Determination of sodium levothyroxine in bulk, tablet, and injection formulations by high-performance liquid chromatography

Potency and Powder X-ray Diffraction (PXRD) Evaluation of Levothyroxine Sodium Tablets under Ambient, Accelerated, and Stressed Conditions

Levothyroxine tablets, although highly prescribed in the United States, have been one of the most frequently recalled products. Because of the importance of the medication, several efforts have been put in place by the United States Food and Drug Administration (US FDA) to control the quality of levothyroxine tablets available to patients using the drug. The choice of excipients used in the formulation has been shown to impact the hygroscopicity and microenvironment, and ultimately the stability of the levothyroxine tablets formulations. Based on information generated from the US FDA Enforcement Report database, one of the main reasons for recalls is the low potency of different batches of the product. The yearly product recall trends for levothyroxine formulations were determined using the FDA Enforcement Report database. Three brands of levothyroxine tablets were selected with excipient lists similar to those products that have been historically recalled. The samples were placed at ambient (~23 °C), accelerated stability (40 °C/75% RH), and stress (50 °C/75% RH) conditions for up to 6 months. Sample potencies were determined at 0, 1.5, 3, and 6 months using the methods for assay and impurities in the United States Pharmacopeia (USP) monograph for levothyroxine tablets. Additional sample monitoring was conducted by overlaying the initial powder X-ray diffractograms (PXRD) of the samples from 0 months with the patterns generated thereafter. There has been a decline in the number of levothyroxine tablets recalled over the years. The highest numbers of recalls were recorded in the years 2013 [33] and 2020 [23]; no recalls occurred in the years 2019 and 2022. All of the brands evaluated met the USP 95.0-105.0% assay requirements at 1.5 months under accelerated conditions; only one of the brands complied at 3 months. Under ambient conditions, two brands were stable at 6 months, with borderline assay results. For stability, levothyroxine was found in microgram quantities in the formulations and PXRD could not detect changes at these low levels. However, we found some distinguishing data for samples under stress conditions.

Development and application of a validated HPLC method for the analysis of dissolution samples of levothyroxine sodium drug products

A rapid, selective, and sensitive gradient HPLC method was developed for the analysis of dissolution samples of levothyroxine sodium tablets. Current USP methodology for levothyroxine (L-T(4)) was not adequate to resolve co-elutants from a variety of levothyroxine drug product formulations. The USP method for analyzing dissolution samples of the drug product has shown significant intra- and inter-day variability. The sources of method variability include chromatographic interferences introduced by the dissolution media and the formulation excipients. In the present work, chromatographic separation of levothyroxine was achieved on an Agilent 1100 Series HPLC with a Waters Nova-pak column (250 mm × 3.9 mm) using a 0.01 M phosphate buffer (pH 3.0)-methanol (55:45, v/v) in a gradient elution mobile phase at a flow rate of 1.0 mL/min and detection UV wavelength of 225 nm. The injection volume was 800 μL and the column temperature was maintained at 28°C. The method was validated according to USP Category I requirements. The validation characteristics included accuracy, precision, specificity, linearity, and analytical range. The standard curve was found to have a linear relationship (r(2)>0.99) over the analytical range of 0.08-0.8 μg/mL. Accuracy ranged from 90 to 110% for low quality control (QC) standards and 95 to 105% for medium and high QC standards. Precision was <2% at all QC levels. The method was found to be accurate, precise, selective, and linear for L-T(4) over the analytical range. The HPLC method was successfully applied to the analysis of dissolution samples of marketed levothyroxine sodium tablets.

Enantioselective resolution of thyroxine hormone by high-performance liquid chromatography utilizing a highly fluorescent chiral tagging reagent

A highly fluorescent chiral tagging reagent, 4-(3-isothiocyanatopyrrolidin-1-yl)-7-(N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole, [R(-)-DBD-PyNCS], was employed to develop an indirect resolution method for efficient separation of thyroxine enantiomers,D-T(4) and L-T(4). The reaction of R(-)-DBD-PyNCS with the thyroxine enantiomers proceeds effectively at 40 degrees C for 20 min in the presence of basic medium to produce the corresponding pair of diastereomers. No racemization occurs during the tagging reaction under the optimized conditions. Various experimental parameters for derivatization reaction including the species of catalyst, the concentration of tagging reagent and reaction temperatures, have been examined to get a highest yield for T(4) derivatives. The structure of T(4) derivatives was identified based on ESI-MS/MS measurements in negative mode. The efficient separation of D-, L-T(4) derivatives was achieved by isocratic elution with water-acetonitrile mobile phase containing 1% AcOH on a reversed phase column utilizing a conventional fluorescence detector. The resolution (Rs) value of the diastereomers derived from thyroxine was 5.1. The calibration curves of both the D-T(4) and L-T(4) were linear over the concentration range of 0.1-20 microg/ml. The limits of detection (S/N = 3) for both D-T(4) and L-T(4) were 0.2 ng per injection. The proposed method was applied to the determination of D-T(4) and L-T(4) in pharmaceutical formulations and human serum samples.

Development of a validated HPLC method for the determination of iodotyrosines and iodothyronines in pharmaceuticals and biological samples using solid phase extraction

Identification, separation and quantitation of iodoaminoacids, is essential for the biological research and the clinical diagnosis of thyroid gland disease. Under this aspect a reversed-phase high-performance liquid chromatographic method was developed for the determination of thyroid gland hormones and some of their primary metabolites, 3,3',5,5'-tetra-iodo-L-thyronine (L-thyroxine), 3,3',5-tri-iodo-L-thyronine, 3,5-di-iodo-L-thyronine, L-thyronine, 3,5-di-iodo-L-tyrosine, 3-iodo-L-tyrosine and l-tyrosine. Analysis was performed on an Inertsil C(18) column with photodiode-array detection, using a 25 min gradient scale program of a binary mobile phase consisted of 0.1% aqueous solution of trifluoroacetic acid at pH 3 as solvent A and acetonitrile as solvent B, at a flow rate of 1 mL/min. Quantitation was performed using were obtained using theophylline as internal standard. The method was applied to commercial pharmaceuticals and biological samples (serum, urine and tissue). Drug-free urine and serum samples were spiked with known concentrations of the analytes standards and pretreated by solid phase extraction to remove matrix interferences. C(18) cartridges were used, yielding recoveries ranging from 87.1% to 107.6% for serum samples and from 92.1% to 98.7% for urine samples. With regard to total-T(4) concentrations in serum samples, results are cross-validated with RIA and found to agree well.

Biosensor for the enantioselective analysis of the thyroid hormones (+)-3,3',5-triiodo-L-thyronine (T3) and (+)-3,3',5,5'-tetraiodo-L-thyronine (T4)

An amperometric biosensor based on L-aminoacid oxidase is proposed for enantioselective assay of (+)-3,3',5-triiodo-L-thyronine (L-T3) and (+)-3,3',5,5'-tetraiodo-L-thyronine (L-T4), due to the fact that only the L enantiomer has the hormonal activity. The construction of the amperometric biosensor is simple and reproducible. The analytical information obtained from enantioselective analysis are reliable. The RSD <1% assured by using the amperometric biosensors for L enantiomers assay as raw materials, and from tablets, demonstrated their suitability for the analysis of T3 and T4 at ppb concentration levels.

Determination of thyroid hormones in pharmaceutical preparations, after derivatization with 9-anthroylnitrile, by high-performance liquid chromatography with fluorescence detection

HPLC with fluorescence detection was used for the determination of low levels of liothyronine sodium and levothyroxine sodium in pharmaceutical preparations after fluorogenic derivatization. 9-Anthroylnitrile in dimethyl sulfoxide was used as a precolumn fluorogenic reagent. The 9-anthroylnitrile derivatives of liothyronine sodium and levothyroxine sodium were separated on a reversed-phase column with acetonitrile-0.02 M sodium dodecylsulfate (pH 3.5 with phosphoric acid) as the eluent. The calibration graphs were linear over a sample concentration range of 0.25-2.5 microg/ml. The detection limits for liothyronine sodium and levothyroxine sodium were 0.2 ng per injection. The proposed method was applied to the determination of thyroid hormones in pharmaceutical preparations.

Identification and quantitation of sodium-thyroxine and its degradation products by LC using electrochemical and MS detection

High performance liquid chromatography (HPLC) was used in combination with an amperometric and mass spectrometric detection to elucidate and quantitate the degradation products and contaminants of the photo-sensitive Na-thyroxine. Using HPLC with amperometric detection, seven decomposition compounds were separated. These products, which occur mostly as contaminants, were then identified by a developed liquid chromatography-mass spectrometry technique. The same HPLC method was also employed to analyze Na-thyroxine and its degradation products in three commercially available brands of Na-thyroxine tablets.

Application of extraction disks in dissolution tests of clenbuterol and levothyroxine tablets by capillary electrophoresis

Sample preparation procedures using octadecyl (C18) extraction disks were developed to obtain accurate and reproducible results for determinations of clenbuterol(20 micrograms per dose) and levothyroxine (100 micrograms per dose) in dissolution media of solid oral dosage forms. Preconcentration of samples allowed final concentrations of 1.1 micrograms/ml of clenbuterol and 4.0 micrograms/ml of levothyroxine to be reached prior to CE analysis. The results obtained by CE were in good agreement with those of HPLC. The precision of the migration time, peak area, peak height and accuracy were determined in both intra-day (n = 6) and inter-day (n = 18) assays. Linearity was demonstrated over the ranges 0.5-80.0 micrograms/ml of clenbuterol and 1.0-30.0 micrograms/ml of levothyroxine. The mean recoveries were higher than 94.0%, ranging from 50 to 125% levels with respect to dose potencies. The proposed methodology may be generally applied to determine drugs at ng/ml concentrations.

Optical purity determination of thyroxine enantiomers in bulk materials by chiral thin layer chromatography

L-thyroxine and D-thyroxine were separated on ligand exchange chiral thin layer chromatographic plates, using a solvent system consisting of acetonitrile:methanol:water 60:15:15 v/v, at a wavelength of 254 nm. The methodology, chiral recognition mechanism(s) involved and its application are discussed.

Kinetics of degradation of levothyroxine in aqueous solution and in solid state

The kinetics of the deiodination of levothyroxine in aqueous solution were studied over the pH range 1 to 12. Temperature dependence of the reaction was also studied. The log k - pH profile indicated that the kinetics of deiodination include proton attack on the anion and dianion in acidic solution and water attack on the anion and dianion in alkaline solution. A possible mechanism of the deiodination was discussed. The solid-state stability of levothyroxine sodium was studied at elevated temperatures; and the compound was found to undergo deamination on heating. The decomposition follows biphasic first-order kinetics, with the most rapid decomposition occurring at the beginning of heating.

Effect of excipients on the stability of levothyroxine sodium tablets

Levothyroxine sodium tablets from two different manufacturers were analysed using the USP-NF method of analysis, a stability-indicating high pressure liquid chromatographic (HPLC) procedure. The results indicate that one particular manufacturer's 0.2-mg pink tablets contain some excipient(s) which act as a catalyst to hasten decomposition after extraction of levothyroxine for analysis. The same tablets from a different batch showed an additional long peak in the chromatogram, which indicated that the excipient(s) may have been changed. The same manufacturer has also used three different types of bottles/lids for the same product during the last year. Good manufacturing practice requires that new compatibilities/stability studies be conducted to assure the quality of the product. Ongoing stability studies are required by the Food and Drugs Administration (FDA). The use-life of 0.2-mg pink tablets of this manufacturer may be short.

Determination of L-thyroxine in reference serum preparations as the o-phthalaldehyde-N-acetylcysteine derivative by reversed-phase liquid chromatography with electrochemical detection

A simple procedure for the assay of L-thyroxine in serum preparations with D-thyroxine as internal standard is described. The L-thyroxine is extracted with acetonitrile, fractionated on a reversed-phase silica cartridge and analysed by reversed-phase high-performance liquid chromatography of the o-phthalaldehyde-N-acetyl-L-cysteine derivative. This derivative is not fluorescent, but may be detected with suitable sensitivity and selectivity with an electrochemical detector.