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1®0 200 Mui/Charge

Figure 11 Mass spectroscopic determination of the photodegradation products of naftifine (methanolic soluton, lOmg/lOOml, Suntest CPS, UVfilter, 30 min) A Total ion-chromatogramm after 30 min irradiation B mass-spectrum of naftifine (RT 11.3 min) C mass-spectrum of photoproduct (1) (RT 8.4 min)

Large differences have been observed between the photoinstability of the topical applied antimycotics. The fastest photodegradation has been observed for naftifine. After 2 hours it was completely decomposed.9 Sulbentine showed high light sensitivity, too. After 4 hours of irradiation only 1.7% of the initial drug content remained intact. The other local antimycotics showed significant, but not that pronounced photodegradation.

Not only the degree of photodegradation has been of interest in these investigations, but also the identification of the degradation products. Figure 10 shows the HPLC chromatogram of an irradiated solution of naftifine. A photodiode array detector has been used for detection. As can be seen the two main photodegradation products (1) and (2) (retention times 5.58 min and 6.78 min, respectively) show spectral deviations to naftifine.

For further information about the nature of the degradation products the irradiated solution has been investigated by a combined HPLC-MS device. It consists of HPLC system connected by an interface to a mass spectrometer.6'11

In the total ion chromatogram the two photodegradation products of naftifine (1) and (2) can be detected. The mass spectra of photodegradation product (1) (C) and (2) (not shown on this Figure) are identical with the mass spectrum of naftifine (B) (Figure 11).9

Photodegradation product (1) could be identified as the cis-isomer of naftifine by comparison with a standard solution (Figure 12). Isolation and nuclear magnetic resonance spectroscopic (NMR) investigations of the photodegradation product 2 proved its identity as the dimer of naftifine.

Figure 12 Chemical structures of trans- naftifine and its photoproduct cis-naftifine

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