*3.1.5.1 Light sources for photodegradation studies*

The majority of therapeutic substances are white in appearance, which means that they may absorb in the UV region depending on their chemical structure.

Grossweiner, 1989 [10], divided the ultraviolet radiation (UV-R) into three sub-bands:


The most commonly sources for photostability studies include: day light, window-glass filtered day light and room light [12]. All these sources can be generated artificially. The artificial light source should have an output with spectral power distribution (SPD) as near as possible to the sunlight. This can be achieved by the use of arc lamps and fluorescent tubes.

## *3.1.5.2 Drug molecules labile to photodecomposition*

A number of medicinal products have been studied for their photostability. Carbonyl, nitroaromatic and *N*-oxide functions, aryl halides, alkenes, polyenes and sulfides are certain chemical functions that are expected to introduce photoreactivity [13].

Photodegradation of a drug is considered of practical significance if the compound absorbs light >300 nm and the photodegradation becomes evident in a short period.

Factors that govern photochemical reaction rate include aerobic (most reactions proceed in presence of oxygen) and anaerobic (N2) conditions, solvents (H2O, organic solvents), buffers, temperature, metals, intensity of radiation and spectral distribution of light, drug concentration and volume of the sample [14].

Thus, in formulations that contain low drug concentrations, the primary photochemical reaction follows first-order kinetics; the kinetics is more complicated at higher concentrations and in the solid state because most of the light is then absorbed near the surface of the product.

The mechanisms of photodegradation are of such complexity as to have been fully elucidated in only a few cases. For example, the phenothiazine chlorpromazine (CLP) is rapidly decomposed under the action of ultraviolet light, the decomposition being accompanied by discoloration of the solutions (**Figure 3**). Chlorpromazine behaves differently towards ultraviolet irradiation under anaerobic conditions.

A polymerization process has been proposed which involves the liberation of HCl in its initial stages [5].

**29**

itself.

**Figure 3.**

**4. Analytical methods**

*The effect of ultraviolet light on chlorpromazine (CLP).*

**4.1 Method development**

*Drug Analysis*

*DOI: http://dx.doi.org/10.5772/intechopen.88739*

The photodegradation of ketoprofen can involve decarboxylation to form an intermediate which then undergoes reduction, or dimerization of the ketoprofen

Prior the development of any method for the analysis of certain compound or formulation, there are many factors must be considered before developing the method and applying it to the intended use. The first step include collecting information about the analyte itself (the analyte structure and its physicochemical properties). The mode of detection should be selected (e.g. UV detection). Sample preparation which may include centrifugation, sonication and filtration. The type of the diluent also plays an integral role in the analysis as it should be transparent and does not interfere in the analysis. The stability of the prepared solution, the mobile phase; stationary phase and mode of elution in case of chromatographic elution. All these factors and much more should be considered, optimized and the

developed method is then validated and applied for the analysis.

*Drug Analysis DOI: http://dx.doi.org/10.5772/intechopen.88739*

*Pharmaceutical Formulation Design - Recent Practices*

*3.1.5.1 Light sources for photodegradation studies*

to the skin and cornea [11].

many chemicals in natural sunlight.

the use of arc lamps and fluorescent tubes.

absorbed near the surface of the product.

*3.1.5.2 Drug molecules labile to photodecomposition*

near-UV because it is near the visible region.

sub-bands:

The majority of therapeutic substances are white in appearance, which means that they may absorb in the UV region depending on their chemical structure. Grossweiner, 1989 [10], divided the ultraviolet radiation (UV-R) into three

1.UV-C: which ranges between 200 and 290 nm and is termed shortwave or far UV. Sunlight at the earth's surface is devoid of this band due to its absorption by molecular oxygen and ozone in the upper atmosphere. Artificial radiation sources such as discharge and germicidal lamps and welding arcs form the sources of UV-C which are used for forced drug photodegradation studies (stress-conditions). These also cause serious damage

2.UV-B band: this covers the region 280–320 nm. It causes sunburn, skin cancer and other biological effects and it is responsible for the direct photoreaction of

3.UV-A band: this is the long wavelength region from 320 to 400 nm, also called

The most commonly sources for photostability studies include: day light, window-glass filtered day light and room light [12]. All these sources can be generated artificially. The artificial light source should have an output with spectral power distribution (SPD) as near as possible to the sunlight. This can be achieved by

A number of medicinal products have been studied for their photostability. Carbonyl, nitroaromatic and *N*-oxide functions, aryl halides, alkenes, polyenes and sulfides are certain chemical functions that are expected to introduce photoreactiv-

Photodegradation of a drug is considered of practical significance if the compound absorbs light >300 nm and the photodegradation becomes evident in a short

Factors that govern photochemical reaction rate include aerobic (most reactions

proceed in presence of oxygen) and anaerobic (N2) conditions, solvents (H2O, organic solvents), buffers, temperature, metals, intensity of radiation and spectral

Thus, in formulations that contain low drug concentrations, the primary photochemical reaction follows first-order kinetics; the kinetics is more complicated at higher concentrations and in the solid state because most of the light is then

The mechanisms of photodegradation are of such complexity as to have been fully elucidated in only a few cases. For example, the phenothiazine chlorpromazine (CLP) is rapidly decomposed under the action of ultraviolet light, the decomposition being accompanied by discoloration of the solutions (**Figure 3**). Chlorpromazine behaves differently towards ultraviolet irradiation under anaerobic

A polymerization process has been proposed which involves the liberation of

distribution of light, drug concentration and volume of the sample [14].

**28**

conditions.

HCl in its initial stages [5].

ity [13].

period.

**Figure 3.** *The effect of ultraviolet light on chlorpromazine (CLP).*

The photodegradation of ketoprofen can involve decarboxylation to form an intermediate which then undergoes reduction, or dimerization of the ketoprofen itself.
