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Trade names | Many [1] [2] |
Other names | PPA; Norephedrine; α-Methyl-β-hydroxyphenethylamine; β-Hydroxyamphetamine |
AHFS/Drugs.com | Multum Consumer Information |
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Routes of administration | By mouth |
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Pharmacokinetic data | |
Bioavailability | High [4] |
Protein binding | 20% [5] [4] |
Metabolism | Minimal (3–4%) [5] [6] [4] |
Metabolites | • Hippuric acid (~4%) [4] [5] • 4-Hydroxynorephedrine (≤1%) [5] [4] |
Onset of action | Oral: 15–30 minutes [4] [7] |
Elimination half-life | 4 (3.7–4.9) hours [4] [7] [6] [8] |
Duration of action | Oral: 3 hours [4] [7] |
Excretion | Urine: 90% (unchanged) [7] [4] |
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CompTox Dashboard (EPA) | |
ECHA InfoCard | 100.035.349 |
Chemical and physical data | |
Formula | C9H13NO |
Molar mass | 151.209 g·mol−1 |
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Phenylpropanolamine (PPA), sold under many brand names, is a sympathomimetic agent which is used as a decongestant and appetite suppressant. [9] [1] [10] [11] It was previously commonly used in prescription and over-the-counter cough and cold preparations. The medication is taken by mouth. [4] [12]
Side effects of PPA include increased heart rate and blood pressure, among others. [13] [14] [15] [12] Rarely, PPA has been associated with hemorrhagic stroke. [11] [16] [13] PPA acts as a norepinephrine releasing agent, thereby indirectly activating adrenergic receptors. [17] [18] [19] As such, it is an indirectly acting sympathomimetic. [17] [18] [19] [10] It was previously thought to act as a mixed acting sympathomimetic with additional direct agonist actions on adrenergic receptors, but this proved not to be the case. [17] [18] [19] Chemically, PPA is a substituted amphetamine and is closely related to ephedrine, pseudoephedrine, amphetamine, and cathinone. [20] [21] [22] [11]
PPA was first synthesized around 1910 and its effects on blood pressure were first characterized around 1930. [21] [11] It was introduced for medical use by the 1930s. [23] [11] The medication was withdrawn from many markets starting in 2000 following findings that it was associated with increased risk of hemorrhagic stroke. [23] [11] It was previously available both over-the-counter and by prescription. [23] [2] [24] [25] PPA remains available for medical and/or veterinary use in some countries. [2]
PPA is used as a decongestant to treat nasal congestion. [13] [14] It has also been used to suppress appetite and promote weight loss in the treatment of obesity and has shown effectiveness for this indication. [26] [27] [28]
PPA was previously available over-the-counter and in certain combination forms by prescription in the United States. [24] [25] However, these forms have all been discontinued. [24] [25] [2] PPA remains available in certain other countries. [2]
PPA produces sympathomimetic effects and can cause side effects such as increased heart rate and blood pressure. [13] [14] [15] [12] It has been associated rarely with incidence of hemorrhagic stroke. [23] [16] [13]
Certain drugs increase the chances of déjà vu occurring in the user, resulting in a strong sensation that an event or experience currently being experienced has already been experienced in the past. Some pharmaceutical drugs, when taken together, have also been implicated in the cause of déjà vu. [29] reported the case of an otherwise healthy male who started experiencing intense and recurrent sensations of déjà vu upon taking the drugs amantadine and PPA together to relieve flu symptoms. He found the experience so interesting that he completed the full course of his treatment and reported it to the psychologists to write up as a case study. Because of the dopaminergic action of the drugs and previous findings from electrode stimulation of the brain, [30] it was speculated that déjà vu occurs as a result of hyperdopaminergic action in the mesial temporal areas of the brain.
There has been very little research on drug interactions with PPA. [4] In one study, PPA taken with caffeine was found to quadruple caffeine levels. [4] In another study, PPA reduced theophylline clearance by 50%. [4]
PPA acts primarily as a selective norepinephrine releasing agent. [19] It also acts as a dopamine releasing agent with around 10-fold lower potency. [19] The stereoisomers of the drug have only weak or negligible affinity for α- and β-adrenergic receptors. [19]
Compound | NE | DA | 5-HT | Ref | ||
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Dextroamphetamine (S(+)-amphetamine) | 6.6–7.2 | 5.8–24.8 | 698–1765 | [32] [33] | ||
S(–)-Cathinone | 12.4 | 18.5 | 2366 | [19] | ||
(–)-Ephedrine | 43.1–72.4 | 236–1350 | >10000 | [32] | ||
(+)-Ephedrine | 218 | 2104 | >10000 | [32] [19] | ||
Dextromethamphetamine (S(+)-methamphetamine) | 12.3–13.8 | 8.5–24.5 | 736–1291.7 | [32] [34] | ||
Levomethamphetamine (R(–)-methamphetamine) | 28.5 | 416 | 4640 | [32] | ||
(+)-Phenylpropanolamine ((+)-norephedrine) | 42.1 | 302 | >10000 | [19] | ||
(–)-Phenylpropanolamine ((–)-norephedrine) | 137 | 1371 | >10000 | [19] | ||
Cathine ((+)-norpseudoephedrine) | 15.0 | 68.3 | >10000 | [19] | ||
(–)-Norpseudoephedrine | 30.1 | 294 | >10000 | [19] | ||
(–)-Pseudoephedrine | 4092 | 9125 | >10000 | [19] | ||
Pseudoephedrine ((+)-pseudoephedrine) | 224 | 1988 | >10000 | [19] | ||
The smaller the value, the more strongly the substance releases the neurotransmitter. See also Monoamine releasing agent § Activity profiles for a larger table with more compounds. | ||||||
PPA was originally thought to act as a direct agonist of adrenergic receptors and hence to act as a mixed acting sympathomimetic, [21] [22] However, PPA was subsequently found to show only weak or negligible affinity for these receptors and has been instead characterized as exclusively an indirectly acting sympathomimetic. [10] [17] [18] [19] It acts by inducing norepinephrine release and thereby indirectly activating adrenergic receptors. [17] [18] [19]
Many sympathetic hormones and neurotransmitters are based on the phenethylamine skeleton, and function generally in "fight or flight" type responses, such as increasing heart rate, blood pressure, dilating the pupils, increased energy, drying of mucous membranes, increased sweating, and a significant number of additional effects.[ citation needed ]
PPA has relatively low potency as a sympathomimetic. [21] It is about 100 to 200 times less potent than epinephrine (adrenaline) or norepinephrine (noradrenaline) in its sympathomimetic effects, although responses are variable depending on tissue. [21]
PPA is readily- and well-absorbed with oral administration. [7] [6] [5] Immediate-release forms of the drug reached peak levels about 1.5 hours (range 1.0 to 2.3 hours) following administration. [4] [6] Conversely, extended-release forms of PPA reach peak levels after 3.0 to 4.5 hours. [4] The pharmacokinetics of PPA are linear across an oral dose range of 25 to 100 mg. [4] Steady-state levels of PPA are achieved within 12 hours when the drug is taken once every 4 hours. [4] There is 62% accumulation of PPA at steady state in terms of peak levels, whereas area-under-the-curve levels are not increased with steady state. [4]
The volume of distribution of PPA is 3.0 to 4.5 L/kg. [4] Levels of PPA in the brain are about 40% of those in the heart and 20% of those in the lungs. [7] The hydroxyl group of PPA at the β carbon increases its hydrophilicity, reduces its permeation through the blood–brain barrier, and limits its central nervous system (CNS) effects. [7] Hence, PPA crosses into the brain only to some extent, has only weak CNS effects, and most of its effects are peripheral. [14] [7] [5] [21] In any case, PPA can produce amphetamine-like psychostimulant effects at very high doses. [21] [7] [5] PPA is more lipophilic than structurally related sympathomimetics with hydroxyl groups on the phenyl ring like epinephrine (adrenaline) and phenylephrine and has greater brain permeability than these agents. [5] [22]
The plasma protein binding of PPA is approximately 20%. [5] [4] However, it has been said that no recent studies have substantiated this value. [4]
PPA is not substantially metabolized. [6] [5] It also does not undergo significant first-pass metabolism. [6] Only about 3 to 4% of an oral dose of PPA is metabolized. [5] Metabolites include hippuric acid (via oxidative deamination of the side chain) and 4-hydroxynorephedrine (via para-hydroxylation). [4] [5] [7] The methyl group at the α carbon of PPA blocks metabolism by monoamine oxidases (MAOs). [7] [5] [14] PPA is also not a substrate of catechol O-methyltransferase. [14] The hydroxyl group at the β carbon of PPA also helps to increase metabolic stability. [5]
Approximately 90% of a dose of PPA is excreted in the urine unchanged within 24 hours. [4] [7] [6] [5] [4] About 4% of excreted material is in the form of metabolites. [4]
The elimination half-life of immediate-release PPA is about 4 hours, with a range in different studies of 3.7 to 4.9 hours. [7] [6] [4] The half-life of extended-release PPA has ranged from 4.3 to 5.8 hours. [4]
The elimination of PPA is dependent on urinary pH. [4] [5] At a more acidic urinary pH, the elimination of PPA is accelerated and its half-life and duration are shortened, whereas at more basic urinary pH, the elimination of PPA is reduced and its half-life and duration are extended. [5] [4] Urinary acidifying agents like ascorbic acid and ammonium chloride can increase the excretion of and thereby reduce exposure to amphetamines including PPA, whereas urinary alkalinizing agents including antacids like sodium bicarbonate as well as acetazolamide can reduce the excretion of these agents and thereby increase exposure to them. [35] [5] [36]
Total body clearance of PPA has been reported to be 0.546 L/h/kg, while renal clearance was 0.432 L/h/kg. [4]
As PPA is not extensively metabolized, it would probably not be affected by hepatic impairment. [4] Conversely, there is likely to be accumulation of PPA with renal impairment due to its dependence on urinary excretion. [4]
Norephedrine is a minor metabolite of amphetamine and methamphetamine, as shown below. [4] It is also a minor metabolite of ephedrine and a major metabolite of cathinone. [4] [7] [5]
Metabolic pathways of amphetamine in humans [sources 1] ![]() |
PPA, also known as α-methyl-β-hydroxyphenethylamine or as β-hydroxyamphetamine, is a substituted phenethylamine and amphetamine derivative. [9] [20] [48] It is closely related to the cathinones (β-ketoamphetamines). [20] The compound exists as four stereoisomers, which include d- (dextrorotatory) and l-norephedrine (levorotatory), and d- and l-norpseudoephedrine. [48] [10] d-Norpseudoephedrine is also known as cathine, [9] [48] and is found naturally in Catha edulis (khat). [49] Pharmaceutical drug preparations of PPA have varied in their stereoisomer composition in different countries, which may explain differences in misuse and side effect profiles. [10] In any case, racemic dl-norephedrine appears to be the most commonly used formulation pharmaceutically. [21] [9] [1] Analogues of PPA include ephedrine, pseudoephedrine, amphetamine, methamphetamine, and cathinone. [20]
PPA, structurally, is in the substituted phenethylamine class, consisting of a cyclic benzene or phenyl group, a two carbon ethyl moiety, and a terminal nitrogen, hence the name phen-ethyl-amine. [50] The methyl group on the alpha carbon (the first carbon before the nitrogen group) also makes this compound a member of the substituted amphetamine class. [50] Ephedrine is the N-methyl analogue of PPA.
Exogenous compounds in this family are degraded too rapidly by monoamine oxidase to be active at all but the highest doses. [50] However, the addition of the α-methyl group allows the compound to avoid metabolism and confer an effect. [50] In general, N-methylation of primary amines increases their potency, whereas β-hydroxylation decreases CNS activity, but conveys more selectivity for adrenergic receptors. [50]
PPA is a small-molecule compound with the molecular formula C9H13NO and a molecular weight of 151.21 g/mol. [51] [8] It has an experimental log P of 0.67, while its predicted log P values range from 0.57 to 0.89. [51] [8] The compound is relatively lipophilic, [5] but is also more hydrophilic than other amphetamines. [7] The lipophilicity of amphetamines is closely related to their brain permeability. [52] For comparison to PPA, the experimental log P of methamphetamine is 2.1, [53] of amphetamine is 1.8, [54] [53] of ephedrine is 1.1, [55] of pseudoephedrine is 0.7, [56] of phenylephrine is -0.3, [57] and of norepinephrine is -1.2. [58] Methamphetamine has high brain permeability, [53] whereas phenylephrine and norepinephrine are peripherally selective drugs. [59] [60] The optimal log P for brain permeation and central activity is about 2.1 (range 1.5–2.7). [61]
PPA has been used pharmaceutically exclusively as the hydrochloride salt. [9] [1]
PPA was first synthesized in the early 20th century, in or around 1910. [21] [11] It was patented as a mydriatic in 1913. [21] The pressor effects of PPA were characterized in the late 1920s and the 1930s. [21] PPA was first introduced for medical use by the 1930s. [23] [11]
In the United States, PPA is no longer sold due to an increased risk of haemorrhagic stroke. [16] In a few countries in Europe, however, it is still available either by prescription or sometimes over-the-counter. In Canada, it was withdrawn from the market on 31 May 2001. [62] It was voluntarily withdrawn from the Australian market by July 2001. [63] In India, human use of PPA and its formulations was banned on 10 February 2011, [64] but the ban was overturned by the judiciary in September 2011. [65]
Phenylpropanolamine is the generic name of the drug and its INN , BAN , and DCF , while phenylpropanolamine hydrochloride is its USAN and BANM in the case of the hydrochloride salt. [9] [1] [10] [2] It is also known by the synonym norephedrine. [9] [1] [2]
Brand names of PPA have included Acutrim, Appedrine, Capton Diet, Control, Dexatrim, Emagrin Plus A.P., Glifentol, Kontexin, Merex, Monydrin, Mydriatine, Prolamine, Propadrine, Propagest, Recatol, Rinexin, Tinaroc, and Westrim, among many others. [9] [1] [2] It has also been used in combinations under brand names including Allerest, Demazin, Dimetapp, and Sinarest, among others. [1] [2]
PPA remains available for medical and veterinary use in certain countries. [1] [2]
There has been interest in PPA as a performance-enhancing drug in exercise and sports. [66] However, clinical studies suggest that PPA is not effective in this regard. [66] [7] PPA is not on the World Anti-Doping Agency (WADA) list of prohibited substances as of 2024. [67]
In Sweden, PPA is still available in prescription decongestants; [68] PPA is also still available in Germany. It is used in some polypill medications like Wick DayMed capsules.
In the United Kingdom, PPA was available in many "all in one" cough and cold medications which usually also feature paracetamol or another analgesic and caffeine and could also be purchased on its own; however, it is no longer approved for human use. A European Category 1 Licence is required to purchase PPA for academic use.
In the United States, the Food and Drug Administration (FDA) issued a public health advisory [69] against the use of the drug in November 2000. In this advisory, the FDA requested but did not require that all drug companies discontinue marketing products containing PPA. The agency estimates that PPA caused between 200 and 500 strokes per year among 18-to-49-year-old users. In 2005, the FDA removed PPA from over-the-counter sale and removed its "generally recognized as safe and effective" (GRASE) status. [70] Under the 2020 CARES Act, it requires FDA approval before it can be marketed again effectively banning the drug even as a prescription drug. [71]
Because of its potential use in amphetamine manufacture, PPA is controlled by the Combat Methamphetamine Epidemic Act of 2005. It is still available for veterinary use in dogs, however, as a treatment for urinary incontinence.
Internationally, an item on the agenda of the 2000 Commission on Narcotic Drugs session called for including the stereoisomer norephedrine in Table I of United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances. [72]
Drugs containing PPA were banned in India on 27 January 2011. [73] On 13 September 2011, Madras High Court revoked a ban on manufacture and sale of pediatric drugs PPA and nimesulide. [74]
PPA remains available for use in veterinary medicine. [25] It is used to control urinary incontinence in dogs. [75] [76]
Amphetamine is a central nervous system (CNS) stimulant that is used in the treatment of attention deficit hyperactivity disorder (ADHD), narcolepsy, and obesity. Amphetamine was discovered as a chemical in 1887 by Lazăr Edeleanu, and then as a drug in the late 1920s. It exists as two enantiomers: levoamphetamine and dextroamphetamine. Amphetamine properly refers to a specific chemical, the racemic free base, which is equal parts of the two enantiomers in their pure amine forms. The term is frequently used informally to refer to any combination of the enantiomers, or to either of them alone. Historically, it has been used to treat nasal congestion and depression. Amphetamine is also used as an athletic performance enhancer and cognitive enhancer, and recreationally as an aphrodisiac and euphoriant. It is a prescription drug in many countries, and unauthorized possession and distribution of amphetamine are often tightly controlled due to the significant health risks associated with recreational use.
Pseudoephedrine, sold under the brand name Sudafed among others, is a sympathomimetic medication which is used as a decongestant to treat nasal congestion. It has also been used off-label for certain other indications, like treatment of low blood pressure. At higher doses, it may produce various additional effects, including psychostimulant, appetite suppressant, and performance-enhancing effects. In relation to this, non-medical use of pseudoephedrine has been encountered. The medication is taken by mouth.
Ephedrine is a central nervous system (CNS) stimulant that is often used to prevent low blood pressure during anesthesia. It has also been used for asthma, narcolepsy, and obesity but is not the preferred treatment. It is of unclear benefit in nasal congestion. It can be taken by mouth or by injection into a muscle, vein, or just under the skin. Onset with intravenous use is fast, while injection into a muscle can take 20 minutes, and by mouth can take an hour for effect. When given by injection it lasts about an hour and when taken by mouth it can last up to four hours.
Dextroamphetamine (INN:dexamfetamine) is a potent central nervous system (CNS) stimulant and enantiomer of amphetamine that is prescribed for the treatment of attention deficit hyperactivity disorder (ADHD) and narcolepsy. It is also used as an athletic performance and cognitive enhancer, and recreationally as an aphrodisiac and euphoriant. Dextroamphetamine is generally regarded as the prototypical stimulant.
Adderall and Mydayis are trade names for a combination drug called mixed amphetamine salts containing four salts of amphetamine. The mixture is composed of equal parts racemic amphetamine and dextroamphetamine, which produces a (3:1) ratio between dextroamphetamine and levoamphetamine, the two enantiomers of amphetamine. In terms of base, rather than salts, the ratio is 3.15:1 for dextro- to levoamphetamine. Both enantiomers are stimulants, but differ enough to give Adderall an effects profile distinct from those of racemic amphetamine or dextroamphetamine, which are marketed as Evekeo and Dexedrine/Zenzedi, respectively. MAS is used in the treatment of attention deficit hyperactivity disorder (ADHD) and narcolepsy. It is also used illicitly as an athletic performance enhancer, cognitive enhancer, appetite suppressant, and recreationally as a euphoriant. It is a central nervous system (CNS) stimulant of the phenethylamine class.
Sympathomimetic drugs are stimulant compounds which mimic the effects of endogenous agonists of the sympathetic nervous system. Examples of sympathomimetic effects include increases in heart rate, force of cardiac contraction, and blood pressure. The primary endogenous agonists of the sympathetic nervous system are the catecholamines, which function as both neurotransmitters and hormones. Sympathomimetic drugs are used to treat cardiac arrest and low blood pressure, or even delay premature labor, among other things.
Phenylephrine, sold under the brand names Neosynephrine and Sudafed PE among numerous others, is a medication used as a decongestant for uncomplicated nasal congestion, used to dilate the pupil, used to increase blood pressure, and used to relieve hemorrhoids. It can be taken by mouth, as a nasal spray, given by injection into a vein or muscle, applied to the skin, or as a rectal suppository.
Phenylacetone, also known as phenyl-2-propanone, is an organic compound with the chemical formula C6H5CH2COCH3. It is a colorless oil that is soluble in organic solvents. It is a mono-substituted benzene derivative, consisting of an acetone attached to a phenyl group. As such, its systematic IUPAC name is 1-phenyl-2-propanone.
Levomethamphetamine, also known as l-desoxyephedrine and sold under the brand name Vicksvapoinhaler among others, is a sympathomimetic, decongestant, and stimulant medication which is used to treat nasal congestion. It is available over-the-counter at low doses as a decongestant in the United States and is taken by inhalation for this use.
4-Methylaminorex is a stimulant drug of the 2-amino-5-aryloxazoline class that was first synthesized in 1960 by McNeil Laboratories. It is also known by its street name "U4Euh" ("Euphoria"). It is banned in many countries as a stimulant.
4-Hydroxyamphetamine (4HA), also known as hydroxyamfetamine, hydroxyamphetamine, oxamphetamine, norpholedrine, para-hydroxyamphetamine, and α-methyltyramine, is a drug that stimulates the sympathetic nervous system.
Cyclopentamine is a sympathomimetic alkylamine, classified as a vasoconstrictor. Cyclopentamine was indicated in the past as an over-the-counter (OTC) medication for use as a nasal decongestant, notably in Europe and Australia, but has now been largely discontinued.
Lisdexamfetamine, sold under the brand names Vyvanse and Elvanse among others, is a stimulant medication that is used to treat attention deficit hyperactivity disorder (ADHD) in children and adults and for moderate-to-severe binge eating disorder in adults. Lisdexamfetamine is taken by mouth. Its effects generally begin within two hours and last for up to 14 hours.
Methamphetamine is a potent central nervous system (CNS) stimulant that is mainly used as a recreational drug and less commonly as a second-line treatment for attention deficit hyperactivity disorder and obesity. Methamphetamine was discovered in 1893 and exists as two enantiomers: levo-methamphetamine and dextro-methamphetamine. Methamphetamine properly refers to a specific chemical substance, the racemic free base, which is an equal mixture of levomethamphetamine and dextromethamphetamine in their pure amine forms, but the hydrochloride salt, commonly called crystal meth, is widely used. Methamphetamine is rarely prescribed over concerns involving its potential for recreational use as an aphrodisiac and euphoriant, among other concerns, as well as the availability of safer substitute drugs with comparable treatment efficacy such as Adderall and Vyvanse. Dextromethamphetamine is a stronger CNS stimulant than levomethamphetamine.
Dopamine beta-hydroxylase (DBH), also known as dopamine beta-monooxygenase, is an enzyme that in humans is encoded by the DBH gene. Dopamine beta-hydroxylase catalyzes the conversion of dopamine to norepinephrine.
Levoamphetamine is a stimulant medication which is used in the treatment of certain medical conditions. It was previously marketed by itself under the brand name Cydril, but is now available only in combination with dextroamphetamine in varying ratios under brand names like Adderall and Evekeo. The drug is known to increase wakefulness and concentration in association with decreased appetite and fatigue. Pharmaceuticals that contain levoamphetamine are currently indicated and prescribed for the treatment of attention deficit hyperactivity disorder (ADHD), obesity, and narcolepsy in some countries. Levoamphetamine is taken by mouth.
A norepinephrine releasing agent (NRA), also known as an adrenergic releasing agent, is a catecholaminergic type of drug that induces the release of norepinephrine (noradrenaline) and epinephrine (adrenaline) from the pre-synaptic neuron into the synapse. This in turn leads to increased extracellular concentrations of norepinephrine and epinephrine therefore an increase in adrenergic neurotransmission.
p-Hydroxynorephedrine (PHN), or 4-hydroxynorephedrine, is the para-hydroxy analog of norephedrine and an active sympathomimetic metabolite of amphetamine in humans. When it occurs as a metabolite of amphetamine, it is produced from both p-hydroxyamphetamine and norephedrine.
4-Hydroxyphenylacetone is the para-hydroxy analog of phenylacetone, an inactive metabolite of amphetamine in humans. When it occurs as a metabolite of amphetamine, it is produced directly from the inactive metabolite phenylacetone.
Peripherally selective drugs have their primary mechanism of action outside of the central nervous system (CNS), usually because they are excluded from the CNS by the blood–brain barrier. By being excluded from the CNS, drugs may act on the rest of the body without producing side-effects related to their effects on the brain or spinal cord. For example, most opioids cause sedation when given at a sufficiently high dose, but peripherally selective opioids can act on the rest of the body without entering the brain and are less likely to cause sedation. These peripherally selective opioids can be used as antidiarrheals, for instance loperamide (Imodium).
{{cite web}}
: CS1 maint: unfit URL (link)The simplest unsubstituted phenylisopropylamine, 1-phenyl-2-aminopropane, or amphetamine, serves as a common structural template for hallucinogens and psychostimulants. Amphetamine produces central stimulant, anorectic, and sympathomimetic actions, and it is the prototype member of this class (39). ... The phase 1 metabolism of amphetamine analogs is catalyzed by two systems: cytochrome P450 and flavin monooxygenase. ... Amphetamine can also undergo aromatic hydroxylation to p-hydroxyamphetamine. ... Subsequent oxidation at the benzylic position by DA β-hydroxylase affords p-hydroxynorephedrine. Alternatively, direct oxidation of amphetamine by DA β-hydroxylase can afford norephedrine.
Dopamine-β-hydroxylase catalyzed the removal of the pro-R hydrogen atom and the production of 1-norephedrine, (2S,1R)-2-amino-1-hydroxyl-1-phenylpropane, from d-amphetamine.
Hydroxyamphetamine was administered orally to five human subjects ... Since conversion of hydroxyamphetamine to hydroxynorephedrine occurs in vitro by the action of dopamine-β-oxidase, a simple method is suggested for measuring the activity of this enzyme and the effect of its inhibitors in man. ... The lack of effect of administration of neomycin to one patient indicates that the hydroxylation occurs in body tissues. ... a major portion of the β-hydroxylation of hydroxyamphetamine occurs in non-adrenal tissue. Unfortunately, at the present time one cannot be completely certain that the hydroxylation of hydroxyamphetamine in vivo is accomplished by the same enzyme which converts dopamine to noradrenaline.
Figure 1. Glycine conjugation of benzoic acid. The glycine conjugation pathway consists of two steps. First benzoate is ligated to CoASH to form the high-energy benzoyl-CoA thioester. This reaction is catalyzed by the HXM-A and HXM-B medium-chain acid:CoA ligases and requires energy in the form of ATP. ... The benzoyl-CoA is then conjugated to glycine by GLYAT to form hippuric acid, releasing CoASH. In addition to the factors listed in the boxes, the levels of ATP, CoASH, and glycine may influence the overall rate of the glycine conjugation pathway.
The biologic significance of the different levels of serum DβH activity was studied in two ways. First, in vivo ability to β-hydroxylate the synthetic substrate hydroxyamphetamine was compared in two subjects with low serum DβH activity and two subjects with average activity. ... In one study, hydroxyamphetamine (Paredrine), a synthetic substrate for DβH, was administered to subjects with either low or average levels of serum DβH activity. The percent of the drug hydroxylated to hydroxynorephedrine was comparable in all subjects (6.5-9.62) (Table 3).
In species where aromatic hydroxylation of amphetamine is the major metabolic pathway, p-hydroxyamphetamine (POH) and p-hydroxynorephedrine (PHN) may contribute to the pharmacological profile of the parent drug. ... The location of the p-hydroxylation and β-hydroxylation reactions is important in species where aromatic hydroxylation of amphetamine is the predominant pathway of metabolism. Following systemic administration of amphetamine to rats, POH has been found in urine and in plasma.
The observed lack of a significant accumulation of PHN in brain following the intraventricular administration of (+)-amphetamine and the formation of appreciable amounts of PHN from (+)-POH in brain tissue in vivo supports the view that the aromatic hydroxylation of amphetamine following its systemic administration occurs predominantly in the periphery, and that POH is then transported through the blood-brain barrier, taken up by noradrenergic neurones in brain where (+)-POH is converted in the storage vesicles by dopamine β-hydroxylase to PHN.
The metabolism of p-OHA to p-OHNor is well documented and dopamine-β hydroxylase present in noradrenergic neurons could easily convert p-OHA to p-OHNor after intraventricular administration.
CHEMISTRY AND STRUCTURE-ACTIVITY RELATIONSHIP OF SYMPATHOMIMETIC AMINES
β-Phenylethylamine (Table 12–1) can be viewed as the parent compound of the sympathomimetic amines, consisting of a benzene ring and an ethylamine side chain. The structure permits substitutions to be made on the aromatic ring, the α- and β-carbon atoms, and the terminal amino group to yield a variety of compounds with sympathomimetic activity. ...N-methylation increases the potency of primary amines ...
Substitution on the α-Carbon Atom
This substitution blocks oxidation by MAO, greatly prolonging the duration of action of non-catecholamines because their degradation depends largely on the action of this enzyme. The duration of action of drugs such as ephedrine or amphetamine is thus measured in hours rather than in minutes. Similarly, compounds with an α-methyl substituent persist in the nerve terminals and are more likely to release NE from storage sites. Agents such as metaraminol exhibit a greater degree of indirect sympathomimetic activity.
Substitution on the β-Carbon Atom
Substitution of a hydroxyl group on the β carbon generally decreases actions within the CNS, largely because it lowers lipid solubility. However, such substitution greatly enhances agonist activity at both α- and β- adrenergic receptors. Although ephedrine is less potent than methamphetamine as a central stimulant, it is more powerful in dilating bronchioles and increasing blood pressure and heart rate.
Metamfetamine acts in a manner similar to amfetamine, but with the addition of the methyl group to the chemical structure. It is more lipophilic (Log p value 2.07, compared with 1.76 for amfetamine),4 thereby enabling rapid and extensive transport across the blood–brain barrier.19
Lipophilicity was the first of the descriptors to be identified as important for CNS penetration. Hansch and Leo54 reasoned that highly lipophilic molecules will partitioned into the lipid interior of membranes and will be retained there. However, ClogP correlates nicely with LogBBB with increasing lipophilicity increasing brain penetration. For several classes of CNS active substances, Hansch and Leo54 found that blood-brain barrier penetration is optimal when the LogP values are in the range of 1.5-2.7, with the mean value of 2.1. An analysis of small drug-like molecules suggested that for better brain permeation46 and for good intestinal permeability55 the LogD values need to be greater than 0 and less than 3. In comparison, the mean value for ClogP for the marketed CNS drugs is 2.5, which is in good agreement with the range found by Hansch et al.22