Hi, a. One error in the treatment could be that the dermatologist did not correctly assess the patient s medical history or potential allergies before prescribing a penicillin-based antibiotic. Another mistake could be that the pharmacist did not properly advise the patient on using the medication or warn them of potential side effects. b. The adverse reaction could be due to an allergic reaction to the penicillin-based antibiotic, or the antibiotic may not have been effective against the specific type of infection the patient had. Additionally, it may be possible that the patient s psoriasis has made him more susceptible to other diseases. c. A suitable alternative treatment would depend on the specific type of infection the patient has and any other underlying medical conditions. A non-penicillin-based antibiotic, such as a macrolide or a tetracycline, could be considered if the patient has a penicillin allergy. Topical or systemic immunomodulatory agents and phototherapy could be treatment options for psoriasis. Additionally, antifungal or antiviral medication may be necessary if the patient has a fungal or viral infection. It is essential to consult with a dermatologist or a specialist to determine the best course of treatment. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Priyanka, General & Family Physician