BIOPHARMACEUTICS & DRUG DISPOSITION
`Biopharm. Drug Dispos. 20: 369–377 (1999)
`
`Pharmacokinetics and Tissue Distribution of Olanzapine in
`Rats
`
`Manickam Aravagiri*, Yaroslav Teper and Stephen R. Marder
`Psychopharmacology Unit, University of California at Los Angeles, VA Greater Los Angeles Healthcare System, Los Angeles, CA, USA
`
`ABSTRACT: The single dose pharmacokinetics of olanzapine in rats, following an oral dose and its
`distribution in the brain and other tissues after repeated oral and intra-peritoneal (i.p.) administration,
`were studied. Olanzapine in plasma, brain, liver, lung, kidney, spleen and fat was assayed at predose,
`0.25, 0.5, 1, 2, 5, 12, 24, 36, 48 h postoral dose of 6 mg/kg and after daily oral and i.p. doses of 0.25, 1, 3,
`and 6 mg/kg/day of olanzapine for 15 consecutive days by a sensitive and specific HPLC method with
`electrochemical detection. Olanzapine was readily absorbed and distributed in plasma and tissues as the
`peak concentrations were reached within 45 min after the oral dose. The terminal half-life of olanzapine
`in plasma was 2.5 h and in tissues it ranged from 3 to 5.2 h. The area under the concentration–time curve
`(AUClast) was lowest in plasma and largest in liver and lung. The AUClast of olanzapine was eight times
`larger in brain and three to 32 times larger in other tissues than that in plasma. After repeated oral doses,
`the plasma and tissue concentrations of olanzapine were generally higher than those after repeated i.p.
`doses. The liver and spleen had the highest concentrations after oral and i.p doses, respectively. In both
`cases, the tissue concentrations were four- to 46-fold higher than that in plasma and correlated with
`administered doses. Likewise, plasma concentrations strongly correlated with the simultaneous brain and
`tissue concentrations (r 2\0.908, pB0.0001). On average, the brain levels were 6.3–13.1 and 5.4–17.6
`times higher than the corresponding plasma level after oral and i.p. doses, respectively. The tissue to
`plasma level ratio of olanzapine was higher in other tissues. The data indicated that olanzapine is rapidly
`absorbed and widely distributed in the tissues of rats after oral and i.p. administration. The plasma
`concentration appears to predict the simultaneous concentration in brain and other tissues. There was no
`marked localized accumulation of olanzapine in any of the regions of the rat brain. Copyright © 1999 John
`Wiley & Sons, Ltd.
`
`Key words: brain–plasma level relationship; HPLC-ECD; olanzapine; pharmacokinetics; rat; regional
`brain distribution; tissue distribution
`
`Introduction
`
`compound
`Olanzapine, a thienobenzodiazepine
`(Figure 1) and a structural congener of clozapine, is
`one of the newer antipsychotic drugs used in the
`treatment of schizophrenia and other psychotic dis-
`orders. Olanzapine has high affinity to the serotonin
`5-HT2A receptor and moderate affinity to dopamine
`D1, D2, D4, serotonin 5-HT2c, 5-HT6, 5-HT7, H1, h
`1-
`adrenergic and muscarinic receptors [1–6]. Clinical
`studies indicate that olanzapine is as effective as
`haloperidol in reducing positive symptoms and su-
`perior in reducing negative symptoms [7–9]. The
`data from a recent PET scan investigation [2,3]
`showed a near saturation of 5-HT2A receptor bind-
`ing in schizophrenic patients receiving olanzapine
`doses as low as 5 mg/day. D2 occupancy increased
`with increasing dose of olanzapine. However, it was
`similar to that observed after risperidone treatment
`
`210c4,
`Bldg.
`Psychopharmacology Unit,
`to:
`* Correspondence
`VAGLAHS, Los Angeles, CA 90073, USA. E-mail: kannan@ucla.edu
`
`Copyright © 1999 John Wiley & Sons, Ltd.
`
`but higher than that seen after clozapine treatment.
`This type of receptor binding profile with a high
`5-HT2A blockade and the avoidance of over block-
`ade of D2 receptor at common therapeutic doses of
`an antipsychotic drug are believed to result in a
`reduced risk of extra pyramidal symptoms [5].
`Olanzapine is well absorbed after oral dosing and
`extensively metabolized to many primary metabo-
`lites such as N-desmethyl, N-oxide, 2-hydroxy-
`methyl, 4%-N-glucuronide and 10-N-glucuronide
`metabolites [10,11]. These metabolites are reputed to
`
`Figure 1. Chemical structure of olanzapine (MW=312.43)
`
`Received 21 September 1999
`Accepted 29 January 2000
`
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`370
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`M. ARAVAGIRI ET AL.
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`have no antipsychotic activity. The 10-N-glu-
`curonide metabolite of olanzapine is the major cir-
`culating metabolite and also the major excreted
`compound in humans [10]. Thus, olanzapine seems
`to be the sole active compound responsible for the
`clinical response. It has been reported that olanza-
`pine concentration in plasma increased with dose
`[12]. Also, plasma levels correlated well with clini-
`cal response [8] and the data revealed that patients
`with plasma concentrations above 9 ng/mL had a
`greater likelihood of responding to treatment.
`The distribution and the concentration of drugs in
`brain may be one of the main determinants of a
`drug’s effects. Similarly, with drugs acting on the
`central nervous system such as antipsychotic drugs,
`the distribution in brain may play a major role in
`determining clinical effects. It has been postulated
`that the brain to plasma level ratios correspond to
`the potency of antipsychotic drugs, [13–15] indicat-
`ing that facile distribution leading to higher concen-
`tration in brain as compared to plasma con-
`centration may be important for the clinical potency
`of antipsychotics. However, in the case of newer
`antipsychotic drugs such as risperidone, this phe-
`nomenon was not clearly observed. The brain to
`plasma concentration ratio after various doses of
`risperidone was many fold lower than that of an
`equipotent or even low potency older antipsychotic
`drugs [16]. Furthermore, with clozapine, a low po-
`tency atypical antipsychotic drug,
`the brain to
`plasma concentration ratio was high, 23 after a
`single i.p. dose [17]. Previous reports have shown
`that older antipsychotics such as haloperidol and
`fluphenazine had persistent brain levels and behav-
`ioral effects long after (up to 3 weeks) the with-
`drawal of drug administration [18,19]. These reports
`suggest that persistence of drugs in brain may be
`one of the reasons for the persistent behavioral
`effects. However, with newer antipsychotics such as
`clozapine there was marked deterioration in mental
`status within 1 week after clozapine withdrawal
`[19], probably due to a different distribution pattern
`of clozapine resulting in sub-therapeutic low con-
`centrations in the brain. In the case of olanzapine,
`an antipsychotic agent chemically and pharmaco-
`logically similar to clozapine, such studies have not
`been reported. However, it has been shown that
`olanzapine was readily distributed in all body tis-
`sues of the rat including the brain after a single oral
`dose of 8 mg/kg of 14[C]olanzapine [20] where total
`radioactivity in the tissues was measured as olanza-
`pine concentration by scintillation counting.
`The results from a single oral dose pharmacoki-
`netic study are reported here, in which olanzapine
`was directly measured in plasma and tissues from
`15 min to 48 h postdose and from a study in which
`olanzapine distribution in the brain and other tis-
`sues were measured after the repeated daily oral
`and intra-peritoneal (i.p.) administration of different
`
`dose levels to rats. The relationship between plasma
`and simultaneous brain and tissue olanzapine con-
`centration, the relationship between tissue concen-
`tration and administered dose and any localized
`accumulation in brain regions are discussed.
`
`Materials and Methods
`
`Chemicals
`Olanzapine and ethyl olanzapine (internal standard)
`were generously donated by Lilly Research Labs,
`Indianapolis, IN, USA. Solvents and chemicals were
`HPLC grade (Fisher Scientific, Los Angeles, CA,
`USA) and used without further purification. Deion-
`ized water was generated using a ROpure-Nano-
`pure water purification system (Barnstead Co.,
`Boston, MS, USA). All centrifugations were carried
`out using a refrigerated centrifuge (Centra GP8R,
`Fisher Scientific, Tustin, CA, USA) at 1725×g.
`
`Animals
`The Animal Research Committee and the Research
`and Development Committee of VA Greater Los
`Angeles Healthcare System approved experimental
`procedures using animals. Principles of laboratory
`animal care (NIH publication no. 85-23, revised
`1985) were followed. Male Sprague–Dawley albino
`rats with body weight 120 g were purchased
`from Harlan Sprague–Dawley, San Diego, CA,
`USA. After 1 week of quarantine from the date of
`arrival, animals were housed five per cage in a
`temperature-regulated room (23–25°C) with a 24 h
`lighting cycle (lights on 06:00–18:00 h). They were
`gently handled for another week and given a daily
`dose of water (0.25–0.5 mL) by oral gavage to
`accustom them to the oral dosing procedure. All
`animals had free access to food and water at all
`times.
`
`Experiment and Tissue Collection
`The olanzapine doses were made in deionized wa-
`ter acidified with citric acid (pH 5.5). Rats were
`given a single oral bolus dose of 6 mg/kg of olanza-
`pine by oral gavage. Four rats for each time-point,
`predose and 0.25, 0.5, 1, 2, 5, 8, 12, 24, 36, and 48 h
`postdose, were sacrificed by decapitation. The trunk
`blood was collected in heparinized glass tubes and
`whole brain and portions of liver, kidney, lung, fat
`and spleen were quickly removed and frozen in dry
`ice.
`Rats in the oral treatment group were given daily
`doses of olanzapine, 0.25 (n=5), 1 (n=8), 3 (n=8)
`and 6 mg/kg/day (n=8), by oral gavage for 15
`consecutive days in the morning (09:00–11:00 h).
`Similarly, rats in i.p. treatment group were given
`daily doses of olanzapine, 0.25 (n=5), 1 (n=8),
`
`Copyright © 1999 John Wiley & Sons, Ltd.
`
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`371
`
`3 (n=8) and 6 mg/kg/day (n=5), by i.p. injections
`for 15 consecutive days in the morning (09:00–11:00
`h). Four rats were treated as controls and received
`water instead for 15 days. On the 15th day, 3 h after
`the last dose, animals were decapitated and trunk
`blood from each rat was collected in heparinized
`glass tubes. Whole brain from four rats in each
`group receiving 1, 3, and 6 mg/kg/day oral doses
`and 1 and 3 mg/kg/day i.p. doses were removed
`and quickly dissected into cerebellum, fronto-pari-
`etal cortex, caudate, midbrain (pons-medulla), hy-
`pothalamus, hippocampus, olfactory tubercle, and
`remainder of the brain. These tissue samples were
`quickly frozen in dry ice. Whole brain from the
`remaining rats and portions of liver, kidney, lung,
`fat and spleen from all the rats were quickly re-
`moved and frozen in dry ice. Blood samples were
`centrifuged at 4°C for 10 min at 1725×g. Plasmas
`were separated and stored at −70°C until analysed.
`All tissues were homogenized in 5 mL of ice-cold
`physiological saline (150 mM NaCl) and the ho-
`mogenates were stored at −70°C until assayed.
`
`Analytical Method
`Aliquots of plasma and tissue homogenates were
`assayed for olanzapine by a modified sensitive high
`performance liquid chromatography with electro-
`chemical detection (HPLC-ECD) method [12].
`Briefly, 100 mL of 100 ng/mL of ethyl olanzapine (10
`ng) as internal standard and 0.5 mL of saturated
`solution of sodium carbonate were added to an
`aliquot of plasma or tissue homogenates (final
`pH10.5, not adjusted). The compounds were ex-
`tracted with 7 mL of 15% methylene dichloride in
`pentane solvent mixture. The supernatant solvent
`layer was removed and evaporated to dryness at
`60°C under a slow stream of nitrogen. The residue
`was dissolved in 150 mL of acetonitrile and analysed
`by the HPLC-ECD method. The mean absolute re-
`coveries for both compounds were 89920% of the
`total spiked amount. The standard curve was made
`in saline and consisted of at least six points ranging
`from 0.25 to 100 ng/mL of olanzapine. Three spiked
`samples (30–1.5 ng/mL) were made in saline and
`used as quality control samples to validate the
`standard curves.
`
`HPLC System
`The compounds were separated on an Ultrasphere
`cyano column (250×4.6 mm i.d., 5 mM particle size,
`Beckman, San Ramon, CA, USA) and eluted isocrat-
`ically. The mobile phase consisted of a mixture of
`an aqueous solution of 45 mM of ammonium ac-
`etate (pH 6.8 not adjusted), methanol and ace-
`tonitrile (8:6:84, vol.). The eluted compounds were
`detected by an electrochemical detector (Decade,
`Varian Chromatography, Walnut Creek, CA, USA)
`
`using a glassy carbon working electrode. The oxida-
`tion potential on the working electrode was +0.77
`V and the response was measured using a combina-
`tion of an auxiliary electrode and an Ag/AgCl refer-
`ence electrode. The detector response was recorded
`by a chromatographic data collection and data anal-
`ysis system (Chromquest, Tehrmoquest Corp., San
`Jose, CA, USA).
`
`Calculations
`The concentrations of olanzapine in unknown sam-
`ples were determined from the standard curve sam-
`ples analysed on the same day. The standard curve
`was constructed by plotting the olanzapine to inter-
`nal standard peak height ratios versus the corre-
`sponding concentration of olanzapine in ng/mL of
`the spiked standard curve samples. Along with each
`batch of unknown samples, a set of standard curve
`samples and spiked QC samples were analysed. All
`the samples were subjected to the same experimen-
`tal and analytical conditions. Noncompartmental
`extra vascular model pharmacokinetic parameters
`were estimated using WinNonlin microcomputer
`software (Scientific Consulting Inc., Cary, NC,
`USA). The statistical and graphical analyses were
`accomplished using commonly available commer-
`cial software packages (Microsoft Excel, Microsoft
`Corp.; Prism, GraphPad Software Inc., San Diego,
`CA, USA).
`
`Results
`
`The lower limit of determination of olanzapine by
`the HPLC-ECD method was 0.25 ng/mL when 0.5
`mL of the sample was used for analysis (signal to
`noise \3). The method is sensitive and precise. The
`inter- and intra-assay variations were less than 15%.
`The standard curves were linear over a range of
`0.25–100 ng/mL of olanzapine with a correlation
`coefficient of \0.997.
`
`Pharmacokinetics
`After the single 6 mg/kg oral dose, olanzapine was
`present in measurable amounts in all tissues up to
`36 h postdose except in fat and plasma where it
`could be measured only up to 12 h, and was present
`in measurable amounts in liver, lung, and brain up
`to 48 h postdose, the last time-point. Noncompart-
`mental pharmacokinetic parameters were calculated
`using WinNonlin software and the results are given
`in Table 1.
`The concentration–time profile of plasma, brain,
`liver and kidney are given in Figure 2 and they
`appeared to follow multi-phase elimination pattern.
`Olanzapine was present in high concentrations in
`all tissues even at the first postdose sampling time
`
`Copyright © 1999 John Wiley & Sons, Ltd.
`
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`Table 1. Mean values of noncompartmental pharmacokinetic parameters from plasma and selected tissues of rat
`following a single oral dose of 6 mg/kg of olanzapine
`
`Tissue
`
`Fat
`Kidney
`Liver
`Lung
`Plasma
`Spleen
`Brain
`
`Cmax
`(ng/mL
`or ng/g)
`
`616
`2821
`5146
`5513
`178
`3592
`1162
`
`tmax
`(h)
`
`0.6
`0.8
`0.7
`0.6
`0.6
`0.6
`0.6
`
`Half-life (t1/2)
`(h)
`
`AUClast
`(ng · h/mL
`or ng · h/g)
`
`AUC

`(ng · h/mL
`or ng · h/g)
`
`3.0
`4.0
`5.2
`4.5
`2.5
`3.9
`5.1
`
`888
`4363
`11 310
`11 229
`340
`7868
`2856
`
`958
`4371
`11 319
`11 247
`346
`7889
`2862
`
`All pharmacokinetic parameters are estimated using a noncompartmental extra vascular input Model (WinNonlin-Model 200).
`AUClast, area under the concentration–time curve up to the last assayed postdose time-point.
`AUC

, area under the concentration–time curve extrapolated to concentration at infinite time postdose.
`Half-life (t1/2), elimination half-life estimated using concentration–time curve from 5 h to last assayed postdose time-point (n=4 at
`each sampling time).
`
`Figure 2. Concentration (mean9S.D.) versus time profiles of olanzapine in plasma, brain, liver and kidney after a single oral dose of
`6 mg/kg of olanzapine to rats (n=4 at each time-point)
`
`Copyright © 1999 John Wiley & Sons, Ltd.
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`
`Table 2. The of mean9S.D. concentrations (ng/g or ng/mL) of olanzapine in brain and other tissues
`of rat at 3 h after the last daily oral and i.p. doses of 0.25, 1, 3 and 6 mg/kg/day for 15 consecutive
`days
`
`Tissues
`
`Olanzapine concentration (ng/g or ng/mL) after daily doses of:
`
`0.25 mg/kg/day
`
`1 mg/kg/day
`
`3 mg/kg/day
`
`6 mg/kg/day
`
`After oral dose
`Kidney
`Liver
`Lunga
`Plasma
`Spleen
`Brain
`
`After i.p. dose
`Kidney
`Liver
`Lung
`Plasmaa
`Spleen
`Brain
`
`6.693.9
`16.195.5
`
`0.790.9
`14.894.0
`6.596.2
`
`5.191.2
`7.595.1
`ND
`
`9.793.0
`2.691.3
`
`6.792.3
`40.396.5
`18.294.6
`0.690.3
`23.994.1
`7.390.9
`
`12.994.9
`15.595.4
`26.9915.6
`0.790.3
`42.2915.4
`9.393.8
`
`40.4923.7
`351.69133.0
`231.99220.7
`9.893.8
`225.39191.7
`51.196.9
`
`30.2913.6
`57.2919.2
`126.6931.7
`3.290.7
`118.3958.0
`19.099.8
`
`97.3945.9
`666.29339.7
`454.89355.2
`21.997.5
`579.39184.0
`151.0987.0
`
`84.9951.1
`143.4940.8
`402.19321.7
`12.094.9
`562.19260.2
`63.1914.7
`
`ND, nondetectable.
`a Olanzapine was present in quantifiable amount in only one of the five rats receiving 0.25 mg/kg/day dose (n=4
`or 5 rats/dose).
`
`at 15 min and reached peak concentrations (Cmax)
`within 45 min (tmax). The terminal half-life (t1/2) of
`olanzapine in plasma was 2.5 h and in other tissues
`it was slightly longer, varying from 3 to 5.2 h. The
`area under the concentration–time curve (AUClast) of
`olanzapine was calculated using the linear trape-
`zoidal rule and it was lowest for plasma and highest
`for liver and lung followed by spleen, kidney, brain
`and fat. The AUClast and AUC

values were similar
`and the difference was less than 2% except for fat
`(5%) where olanzapine was not present in quantifi-
`able levels after the 12 h postdose time-point.
`
`Tissue Distribution After Repeated Oral
`Administration of Various Doses of Olanzapine
`for 15 Days
`Following oral administration, olanzapine was
`present in measurable amounts in all tissues and the
`whole brain at all doses except in fat and lung (Table
`2). In fat tissue, it was nondetectable at 0.25 and 1
`mg/kg/day doses. In lung, olanzapine was present in
`measurable amount only in one of five rats receiving
`0.25 mg/kg/day. At a given dose there were large
`inter-individual variations observed in the tissue
`concentrations of olanzapine in all tissues. Olanza-
`pine was present in tissues at higher concentration
`than in plasma at all dose levels. The liver had the
`highest concentration followed by the spleen, lung,
`brain and kidney (Table 2).
`Olanzapine levels in brain regions varied widely
`and the concentrations were very low after the 1
`mg/kg/day oral dose, but were present in measurable
`amounts after 3 and 6 mg/kg/day oral doses (Figure
`3). Also, olanzapine was nondetectable in hippocam-
`pus and hypothalamus at the 1 mg/kg/day dose.
`
`Figure 3. Mean9S.D. concentration of olanzapine in plasma and
`in various brain regions of the rat after daily oral doses of 1, 3
`and 6 mg/kg/day and daily i.p. doses of 1 and 3 mg/kg/day for
`15 consecutive days. The olanzapine concentrations were deter-
`mined at 3 h after the last dose (n=4 rats/dose). OT, olfactory
`tubercle; Rest-brain, remainder of the brain
`
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`However, at the 3 mg/kg/day dose, the cortex, cau-
`date, cerebellum and hypothalamus had concentra-
`tions
`similar
`to whole
`brain, whereas
`the
`hippocampus and the rest of the brain had two- to
`threefold higher concentration. Furthermore, after
`the 6 mg/kg/day dose, olanzapine concentrations in
`caudate and cerebellum were two-
`to threefold
`lower than the whole brain concentrations. In other
`brain regions the levels were similar to whole brain
`levels.
`The tissue olanzapine concentrations increased
`with increasing oral dose (Table 2). The relationship
`between tissue levels and dose was significant in all
`tissues (r 2=0.69–0.83, pB0.0001) except in lung
`where the correlation was low but still significant
`(r 2=0.419, pB0.007). There was also a significant
`direct relationship between plasma levels and corre-
`sponding simultaneous concentrations in brain and
`other tissues (r 2\0.908, pB0.0001, Figure 4). The
`ratio of tissue to plasma concentration of olanzapine
`(Figure 5) was high for liver, spleen, and lung
`followed by kidney and brain. These ratios are
`/AUCplasma
`consistent with the ratios of AUCtissue
`after the single oral dose. After oral doses, the mean
`values of brain to simultaneous plasma concentra-
`tion ratio varied from 6.3 to 13.1.
`
`Figure 4. Scatter plot of olanzapine concentration in plasma and
`brain of rats after the daily oral and i.p. doses of 0.25, 1, 3 and 6
`mg/kg/day for 15 consecutive days. The olanzapine concentra-
`tions were determined at 3 h after the last dose (n=4 or 5
`rats/dose)
`
`Figure 5. Tissue to plasma concentration ratio of olanzapine
`(mean9S.D.) after the daily oral and i.p. doses of 0.25, 1, 3 and
`6 mg/kg/day for 15 consecutive days to rats. The olanzapine
`concentrations were determined at 3 h after the last dose (n=4
`or 5 rats/dose)
`
`Tissue Distribution After Repeated i.p.
`Administration of Various Doses of Olanzapine
`for 15 Days
`After i.p. doses there were large variations in the
`tissue concentrations of olanzapine (Table 2). A
`general trend was observed that, after i.p. doses, the
`olanzapine levels were lower than that observed
`after similar oral doses in plasma and tissues (Table
`2). After i.p. doses, olanzapine levels were highest
`in spleen followed by lung, liver, kidney and the
`brain. Olanzapine concentrations
`in the brain,
`spleen, kidney and plasma showed strong direct
`relationships with i.p. dose (r 2=0.711–0.918, pB
`0.0001) but lung, liver and fat showed weak rela-
`tionships (r 2=0.368, 0.465 and 0.408, respectively,
`pB0.06).
`Following i.p. doses, the olanzapine concentra-
`tions in all tissues were higher than the simulta-
`neous plasma
`levels. The
`brain to plasma
`concentration ratios after i.p. doses were similar to
`those observed after oral doses (Figure 5) and
`varied from 5.4 to 17.6. The olanzapine levels in
`brain regions after i.p. doses were comparable to
`whole brain levels. Furthermore, a significant direct
`relationship was observed between plasma levels
`and corresponding simultaneous levels in the brain
`
`Copyright © 1999 John Wiley & Sons, Ltd.
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`
`(Figure 4), kidney, lung, liver and spleen (r 2\0.772,
`pB0.0001).
`
`Discussion
`
`Oral and i.p. doses were carefully given so that
`there were no injuries to the internal organs of the
`animals. Animals tolerated olanzapine well, even at
`the high dose of 6 mg/kg/day. There was no observ-
`able distress, such as loss of body weight, due to the
`olanzapine administration. All animals appeared to
`be in good health until the end of the study. Olan-
`zapine metabolites were not available to the authors
`to check their interference in the HPLC-ECD analy-
`sis. However,
`there were no indications of any
`unknown peak in the chromatogram interfering
`with the olanzapine or the internal standard peaks.
`Olanzapine concentrations lower than 0.25 ng/mL
`or ng/g (lower limit of determination of the assay)
`were excluded from the data analysis.
`Olanzapine was present at high concentrations in
`plasma and tissues at the 15 min postdose, first
`sample, after the single oral dose. The fact that Cmax
`was reached within 45 min postdose indicated that
`olanzapine was rapidly absorbed after oral adminis-
`tration and readily distributed in various tissues.
`Olanzapine was more rapidly eliminated from
`plasma with a t1/2 of 2.5 h than from other tissues
`where t1/2 varied from 3 to 5.2 h. The AUClast and
`AUC

were very similar and the difference be-
`tween them was less than 2%. The AUCs for plasma
`was eight- to 32-fold smaller than that found in
`other tissues. Similar results were observed in a
`previously reported study [20] in which a single
`oral dose of 8 mg/kg of [C14]olanzapine was given
`to male Fischer-344 rats. The total radioactivity in
`various tissues was measured as the concentration
`of olanzapine from 2 to 96 h postdose. In most
`tissues, with the exception of liver, kidney, thyroid,
`and Harderian gland, the radioactivity was nonde-
`tectable after 48 h postdose. The time to reach peak
`radioactivity (tmax) in most tissues was 2 h, the first
`postdose time-point, except in liver, kidney and
`spleen where it was 6 h, the second postdose time-
`point. These longer tmax in these tissues as com-
`pared to the tmax of 45 min in the current report
`may in part be due to the fact that the first postdose
`sample time was 2 h and that the measured total
`radioactivity would be a combined total of olanza-
`pine and its radioactive metabolites. Furthermore,
`this may be one of the reasons, apart from the larger
`dose of [C14]olanzapine and different rat strain used
`in the reported study, for the difference in the t1/2 of
`=2 h to 2 days) as
`olanzapine in various tissues (t1/2
`=3–5.2 h) estimated in the
`compared to those (t1/2
`current report. The AUCs of olanzapine in various
`tissues were similar in both reports. Although the
`
`absolute values of AUCs are understandably differ-
`ent, the pattern was similar in that the AUC of
`plasma or blood was lowest and that of liver was
`the highest followed by lung, spleen, kidney and
`brain.
`The t1/2 of olanzapine in plasma and tissues
`varied from 2.5 to 5.2 h (Table 1). Therefore, the
`tissue concentrations determined in this study, 3 h
`after the 15th consecutive daily doses of olanzapine
`might be considered as apparent steady-state con-
`centrations. Under this steady-state condition, any
`variation in tissue levels resulting from the differ-
`ences in the rate of distribution into the various
`tissues will be small. Furthermore, the tmax after a
`single oral dose of olanzapine in most tissues of rat
`was 45 min. In the current study, tissues were
`collected 3 h after the last dose and hence the
`determined tissue concentrations of olanzapine
`were not peak concentrations.
`Olanzapine was readily absorbed and widely dis-
`tributed into tissues after oral doses. Liver, a major
`organ of xenobiotic detoxification, had the highest
`concentration of olanzapine after oral doses fol-
`lowed by spleen, lung, kidney and brain (Table 2).
`The olanzapine concentration in plasma was lower
`than the simultaneous concentration in all the other
`tissues analysed indicating that olanzapine is read-
`ily distributed into tissues. However, in fat tissue,
`the levels were similar to plasma but there was no
`relationship found between dose and olanzapine
`level. The concentration of olanzapine in other tis-
`sues increased with increasing dose. Plasma con-
`centrations showed a significantly strong linear
`correlation with simultaneous tissue concentrations,
`including whole brain, indicating that plasma olan-
`zapine concentrations represent a good predictor of
`tissue concentrations.
`The brain to plasma concentration ratio after oral
`doses varied widely within doses and between
`doses. The mean value of the ratio at different oral
`doses varied from 6.3 to 13.1. The value of brain to
`plasma concentration ratio was high at low dose
`and low at high doses and it did not change signif-
`icantly between 3 and 6 mg/kg/day doses. After the
`oral doses, olanzapine concentrations in various
`brain regions indicated that there was no selective
`accumulation of olanzapine into any region of the
`rat brain.
`Olanzapine concentrations in plasma and tissues
`after i.p. doses were consistently lower than that
`obtained after oral doses, indicating that olanzapine
`was more readily absorbed and distributed into
`tissues after oral doses than after i.p. doses. The
`spleen had the highest olanzapine level after i.p.
`dose followed by lung,
`liver, kidney and brain.
`Lower olanzapine levels in liver tissues were ex-
`pected after i.p. doses as olanzapine was slowly
`absorbed into the systemic circulation from the site
`of i.p. injection, resulting in lower concentrations in
`
`Copyright © 1999 John Wiley & Sons, Ltd.
`
`Biopharm. Drug Dispos. 20: 369–377 (1999)
`
`7 of 9
`
`Alkermes, Ex. 1034
`
`

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`376
`
`M. ARAVAGIRI ET AL.
`
`tissues including liver. Olanzapine did not show
`any preferential accumulation to any of the brain
`regions analysed. In many of the rats receiving 1
`and 3 mg/kg/day i.p. doses, olanzapine was not
`present in detectable amounts in the cerebellum,
`hippocampus and hypothalamus. However,
`in
`other brain regions, it was present in concentrations
`similar to the whole brain. Furthermore, it is impor-
`tant to note that the olfactory tubercle, which had
`been suggested as one of the possible sites of action
`of newer antipsychotics [21], had substantial con-
`centrations of olanzapine after both oral and i.p.
`administrations. The tissue to plasma concentration
`ratios for the whole brain after i.p. doses were
`similar to those found after oral doses and the mean
`value at different doses varied from 5.4 to 17.6.
`The brain to plasma concentration ratio of an-
`tipsychotics varies widely among newer antipsy-
`chotics from a low ratio of 0.22 with risperidone [16]
`to a high ratio of 24 with clozapine [17], and among
`older antipsychotics the ratio was 22 with haloperi-
`dol [14] and 34 with fluphenazine [15]. The brain to
`plasma ratio of olanzapine was moderate after oral
`and i.p. doses and varied from 5.4 to 17.6. The brain
`to plasma ratio of olanzapine does not seem to
`depend upon its lipophilicity (log P, P=octanol–
`water partition coefficient) or its plasma protein
`binding capacity [10]. Although the lipophilicity of
`olanzapine (log P at pH 7.4=2.23,
`log P union-
`ized=2.97, personal communication from Lilly Re-
`search Labs) was less than that of risperidone [22]
`(log P=3.04), the brain to plasma olanzapine ratio
`ranged from 5.4 to 17.6. These values are many fold
`higher than the value of 0.22 for risperidone. Thus,
`the brain to plasma level ratio of antipsychotics
`probably represents a complex situation involving
`many factors, including unbound drug concentra-
`tion in plasma, ability to cross the blood–brain
`barrier, ability to accumulate in brain, metabolism,
`pharmacokinetics and the lipophilicity of
`these
`drugs. The relationship between the brain to plasma
`level
`ratio of an antipsychotic agent and its
`lipophilicity or its antipsychotic potency needs fur-
`ther study with other newer antipsychotics. The
`moderate brain to plasma concentration ratio for
`olanzapine may be one of the reasons for the gener-
`ally observed low incidence of extra-pyramidal
`symptoms in patients treated with olanzapine as
`compared to the treatment with conventional an-
`tipsychotics such as fluphenazine and haloperidol.
`Both the later antipsychotics showed higher brain to
`plasma ratio and higher incidence of extra-pyrami-
`dal symptoms [13,14,18].
`Although the oral and i.p. doses (1–6 mg/kg/day)
`administered to rats were generally higher than the
`normal therapeutic doses administered to humans
`(0.1–0.5 mg/kg/day), such high doses are routinely
`used in animal studies [20]. Due to a lack of
`availability of radiolabeled olanzapine, such high
`
`doses are necessary to facilitate the direct determi-
`nation of tissue concentrations. Moreover, with a
`lower limit of quantification of 0.25 ng/mL for the
`assay method, the nondetectable concentrations en-
`countered in tissues should be viewed with caution,
`especially with the low-weight brain regional tis-
`sues such as caudate, hippocampus and hypothala-
`(2 mg tissue/mL). The nondetectable
`mus
`concentration encountered in these tissues may ac-
`tually be different.
`
`Summary
`
`In conclusion, orally administered olanzapine was
`rapidly absorbed, widely distributed and readily
`eliminated from plasma and tissues of rat. Plasma
`and tissue olanzapine concentrations significantly
`correlated with dose after both oral and i.p. admin-
`istrations. Olanzapine appears to evenly distribute
`in the brain and there is no marked preferential
`accumulation observed in any of the brain regions.
`The plasma concentration seems to predict
`the
`simultaneous concentrations in the brain and other
`tissues. Although the receptor binding affinities for
`olanzapine in tissues from the rat and human were
`quite similar [4], the application of the data from a
`rat study to a human population should be carried
`out with caution.
`
`Acknowledgements
`
`This work was supported by the University of Cali-
`fornia at Los Angeles Mental Health Clinical Re-
`search Center for the Study of Schizophrenia, VA
`Greater Los Angeles Healthcare System, and Na-
`tional Institute