Photoallergy to topical agents
Photoprotection by oral or topical agents
Our purpose in clinical phototoxicity studies is to detect whether or not an investigational drug, laser, Light Emitting Diode (LED) or other light source can potentially cause cutaneous phototoxicity in man. A clinical study will help determine how severe such phototoxicity (if detected) is and which wavelengths of light are clinically important, leading to appropriate advice on precautions for labelling (if needed). Photosafety regulatory guidelines were introduced in Europe and the USA and it has become increasingly important to define drug phototoxicity risk for patients, regulatory authorities and the pharmaceutical industry. Our protocols provide tests to wavelengths across the ultraviolet B (UVB), ultraviolet A (UVA) and visible parts of the optical radiation spectrum, through monochromator phototesting, which can divide light into several wavebands to which the subject is exposed. Spectratox also often uses a solar simulator but it is important that this is an adjunct to, not instead of, the monochromator. This is because testing only with a solar simulator could potentially miss drug induced UVA phototoxicity that might be very relevant in many situations. A solar simulator is a simulator of middle of the day equatorial sunlight at sea-level on a cloudless day. Spectratox usually compares the investigational drug with a placebo group and with a positive control group. The two main reasons for a positive control are that it ensures that the test system works and it is a measure to ensure blinding by those assessing phototoxic responses. The endpoint is to establish the Phototoxic Index (PI) of the drug under investigation and the main wavelengths involved and how any phototoxicity compares with that of the positive control and placebo, in order to ascertain the significance and clinical relevance of any findings. Studies are generally undertaken in healthy volunteers, although in some instances selected patient group may be investigated.
Phototoxicity may also be an issue for drugs and chemicals that absorb UV and/or visible radiation and are applied topically, or accumulate in the skin following administration by other routes. We are also able to investigate possible photoallergy to topically applied drugs by photopatch testing. Patch testing is a method for detecting an allergic response to a substance that comes into contact with the skin, whilst photopatch testing is method for detecting a photoallergic response to a substance in the presence of light.
We have experience and expertise in undertaking healthy volunteer studies of potentially photoprotective compounds, such as nutraceuticals and antioxidants, which may be investigated through either the systemic or topical route of delivery. Through the use of monochromator phototesting of volunteers in the absence or presence of the potential photoprotective agent we are able to define the photoprotective index (PPI) of the compound.