Bioequivalence and Bioavailability Forum

Dear Manan!

❝ i do have a literature wherein it is mentioned that Montelukast shows instability when exposed to light leading to formation of cis-isomer as a major photoproduct and the degradation rate is least in sodium light then in UV or daylight.

From the Abstract of

MM Al Omari, RM Zoubi, EI Hasan, TZ Khader and AA Badwan
Effect of light and heat on the stability of montelukast in solution and in its solid state
Journal of Pharmaceutical and Biomedical Analysis 45/3, 465-471 (2007)

Montelukast in solution showed instability when exposed to light leading to the formation of its cis-isomer as the major photoproduct. The rate of photodegradation of Montelukast in solution exposed to various light sources increases in the order of; sodium < neon < tungsten < daylight < UV (254 nm). The extent of photodegradation was influenced by solvent type, where Montelukast was found to be most stable in 70% methanol. In solid state, Montelukast showed more than 20% decrease in its potency after exposure to daylight for 1 week. Also unpacked Montelukast chewable tablets, exposed to daylight for 2 weeks, showed a decrease of about 10% with the formation of Montelukast S-oxide as a major photoproduct. On the other hand, Montelukast film-coated tablets either unpacked or in its immediate pack showed excellent stability under the same condition.

(my emphases)

❝ […] therefore it is better to carry out the trial in dark to avoid exposure to direct light.

In the light of the above:
Performing the clinical part »in dark conditions« does not make sense at all. Look at the data. Chewable tablets are expected to show a degradation of 0.03% (!!) after one hour in daylight. I don’t think it shall take that long to dispense them to the subjects.
Concerning bioanalytics – simply test it! Hint: Sometimes it’s sufficient to wrap stock solutions in aluminium foil.