1. CHAPTER 10-3 Dr. Dipa Brahmbhatt VMD MpH dbrahmbh@yahoo.com
Antimicrobials
CHAPTER 10-3
Dr. Dipa Brahmbhatt VMD MpH

2. Objectives Mechanisms of action of antibiotics
Adverse drug reactions and how to mitigate these
Selection of antibiotics: Ab resistance, drug absorption, distribution, location of bacteria and drug elimination
Antifungal drugs: Advantages, Disadvantages and side effects

3. Antifungal Agents Antifungals are chemicals used to treat
diseases caused by fungi (mold or yeast)
Some fungal diseases are superficial (dermatophytosis); others are deep or systemic (blastomycosis, cryptococcosis, histoplasmosis, coccidioidomycosis, candidiasis, sporotrichosis, aspergillosis)
Diagnosed by fungal media or serologic tests
Fungal infections are difficult to treat, and it takes a long course of drug treatment to resolve these infections.
Most have severe SE

4. Blastomycosis - Dog
Thoracic radiograph from a dog with blastomycosis, showing diffuse
miliary to nodular interstitial infiltrate

5. Ringworm

6. Microsporum canis

7. Categories of Antifungals
Polyene antifungal agents
Imidazole antifungal agents
Antimetabolic antifungal agents
Superficial antifungal agents

9. Polyene antifungals Work by binding to the fungal cell membrane
Examples:
Nystatin (Panalog®)
frequently prescribed for proliferation of Candida albicans in
the GI tract; a common result of antitiotic therapy
Topical, oral, or IV
Amphotericin B (Fungizone®): -cidal/static
Damages fungi-ergosterol makes cell membrane permeable
Binds to lipoproteins (cholesterol): liver, spleen, lung
used IV for systemic mycoses (deep mycoses) – rapid onset of action (hrs.)
light sensitive, and is usually given through a filter system because it can precipitate out of solution
SE: extremely nephrotoxic (most dogs): vasoconstrictive > anoxia > cell damage, fever, anorexia and nausea
Monitor: urinalysis, BUN and Creatine
Also found in creams, lotions,and ointments

10. Imidazole antifungals - AZOLES
MOA: leakage of the fungal cell membrane (ergosterol)
Safer than Amphotericin B and used for deep/systemic mycosis
Onset of action (-cidal): 2-5 days
Examples:
Ketoconazole: Mostly PO (and topical)
Itraconazole: PO
Fewer side effects than Ketoconazole and
Miconazole
Fluconazole (Diflucan®): Mostly PO (and IV)
Especially useful in treating CNS infections
Miconazole (Monistat®, Conofite®)
Parenteral and topical forms only
Clotrimazole: topical. Intranasal infusion: aspergillosis

11. Imidazole antifungals - AZOLES
SE:
GI (more with ketoconazole), vomiting – high doses (cats: split dose for less SE)
Ketoconazole: hepatotoxicity (especially if impaired before): monitor but Alanine aminotransferase: ALT will go up and if this is only change continue using drug
Use with caution in breeding dogs: reduce steroid production in dogs: reduce – testosterone, glucocorticoids

12. Imidazole antifungals
Voriconazole
If resistant to other imidazoles: Aspergillus, Candida, Cryptococcus & Fusarium
Like amphotericin B but fewer SE
Orally, can penetrate CNS. Injectable (many SE)
SE: Hepatotoxic, renal toxicity and anemia

13. Superficial antifungals
Work by disrupting fungal cell division: -static
E.g. griseofulvin (replaced itraconazole), an oral medication used to treat dermatophyte infections: Trichophyton mentagrophytes, Microsprum canis/gypseum
Administer with a fatty meal
Oral powder (horses) and tablets. Ultramicrosize better absorbed than microsize formulation
Dose for cat (conjugation prob) is LOWER than dogs
SE: Gastrointestinal (anorexia, v/d) and teratogenic side effects in cats: cleft palate, skeletal/ skull/ nervous system deficits. Anemia and leukopenia are rare.
Do not administer to pregnant, kittens or breeding animals

14. Antimetabolic antifungals
Work by interfering with the metabolism of RNA and proteins
An example is flucytosine (Ancoban)
usually used in combination with other antifungals for Cryptococcus
Well absorbed by the GI tract
Main side effect = bone marrow abnormalities

15. Antifungal Agents Other antifungals
Lufenuron (milbemycin oxime) is used to treat ringworm in cats
Lyme sulfur is used topically to treat ringworm

16. Antiviral Agents
Viruses are intracellular invaders that alter the host cell’s metabolic pathways
Antiviral drugs act by preventing viral penetration of the host cell or by inhibiting the virus’s production of RNA or DNA
Antiviral drugs used in veterinary practice are:
Acyclovir (Zovirax®) interferes with the virus’s synthesis of DNA
used to treat ocular feline herpes virus infections
Tablets, suspension, injectable
Interferons protect host cells from a number of different viruses
Roferon-A® - an interferon inducer
used to treat ocular feline herpes virus infection and FeLV
Stimulates noninfected cells to produce antiviral proteins

17. References
Romich, J.A. Pharmacology for Veterinary Technicians, 2nd edition
Bill, R.L. Clinical Pharmacology and Therapeutics for the Veterinary Technician, 3rd edition