Anti-virals & anti-fungals Flashcards
What is an anti-viral agent?
Medication that helps body fight off viruses
Only interferon is licensed for veterinary use
What is the difference between an anti-viral and a viricide?
Anti-virals work inside host to inhibit viral replication
Viricides destroy viruses outside host (e.g. Virkon)
How do anti-viral drugs work?
Stop viral replication inside host cells
Block viral attachment/entry into cells
Enhance immune response against virus
Why do antiviral drugs have a narrow therapeutic margin?
Since viruses use host cell machinery for replication, antiviral drugs can also affect normal host pathways
This increases risk of toxicity & limits treatment options compared to antibacterial or antifungal drugs
What is a virustatic drug, and why is it not always effective?
Inhibits 1 step in viral replication but doesn’t kill virus
Only temporarily halts replication, meaning virus may resume growth if drug is stopped
What are the two main antiviral treatments for feline herpesvirus (FHV-1)?
Trifluridine – topical nucleoside analogue used for ocular herpes infection
Famciclovir – Oral (systemic) nucleoside analogue that reduces respiratory & ocular signs
Why are antivirals rarely used for feline calicivirus (FCV)?
Most antivirals are ineffective or toxic to cats, so treatment focuses on supportive care
What is Feline interferon w & what is it used for
Immunomodulator with possible antiviral activity
Used in:
- FCV
- Feline Chronic Gingivostomatitis (FCGS)
- FeLV
- FIV
- Canine parvovirus
What antiviral is sometimes used for FIP (cat coronavirus)
Remdesivir (protease inhibitor)
What antiviral is used for Pacheco’s disease (a herpesvirus) in birds, and how does it work?
Aciclovir (nucleoside analogue)
It incorporates into viral DNA, causing chain termination & stopping viral replication
Resistance is increasing, making treatment less effective
How do azoles (anti-fungals) (e.g. itraconazole, ketoconazole) work?
Inhibit cytochrome P450, blocking ergosterol synthesis in fungal cell membranes, leading to membrane instability & fungal cell death
How do allylamines (anti-fungals) (e.g. terbinafine) work?
Inhibit squalene epoxidase (key enzyme in ergosterol synthesis) causing ergosterol depletion & toxic buildup, leading to fungal cell death
How do polyenes (anti-fungals) (e.g. Amphotericin B, Nystatin) work?
Bind to ergosterol in fungal cell membranes, creating pores that cause leakage of intracellular contents, leading to fungal cell death
How do pyrimidine analogues (anti-fungals) (e.g. 5-fluorocytosine) work?
5-Fluorocytosine is converted by fungal cells into 5-fluorouracil, which inhibits DNA & RNA synthesis, stopping fungal replication
What are cellular toxins, and how do they work against fungi?
Cellular toxins are non-specific antimicrobials that have antifungal activity by disrupting fungal cells through chemical toxicity or membrane damage
What are examples of cellular toxins with antifungal activity, and how do they work?
Silver sulfadiazine
- Releases silver in concentrations that are toxic to bacteria & yeasts
Chlorhexidine (Hibiscrub) – antiseptic
- Binds to skin & forms protective layer
Virkon - disinfectant
- Per-oxygen compound that oxidises sulphur bonds in proteins & enzymes disrupting function of cell membrane
What antifungal treatments are used for Malassezia otitis externa in cats and dogs?
Commonly used antifungals: Nystatin, Miconazole
Off-license in cats: Clotrimazole, Posaconazole
Silver sulfadiazine: Used for Pseudomonas-resistant infections
(Note: above products also contain steroid & antibiotics - polypharmacy formulations)
What antifungal treatments are used for Malassezia skin infections in cats and dogs?
Topical treatments:
- Miconazole (shampoo)
What are the most commonly used antifungals for ringworm (dermatophytosis) in cats and dogs?
Itraconazole - off licence in dogs; oral; systemic treatment
Ketoconazole - do NOT use in cats; oral; systemic treatment
Enilconazole - off licence in cats; skin rinse
Miconazole - shampoo; adjunctive treatment
What antifungals are used to treat ringworm in rabbits and small mammals?
Itraconazole
Enilconazole
Miconazole
Chlorhexidine
Clotrimazole
All are off license
What antifungals are used to treat ringworm in horses?
Enilconazole (On-license; skin rinse)
Miconazole (Off-license; shampoo)
What antifungal is used to treat fungal keratitis (keratomycosis) in horses?
Clotrimazole (Off-license; cream)
How is ringworm in cattle typically treated?
Enilconazole (Licensed skin rinse, but rarely used)
Usually self-limiting; exposure to UV light & environmental decontamination are main treatments
What are the common fungal infections in non-food-producing birds, and how are they treated?
Candidiasis & Aspergillosis are most common fungal infections
Licensed treatments: Itraconazole, Voriconazole
Off-license treatments: Nystatin, Amphotericin B
No treatments used in commercial poultry, affected birds are culled
What antifungals are used for fungal dermatitis in reptiles?
Itraconazole (Off-license)
F10 products (Disinfectants)
