## 4 Biological Activity  
Ciclopirox has a broad spectrum of activity against dermatophytes (_Trichophyton_ spp., _Microsporum_ spp., and _Epidermophyton floccosum_), yeasts (_Candida_ spp., _Malassezia furfur_, _Cryptococcus neoformans_, and _Saccharomyces cerevisiae_) and molds (e.g., _Aspergillus_ spp. and _Fusarium solani_). The activity was described as fungicidal and fungistatic activity depending on the concentration and the duration of use. The antifungal dose-response curve for ciclopirox is steep, meaning small dosage adjustments significantly impact efficacy. Minimum inhibitory concentration (MIC) data show variability among studies, yet MIC values generally remain below those achieved with topical application. Ciclopirox is more effective against tested species compared to itraconazole and ketoconazole, showing stronger action on yeasts than on dermatophytes, with narrower MIC ranges compared \begin{table}
\begin{tabular}{l l} \hline \hline
**Structural Feature** & **Effect on Activity** \\ \hline Hydroxypyridone core & Essential for biological activity \\ \hline Sixth position (lipophilic substituent) & Hexyl or benzyl preferred; -OMe or -OH \\  & enhance activity \\ \hline Position of hexyl ring & Moving from the sixth position significantly \\  & reduces efficacy \\ \hline Fourth position & Small groups (-Me, -OH) necessary for high activity \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Structure-activity relationships (SAR) of ciclopirox and derivatives. to other azoles and terbinafine. Although models are less sensitive to ciclopirox, it remains effective against _Aspergillus_ and _Penicillium_ species and is also effective against _Malassezia_ yeasts linked to dandruff and related skin conditions [5]. Sporicidal activity has also been demonstrated, as shown by [PERSON] et al. The treatment of onychomycosis is associated with a high risk of recurrence, potentially due to the survival of dormant fungal spores within the affected nail keratin. An in vitro study demonstrated that amorolfine and ciclopirox exhibited comparable sporicidal activity against various spores, outperforming fluconazole and bifonazole, and requiring concentrations 10-1000 times higher than the minimum inhibitory concentration to achieve sporicidal efficacy [17]. Ciclopirox has also demonstrated antibacterial activity against Gram-negative bacteria (e.g., _Pseudomonas aeruginosa_, _Proteus mirabilis_, _Escherichia coli_, and _Klebsiella pneumoniae_) and Gram-positive bacteria (e.g., _Staphylococcus aureus_, b-hemolytic _Streptococcus_ group A, _Microoccus luteus_ and _sedtantarius_, _Corynebacterium minutissimum_, _Brevbacterium_ spp. and _Corynebacterium_ spp.). This property is crucial since superficial fungal infections can be complicated by secondary bacterial infections. Ciclopirox exhibits a broader antibacterial activity than other topical antifungals, especially against Gram-negative bacteria and antibiotic-resistant Gram-positive strains. In cases of tinea pedis with bacterial complications, 1% ciclopirox cream significantly reduced bacterial counts within 15 days and demonstrated clinical efficacy against infections caused by _Staphylococcus aureus_ and _Streptococcus pyogenes_[18]. It is worth emphasizing that, with regard to SD, ciclopirox also shows anti-inflammatory activity through its impact on arachidonic acid cascade, resulting in the inhibition of the synthesis of leukotrienes and prostaglandamions. Studies have confirmed that ciclopirox significantly suppresses UVB-induced erythema compared to various antifungal agents and hydrocortisone. Additionally, one study indicated that ciclopirox alone achieved symptom improvement comparable to that of a combination treatment with hydrocortisone, suggesting that ciclopirox provides both antifungal and anti-inflammatory benefits without the associated risks of corticosteroids [18]. Furthermore, [PERSON] et al.