Although these 2 subcategories of photosensitivity may be difficult to distinguish because of similar clinical manifestations, several notable differences exist.
Phototoxic reactions can occur in any patient who receives sufficient quantities of the drug and is exposed to enough light. Compared with photoallergic reactions, they require higher doses of the drug to occur and can appear at first drug exposure. Common phototoxic reactions are sunburns to the exposed areas of the skin, and later, hyperpigmentation to the same areas.
Photoallergic reactions are less common than phototoxic reactions and result from cell-mediated immunity. Unlike phototoxicity, a photoallergic reaction requires only a small amount of an offending agent and may be delayed for several days after exposure to light and the drug.
The sites most frequently involved in photosensitivity reactions are those commonly exposed to light: the face, nuchal region, anterior portions of the leg, and the dorsa of the hands. The reactions typically look like an exaggerated sunburn with edema and erythema. In severe cases, however, blisters may form and patients will report burning, tenderness, and pain.
Occurs most commonly with the use of tetracyclines. Associated with tetracyclines and dapsone. Resolves after discontinuation of the offending drug. These exhibit varying degrees of photosensitivity, and mostly cause phototoxic reactions. Photosensitivity potential is increased with halogenation at the C-8 position and in compounds with a longer half-life and bioavailability.
Levofloxacin and ciprofloxacin—2 of the most commonly used fluoroquinolones today—possess relatively low phototoxic potential. These are well-known causes of phototoxic reactions. What if antibiotics could be deactivated after use so that they no longer accumulate in the environment where they encourage the emergence of resistant bugs?
A team at the University of Groningen has demonstrated a way to switch off antibiotic agents after just a few hours using warmth or sunlight.
The basic concept is to equip drug molecules with chemical components that change shape in response to heat or light. Many drugs work by sticking to and deactivating particular enzyme molecules in the body, disabling their function.
Antibiotics typically work by disrupting functions that are essential to the survival of bacterial cells. So if a drug changes shape, it might no longer work. Light-switchable drugs have been explored in other fields such as cancer therapy, but not for antibiotics. Organic chemist Ben Feringa at Groningen and his co-workers used an existing light-switchable unit called azobenzene, which consists of two benzene molecules joined together by two nitrogen atoms linked by a double chemical bond.
The double bond prevents the benzene group at each end from rotating around the "axle" linking them. They must remain either both on the same side of the molecule in a flattened C shape, or on opposite sides like a Z. These two different forms are called isomers: molecules with the same molecular formula but different structures and properties. Crucially, heat and light can temporarily loosen up the bond between the nitrogen atoms, allowing them to rotate. Continue Reading. Popular Emailed Recent Loading Please login or register first to view this content.
0コメント