Kamal M. Matar

Quantification of levetiracetam in human plasma by liquid chromatography-tandem mass spectrometry : Application to therapeutic drug monitoring

A rapid, selective, reliable, precise, accurate, and reproducible tandem mass spectrometric (MS-MS) method for the quantification of levetiracetam (LEV) in human plasma using adenosine as an internal standard (IS) has been developed and validated. The drug and IS were extracted by solid phase extraction (SPE) technique and analyzed on Symmetry((R)) C(18) column (5 microm, 3.9 mm x 50 mm) using a mobile phase of methanol-water-formic acid (97:03:0.25, v/v/v) at a flow rate of 0.2 ml/min. Quantitation was achieved using a positive electrospray ionization (ESI+) interface employing multiple reaction monitoring (MRM) mode at MRM transitions m/z 171>126 and m/z 268>136 for LEV and IS, respectively. The method was validated over the concentration range of 1.0-40 microg/ml (r>0.99) with a limit of quantification of 1.0 microg/ml (R.S.D.%; 4.1 and Bias%; -9.0 to + 11.0%). Intra- and inter-run precision of LEV assay at three concentrations ranged from 0.6 to 8.9% with accuracy (bias) varied from -4.0 to 8.6% indicating good precision and accuracy. Analytical recoveries of LEV and IS from spiked human plasma were in the range of 91.7-93.4% and 80.2-84.1%, respectively. Stability of LEV in human plasma samples at different conditions showed that the drug was stable under the studied conditions. Matrix effect study showed a lack of matrix effect on mass ions of LEV and IS. The described method compared well with the commercial HPLC-UV method of Chromsystem (r(2)=0.99). The suitability of the developed method for therapeutic drug monitoring was demonstrated by measuring LEV in human plasma samples of epileptic patients treated with LEV.

Therapeutic drug monitoring of topiramate by liquid chromatography-tandem mass spectrometry

BACKGROUND Topiramate (TPM) is a new antiepileptic drug (AED) used worldwide in patients with various types of epilepsies and also for prophylaxis of migraine. A rapid, selective, reliable, precise, accurate, and reproducible tandem mass spectrometric (MS/MS) method for quantification of TPM in human plasma using topiramate-d12 as an internal standard (IS) has been developed and validated to be used routinely for TDM of TPM. METHODS The drug and IS were extracted by ether and analyzed on Symmetry C18 column. Quantitation was achieved using ESI-interface employing MRM mode. RESULTS The method was validated over the concentration range of 0.5-30 microg/ml (r>0.99). Intra- and inter-run precisions of TPM assay at three concentrations ranged from 0.7 to 7.8% with accuracy (bias) varied from -10.0 to 2.1% indicating good precision and accuracy. Analytical recoveries of TPM and IS from spiked human plasma were in the range of 84.1 to 90.0% and 90.0 to 111.0%, respectively. Stability of TPM in human plasma samples at different conditions showed that the drug was stable under the studied conditions. Matrix effect study showed a lack of matrix effect on mass ions of TPM and IS. CONCLUSION The described method compared well when assessed by Heathcontrol TDM theme program (r>0.99). The suitability of the developed method for TDM was demonstrated by measuring TPM in human plasma samples of epileptic patients treated with TPM. The proposed method is appropriate for routine TDM of TPM.

Pharmacokinetics of artesunate alone and in combination with sulfadoxine/pyrimethamine in healthy Sudanese volunteers.

Artesunate (AS) in combination with sulfadoxine/pyrimethamine (SP) is the first-line therapy for management of uncomplicated Plasmodium falciparum malaria in Sudan. The objective of this study was to assess the potential impact of SP on the pharmacokinetics of AS and its active metabolite, dihydroartemisinin (DHA), in healthy adults. A single-dose, randomized, open-label, crossover study design with a washout period of three weeks was performed with 16 volunteers. After oral administration of AS alone or in combination with SP, Tmax values of AS and DHA were significantly prolonged in the combination group (P < 0.05). However, there was no significant effect on the other pharmacokinetic parameters (P > 0.05). The t1/2 values of AS and DHA were significantly higher in females than in males (P < 0.05). The present findings suggest that co-administration of SP with AS has no clinically relevant impact on the pharmacokinetics of AS or DHA in healthy persons.

Amikacin Population Pharmacokinetics in Critically Ill Kuwaiti Patients

Amikacin pharmacokinetic data in Kuwaiti (Arab) intensive care unit (ICU) patients are lacking. Fairly sparse serum amikacin peak and trough concentrations data were obtained from adult Kuwaiti ICU patients. The data were analysed using a nonparametric adaptive grid (NPAG) maximum likelihood algorithm. The estimations of the developed model were assessed using mean error (ME) as a measure of bias and mean squared error (MSE) as a measure of precision. A total of 331 serum amikacin concentrations were obtained from 56 patients. The mean (±SD) model parameter values found were V c = 0.2302 ± 0.0866 L/kg, k slope = 0.004045 ± 0.00705 min per unit of creatinine clearance, k 12 = 2.2121 ± 5.506 h−1, and k 21 = 1.431 ± 2.796 h−1. The serum concentration data were estimated with little bias (ME = −0.88) and good precision (MSE = 13.08). The present study suggests that amikacin pharmacokinetics in adult Kuwaiti ICU patients are generally rather similar to those found in other patients. This population model would provide useful guidance in developing initial amikacin dosage regimens for such patients, especially using multiple model (MM) dosage design, followed by appropriate Bayesian adaptive control, to optimize amikacin dosage regimens for each individual patient.

A pharmacokinetic study of a topical anesthetic (EMLA®) in mouse soft tissue laceration

The use of topical anesthesia instead of injection of local anesthetics for managing soft tissue lacerations in the emergency situations may be a relief for both patients and surgeons. Topical anesthesia in the form of a cream eutectic mixture of local anesthetics (EMLA®) containing 2.5% lidocaine and 2.5% prilocaine has been reported as an efficient anesthetic on skin before venipuncture anesthesia and as an alternative to injection anesthesia in some minor surgery situations. The aim of this study was to compare the pharmacokinetics of EMLA® when applied in a laceration with topical skin application in the mouse. A total of 120 Albino Laboratory-bred strain mouse (BALB-c) male mice were divided into three groups with regard to application mode of EMLA®. Group A: with laceration, 48 mice; Group B: on intact shaved skin, 48 mice; Group C: control group (24 mice) with same procedures but without application of EMLA®. Blood levels were collected at 0, 10, 20, 30, 45, 60, 75, and 90 min post-EMLA® application. Plasma sample analysis was carried out by employing liquid chromatography coupled with tandem mass spectrometric (LC-MS/MS) method, and the pharmacokinetic analysis of the mouse plasma samples was estimated by standard non-compartmental methods. The pharmacokinetic parameters of lidocaine and prilocaine were significantly altered following EMLA® application to lacerated mouse skin in contrast to intact skin. The absorption of lidocaine and prilocaine was rapid following application of EMLA® to lacerated and intact mouse skin. Maximum drug plasma concentration (C(max) ) and area under the drug plasma concentration-time curve (AUC) values of lidocaine were significantly increased by 448.6% and 161.5%, respectively, following application of EMLA to lacerated mouse skin in comparison with intact mouse skin. Similarly, prilocaines C(max) and AUC values were also increased by 384% and 265.7%, respectively, following EMLA application to lacerated mouse skin, in contrast to intact skin. Further pharmacokinetic studies on different carriers of lidocaine/prilocaine are warranted before any firm conclusions for the clinic can be drawn.

Quantification of Vigabatrin in Human Plasma by Liquid Chromatography–Electrospray Tandem Mass Spectrometry

Abstract A simple, rapid, and accurate liquid chromatographic‐mass spectrometric method for quantification of vigabatrin (VGB) in human plasma using 4‐phenyl‐4‐aminobutanoic acid as an internal standard (IS) has been developed and validated. The method involves deproteinization of plasma sample with acetonitrile followed by detection of analytes by tandem mass spectrometry. The drug and the IS were chromatographed using XTerra™ C18 column and a mobile phase consisting of acetonitrile/water (50∶50 v/v) and 0.025% formic acid, at a flow rate of 0.1 mL/min. The effluents were detected in multiple reaction monitoring (MRM) mode using MRM transitions m/z 129.57 > 70.99 and m/z 179.7 > 116.92 for VGB and IS, respectively. The method is significantly fast, as the run‐cycle time was <3 min run‐to‐run. The described method was linear over the VGB concentration range of 0.5–10 µg/mL (r > 0.999), with a limit of detection of 0.05 µg/mL. The intra‐day coefficient of variation [CV (%)] ranged from 3.84% to 6.53% and the percentage deviation from the nominal value (%DEVs) was in the range of −4.93% to −2.03%. Inter‐day CV and %DEVs ranges were 2.78% to 9.15% and −4.91% to 6.67%, respectively. Mean recovery percentage of VGB in spiked human plasma samples was 99.59%. The stability study indicates that VGB in plasma is stable for at least 4 weeks when stored at −20°C. This developed method is significantly important in clinical practice for monitoring VGB plasma levels, particularly in pharmacokinetic studies and bioavailability/bioequivalence studies.

Therapeutic Drug Monitoring of Gentamicin: Evaluation of Five Nomograms for Initial Dosing at Al-Amiri Hospital in Kuwait

Objective: To compare five published nomograms (Thomson guidelines, Mawer nomogram, rule of eights, Hull-Sarubbi table and Dettli method) for calculating the initial gentamicin dosage regimen in a Kuwaiti population. Materials and Methods: Based on measured peak and trough gentamicin concentrations, the elimination rate constant and volume of distribution of gentamicin were calculated for each patient (n = 56), using a modified two-point Sawchuk-Zaske method. The calculated individual set of pharmacokinetic parameters and the initial dose regimen recommended by each of the five methods were used to predict the steady-state peak and trough of gentamicin concentrations. Results: The Thomson guidelines produced consistent results in predicting gentamicin concentrations within the target ranges of peak plus trough, peak only and trough only (63, 75 and 75%, respectively). The Mawer nomogram, Hull-Sarubbi table and Dettli methods achieved similar percentages of patients (46–50%) within the target ranges (5–10 mg · l–1 for peak and 0.5–2 for trough), whereas empirical dosing and the rule of eights showed the lowest percentages of patients within the peak plus trough target range (25 and 37%, respectively). However, with respect to the underdosing target range (predicted concentration <5 mg · l–1), the Thomson guidelines showed that 21% of patients were underdosed. Conclusion: The results show that a large number of patients (37–63%) were outside the target ranges in all initial gentamicin dosing methods evaluated in this study. Therefore, serum concentration measurement can be advised to assist in the optimization of gentamicin dose selection.

Quantitative Determination of Clavulanic Acid in Plasma by HPLC: Application to a Pharmacokinetic Study

Abstract A rapid, simple, accurate, sensitive, and reproducible high performance liquid chromatographic (HPLC) method for quantification of clavulanic acid (CA) in human plasma using metronidazole as an internal standard has been developed and validated. Following derivatization with imidazole, plasma protein was precipitated using acetonitrile. The drug and the internal standard were eluted from a 4‐µm stainless steel Novapak® C18 column (150 × 3.9 mm2 I.D.) at room temperature, with a mobile phase consisting of 4% methanol in 0.01 M potassium dihydrogen phosphate buffer (pH adjusted to 3.2), at a flow rate of 1.8 mL/min. The effluent was monitored using a UV detector set at 311 nm. Each analysis required no longer than 8 min. Quantitation was achieved by measurement of the peak height ratio of the drug to the internal standard, and the limit of quantification of CA in plasma was 100 ng/mL. The intraday coefficient of variation (C.V., %) ranged from 3.30% to 3.93% and interday C.V. ranged from 1.74% to 2.74% at three different concentrations. The mean relative recovery was 100.35% and the mean absolute recovery was 97.63%. A stability test shows that CA is stable in plasma for at least 4 weeks when stored at −70°C. The method was successfully applied in a bioavailability/bioequivalence study involving amoxicillin/CA combination (250/62.5 mg) administered orally to 24 healthy volunteers.

Bradykinin-forming components in Kuwaiti patients with type 2 diabetes.

Diabetes is the most common risk factor in inducing hypertension, nephropathy and retinopathy. The bradykinin (BK)-forming system has been proposed to protect cardiovascular and renal functions. We therefore evaluated urinary active and proactive kallikrein, total kininogen, plasma tissue kallikrein, plasma creatinine, plasma glucose and plasma HbA1c in newly diagnosed untreated type 2 diabetic patients and healthy subjects. In diabetic patients, urinary and plasma tissue kallikrein concentrations were significantly increased. In addition, plasma prekallikrein levels were also significantly higher. However, urinary kininogen values were significantly reduced in diabetic patients when compared with healthy subjects. This is the first investigation among Kuwaiti Arab patients with type 2 diabetes showing abnormal activities in the BK-forming system. High levels of plasma prekallikrein may be a risk factor for developing high blood pressure as well as nephropathy. The urinary and plasma tissue kallikrein concentrations were higher in diabetic patients, which could indicate the hyperactivities of these components, and may result in increased levels of plasma glucose to induce diabetes. Furthermore, the urinary kininogen levels were reduced in diabetic patients. These alterations might reflect the utilization of urinary kininogen to form BK, a potent inflammatory agent. However, this hypothesis needs further investigation.

A simple and accurate liquid chromatography–tandem mass spectrometry method for quantification of zonisamide in plasma and its application to a pharmacokinetic study

Zonisamide (ZNM) is an antiepileptic drug that is used as an adjunctive therapy in the treatment of adults with partial seizures. An LC-MS/MS method for quantification of ZNM in human and rabbit plasma using (2)H4,(15)N-Zonisamide as an internal standard (IS) has been developed and validated. The drug and IS were extracted by ether and analyzed on Symmetry(®) C18 column. Quantitation was achieved using ESI-interface employing MRM mode. The method was validated over the concentration range of 0.5-50μg/mL and 0.5-30μg/mL (r(2)>0.99) in human and rabbit plasma samples, respectively. Intra- and inter-run precision of ZNM assay in human and rabbit plasma samples ranged from 0.8 to 8.5% with accuracy (bias) varied from -11.3 to 14.4% indicating good precision and accuracy. Stability of ZNM in human and rabbit plasma samples at various conditions showed that the drug was stable under the studied conditions. Analytical recoveries of ZNM and IS from spiked human and rabbit plasma samples were in the range of 70.8-77.3% and 85.6-110.4%, respectively. Matrix effect study showed a lack of matrix effect on mass ions of ZNM and IS. The developed method was successfully applied for a pharmacokinetic study by measuring ZNM in rabbit plasma samples. Moreover, the method is routinely utilized for TDM of ZNM.