ORIGINAL RESEARCH ARTICLE
Clin. Pharmacokinet. 22 (2): 152-161, 1992 0312-5963/92/0002-0152/$05.00/0 © Adis International Limited. All rights reserved. CPK1114a
Pharmacokinetics of Raclopride Formulations Influence of Prolactin and Tolerability in Healthy Male Volunteers Gunilla Mavin-Osswald, Anna-Lena Nordstrom, Margareta Hammarlund-Udenaes, Anita Wahlen and Lars Farde Department of Clinical Pharmacology, Astra Research Centre, SOdertalje, Department of Psychiatry and Psychology, Karolinska Hospital, Stockholm, and Department of Biopharmaceutics and Pharmacokinetics, Uppsala University, Uppsala, Sweden
Summary
The pharmacokinetic and pharmacodynamic properties of raclopride, a new antipsychotic, were investigated in 16 healthy men. Single 4mg doses were administered as intravenous infusion, oral solution and 2 extended release (ER) formulations. Total plasma clearance was about 100 mljmin (6.0 L/h), of which renal clearance accounted for 0.2 mljmin, indicating extensive metabolism. The volume of distribution was 1.5 L/kg; mean absolute bioavailability was 65 to 67% following the oral solution and the ER formulations. A transient increase in plasma prolactin levels followed both the intravenous infusion and the oral solution. The ER formulations resulted in a lower increase, which appeared later. However, the area under the prolactin level curve was similar after administration of all dosage forms. The frequency and severity of the most commonly reported side effects (tiredness and restlessness) were higher after the intravenous infusion than after the ER capsules. These findings indicate that such capsules may be advantageous for clinical antipsychotic treatment with raclopride.
Raclopride is a new potential antipsychotic drug of benzamide structure with a high selectivity and affinity for central D2-dopamine receptors (fig. I) [Kohler et al. 1985; Ogren et al. 1986). It is a pure enantiomer with high lipophilicity. The selective
CI
CI
OH
?~CON" OCH3
-CHz>C)
'-
N
H
I
CzHs
Fig. 1. Chemical formula of raclopride.
binding to central D2-dopamine receptors in the human brain has been confirmed with [I ICJraclopride by positron emission tomography (Farde et al. 1986, 1989a). Like conventional neuroleptics, raclopride increases plasma prolactin levels in humans by blockade of dopamine Dz-receptors in the anterior pituitary (Meltzer et al. 1978; Muller et a!. 1983). The increase is dose related and of short duration, as has been demonstrated in healthy volunteers and patients (Farde et al. 1988, 1989b). Thc prolactin increase might contribute to side effects such as menstrual disturbances, galactorrhoea and impotence.
153
Rac10pride Kinetics and Dynamics
Raclopride has been generally well tolerated (Cookson et al. 1989; Farde et al. 1988, I 989b). The most frequently reported side effects in healthy volunteers and in patients have been akathisia and tiredness (Cookson et al. 1989; Farde et al. 1988, 1989b; Wahlen et al. 1988). Akathisia is one of the most common side effects during treatment with antipsychotic drugs and is an important clinical problem (Adler et al. 1989). Initial data from healthy volunteers suggest that there may be a relationship between the rate of drug absorption and the occurrence of akathisia (Wahlen et al. 1988). A formulation with a slower rate of absorption might induce fewer and less severe side effects. This is the first study where raclopride has been administered intravenously and compared with oral administration to determine absolute bioavailability, volume of distribution and clearance. A second objective was to study the influence of the rate of administration on side effects and prolactin levels. In order to accomplish this the same dose was administered at different rates by using short intravenous infusion, oral solution and 2 oral extended release formulations.
Subjects and Methods Subjects The study enrolled 16 healthy male Caucasian volunteers between the ages of 21 and 38 years (mean 29 years). They were nonobese with a mean (± SD) weight of 78 ± 12kg and a height of 181 ± 7cm. They were healthy according to medical history, physical examination, electrocardiograph (ECG) and laboratory tests. The participants were phenotyped regarding their capacity to hydroxylate debrisoquine and mephenytoin (Mahgoub et al. 1977; Wedlund et al. 1984). It is not yet known whether the disposition of raclopride is affected by these enzymes, as its metabolic fate is currently under investigation. However, polymorphic hydroxylation has been reported for some neuroleptic compounds, i.e. thioridazine (von Bahr et al. 1991a) and perphenazine (Dahl-Puustinen et al. 1989). The study was approved by the ethical committee at the Karolinska Hospital in Stockholm,
and was performed according to the Helsinki declaration. Each volunteer gave signed informed consent to participate. Study Design The study was performed according to a randomised crossover design. Each subject received a different formulation of raclopride tartrate at each of 4 experimental sessions at weekly intervals. In each experiment raclopride tartrate 4mg, corresponding to raclopride 2.8mg, was administered. The mean actual dose of raclopride tartrate administered intravenously was 3.6 ± 0.5mg. The formulations included an intravenous infusion given over a IO-min period, an oral solution and 2 extended release (ER) capsule formulations. Drug Formulations The solution of raclopride for intravenous administration was prepared immediately before use by adding a stock solution of raclopride tartrate 2 mg/ml to physiological saline. The final concentration was 0.18 ± 0.02 mg/ml. The oral solution was administered as 4ml of an aqueous solution of raclopride tartrate I mg/ml. The two 4mg ER formulations, consisting of microcapsules, had different in vitro dissolution profiles according to the USP XXI paddle method (United States Pharmacopoeia Convention 1985) with water at 50 rpm at 37"C (n = 6). The formulation with a faster rate of in vitro dissolution with a release of 40, 80 and >85% after 3, 6 and 12h, respectively, is designated as ERr. The corresponding release values for the formulation with a slower in vitro dissolution rate (ERs) were 10, 60 and >85%. The raclopride formulations were produced and supplied by Astra Research Centre AB, Sweden. Experimental Conditions Both intravenous and oral doses of raclopride were administered at 8am, together with 150mi of tap water. Before drug administration all study participants had fasted for a minimum of 8h with
Clin. Pharmacokinet. 22 (2) 1992
154
the exception of a glass of water taken at least 1h before administration. Immediately before the dose the volunteers were required to empty their bladders. To ensure proper diuresis during the study days, the water intake was standardised to 150ml per hour during the first 12h. With the exception of this standardised water intake all volunteers continued fasting for 4h after drug administration. Lunch was served after the 4h sample, a light meal after 6h and a dinner 9h after drug intake. Caffeine-containing beverages were not allowed during the first 6h of each experimental session. No other drugs or alcohol were allowed during the 48h prior to or during each experimental session. The participants remained at the department for at least the first 8h and stayed overnight. A maximum of 4 volunteers were examined simultaneously. The infusion was administered via an infusion pump (IMED 960) over exactly 10 min (2 mljmin) and was given through an intravenous cannula in 1 antecubital vein, with blood sampled from the contralateral arm. In all sessions the volunteers were recumbent during the first hour after drug administration. Blood and Urine Sampling Blood samples (5ml) were drawn into heparinised 'Venoject' tubes for analysis of plasma concentrations of raclopride and prolactin. Plasma was separated by centrifugation within Ih and transferred to polypropylene tubes ('Nunc' tubes). The samples were stored at -20°C until analysed. Following the intravenous infusion, samples were collected from an indwelling catheter during the first 2h, after which heparinised 'Venoject' tubes were used. Specimens were drawn immediately before the dose and at 4, 8, 10, ll, 12, 15, 20, 30, 40, 50, 60, 75 and 90 min and 2, 3, 4, 6, 8, 10, 12, 16, 24, 26 and 30h after the start of the infusion. With the oral solution the samples were drawn before and at 10, 20, 30, 40, 50, 60 and 90 min and 2, 4, 6, 8, 10, 12, 16, 24, 28 and 32h after administration. After administration of the extended release capsules the samples 'were drawn before and at 30, 60
and 90 min and 2, 3,4, 5, 6, 8, 10, 12, 16, 24, 28, 32 and 36h. Urine was collected before administration and between and 2, 2 and 4, 4 and 6, 6 and 8, and 8 and 12h, and at 12h intervals up to 36h after administration. All urine was kept refrigerated during each interval. Thereafter an aliquot was transferred to 'Nunc' tubes and stored at -20T until assayed.
°
Adverse Events After administration of raclopride the study participants were observed by the investigator for 10h. The volunteers were also told to keep their own notes with respect to unusual experiences. In addition, subjective experiences were recorded by the investigator after open questioning 8 and 30h after raclopride administration. An open question was followed by specific questions about restlessness. Akathisia was rated according to the rating scale for drug-induced akathisia by Barnes (1989). The scale takes both subjectively reported restlessness and observed motor restlessness into account. The rating ofakathisia represents peak severity. Inner restlessness without a desire to move was rated as questionable akathisia. Analytical Procedures Plasma and urine concentrations of raclopride were determined after alkaline extraction and reversed phase high performance liquid chromatography (HPLC). An appropriate amount of the internal standard (raclopride with propyl instead of ethyl on the pyrrolidine moiety) was added to 0.5ml of plasma or urine. The sample was alkali sed with 0.5ml carbonate buffer (0.05 moljL, pH 10) followed by extraction using diethylether/n-hexane (80: 20 v/v). After centrifugation the organic phase was transferred to a small glass tube and evaporated to dryness. The residue was dissolved in phosphate buffer pH 2 and injected on to the HPLC column (YMC S-3 120A ODS, 100 x 4.6mm). The mobile phase was a mixture of phosphate buffer pH 2 and acetonitrile (58: 42 v/v) with the addi-
Rac\opride Kinetics and Dynamics
tion of decyl sodium sulphate 1.2 mmol/L. Raclopride and the internal standard were detected by fluorescence with excitation and emission wavelengths of 328 and 458nm, respectively. The absolute recovery in the extraction was 95% for both raclopride and its internal standard. The intra-assay precision [coefficient of variation (CV)] for the spiked plasma samples was 18.3% at 2 nmol/L (limit of quantification) and 2.6% at 100 nmolfL. The inter-assay precision (CV) for the spiked control samples in the present study was 25% at 2 nmolfL and 6.5% at 100 nmol/L. Concentration values deviating from the expected pharmacokinetic curve were generally confirmed by reanalysis. The stability of raclopride in plasma and urine has been investigated (Briem, unpublished data). From the results it can be concluded that raclopride is stable in plasma and urine for at least I year when stored at - 20°e. The free concentration of raclopride in plasma was determined in the samples collected 30 min after intravenous administration. The samples were held at 37°C and plasma pH was adjusted to pH 7.4 using carbon dioxide. Plasma was then transferred to an ultrafiltration device (Amicon micropartition system with YMT membrane) and centrifuged, after which the raclopride concentration in the ultrafiltrate was determined according to the procedure described above.
155
calculated as the amount excreted in the urine divided by the available dose. Renal clearance (CLR) was calculated as the amount excreted divided by the AUe. The apparent volumes of distribution during the terminal phase (Vz) and at steady-state (V 55) were calculated as Vz = CL/Az and Vss = Doselv x AUMC/AUC2, where AUMC is the area under the moment curve. The bioavailability (F) was calculated as:
0= 0= • = • =
Mean values
1000 500
SOL ERs ER, IV
100 50 ::J'
:aE
10
.s c
.Q
~c
1 0
Q)
u
5
10
15
20
25
30
35
40
c 0
Q)
"C
·c
a.
Pharmacokinetic calculations were performed according to standard procedures (Gibaldi & Perrier 1982). Individual maximum plasma concentrations of raclopride (Cmax ) and the time to reach the peak concentration (tmax) were determined. The areas under the plasma raclopride concentrationtime curves (AUC(O-t» were calculated using the linear trapezoidal rule. The total area under the curve (AUC) was calculated by extrapolation to time infinity by adding the term Ct/Az, where Ct is the calculated concentration at time t and Az is the slope ofthe terminal phase. The half-lives (t'l2) were estimated from the terminal phase. Systemic clearance (CL) was calculated as DoseIV/AUe. The fraction of raclopride excreted unchanged (fe) was
x 100
AUCreference x Dosetest
The unbound fraction in plasma (fu) was calculated from the unbound concentration divided
u
Pharmacokinetic Calculations
AU Ctest x DOSereference
F(%) =
1000 500
Values in 1 volunteer
0
U
l'! as E Ul as
c::
100 50 10
1~~.--.--.---r--.---r--~-.
o
5
10
15
20
25
30
35
40
Time (h)
Mean (± SD) plasma rac10pride concentration-time profiles in 16 healthy male volunteers, and in I volunteer with secondary peaks in the profile, following single doses of rac10pride tartrate 4mg administered as an intravenous infusion (IV) [n = 15], an oral solution (SOL) and 2 extended release capsules [fast (ERr) and slow (ERs) dissolution]. Fig. 2.
Clin. Pharmacokinet. 22 (2) /992
156
Table I. Mean (± SO) basic pharmacokinetic parameters of raclopride following intravenous administration of raclopride tartrate 3.6 ± 0.5mg to 15 healthy volunteers
Drug
Total Unbound
F ("!o)
Cl (ml/min)
ClR (ml/min)
Vz
v••
t1(,
(l/kg)
(l/kg)
(h)
65 ± 15
97 ± 19 1760 ± 670
0.16 ± 0.13 2.9 ± 2.4
1.1 ± 0.4 19 ± 8
14
26 ± 13
1.5 ± 0.6
± 5
Abbreviations: F = bioavailability; Cl = total plasma drug clearance (for l/h multiply by 0.06); ClR renal clearance; Vz = volume of distribution during the terminal phase; V•• = volume of distribution at steady-state; t1(, = elimination half-life.
by the total concentration in plasma from samples collected 30 min after the start of the intravenous infusion. Clearance and volume of distribution (Vd) based on unbound drug were calculated in each volunteer. For prolactin, the values Cmax,PRL, tmax,PRL, AVCcO-12h),PRL, AVC(O-24h),PRL and time above the upper normal limits during 24h were calculated for each volunteer and session. The area under the prolactin level-time curve was estimated by the linear trapezoidal rule. Statistical Analysis Nonparametric methods were used because it cannot be assumed that the population distribution follows a specific parametric distribution. To analyse the bioavailability, 95% confidence intervals were calculated in the logarithmic scale by using the Wilcoxon sign rank statistic, after which the limits were exponentiated. Hypotheses concerning differences in pharmacokinetics and adverse events between the formulations were analysed using the Wilcoxon sign rank statistic for paired comparisons (Lehmann 1975). A value of p < 0.05 was considered statistically significant. Release 5.16 of the SAS® system under VMS™ (SAS 1985a,b) was used for the analysis of data. The results are presented as mean ± SD.
Results Pharmacokinetics of Raciopride Time curves for the mean plasma raciopride concentrations following different rates of drug administration are shown in figure 2. The Cmax
values were highest after the intravenous infusion and decreased with slower rates of absorption. After administration of the oral solution, rac10pride was absorbed with a t max of OAh compared with 0.2h after intravenous infusion. Following administration of the extended release capsules (ERfand ERs), raciopride C max was reached at 5 and 7h, respectively. Secondary peaks were observed in all the individual plasma concentration curves, as shown by the curves from I volunteer (fig. 2.). The pharmacokinetic parameters of racIopride are given in table I. The fu was 6 ± 2%; CL was 97 ± 19 ml/min, equivalent to 1.3 ± 0.3 mljmin/ kg. RacIopride is most probably extensively metabolised, since less than 1% was excreted unchanged by the kidneys (table II). The interindividual variability was 3-fold in Vss and 2-fold in CL. Following intravenous administration the terminal half-life (tl12"\') was 14 ± 5h (range 504 to 23.7h). There were no statistically significant differences in the elimination half-life (tl12) between the intravenous and oral doses. The absolute bioavailability of the oral solution was 65%, and the mean residual AVC was between 12 and 18% of the total AVC after the 4 doses. Bioequivalence in extent of bioavailability was found between the extended release capsules and the oral solution (table II). Two subjects were slow hydroxylators of debrisoquine or mephenytoin. Their Vd and CL were in the lower range while their Cmax values were in the upper range, and thus not markedly different from the other volunteers. One subject had a considerably shorter til> after the intravenous infusion compared with the other
Raclopride Kinetics and Dynamics
157
doses (2h vs 9 to 13h). No secondary peak appeared after the intravenous infusion; the subject had diarrhoea in the afternoon following the intravenous dose and was therefore not included in the calculation of the mean pharmacokinetic parameters. Prolactin Levels The intravenous infusion resulted in a plasma prolactin curve resembling that after the oral solution, with similar Cmax values (fig. 3, table III), although the latter were significantly lower following the extended release capsules. However, the AUC(0-24h),PRL was similar after all 4 doses. Prolactin levels increased immediately after the intravenous dose and the oral solution. After administration of the extended release formulations there was a marked lag-time (1.5 and 3h for ERr and ERs, respectively) before the onset of prolactin release (fig. 3). The mean raclopride concen-
trations at the time of onset were 8 and 12 nmol/ L, respectively. Following administration of the rapid formulations (intravenous infusion and oral solution) the t max of prolactin occurred later than the t max of raclopride. However, when the ER formulations were administered, tmax,PRL occurred earlier than the t max of raclopride (tables II, III). The duration of the increase in prolactin levels above the upper normal limit of 20 ~g/L was about 4h following all 4 doses of raclopride (table III). Adverse Events
Tiredness, restlessness and discomfort were the most frequent subjectively reported adverse events (table IV). After administration of the extended release capsules there were fewer, and less severe, adverse events compared with the intravenous infusion or the oral solution.
Table II. Mean (± SO) pharmacokinetic parameters of raclopride following single doses given as intravenous infusion (IV) [n = 15], oral solution (SOL) and 2 extended release capsules [last (ERd and slow (ERs) dissolution] 01 raclopride tartrate 4mg to 16 healthy volunteers Parameter Cmax (nmoI/L) tmax (h)
AUC (nmoI/L' h)
tv. (h) F(%) fe (%) CLR (ml/min)
Iva
SOL
481 ± 85 0.18 ± 0.03
1259 ± 273
211 ± 44 0.45 ± 0.20
891 ± 229
ERI 62 ± 15 4.8 ± 1.2
918 ± 255
ERs 45 ± 11 6.8 ± 2.3
912 ± 232
p-Value
Clin. Pharmacokinet. 22 (2): 152-161, 1992 0312-5963/92/0002-0152/$05.00/0 © Adis International Limited. All rights reserved. CPK1114a
Pharmacokinetics of Raclopride Formulations Influence of Prolactin and Tolerability in Healthy Male Volunteers Gunilla Mavin-Osswald, Anna-Lena Nordstrom, Margareta Hammarlund-Udenaes, Anita Wahlen and Lars Farde Department of Clinical Pharmacology, Astra Research Centre, SOdertalje, Department of Psychiatry and Psychology, Karolinska Hospital, Stockholm, and Department of Biopharmaceutics and Pharmacokinetics, Uppsala University, Uppsala, Sweden
Summary
The pharmacokinetic and pharmacodynamic properties of raclopride, a new antipsychotic, were investigated in 16 healthy men. Single 4mg doses were administered as intravenous infusion, oral solution and 2 extended release (ER) formulations. Total plasma clearance was about 100 mljmin (6.0 L/h), of which renal clearance accounted for 0.2 mljmin, indicating extensive metabolism. The volume of distribution was 1.5 L/kg; mean absolute bioavailability was 65 to 67% following the oral solution and the ER formulations. A transient increase in plasma prolactin levels followed both the intravenous infusion and the oral solution. The ER formulations resulted in a lower increase, which appeared later. However, the area under the prolactin level curve was similar after administration of all dosage forms. The frequency and severity of the most commonly reported side effects (tiredness and restlessness) were higher after the intravenous infusion than after the ER capsules. These findings indicate that such capsules may be advantageous for clinical antipsychotic treatment with raclopride.
Raclopride is a new potential antipsychotic drug of benzamide structure with a high selectivity and affinity for central D2-dopamine receptors (fig. I) [Kohler et al. 1985; Ogren et al. 1986). It is a pure enantiomer with high lipophilicity. The selective
CI
CI
OH
?~CON" OCH3
-CHz>C)
'-
N
H
I
CzHs
Fig. 1. Chemical formula of raclopride.
binding to central D2-dopamine receptors in the human brain has been confirmed with [I ICJraclopride by positron emission tomography (Farde et al. 1986, 1989a). Like conventional neuroleptics, raclopride increases plasma prolactin levels in humans by blockade of dopamine Dz-receptors in the anterior pituitary (Meltzer et al. 1978; Muller et a!. 1983). The increase is dose related and of short duration, as has been demonstrated in healthy volunteers and patients (Farde et al. 1988, 1989b). Thc prolactin increase might contribute to side effects such as menstrual disturbances, galactorrhoea and impotence.
153
Rac10pride Kinetics and Dynamics
Raclopride has been generally well tolerated (Cookson et al. 1989; Farde et al. 1988, I 989b). The most frequently reported side effects in healthy volunteers and in patients have been akathisia and tiredness (Cookson et al. 1989; Farde et al. 1988, 1989b; Wahlen et al. 1988). Akathisia is one of the most common side effects during treatment with antipsychotic drugs and is an important clinical problem (Adler et al. 1989). Initial data from healthy volunteers suggest that there may be a relationship between the rate of drug absorption and the occurrence of akathisia (Wahlen et al. 1988). A formulation with a slower rate of absorption might induce fewer and less severe side effects. This is the first study where raclopride has been administered intravenously and compared with oral administration to determine absolute bioavailability, volume of distribution and clearance. A second objective was to study the influence of the rate of administration on side effects and prolactin levels. In order to accomplish this the same dose was administered at different rates by using short intravenous infusion, oral solution and 2 oral extended release formulations.
Subjects and Methods Subjects The study enrolled 16 healthy male Caucasian volunteers between the ages of 21 and 38 years (mean 29 years). They were nonobese with a mean (± SD) weight of 78 ± 12kg and a height of 181 ± 7cm. They were healthy according to medical history, physical examination, electrocardiograph (ECG) and laboratory tests. The participants were phenotyped regarding their capacity to hydroxylate debrisoquine and mephenytoin (Mahgoub et al. 1977; Wedlund et al. 1984). It is not yet known whether the disposition of raclopride is affected by these enzymes, as its metabolic fate is currently under investigation. However, polymorphic hydroxylation has been reported for some neuroleptic compounds, i.e. thioridazine (von Bahr et al. 1991a) and perphenazine (Dahl-Puustinen et al. 1989). The study was approved by the ethical committee at the Karolinska Hospital in Stockholm,
and was performed according to the Helsinki declaration. Each volunteer gave signed informed consent to participate. Study Design The study was performed according to a randomised crossover design. Each subject received a different formulation of raclopride tartrate at each of 4 experimental sessions at weekly intervals. In each experiment raclopride tartrate 4mg, corresponding to raclopride 2.8mg, was administered. The mean actual dose of raclopride tartrate administered intravenously was 3.6 ± 0.5mg. The formulations included an intravenous infusion given over a IO-min period, an oral solution and 2 extended release (ER) capsule formulations. Drug Formulations The solution of raclopride for intravenous administration was prepared immediately before use by adding a stock solution of raclopride tartrate 2 mg/ml to physiological saline. The final concentration was 0.18 ± 0.02 mg/ml. The oral solution was administered as 4ml of an aqueous solution of raclopride tartrate I mg/ml. The two 4mg ER formulations, consisting of microcapsules, had different in vitro dissolution profiles according to the USP XXI paddle method (United States Pharmacopoeia Convention 1985) with water at 50 rpm at 37"C (n = 6). The formulation with a faster rate of in vitro dissolution with a release of 40, 80 and >85% after 3, 6 and 12h, respectively, is designated as ERr. The corresponding release values for the formulation with a slower in vitro dissolution rate (ERs) were 10, 60 and >85%. The raclopride formulations were produced and supplied by Astra Research Centre AB, Sweden. Experimental Conditions Both intravenous and oral doses of raclopride were administered at 8am, together with 150mi of tap water. Before drug administration all study participants had fasted for a minimum of 8h with
Clin. Pharmacokinet. 22 (2) 1992
154
the exception of a glass of water taken at least 1h before administration. Immediately before the dose the volunteers were required to empty their bladders. To ensure proper diuresis during the study days, the water intake was standardised to 150ml per hour during the first 12h. With the exception of this standardised water intake all volunteers continued fasting for 4h after drug administration. Lunch was served after the 4h sample, a light meal after 6h and a dinner 9h after drug intake. Caffeine-containing beverages were not allowed during the first 6h of each experimental session. No other drugs or alcohol were allowed during the 48h prior to or during each experimental session. The participants remained at the department for at least the first 8h and stayed overnight. A maximum of 4 volunteers were examined simultaneously. The infusion was administered via an infusion pump (IMED 960) over exactly 10 min (2 mljmin) and was given through an intravenous cannula in 1 antecubital vein, with blood sampled from the contralateral arm. In all sessions the volunteers were recumbent during the first hour after drug administration. Blood and Urine Sampling Blood samples (5ml) were drawn into heparinised 'Venoject' tubes for analysis of plasma concentrations of raclopride and prolactin. Plasma was separated by centrifugation within Ih and transferred to polypropylene tubes ('Nunc' tubes). The samples were stored at -20°C until analysed. Following the intravenous infusion, samples were collected from an indwelling catheter during the first 2h, after which heparinised 'Venoject' tubes were used. Specimens were drawn immediately before the dose and at 4, 8, 10, ll, 12, 15, 20, 30, 40, 50, 60, 75 and 90 min and 2, 3, 4, 6, 8, 10, 12, 16, 24, 26 and 30h after the start of the infusion. With the oral solution the samples were drawn before and at 10, 20, 30, 40, 50, 60 and 90 min and 2, 4, 6, 8, 10, 12, 16, 24, 28 and 32h after administration. After administration of the extended release capsules the samples 'were drawn before and at 30, 60
and 90 min and 2, 3,4, 5, 6, 8, 10, 12, 16, 24, 28, 32 and 36h. Urine was collected before administration and between and 2, 2 and 4, 4 and 6, 6 and 8, and 8 and 12h, and at 12h intervals up to 36h after administration. All urine was kept refrigerated during each interval. Thereafter an aliquot was transferred to 'Nunc' tubes and stored at -20T until assayed.
°
Adverse Events After administration of raclopride the study participants were observed by the investigator for 10h. The volunteers were also told to keep their own notes with respect to unusual experiences. In addition, subjective experiences were recorded by the investigator after open questioning 8 and 30h after raclopride administration. An open question was followed by specific questions about restlessness. Akathisia was rated according to the rating scale for drug-induced akathisia by Barnes (1989). The scale takes both subjectively reported restlessness and observed motor restlessness into account. The rating ofakathisia represents peak severity. Inner restlessness without a desire to move was rated as questionable akathisia. Analytical Procedures Plasma and urine concentrations of raclopride were determined after alkaline extraction and reversed phase high performance liquid chromatography (HPLC). An appropriate amount of the internal standard (raclopride with propyl instead of ethyl on the pyrrolidine moiety) was added to 0.5ml of plasma or urine. The sample was alkali sed with 0.5ml carbonate buffer (0.05 moljL, pH 10) followed by extraction using diethylether/n-hexane (80: 20 v/v). After centrifugation the organic phase was transferred to a small glass tube and evaporated to dryness. The residue was dissolved in phosphate buffer pH 2 and injected on to the HPLC column (YMC S-3 120A ODS, 100 x 4.6mm). The mobile phase was a mixture of phosphate buffer pH 2 and acetonitrile (58: 42 v/v) with the addi-
Rac\opride Kinetics and Dynamics
tion of decyl sodium sulphate 1.2 mmol/L. Raclopride and the internal standard were detected by fluorescence with excitation and emission wavelengths of 328 and 458nm, respectively. The absolute recovery in the extraction was 95% for both raclopride and its internal standard. The intra-assay precision [coefficient of variation (CV)] for the spiked plasma samples was 18.3% at 2 nmol/L (limit of quantification) and 2.6% at 100 nmolfL. The inter-assay precision (CV) for the spiked control samples in the present study was 25% at 2 nmolfL and 6.5% at 100 nmol/L. Concentration values deviating from the expected pharmacokinetic curve were generally confirmed by reanalysis. The stability of raclopride in plasma and urine has been investigated (Briem, unpublished data). From the results it can be concluded that raclopride is stable in plasma and urine for at least I year when stored at - 20°e. The free concentration of raclopride in plasma was determined in the samples collected 30 min after intravenous administration. The samples were held at 37°C and plasma pH was adjusted to pH 7.4 using carbon dioxide. Plasma was then transferred to an ultrafiltration device (Amicon micropartition system with YMT membrane) and centrifuged, after which the raclopride concentration in the ultrafiltrate was determined according to the procedure described above.
155
calculated as the amount excreted in the urine divided by the available dose. Renal clearance (CLR) was calculated as the amount excreted divided by the AUe. The apparent volumes of distribution during the terminal phase (Vz) and at steady-state (V 55) were calculated as Vz = CL/Az and Vss = Doselv x AUMC/AUC2, where AUMC is the area under the moment curve. The bioavailability (F) was calculated as:
0= 0= • = • =
Mean values
1000 500
SOL ERs ER, IV
100 50 ::J'
:aE
10
.s c
.Q
~c
1 0
Q)
u
5
10
15
20
25
30
35
40
c 0
Q)
"C
·c
a.
Pharmacokinetic calculations were performed according to standard procedures (Gibaldi & Perrier 1982). Individual maximum plasma concentrations of raclopride (Cmax ) and the time to reach the peak concentration (tmax) were determined. The areas under the plasma raclopride concentrationtime curves (AUC(O-t» were calculated using the linear trapezoidal rule. The total area under the curve (AUC) was calculated by extrapolation to time infinity by adding the term Ct/Az, where Ct is the calculated concentration at time t and Az is the slope ofthe terminal phase. The half-lives (t'l2) were estimated from the terminal phase. Systemic clearance (CL) was calculated as DoseIV/AUe. The fraction of raclopride excreted unchanged (fe) was
x 100
AUCreference x Dosetest
The unbound fraction in plasma (fu) was calculated from the unbound concentration divided
u
Pharmacokinetic Calculations
AU Ctest x DOSereference
F(%) =
1000 500
Values in 1 volunteer
0
U
l'! as E Ul as
c::
100 50 10
1~~.--.--.---r--.---r--~-.
o
5
10
15
20
25
30
35
40
Time (h)
Mean (± SD) plasma rac10pride concentration-time profiles in 16 healthy male volunteers, and in I volunteer with secondary peaks in the profile, following single doses of rac10pride tartrate 4mg administered as an intravenous infusion (IV) [n = 15], an oral solution (SOL) and 2 extended release capsules [fast (ERr) and slow (ERs) dissolution]. Fig. 2.
Clin. Pharmacokinet. 22 (2) /992
156
Table I. Mean (± SO) basic pharmacokinetic parameters of raclopride following intravenous administration of raclopride tartrate 3.6 ± 0.5mg to 15 healthy volunteers
Drug
Total Unbound
F ("!o)
Cl (ml/min)
ClR (ml/min)
Vz
v••
t1(,
(l/kg)
(l/kg)
(h)
65 ± 15
97 ± 19 1760 ± 670
0.16 ± 0.13 2.9 ± 2.4
1.1 ± 0.4 19 ± 8
14
26 ± 13
1.5 ± 0.6
± 5
Abbreviations: F = bioavailability; Cl = total plasma drug clearance (for l/h multiply by 0.06); ClR renal clearance; Vz = volume of distribution during the terminal phase; V•• = volume of distribution at steady-state; t1(, = elimination half-life.
by the total concentration in plasma from samples collected 30 min after the start of the intravenous infusion. Clearance and volume of distribution (Vd) based on unbound drug were calculated in each volunteer. For prolactin, the values Cmax,PRL, tmax,PRL, AVCcO-12h),PRL, AVC(O-24h),PRL and time above the upper normal limits during 24h were calculated for each volunteer and session. The area under the prolactin level-time curve was estimated by the linear trapezoidal rule. Statistical Analysis Nonparametric methods were used because it cannot be assumed that the population distribution follows a specific parametric distribution. To analyse the bioavailability, 95% confidence intervals were calculated in the logarithmic scale by using the Wilcoxon sign rank statistic, after which the limits were exponentiated. Hypotheses concerning differences in pharmacokinetics and adverse events between the formulations were analysed using the Wilcoxon sign rank statistic for paired comparisons (Lehmann 1975). A value of p < 0.05 was considered statistically significant. Release 5.16 of the SAS® system under VMS™ (SAS 1985a,b) was used for the analysis of data. The results are presented as mean ± SD.
Results Pharmacokinetics of Raciopride Time curves for the mean plasma raciopride concentrations following different rates of drug administration are shown in figure 2. The Cmax
values were highest after the intravenous infusion and decreased with slower rates of absorption. After administration of the oral solution, rac10pride was absorbed with a t max of OAh compared with 0.2h after intravenous infusion. Following administration of the extended release capsules (ERfand ERs), raciopride C max was reached at 5 and 7h, respectively. Secondary peaks were observed in all the individual plasma concentration curves, as shown by the curves from I volunteer (fig. 2.). The pharmacokinetic parameters of racIopride are given in table I. The fu was 6 ± 2%; CL was 97 ± 19 ml/min, equivalent to 1.3 ± 0.3 mljmin/ kg. RacIopride is most probably extensively metabolised, since less than 1% was excreted unchanged by the kidneys (table II). The interindividual variability was 3-fold in Vss and 2-fold in CL. Following intravenous administration the terminal half-life (tl12"\') was 14 ± 5h (range 504 to 23.7h). There were no statistically significant differences in the elimination half-life (tl12) between the intravenous and oral doses. The absolute bioavailability of the oral solution was 65%, and the mean residual AVC was between 12 and 18% of the total AVC after the 4 doses. Bioequivalence in extent of bioavailability was found between the extended release capsules and the oral solution (table II). Two subjects were slow hydroxylators of debrisoquine or mephenytoin. Their Vd and CL were in the lower range while their Cmax values were in the upper range, and thus not markedly different from the other volunteers. One subject had a considerably shorter til> after the intravenous infusion compared with the other
Raclopride Kinetics and Dynamics
157
doses (2h vs 9 to 13h). No secondary peak appeared after the intravenous infusion; the subject had diarrhoea in the afternoon following the intravenous dose and was therefore not included in the calculation of the mean pharmacokinetic parameters. Prolactin Levels The intravenous infusion resulted in a plasma prolactin curve resembling that after the oral solution, with similar Cmax values (fig. 3, table III), although the latter were significantly lower following the extended release capsules. However, the AUC(0-24h),PRL was similar after all 4 doses. Prolactin levels increased immediately after the intravenous dose and the oral solution. After administration of the extended release formulations there was a marked lag-time (1.5 and 3h for ERr and ERs, respectively) before the onset of prolactin release (fig. 3). The mean raclopride concen-
trations at the time of onset were 8 and 12 nmol/ L, respectively. Following administration of the rapid formulations (intravenous infusion and oral solution) the t max of prolactin occurred later than the t max of raclopride. However, when the ER formulations were administered, tmax,PRL occurred earlier than the t max of raclopride (tables II, III). The duration of the increase in prolactin levels above the upper normal limit of 20 ~g/L was about 4h following all 4 doses of raclopride (table III). Adverse Events
Tiredness, restlessness and discomfort were the most frequent subjectively reported adverse events (table IV). After administration of the extended release capsules there were fewer, and less severe, adverse events compared with the intravenous infusion or the oral solution.
Table II. Mean (± SO) pharmacokinetic parameters of raclopride following single doses given as intravenous infusion (IV) [n = 15], oral solution (SOL) and 2 extended release capsules [last (ERd and slow (ERs) dissolution] 01 raclopride tartrate 4mg to 16 healthy volunteers Parameter Cmax (nmoI/L) tmax (h)
AUC (nmoI/L' h)
tv. (h) F(%) fe (%) CLR (ml/min)
Iva
SOL
481 ± 85 0.18 ± 0.03
1259 ± 273
211 ± 44 0.45 ± 0.20
891 ± 229
ERI 62 ± 15 4.8 ± 1.2
918 ± 255
ERs 45 ± 11 6.8 ± 2.3
912 ± 232
p-Value
