Development and validation of liquid chromatography tandem mass spectrometry method quantitative determination of polymyxin B1, polymyxin B2, polymyxin B3 and isoleucine-polymyxin B1 in human plasma and its application in clinical studies

Development and validation of a liquid chromatography-tandem mass spectrometry method for the determination of polymixin B1, B2, ile-B1, E1, and E2 in human plasma and its clinical pharmacokinetic application

Polymyxin B (PB) and Polymyxin E (PE, also called colistin) are used as the last treatment resort for multidrug-resistant Gram-negative bacterial infections. The nephrotoxicity and neurotoxicity of polymyxins limit their clinical use, and guidelines recommend therapeutic drug monitoring (TDM) to optimize efficacy and reduce toxicity. However, there are limited analytical methods available for the determination of PB and PE. This study aimed to develop a simple and robust liquid chromatography with tandem mass spectrometry (LC-MS/MS) analytical method for determining the main compounds of PB and PE, namely PB1, PB2, ile-PB1, PE1, and PE2, in human plasma and to investigate of their pharmacokinetics in critically ill patients with the use of PB and PE, respectively. Plasma PB1, PB2, ile-PB1, PE1, and PE2 were chromatographically separated on a Welch LP-C18 column and detected using electrospray ionization mode coupled with multiple reaction monitoring. The calibration curve showed acceptable linearity over 20-10,000 ng/mL for PB1, PE1, and PE2 and 10-5000 ng/mL for PB2 and ile-PB1 in the plasma, respectively. After validation following approved guidelines, this method was successfully applied for PB and PE pharmacokinetic analysis and TDM in critically ill patients. Additionally, the composition of PB1, PB2, ile-PB1, PE1, and PE2 remains unchanged from 0 to 12 h after entering the patient's body.

Condensation methodology for quantification of Polymyxin B fluorimetrically: application to pharmaceutical formulations and greenness assessment

The appearance of multidrug-resistant Gram-negative bacterial infections, along with the lack of newly discovered antibiotics, resulted in the return to old antimicrobial medications like Polymyxins. As a result, the suggested technique aims to develop a fast, environmentally friendly, and sensitive fluorimetric method for quantifying Polymyxin B. The investigated approach depends on generating a highly fluorescent derivative by a condensation pathway between the studied drug and ninhydrin in the presence of phenylacetaldehyde and then estimated spectrofluorimetrically. After the reaction conditions were well optimized, the fluorescent product was estimated at emission wavelength (λem) = 475.5 nm (following excitation at a wavelength (λex) = 386 nm. The developed calibration plot displayed rectilinear throughout the following range (0.2-3 µg mL- 1), and the calculated limit of detection and quantification were 0.062 µg mL- 1 and 0.187 µg mL- 1, respectively. As a consequence, the drug's ophthalmic and intravenous pharmaceutical forms were both successfully quantified with an excellent degree of recovery. Finally, the methodology's greenness was assessed utilizing Analytical Eco-Scale scores.

Combinatorial metabolic engineering of Bacillus subtilis for de novo production of polymyxin B

Polymyxin is a lipopeptide antibiotic that is effective against multidrug-resistant Gram-negative bacteria. However, its clinical development is limited due to low titer and the presence of homologs. To address this, the polymyxin gene cluster was integrated into Bacillus subtilis, and sfp from Paenibacillus polymyxa was expressed heterologously, enabling recombinant B. subtilis to synthesize polymyxin B. Regulating NRPS domain inhibited formation of polymyxin B2 and B3. The production of polymyxin B increased to 329.7 mg/L by replacing the native promoters of pmxA, pmxB, and pmxE with PfusA, C2up, and PfusA, respectively. Further enhancement in this production, up to 616.1 mg/L, was achieved by improving the synthesis ability of 6-methyloctanoic acid compared to the original strain expressing polymyxin heterologously. Additionally, incorporating an anikasin-derived domain into the hybrid nonribosomal peptide synthase of polymyxin increased the B1 ratio in polymyxin B from 57.5% to 62.2%. Through optimization of peptone supply in the fermentation medium and fermentation in a 5.0-L bioreactor, the final polymyxin B titer reached 962.1 mg/L, with a yield of 19.24 mg/g maltodextrin and a productivity of 10.02 mg/(L·h). This study demonstrates a successful approach for enhancing polymyxin B production and increasing the B1 ratio through combinatorial metabolic engineering.

Determination of polymyxin B in human plasma and epithelial lining fluid using LC-MS/MS and its clinical application in therapeutic drug monitoring

Polymyxin B (PB) is currently one of the last resort treatment options against carbapenem-resistant gram-negative bacterial pathogens. Pharmacokinetics/pharmacodynamics (PK/PD) guided therapeutic drug monitoring (TDM) of antibiotics is critical for optimizing dosage regimens to maximize efficacy, minimize toxicity, and delay the emergence of resistance. Currently, methods for determining PB in human plasma and epithelial lining fluid (ELF) are limited. In this study, we developed and validated a simple method for PB determination in human plasma and ELF using LC-MS/MS. Protein precipitation of the sample was conducted with 0.1% formic acid-acetonitrile. Polymyxin B1 and B2 were separated on a C₁₈ column and detected within 4 min by the mass spectrometer in the positive mode coupled with multiple reaction monitoring. The calibration curve range was 0.156-10.0 and 0.0156-1.00 μg/mL in the plasma for polymyxin B1 and B2, respectively, and was 0.0625-2.00 and 0.00625-0.200 μg/mL for polymyxin B1 and B2, respectively in bronchoalveolar lavage fluid. The accuracy of the intra- and inter-assay studies ranged from 80.6% to 114.9%, and the coefficients of variation for intra- and inter-day assays were less than 14.8%. Among a considerable number of patients, the average steady-state plasma concentration of PB was suboptimal. Moreover, the exposure to PB in patients with acute kidney injury (AKI) was considerably higher than that in patients without AKI. Meanwhile, a higher concentration of PB in ELF could be achieved than that in plasma after PB nebulization treatment. The established method was proven to be rapid, simple, and suitable for TDM of PB and PK/PD studies in human plasma and ELF.

Population pharmacokinetic analysis and dosing optimization of polymyxin B in critically ill patients

Objectives: Since the global broadcast of multidrug-resistant gram-negative bacteria is accelerating, the use of Polymyxin B is sharply increasing, especially in critically ill patients. Unsatisfactory therapeutic effects were obtained because of the abnormal physiological function in critically ill patients. Therefore, the determination of optimal polymyxin B dosage becomes highly urgent. This study aimed to illustrate the polymyxin B pharmacokinetic characteristics by defining the influencing factors and optimizing the dosing regimens to achieve clinical effectiveness.

Methods: Steady-state concentrations of polymyxin B from twenty-two critically ill patients were detected by a verified liquid chromatography-tandem mass spectrometry approach. The information on age, weight, serum creatinine, albumin levels, and Acute Physiology and Chronic Health Evaluation-II (APACHE-II) score was also collected. The population PK parameters were calculated by the non-parametric adaptive grid method in Pmetrics software, and the pharmacokinetic/pharmacodynamics target attainment rate was determined by the Monte Carlo simulation method.

Results: The central clearance and apparent volume of distribution for polymyxin B were lower in critically ill patients (1.24 ± 0.38 L h-1 and 16.64 ± 12.74 L, respectively). Moreover, albumin (ALB) levels can be used to explain the variability in clearance, and age can be used to describe the variability in the apparent volume of distribution. For maintaining clinical effectiveness and lowering toxicity, 75 mg q12 h is the recommended dosing regimen for most patients suffering from severe infections.

Conclusion: This study has clearly defined that in critically ill patients, age and ALB levels are potentially important factors for the PK parameters of polymyxin B. Since older critically ill patients tend to have lower ALB levels, so higher dosages of polymyxin B are necessary for efficacy.

The Determination of Polymyxin B in Critically Ill Patients by the HPLC-MS/MS Method

Polymyxin B (PB) is a dose-dependent drug used to treat multidrug-resistantgram-negative bacteria, for which a suitable method is needed to determine clinical samples. A simple, economical, and efficient high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS) method was developed and validated for polymyxin B1 (PB1), polymyxin B1-Ile (PB1-I), polymyxin B2 (PB2), and polymyxin B3 (PB3) in human plasma. Chromatographic column was Waters BEH C18 column (2.1 × 50 mm, 1.7 μm). Phase A was water with 0.2% formic acid (FA), and phase B was acetonitrile containing 0.2% FA. The elution method is gradient elutio. The total analysis time was 5 min. The pretreatment method involved protein precipitation using acetonitrile containing 0.2% trifluoroacetic acid and 0.1% FA as the precipitant. The recovery rate was 92-99%. The total quantity of PB1 and PB1-I was measured in the linear range of 100-8000 ng/mL. Simultaneously, the total amounts of PB2 and PB3 were measured in the linear range of 11.9-948.5 ng/mL. This validated method was successfully applied to the pharmacokinetics of PB in critically ill patients.

Synthesis and Evaluation of Polymyxins Bearing Reductively Labile Disulfide-Linked Lipids

Polymyxins are a class of lipopeptide anti-infective agents with potent and specific activity against Gram-negative bacteria. While toxicity concerns associated with polymyxin B and E (colistin) have historically limited their clinical application, today they are increasingly used as last-resort antibiotics given the rise of multidrug-resistant Gram-negative pathogens. The adverse side effects of polymyxins are well known, particularly as related to their nephrotoxicity. Here, we describe the synthesis and evaluation of a novel series of polymyxin analogues, aimed at reducing their nephrotoxic effects. Using a semisynthetic approach, we explored modifications of the exocyclic part of the polymyxin scaffold, namely, the terminal amino acid and lipophilic tail. By incorporating a reductively labile disulfide linkage in the lipid tail, we obtained novel polymyxins that exhibit potent antibacterial activity on par with polymyxin B but with reduced toxicity toward human renal proximal tubular epithelial cells.

Evaluation and Validation of the Limited Sampling Strategy of Polymyxin B in Patients with Multidrug-Resistant Gram-Negative Infection

Polymyxin B (PMB) is the final option for treating multidrug-resistant Gram-negative bacterial infections. The acceptable pharmacokinetic/pharmacodynamic target is an area under the concentration–time curve across 24 h at a steady state (AUC_ss,24h) of 50–100 mg·h/L. The limited sampling strategy (LSS) is useful for predicting AUC values. However, establishing an LSS is a time-consuming process requiring a relatively dense sampling of patients. Further, given the variability among different centers, the predictability of LSSs is frequently questioned when it is extrapolated to other clinical centers. Currently, limited data are available on a reliable PMB LSS for estimating AUC_ss,24h. This study assessed and validated the practicability of LSSs established in the literature based on data from our center to provide reliable and ready-made PMB LSSs for laboratories performing therapeutic drug monitoring (TDM) of PMB. The influence of infusion and sampling time errors on predictability was also explored to obtain the optimal time points for routine PMB TDM. Using multiple regression analysis, PMB LSSs were generated from a model group of 20 patients. A validation group (10 patients) was used to validate the established LSSs. PMB LSSs from two published studies were validated using a dataset of 30 patients from our center. A population pharmacokinetic model was established to simulate the individual plasma concentration profiles for each infusion and sampling time error regimen. Pharmacokinetic data obtained from the 30 patients were fitted to a two-compartment model. Infusion and sampling time errors observed in real-world clinical practice could considerably affect the predictability of PMB LSSs. Moreover, we identified specific LSSs to be superior in predicting PMB AUC_ss,24h based on different infusion times. We also discovered that sampling time error should be controlled within −10 to 15 min to obtain better predictability. The present study provides validated PMB LSSs that can more accurately predict PMB AUC_ss,24h in routine clinical practice, facilitating PMB TDM in other laboratories and pharmacokinetics/pharmacodynamics-based clinical studies in the future.

Enhancement of sensitivity and quantification quality in the LC-MS/MS measurement of large biomolecules with sum of MRM (SMRM)

Liquid chromatography (LC) coupled with tandem mass spectrometry (MS/MS) provides a simple and efficient means for the measurement of analytes in biological matrices with high selectivity and specificity. LC-MS/MS plays an important role in the pharmaceutical industry and biomedical research, but it requires analytes to be in an ionized form in order to be detected. This can pose a challenge for large molecules such as proteins and peptides, because they can exist in multiple charged forms, and this will reduce the total analyte signal by distributing it into multiple ion peaks with a different number of charges in a mass spectrum. In conventional LC-MS/MS analysis of such macromolecules, one charged form is selected as the precursor ion which is then fragmented by collision-induced dissociation (CID) in MS/MS to generate product ions, a process referred to as multiple-reaction monitoring (MRM). The MRM method minimizes interference from endogenous molecules within biological matrices that share the same molecular weight of the precursor ion, but at the expense of signal intensity as compared to precursor ion intensity. We describe here an approach to boost detection sensitivity and expand dynamic range in the quantitation of large molecules while maintaining analytical specificity using summation of MRM (SMRM) transitions and LC separation technique. Protein image from PDB-101 (PDB101.rscb.org).

A Simple and Robust Liquid Chromatography With Tandem Mass Spectrometry Analytical Method for Therapeutic Drug Monitoring of Plasma and Cerebrospinal Fluid Polymyxin B1 and B2

BACKGROUND

Polymyxin B is used as the last treatment resort for multidrug-resistant gram-negative bacterial infections. This study aimed to develop and validate a simple and robust liquid chromatography with tandem mass spectrometry analytical method for therapeutic drug monitoring of plasma and cerebrospinal fluid (CSF) polymyxin B1 and B2.

METHODS

Plasma and CSF polymyxin B1 and B2 were chromatographically separated on a Thermo Hypersil GOLD aQ C18 column and detected using electrospray ionization mode coupled with multiple reaction monitoring. Blood and CSF samples for pharmacokinetic analysis were collected from 15 polymyxin B-treated patients.

RESULTS

The calibration curve showed acceptable linearity over 0.2-10 mcg/mL for polymyxin B1 and 0.05-2.5 mcg/mL for B2 in the plasma and CSF, respectively. After validation, according to the Food and Drug Administration (FDA) method validation guideline, this method was applied for polymyxin B1 and B2 quantification in over 100 samples in a clinical study.

CONCLUSIONS

A simple and robust method to measure polymyxin B1 and B2 in human CSF was first exploited and validated with good sensitivity and specificity, and successfully applied in polymyxin B pharmacokinetic analysis and therapeutic monitoring in Chinese patients.

Development of ELISA formats for polymyxin B monitoring in serum of critically ill patients

Treating infections in critically ill patients often requires the use of last-line antibacterial drugs such as polymyxins with a narrow therapeutic window and high toxicity. In critically ill patients, the drug pharmacokinetics changes significantly, and as a result, the antibiotic concentrations in blood and infection foci become suboptimal, which leads to therapeutic failures or toxic manifestations. For timely dosage adjustments, a competitive ELISA-based method using antibodies to polymyxin В (PMB) was developed. Among the several considered assays, a direct antibody-coated format was selected for its short duration (1.5 h) and the best agreement with the LC-MS/MS data (R² = 98 %). The assay dynamic measurement range (IC₂₀-IC₈₀) could be substantially shifted by changing the ratio of immunoreagents. To conveniently measure the therapeutic range of PMB concentrations, it was adjusted to 5.0-192 ng/mL, allowing the samples to be analyzed after a simple 100-fold dilution with the assay buffer. The ELISA sensitivity expressed in half-inhibition concentration (IC₅₀) and the limit of detection were 30.6 and 1.8 ng/mL, respectively. The assay cross-reactivity towards the related analogue colistin (COL) was 95 %, and this compound could also be adequately quantified by the same assay. The PMB and COL recovery from the spiked serum samples was similar and constituted 98-109 %. The trial drug monitoring was carried out in 3 patients with Gram-negative sepsis, and the established pharmacokinetic profiles of PMB revealed the necessity for individual dosage adjustment.

Performance of Population Pharmacokinetic Models in Predicting Polymyxin B Exposures

Polymyxin B is the last line of defense in treating multidrug-resistant gram-negative bacterial infections. Dosing of polymyxin B is currently based on total body weight, and a substantial intersubject variability has been reported. We evaluated the performance of different population pharmacokinetic models to predict polymyxin B exposures observed in individual patients. In a prospective observational study, standard dosing (mean 2.5 mg/kg daily) was administered in 13 adult patients. Serial blood samples were obtained at steady state, and plasma polymyxin B concentrations were determined by a validated liquid chromatography tandem mass spectrometry (LC-MS/MS) method. The best-fit estimates of clearance and daily doses were used to derive the observed area under the curve (AUC) in concentration–time profiles. For comparison, 5 different population pharmacokinetic models of polymyxin B were conditioned using patient-specific dosing and demographic (if applicable) variables to predict polymyxin B AUC of the same patient. The predictive performance of the models was assessed by the coefficient of correlation, bias, and precision. The correlations between observed and predicted AUC in all 5 models examined were poor (r² < 0.2). Nonetheless, the models were reasonable in capturing AUC variability in the patient population. Therapeutic drug monitoring currently remains the only viable approach to individualized dosing.

Estimation of the area under concentration-time curve of polymyxin B based on limited sampling concentrations in Chinese patients with severe pneumonia

AIMS

The efficacy and toxicity of polymyxin B (PB) are closely related to its pharmacokinetic/pharmacodynamic (PK/PD) index area under the concentration-time curve (AUC) to minimum inhibitory concentration (MIC) ratio. The purpose of this study was to obtain PK data for PB in Chinese severe pneumonia patients and establish appropriate blood sampling time points for the PB therapeutic drug monitoring (TDM).

SUBJECT AND METHOD

After treatment with at least four doses of PB (50 IU, q12h), the blood samples were collected immediately after the end of infusion (C₀) and 1.5, 2, 4, 6, 8, and 12 h (C_1.5, C₂, C₄, C₆, C₈, C₁₂) after PB administration. The PB blood plasma concentrations were determined using an ultra-performance liquid chromatography-tandem mass spectrometer (UPLC-MS/MS). All 42 patients were randomly divided into modeling (n = 24) and validation (n = 18) groups. The relationship between AUC_ss,24h and PB plasma concentration at each time point in modeling group was analyzed using limited sampling strategy and a PK method based on one-compartment with correction model.

RESULTS

C₆ scheme was found to provide the most accurate prediction of AUC_ss,24h values (r² = 0.984) with the target value of 1.9-4.2 μg/ml at steady state to reach the 50-100 μg h/ml criteria of AUC_ss,24h. C₀ with target value of 1.0-2.8 μg/ml can be considered an alternative sampling scheme (r² = 0.900) but prediction deviation may exist. C₀ and C_max sampling scheme also demonstrated good predicting ability of AUC values using PK model.

CONCLUSION

This study provides a clear plan for the implementation of TDM of PB, which is useful for optimizing the dosing regimen and individualizing treatment in severe pneumonia patients.

Therapeutic drug monitoring of polymyxin B by LC-MS/MS in plasma and urine

Background: A robust and rapid method for therapeutic drug monitoring (TDM) is urgently needed for polymyxin B, which is a last-line antibiotic for multidrug-resistant gram-negative bacteria infection. Methodology: A 3-min run of LC-MS/MS method was established to determine the main components of polymyxin B (polymyxin B1 and B2) in human plasma or urine. Solid-phase extraction was employed to eliminate the matrix effect from complicated samples from patients. Results: The calibration range was 0.050-5.00 and 0.0110-0.549 μg/ml for polymyxin B1 and B2, respectively, in plasma and urine. The precision and accuracy of quality controls, matrix effect, extraction recovery and stability were all validated and satisfied with the ICH requirements. The method was successfully applied to a pharmacokinetic study in healthy subjects and TDM in patients. Conclusion: The rapid LC-MS/MS method was validated for polymyxin B in plasma and urine, and robust for TDM.

Control of the polymyxin analog ratio by domain swapping in the nonribosomal peptide synthetase of Paenibacillus polymyxa

Polymyxins are used as the last-line therapy against multidrug-resistant bacteria. However, their further clinical development needs to solve problems related to the presence of heterogeneous analogs, but there is still no platform or methods that can regulate the biosynthesis of polymyxin analogs. In this study, we present an approach to swap domains in the polymyxin gene cluster to regulate the production of different analogs. Following adenylation domain swapping, the proportion of polymyxin B1 increased from 41.36 to 52.90%, while that of B1-1 decreased from 18.25 to 3.09%. The ratio of polymyxin B1 and B3 following starter condensation domain swapping changed from 41.36 and 16.99 to 55.03 and 6.39%, respectively. The two domain-swapping strains produced 62.96% of polymyxin B1, 6.70% of B3 and 3.32% of B1-1. This study also revealed the presence of overflow fluxes between acetoin, 2,3-butanediol and polymyxin. To our best knowledge, this is the first report of engineering the polymyxin synthetase gene cluster in situ to regulate the relative proportions of polymyxin analogs. This research paves a way for regulating lipopeptide analogs and will facilitate the development of novel lipopeptide derivatives.

A Review of the Clinical Pharmacokinetics of Polymyxin B

Polymyxin B remains an antibiotic of last resort because of its toxicities. Although newer therapies are becoming available, it is anticipated that resistance to these agents will continue to emerge, and understanding the safest and most efficacious manner to deliver polymyxin B will remain highly important. Recent data have demonstrated that polymyxin B may be less nephrotoxic than colistin. Pharmacokinetically, polymyxin B is primarily eliminated via non-renal pathways, and most do not recommend adjusting the dose for renal impairment. However, some recent studies suggest a weak relationship between polymyxin B clearance and patient creatinine clearance. This review article will describe the clinical pharmacokinetics of polymyxin B and address relevant issues in chemistry and assays available.

Fluorescent aptasensor for detection of four tetracycline veterinary drugs in milk based on catalytic hairpin assembly reaction and displacement of G-quadruplex

Based on a novel signal amplification strategy by catalytic hairpin assembly and displacement of G-quadruplex DNA, an enzyme-free, non-label fluorescent aptasensing approach was established for sensitive detection of four tetracycline veterinary drugs in milk. The network consisted of a pair of partially complementary DNA hairpins (HP1 and HP2). The DNA aptamer of four tetracycline veterinary drugs was located at the sticky end of the HP1. The ring region of HP1 rich in G and C could form a stable G-quadruplex structure, which could emit specific fluorescence signal after binding with the fluorescent dye and N-methylmesoporphyrin IX (NMM). When presented in the system, the target analytes would be repeatedly used to trigger a recycling procedure between the hairpins, generating numerous HP1-HP2 duplex complexes and displacing G-quadruplex DNA. Thus, the sensitive detection of target analytes was achieved in a wide linear range (0-1000 μg/L) with the detection limit of 4.6 μg/L. Moreover, this proposed method showed high discrimination efficiency towards target analytes against other common mismatched veterinary drugs, and could be successfully applied to the analysis of milk samples. Graphical abstract Schematic of target analyte detection based on catalytic hairpin assembly reaction and displacement of G-quadruplex.

A Rapid and Semi-Quantitative Gold Nanoparticles Based Strip Sensor for Polymyxin B Sulfate Residues

Increasing attention is now being directed to the utilization of polymyxin B (PMB) as a last-line treatment for life-threatening infections caused by multidrug resistant Gram-negative bacteria. Unfortunately, polymyxins resistance is also increasingly reported, leaving a serious threat to human health. Therefore, the establishment of rapid detection methods for PMB residues is highly essential to ensure public health. In this study, two monoclonal antibodies (mAb; 2A2 and 3C6) were obtained using PMB-bovine serum albumin as the immunogen and PMB-ovalbumin as the coating antigen, which were prepared with N-(γ-maleimidobutyryloxy) succinimide ester and glutaraldehyde as cross-linking agents, respectively. Through an indirect competitive enzyme-linked immunosorbent assay, resultant two mAbs were compared and the results indicated that 3C6 showed higher sensitivity with a half maximum inhibition concentration of 13.13 ng/mL. Based on 3C6, a gold nanoparticles (AuNPs)-based immunochromatographic test (ICT) strip was then established, the mechanism of which is that free PMB competes with the fixed coating antigen to combine with mAb labeled by AuNPs. Using ICT strip to detect milk and animal feed samples revealed the visible detection limits were 25 ng/mL and 500 μg/kg, respectively and the cutoff limits were 100 ng/mL and 1000 μg/kg, respectively. The ICT strip provides results within 15 min, facilitating rapid and semi-quantitative analysis of PMB residues in milk and animal feed.

Population Pharmacokinetics of Polymyxin B

Polymyxin B is used as a last treatment resort for multidrug-resistant Gram-negative bacterial infections. The objectives of this study were to examine the population pharmacokinetics of polymyxin B and investigate factor(s) influencing pharmacokinetic variability. Four serial blood samples each were collected from 35 adult patients at steady state. The concentrations of individual polymyxin B components were analyzed using a validated liquid chromatography / tandem mass spectrometry assay and combined to derive total concentrations. A maximum likelihood expectation maximization approach was used to fit the data. Various demographic variables were investigated as potential covariates for clearance and volume of distribution (V_d ) using linear regression analysis. A one-compartment model fit to the data satisfactorily (r²  = 0.96). The best-fit mean ± SD for clearance and V_d were 2.5 ± 1.1 L/h and 34.3 ± 16.4 L, respectively. Creatinine clearance was found to be a statistically significant covariate of clearance, but the magnitude was deemed clinically insignificant.