Antifungals Flashcards
Characteristics of fungi
Eurkaryotic. Asexual or sexual reproduction. Cell wall containing chitin and glucan and cell membrane containing ergosterol.
Different ways of living for fungi
Saphrophtyic = on dead, organic matter. Parasitic = at the cost of a living organism. Symbiotic = in a relationship with another living organism.
Classification of fungi
Yeasts/blastophores. Yeast-like fungi that produce mycelium/hyphae/filamentous like structure. Filamentous fungi with true mycelium/hyphae. Dimorphic fungi which can grow as yeast or filamentous fungi with hyphae/mycelium.
Types of fungi infections
Cutaneous = Trichophyton e.g tinea pedis ir Candida albicans ausing oral and vaginal candidosis. Subcutaneous = implantation of fungi beneath skin by animal or tree scratch e.g. Sporotrichosis by Sporothrix schenckii. Systemic fungal infections = opportunistic or true infections, invasive. e.g. Systemic candidosis, Aspergillosis by Aspergillus fumigatus.
Diagnosis of fungal infections
Microscopy and culture
Diagnosis of Candidosis
Culture = white colonies. Microscopy = not very useful, shows dimorphic. Matrix assisted Laser Desorption Ionisation Time of Flight Spectroscopy.
Spread of subcutaneous fungal infection
E.g. Sporotrichosis from Sporothrix ischenckii associated with sphagnum moss. Spreads up lymph system emerging at intervals to give symptoms.
Systemic Candidosis Infection
Commonly Candidaemia (in blood). Also infect peritoneum, meninges, heart, eye and brain.
Risk factors for systemic candidosis
IV drug use (heroin low pH and candida likes low pH). Central venous catheters, gut sugery, antibiotics, immune suppression, premature, diabetes, cancer.
Why are Abx a risk factor for fungal infections
Broad-spec kill commune micro-flora which compete with fungus for resources in body.
Types of Aspergillosis infections
Allergic Bronchopulmonary Aspergillosis (RF=asthma or CF). Severe asthma with fungal sensitisation. Aspergilloma (in old TB cavity). Aspergillus sinusitis. Chronic pulmonary aspergillosis (RF=lung pathology e.g. COPD). Invasive Aspergillosis.
Invasive Aspergillosis
RF=immunocompromised esp neutropenic leukaemia. Primary infection is pulmonary aspergillosis then spreads via lung vessels to become systemic and invasive. Active tissue and blood vessel invasion. Common organs include brain, skiin and kidney. High mortality.
Diagnosis of invasive aspergillosis in immunocompromised
Chest X-ray and CT - HALO sign, culture bronchoscopy alveolar lavage, antigen test, PCR test for DNA, biopsy.
Diagnosis of invasive aspergillosis in immune competent.
chest x-ray and CT. Culture sputum. antibody test.
Most common pathogen for invasive aspergillosis
Aspergillus fumigatus.
Mucoromycosis
pathogen = mucormycetes moulds e.g. Mucor or Lichtheimia. Rhino-cerbral or pulmonary (if immunocompromised or poor DM control) infection. Rapid progressing, difficult diagnosis, rare.
Cryptococcosis
Pathogen = Cryptococcus neoformans yeast. Infects pulmonary system and meningitis. RF = immunocompromised. Diagnosis = India ink staining of culture. Antigen test
Histoplasmosis
An example of a true invasive infection. Pathogen = Histoplasma capsulatum, dimorphic fungus as mould in environment and yeast inside human. Principally a pulmonary infection as Conidia inhaled from bird or bat roost shredding. Diagnosis = CXR, culture and microscopy.
5 classes of antifungal treatment
Pyrimidine, Polyenes, Allyamine, Azoles, Echinocandins.
Drugs which act on DNA and protein synthesis
Pyrimidine .e.g. 5 fluorocytosine
Antifungal acting on plasma membrane
Polyene e.g. amphotericin B
Anti fungal acting on ergosterol biosynthesus
Allyamine and Azole e.g. terbinafine and fluconazole
Antifungal acting on beta 1-3, glucan synthesis of cell wall
Echinocandins e.g. caspofungin
Active Pyrimidines
5-Fluorocytosine is taken up by a fungal-cell specific cytosine permeate. It is converted to a false nucleotide: 5-fluorouracil by fungal deaminase (also in bacteria). Phosphorylated to either fluorouridine triphosphate or fluorodeoxyuridine monophosphate.
Action of pyrimidines
Inhibit DNA and RNA synthesis. Monophosphate form decreases raw materials for DNA synthesis by inhibition of thymidylate synthetase. Triphisphate form is incooperated into RNA strand and prevents RNA translation.
Use of pyrimidines
Used in severe systemic infections and meningitis due to fungi.
Selective toxicity of pyrimidines
Humans lack deaminase to form active form. As bacteria have enzyme can kill gut microflora but only at low level.
Pharmacokinetics of pyrimidines and ADR
Water soluble, readily absorbed and wide distribution, short half life, urine excretion, IV administration. ADR: bone marrow suppression, GI upset.