Griseofulvin
Griseofulvin is a fungistatic antibiotic used primarily in veterinary medicine to treat **dermatophytic fungal infections** (ringworm) of the skin, hair, and claws. **Key Clinical Points:** * It is highly specific to dermatophytes (e.g., *Trichophyton*, *Microsporum*, and *Epidermophyton*). * It has **no efficacy** against bacteria, other pathogenic fungi, or *Malassezia* yeasts. * **Clinical Pearl:** Due to its potential for significant adverse effects (especially bone marrow suppression and teratogenicity) and the need for prolonged therapy, griseofulvin is increasingly being replaced in modern veterinary practice by newer, safer antifungals such as **itraconazole** and **terbinafine**. * Dosing differs significantly between the **microsize** and **ultramicrosize** formulations due to differences in gastrointestinal absorption.
Mecanismo: Griseofulvin is a fungistatic agent. It enters susceptible fungal cells and binds to **tubulin**, which disrupts the structure of the **mitotic spindle** → arresting the metaphase of cell division. Additionally, griseofulvin binds to newly synthesized **keratin** in the host. As new skin, hair, and nails grow, the keratin-griseofulvin complex makes these newly formed tissues resistant to fungal invasion, allowing the infected, older tissues to be shed.
Dosificación por especie
- Susceptible dermatophytic infections · Microsize: 50-120 mg/kg PO; divided daily. Ultramicrosize: 10-15 mg/kg PO twice daily. · PO · divided daily or twice daily · 4-6 weeks or longer · Give with a fatty meal. Treat until culture is negative.
- Susceptible dermatophytic infections · Microsize: 50 mg/kg PO once daily or 25 mg/kg PO q12h for 42-70 days; Ultramicrosize: 5-10 mg/kg PO once daily for 42 days. · PO · once daily or q12h · 42-70 days · Give following a fatty meal or administration of corn oil. Continue for at least 2 weeks after resolution of signs and at least 5 months for onychomycosis.
- Susceptible dermatophytic infections · Microsize: 50 mg/kg PO once daily with fatty meal. · PO · once daily · Prolonged · Used with topical therapy. May double dose in resistant cases. If GI distress occurs may divide dose and give twice daily with food. Begin taking cultures after 4 weeks. Continue therapy for 2 weeks beyond clinical cure and when 2-3 negative cultures are obtained at weekly intervals.
- Feline eosinophilic granuloma complex · Microsize: 25 mg/kg PO twice daily with food. · PO · twice daily · At least one month · Give at least for one month to judge efficacy.
- Susceptible dermatophytic infections · Ultramicrosize: 10-20 mg/kg PO once daily for 1-2 weeks. 100 mg/kg PO given twice (or more) 1 week apart may also be effective. · PO · once daily or weekly · 1-2 weeks · Not FDA-approved for use in food animals and can be very expensive.
- Susceptible dermatophytic infections · 20 mg/kg PO once daily for 6 weeks · PO · once daily · 6 weeks
Vías de administración
Contraindicaciones
- Pregnancy (known teratogen)
- Known hypersensitivity to griseofulvin
- Hepatocellular failure
- Horses intended for food
Efectos adversos
- Anorexia
- Vomiting
- Diarrhea
- Anemia
- Neutropenia
- Leukopenia
- Thrombocytopenia
- Depression
- Ataxia
- Hepatotoxicity
- Dermatitis/photosensitivity
- Toxic epidermal necrolysis
- Teratogenesis
Interacciones farmacológicas
- Alcohol · Griseofulvin may potentiate the effects of alcohol.
- Aspirin · Griseofulvin may decrease salicylate levels.
- Cyclosporine · Griseofulvin may decrease cyclosporine levels.
- Phenobarbital · May decrease griseofulvin blood concentrations by inducing hepatic microsomal enzymes and/or reducing absorption. Dosage adjustment may be necessary.
- Theophylline · May decrease theophylline half-life and levels in some patients.
- Warfarin · May reduce the anticoagulant activity of coumarin anticoagulants; adjustment may be required.
Monitorización
- Clinical efficacy; fungal culture
- Adverse effects
- CBC; before therapy and q1-3 weeks during therapy
- Liver enzymes (if indicated)
Sobredosis
Specifics regarding acute toxicity are limited. Significant overdoses should be managed with gut emptying, activated charcoal, and cathartic administration unless contraindicated. Horses have tolerated 100 mg/kg PO for 20 days without apparent ill effect.
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