4): 319–325. PMID729356.
^Ziegler MG (1989). "Catecholamine Measurement in Behavioral Research". Handbook of Research Methods in Cardiovascular Behavioral Medicine. Boston, MA: Springer US. pp. 167–183. doi:10.1007/978-1-4899-0906-0_11. ISBN978-1-4899-0908-4.
^Ziegler MG, Lake CR, Ebert MH (August 1979). "Norepinephrine elevations in cerebrospinal fluid after d- and l-amphetamine". European Journal of Pharmacology. 57 (2–3): 127–133. doi:10.1016/0014-2999(79)90358-3. PMID114399.
^Cheetham SC, Kulkarni RS, Rowley HL, Heal DJ (2007). The SH rat model of ADHD has profoundly different catecholaminergic responses to amphetamine's enantiomers compared with Sprague-Dawleys. Neuroscience 2007, San Diego, CA, Nov 3-7, 2007. Society for Neuroscience. Archived from the original on 27 July 2024. Both d- and l-[amphetamine (AMP)] evoked rapid increases in extraneuronal concentrations of [noradrenaline (NA)] and [dopamine (DA)] that reached a maximum 30 or 60 min after administration. However, the [spontaneously hypertensive rats (SHRs)] were much more responsive to AMP's enantiomers than the [Sprague-Dawleys (SDs)]. Thus, 3 mg/kg d-AMP produced a peak increase in [prefrontal cortex (PFC)] NA of 649 ± 87% (p<0.001) in SHRs compared with 198 ± 39% (p<0.05) in SDs; the corresponding figures for [striatal (STR)] DA were 4898 ± 1912% (p<0.001) versus 1606 ± 391% (p<0.001). At 9 mg/kg, l-AMP maximally increased NA efflux by 1069 ± 105% (p<0.001) in SHRs compared with 157 ± 24% (p<0.01) in SDs; the DA figures were 3294 ± 691% (p<0.001) versus 459 ± 107% (p<0.001).
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† References for all endogenous human TAAR1 ligands are provided at List of trace amines
‡ References for synthetic TAAR1 agonists can be found at TAAR1 or in the associated compound articles. For TAAR2 and TAAR5 agonists and inverse agonists, see TAAR for references.