Photodecomposition of drugs

Electron Transfer-Mediated Photodegradation of Phototoxic Antipsychotic Drug Quetiapine

Quetiapine (QTP) (1), a psychotropic agent belonging to a chemical class, dibenzothiazepine derivatives, is photosensitive and photolabile. Its photochemistry was studied in the presence of an electron donor N,N-dimethylaniline (DMA) and an electron acceptor 1,4-dicyanobenzene (DCB) under anaerobic conditions. This resulted in photoinduced electron transfer-mediated transformation of drug QTP. Irradiation of Quetiapine (QTP, 1) in the presence of electron donor N,N-dimethylaniline (DMA) under anaerobic conditions in a photochemical reactor afforded one major photoproduct 2 when irradiation of QTP (1) was carried out in the presence of electron acceptor 1,4-dicyanobenzene (DCB) under similar conditions; it afforded 3 as a major photoproduct. These photoproducts were isolated and characterized on the basis of their spectral (IR, UV, 1H NMR, 13C NMR, and mass spectra) studies. The photophysical properties of Quetiapine were also determined in several solvents to investigate the relevance of the molecular structure in their photophysics and consequently in their photochemistry.

Photostability testing using online reactor HPLC hyphenation and mass spectrometric compound identification illustrated by ketoprofen as model compound

Investigations on the photochemical stability of pharmaceutical substances are mandatory in drug development and licensing as photo-induced degradation of an active pharmaceutical ingredient (API) may not only lead to decreased API concentrations but also to toxic or reactive products. Thus, the US Food and Drug Administration (FDA) and the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) issued Guidance for Industry Q1B "Photostability Testing of New Drug Substances and Products" for testing of pure but also packed drugs. However, photoproducts are also known to be generated in vivo under sunlight exposure of the skin and lead to considerable amounts of adverse drug effects. Herein we present an alternative system that may be used for photostability testing mimicking both situations. It combines a tailored photoreactor with an exchangeable pen light source and a modified HPLC system with online-SPE. Identification of photoproducts may be performed using mass spectrometry. The potential of accurate mass spectrometry as a tool for identification of photoproducts was demonstrated as well. A comparison of the online photoreactor system and the traditional photochamber irradiation was performed using ketoprofen for proof of concept. In both designs acetylbenzophenone and ethylbenzophenone were detected as main photoproducts. The new device allows for fast and easy photostability studies that may help to reduce time consuming in vitro experiments and animal trials. Using state of the art instruments kinetic studies could also easily be performed with qualitative and quantitative perspectives combined into one experimental design with only very low amounts of API needed. This may be useful in early drug development, where only small amounts of API are available. Scale-up may also be easily realized for the generation of reference material for quantification and quality control (QC) processes as well as for toxicity testing.

Photo- and Thermal-Stability Studies on Benzimidazole Anthelmintics by HPLC and GC-MS

Photo- and thermal-stability of the anthelmintics Albendazole, Mebendazole and Fenbendazole as in solid as in solution form has been investigated, by using a Xenon arc lamp as a radiation source, according to the ICH guideline for the drug stability tests. The degradation process was monitored by a HPLC method. All drugs showed high photosensitivity in solution but a reliable stability in solid form and when exposed to a temperature up to 50 degrees C. Two main degradation products from hydrolysis of the carbamic groups were identified by GC-MS. Validation studies demonstrated high accuracy (recovery 94 to 106%) and precision (RSD under 4.6%) of the HPLC method. The analytical procedure was successfully applied to the control of the drugs in the respective pharmaceutical formulations.

Effect of light intensity and wavelengths on photodegradation reactions of riboflavin in aqueous solution

A study of the effect of light intensity and wavelengths on photodegradation reactions of riboflavin (RF) solutions in the presence of phosphate buffer using three UV and visible radiation sources has been made. The rates and magnitude of the two major photodegradation reactions of riboflavin in phosphate buffer (i.e., photoaddition and photoreduction) depend on light intensity as well as the wavelengths of irradiation. Photoaddition is facilitated by UV radiation and yields cyclodehydroriboflavin (CDRF) whereas photoreduction results from normal photolysis yielding lumichrome (LC) and lumiflavin (LF). The ratios of the photoproducts of the two reactions at 2.0 M phosphate concentration, CDRF/RF (0.09-0.22) and CDRF/LC (0.54-1.75), vary with the radiation source and are higher with UV radiation than those of the visible radiation. On the contrary, the ratios of LF/LC (0.15-0.25) increase on changing the radiation source from UV to visible. The rate is much faster with UV radiation causing 25% degradation of a 10(-5) M riboflavin solution in 7.5 min compared to that of visible radiations in 150-330 min.

Isolation and structural elucidation of degradation products of alprazolam: photostability studies of alprazolam tablets

Accelerated thermal, hydrolytic, and photochemical degradations of alprazolam were performed under several reaction conditions. The stress studies revealed the photolability of the drug as the most adverse stability factor; the main photodegradation products were isolated and properly characterized as: triazolaminoquinoleine; 5-chloro-[5"-methyl-4H-1,2,4-triazol-4-yl]benzophenone, and 1-methyl-6-phenyl-4H-s-triazo-[4,3-alpha][1,4]benzodiazepinone. Accelerated pH-dependent studies show that the photoinstability increases as the pH decreases; at pH 9.0, photodegradation does not occur, therefore, the photochemical degradation of alprazolam was performed in buffered solutions at pH 2.0 and 3.6. The higher rate of reaction was observed at pH = 2.0; consequently, acidic conditions should be avoided and appropriate light protection is recommended during the drug-development process, storage, and handling. The main degradation route for alprazolam tablets is also photochemical.

Formulation and stability testing of photolabile drugs

Exposure of a drug to irradiation can influence the stability of the formulation, leading to changes in the physicochemical properties of the product. The influence of excipients of frequently used stabilizers is often difficult to predict and, therefore, stability testing of the final preparation is important. The selection of a protective packaging must be based on knowledge about the wavelength causing the instability. Details on drug photoreactivity will also be helpful in order to minimize side-effects and/or optimize drug targeting by developing photoresponsive drug delivery systems. This review focuses on practical problems related to formulation and stability testing of photolabile drugs.

In vitro studies of the phototoxic potential of the antidepressant drugs amitriptyline and imipramine

Amitriptyline and imipramine, two tricyclic antidepressant drugs, have been studied to evaluate their phototoxic potential using various models. Reactive oxygen species production was investigated. A negligible production of singlet oxygen was observed for both compounds whereas a significant production of superoxide anion was noted for amitriptyline in particular. Moderate red blood cell lysis under UVA light (365 nm) was induced in the presence of the two drugs at a concentration of 50 microM. Cellular phototoxicity was investigated on a murine fibroblast cell line (3T3). The two drugs were phototoxic causing cell death at a concentration of 100 microM and a UVA dose in the range of 3.3-6.6 J/cm2. Furthermore, the two drugs photosensitized the peroxidation of linoleic acid, as monitored by the formation of dienic hydroperoxides. The presence of BHA and GSH, two free radical scavengers, significantly reduced the lipid oxidation photoinduced by the drugs, suggesting a predominant involvement of radical species. Finally, the involvement of nucleic acids in the phototoxicity mechanism was also investigated using a pBR322 plasmid DNA as a model.

Photodegradation studies on Atenolol by liquid chromatography

The photostability of the beta-blocker drug Atenolol was evaluated at pH 9, 7.4 and 4.0. The drug was exposed to UVA-UVB radiations and the photoproducts were detected by reversed phase LC methods. The photodegradation was found to increase with the pH value decreasing. The major photodegradation product at pH 7.4 was identified as 2-(4-hydroxyphenyl)acetamide. The LC method developed for routine analyses (column: C-18 Alltima; mobile phase: TEA acetate (pH 4; 0.01 M)-acetonitrile 96:4) was found to be suitable for the stability indicating determination of Atenolol in pharmaceutical dosage forms.

Photodegradation of irinotecan (CPT-11) in aqueous solutions: identification of fluorescent products and influence of solution composition

The photodegradation of irinotecan (CPT-11), the semi-synthetic derivative of the antitumor alkaloid 20(S)-camptothecin, has been investigated. The drug was exposed to laboratory light for up to 5 days in 0.9% saline solution (pH 8.5). Five significant photodegradation products were observed and a high-performance liquid chromatography (HPLC) assay was employed to isolate them from CPT-11 using gradient conditions. The structures were elucidated by nuclear magnetic resonance spectroscopy and tandem mass spectrometry and shown to be the result of extensive modifications of the lactone ring of CPT-11. Three of the compounds were found to belong to the mappicine group of alkaloids. In addition, the effect of light on the stability of CPT-11 in aqueous solutions and biological fluids was also assessed. Potassium phosphate buffers (0.05 M, pH 5.0-8.2) and saline, plasma, urine, and bile solutions containing 20 microM CPT-11 were equilibrated in the dark for 24 h before being exposed to laboratory light for up to 171 h at ambient temperature. Four of the five identified photodegradation products were observed and quantitated by isocratic HPLC, using a different detection mode (fluorescence) than the one used for gradient elution. In general, CPT-11 was found to be unstable under neutral and alkaline conditions for all solutions investigated, with the exception of bile. We conclude that CPT-11 is photolabile and that care should be taken to protect samples, particularly those intended for the isolation and identification of novel metabolites of CPT-11.

Photostability determination of commercially available nifedipine oral dosage formulations

Nifedipine (NIF), a 1,4-dihydropyridine calcium channel antagonist, undergoes photodegradation to dehydronifedipine (DNIF) upon exposure to ultraviolet (UV) light and to the nitroso analogue of dehydronifedipine (NDNIF) when exposed to sunlight. NIF photodegradation products do not contribute to clinical activity, thus the content of NIF must remain uniform between equipotent formulations. Large differences in light stability between bioequivalent NIF products could potentially result in the therapeutic failure of unstable preparations. Consequently, if large photostability differences do exist between NIF preparations, product substitution may not be warranted. The light stability of 10 intact immediate- or controlled-release oral NIF formulations, obtained from several European and North American manufacturers, was studied using direct continuous artificial sunlight exposure extending over a 12-week period. The content of both NIF and NDNIF for each product was measured to determine the extent of photodecomposition using a specific and sensitive reversed-phase high pressure liquid chromatographic (HPLC) method. In addition, NIF photodegradation was measured using both pure NIF powder and methanolic NIF solution to determine the effectiveness of the artificial sunlight source used in this study. After 12 weeks of artificial sunlight exposure, less than 3% of NDNIF (w/w initial NIF content) was present in each of the 10 tested dosage forms. Photodegradation was greater than 10% (w/w initial NIF content) in approximately 5-10 min (mean t1/2 = 31 min), and in approximately 24 h (mean t1/2 = 7.7 days) of artificial sunlight exposure for methanolic NIF solution and pure NIF powder samples, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Photolytic destruction and polymeric resin decontamination of aqueous solutions of pharmaceuticals

Amoxicillin, ampicillin, bleomycin, carmustine, cephalothin, dacarbazine, lomustine, metronidazole, norethindrone, streptozocin, sulfamethoxazole, and verapamil were completely degraded in solution, without the production of mutagenic residues, by photolysis using a medium-pressure mercury lamp in an all-quartz apparatus. A stream of air was passed through the solution and for amoxicillin, ampicillin, bleomycin, lomustine, metronidazole, and norethindrone it was necessary to add hydrogen peroxide. Dilute aqueous solutions of ampicillin, bleomycin, carmustine, cephalothin, lomustine, norethindrone, streptozocin, trimethoprim, and verapamil can be decontaminated using polymeric Amberlite resins.

Photochemical decomposition of midazolam. III--Isolation and identification of products in aqueous solutions

Midazolam, 8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5- a][1,4]benzodiazepine, decomposes photochemically in aqueous solution both under irradiation from a high-pressure mercury lamp and in normal daylight. The main decomposition product under the artificial radiation was 6-(8-chloro-1-methyl-4,5-dihydro-2,5,10b-triaza-benzo[e]-azulen -6-ylidene)- cyclohexa-2,4-dienone, which was not present in the solution exposed to daylight. 6-Chloro-2-methyl-4-(2-fluorophenyl)quinazoline was formed in both irradiation experiments and was the main decomposition product in normal daylight. Several minor products were formed in both solutions, the amounts depending on the pH of the solution. Only one decomposition product was formed in acidic solutions (pH < 2) irradiated with the high-pressure mercury lamp but numerous products were formed at higher pH.