Photochemical and photophysical properties of piroxicam and benoxaprofen in various solvents

A theoretical and spectroscopic study of conformational structures of piroxicam

Piroxicam (PRX) has been widely studied in an attempt to elucidate the causes and mechanisms of its side effects, mainly the photo-toxicity. In this paper fluorescence spectra in non-protic solvents and different polarities were carried out along with theoretical calculations. Preliminary potential surfaces of the keto and enol forms were obtained at AM1 level of theory providing the most stable conformers, which had their structure re-optimized through the B3LYP/CEP-31G(d,p) method. From the optimized structures, the electronic spectra were calculated using the TD-DFT method in vacuum and including the solvent effect through the PCM method and a single water molecule near PRX. A new potential surface was constructed to the enol tautomer at DFT level and the most stable conformers were submitted to the QST2 calculations. The experimental data showed that in apolar media, the solution fluorescence is raised. Based on conformational analysis for the two tautomers, keto and enol, the results indicated that the PRX-enol is the main tautomer related to the drug fluorescence, which is reinforced by the spectra results, as well as the interconvertion barrier obtained from the QST2 calculations. The results suggest that the PRX one of the enol conformers presents great possibility of involvement in the photo-toxicity mechanisms.

Drug-induced cutaneous photosensitivity: incidence, mechanism, prevention and management

The interaction of sunlight with drug medication leads to photosensitivity responses in susceptible patients, and has the potential to increase the incidence of skin cancer. Adverse photosensitivity responses to drugs occur predominantly as a phototoxic reaction which is more immediate than photoallergy, and can be reversed by withdrawal or substitution of the drug. The bias and inaccuracy of the reporting procedure for these adverse reactions is a consequence of the difficulty in distinguishing between sunburn and a mild drug photosensitivity reaction, together with the patient being able to control the incidence by taking protective action. The drug classes that currently are eliciting a high level of adverse photosensitivity are the diuretic, antibacterial and nonsteroidal anti-inflammatory drugs (NSAIDs). Photosensitising chemicals usually have a low molecular weight (200 to 500 Daltons) and are planar, tricyclic, or polycyclic configurations, often with heteroatoms in their structures enabling resonance stabilisation. All absorb ultraviolet (UV) and/or visible radiation, a characteristic that is essential for the chemical to be regarded as a photosensitiser. The photochemical and photobiological mechanisms underlying the adverse reactions caused by the more photoactive drugs are mainly free radical in nature, but reactive oxygen species are also involved. Drugs that contain chlorine substituents in their chemical structure, such as hydrochlorthiazide, furosemide and chlorpromazine, exhibit photochemical activity that is traced to the UV-induced dissociation of the chlorine substituent leading to free radical reactions with lipids, proteins and DNA. The photochemical mechanisms for the NSAIDs that contain the 2-aryl propionic acid group involve decarboxylation as the primary step, with subsequent free radical activity. In aerated systems, the reactive excited singlet form of oxygen is produced with high efficiency. This form of oxygen is highly reactive towards lipids and proteins. NSAIDs without the 2-arylpropionic acid group are also photoactive, but with differing mechanisms leading to a less severe biological outcome. In the antibacterial drug class, the tetracyclines, fluoroquinolones and sulfonamides are the most photoactive. Photocontact dermatitis due to topically applied agents interacting with sunlight has been reported for some sunscreen and cosmetic ingredients, as well as local anaesthetic and anti-acne agents. Prevention of photosensitivity involves adequate protection from the sun with clothing and sunscreens. In concert with the preponderance of free radical mechanisms involving the photosensitising drugs, some recent studies suggest that diet supplementation with antioxidants may be beneficial in increasing the minimum erythemal UV radiation dose.

Photoreactivity of the nonsteroidal anti-inflammatory 2-arylpropionic acids with photosensitizing side effects

The photoreactivity of the nonsteroidal anti-inflammatory 2-arylpropionic acids benoxaprofen, carprofen, naproxen, ketoprofen, tiaprofenic acid, and suprofen is reviewed with special emphasis on fundamental photophysical and photochemical properties. The absorption and emission properties of the excited states of these drugs as well as their main photodegradation routes are summarized. The photochemical mechanisms are discussed on the basis of product studies and detection of short-lived intermediates by means of laser flash photolysis. After dealing with the unimolecular processes, attention is focused on the photosensitized reactions of key biomolecules, such as lipids, proteins or nucleic acids. Finally, a short section on the photobiological effects on simple biological models is also included. Although some earlier citations are included, the literature coverage is in general limited to the last decade.

Hydrogen bonding in a non-steroidal anti-inflammatory drug--Naproxen

Photophysical properties of a non-steroidal anti-inflammatory drug, Naproxen (6-methoxy alpha-methyl-2-naphthalene acetic acid sodium salt), were investigated in solvents of different polarity, hydrogen donor ability and also in cyclodextrins. The results indicate that in all cases the emitting state is the 1L(b) singlet. In alcoholic solvents, an intermolecular hydrogen bond is responsible for the observed photophysical behaviour of the probe whereas in non-protic solvents (polar and weakly polar) an intramolecular hydrogen bond type is postulated to rationalize the data found. In water, the non-radiative rate constant has a value similar to those found in aqueous solutions of alpha- and beta-cyclodextrins where the probe form complexes. The behaviour in water is explained by a water-structure enforced hydrophobic effect. The spectroscopic results are interpreted on the basis of a multiple-parameter model that considers specific solute-solvent interactions. These were also observed in the ground state and detected by Fourier transform infrared spectroscopy. Molecular mechanics (MM) and molecular orbital (AM1) calculations also support the existence of two conformations (rotamers) in Naproxen with non-equivalent intramolecular hydrogen bond-like formation.

Oxicam-induced photosensitivity. Patch and photopatch testing studies with tenoxicam and piroxicam photoproducts in normal subjects and in piroxicam-droxicam photosensitive patients

BACKGROUND

The mechanism of piroxicam-induced photosensitivity is unknown. It was first attributed to metabolites of the drug produced in vivo but further photochemical studies disclosed that piroxicam was not stable to light, forming at least two photoproducts. Photosensitivity reactions to droxicam and tenoxicam have been not reported.

OBJECTIVE

The aim of this study was to determine whether piroxicam photoproducts contribute to the light reactions induced by this drug, to describe a case of droxicam-induced photosensitivity and to study the in vivo photosensitizing potential of tenoxicam.

METHODS

Patch and photopatch tests with two major photoproducts of piroxicam, with different preparations of UVA-preirradiated piroxicam, and with low and high concentrations of tenoxicam were performed in normal volunteers and in piroxicam-photosensitive patients. Phototesting studies were also performed before and after the oral administration of tenoxicam in both groups of subjects.

RESULTS

Positive patch test responses were obtained in piroxicam-photosensitive patients only with the preirradiated piroxicam preparations. Phototesting studies with tenoxicam were normal in both groups.

CONCLUSION

Minor or intermediate piroxicam photoproducts are more likely to be responsible for the photosensitivity reactions induced by this drug.

Mechanism of DNA cleavage mediated by photoexcited non-steroidal antiinflammatory drugs

DNA damage photoinduced by four nonsteroidal antiinflammatory drugs (NSAID) have been investigated by neutral agarose gel electrophoresis. Upon irradiation at 300 nm, in phosphate buffered solution, benoxaprofen, naproxen, ketoprofen, tiaprofenic acid photosensitized the formation of single-strand breaks (SSB) in double stranded supercoiled phi X174 DNA. The efficiency of the cleavage is higher in argon saturated solutions than in aerated solutions and it is not correlated with the quantum yield of photodegradation of the drugs. Simultaneously with the DNA strand breaks, NSAID promote a weak reduction of the electrophoretic mobility of the supercoiled form that may be attributed to the formation of pyrimidine dimers or other DNA unwinding products. These photodimerization processes suggest the involvement of a triplet-triplet energy transfer between NSAID and DNA. Addition of mannitol and superoxide dismutase decreases the efficiency of the cleavage suggesting that HO. and O2.- are involved in the DNA cleavage. Unexpectedly, addition of sodium azide quenches the cleavage both in aerated or in deaerated solutions. Substituting H2O by D2O does not change the number of SSB thus suggesting that 1O2 does not take an important place in the cleavage of DNA. From our data we tentatively assume that the cleavage occurs through a radical mechanism that may involve in a first step an energy or an electron transfer. Gel sequencing on NSAID-photoinduced DNA breakage exhibits no particular specificity except in the case of benoxaprofen where a slight selectivity for cytosine is observed.