Drugs trace impurities

RP-HPLC determination of trace impurities of the toxic 4-aminopyridine in the central system-stimulating drug 3,4-diaminopyridine can be performed on condition that the impurity has a lower retention time. This was accomplished on applying ion pairing with dodecanesulfonate to maximize selectivity LOD 50 ppm of the impurity in the drug154. 

Eckers et al. used on-line coupled reversed-phase LC to a Q-TOF mass spectrometer, and have successfully identified trace imparities in cimetidine. In an earlier paper published by Haskins et al., they successfully identified four chromatographically unresolved reaction by-products in cimetidine, using LC-FTMS. Another example nsing fast LC coupled with a Q-TOF mass spectrometer was the identification of cimetidine-related drug substance impurities reported by Lee et al. The exact masses for six impurities were determined with an experimental error of less than 3.1 ppm. 

S. Klick, Evaluation of different injection techniques in the gas chromatographic determination of thermolabile trace impurities in a drug substance. Journal of Chromatography A, 1995, 689(1), 69-16. 

C. Eckers,N. Haskins and J. Langridge.The use of liquid chromatography combined with a quadrupole time-of-flight analyzer for the identification of trace impurities in drug substance. Rapid Communications in Mass Spectrometry, 1997,11(17), 1916-1922. 

Haskins NJ, Eckers C, Organ AJ, Dunk MF, Winger BE. The use of electrospray ionization with Fourier transform ion cyclotron resonance mass spectrometry in the analysis of trace impurities in a drug substance. Rapid Commun Mass Spectrom. 1995 9 1027-1030. 

Nicolas and Scholz, 1998) and ion trap mass (Tiller et al., 1997a) spectrometers have been benchmarked as a routine tool for the characterization of trace impurities in drug substances. 

Pharmaceutical Purity. A safety profile of a generic drug can differ from that of the brand-name product because different impurities may be present in each of the drugs (154). Impurities can arise out of the manufacturing processes and may be responsible for adverse interactions that can occur. For example, serious adverse reactions (Lyell syndrome) were observed upon the use of isoxicam in 1985. These seemed to have resulted from trace elements of a manufacturing by-product that was within the manufacturing quality control specifications. 

In drug preparations, sensitivity is not a particular problem as there is always sufficient of the active constituent present. Suitable extraction procedures should be carried out and each fraction should then be subjected to chromatographic analysis. The mass spectra, together with the appropriate retention parameters, may then be used for identification purposes. In many cases mass spectrometric analysis is undertaken as confirmation of an identification based on the physical characteristics such as size, colour, markings, etc., of the tablet or capsule. Mass spectrometry may be used not only to identify the major components but also the trace impurities. This information may be used for quality control purposes, and may enable the route of manufacture of certain drugs to be determined. 

Kamberi, M., Riley, C.M., Ma, X., Huang, C.W.J. A validated, sensitive HPLC method for the determination of trace impurities in acetaminophen drug substance. J. Pharm. Biomed. Anal. 34, 123-128 (2004)... 

Shinde, V., Trivedi, A., Upadhayay, P.R., Gupta, N.L., Kanase, D.G., Chikate, R.C. Degradation mechanism for a trace impurity in quinapril drug by tandem mass and precursor ions studies. Rapid Commun. Mass Spectrom. 21, 3156-3160 (2007)... 

Fig. 8 MS/MS (product ion) ESI mass spectra of two isobaric trace level drug product impurities acquired on a triple quadrupole mass spectrometer (note that in both spectra the parent ion is the [M + H] m/z 722).

C. Eckers, N.J. Haskins, J. Langridge, The use ofLC combined with a Q-TOF-MSfor the identification of trace impurities in drug substance. Rapid Commun. Mass Spectrom., 11 (1997) 1916. 

Vaidya, V. V., Khanolkar, M. and Gadre, J. N. Generation of trace impurity profile for tolnaftate by reverse phase high performance liquid chromatography. Indian Drugs 37 521-523, 2000. 

Eckers, C. Haskins, N. Langridge, J. The Use of Liquid Chromatography Combined With a Quadrupole Time-of-Flight Analyzer for the Identification of Trace Impurities in Drug Substance, Rapid Commun. Mass Spectrom. 11(17), 1916-1922(1997). 

Figure 6.7 shows an example of an HPLC analysis of impurity testing of a drug product stored for 6 months under accelerated stability conditions (40°C/75% RH). Note that to maximize sensitivity of the trace impurity peaks,... 

For methods to measure trace impurity, the sample can be saturated with respect to the active ingredient because the solubility of the impurity is independent of the solubility of the drug. This technique, sometimes called the swish technique, allows for the use of small diluent volume and is an excellent technique for analysis of traces impurities such as degradants or residual solvents. However, recovery experiments are critical to demonstrate that the analyte is not adsorbed or entrapped by the solid drug. 

Table 10.16 summarizes some applications of HPLC in Pharmaceutical Chemistry which encompass drug stability studies, the determination of trace impurities or decomposition products in bulk drug samples, and the assay of drugs and metabolites in body fluids. 

Eckers, C. Laures, A.M. Giles, K. Major, H. Pringle, S. Evaluating the utihty of ion mobility separation in combination with high-pressure liquid chromatography/mass spectrometry to facihtate detection of trace impurities in formulated drug products. Rapid Commun. Mass Spectrom. 2007, 21,1255-1263. 

Before the performance of method transfer activities involving protocols and acceptance criteria, it was customary for a receiving laboratory to repeat some or all of the validation experiments. This laboratory was thereby deemed to be qualified when the results were demonstrated to meet the acceptance criteria described in the validation protocol. The choice of validation parameter(s) depends highly on the type of method being transferred. For example, content uniformity assays to determine consistency of product potency depend heavily on the method and system precision. As a second example, a determination of trace impurities in an API could not be reproduced between two sites if their instruments did not yield similar limits of detection and/or quantitation. A detailed discussion on the rational choice of validation parameters that would need to be repeated by the receiving laboratory is beyond the scope of this chapter. The reader is referred to the method validation chapters by Wood (in-process methods) and Clarke and Bretnall (API and drug product methods) for additional information on this subject. 

A final drug substance, which will be sold by the pharmaceutical industry, must be free of even the smallest trace impurities. The chemist must remove the impurities, using the various separation techniques that we have already discussed in the previous section. 

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