Photostability of drugs and drug formulations second edition

Photostability testing of drug substances and products is conducted according to ICH Q1B guideline [ ], with the choice of an appropriate light source being an important consideration for the uniformity of the results. View at Google Scholar K. Solvents can exert considerable influence on the stability of the photosensitive drugs in the pharmaceutical formulations. Spectral Regions of the UV, Visible, and Solar Radiation The spectral regions of the UV, visible, and solar light involved in the photochemical reactions are as follows:

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This occurs in the presence of an electron acceptor as a result of photoionization see 4particularly in molecules having an anionic state.

Photostability of Drugs and Drug Formulations - CRC Press Book

The reaction rates of these compounds are a linear function of the solvent dielectric constant. The country you have selected will result in the following: Mefloquine 19 in aqueous solutions undergoes photoelimination to form 2,8-bis trifluoromethyl hydroxyquinoline 20 [ 56 ] [Figure formjlations ]. These may be followed by additional reactions forming free radicals and subsequently the final products see 8 — 11as a result of the photodegradation of the drug substances. The presence of the following chemical functional dormulations in the drug molecules [ 10 ] is usually necessary for the occurrence of photochemical reactions: View at Google Scholar A.

For Instructors Request Inspection Copy. Photostability The photostability of a drug substance may be defined as the response of the drug or drug product to the exposure to solar, UV, and visible light in the solid, semisolid, or liquid state that leads to a physical or chemical change.


The various modes of photodegradation of drugs with examples of selected compounds are presented. The use of dermatological preparations or other drugs in the treatment of these disorders by application as a thin film on the skin can lead to rapid photodegradation on exposure to light. These reactions may proceed through free radical intermediates, involving several steps to form the final products.

Regulations Methodologies and Best PracticesK. View at Google Scholar J.

The photodegradation of the drug substances may occur by zero-order, first-order, and second-order reactions or by simultaneous parallel reactions to give two or three products and by consecutive reactions involving intermediate species to give the final product. The ISC is highly efficient for the photochemically active molecules. It could be through conference attendance, group discussion or directed reading to name just a few examples.

On combining the constant terms into an overall constantthe expression may be stated in the form of a first-order equation: View at Google Scholar N. The dimerization reaction is shown in Figure 6.

Photostability of Drugs and Drug Formulations

Riboflavin also forms a complex between the ribityl side chain and boric acid drigs in the formulatins of the vitamin []. The major reaction leads to N-dealkylation to give several products including 9 — 11which have been identified by MS and NMR spectrometry [ 49 ].

These studies indicate that the solvent characteristics such as dielectric constant and viscosity should be given due consideration in the formulation of drugs to achieve photostabilization.

All these processes occur mostly within nanosecond to formulatios after the excitation and may be studied by laser flash photolysis, time-resolved spectroscopy, and other techniques [ 39 ]. The biradical is oxidized to form formylmethylflavin [FMF] 31an intermediate product isolated by Smith and Metzler [ 76 ].


In view of the photosensitivity and photoinstability of drugs and adjuvants, photostqbility of the photostability of these substances and their formulated products is necessary to evaluate the following: Indexed in Science Citation Index Expanded. The sensitivity of a drug to a particular spectral region of light may forrmulations with its chemical structure, photoreactivity, and nature of the swcond form. These aspects involve the study of the kinetics of the photodegradation reactions.

This may imply the involvement of a polar intermediate in the reaction pathway [ 62 ]. The value of at a particular wavelength is given by where and are the incident and the transmitted light intensities, respectively, and is the absorbance of the sample at the irradiation wavelength. Some of the dealkylation reactions are shown in Figure 3.

The photoprotection of the solid dosage forms may also be achieved by the use of opaque blisters and capsules [ — ]. The kinetics of the photoaddition reactions of RF has been studied [ 43 ]. This results formulatiosn the absorption of light by the excipients at the expense of the drug and thus protecting it from photodegradation.

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