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`ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Nov. 1988, p. 1699-1704
`0066-4804/88/111699-06$02.00/0
`Copyright © 1988, American Society for Microbiology
`
`Vol. 32, No. 11
`
`Pharmacokinetics and Metabolism of Rimantadine Hydrochloride
`in Mice and Dogs
`HOWARD E. HOFFMAN,'* JANET C. GAYLORD,2 JOHN W. BLASECKI,3 LAMAAT M. SHALABY,4
`AND CHARLES C. WHITNEY, JR.5
`Medical Research, Pharmaceuticals Division, Medical Products Department, E. I. du Pont de Nemours & Co., Inc.,
`Barley Mill Plaza 2611230, Wilmington, Delaware 198981; Drug Metabolism Section, Pharmaceuticals Division,
`Medical Products Department, E. I. du Pont de Nemours & Co., Inc., Stine-Haskell Research Center, Newark,
`Delaware 197142; Chemotherapy Research Section, Pharmaceuticals Division, Medical Products Department,
`E. I. du Pont de Nemours & Co., Inc., Glenolden Laboratory, Glenolden, Pennsylvania 190363; and Agricultural
`Products Department4 and Analytical Research and Development, Pharmaceuticals Division,5 Experimental Station,
`E. I. du Pont de Nemours & Co., Inc., Wilmington, Delaware 19738
`Received 11 April 1988/Accepted 16 August 1988
`
`We studied the pharmacokinetics and metabolism of rimantadine hydrochloride (rimantadine) following
`single-dose oral and intravenous administration in mice and dogs. Absorption of the compound in mice was
`rapid. Maximum concentrations in plasma occurred at less than 0.5 h after oral administration, and the
`elimination half-life was 1.5 h. Peak concentrations in plasma following oral administration were markedly
`disproportional to the dose (274 ng/ml at 10 mg/kg, but 2,013 ng/ml at 40 mg/kg). The bioavailability after an
`oral dose of 40 mg/kg was 58.6%. Clearance was 4.3 liters/h per kg, and the volume of distribution was 7.6
`liters/kg at 40 mg/kg. In contrast to the results observed in mice, absorption of the compound in dogs was slow.
`Maximum concentrations in plasma occurred at 1.7 h after oral administration, and the elimination half-life
`was 3.3 h. A further difference was that peak concentrations in plasma were approximately proportional to the
`dose. Following administration of a single oral dose of 5, 10, or 20 mg/kg, maximum concentrations in plasma
`were 275, 800, and 1,950 ng/ml, respectively. The bioavailability after an oral dose of 5 mg/kg was 99.4 o.The
`clearance was 3.7 liters/h per kg, and the volume of distribution was 13.8 liters/kg at 5 mg/kg. Mass balance
`studies in mice, using [methyl-'4CJrimantadine, indicated that 98.7% of the administered dose could be
`recovered in 96 h. Less than 5 % of the dose was recovered as the parent drug in dog urine within 48 h. Finally,
`gas chromatography-mass spectrometry studies, done with mouse plasma, identified the presence of two
`rimantadine metabolites. These appeared to be ring-substituted isomers of hydroxyrimantadine.
`
`Rimantadine hydrochloride (rimantadine), which is chem-
`ically related to the anti-influenza A drug amantadine hydro-
`chloride (amantadine, Symmetrel), has been reported to be
`effective against influenza A in human studies and in mouse
`model systems (2, 7, 11). It is being used in the USSR for
`both prophylaxis and therapy of influenza A infections (12).
`The pharmacokinetics and metabolism of rimantadine in
`humans have been reported (F. G. Hayden and H. E. Hoff-
`man, Abstr. 14th Annu. UCLA Symp., J. Cell. Biochem.,
`suppl. 96, p. 276, 1985; L. P. Van Voris, J. Bartram, H. E.
`Hoffman, L. M. Shalaby, J. C. Gaylord, L. S. Davis, and
`F. G. Hayden, Program Abstr. 23rd Intersci. Conf, Antimi-
`crob. Agents Chemother, abstr. no. 684, 1983) for healthy
`subjects, but no animal studies have been reported. We have
`studied rimantadine kinetics and metabolism in mice (mice
`are used for most influenza model infections) and in dogs.
`
`MATERIALS AND METHODS
`Rimantadine assay. (i) Plasma. The rimantadine level in
`plasma was analyzed as previously described (3), with
`modifications for measuring the levels in urine, feces, and
`tissues.
`A 1-ml sample of plasma was extracted by using cyano
`Bond Elut disposable extraction columns (Analytichem In-
`ternational). The extracted rimantadine was derivatized with
`pentafluorobenzoyl chloride (PFB) (Aldrich Chemical Co.,
`Inc.), yielding the pentafluorobenzoyl derivative of rimanta-
`
`* Corresponding author.
`
`dine, which was then analyzed by gas chromatography (HP
`5880A; Hewlett-Packard Co.) with an electron capture de-
`tector (6). PFB-amantadine was used as the internal standard
`and was prepared in house. The oven temperature was
`programmed for 240°C for 5 min, followed by a temperature
`gradient of 5°C/min for 6 min, to 270°C. The 6-ft (1.83-m)
`column was packed with 10% OV-1 (Ohio Valley Specialty
`Chemical, Inc.) on Chromasorb W (Hewlett-Packard Co.).
`The method was linear between 10 and 10,000 ng/ml in
`plasma-free solutions. The limit of detection was 5 ng/ml.
`However, linearity in biological solutions, such as plasma or
`tissue extracts, was restricted to a narrower range and was
`determined for each analysis. Samples were assayed only in
`the linear portion of the curve. Absolute recovery from
`plasma ranged from 54% at 50 ng/ml to 72% at 1,000 ng/ml.
`Reproducibility was 7% relative standard deviation. Riman-
`tadine in plasma was stable when stored at -20°C for 5
`weeks.
`The resultant peaks on the chromatograms indicated that
`the method was highly specific. Retention times were repro-
`ducible regardless of the biological fluids, and there was no
`interference from other substances in the extracts. Retention
`times for principal peaks were as follows: internal standard,
`4.3 min; rimantadine, 6.6 min; metabolite M-1, 9.9 min; and
`metabolite M-2, 12.2 min.
`(ii) Mouse lung assay. Individual lungs were each homog-
`enized in 3 ml of 5 N NaOH. A 1-ml sample of the resulting
`homogenate was added to 5 ml of 5 N NaOH-50 mg of NaCl-
`15 ml of hexane. After 30 min on a wrist action shaker and
`
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`1700
`
`HOFFMAN ET AL.
`
`ANTIMICROB. AGENTS CHEMOTHER.
`
`centrifugation to separate the phases, the hexane layer was
`removed and evaporated to dryness. The residue was dis-
`solved in 1 ml of toluene and derivatized as with the plasma
`extracts. Recovery of rimantadine from mouse lungs was
`42%.
`(iii) Standard curves. Standards were prepared in each
`biological fluid analyzed, i.e., mouse, rat, and dog plasma;
`lung extracts; and dog and mouse urine. A standard curve
`was prepared from the peak height ratios by linear regression
`analysis, and concentrations were computed from the re-
`gression equation. Four to six points were used in each
`regressiQn analysis.
`(iv) 1-Glucuronidase hydrolysis. Glucuronide conjugation
`was determined by using P-glucuronidase supplied by Sigma
`Chemical Co. (kit 325). The enzyme, at a final concentration
`of 10 U/ml of urine, was incubated with dog urine for 2 h at
`37°C. ,-Glucuronidase activity was monitored by hydrolyz-
`ing phenolphthalein glucuronic acid. After incubation, the
`urine samples were extracted as described above.
`(v) Urine assay. A 1-ml sample of urine was placed in 5 ml
`of 5 N NaOH and extracted as described for the mouse lung
`assay.
`[14C]rimantadine methods. [14C]rimantadine (specific ac-
`tivity, 5.34 mCi/mmol), prepared by Du Pont, NEN Re-
`search Products, was labeled at the methyl group. Its radio-
`chemical purity was 98%.
`Virus preparation. Influenza virus A/Bangkok/1/79 (H3N2)
`was prepared by serial passage in CD-1 mice inoculated
`intranasally with 50 ,ul of an appropriately diluted stock
`preparation. At about 36 h postinfection, lungs were surgi-
`cally excised under aseptic conditions and homogenized in
`phosphate-buffered saline containing bovine serum albumin
`(0.2%), penicillin (100 IU/ml), and kanamycin (25 ,i.g/ml).
`The homogenate was frozen and thawed three times and
`clarified by centrifugation. The supernatant was collected
`and stored frozen at -70°C in 1-ml aliquots.
`CD-1 female mice (Sendai virus free), 20 to 30 days of age
`and weighing an average of 15 g, were each infected intra-
`nasally, under light anesthesia, with 50 ,ul of influenza virus
`A/Bangkok/1/79 (H3N2) at dilutions of 10-3.8, 10-4.8, and
`10-5 , respectively, with 12 mice per dilution level. Virus
`dilutions were made in phosphate-buffered saline (pH 7.2),
`as described above. The virus preparation yielded a 50%
`lethal dose of 10-5.24 and a 90% lethal dose of 10-4.25.
`Sample preparation for liquid scintillation counting. (i)
`Radiometric assay. Samples were counted in a Packard Prias
`scintillation spectrometer with Atomlight (Du Pont, NEN) as
`the scintillation fluid.
`(ii) Standards. Using the external standard system, we
`determined counting efficiencies with graded quenched stan-
`dards programmed into the Prias counter. The radioactivity
`in the test sample was measured as counts per minute,
`corrected for quenching, and reported as disintegrations per
`minute.
`(iii) Plasma, urine, and cage wash. A measured volume of
`plasma, urine, or liquid used for washing the cages was
`placed into a scintillation vial containing 7 ml of Atomlight
`and counted in the liquid scintillation counter.
`(iv) Feces. Feces samples (50 to 500 mg) were oxidized in
`a Packard Tri-Carb sample oxidizer, and the 14C02 was
`trapped in Carbosorb (Packard) absorbent with Permafluor
`(Packard) as the scintillant. All samples were counted in
`triplicate when possible, and control and spiked [14C]ri-
`mantadine standards were run concurrently with the exper-
`imental samples. The mean 14C recoveries from feces spiked
`
`with known amounts of labeled rimantadine and subjected to
`combustion were 94.3%.
`Animal treatments. (i) Mice. Groups of six nonfasted
`female mice (mean weight, 22 g) were dosed perorally with
`10 or 40 mg of rimantadine per kg, formulated in saline at 1
`mg/ml. An additional group received 40 mg/kg intrave-
`nously. Blood was drawn by intracardiac puncture into
`heparin-containing tubes and pooled, and plasma was pre-
`pared. Blood samples were taken at 0, 0.5, 1, 2, 3, 4, 6, 8, 10,
`12, and 24 h after dosing.
`To determine the effects of virus infection on the pharma-
`cokinetics of rimantadine, mice (five per time interval) were
`infected intranasally with influenza virus A/Bangkok/1/79
`(H3N2), as above, at a virus dilution of 10-4.8, and dosed
`orally with the drug (40 mg/kg) at 72 h postinfection. Unin-
`fected control mice simultaneously received the same oral
`doses of rimantadine. At 0, 0.25, 0.5, 1, 2, 4, 6, 8, 12, 16, 24,
`and 48 h after drug dosing, blood was collected, pooled, and
`then centrifuged to separate the plasma. The lungs were
`excised at the same time points, and all samples were frozen
`until assayed.
`(ii) Dogs. Female beagles were dosed with rimantadine at
`5, 10, and 20 mg/kg perorally and 5 mg/kg intravenously.
`Rimantadine was formulated in water at 5 mg/ml for peroral
`dosing and in sterile saline for intravenous dosing. The dogs
`were fasted overnight and treated with drug in the morning.
`Blood was collected from the jugular vein at 0.5, 1, 2, 4, 6, 8,
`10, 12, 16, and 24 h in sodium heparin-containing tubes. All
`samples from dogs were assayed separately.
`(iii) Material balance study in mice. [14C]rimantadine was
`dissolved in water (1 mg/ml) at a specific activity of 3.2 uCi/
`mg. Three groups of two Charles River CD female mice each
`were given a single oral dose of 40 mg of [14C]rimantadine
`per kg and placed into metabolism chambers. Groups 1 and
`3 received a total dose of 4.86 ,Ci, and group 2 received 5
`,uCi. Urine and feces were collected at 24-h intervals during
`the study. Samples (Q ml) of the urine and cage-washing
`liquid were counted in triplicate. Fecal samples were oxi-
`dized prior to liquid scintillation counting.
`Mass spectrometry. The gas chromatography separations
`were made on a 15-m J&W DB-1, 0.25-mm (inner diameter)
`capillary column which was directly interfaced to a Finnigan
`model 4500 mass spectrometer. The column temperature
`was programmed from 200 to 260°C at 10°C/min. Mouse
`plasma extract, containing rimantadine and its metabolites,
`was reacted with PFB and dissolved in toluene. The deriva-
`tized sample was initially analyzed by capillary gas chroma-
`tography-mass spectrometry in the electron impact mode,
`and to enhance the molecular (M+) ion, the gas chromatog-
`raphy-mass spectrometry was rerun with chemical ioniza-
`tion.
`Pharmacokinetic calculations. All pharmacokinetic param-
`eters were determined with the RS-1 computer program
`(BBN Research Systems, Cambridge, Mass.). The area
`under the concentration-time curve from zero to infinity
`(AUCo,) was calculated by summing the area to the last
`measured time point (Clast) determined by the linear trape-
`zoidal rule, and the extrapolated area was determined by
`Ciast/kel, where ke, is the elimination rate constant and was
`determined from the slope of the terminal portion of the In
`concentration-time curve. The half-life (t1/) was 0.693/ke.
`The clearance (CL) was D/AUC, and the volume of distri-
`bution (V) was CL/kel.
`
`

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`VOL. 32, 1988
`
`RIMANTADINE PHARMACOKINETICS AND METABOLISM
`
`1701
`
`TABLE 1. Pharmacokinetics of rimantadine in mice'
`t412 CL (liters/h
`Tmax
`Cmax
`Dose
`(mg/kg) (ng/ml)
`(h)
`(h)
`per kg)
`0.5
`1.253
`10
`274
`0.5
`2.063
`2,013
`40
`
`AUC
`(ng- h/ml)
`555
`5,421
`
`F
`V
`(liters/kg) (%)
`
`58.6
`
`Route
`
`Oral
`
`i.v.b
`1.224
`9,247
`0.5
`40
`a Plasma was pooled from six mice per period.
`b i.V., Intravenous.
`
`4.3
`
`7.6
`
`RESULTS
`Mouse pharmacokinetics. Plasma pharmacokinetic data for
`mice are summarized in Table 1. Oral absorption was rapid,
`with the maximum concentration in plasma (Cmax) occurring
`at 30 min, the earliest time point measured (Fig. 1). The
`elimination half-life (t112) was between 1 and 2 h. V was 7.6
`liters/kg, which suggests extensive distribution of the drug
`into tissues. CL was 4.3 liters/h per kg. The increase in AUC
`values was not proportional to the dose. The bioavailability
`of rimantadine in mice after oral administration of 40 mg/kg
`was 58.6%.
`Influenza A virus-infected mice. In a separate study, nor-
`mal and influenza virus-infected mice were compared (Table
`2). Peak levels in both plasma and lungs decreased in
`infected mice, and the peak time in the lungs increased from
`0.25 to 2.0 h, whereas it remained the same in plasma. Thus,
`infection both decreases and delays the uptake of rimanta-
`dine in the lungs. However, AUC values for lungs from
`infected and noninfected mice were not different (Table 2),
`nor were the AUC,ung/AUCplasma ratios. The ratio for normal
`mice, 45.7, is similar to that for infected mice, 48.5, suggest-
`ing that the virus infection does not alter the total impact of
`rimantadine during the period studied.
`
`10000-
`
`-m
`
`13-~
`
`0
`
`N
`
`TABLE 2. Pharmacokinetic parameters in mouse plasma and
`lungs from uninfected and influenza A virus-infected mice given a
`single oral dose of 40 mg/kg
`k(el)
`(h'1)
`
`t2
`(h)
`
`AUC
`(ng.- h/ml)
`
`Cmax
`(nglml)
`
`Tma. (h)
`mx
`
`Specimen
`
`na
`
`Plasma
`Uninfected
`Infected
`
`6
`5
`
`0.324
`0.299
`
`2.1
`2.3
`
`7,631
`6,667
`
`2,169
`1,436
`
`0.25
`0.25
`
`Lung
`1.8
`0.385
`Uninfected
`6
`Infected
`0.156
`4.4
`5
`a n, Number of mice per period.
`b A second Cmax occurred at 2 h.
`
`348,546
`323,457
`
`74,251
`45,436
`
`0.25 (2.0)b
`2.00
`
`Dog plasma pharmacokinetics. Plasma pharmacokinetic
`data for dogs are shown in Table 3. The t112s were 2.9, 3.4,
`and 3.7 h for oral administration of 5, 10, and 20 mg/kg,
`respectively, and 2.6 h for a 5-mg/kg intravenous dose. As
`found for mice, the increase in AUC values for dogs was not
`proportional to the dose. The bioavailability after a 5-mg/kg
`oral dose was 99.5%, nearly twice that found in mice (58.6%)
`after a 10-mg/kg dose. The values for the time to maximum
`concentration of drug (Tmax) were 1 h at 5 mg/kg and 2 h at
`10 and 20 mg/kg. Cmax increased with increasing dose, but
`the increase was not proportional to the dose. CL was 3.7
`liters/h per kg, similar to that for mice, and V was 13.8 liters/
`kg.
`Metabolism studies. Mouse plasma extracts contained two
`metabolites: M-1, with a retention time of 9.9 min, and M-2,
`with a retention time of 12.2 min. Both rimantadine and M-1
`were observed at the earliest time sampled (0.5 h). M-1 and
`M-2 were also found in mouse urine.
`Concentrations of M-1 and rimantadine in mouse lungs
`
`\>Elss~~~I-
`
`M...,
`".%_S
`
`z z0P zI
`
`M z0 4
`
`*
`
`0
`
`2
`
`4
`
`6
`HOURS
`FIG. 1. Concentration of rimantadine in uninfected mouse plasma after a single dose. Groups of six nonfasted female mice, weighing 20
`to 23 g, were dosed at 10 mg/kg perorally (U), 40 mg/kg perorally (O), and 40 mg/kg intravenously (@) and bled by cardiac puncture into
`heparinized tubes. The serum was pooled. The mean variation of the method for replicate samples was 7% (coefficient of variation).
`
`S
`
`10
`
`12
`
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`1702
`
`HOFFMAN ET AL.
`
`ANTIMICROB. AGENTS CHEMOTHER.
`
`TABLE 3. Pharmacokinetics of rimantadine in dogs
`
`Route
`
`Oral
`
`Dose
`(mg/kg)
`
`5
`10
`20
`
`a
`
`n
`
`3
`2
`1
`
`k
`(h-')
`
`0.242
`0.202
`0.190
`
`t1/2
`(h)
`
`2.86
`3.43
`3.65
`
`AUC
`h/ml)
`(ng
`(±SD)
`1,353 (236)
`4,066 (263)
`11,520
`
`Cmax
`(ngml)
`(±SD)
`275 (47)
`788 (16)
`1,950
`
`i.V.b
`5
`3
`0.267
`2.60
`1,361 (94)
`a n, Number of animals per dose level used. Samples from each dog were assayed separately.
`b i.V., Intravenous.
`
`T.CL
`(h)
`(liter/h per kg)
`
`V
`(liter/kg)
`
`1.0
`2.0
`2.0
`
`3.7
`
`13.8
`
`F(%)
`
`99.4
`
`were measured after oral dosing. Peak concentrations of
`rimantadine were observed at 0.5 h, whereas M-1 concen-
`trations peaked at 2 h after dosing. A plot of the concentra-
`tions of rimantadine and M-1 in lung tissues is shown in Fig.
`2. Metabolite M-2 in mouse lungs was not determined
`quantitatively owing to poor chromatographic resolution but
`was found in mouse and rat plasma and human, mouse, and
`dog urine with a retention time of about 12 min.
`Dog urine (0 to 24 h) (see Table 5) and plasma also
`contained an abundance of M-1 and M-2 after a single oral
`10-mg/kg dose. The M-1 concentration in dog plasma peaked
`at 2 h and reached approximately one-half the Cmax of
`rimantadine. The pharmacokinetics of the metabolites were
`not analyzed owing to the absence of pure compound and the
`resultant inability to develop suitable methods.
`Structural elucidation of metabolites by gas chromatogra-
`phy-mass spectrometry. Rimnantadine metabolites in mouse
`plasma were identified by mass spectrometry as rimantadine
`having a hydroxyl group on the adamantane ring. The
`metabolites were separated from other components on a
`
`capillary gas chromatograph, and the fragmentation patterns
`were investigated by both electron impact and chemical
`ionization mass spectrometry. Comparison of the chemical
`ionization mass spectra for both rimantadine and the metab-
`olite indicated a gain of 16 mass units on the adamantane ring
`of the metabolite. This suggested the presence of a hydroxyl
`group. The spectral data suggested that the isolated riman-
`tadine PFB metabolite had a molecular weight of 389 and
`made up of the structure shown in Fig. 3.
`Preparation of the trimethylsilyi derivatives for both PFB
`rimantadine and the metabolite confirmed that the hydroxyl
`group is on the adamantane ring of the metabolite. Our
`studies of human urine extracts showed that there are three
`isomers of hydroxyrimantadine: the 1-, 2-, and 3-hydroxyri-
`mantadines (Van Voris et al., 23rd ICAAC).
`Material balance in mice and dogs. Most of the radioactiv-
`ity (69.4%) excreted by mice after 24 h was found in the
`urine; with only 1.7% excreted in feces (Table 4). During the
`next 24 h, 13.8% was excreted in urine, while only 1.1% was
`
`10000-
`
`1000-
`
`100-
`
`NQ
`
`Z-N
`NS'.
`
`z z z 0M
`
`-
`La
`
`z%
`
`z0P
`
`HOURS
`FIG. 2. Concentration of rimantadine and metabolite M-1 in mouse lungs after a single oral dose of 40 mg/kg. Each point represents the
`mean of rimantadine (-) or.M-1 (I) levels in extracts from two lungs collected at 0.5, 1, 2, 4, 6, 8, 10, and 12 h after dosing. The rimantadine
`high-pressure liquid chromatography retention time was 7.0 min, and that of M-1 was 9.1 min.
`
`UI
`
`SF
`
`0
`
`2
`
`4
`
`Il
`
`12
`
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`
`VOL. 32, 1988
`
`RIMANTADINE PHARMACOKINETICS AND METABOLISM
`
`1703
`
`F
`
`F
`
`CH3 0
`HC -NC
`
`...OH
`
`FIG. 3. Structure of isolated rimantadine PFB metabolite.
`
`found in feces. The total percentages of the dose after 96 h
`were 89.4% in urine and 3.7% in feces.
`Dog urine was analyzed for rimantadine and metabolites
`M-1 and M-2 (Table 5). High-pressure liquid chromatogra-
`phy analysis of the metabolites gives estimates only, based
`on the assumption that the absorption spectra were similar to
`those of rimantadine. The amounts of intact rimantadine
`were less than 2% in the first 24 h, regardless of dose, and
`less than 1% in the second 24 h. The major excretion product
`was M-1. The discrepancy between the dogs receiving 10
`mg/kg is unexplainable. Approximately 50% of the recov-
`ered drug was M-1, while M-2 accounted for 10% or less.
`The total percentages of the 10-mg/kg dose recovered were
`69.4% for dog 75 and 58% for dog 76. At 20 mg/kg, 61.6%
`was recovered. All values increased 20% following ,B-gluc-
`uronidase hydrolysis. The data in Table 5 were collected
`after enzyme hydrolysis.
`
`DISCUSSION
`In both mice and dogs, absorption of rimantadine was
`rapid. No significant differences in t1/2 were noted. The
`differences observed in bioavailability between mice and
`dogs were not directly comparable owing to differences in
`dose. It is probable that bioavailabiity is not constant with
`dose; this should be studied.
`Infection of mice with influenza A virus 72 h prior to oral
`administration of rimantadine significantly altered the drug
`disposition from that in uninfected mice. Reduction in the
`uptake of rimantadine by lung tissue from infected mice has
`been previously reported (4), and our results confirm this
`finding (Table 2). The rimantadine concentrations in plasma
`and lungs at the time of peak concentration in virus-infected
`mice were approximately one-half those in uninfected mice.
`The lung elimination half-life lengthened from 1.8 h in
`uninfected mice to 4.4 h in infected mice. The net effect of
`these changes, however, resulted in equivalent AUC values.
`Although rimantadine concentrations in lungs were not
`determined, Schulman demonstrated that doses of 25 mg of
`rimantadine per kg dramatically reduced lung lesions and
`virus titers in mice (8). Studies of virus titers in lungs versus
`drug concentrations in lungs and plasma would be of inter-
`est.
`
`TABLE 4. [14C]rimantadine mouse material balance study
`
`Collection
`interval (h)
`
`0-24
`24-48
`48-72
`72-96a
`
`Mean % administered dose ± SD in:
`
`Urine
`
`Feces
`
`69.4
`13.8
`4.3
`1.9
`
`5.0
`1.0
`3.0
`1.0
`
`1.7 ± 0.5
`1.1 ± 0.2
`0.3 ± 0.2
`0.6 ± 0.7
`
`a At 96 h, the cage wash activity was 5.6 + 0.1%. Total recovery was
`98.7%.
`
`TABLE 5. Recovery of total rimantadine and metabolites in the
`urinea of dogs given single oral doses of rimantadine
`
`Collection interval (h)
`and substance
`
`Dog 75b
`
`% of dose in:
`Dog 76b
`
`Dog 74C
`
`0-24
`Rimantadine
`M-1
`M-2
`
`1.6
`15.9
`2.4
`
`1.2
`43.7
`10.0
`
`1.8
`46.6
`6.5
`
`24-48
`0.1
`Rimantadine
`0.3
`0.8
`2.3
`5.3
`39.9
`M-1
`1.3
`8.8
`0.5
`M-2
`a Urine was treated with ,3-glucuronidase for 2 h at 37°C before extraction
`(see text).
`b Dose was 10 mg/kg.
`c Dose was 20 mg/kg.
`
`After administration of one oral dose of [14C]rimantadine
`to mice, 89.4% of the radioactivity was found in the urine
`and 3.7% was found in the feces. Most of the radioactivity
`was excreted during the first 24 h, and only 1.9% of the dose
`was recovered during the period from 72 to 96 h.
`Dogs receiving oral doses of 10 or 20 mg/kg excreted very
`little intact rimantadine. The main excretion product was
`M-1, which made up about half of the administered dose;
`M-2 was about 10%, and rimantadine was less than 5%. Only
`58 to 69% of administered drug was recovered in 48 h in the
`three dogs. This may in part be due to further metabolism of
`M-1 and M-2 into smaller, as yet unidentified products.
`Further, until standards of M-1 and M-2 can be prepared and
`analyzed, quantification of these remains only an estimate.
`The metabolites identified in mouse and dog urine, M-1
`and M-2, are ring-hydroxylated derivatives of rimantadine.
`Other investigators have noted ring hydroxylation of ada-
`mantane derivatives in vivo. Wesemann et al. (10) demon-
`strated the presence of a ring-hydroxylated metabolite
`Spiers
`of 1-amino-3,5-dimethyladamantane
`in
`the
`rat.
`and Chatfield (9), studying a novel adamantane derivative,
`N-methyl-1-(2-phenyladamant-1-yl)-2-aminopropane hydro-
`chloride, in humans, determined that two isomers of a
`ring-hydroxylated metabolite were excreted. The ring posi-
`tion of hydroxylation was not determined. Less than 1% of
`the dose was excreted unchanged. Approximately 30% of
`the dose was excreted as conjugated hydroxyl metabolites.
`The metabolism of amantadine is less clear. Recent stud-
`ies by Koppel and Denzer (5) have shown small quantities of
`eight metabolites recovered from a patient under a therapeu-
`tic dosing regimen. A major metabolic pathway was N
`acetylation, with several other unusual metabolic pathways
`observed. However, no metabolites were detected with a
`hydroxylated adamantane ring system.
`Differences between the metabolism and kinetics of riman-
`tadine and amantadine are noteworthy. For both, >90% is
`excreted in the urine, with trace amounts in the feces.
`However, the percentage of unchanged amantadine found in
`mouse urine was 63% (9), several times that found for intact
`rimantadine. In humans, amantadine is excreted largely
`unchanged in urine, whereas less than 10% of rimantadine is
`excreted intact (Van Voris et al., 23rd ICAAC) in urine.
`Little has been reported about the concentration of either
`drug in lung tissue. Bleidner et al. (1) reported the Cmax in
`mouse lungs at 0.25 h to be 59 ,ug/g following a single oral
`dose of 25 mg/kg. The concentration of amantadine in blood
`was 4 .pg/ml. The ratio Cmaxjung/Cmaxblood of 15 was half the
`
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`1704
`
`HOFFMAN ET AL.
`
`ANTIMICROB. AGENTS CHEMOTHER.
`
`ratio reported here for rimantadine, owing to the lower
`concentrations of rimantadine than amantadine in plasma.
`
`ACKNOWLEDGMENTS
`We acknowledge the excellent technical assistance given to this
`study by Robert Agnor, Sudhendu Dasgupta, and Barbara Massello.
`
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