Antifungal Agents. Polyenes Azoles Allyl and Benzyl Amines Other antifungals

Transcription

1 OPTO 6434 General Pharmacology Antifungal Agents Dr. Alison McDermott Room 254 HBSB, Phone Fall 2015 Reading: Chapter 50 Brody s Human Pharmacology by Wecker et al. 5 th edn. Polyenes Azoles Allyl and Benzyl Amines Other antifungals 1. Fungi and Fungal Infections (Mycoses) Less common than bacterial/viral infections Some cause disease in otherwise healthy humans most ONLY when host defences reduced e.g. loss of mechanical barrier, immunosuppression, diabetes Most dermatological and just unsightly but if systemic can be life-threatening e.g. mortality rate for invasive candida 30-50% Typically requires long term therapy (weeks to months) Examples of infection (see diagram p2) 1

2 2

3 2. Polyenes Amphotericin B, Nystatin, Natamycin Macrocyclic lactones with hydrophobic and hydrophilic regions Bind to ergosterol and form pores which make the fungal cell leaky Resistance: replacement of ergosterol by precursors Amphotericin B Active against candida, aspergillus, cryptococcus, coccidioidomyces, sporothrix, histoplasma, blastomyces. Formulations: (a) mixed with deoxycholate for IV (e.g. Fungizone) Side effects high% renal toxicity, fever, headache, normochromic normocytic anaemia (b) complexed with lipids (e.g. Abelcet) IV, much less renal toxicity than cholate formulation Side effects - fever & chills Interactions: with anti-neoplastic drugs leads to renal toxicity, with corticosteroids causes cardiac dysfunction Nystatin Topical For cutaneous/mucocutaneous and oral Candida Natamycin Active against candida, aspergillus, fusarium and others 5% ophthalmic suspension (Natacyn) for blepharitis, conjunctivitis & keratitis 3

4 3. Azoles Imidazoles (2 N) and triazoles (3N) Triazoles are most recent, are metabolised more slowly and are more specific for fungi Inhibit sterol 14-α-demethylase no ergosterol; 14-α-methylsterols build up and disturb cell membrane. squalene squalene epoxide lanosterol ergosterol X Resistance due to over-production of demethylase, or mutated demethylase Systemic Azoles: Fluconazole (e.g. Diflucan) Ketoconazole (e.g. Nizoral) Itraconazole (e.g. Sporanox) Voriconazole (e.g. Vfend, also used off-label topically for fungal keratitis) Posaconazole (Noxafil) For serious infections: systemic candidiasis, cryptococcus etc.. Fluconazole crosses blood brain barrier Side effects: Minor: headache, neausea, abdominal pain. Major: hepatic toxicity & anaphylaxis Voriconazole may cause visual disturbances Drug interactions: Reduced cyclosporine clearance renal toxicity Serious cardiac problems with e.g. cisapride (antacid), triazolam (anti-insomnia) Topical Azoles e.g. ketoconazole, econazole, terconazole For superficial and cutaneous infections Many available OTC Side effects: redness, stinging, itching 4

5 4. Allyl and Benzyl Amines Inhibit squalene epoxidase (squalene to squalene epoxide) no ergosterol squalene squalene epoxide lanosterol ergosterol X Naftifine (Naftin) & Butenafine (Mentax) Topical only for ringworm (tinea corporis etc) Side-effects redness, itchiness, dryness Terbinafine (Lamisil) Topical for ringworm (tinea corporis etc) Oral for Tinea unguium, side effects: GI upset, liver test abnormalities, rash 5. Other systemic antifungals Flucytosine (Ancobon) Antimetabolite that interferes with DNA synthesis Griseofulvin (Grifulvin) Blocks microtubule formation so inhibits cell division Echinocandins Caspofungin acetate (Cancidas), Anidulafungin (Eraxis), Micafungin (Mycamine) Inhibit glucan synthase and hence synthesis of B 1,3 D- glucans which are essential cell wall components 5

6 Antifungals : Overview Uses: Topical application Level of infection (cream, oral suspension powder, etc..) Superficial (e.g. versicolor) Azoles NA Systemic (Oral or IV) Cutaneous Dermatophyte (e.g. tinea pedis) Candida (skin/mucus membrane) Azoles Allyl and benzyl amines Azoles Polyenes Allyl and benzyl amines (terbinafine) Griseofulvin Azoles (Itraconazole) Azoles (fluconazole, Ketoconazole) Subcutaneous (e.g. sporothrix) NA Azoles (itraconazole) Amphotericin B Systemic (e.g. histoplasma, candida) NA Amphotericin B Flucytosine Azoles (Fluconazole, Itraconazole, Ketoconazole, Voriconazole, Posaconazole) Echinocandins Modes of Action 6