Drug-Induced Photosensitivity and the Major Culprits

Photosensitivity is a condition that occurs when sunlight or artificial forms of radiation interact with a medication to produce an adverse cutaneous drug eruption. This adverse reaction may increase the incidence of skin cancer and can be prevented with proper counseling. There are 2 major types of photosensitivity: phototoxic reactions, which occur when an individual is exposed to both high doses of medication and radiation, and photoallergic reactions, which require an immune-mediated response. Several classes of drugs are commonly implicated in photosensitivity reactions, including tetracyclines, floroquinolones, sulfonamides, diuretics, phenothiazine antipsychotics, and nonsteroidal anti-inflammatory drugs. This review will discuss photosensitivity reactions, the most commonly reported photosensitizing agents, and treatment and prevention measures for the condition.

Solvent dependence of the photophysical properties of 2-chlorothioxanthone, the principal photoproduct of chlorprothixene

2-chlorothioxanthone (CTX) is used as photoinitiator for the reticulation of synthetic resins and for the preparation of pharmaceuticals. It was previously determined that CTX is the primary photoproduct of z-chlorprothixene (CPTX) when irradiated at 313 nm and is formed in an autocatalyzed reaction through an energy-transfer mechanism (Piñero et al. [2009] Photochem. Photobiol., 85, 895-900). In this work, the photophysical properties of CTX were measured in acetonitrile/water solutions to determine if their magnitude can affect the side effects of CPTX. The results show that CTX has higher absorption coefficients in the visible region (400-420 nm) and higher triplet quantum yields than its parent compound. Similar to TX, both properties strongly depend on the solvent polarity/hydroxylicity. The quantum yield of the triplet intermediate is very close to the value of the phenothiazine triplets. The phenothiazines are the most phototoxic antidepressants. Therefore, given the appropriate microenvironment, the photosensitization side effects of CPTX can be intensified on the production of CTX.

Photophysics and photochemistry of z-chlorprothixene in acetonitrile

Chlorprothixene (CPTX, Taractan) is a low potency antipsychotic mainly used for the treatment of psychotic disorders (e.g. schizophrenia) and acute mania occurring as part of bipolar disorders. As in the case of other numerous drugs used in the treatment of psychiatric disorders, CPTX presents geometric isomerism. Therefore, in vitro irradiation induces a rapid Z/E isomerization, which can affect its pharmacokinetic properties. This photoisomerization is not dependent on the oxygen concentration. The Z/E quantum yields determined for zCPTX in acetonitrile are 0.22 and 0.21 in anaerobic and aerobic environments, respectively. In the presence of water, both isomers decompose to produce 2-chlorothioxanthone (CTX) after prolonged irradiation. This process strongly depends on the water concentration and the irradiation time, i.e. it is autocatalyzed by the CTX through a triplet-energy transfer mechanism. The protonation state of the terminal amino group, on the other hand, has no effect on the isomerization process, but inhibits the formation of CTX. These results indicate that the phototoxicity of zCPTX is somehow affected by the formation of CTX.