<prompt> All of the following drugs are effective in the treatment of pityriasis versicolor, except:Selenium disulphideKetoconazoleGriseofulvinClotrimazole  <response>: Ans. C. GriseofulvinPityriasis versicolor is caused by yeastlike microorganism Pityrosporum ovale. Pale, scaling macules develop insidiously over the skin of the chest and back in young adults. Tropical imidazole creams miconazole, clotrimazole, econazole applied once daily for 6 weeks or use of ketoconazole shampoo to wash the affected areas once daily for 5 days are usually sufficient. Older medicines such as 20 sodium thiosulfate solution and selenium disulphide shampoo are also effective, as is the oral itraconazole for 7 to 15 days. 