Open-label, single-dose pharmacokinetic study of modafinil tablets: influence of age and gender in normal subjects.

An open-label, single-center, single-dose, parallel-group study was performed in healthy young males and females as well as healthy elderly males to examine the influence of age and gender on the pharmacokinetics of modafinil following administration of a single 200 mg oral dose. Twelve subjects were enrolled in each of the following three groups: young males, young females, and elderly males. Each fasted (overnight) subject received 2 x 100 mg modafinil tablets. Blood and urine samples were collected at various times up to 72 hours postdose for the determination of plasma and urine levels of modafinil as well as the acid and sulfone metabolites. The plasma concentrations of the individual isomers, d- and l-modafinil, were also determined. Pharmacokinetic parameters were determined by noncompartmental methods. Modafinil was well tolerated at a single oral dose of 200 mg. The most commonly reported adverse events were headache, fever, pharyngitis, and asthenia. There were no clinically meaningful differences with respect to the incidence rate of treatment-emergent adverse events among the young female, young male, and old male groups. Modafinil was rapidly absorbed after oral dosing and slowly cleared (t1/2 approximately 11-14 hr) from the body. Modafinil acid was the major urinary metabolite, which accounted for 35% to 60% of the dose. Results from this study indicated that there were age and gender effects on modafinil clearance processes. In this regard, the clearance rate of modafinil in males decreased with age while young females cleared modafinil at a faster rate than young males. Stereospecific pharmacokinetics of modafinil were also demonstrated. The d-modafinil was eliminated three times faster than the l-modafinil.

A double-blind, placebo-controlled, ascending-dose evaluation of the pharmacokinetics and tolerability of modafinil tablets in healthy male volunteers.

A randomized, double-blind, placebo-controlled, ascending-dose study was conducted to evaluate the pharmacokinetic and safety profiles of increasing modafinil doses (200 mg, 400 mg, 600 mg, 800 mg) administered orally over a 7-day period in normal healthy male volunteers. Eight subjects (six modafinil; two placebo) were randomized to each of the four dose groups. Modafinil or a placebo was administered once daily for 7 days. Serial blood samples were obtained following administration of the day 1 and day 7 doses for characterization of pharmacokinetics, and trough samples were obtained prior to dosing on days 2 through 6 to assess the time to reach the steady state. Pharmacokinetic parameters were calculated using noncompartmental methods. Modafinil steady state was reached after three daily doses. Modafinil pharmacokinetics were dose and time independent over the range of 200 mg to 800 mg. Steady-state pharmacokinetics of modafinil were characterized by a rapid oral absorption rate, a low plasma clearance of approximately 50 mL/min, a volume of distribution of approximately 0.8 L/kg, and a long half-life of approximately 15 hr. Modafinil was primarily eliminated by metabolism. Modafinil acid was the major urinary metabolite. Stereospecific pharmacokinetics of modafinil were demonstrated. The d-modafinil enantiomer was eliminated at a threefold faster rate than 1-modafinil. Modafinil 200 mg, 400 mg, and 600 mg doses were generally well tolerated. The modafinil 800 mg dose panel was discontinued after 3 days of treatment due to the observation of increased blood pressure and pulse rate. The safety data from this study suggest that the maximum tolerable single daily oral modafinil dose, without titration, may be 600 mg.

Comparison of the single-dose pharmacokinetics and tolerability of modafinil and dextroamphetamine administered alone or in combination in healthy male volunteers.

An open-label, randomized, crossover study was performed in healthy male volunteers to evaluate the potential pharmacokinetic and pharmacodynamic interactions and tolerability of single oral doses of modafinil (200 mg) and dextroamphetamine (10 mg). Blood samples were collected for determination of plasma levels of modafinil, the acid and sulfone metabolites of modafinil, and dextroamphetamine at intervals through 48 hours after administration for each treatment. Vital signs (blood pressure and pulse rate) were measured through 48 hours, and electrocardiograms were measured through 24 hours after administration. Pharmacokinetic parameters were determined using noncompartmental methods. The data collected in this study of 24 healthy volunteers suggest that concomitant administration of single oral doses of modafinil and dextroamphetamine has no clinically significant effects on the pharmacokinetic profile of either agent. Although there was a slightly greater incidence of adverse events when modafinil and dextroamphetamine were administered together, the concomitant administration of the two drugs was well tolerated.

Single-dose pharmacokinetics of modafinil and methylphenidate given alone or in combination in healthy male volunteers.

Modafinil is a novel wake-promoting agent being developed for treatment of excessive daytime sleepiness associated with narcolepsy. An open, 3 x 3 Latin square, randomized, cross-over study was performed in healthy males to compare the pharmacokinetics of single-dose oral modafinil (200 mg) and methylphenidate (40 mg) administered alone or in combination. Blood samples were obtained for analysis of d- and l-threo-methylphenidate and modafinil and its acid and sulfone metabolites. Pharmacokinetic parameters were determined by noncompartmental methods, but could not be evaluated for modafinil sulfone due to plasma levels that were close to the assay quantitation limit. Although sporadic differences in plasma concentrations were observed between treatments, coadministration of modafinil and methylphenidate did not significantly alter the plasma concentrations of modafinil, modafinil acid, modafinil sulfone, or methylphenidate enantiomers compared with administration of these agents alone. Half-life (t1/2), maximum concentration (Cmax), area under the concentration-time curve (AUC0-infinity), total clearance (Cl/F), and apparent volume of distribution (Vd/F) for modafinil and t1/2, Cmax, and AUC0-infinity for modafinil acid were not affected by concomitant administration of methylphenidate. Small but statistically significant increases in time to Cmax (tmax) were observed for modafinil and modafinil acid after methylphenidate coadministration compared with modafinil alone. Modafinil coadministration did not significantly alter the pharmacokinetics of d- or l-threo-methylphenidate, except for a small decrease in Vd/F of l-threo-methylphenidate. Concomitant methylphenidate may cause a delay in the oral absorption of modafinil, but this delay might not be relevant clinically. Coadministration did not alter the extent of oral absorption and disposition of either agent. Therefore, a pharmacokinetic interaction between modafinil and methylphenidate would be unlikely.

CCK satiety is differentially mediated by high- and low-affinity CCK receptors in mice and rats.

Cholecystokinin-JMV-180 (JMV-180) is an analogue of cholecystokinin C-terminal octapeptide (CCK-8), which has been shown to be an agonist at the proposed CCK pancreatic high-affinity site and a functional antagonist at the pancreatic low-affinity site in rats and to have agonist activity at both high- and low-affinity sites in the mouse. In this study we used JMV-180 to evaluate the potential participation of these two CCK-A sites in the satiety effect of CCK-8 in rats and mice. When tested at doses that ranged from 0.01 to 9.2 mumol/kg, JMV-180 did not reliably affect food intake of solid or liquid test diets in rats. When combined with CCK-8 (3.2 or 8.5 nmol/kg) JMV-180 dose dependently reversed the satiety effect of CCK-8. In contrast to these results in the rat, both JMV-180 (3.7-14.8 mumol/kg) and CCK-8 (1.7-6.8 nmol/kg) dose dependently reduced the intake of 20% sucrose in mice. Both CCK-8- and JMV-180-induced suppression of food intake were attenuated by the CCK-A antagonist MK-329 (24.8 nmol/kg). The results of these studies suggest that agonist activity at sites pharmacologically similar to the CCK pancreatic high-affinity site is not sufficient for expression of CCK satiety, whereas agonist activity at low-affinity-like sites is necessary to reduce food intake. Thus the anorexic activity of CCK appears to be mediated through an interaction with a receptor site pharmacologically similar to the pancreatic low-affinity CCK receptor site.

Satiety induced by endogenous and exogenous cholecystokinin is mediated by CCK-A receptors in mice.

To investigate the relative participation of peripheral (CCK-A) and central (CCK-B) cholecystokinin (CCK) receptors in satiety induced by endogenous CCK, we examined the effect of the CCK-A antagonist MK-329 (10-315 micrograms/kg) and the CCK-B antagonist L 365260 (0.1-315 micrograms/kg) on intake of a 20% sucrose solution in mildly food-deprived mice. Intraperitoneal injection of MK-329 elicited a dose-related increase in sucrose consumption with a minimal effective dose of 31.5 micrograms/kg. This dose increased sucrose intake 23% and the highest dose tested, 315 micrograms/kg, increased sucrose intake 63% above baseline. In contrast to MK-329, intraperitoneal administration of L 365260 had no effect on sucrose intake at doses up to 315 micrograms/kg. To examine the contribution of these two CCK receptor subtypes in satiety induced by exogenous CCK, CCK-8 (8 micrograms/kg) was administered alone and in combination with MK-329 and L 365260. MK-329 (10 micrograms/kg) significantly attenuated the satiety effect of CCK-8, and L 365260 (100 micrograms/kg) was without effect. These results suggest that the peripheral CCK receptor subtype mediates satiety induced by endogenous and exogenous CCK in the mouse.

(-)threo-chlorocitric acid decreases sham feeding of sucrose in rats.

The contribution of changes in rate of gastric emptying to the anorectic effect of (-)-threo-chlorocitric acid (chlorocitrate) was assessed by examining the effect of this drug in sham feeding rats, a preparation where gastric distention does not occur. Gavage administration of chlorocitrate (100-400 mg.kg-1) decreased sham and real feeding of 20% sucrose in a dose-related manner. In sham-feeding rats, the minimal effective dose was 200 mg.kg-1. The anorectic effect was evident at 60 min after 200 mg.kg-1 and 30 min after 400 mg.kg-1. In real-feeding rats, the minimal effective dose was 100 mg.kg-1 and for all doses tested the effect was apparent at the 15-min time point. In a second experiment, the effect of chlorocitrate (100-400 mg.kg-1) on gastric emptying of 20% sucrose was examined. Chlorocitrate (200 and 400 mg.kg-1) had a modest but significant inhibitory effect on gastric emptying; however, the effect was not dose-related. Inasmuch as chlorocitrate decreased sham feeding, its anorectic effect cannot be solely attributed to inhibition of gastric emptying. However, because chlorocitrate was more potent in the real-feeding condition relative to sham feeding, and the time course of the response in the two feeding conditions was different, part of chlorocitrate's anorectic effect may depend on postingestive cues such as gastric distention.

Localization of efferent function in the dorsal motor nucleus of the vagus.

To investigate the spatial organization of the vagal preganglionic neurons that control gastric acid, insulin and glucagon secretion, as well as bradycardia, these variables were simultaneously monitored before, during, and after monopolar stimulation (50 microA, 1 ms, 50 Hz) through semimicroelectrodes (tip 25-50 microns) in urethan-chloralose-anesthetized rats. Gastric acid, insulin, and glucagon secretion were elicited by stimulation of the dorsal motor nucleus of the vagus (DMV), whereas heart rate, mean arterial blood pressure, and plasma glucose were not affected. Post hoc analyses were used to characterize the viscerotopic patterns within the DMV. For each of the three positive responses, the "center of gravity" (centroid) of 205 stimulation sites was located within the DMV at approximately the midanterioposterior extent of the nucleus. Vectors of response effectiveness around the centroids as well as comparisons of different groups of DMV electrodes established that effective sites were found throughout the full rostrocaudal extent of the DMV. Comparisons of left vs. right DMV sites indicated that gastric acid, insulin, and glucagon secretion are influenced equally by the two sides of the brain stem. The differences in response strength observed in the DMV were best described in terms of the discrete medial and lateral longitudinal columns of the DMV. The centroid point for gastric acid was in the medial DMV, and the points for insulin and glucagon were in the lateral DMV. Further, medial placements were significantly more effective than lateral ones in eliciting gastric acid secretion; lateral placements were more effective than medial ones in eliciting insulin secretion. Although the effect was not significant in the case of glucagon, the trend paralleled the pattern for insulin.

Vagal stimulation-induced gastric acid secretion in the anesthetized rat.

The dynamics of gastric acid secretion induced by electrical stimulation of the cervical vagus in the anesthetized rat were investigated using a continuous collection-titration system permitting high temporal resolution. Stimulation with pulse rates of 2 or 4 impulses/s (pps) produced maximal gastric acid responses with small cardiovascular effects. With continuous stimulation, secretion was sustained for at least 1 h. Frequency-response profiles suggested that the parietal cells are innervated predominantly by fine-caliber C-fibers. Continuous stimulation was 3 times as effective as stimulation in bursts of higher frequencies. The minimal latency for the onset of secretion was 2.6 min at 4 pps, however, one- and two-min stimulations still produced proportionate but delayed secretory responses. It is concluded that, with low frequency cervical vagus stimulation, the rat stomach preparation described and employed in the present experiment is a useful model for further studies on the interaction of neural and humoral factors on gastric acid secretion.

A method for large volume blood sampling and transfusion in rats.

A new protocol that makes it feasible to withdraw large volumes of whole blood from an individual rat within 1 h or less is described. This method involves the use of indwelling catheters for withdrawal of blood from the inferior vena cava with concurrent isovolemic replacement of whole blood into the superior vena cava. Simultaneity of the transfusion and withdrawal, strict equality of volumes, and a smooth exchange of blood are assured by the use of separate channels of the same multiple-channel peristaltic pump for withdrawal and replacement. Validation experiments using both anesthetized and unanesthetized rats indicate that several responses remain essentially undisturbed during large volume blood sampling; these parameters include blood pressure, heart rate, hematocrit, plasma hormones including insulin and glucagon, plasma glucose levels, and feeding behavior. Considerations of technical and physiological limitations of the protocol, including choice of catheters and catheter placement, pump, sampling parameters, and obtaining donor blood, are discussed.

Precise estimation of carcass fat from total body water in rats and mice.

We investigated the utility of carcass water for predicting adiposity in a sample of 373 rats and mice from nine studies involving several models of obesity and experimental manipulations. A single regression equation was derived for estimating percentage carcass fat--%FAT predicted = -1.272 X %WATER + 95.96 (r = -.988). The function is linear across the range of %FAT observed (6.6% to 68.8%) and fits very well the data of each of the nine experiments. Comparisons between this function and the Lee Index as measures of obesity indicate, by contrast, the considerable imprecision of the latter method. Because studies in our analysis employed formalin fixation, we also provide an equation for use with unfixed tissue. This corrected function accounts for 97.8% of the variance in independent data from 19 published reports. We suggest that both of the functions presented here have general applicability for precise determination of body composition of rats and mice and, further, that the body water analysis offers significant advantages in terms of reduced time and expense.

Effects of guanethidine sympathectomy on ventromedial hypothalamic obesity.

Since ventromedial hypothalamic (VMH) lesions apparently produce chronic increases in parasympathetic activity and decreases in sympathetic responses, two experiments were performed to determine whether decreases in sympathetic tone alone are sufficient either to produce elements of the VMH syndrome or to potentiate the expression of the syndrome in animals with lesions. In experiment 1, rats that had been injected with guanethidine sulfate for 5 wk (40 mg X kg-1 X day-1) to produce a permanent sympathectomy (SympX) were maintained on a high-fat diet and subsequently subjected to VMH lesions. In experiment 2, adrenal-demedullated animals were treated with guanethidine for 6 wk and then subsequently underwent VMH lesions. SympX in the studies (81 and 85% depletion of superior cervical ganglia neurons, respectively) did duplicate the effects of VMH lesions on salivary gland weights. In neither experiment, however, did SympX alone or in combination with demedullation mimic the effects of VMH lesions on food intake, body weight, or body fat. Determinations of free fatty acids (FFAs) in the experiments confirmed that VMH lesions elevate basal FFA levels, but they also indicated that effective VMH lesions need not impair the FFA mobilization to 2-deoxyglucose challenges as some basomedial hypothalamic lesions do. In addition, experiment 2, which employed a prolonged period of high-fat feeding, revealed that SympX plus adrenal demedullation could potentiate (a 13% increase) the effects of VMH lesions on body weight. The results taken together do not support the conclusion that a preponderance of the VMH syndrome can be accounted for by the type of reduction in sympathetic tone produced by guanethidine.

Bipiperidyl mustard produces brain lesions and obesity in the rat.

A single injection of N,N'-bis(beta-chloroethyl)-4,4'-bipiperidine (BPM) into 30-day old rats produced brain lesions in the ventromedial hypothalamus, the dorsal vagal complex (dorsal motor nucleus of the vagus and nucleus of the solitary tract), and the medial septum. The brain lesions were associated with a chronic increase in the rate of body weight gain and the development of obesity. The lesions are similar to those seen in mice following BPM or gold thioglucose administration, however, the development of the obesity in the rat follows a more protracted time course.

Neural pathways involved in the hypothalamic integration of autonomic responses.

Recent mapping studies of hypothalamic and autonomic mechanisms have considerably extended our understanding of the anatomy of this system. The pattern of connections emerging from physiological, anatomical, and histochemical experiments suggests several conclusions about the functional organization of the system as well. Recent evidence supports the idea that the hypothalamic (and other limbic) areas involved in the control of ingestion and metabolism form the rostral pole of a longitudinally and hierarchically organized system that elaborates autonomic responses that influence the energy economy of the animal. Substantially the same pathways are apparently responsible for the modulation of ingestive behavior as well. This circuitry, the "visceromotor system" in Nauta's terminology, seems to weld afferent inputs, particularly those of the gustatory and visceral receptors, into a coordinated integrative control strategy influencing autonomic responses. In addition, the system seems to have unique tissue properties, at least at its two periventricularly located sites of integration with special access to both humorally and ventricularly circulated substrates. These nodes, the basomedial hypothalamus and the vagal complex of the medulla, seem to share similar biochemical specializations reflected in susceptibility to goldthioglucose toxicity, specific insulin binding, and susceptibility to alloxan diabetes.

Neural pathways involved in the hypothalamic integration of autonomic responses.

Recent mapping studies of hypothalamic and autonomic mechanisms have considerably extended our understanding of the anatomy of this system. The pattern of connections emerging from physiological, anatomical, and histochemical experiments suggests several conclusions about the functional organization of the system as well. Recent evidence supports the idea that the hypothalamic (and other limbic) areas involved in the control of ingestion and metabolism form the rostral pole of a longitudinally and hierarchically organized system that elaborates autonomic responses that influence the energy economy of the animal. Substantially the same pathways are apparently responsible for the modulation of ingestive behavior as well. This circuitry, the "visceromotor system" in Nauta's terminology, seems to weld afferent inputs, particularly those of the gustatory and visceral receptors, into a coordinated integrative control strategy influencing autonomic responses. In addition, the system seems to have unique tissue properties, at least at its two periventricularly located sites of integration with special access to both humorally and ventricularly circulated substrates. These nodes, the basomedial hypothalamus and the vagal complex of the medulla, seem to share similar biochemical specializations reflected in susceptibility to goldthioglucose toxicity, specific insulin binding, and susceptibility to alloxan diabetes.