Influence of food on the oral bioavailability of loratadine and pseudoephedrine from extended-release tablets in healthy volunteers

The effect of a high-fat breakfast on the bioavailability of the components of an extended-release tablet containing 10 mg loratadine in the immediate-release coating and 240 mg pseudoephedrine sulfate in the extended-release core was studied in 24 healthy male volunteers in a single-dose, two-way crossover study. The drug was administered after a 10-hour overnight fast or within 5 minutes of consuming a standardized high-fat breakfast. Serial blood samples were collected over a 48-hour period, and plasma was analyzed for loratadine and its active metabolite descarboethoxyloratadine (DCL), and pseudoephedrine. For pseudoephedrine, maximum concentration (Cmax) and area under the concentration-time curve extrapolated to infinity (AUCzero-infinity) were similar after both treatments, indicating no relevant food effect on the bioavailability of pseudoephedrine. Also, the absorption profiles of pseudoephedrine (from Wagner-Nelson analysis) were similar for the fed and fasted treatments, indicating no apparent differences in absorption. Plasma concentration-time profiles and values for Cmax and AUCzero-infinity of DCL were similar for the two treatments, indicating no relevant food effect on the pharmacokinetics of DCL. In contrast, for loratadine, administration with food resulted in a significantly increased mean Cmax (53%) and AUC from time zero to the final quantifiable sample (AUCif) (76%). However, the resultant Cmax and AUC of loratadine under fed conditions were well below those previously obtained at steady-state after multiple-dose administration of loratadine (40 mg/day) that were shown to be safe and well-tolerated in several clinical studies. The effect of food on the bioavailability and pharmacokinetic profiles of the components of a combination loratadine/pseudoephedrine extended-release tablet is not likely to be clinically significant.

National Association of Medical Examiners Pediatric Toxicology (PedTox) Registry Report 3. Case submission summary and data for acetaminophen, benzene, carboxyhemoglobin, dextromethorphan, ethanol, phenobarbital, and pseudoephedrine

Data are presented from the National Association of Medical Examiners' (St. Louis, MO, U.S.A.) Pediatric Toxicology (PedTox) Registry. A total of 839 case reports have been submitted to the registry. Reported here are the concentrations of several drugs and potentially toxic substances observed in children who have died of various causes, often non-drug-related. Except for carbon monoxide, for each of the substances addressed in this report, there is insufficient information in the literature to distinguish "lethal" from "non- or sublethal" concentrations in children, and the data are presented only to provide a working frame of reference. For 30 infants whose deaths were attributed to causes other than phenobarbital, the median blood phenobarbital concentration was 7.8 mg/L, with a range of 0.1-22.4 mg/L. For eight infants whose deaths were not attributed to ethanol, the mean blood ethanol concentration was 0.029 gm/dl and ranged from 0.011 gm/dl to 0.050 gm/dl. Blood dextromethorphan concentrations in seven infants showed a mean of 0.38 mg/L and ranged from 0.10 mg/L to 0.95 mg/L. In 15 infants, blood pseudoephedrine concentrations ranged between 0.07 mg/L and 13.0 mg/L, with a mean concentration of 3.55 mg/L. Blood carboxyhemoglobin saturations for 38 children aged < or = 5 years, who died in fires and were dead on the scene and not resuscitated, ranged between 29% and 94%, with a mean saturation of 64%. Blood benzene concentrations in eight children aged < or = 6 years who died in fires and were dead on the scene showed a mean concentration of 2.3 mg/L and a range of 0.2-4.9 mg/L. For 33 children aged < or = 5 years whose deaths were attributed to nondrug causes, the mean blood acetaminophen concentration was 9.9 mg/L, and the range was 1.0-34.5 mg/L. These data are not well controlled in terms of testing methodology or cause of death determinations and should not be used as the sole source of information when assessing whether or not a death is caused by one of these substances. Further data and controlled studies are needed to work toward establishing lethal concentrations of certain drugs and toxic substances in children, and the reporting of cases to the PedTox Registry is encouraged.

Thermogenic, anti-obesity effects of bofu-tsusho-san in MSG-obese mice

OBJECTIVE

To investigate the hypothesis that anti-obesity action of bofu-tsusho-san (TJ-62) works via activating the brown adipose tissue thermogenesis and inhibiting the phosphodiesterase activity.

DESIGN

MSG obese mice and lean controls were fed a diet including 1.4% or 4.7% TJ-62 of weight of food for 8 weeks. Another group of MSG obese mice were fed with 1-ephedrine (1-E) + d-pseudoephedrine (d-PE) of equivalent amounts as contained in TJ-62 (4.7%) for 8 weeks. Yet another group of MSG obese mice were further supplemented with Glycyrrhizae Radix (GR) extract + Forsythiae Fructus (FF) extract + Schizonepetae Spica (SS) extract (that inhibited phosphodiesterase activity) of amounts contained in TJ-62 (4.7%) for 8 weeks.

MEASUREMENTS

The following were measured: The concentration of ephedrine and its congeners in TJ-62; the inhibitory effect of TJ-62 on phosphodiesterase activity; body weight; food intake; retroperitoneal white adipose tissue (RWAT) weight; interscapular brown adipose tissue (IBAT) weight; mitochondrial protein content in IBAT; cytochrome c oxidase activity in IBAT; guanosine-5'-diphosphate (GDP) binding in IBAT mitochondria.

RESULTS

One gram of TJ-62 contained 3.33 mg of 1-E and 0.73 mg of d-PE. One mg of TJ-62 was equivalent to 2.5 mg of caffeine in the inhibitory effect on phosphodiesterase activity. After feeding with TJ-62, GDP binding was significantly increased in a dose dependent manner. Body weight and RWAT weight decreased in both MSG obese mice and lean controls. Food intake was not changed by TJ-62. Feeding with 1-E + d-PE produced responses of about 70% of those of TJ-62. These responses were, furthermore, enhanced by the addition of the three extracts to the levels that were similar to those produced by TJ-62.

CONCLUSION

Bofu-tsusho-san (TJ-62) works via activating the BAT thermogenesis and inhibiting the phosphodiesterase activity in mice.

Bioavailability of pseudoephedrine from controlled release formulations in the presence of guaifenesin in human volunteers

A multiple-dose bioequivalence study with six healthy human volunteers was conducted. The bioavailability of an experimental controlled release tablet containing pseudoephedrine was compared with a marketed controlled release pseudoephedrine capsule in a three-way crossover study. Plasma samples, collected serially after oral drug administration, were analyzed for pseudoephedrine content using a specific HPLC method with UV detection. The bioavailability parameters, area under the concentration-time curve (AUC), maximum plasma concentration Cmax, and time to peak (Tmax) were obtained from the plasma concentration-time data. Additionally, model independent pharmacokinetic parameters were estimated. Analysis of variance of the data revealed no statistically significant differences between the test and the reference formulation. The presence of guaifenesin in the sustained release tablet did not influence pseudoephedrine bioavailability. The relative bioavailability of the tablet dosage form with respect to the capsule was found to be 100.8%. Classical and Westlake 95% confidence limits as well as the two one-sided t test, proposed by Schuirmann, and the Anderson-Hauck power analysis supported the inference that the two formulations demonstrated comparable bioavailabilty, even in the presence of guaifenesin. Using a non-linear regression program, it was found that the pharmacokinetics of pseudoephedrine followed a simple one-compartment disposition model with no lag time. Additionally, an in vitro-in vivo correlation, based on the estimation of cumulative relative fraction absorbed, was developed between the absorption of pseudoephedrine in humans and the in vitro dissolution time.

In vitro and in vivo evaluation of a once-daily controlled-release pseudoephedrine product

The functionality of a once-daily, osmotic dosage form--gastrointestinal therapeutic system (pseudoephedrine HCl) or GITS (PeHCl)--was studied in vitro and in vivo. The in vitro release profiles were close to identical from pH 1 to 7.5 and between USP apparatus 2 and 7, independent of paddle speeds from 50 to 200 rpm; GITS also released drug at the normal rate in aqueous media after incubation in bile salts or fatty media. Both strengths of GITS (PeHCl)--240 and 120 mg--were then compared with a commercially available pseudoephedrine solution given every 6 hours and a timed-release 12-hour pseudoephedrine capsule given every 12 hours in a randomized 4-way crossover study in 24 healthy men. All four formulations were equivalent in total drug absorbed. Both GITS treatments had AUCinf values equivalent to those of PeHCl solution and capsules, and Cmax values equivalent to PeHCl capsules. Cmax for GITS and capsule treatments were each significantly lower than for solution, but the differences were small (14-17%). A one-to-one correlation was shown between rate of absorption and in vitro release profiles for the GITS products, indicating that drug release from GITS controls absorption. Insensitivity to conditions of in vivo release accounts for the close in vitro/in vivo correlation of release rates. In a second randomized crossover trial (12 men), the effect of a high-fat breakfast on GITS performance was evaluated. Mean pseudoephedrine concentrations in plasma were close to identical with or without the breakfast, and the treatments were bioequivalent.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of guaifenesin in human plasma by liquid chromatography in the presence of pseudoephedrine

A sensitive and specific liquid chromatography (LC) procedure was developed and validated for the determination of guaifenesin in human plasma in the presence of pseudoephedrine. Guaifenesin was extracted from plasma at pH 6.9-7.1 using methanol-methylene chloride (5:95, v/v) containing the internal standard mephenesin and pseudoephedrine. The organic layer was separated and evaporated to dryness and the residue reconstituted with the mobile phase containing methanol-acetonitrile-phosphate buffer (0.05 M) (11:11:78, v/v/v) containing 4 mM heptane sulphonic acid and 1% glacial acetic acid. The separation was performed on a mu Bondapak C18 column. The flow rate was 1.0 ml min-1. The retention times for guaifenesin and mephenesin were 7.9 and 15.7 min, respectively. Linearity of response was observed in the concentration ranges of 50-1000 ng ml-1 and 1-4 micrograms ml-1. Accuracy was within 15.4% of the true value for the inter-day and intra-day analysis. The precision, as measured by the RSD, ranged from 4.8 to 8.7% for intra-day. The reproducibility of inter-day ranged from 5.0 to 8.4%. The per cent recovery from plasma ranged from 88.6 to 97.6. Data are presented to illustrate the practicality of the method for the evaluation of guaifenesin plasma levels in the presence of pseudoephedrine after multiple oral administration of two sustained release tablets containing 600 mg of guaifenesin per tablet to six male healthy volunteers. The mean half-life of guaifenesin in human subjects was found to be 2.88 h and ranged from 1.36 to 5.25 h.

[Determination of pseudoephedrine in human plasma by gas chromatography with a mass selective detector (GC-MSD)]

A specific and sensitive method has been established for the analysis of pseudoephedrine (PE) in human plasma by gas chromatography with a mass selective detector (GC-MSD). PE and ephedrine (E, internal standard) reacted with trifluoroacetic anhydride (TFAA) and the derivatives were separated by a HP-5 capillary column. PE-TFA and E-TFA were quantitatively measured by selected ion monitoring (m/z = 154). The detection limits for E and PE were 1 ng/ml plasma. The recoveries were about 99%.

Cardiovascular effects of pseudoephedrine in medically controlled hypertensive patients

BACKGROUND

Oral sympathomimetics are effective in the treatment of nasal congestion through stimulation of alpha-adrenergic receptors in the blood vessels of the nasal mucosa. This vasoconstrictor activity has resulted in the general recommendation that such pressor amines not be used in patients with hypertension. No prospective studies have examined the safety of sustained-release pseudoephedrine in hypertensive patients.

METHODS

Volunteers (N = 28) with controlled hypertension participated in a randomized, double-blind, placebo-controlled, crossover study that examined the cardiovascular effects of 120 mg of sustained-release pseudoephedrine taken on a twice daily basis. Physician-investigators measured blood pressure and heart rate using mercurial sphygmomanometers during acute and steady-state phases. Compliance was verified with pill counts and serum drug levels. Symptom questionnaires were completed by the volunteers.

RESULTS

While a strong statistical correlation was found over time, with minimal increases in mean arterial pressure and heart rate, pseudoephedrine administration did not result in statistically significant changes in any cardiovascular parameter. Mild disturbances in sleeping pattern and urinary retention in some male subjects were the only significant symptoms detected.

CONCLUSIONS

We conclude that while sustained-release pseudoephedrine appears safe for the majority of medically controlled hypertensive patients without statistically significant effects on blood pressure or heart rate our studies did show an upward trend in these parameters which, in a larger population of hypertensive patients, may prove to be clinically significant.

Exercise alters the pharmacokinetics of midazolam

Six healthy volunteers received 15 mg midazolam, 50 mg ephedrine, or placebo orally before a 50-minute aerobic treadmill exercise and in a control session. Plasma drug concentrations for pharmacokinetic calculations were estimated from samples drawn up to 24 hours after drug intake. Heart rate, blood pressure, critical flicker fusion test, Maddox wing test, and visual analog scales relating to mood and feelings of tiredness were included in the sessions as pharmacodynamic measures. These tests were made at 35, 55, and 75 minutes and at 2, 2 1/2, 3 1/2, and 5 hours after drug intake. Exercise impaired the absorption of midazolam and counteracted the midazolam-induced decrement in flicker fusion threshold. Whether the effect on flicker fusion was caused mainly by the pharmacokinetic changes or by a general alerting effect of exercise cannot be verified by this experiment. The kinetics of ephedrine was not affected by exercise, but exercise enhanced the tachycardic response to ephedrine and abolished its pressor effect.

Pseudoephedrine accumulation in renal failure

Neuropsychiatric complications, such as metabolic encephalopathy, are common occurrences in end-stage renal disease (ESRD) patients. Frequently, metabolic encephalopathy develops in relationship to the multiple pharmacologic therapies routinely employed in this population. Such polypharmacy often leads to adverse drug reactions, drug-drug interactions, or dosage error. In this regard, over-the-counter (OTC) medications are commonly perceived as being "somewhat benign" when, in fact, their potential for adverse effect may be significant. The authors describe the course of a 64-year-old hemodialysis patient who became intoxicated on conventional doses of pseudoephedrine only to regain neurologic integrity upon discontinuation of the medication.

Detection of oxilofrine in plasma and urine by high-performance liquid chromatography with electrochemical detection and comparison with gas chromatography-mass spectrometry

A high-performance liquid chromatographic (HPLC) method with electrochemical detection for the determination of oxilofrine [1-(4-hydroxyphenyl)-2-methylaminopropanol] in human plasma and urine (before and after cleavage of the metabolic conjugates) is described. Isolation from biological fluids is performed batchwise by weak acid cation exchange. Separation of plasma and urine components is achieved on a reversed-phase C18 column as an ion pair with heptanesulphonic acid. For amperometric detection the potential of the electrode was set at 0.95 V versus an Ag/AgCl reference electrode. The detection limit for oxilofrine in plasma is 1 ng/ml and in urine 12.5 ng/ml at a signal-to-noise ratio of 2.0 using 1.0 ml of plasma and 0.02 ml of urine. The method was compared with a gas chromatographic-mass spectrometric method and showed a good concordance for plasma (r = 0.996) and urine (r = 0.994). With the HPLC method it is also possible to determine related sympathomimetic drugs, e.g., etilefrine, norefenefrine or octopamine, after a slight modification of the mobile phase.

Sensitive quantification of pseudoephedrine in human plasma and urine by high-performance liquid chromatography

An assay for the selective quantification of pseudoephedrine in human plasma and urine was developed using high-performance liquid chromatography with UV detection at 205 nm. Analyte and internal standard were extracted from alkaline plasma or urine into a mixture of n-hexane and diethyl ether, and the organic phase was back-extracted into dilute acid. The chromatographic system comprises microparticulate cyanopropyl-silica as stationary phase and a ternary solvent mixture with ion-pair reagents as mobile phase. Using 0.25 ml plasma, the lower limit of quantification was 25 ng/ml with excellent linearity up to 1000 ng/ml. In urine, the calibration ranged from 2.5 to 100 micrograms/ml. The selectivity of the method was demonstrated for several pharmaceuticals with similar structures. The validated method was applied to a pharmacokinetic study with a single oral dose of 100 mg of pseudoephedrine in two galenic formulations. Precision and accuracy data of the assay and calculated pharmacokinetic parameters are presented.

Influence of a standard meal on the absorption of controlled-release pseudoephedrine capsules

The influence of a standard meal on the extent and rate of absorption of pseudoephedrine from a controlled-release (CR) capsule formulation (Pennkinetic System) was studied in 16 normal male volunteers. Equivalent single doses of an immediate-release (IR) pseudoephedrine reference syrup and the CR capsules were each studied under both fasted and postprandial conditions. Pharmacokinetic analysis evaluated the fraction of drug absorbed over time as determined by the Wagner-Nelson method. The area under the drug concentration versus time curve (AUC) results were not influenced by food or formulation, indicating that the CR formulation was absorbed to the same extent as the IR syrup. The maximum plasma concentration (Cmax) and the time to maximum concentration (tmax) tabulations under fasted conditions indicated that the CR preparation peaked at a lower level and a later time than the IR syrup. Food minimally affected the Cmax of the IR formulation, but did not affect that of the CR formulation. Food delayed the tmax of both the IR and CR preparations by less than 1 h, but only the delay of the CR formulation was statistically significant. Neither delay was considered clinically meaningful. The results of this study strongly suggest that the pharmacokinetic profile of the CR pseudoephedrine capsules was minimally affected by the presence of food.

Five cases of fatal overdose from caffeine-containing "look-alike" drugs

Five cases of death from ingestion of "look-alike" dose forms are reported. "Look-alikes" are widely used non-prescription drugs sold as appetite suppressants or stimulants. Three of the cases had taken caffeine/ephedrine combinations, and two had taken caffeine only. All had lethal concentrations of caffeine detected in the blood (130 to 344 mg/L), and three had high ephedrine concentrations from 3.5 to 20.5 mg/L. Caffeine and ephedrine were measured in body fluids and tissues (when available) by SIM gas chromatography/mass spectrometry (GC/MS) after extraction with diethyl ether.

Pseudoephedrine and triprolidine in plasma and breast milk of nursing mothers

Plasma and milk concentrations of pseudoephedrine and triprolidine were determined (by radioimmunoassay) in three lactating mothers over 12-48 h after ingestion of a combination medication containing 60 mg of pseudoephedrine hydrochloride and 2.5 mg of triprolidine hydrochloride monohydrate. Pseudoephedrine concentrations in milk were consistently higher than those in plasma. The total amount of drug in milk, as judged by areas under the respective curves (AUC), was two to three times greater than in plasma. Triprolidine concentrations in milk and plasma were more variable between subjects than those of pseudoephedrine. AUC values for milk and plasma were similar for one subject, while the plasma value exceeded that for milk in another woman. The fraction of the dose excreted in milk was estimated to be 0.4-0.7% for pseudoephedrine and 0.06-0.2% for triprolidine.

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.

Stereospecific radioimmunoassays for d-pseudoephedrine in human plasma and their application to bioequivalency studies

Antiserum to d-pseudoephedrine was raised in New Zealand White rabbits in response to immunization with a conjugate of bovine serum albumin and d-pseudoephedrine-N-3-propionic acid. The hapten was prepared by reaction of methyl acrylate with d-pseudoephedrine, followed by ester hydrolysis. Sodium boro[3H]hydride reduction of dl-ephedrine gave [alpha-3H]-dl-ephedrine, and a Welsh rearrangement with acetic anhydride followed by deacetylation gave [alpha-3H]-dl-pseudoephedrine, which was used as a radioligand in radioimmunoassay procedures for direct plasma analyses. Three sensitive radioimmunoassay procedures were developed, two using [3H]pseudoephedrine as the radioligand and either adsorption on coated charcoal or polyethylene glycol precipitation for separation of antibody-bound from free radioligand. The third method used an [125I]tyrosine methyl ester analog of pseudoephedrine and charcoal separation, preceded by extraction and derivatization of pseudoephedrine with methyl acrylate. All three assays could detect less than or equal to 2.5 ng of pseudoephedrine/ml. The antiserum was stereospecific, showing low cross-reactivities with l-pseudoephedrine and d- and l-ephedrines. d-Norpseudoephedrine and some other related compounds also had low cross-reactivity in these radioimmunoassay procedures. Excellent agreement was found between pseudoephedrine concentrations in human plasma determined by radioimmunoassay and by a standard GLC method. The utility of radioimmunoassay was illustrated by application of one of these procedures to an assessment of the bioequivalence of immediate- and sustained-release pseudoephedrine formulations in normal volunteers. A sustained-release preparation containing 120 mg of pseudoephedrine hydrochloride given every 12 hr was shown by AUC comparisons to be bioequivalent to an immediate-release tablet (containing 60 mg of pseudoephedrine hydrochloride) given every 6 hr.

Renal excretion of pseudoephedrine in the rat

Pseudoephedrine is an organic base used in the treatment of upper respiratory tract disorders. Surgical techniques and experimental procedures were developed to study the renal elimination mechanisms for this drug in the rat. The ability to measure renal clearance accurately and to demonstrate renal secretion by a carrier-mediated transport system was verified by comparing results from N'-methylnicotinamide (NMN) excretion studies with literature results. Renal tubular secretion of NMN was shown to be saturable and was inhibited by mepiperphenidol to the same extent as that reported in the literature. Pseudoephedrine was cleared by the kidney at a rate in excess of inulin and close to or possibly greater than renal plasma flow. In addition to filtration and secretion, pseudoephedrine appeared to be subject to pH dependent passive reabsorption. When the secretion of pseudoephedrine was studied in detail, it was found to be nonsaturable for plasma levels of pseudoephedrine ranging from 0.16 to 1.5 microgram/ml. Secretion, however, was inhibited by mepiperphenidol suggesting a carrier-mediated process.

Electron-capture GLC determination of pseudoephedrine in serum

A GLC assay was developed for pseudoephedrine in serum using 3-methylamino-1-phenyl-1-propanol as an internal standard. After extraction from serum with benzene under alkaline conditions, pseudoephedrine was derivatized with pentafluorobenzyl bromide and quantitated by electron-capture GLC. The method has a detection limit of approximately 0.02 microgram/ml of serum using 1-ml samples.

Simple and specific electron-capture GLC assay for plasma and urine ephedrine concentrations following single doses

An electron-capture GLC procedure for determination of plasma ephedrine concentrations is described. The procedure is capable of determining 2 ng/ml of ephedrine and is adequate for following profiles after 25-mg single doses. Pentane extraction of the drug and the internal standard and formation of the N-pentafluorobenzoyl derivatives were followed by GLC. Plasma ephedrine concentrations following a 24-mg dose of ephedrine hydrochloride to a human volunteer are presented. Formation of N-trifluoroacetyl, N-pentafluoropropionyl, N-heptafluorobutryl, and N-pentafluorobenzoyl derivatives and their GLC-mass spectrometric identification are discussed together with comparative electron-capture sensitivities of these derivatives toward a nickel-63 detector. The detection of the N-pentafluorobenzoyl derivative of ephedrine is at least 100-fold greater in sensitivity than detection of the N-trifluoroacetyl derivative.

Pseudoephedrine pharmacokinetics in the rat using a microanalysis technique

A microanalytical procedure was developed using a gas chromatographic-electron capture technique which is capable of detecting 2 ng pseudoephedrine in 20 microliter plasma samples. Standard curves for pseudoephedrine are linear over the concentration range 0.1--1.6 microgram/ml. Plasma and urine concentrations of pseudoephedrine were followed in 3 rats after intravenous dosing. Derived pharmacokinetics parameters exhibited little inter-animal variation. Average plasma clearance was 67.6 ml/min/kg, with renal clearance averaging 30.3 ml/min/kg. This latter value is approximately 4X the glomerular filtration rate in the rat.

Pharmacokinetics and locomotor activity increasing effect of ephedrine in mice

Ephedrine has stimulating effects on the CNS which have been shown as increased locomotor activity, for example. No studies on the relationship between this pharmacological effect and blood levels of the drug have been reported. In the present study this question was investigated in mice after intravenous and oral administration of ephedrine. It was concluded that after intravenous injection of ephedrine the blood concentration data fitted best with the two-compartment open model but after oral administration of the drug with the one-compartment model. The locomotor activity stimulating effect of the drug did not have a linear relationship to the drug levels in the central or in the tissue compartment. This suggests that the mechanism of the locomotor activity increasing effect of ephedrine is indirect.