Dr.Sanjib Das Reading assignments: Katzung’s Basic & Clinical Pharmacology, 13 th Edi,Ch-48,p ;

III. Antifungal Chemotherapy –Understand why selective toxicity against fungal pathogens is more difficult to achieve than is antibacterial selectivity –Know the mechanisms of action, pharmacokinetics, and clinical uses of the antifungal drugs –Know the adverse effects of antifungal drugs A. Antifungal azoles B. Membrane-active agents C. Antimetabolites D. Griseofulvin E. Terbinafine

Overview of Fungal Infections Fungal infections can be broadly divided into three groups: Systemic Mycoses Subcutaneous Mycoses Superficial Mycoses

Systemic Mycoses - Most common causative organisms belong to the genera Aspergillus, Blastomyces, Candida, Coccidioides, Cryptococcus, and Histoplasma. -Type of infection Soft Tissue Infection, UTI, Pneumonia, Meningitis, or Septicemia (Fungemia ). Systemic Mycosis Occurs both in immunocompetent and immunocompromised individuals- Blastomycosis Coccidioidomycosis and Histoplasmosis Systemic fungal infection that occurs ONLY in immunocompromised or debilitated persons- Aspergillosis Candidiasis Cryptococcosis, and Mucormycosis

Subcutaneous Mycoses are often caused by puncture wounds contaminated with soil fungi. Chromomycosis,(Warty nodules that progress to "cauliflower-like" appearance at site of inoculation ) Pseudallescheriasis(Myceto ma, Draining sinus tracts at site of inoculation ) Sporotrichosis.( Nodules and ulcers along lymphatics at site of inoculation)

Superficial Mycoses: -Infections of the nails, skin and mucous membrane -Restricted to epidermis (dead layer) as those organisms live on keratin Caused by either -DERMATOPHYTES OR YEASTS Dermatophyte causing infections are -Epidermophyton -Microsporum, and -Trichophyton. - These infections usually present as a rash with pruritus and erythema. -Some dermatophytes are called Ringworm and infection caused by them is annular, scaling rash w/ a clear center. -Dermatophyte infections of the nails (Tinea unguium or Onychomycosis) Tinea pedis (athlete’ foot), Tinea capitis (ringworm of the scalp), Tinea corporis (ringworm of the body), and Tinea cruris (“jock itch”).

Yeasts causing infections are -Candida albicans -other Candida species. Patients may present with Thrush (oral candidiasis), Vaginal candidiasis, or Candida infections of the axilla, groin, and gluteal folds (including diaper rash).

Candida granuloma & chilosis

Polyene Antibiotics - Amphotericin B -Natamycin -Nystatin Azole Derivatives -Clotrimazole -Econazole -Fluconazole -Itraconazole -Ketoconazole -Miconazole Allylamine Drugs -Naftifine -Terbinafine Echinocandin -Anidulafungin -Caspofungin (prototype) -Caspofungin (prototype) -Micafungin Other Antifungal Drugs -Ciclopirox -Flucytosine -Griseofulvin -Tolnaftate

Anti-Fungal Chemotherapy Fungi are eukaryotes Very difficult to achieve selective toxicity Commonly occur in debilitated or immunosuppressed patientsCommonly occur in debilitated or immunosuppressed patients Terbinafine KetoconazoleFluconazoleItraconazoleVoriconazole Nystatin Amphoterecin B Liposoamal Ampt B Caspofungin An intravenous drug that inhibits the synthesis of glucan, a major fungal cell wall component. Use: invasive aspergillosis in patients who failed amphotericin B therapy amphotericin B amphotericin B

Mechanism of Antifungal Drugs

A gene coding an enzyme that synthesizes a particular fungal cell wall polysaccharide is mutated. A fungal pathogen might, in this way, develop resistance to which of the following agents? A fungal pathogen has been found accumulating low ergosterol in the cell membrane. Which drug probably would not work against this pathogen (due to development of resistance) if to be prescribed ? A fungal pathogen has been found activating a type of ATP binding cassettes on the cell membrane & thus enhances efflux of an an antifungal drug. Which drug is it? Exploring Mech. of Resistance from Mech. of Actions

Figure out each group of drugs as fungostatic/fungocidal by logically exploring Mech. of Actions…..not always true as dose, type of organism also determine the aforesaid properties

Amphotericin B-- -Polyene antibiotic ergosterol -Binds to ergosterol in fungal membranes & forms artificial “ pores” -Resistant strain have low ergosterol Pharmacokinetics Pharmacokinetics-- -Must give IV or intrathecal -Very slow excretion, t ½ about 2 weeks (biphasic half life, with an initial half life of about 24 hours and a terminal half life of 15 days.)

Preparations Amphotericin B is available in two parenteral formulations for systemic and subcutaneous infections: -a deoxycholate complex (conventional) and -a new Amphotericin B Lipid Complex (also called Liposomal Amphotericin B- Liposomal Amphotericin B-- "reservoir" of amphotericin) –Liposome has lower affinity for drug than does fungal membrane (ergosterol),Higher affinity for drug than does patient membrane (cholesterol) [Drug in Fungal Membrane] [Drug in Liposome] [Drug in Human Membrane] [conc] [conc] Amphotericin B lipid complex protects kidneys and other organs from the drug’s toxicity while preserving its antifungal activity.

An analogy

Clinical Uses Logically DOC or Co-DOC in most of the Severe Systemic Mycoses such as Aspergillus (high dose), Candida, Cryptococcus, Histoplasma, Mucor, Sporothrix. FlucytosineOften (but not always) combined with Flucytosine –Delay resistance –Use lower doses due to synergism Adverse effects Infusion related-(immediate) Usually see chills, fever, nausea, vomiting, headache (Usually due to Histamine release) Alleviated partly by pretreatment with NSAIDs,H1 antihistaminics Amphotericin B: Clinical Aspects Magic bullet for numerous bad fungi but amphoterrible for host

Adverse effects----contd….. Dose dependant Nephrotoxicity commonNephrotoxicity (as ATN) includes ↓GFR, tubular acidosis,↓K+ & Mg++ & anemia through ↓erythropoietin. Nephrotoxicity common, often irreversible (Reduced with liposomal preparation) Numerous other common adverse effects Mixed infection or Empirical therapy-N+N=NO

Pt. receiving a systemic antifungal drug developed puffiness or face, oliguria, swelling of hands & feet,dizziness, palpitation and tremor. An ECG reveals tall T wave,ST segment depression & frequent premature ventricular beats. Lab. Investigation suggests Hgb of 5.5 mg/dl & serum potassium level of below 1.5mEq/L. Pull out the key information from this vignette to diagnose this clinical condition. Which drug possibly can cause this? Co- administration of which diuretic would result into reduced efficacy of it’s own?

Mechanism cytosine deaminase—converted to 5-fluorouracilActivated by fungal cytosine deaminase—converted to 5-fluorouracil which after triphosphorylation is incorporated into fungal RNA which after triphosphorylation (FUTP) is incorporated into fungal RNA (↓RNA synthesis) 5FU also forms 5-Flurodeoxyuridine monophosphate (5 –Fd-UMP) which inhibits Thymidylate synthase →↓Thymine (↓DNA synthesis) Pharmacokinetics Orally effective, widely distributed, including CNS Excreted in urine-- urine levels 10x serum levels Adverse Effects Low toxicity to patient (not activated in mammalian cells) Clinical Use Narrow spectrum Resistance develops rapidly, use only with amphotericin BResistance develops rapidly, use only with amphotericin B Flucytosine

Anti-Fungal Azoles Mechanism Inhibit ergosterol synthesis (fungal CYPs) by inhibiting 14 α demethylase,a fungal CYP450 enzyme,which converts Lanosterol to Ergosterol (1. cross inhibition of host CYP450 2.decreased host cholesterol synthesis with some of these drugs) Resistance occurs due to decreased intracellular accumulation of azoles (other antimicrobials using pump?) Imidazoles include Ketoconazole (topical & systemic), Miconazole (topical), Econazole (topical) and Clotrimazole (topical). The Triazoles include Itraconazole (Both topical & systemic), Fluconazole (Both topical & systemic) & Voriconazole (Both topical & systemic). One Imidazole (Ketoconazole,a bad choice although) & all Triazoles (Itraconazole, Fluconazole and Voriconazole) are used to treat systemic infections.

Ketoconazole Ketoconazole— -1st effective oral antifungal for systemic disease -Absorbed and distributed, except to CNS Itraconazole Itraconazole- - Broader spectrum but does not cross BBB, fewer adverse effects than ketoconazole -DOC in Blastomycoses,Sporotrichoses Voriconazole– Voriconazole– effective against a variety of fungal infections, including invasive Aspergillosis, fluconazole-susceptible and -resistant Candida infections, and Cryptococcus neoformans Fluconazole Fluconazole– -Water-soluble azole -DOC or Co-DOC in most systemic fungal infection (less toxic than AMB) -Good CSF delivery (prophylaxis & supression of cryptococcal meningitis) -more selective for fungal P450s Clotrimazole & Miconazole- Used topically

Pharmacokinetics -effective orally -absorption of Ketoconazole is ↓ by antacids (as azoles slightly acidic) -absorption of Itraconazole is ↑ by food(as acidity increases with food) -only fluconazole penetrates into CSF and can be used in meningeal infection. -ketoconazole & Itraconazole are metabolized by liver enzymes -inhibition of hepatic CYP450s S/E -↓Steroid synthesis including cortisol & testosterone-Altered metabolism & Antiandrogenic effects respectively (cross inhibition of host 14 alfa demethylase responsible for host steriod synthesis) -elevated LFT & rare hepatotoxicity

Echinocandin Antifungal Drugs Examples –Anidulafungin –Caspofungin (prototype) –Micafungin Mechanism of action β(1,3)-D-glucan –Inhibits the synthesis of β(1,3)-D-glucan, which is an essential component of the fungal cell wall UsesUses –Treatment of invasive Aspergillus infections in patients who are refractory or intolerant of other therapy –Treatment of candidemia and other Candida infections (1) Intra-abdominal abscesses (2) Esophageal and peritonitis in pleural space (3) Empirical treatment for presumed fungal infections in febrile neutropenic patients Adverse effectsAdverse effects – Hypotension and tachycardia –Fever, chills and headache –Rash –Anemias –Hypokalemia

Topical antifungal agents— Nystatinamphotericin BNystatin-- Similar to amphotericin B, too toxic for systemic use.Swish & swallow in oral candidiasis,topical for diaper rash or vaginal candidiasis. Systemic Drugs for Topical Infection--Griseofulvin –Active only against Dermatophytes (Administered orally), concentrates in newly formed keratinized tissue. –Act by disrupting microtubular structure –Delivery for treatment of ringworm athlete's foot –Disrupts the mitotic spindle in fungal cells A/E : -Potent CYP450 Inducer -Disulfiram like effectTerbinafine –Similar pharmacokinetics to griseofulvin, but also can be used topically squalene epoxidase –Inhibits squalene epoxidase (ergosterol synthesis) A/E : -Possible Hepatotoxicity Anti-Fungal Agents for Mucocutaneous Infections

 tremetodes & cestodes cestodes PCP  strongyloidiasis

A 55-year-old construction worker had a mild respiratory infection with flu-like symptoms that resolved in less than 2 weeks. Two months later, a chest radiograph revealed numerous diffuse calcific densities confirming a diagnosis of primary histoplasmosis. Which of the following binds to ergosterol and would be appropriate for treating this patient? A.Amphotericin B B.Flucytosine C.Itraconazole D.Nystatin E.Terbinafine Answer: A Amphotericin B & nystatin bind to ergosterol; toxicity due to binding to cholesterol in host cells

PowerPoint Slides  Several of the PowerPoint slides are Copyright © , the American Society for Pharmacology and Experimental Therapeutics (ASPET). All rights reserved.  Some of slides in this session are from the above mentioned format and are free for use by members of ASPET.  Some others are from various sources like text book, recommended books, slides of Dr. S. Akbar (ex. professor, Pharmacology,MUA).  Core concepts of various USMLE High yield review series like Kaplan,BRS etc. are thoroughly explored & integrated whenever necessary