Steric aspects of adrenergic drugs

Study of pH Stability of R-Salbutamol Sulfate Aerosol Solution and Its Antiasthmatic Effects in Guinea Pigs

Currently, all commercial available nebulized salbutamol in China is in its racemic form. It is known that only R-salbutamol (eutomer) has therapeutic effects, while S-salbutamol (distomer) may exacerbate asthma after chronic use. Therefore, it is an unmet clinical need to develop R-salbutamol as a nebulized product that is more convenient for young and old patients. In our study, a stable aerosol solution of R-salbutamol sulfate was established, and its antiasthmatic effects were confirmed. The decomposition rate and racemization effect of the R-salbutamol sulfate solution were evaluated over a pH range from 1 to 10 (except pH=7, 8) at 60°C. The aerodynamic particle size of the R-salbutamol sulfate solution and commercial RS-salbutamol sulfate solution were both tested in vitro by Next-Generation Impactor (NGI) in 5°C. Laser diffractometer was used to characterize the droplet-size distribution (DSD) of both solutions. We next conducted an in vivo animal study to document the antiasthmatic effect of R-salbutamol aerosol sulfate solution and determine the relationship to RS-salbutamol. The results showed that the R-salbutamol sulfate solution was more stable at pH 6. In vitro comparison studies indicated that there was no distribution difference between R-salbutamol sulfate solution and the commercial RS-salbutamol solution. The animal results showed that R-salbutamol was more potent than RS-salbutamol against the same dose of histamine challenge. Unlike commercial RS-salbutamol, which was acidified to a pH of 3.5 to extend bench life but may cause bronchoconstriction in asthmatic patients, the neutralized R-salbutamol solution was more suitable for clinic use.

Comparison of enantiomers of SPFF, a novel beta2-Adrenoceptor agonist, in bronchodilating effect in guinea pigs

Previous study on racemic SPFF [2-(4-amino-3-chloro-5-trifluomethyl-phenyl)-2-tert-butylamino-ethanol hydrochloride], a novel beta2-adrenoceptor agonist, has validated that it is a potent, long-acting bronchodilator with relative higher beta2-adrenoceptor selectivity. On the basis of this study, we compared the pharmacological properties of SPFF and its enantiomers ((-)-SPFF and (+)-SPFF) in guinea pigs taking isoprenaline or salbutamol (SAB) as referenced drugs. For the relaxation of both normal and precontracted trachea strips in vitro, (-)-SPFF was found more potent than (+/-)-SPFF or (+)-SPFF. Moreover, we confirmed that the bronchodilator effect of (-)- and (+)-enantiomers were due to activation of the beta2-adrenoceptor because this effect was antagonized by a specific beta2-adrenoceptor antagonist, ICI-118551, with similar pA2 values to those of (+/-)-SPFF. Radioligand binding assay revealed that affinity of (-)-enantiomer to beta2-adrenoceptor was 6 and 164 fold greater than that of (+/-)- and (+)-SPFF, respectively. In addition, isomeric difference of overall selectivity between (-)-SPFF and (+)-SPFF was 10.7 fold for lung versus atria. (-)-SPFF displayed almost the same protective effect against bronchospasm induced by histamine-acetylcholine aerosol in conscious guinea pigs as (+/-)-SPFF did. However, the latent time of (+)-SPFF (1 mg.kg(-1)) was significantly shorter than that of (+/-)- and (-)-SPFF at the same doses. Finally, in the inhibition of histamine-induced increase of pulmonary resistance (RL) in anesthetized guinea pigs, (-)-SPFF was 1.3 and 3.5 times more potent than (+/-)- and (+)-SPFF. Correspondingly, in inhibiting the decrease of pulmonary compliance (CL) , the potencies of (-)- and (+)-enantiomers were approximately equivalent to that of (+/-)-SPFF. Furthermore, a study on the long-lasting action of the test drugs had shown that the effects of (-)-SPFF (30 microg.kg(-1)), (+/-)-SPFF (30 microg.kg(-1)) and (+)-SPFF (100 microg.kg(-1)) in inhibiting the increase of RL all lasted for 4 h. Nevertheless, the effects of (-)- and (+)-enantiomers were slightly lower 4 h after intraduodenal administration in inhibiting the decrease of CL. In conclusion, (-)-SPFF may be beneficial for the treatment of asthma because of its more potent efficacy and higher adrenoceptor affinity than (+/-)- or (+)-SPFF.

Beta-adrenoceptor agonists and asthma--100 years of development

Inhaled beta(2)-adrenoceptor agonists are by far the most effective and safe bronchodilators currently available. They have not been surpassed by any other bronchodilating principle. The way to this position has been long and started with the first successful treatment of acute, severe asthma with s.c. injections of adrenaline 100 years ago. Over the years, synthetic congeners of adrenaline have been produced and tested for their pharmacological properties. During the first decades, little attention was given airway smooth muscle. The discovery of isoprenaline in 1940 was the first major step towards selective bronchodilation. This compound became a key tool for the classification of adrenoceptors into alpha and beta. Salbutamol and terbutaline were the first to show a significant attenuation of the cardiostimulant effect and confirmed the subdivision of beta-adrenoceptors into beta(1) and beta(2). Much effort was made to eliminate the next dose-limiting side effect, skeletal muscle tremor but in vain. Prolonged duration of action was achieved in three ways: with bambuterol, an orally active carbamate ester prodrug of terbutaline, salmeterol, an inhaled beta(2)-adrenoceptor agonist emerging from a purposeful research project, and formoterol which was found, accidentally, to have a long duration of action when inhaled. Throughout the 20th century, beta-adrenoceptor agonists have been developed and marketed as racemates. The pharmacological activity usually resides in the (R)-enantiomer. Despite claims for the opposite, there is so far no compelling evidence that the presence of the less active (S)-enantiomer is of any harm to the patient. One hundred years of experience of structural modifications of adrenaline has shown that the possibilities to modify the properties of this endogenous prototype appear to be unlimited.

Vasorelaxant effects of racemic betaxolol and its R- and S- isomers on bovine retinal vessels

PURPOSE

RS-Betaxolol (equimolar R- and S- isomers) lowers intraocular pressure and dilates precontracted retinal and posterior ciliary arteries in vitro. Betaxolol's vasorelaxant effect is thought to involve the inhibition of calcium influx into vascular smooth muscle and is unrelated to its stereoselective beta-adrenergic blocking action. The authors assessed the vasodilatory effect of RS-betaxolol on different diameters of bovine retinal arterioles and venules, and these responses were compared with the responses induced by R- and S-betaxolol isomers in vitro.

METHOD

In-vitro preparations of the bovine retinal microcirculatory system were perfused continuously with oxygenated, heparinized physiological salt solution at 37 degrees C. Diameters of retinal arterioles and venules were measured using video imaging. The retinal vessels were preconstricted with 40 mM KCl, and concentration-response curves for vasodilation were obtained for RS-betaxolol, R-betaxolol, and S-betaxolol.

RESULTS

Baseline diameters of first-order (A1) and second-order (A2) branches of retinal arterioles were 50 +/- 0.6 microm and 39 +/- 1 microm, respectively (n = 20), whereas diameters of first-order (V1) and second-order (V2) branches of venules were 75 +/- 0.8 microm and 50 +/- 0.4 mM, respectively (n = 20). The diameters of all sizes of retinal arterioles and venules were significantly reduced (i.e., vasoconstricted) in the presence of 40 mM KCl (n = 20). These preconstricted vessels were relaxed in a dose-dependent manner by cumulative additions of RS-betaxolol, R-betaxolol, and S-betaxolol. The dose-response curves of these compounds were not significantly different.

CONCLUSION

RS-Betaxolol, R-betaxolol, and S-betaxolol were equiactive and produced concentration-dependent vasodilatation of all sizes of retinal arterioles and venules studied.

Quantitative structure-activity relationships of cardiotonic agents

Quantitative structure-activity relationships (QSARs) of different cardiotonic agents are presented. A critical analysis of all QSARs provides a very vivid picture of the mechanisms of varying cardiotonic agents. The cardiotonics can be broadly put into 2 categories: cardiac glycosides and nonglycoside cardiotonics, which include phosphodiesterase of type III (PDE III) inhibitors, sympathomimetic (adrenergic) stimulants, A1-selective adenosine antagonists, Ca2+ channel activators and vasopressin antagonists. For cardiac glycosides, QSARs reveal that the position of carbonyl oxygen in their lactone moiety and shifting of the lactone ring from its original position or its replacement by another group would be crucial for their activity. The carbonyl group or its isostere like CN is indicated to be the sole binding entity and the hydrogen bonding through this group is considered to be the most likely binding force. For nonglycoside cardiotonics that include PDE III inhibitors and A1-selective antagonists, a five-point model has been established for their activity, the salient features of which are: (1) the presence of a strong dipole, (2) an adjacent acidic proton, (3) a methyl-sized lipophilic space, (4) a relatively flat overall topography and (5) a basic or hydrogen-bond acceptor site opposite to the dipole. For Ca2+ channel activators, the importance of steric, electrostatic, lipophilic and hydrogen-bonding properties of molecules is indicated, while for vasopressin antagonists the lipophilic and electronic properties are suggested to be the most important.

Central alpha1-adrenoceptors: their role in the modulation of attention and memory formation

Adrenoceptors presently are classified into three main subclasses: alpha1-, alpha2-, and beta-receptors, each with three (perhaps more) subtypes. All three alpha1-adrenoceptor subtypes are present in rat brain. The purpose of this review is to assess the role of alpha1-adrenoceptors in the modulation of synaptic transmission and plasticity, as well as their ability to modulate higher cerebral functions, such as attentional and memory processes. However, since there are no truly subtype-specific agonists or antagonists available at present, it is virtually impossible to allocate a particular central effect to one or other of the subtypes. The activation of alpha1-adrenoceptors reduces the firing probability and glutamate release in the cornu ammonis of the hippocampus. Alpha1-Adrenoceptors may flexibly modulate weak and strong activation of the pyramidal neurones in the neocortex. Alpha1-Adrenoceptors play only a minor role in the modulation of long-term potentiation in the hippocampus, and may influence many brain functions also via non-neuronal mechanisms. since glial cells can express alpha1-adrenoceptors. At the behavioural level, the activation of alpha1-adrenoceptors promotes vigilance and influences working memory and behavioural activation, while having only a minor role in the modulation of long-term memory.

Comparisons of beta-adrenergic blocking properties of S- and R-timolol in humans

In animals, the R-enantiomer of timolol causes a significant reduction in intraocular pressure but had only 1/80 the activity of the S-enantiomer at extraocular receptors. The beta 1- and beta 2-adrenoceptor blocking properties of orally administered R- and S-timolol were compared in a double-blind placebo controlled trial in two groups of healthy men. Each subject in group A (n = 6) received placebo, 1 and 3 mg S-timolol and 25 and 75 mg R-timolol in random order, group B (n = 5) received placebo, 0.5, and 1 mg S-timolol and 3 and 10 mg R-timolol. In both groups, R- and S-timolol comparably inhibited isoproterenol-induced increases in heart rate (P < .05), forearm blood flow (P < .05, except at 3 micrograms/minute of isoproterenol after the R-doses in group B), and finger tremor (P < .05) in comparison with placebo. The findings for the R-enantiomer in this study were unexpected based on the animal studies and previous studies that demonstrated marked differences in beta blocking effects of other beta-blockers in which the R-enantiomers were less inhibitory.

Biological significance of the enantiomeric purity of drugs

The knowledge that enantiomers of chiral compounds may differ widely in biological activity, qualitatively as well as quantitatively, is not new. Nevertheless most of the pharmacological data available to date on chiral drugs are obtained from experiments with racemates which assume that the biological activity generally resides in one of the enantiomers. With the advancements made in stereospecific synthesis and stereoselective analysis of drugs pharmacologists are now offered new possibilities to explore the steric aspects of drug action. This survey will discuss pharmacological data obtained with enantiomer pairs of phenylethylamine derivatives which interact with adrenergic mechanisms. The degree of resolution is seldom specified in published work on stereoselectivity of drugs. In a recent study from our laboratory the enantiomers of the beta 2-adrenoceptor agonist formoterol and their diastereomers have been evaluated. We found that the (R;R)-enantiomer was by far the most potent. However, the relative potencies obtained for the (R;S)-, (S;R), and (S;S)-isomers were critically dependent on the degree of enantiomeric purity. It is concluded that the certainty of potency ratios observed for chiral drugs is limited by the enantiomeric purity and by unspecific effects of the least active enantiomer at very high concentrations.

Chiral high-performance liquid chromatographic separations of vinca alkaloid analogues on alpha 1-acid glycoprotein and human serum albumin columns

Separations of the stereoisomers of a series of tetracyclic and pentacyclic vinca alkaloid analogues having two or three chiral centres were performed on Chiral-AGP and Chiral-HSA high-performance liquid chromatographic columns. Phosphate buffers with pH 5-7 containing 5-35% acetonitrile or 2-propanol were used as mobile phases. The results were in accordance with previous binding data obtained with native AGP and on an HSA-Sepharose column. Whereas on Chiral-AGP the retention of the trans isomers having 1(R),12b(S)-indolo[2,3-a]quinolizidine or the corresponding 3(S),16(R)-eburnane absolute configurations was exceedingly high, on Chiral-HSA the trans isomers, independently of their absolute configurations, were more retained. Eburnane-type compounds could also be separated according to the configuration of the chiral centre at position 14. A comparison of the chromatographic properties of the vinca alkaloids on the Chiral-AGP and Chiral-HSA columns demonstrates that these compounds are bound with higher affinity to the AGP phase. The AGP column resolves a very broad range of vinca alkaloids compared with the HSA column. Higher stereoselectivity and a much better chromatographic performance were also obtained on the Chiral-AGP column.

Hemodynamic effects of 1-[3,4-dihydroxyphenyl]-1,2-diaminoethane versus norepinephrine during ventricular fibrillation and cardiopulmonary resuscitation

We hypothesized that substitution of the hydroxyl group (OH) on the beta carbon of norepinephrine (NE) with an amino group would yield a compound, 1-(3,4-dihydroxyphenyl)-1,2-diaminoethane (DHPDAE), that would maintain the hemodynamic properties of NE during CPR, but would decrease the rate of post-defibrillation dysrhythmias. Six mixed breed swine weighing greater than 28 kg were studied. The animals were instrumented for cerebral (CBF) and myocardial blood flow (MBF) measurements. Ventricular fibrillation (VF) was induced. After 10 min of VF, CPR was begun. After 3 min of CPR, 2.5 mg/kg of DHPDAE was administered and CPR continued. Defibrillation was attempted 3.5 min after drug administration. CBF, MBF and defibrillation rates were compared to an historical control group receiving 0.16 mg/kg of NE. Outcome variables were compared using a Wilcoxon Rank Sum test and Fisher-exact test. NE significantly improved CBF and MBF compared to DHPDAE. All the animals in the NE group were successfully defibrillated into a perfusing rhythm. Sixty percent of the NE treated animals experienced post-defibrillation ventricular dysrhythmias. None of the animals in the DHPDAE were successfully defibrillated into a perfusing rhythm. Substitution of the hydroxyl group on the beta-carbon of NE with an amino group significantly decreases the hemodynamic properties of the parent molecule.

Chirality: pharmacokinetics and pharmacodynamics in 3 dimensions

1. Biological macromolecules are able to distinguish between enantiomeric substrates. A three-point interaction between the drug enantiomers and the macromolecule (Easson-Stedman hypothesis) can frequently account for this selectivity. 2. Significant pharmacodynamic differences between enantiomers are more the rule than the exception. 3. Pharmacokinetic differences between enantiomers are, in general, not as great as the pharmacodynamic differences. However, stereoselective protein binding, metabolism and renal clearance are still very important aspects of understanding drug disposition and the time course of drug action. 4. There may be pharmacokinetic and pharmacodynamic enantiomer-enantiomer interactions. Consequently, the activity and disposition of a racemic drug may not be the simple sum of the activities and disposition of the individual enantiomers. 5. Enantiomers have been used as sensitive 3-dimensional probes to establish structure-activity relationships, to provide insights into genetic polymorphism of drug metabolism, and to provide insights into other aspects of drug disposition. 6. A need for a 3-dimensional understanding of pharmacodynamics and pharmacokinetics is implicit in the asymmetric nature of biological environments.

Non-prescription sympathomimetic agents and hypertension

In recent years, considerable attention has been focused on the pressor effects of nonprescription sympathomimetic agents. The impact and usage of these agents especially ephedrine, pseudoephedrine, phenylpropanolamine and phenylephrine, in hypertensive patients has been the topic of constant debates. The present review is an attempt to report and evaluate all the clinical trials and cases of pressor reactions associated with these 4 agents. The study protocols used in these clinical trials are examined and comments made on any diversion from the standard design. Many factors are found to cause the discrepancies in the data available. It is concluded that ephedrine and phenylpropanolamine are best avoided by hypertensive patients due to higher probability of causing pressor reactions. Data on pseudoephedrine and phenylephrine appear to indicate non-significant effects on blood pressure of normotensive subjects when used at the recommended oral dose as nasal decongestants. Phenylephrine is also commonly employed in nasal and eye drops and the limited data available appear to support its usage in hypertensive patients. However, it is noted that most of the clinical trials involve normotensive subjects and the majority of the results could not be verified due to inadequacies in the study design. This paucity and inconclusive information on hypertensive patients warrants further investigations with emphasis on the study protocols used.

Ophthalmic beta-blockers since timolol

In the twenty years since beta-blockers were proposed for treatment of glaucoma, use of topical timolol has increased to account for 70% of all glaucoma medications used. The objective of this article is to review the "newer" beta-blockers, and to address the generalization that "all ophthalmic beta-blockers are the same." The review concentrates on agents that have been studied as topical treatments for patients with elevated intraocular pressure. Sections on pharmacology and design of clinical trials are included to aid the ophthalmologist in evaluating the new drugs and published clinical reports. The major questions to consider in evaluating the therapeutic potential of a new beta-blocker for the treatment of glaucoma involve efficacy and safety: Is the drug as effective as timolol? Does it have a duration of action at least as long as timolol? Does it have ocular toxicity? Is it comfortable? What are its systemic effects?

New sulfamoylphenethylamines, potent alpha 1-adrenoceptor antagonists

The (+)-isomer of amosulalol, a combined alpha- and beta-adrenoceptor antagonist, was one log unit order more potent and less potent than the (-)-isomer in blocking alpha 1- and beta 1-adrenoceptors, respectively, in anaesthetized rats. Nine newly synthesized desoxy compounds derived from amosulalol and its analogues were found to possess potent alpha 1-adrenoceptor blocking activity and to be practically devoid of beta 1-adrenoceptor blocking activity. Among the desoxy derivatives, YM-12617 was more potent than prazosin in blocking alpha 1-adrenoceptors in anaesthetized rats and in reducing blood pressure, total peripheral resistance and left ventricular work in anaesthetized dogs.

Interaction of clonidine, its methylene-bridged analog, St 1913, and the benzylic hydroxyl-substituted derivative, St 1965, with alpha 1- and alpha 2-adrenoreceptors

The effects of benzylic hydroxyl substitution on the activity of a close structural analog of clonidine was assessed at alpha 1- and alpha 2-adrenoreceptors both in vitro and in vivo in order to uncover possible differences that this substitution may have on the effects of imidazolines and phenethylamines at adrenoreceptors. In all test systems, the presence of the benzylic hydroxyl group was associated with a consistent and marked decrease in activity. These findings are in agreement with our previous studies with imidazolines having different pharmacological profiles and different physicochemical properties than the clonidine derivatives reported herein. We conclude, therefore, that the deleterious effects of the benzylic hydroxyl group is ubiquitous among imidazolines and, more importantly, is in marked contrast to the 100-1000 fold enhancement in activity that the benzylic hydroxyl substituent (i.e. beta-hydroxyl group) produces for the phenethylamines. The results support the concept that imidazolines and phenethylamines may interact differently with alpha-adrenoreceptors.

Stereospecific radioimmunoassays for l-ephedrine and d-ephedrine in human plasma

Haptens were prepared by the reaction of d-ephedrine or l-ephedrine with methyl acrylate and subsequent alkaline hydrolysis of the methyl ester groups. The haptens were coupled to bovine serum albumin by a mixed anhydride method, and the resulting drug-protein conjugates were used to immunize rabbits. Antisera raised to these conjugates were highly stereospecific. Neither antiserum cross-reacted with the optical antipode of its substrate nor with racemic pseudoephedrine. Separate radioimmunoassays (RIAs), developed for d-ephedrine and l-ephedrine, were used to measure the concentrations of the enantiomers of ephedrine in the blood of two volunteers dosed with racemic ephedrine. The RIAs were validated by comparing the sum of the concentrations of the enantiomers, determined by RIA, with total ephedrine concentrations determined by a nonstereoselective GLC-ECD method.

The molecular structure of adrenergic and dopaminergic substances

At the end of the last century it was established that the different nerve cells along a neuronal path do not come into direct physical contact with one another, but that there are narrow gaps between them, called synapses (Sherrington, 1897; Ramón y Cajal, 1906). Elliot (1905) made the basic experimental observation that the propagation of nerve impulses across a synapse might be mediated by specific chemical agents (see Fig. i). Such substances are now called neurotransmitters, and some 20 different compounds putatively responsible for synaptic transmission in different parts of the nervous system are known at present, e.g. a few recently isolated polypeptides. The most extensively studied transmitters are acetylcholine and the catecholamine group, consisting of dopamine (a), noradrenaline (b), and adrenaline (c).

Effect of fluorine substitution on the agonist specificity of norepinephrine

Substitution of fluorine for hydrogen in position 2, 5, or 6 of the aromatic ring of norepinephrine markedly alters the alpha- and beta-adrenergic agonist properties of norephinephrine. The 6-fluoro isomer is an beta-adrenergic agonist with virtually no beta agonist activity, while the 2-fluoro isomer is a beta-adrenergic agonist with little alpha activity. The 5-fluoro isomer is equipotent with norepinephrine as an alpha agonist and significantly more potent as a beta agonist. The possible physiochemical basis for these differences is discussed.

Cocaine and pseudococaine: comparative effects on electrical after-discharge in the limbic system of cats

The effects of cocaine and its dextroisomer pseudococaine on electrical after-discharge (AD) evoked by electrical stimulation of the hippocampus or amygdala were studied in cats with electrodes implanted in the brain. Intravenous injection of cocaine (2.0 to 4.0 mg/kg doses) produced a suppressive effect on the AD while producing low-voltage fast waves (LVFWs) in the electrical activities of the brain (EEG) associated with behavioral excitation. In contrast, pseudococaine at the same dose as cocaine failed to show a significant suppressive effect on the AD except at high doses (5.0 mg/kg). Pseudococaine produced high-voltage slow waves (HVSWs) in the EEG associated with behavioral depression. A linear dose-response relationship was observed for the suppressive effect of cocaine on the AD. The results suggested that the limbic system may be involved as a primary site of action of cocaine in the central nervous system (CNS).

Comparative effects of cocaine and pseudococaine on EEG activities, cardiorespiratory functions, and self-administration behavior in the rhesus monkey

The effects of cocaine and pseudococaine on the EEGs, heart and respiratory rates, and self-administration behavior were studied in rhesus monkeys. An intravenous injection of cocaine (2.5 and 4.0 mg/kg) in the monkey produced low-voltage fast waves (LVFWs) in the EEGs and behavioral hyperexcitation accompanied by marked increases in the heart and respiratory rates with mydriasis and excessive salivation. In contrast, pseudococaine produced high-voltage slow waves (HVSWs) in the EEGs and behavioral depression accompanied by the same symptoms of the autonomic functions as those produced by cocaine. Both isomers were self-administered by the monkeys. During cocaine self-administration sessions, the animals showed hyperexcitation in their overall behavior, while with pseudococaine they showed almost normal behavioral responses. These results suggest that cocaine produced excitatory effects and pseudococaine inhibitory effects on the EEGs and behavior. Both isomers stimulate the heart and respiratory rates, and were self-administered by the monkeys.

A brief review of some properties of alpha-methylnorepinephrine

The research literature can be confusing because of the vast number of nonproprietary names used by various authors for a specific drug. An attempt is made here to clarify the ambiguity regarding the stereoisomer, (-) erythro-alpha-methylnorepinephrine. This agent is used in dentistry as a vasoconstrictor (Neo-Cobefrin) and although its pharmacologic activilty is weaker than that of (-) norepinephrine, it appears that this agent can have significant pharmacologic effects at higher doses. Effects reported have consisted of decreased or increased blood pressure because of the activation of beta receptors or alpha receptors, respectively.

Metabolism and excretion of diethylpropion in man under acidic urine conditions

After oral administration, diethylpropion is rapidly and extensively metabolized in man by N-de-ethylation and stereoselective carbonyl reduction. The unchanged drug excreted in acidic urine represents about 2% of the dose, while the total metabolites determined account for some 85%. The excretion curves indicate that the probable contribution of the parent compound to the observed activity is small. The major metabolites, together representing about 70% of the dose, are N-ethylaminopropiophenone, (+)-N-diethylnorpseudoephedrine, (+)-N-ethylnorpseudoephedrine, (-)-norephedrine and (-)-norpseudoephedrine. The other stereoisomers of the three amino-alcohols, and aminopropiophenone, are present in minor amounts.