A 20 year old young female had history of recurrent acne on the face treated with many antibiotics like clindamycin ,tetracycline erythromycin and others. Now she complained of multiple hyperpigmented spots at the site of old acne lesions.Which of the following drug might have been responsible for this-

minocycline following prolonged therapy for 1-2 years with high dose 100-200mg/day, causes blue black pigmentation. this is observed in three patterns : 1: localised type occuring at the sites of previous inflammation -acne scars 2: pretibial area 3: generalised with predominance over the sunexposed areas IADVL textbook of dermatology: pigmentary disorders page 787