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* From the Infectious Disease Pharmacokinetics Laboratory (Drs. Malone and Peloquin, and Mr. Childs), National Jewish Medical and Research Center, Denver, CO; and the School of Pharmacy (Dr. Fish) and the School of Medicine (Dr. Spiegel), University of Colorado Health Sciences Center, Denver, CO.
Correspondence to: Charles A. Peloquin, PharmD, Infectious Disease Pharmacokinetics Laboratory, National Jewish Medical and Research Center, 1400 Jackson St, Denver, CO 80206; e-mail: Peloquinc{at}njc.org
| Abstract |
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Design: Open-label, pharmacokinetic study
Setting: Outpatient long-term hemodialysis unit
Participants: Eight long-term hemodialysis patients
Interventions: Single oral doses of CS, 500 mg, ETA, 500 mg, PAS, 4,000 mg, and CFZ, 200 mg, were given 2 h (4 h for PAS) prior to hemodialysis (median blood flow rate, 400 mL/min; median dialysate flow rate, 600 mL/min; median hemodialysis time, 3.5 h).
Measurements and results: Arterial and venous serum samples were collected at the beginning and end of hemodialysis, and hourly during hemodialysis. Dialysate fluid was collected for the duration of hemodialysis. All samples were assayed for drug concentrations using validated high-performance liquid chromatography (for ETA and PAS), capillary electrophoresis (for CS), and colorimetry (for CFZ). Dialysate samples were analyzed for acetyl-PAS. Median recoveries of drug in dialysate were 56% (CS), 2.1% (ETA), 6.3% (PAS parent compound), and 0% (CFZ) of the doses administered. Acetyl-PAS was dialyzed to a greater extent than its parent compound. Median hemodialysis clearances calculated by dividing the amount recovered in dialysate by the serum area under the curve during dialysis were 189 (CS), 58 (ETA), 206 (PAS), and 0 (CFZ) mL/min.
Conclusions: ETA, CFZ, and PAS were not significantly dialyzed. CS is significantly removed by hemodialysis and should be dosed after hemodialysis.
Key Words: hemodialysis, cycloserine, ethionamide, para-aminosalicylate, clofazimine, tuberculosis, pharmacokinetics
| Introduction |
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Drug-resistant TB is a global concern.16 Second-line antitubercular agents such as cycloserine (CS), ethionamide (ETA), para-aminosalicylate (PAS), and clofazimine (CFZ) are used to treat drug-resistant TB.17 18 The disposition of these agents in patients receiving hemodialysis is unknown. The present study examines the effect of hemodialysis using high-flux dialyzers on the removal of these antimycobacterial drugs from serum and reports drug recovery by dialysate collection.
| Materials and Methods |
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Hemodialysis Procedure
At the time of study participation, subjects received their
usually prescribed hemodialysis regimens. Dialyzer type, blood,
dialysate and ultrafiltrate flow rates, and duration of hemodialysis
were not changed for study purposes. All of these parameters and the
number of times the dialyzer had been previously used were recorded.
The system used for all patients composed of a hemodialysis machine
(Centrysystem3; Cobe Laboratories; Lakewood, CO) with a high-flux
dialyzer (Fresenius Hemoflow; Fresenius USA, Inc; Walnut Creek, CA) and
a single-pass dialysate flow.
Medications
Subjects were given single oral doses of CS (Seromycin; Dura
Pharmaceuticals; San Diego, CA), 500 mg, ETA (Trecator-SC;
Wyeth-Ayerst; Philadelphia, PA), 500 mg, CFZ (Lamprene; Novartis; East
Hanover, NJ), 200 mg, and PAS (PASER granules; Jacobus Pharmaceutical
Company, Inc; Princeton, NJ), 4,000 mg. The subjects were instructed to
take the PAS with an acidic beverage such as fruit juice 4 h prior
to a regularly scheduled hemodialysis session. The other medications
were to be taken all at once 2 h later. The subjects were asked
not to eat anything for 1 h before or after taking study
medications. Subjects were contacted by telephone when medications were
due and were reminded to take them according to the study protocol.
Sample Collection
Blood samples of 8 mL each to be analyzed for CS, ETA, CFZ, and
PAS concentrations were taken from ports in the arterial and venous
tubing of the dialyzer at the start of the hemodialysis session and
then were taken hourly, with final samples taken as hemodialysis was
discontinued. Samples were collected in plain red-top vacuum tubes,
placed on ice, and centrifuged within 60 min of collection. Serum then
was harvested into labeled polypropylene tubes and stored at -70°C
until assayed. Samples were frozen within 90 min of collection. For the
duration of the dialysis session, all dialysate/ultrafiltrate fluid
leaving the system was collected in 20-L containers. When each
container approached full, it was removed from the system and the
collected volume was recorded. From each container, an 80-mL
dialysate/ultrafiltrate sample was collected and frozen promptly at
-70°C. The remainder of the fluid was discarded.
Sample Analysis
Serum samples were assayed for drug concentrations according to
validated procedures at the Infectious Disease Pharmacokinetics
Laboratory at National Jewish Medical and Research Center in Denver,
CO.
CS
Serum analyses were performed using a validated capillary
electrophoresis (CE) assay on a CE system (Model 270A-HT; Hewlett
Packard; Wilmington, DE) with ultraviolet detection. The six-point
serum standard curves for CS ranged from 2.0 to 50.0 µg/mL. The
absolute recovery of CS from serum was 92.3%, as determined by
comparing peak height counts across four serum curves to an unextracted
solvent curve. The within-day precision (coefficient of variation
[CV] percentage) of validation quality control (QC) samples
was 3.5 to 10.7% CV, and the overall validation precision was
5.7 to 12.3% CV. QC sample concentrations were 7.5, 15, and 30
µg/mL. For one patient who had an obvious interference with
the CE method, serum samples were analyzed using a colorimetric method.
All dialysate samples were analyzed colorimetrically. The colorimetric
method used a spectrophotometer (model DU-20; Beckman Instruments, Inc;
Fullerton, CA), and its overall validation precision was 3.7 to
9.6% CV.
ETA
All ETA assays were performed using a validated high-performance
liquid chromatography assay using a pump (model 510; Waters; Milford,
MA) and a gradient controller with a solvent select valve (model 680;
Waters), a fixed-volume autosampler (model 8875; Spectra Physics; San
Jose, CA), an ultraviolet detector (model 486; Waters), a computer
(Macintosh IIci; Apple Computers, Inc; Cupertino, CA), and a
high-performance liquid chromatography data management system (Dynamax;
Rainin; Woburn, MA). The six-point standard curves for the ETA assay
ranged from 0.2 to 10 µg/mL, with linearity extending well above this
range. The absolute recovery of ETA from serum was 90.7% of CV, as
determined by comparing peak height counts across four serum curves to
an unextracted solvent curve. The within-day precision of validation QC
samples was 0.4 to 6.4% CV, and the overall validation precision was
0.8 to 4.7% CV. QC sample concentrations were 0.5, 1.5, and 7.0
µg/mL. The dialysate method was a modification of the serum method
with similar recovery and reproducibility.
CFZ
Serum and dialysate samples were analyzed using a colorimetric
method. The colorimetric method used a spectrophotometer (DU-20;
Beckman Instruments, Inc), and its overall validation precision
was 4.1 to 10.7% CV
PAS
All PAS assays were performed using the same equipment as the
ETA assays, with the exception of the use of a fluorescence detector
(model FL-750; McPherson; Chelmsford, MA) with a high-sensitivity
attachment. The six-point standard curves for the PAS assays ranged
from 1 to 100 µg/mL, with linearity extending well above this range.
The absolute recovery of PAS from serum was 90.6%, as determined by
comparing peak height counts across four serum curves to an unextracted
solvent curve. The within-day precision of validation QC samples was
0.7 to 7.1% CV, and the overall validation precision was 3.2 to 10.6%
CV. QC sample concentrations were 15, 30, and 80 µg/mL. The dialysate
method was a modification of the serum method, with similar recovery
and reproducibility. After a prominent peak on the PAS chromatograms
was identified as acetyl-PAS, a standard curve for acetyl-PAS in
dialysate was made in the same manner as the PAS curve in dialysate.
This was assayed along with a representative dialysate sample from each
subject and was used to estimate the recovery of acetyl-PAS.
For all four drugs, concentrations in dialysate were often too low to be quantified, therefore, samples were concentrated 10-fold by lyophilizing 10-mL aliquots of the dialysate and reconstituting the samples to a volume of 1.0 mL. These assay results were divided by a factor of 10 to determine the dialysate concentrations.
Hemodialysis Clearance Determination
The dialyzer extraction ratio (ER), an indicator of the
dialyzer's capability of removing drug, was calculated using serum
drug concentrations as follows19
20
:
![]() |
Previously published equations for calculating hemodialysis clearance
(ClHD) were used20
21
![]() | (1) |
![]() | (2) |
![]() | (3) |
![]() | (4) |
The ER calculation and equations 1 and 2 were applied to samples collected 1 and 2 h into hemodialysis and at the end of hemodialysis. The median of the three values for each subject was used to determine a median value for the group. Calculations using recovery of drugs in dialysate (given in equations 3 and 4 ) are preferred to those based on the ER (given in equations 1 and 2 ).20 21
Calculations for AUC were made using the linear trapezoidal rule programmed into computer spreadsheets (Excel 97; Microsoft; Redmond, WA). Drug recovery in dialysate was calculated by multiplying the concentration of each dialysate sample by the total volume of the corresponding collection. Drug recovery as a percentage of the dose administered was determined by dividing the total amount of drug recovered in dialysate by the administered dose. Acetyl-PAS recovery expressed as PAS equivalents was used to calculate the percent of dose recovery. No corrections for expected bioavailability of the four drugs were made because bioavailability of the drugs in this patient population has not been studied.
Statistical Analysis
All statistical analyses were performed using computer software
(JMP, version 3.2; SAS Institute; Cary, NC). Means with standard
deviations and medians with ranges were determined for patient
demographics and hemodialysis procedure characteristics as well as
dialyzer ERs and clearance calculations.
| Results |
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| Discussion |
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CS
CS was significantly removed, with a median recovery in dialysate
of 56% of the dose administered. Because CS is primarily renally
excreted, it may accumulate in renal failure, predisposing the patient
to CNS toxicities.28
We recommend that CS be used in its
normal dose of 250 to 500 mg, but that it be given only three times a
week after dialysis. This should avoid premature removal of CS during
dialysis and accumulation between dialysis sessions.
ETA
Drug recovery of ETA, 2.1% of the dose, in dialysate was lower
than expected based on hemodialysis clearances calculated from the ER.
Drug adherence to the dialysis membrane may have occurred. However, ETA
is rapidly metabolized by the liver, with a serum elimination half-life
of 2 to 3 h.28
It appears that hemodialysis does not
effectively compete with metabolism for elimination of ETA from the
body, which is the more likely explanation for the discrepancy between
the observed ER and drug recovery. Dosage adjustment of ETA for renal
failure or hemodialysis does not appear to be warranted.
PAS
PAS is normally rapidly metabolized in the GI tract and liver with
an elimination half-life of 0.6 to 2.0 h.26
Traditionally, PAS has been avoided in renal failure due to concern
regarding accumulation of its inactive acetyl-PAS metabolite, which is
eliminated renally.29
There is also concern regarding
recommendations that salicylates be avoided in renal failure because of
their potential to exacerbate GI symptoms and platelet dysfunction
associated with uremia.30
Although PAS has rarely been
associated with peptic ulcers and gastric bleeding,31
PAS
does not appear to have the antiplatelet effects associated with
aspirin. Few reports are available regarding experience with PAS in
patients with renal failure. Case reports involving five patients
indicate that PAS has been used in patients with renal failure in doses
ranging from 2 to 6 g after dialysis to 4.5 to 12 g/d. The dosage
forms have not been indicated.4
6
32
33
The patient who
received 12 g/d experienced upper GI bleeding attributed to
drug-induced gastritis.4
Our results suggest that hemodialysis is capable of removing PAS and acetyl-PAS. The chromatograms of PAS dialysate specimens displayed a large peak which we confirmed to be acetyl-PAS. Comparing the heights of these peaks to an acetyl-PAS standard curve allowed us to estimate recovery of acetyl-PAS in dialysate. In all subjects, including those that had only nondetectable or trace levels of PAS in serum, acetyl-PAS was detected in dialysate. Overall, recovery of acetyl-PAS was greater than that of its parent compound, confirming that metabolism remains the primary mode of elimination. The extent of absorption of the delayed-release PAS formulation is unknown. The low recoveries we observed may reflect incomplete absorption rather than low clearance by dialysis. The wide variation in recoveries of the parent and metabolite likely reflects variations in drug release from the delayed-release PAS formulation and in drug absorption among the individual subjects.
If PAS is used in a long-term hemodialysis patient, supplemental dosing to account for dialysis removal does not appear warranted. Due to the fact that acetyl-PAS is dialyzable, we suggest that PAS may be used in its usual dose of 4,000 mg twice daily, as is currently done for patients with normal renal function.34
CFZ
Extensive dialyzability of CFZ was not expected due to this
drug's relatively large molecular size, lipophilicity, and wide
deposition into tissues.28
Because CFZ dialysate
concentrations were nondectable or at trace levels for all subjects,
the results of calculations using equations 3
and 4
are zero.
Although protein binding affects the dialyzability of drugs, it does not appear that protein binding characteristics of the drugs studied contributed significantly to the results. ETA and CS are not significantly protein bound.22 The extent of protein binding of CFZ is unknown, however, properties of CFZ described above may explain the observation that it was not dialyzable as well as any protein binding that may have occurred. PAS is 50 to 73% protein bound.22 This degree of protein binding is generally not considered clinically significant, however, this degree of protein binding could create a ceiling for the amount of drug that could be recovered in dialysate. The total recovery of PAS, as parent and metabolite, observed (6 to 47%) is consistent with the expected degree of protein binding.
As part of their prescribed dialysis regimens, five subjects used one model of dialyzer (model F80B; Fresenius USA, Inc; Walnut Creek, CA), and three subjects used another one (model F50B; Fresenius). These are both polysulfone dialyzers with surface areas of 1.8 m2 and 1.0 m, respectively.2 Manufacturer product information indicates that the F50B has lower clearances of urea, creatinine, phosphate, and vitamin B-12 than the F80B. For CS and ETA, observed hemodialysis clearances tended to be lower for subjects using the F50B than for subjects using the F80B dialyzer. The differences were not statistically significant, however, this study did not have the statistical power to detect such a difference.
Although somewhat problematic, using the oral dosage forms of CS, ETA, PAS, and CFZ that are available for routine clinical use may have enhanced applicability of the results. Administering study medications IV would have avoided problems associated with prolonged or incomplete absorption and facilitated complete distribution prior to starting dialysis. Injectable dosage forms of CS, ETA, CFZ, and PAS are not, however, available.
In some cases, drug absorption was not complete at the start of hemodialysis. If serum concentrations were higher during hemodialysis, drug recoveries and AUCs may have been higher. Hemodialysis clearances calculated from the AUCs should, however, still be valid because the AUCs during dialysis were used only in combination with corresponding dialysate concentrations.
We were unable to determine drug clearances between hemodialysis sessions or postdialysis rebound in drug concentrations due to logistical constraints. These limitations do not alter our conclusions, which are based primarily on the observed recoveries of drug in dialysate.
Administration of study medications was not directly monitored. A few subjects did not have measurable serum concentrations of some of their study medications. It is possible that these subjects did not take all the medications as instructed. Additionally, some individuals may have absorption difficulties. In the five subjects with measurable PAS concentrations, the median observed Cmax was 8.8 mg/L compared to 15.3 mg/L previously observed in healthy volunteers after a single 4,000-mg dose of PAS granules.25
The data in Table 2 suggest that ETA absorption is delayed in long-term hemodialysis patients. However, samples were not taken early enough to assess the Cmax for this drug appropriately. The observed Cmax levels for CS and CFZ are close to that expected after administration of a single dose.
| Conclusion |
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| Acknowledgements |
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| Footnotes |
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This research was funded by the Potts Memorial Foundation, the TB Foundation of Virginia, and National Institutes of Health grant 1RO1 AI37845.
Received for publication February 19, 1999. Accepted for publication May 12, 1999.
| References |
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