Bioavailability of Higher Dose Methotrexate
`Comparing Oral and Subcutaneous Administration in
`Patients with Rheumatoid Arthritis
`
`MONIQUE HOEKSTRA, CEES HAAGSMA, CEES NEEF, JOHANNES PROOST, ANTONIUS KNUIF,
`and MART van de LAAR
`
`ABSTRACT. Objective. To determine the bioavailability of higher oral doses of methotrexate (MTX) in adult
`patients with rheumatoid arthritis (RA).
`Methods. A pharmacokinetic analysis was performed in 15 patients with RA taking a stable dose of
`MTX (≥ 25 mg weekly). Separated by 2 weeks, a pharmacokinetic analysis was performed in each
`patient after oral and subcutaneous administration of the same dose of MTX. MTX serum concen-
`trations were measured by a fluorescence polarization immunoassay. Pharmacokinetic analysis was
`performed with an iterative 2-stage Bayesian population procedure, obtaining population and indi-
`vidual pharmacokinetic parameters.
`Results. The median MTX dose was 30 mg weekly (range 25–40 mg). A 2-compartment model best
`described the serum MTX concentration versus time curves. The mean bioavailability after oral
`MTX was 0.64 (range 0.21–0.96) compared to subcutaneous administration. There was a statistically
`significant difference in the bioavailability of the 2 administration regimens.
`Conclusion. Bioavailability of a higher oral dose of MTX in adult patients with RA is highly vari-
`able, and on average two-thirds that of the subcutaneous administration. To improve efficacy of
`MTX at dosages of 25 mg weekly or more, a change to parenteral administration should be consid-
`ered. (J Rheumatol 2004;31:645–8)
`
`Key Indexing Terms:
`METHOTREXATE PHARMACOKINETICS RHEUMATOID ARTHRITIS
`
`Methotrexate (MTX) is commonly used in weekly single-
`dose regimens in the treatment of rheumatoid arthritis (RA).
`A dose-effect relation was established for doses of 7.5–25
`mg per week1,2. In clinical trials in RA, the MTX dose is
`increased up to 25 mg weekly, until efficacy is reached. It is
`not clear whether even higher oral doses of MTX are more
`effective. Efficacy of high intravenous doses of MTX
`(40–500 mg/m2), in patients with refractory RA, was
`described in several studies3-5.
`The bioavailability of oral MTX could be a limiting
`factor for its efficacy. Oral MTX is absorbed in the proximal
`intestine by a specific transport mechanism, and a relation
`between dose and absorption of oral MTX was observed in
`2 clinical studies6,7. Pharmacokinetic studies in adult
`
`From the Department of Rheumatology, and the Department of Clinical
`Pharmacology, Medisch Spectrum Twente, Enschede; and the Department
`of Pharmacokinetics and Drug Delivery, University Centre for Pharmacy,
`Groningen, The Netherlands.
`M. Hoekstra, MD, Rheumatologist; C.J. Haagsma, MD, Rheumatologist;
`M.A.F.J. van de Laar, MD, Rheumatologist, Department of Rheumatology,
`Medisch Spectrum Twente; C. Neef, PhD, Hospital Pharmacist; A.J.H.
`Knuif, Pharmaceutical Analyst, Department of Clinical Pharmacology,
`Medisch Spectrum Twente; J.H. Proost, PhD, Pharmacist, Department of
`Pharmacokinetics and Drug Delivery, University Centre for Pharmacy.
`Address reprint requests to Dr. M. Hoekstra, Department of
`Rheumatology, Medisch Spectrum Twente, PO Box 50000, 7500 KA
`Enschede, The Netherlands. E-mail: m.hoekstra@ziekenhuis-mst.nl
`Submitted May 22, 2003; revision accepted October 27, 2003.
`
`patients with RA show comparable bioavailability of oral
`and parenteral MTX in doses up to 25 mg weekly8-11. In
`these studies the mean relative bioavailability of oral MTX,
`compared to intramuscular administration, ranged from 0.85
`to 1.0. In other studies, using 15 mg MTX and 10 mg/m2
`MTX, bioavailability of oral compared to intravenous MTX
`was 0.67 and 0.70, respectively12,13. In a comparison of 25
`mg MTX, the mean bioavailability after oral administration
`was 73% compared to the intravenous route14. Despite the
`impression given by a few studies8,15, it is not certain that the
`bioavailability of intravenous, intramuscular, and subcuta-
`neous MTX is strictly comparable.
`Pharmacokinetic studies in patients with malignant
`diseases have shown that the absorption of higher doses of
`MTX (≥ 25 mg weekly) is incomplete6,16-19. The relative
`bioavailability of 40 mg/m2 oral MTX in a study in children
`with acute lymphoblastic leukemia was 42%; in adult
`patients with solid tumors using 15 mg/m2 MTX this was
`57%18,17. Another study in 15 children19 showed a decreased
`absorption of oral MTX at doses > 12 mg/m2. However, the
`results of pharmacokinetic studies in disorders other than
`RA, and even more so in children, cannot be extrapolated to
`adult patients with RA.
`Although a clear relation between pharmacokinetic para-
`meters and efficacy has not been demonstrated in RA, it
`seems likely that improvement of the bioavailability of
`MTX will lead to better efficacy, given the dose-effect rela-
`
`Hoekstra, et al: Bioavailability of MTX
`
`645
`
`MEDAC Exhibit 2016
`ANTARES v. MEDAC
`IPR2014-01091
`Page 00001
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`

`
`tion1,2. This idea is supported by a study in patients with
`psoriasis in which a relation was found between the area
`under the curve of the time versus MTX concentration and
`a decrease in the Psoriasis Activity and Severity Index
`(PASI)20.
`The bioavailability of higher MTX doses can be
`improved by parenteral administration. To study this option,
`we performed a crossover pharmacokinetic study in adult
`patients with RA, comparing the bioavailability of oral and
`subcutaneous MTX at doses ≥ 25 mg weekly.
`
`MATERIALS AND METHODS
`Patients and MTX administration. Patients with RA, who were treated with
`MTX in a stable (≥ 3 months) dose of ≥ 25 mg weekly, oral or parenteral,
`were studied. Consecutive outpatients fulfilling these inclusion criteria
`were invited to participate. The local ethics committee approved the study
`and written informed consent was obtained from each patient.
`Baseline data were gathered on diagnosis, age, sex, disease duration,
`dose, serum creatinine, folic acid supplementation, and use of disease
`modifying antirheumatic drugs (DMARD), nonsteroidal antiinflammatory
`drugs (NSAID), and prednisolone. Pharmacokinetics were studied twice in
`each patient with a 2-week interval: once with their regular MTX dose by
`oral route of administration, and once with the same dose of MTX by
`subcutaneous administration in random order. Folic acid supplementation
`was allowed, but not on the day of MTX intake. Leukopenia, thrombo-
`cytopenia, and transaminase elevations were reasons for exclusion.
`Patients were admitted in the hospital in the morning. They were
`allowed to have breakfast at home, at least 1.5 hour before MTX intake.
`Comedication was continued during both sampling episodes. Other
`DMARD and prednisone were allowed, with stable doses throughout the
`study. The concurrent medication was taken at least 1.5 hour before and
`more than 2 hours after MTX intake. Oral MTX was administered with
`water. MTX was injected subcutaneously in the upper leg in all patients by
`the examiner. Blood samples were drawn from an indwelling catheter at
`Time 0 (preadministration) and at 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 2, 4, 6, 8,
`12, 24, and 48 h after administration of MTX. The blood samples were
`centrifuged and the serum stored at –20°C until analysis.
`MTX assay. MTX serum concentrations were determined using a fluores-
`cence polarization immunoassay technique (MTXII: list no. 7A12, TDX-
`Abbott Diagnostics, North Chicago, IL, USA)21. The lower detection limit
`was 10 μg/l. At 10 μg/l the coefficient of variation of the test is 15%. The
`standard deviation (SD) of the test is described by the formula: SD = 4.76
`+ 0.05*C, where C = concentration.
`Pharmacokinetic analysis. The MTX concentration data of both adminis-
`trations from all patients were analyzed simultaneously by an iterative 2-
`stage Bayesian analysis using the program MW\Pharm, version 3.5422,23.
`The pharmacokinetic model was a one-compartment (parameters ke, V1) or
`a 2-compartment model (parameters ke, V1, k12, k21), with first-order
`absorption with a lag-time for oral and subcutaneous administration, with
`parameters F (bioavailability), ka (absorption rate constant), and Tlag (lag-
`time) for each route of administration. Since absolute bioavailability cannot
`be assessed without an intravenous reference administration, the analysis
`was performed assuming that bioavailability of the subcutaneous adminis-
`tration was 100%. Measurement data were weighted according to the reci-
`procal of their variance (1/SD2). A log-normal distribution for the
`pharmacokinetic population parameters was assumed. Goodness-of-fit was
`evaluated from visual inspection of the measured and calculated data
`points. The choice between a one- and 2-compartment model was based on
`Akaike’s Information Criterion (AIC)24.
`MTX clearance (CL), volume of distribution (V), elimination half-life
`(t2), and for each route of administration the area under the concentration-time
`profile (AUC), time to maximum concentration (Tmax), and maximum concen-
`
`tration (Cmax) were calculated from the model parameters for each patient.
`Statistical analysis. To compare the values of the pharmacokinetic parame-
`ters of the oral and subcutaneous route of administration, a signed-rank test
`was employed. A 2-sided p value < 0.05 was considered significant.
`
`RESULTS
`Fifteen patients with RA were studied. Patient characteris-
`tics are presented in Table 1. All patients received folic acid
`supplementation in varying doses (5–25 mg weekly), but
`not on the day of MTX intake. Three patients concurrently
`used hydroxychloroquine, one chloroquine, one sulfasa-
`lazine, and one aurothiomalate. Low dose prednisolone
`(≤ 10 mg daily) was used by 8 patients, and NSAID by 11
`patients.
`A 2-compartment model fitted significantly better to the
`data than a one-compartment model (AIC value –250 and
`–956 for the one- and 2-compartment model, respectively).
`The mean bioavailability (F) was 0.64, with a rather large
`range from 0.21 to 0.96. The pharmacokinetic parameters
`with paired statistical analysis are shown in Table 2. The
`AUC of oral MTX was significantly lower than the AUC of
`the subcutaneous route of administration (p < 0.001). The
`fitted mean time-concentration curves of oral and subcuta-
`neous administration are presented in Figure 1.
`
`DISCUSSION
`The bioavailability of oral MTX (≥ 25 mg weekly) was
`highly variable, and was significantly less compared to
`subcutaneously administered MTX in patients with RA. It
`varied between 0.21 and 0.96, with a mean of 0.64.
`In the design of our study comedication was continued,
`and patients were allowed to have breakfast at home before
`coming to the hospital. Because of the time between comed-
`ication, breakfast, and MTX administration, an effect on
`MTX absorption is unlikely. Further, the effect of food has
`been extensively studied and no effect on MTX absorption
`was found9,13.
`The majority of pharmacokinetic studies in adult patients
`with RA have used low doses of MTX. In studies using
`MTX doses of 7.5 to 20 mg weekly, bioavailability after oral
`compared to parenteral administration ranged from 0.67 to
`1.08-13. Only one study compared 25 mg oral and intra-
`venous MTX, in 18 patients with rheumatic diseases14. The
`bioavailability of oral MTX was 0.73, somewhat higher than
`what we found, but in our study most patients used higher
`
`Table 1. Patient characteristics (n = 15: 11 women, 4 men).
`
`Age, yrs
`Disease duration, yrs
`Weight, kg
`Creatinine clearance, ml/min
`Dose, mg weekly
`Dose, mg/kg
`
`Median
`
`Range
`
`61
`7
`76
`80
`30
`0.40
`
`31–72
`2–32
`63–110
`57–124
`25–40
`0.27–0.57
`
`646
`
`The Journal of Rheumatology 2004; 31:4
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`

`
`Table 2. Pharmacokinetic parameters of oral and subcutaneous route of administration (n = 15). Signed-rank test, p value < 0.05 is significant.
`
`Oral
`
`Subcutaneous
`
`p
`
`AUC
`
`Lag-time
`
`ka
`
`2466
`(785)
`3786
`(873)
`0.001
`
`0.36
`(0.18)
`0.06
`(0.05)
`< 0.001
`
`0.87
`(0.29)
`0.36
`(0.10)
`< 0.001
`
`Tmax
`
`1.2
`(0.3)
`1.7
`(0.3)
`0.001
`
`Cmax
`
`594
`(208)
`519
`(142)
`0.30
`
`V1
`
`9.6
`(2.0)
`
`V
`
`k12
`
`k21
`
`ke
`
`34.5
`(8.1)
`
`0.81
`(0.31)
`
`0.55
`(0.04)
`
`0.88
`(0.11)
`
`CL
`
`8.4
`(2.2)
`
`t2 el
`
`2.9
`(0.5)
`
`Values are mean (standard deviation). AUC: area under curve (0–48 hours) in h.μg/l; lag-time in hours; ka: absorption rate constant; Tmax: time to maximum
`concentration (hours); Cmax: maximum concentration (μg/l); V1: volume of distribution of first compartment; V: volume of distribution (liter); k12: rate
`constant of transport between compartment 1 and 2; k21: rate constant of transport between compartment 2 and 1; ke: elimination rate constant; CL: total
`body clearance (liter/hour); t2 el: half-life of elimination (hours).
`
`effect. Decreasing bioavailability with an increasing dose
`favors an absorption limitation. The number of patients in
`our study with different MTX doses was too small to draw
`conclusions about a dose-bioavailability relation. However,
`there is a positive relation between the subcutaneous AUC
`and the dose of MTX (linear regression; R2 = 0.33, p =
`0.03), whereas the oral AUC does not increase with an
`increasing dose. Hamilton, et al studied 21 RA patients on
`more occasions. They found a decreasing bioavailability
`with an increasing oral dose, mean maximum dose being 17
`mg/week7. These results support the idea of an absorption
`limitation of oral MTX with an increasing dose. The finding
`of higher bioavailability of oral split high dose MTX,
`compared to a single dose, in patients with solid tumors25
`supports a reduced bioavailability due to an absorption limi-
`tation. However, to pursue this question for the MTX doses
`we use in RA, an additional study is needed that directly
`compares a single-dose with a split-dose regimen.
`Although controlled trials studying the effect of higher
`doses of MTX are lacking, higher dosing of MTX may be
`clinically useful. A dose escalation study in 54 patients with
`RA concluded that increasing the intramuscular MTX dose
`from 15 to 45 mg weekly did not result in improved disease
`control26. However, the number of patients was small, and
`detailed data about baseline disease activity scores were not
`provided. In our opinion, additional controlled trials are
`needed to evaluate the effect of higher doses of MTX, which
`are in fact widely used in rheumatology practice. In our
`observational study of MTX use in 1022 RA patients, we
`found that 12% of the patients reached a maximum dose of
`≥ 25 mg weekly (maximum 40 mg weekly)27.
`Our data suggest that doses between 25 and 40 mg MTX
`per week, administered orally, result in limited bioavail-
`ability. Bioavailability is enhanced by the subcutaneous
`route of administration, and this may increase efficacy.
`
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`
`647
`
`Page 00003
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