Griseofulvin

Introduction Overview

Generic Name

griseofulvin

Brand Name

Grifulvin V, Fulvicin P/G, Fulvicin U/F, Gris-PEG, Grisactin Ultra, Grisactin 250, Grisactin 500, Griseofulicin, Griseofulvic

Dosage Form

oral suspension (microcrystalline 125 mg/5 mL), oral tablet (microcrystalline 500 mg; ultramicrocrystalline 125 mg; ultramicrocrystalline 250 mg)

Drug Class

Miscellaneous antifungals

Pharmacokinetics

Absorption: Griseofulvin is administered orally and exhibits variable absorption depending on its formulation and particle size. The microcrystalline and ultramicrosize preparations have differing bioavailability, with ultramicrosize formulations demonstrating enhanced absorption. The presence of fatty meals significantly increases griseofulvin absorption due to improved dissolution and gastrointestinal retention. Peak plasma concentrations are typically achieved within 2 to 6 hours after oral administration, and steady-state levels are reached after continuous dosing. Factors such as gastrointestinal motility and pH can influence absorption, and concurrent use of antacids may affect bioavailability.

Distribution: Once absorbed, griseofulvin exhibits extensive distribution into keratin precursor cells, which is critical for its therapeutic effect on dermatophytic infections of skin, hair, and nails. It binds extensively to plasma proteins, predominantly albumin, with a plasma protein binding rate of approximately 90%. This binding limits free drug concentration in plasma but facilitates its accumulation in keratinized tissues. The drug concentrates within newly forming keratin where it exerts its antifungal effect, making it highly effective for skin and nail infections. Griseofulvin can cross the placental barrier and appears in breast milk but in minimal amounts.

Metabolism: Griseofulvin undergoes hepatic metabolism primarily by the cytochrome P450 enzyme system, especially CYP3A4 isoenzymes. It is metabolized to various inactive metabolites, including 6-desmethylgriseofulvin, which are further conjugated. The extent of metabolism may vary in individuals with hepatic impairment or co-administration of enzyme-inducing or inhibiting agents. Metabolic rate affects both the plasma half-life and the duration of antifungal activity. Some metabolites have been implicated in hypersensitivity reactions.

Elimination: The elimination half-life of griseofulvin ranges from 9 to 24 hours, considering both plasma elimination and tissue release. The drug and its metabolites are predominantly excreted in the feces via biliary secretion, with a smaller fraction eliminated through the urine. Due to its extensive keratin binding, elimination is prolonged as bound drug is slowly released from keratinized tissues. Renal clearance is minor but clinically significant in cases of renal dysfunction. Dose adjustments may be necessary in patients with severe hepatic or renal impairment to avoid toxicity. The prolonged elimination phase is clinically relevant for dosing intervals and treatment duration in fungal infections.

Dosage Forms

Available Dosage Forms: Griseofulvin is available in multiple oral formulations designed to optimize absorption and patient adherence. These include oral suspension and oral tablets in different particle sizes. Specifically, the oral suspension is a microcrystalline formulation available at 125 mg/5 mL. Oral tablets are available as microcrystalline at 500 mg strength, and ultramicrocrystalline at 125 mg and 250 mg strengths. These varied forms allow clinicians to tailor therapy to patient needs, including pediatric dosing and tolerance considerations.

Dosages for Adults and Adolescents: The dosing regimen for griseofulvin in adults and adolescents varies according to the severity and site of infection. For dermatophytosis of the skin, typical dosages range from 500 mg to 1000 mg taken once daily, or divided doses across the day, with treatment duration typically spanning 2 to 6 weeks. For more invasive infections such as tinea capitis or onychomycosis, prolonged treatment periods of 6 to 12 weeks or longer may be required to achieve clinical cure. Ultramicrosize formulations generally require lower dosage to achieve similar plasma levels compared to microcrystalline forms.

Specific Patient Populations: Pediatric patients over 2 years old can be treated with griseofulvin; dosing is adjusted by body weight, typically 10-20 mg/kg/day. Pediatric dosing often employs the oral suspension or appropriately sized tablets. Griseofulvin is contraindicated in patients with porphyria or liver failure. It is not recommended for use in pregnant women due to teratogenicity risk, particularly within the first trimester. Lactating mothers should avoid griseofulvin as the drug is excreted in breast milk and may harm the infant. Elderly patients and those with hepatic or renal impairment require careful dosing evaluation. The pharmacokinetic profile necessitates longer treatment durations in nail infections due to prolonged keratin turnover.

Mechanism Of Action

Griseofulvin exerts its antifungal effects primarily through disruption of fungal cell mitosis and inhibition of fungal cell division. Mechanistically, griseofulvin binds to fungal microtubules, which are essential components of the mitotic spindle apparatus. By binding to tubulin proteins, it interferes with the formation of the spindle fibers necessary for chromosomal segregation during mitosis, leading to mitotic arrest and eventual fungal cell death.

At the cellular level, this disruption impairs fungal replication, effectively halting the proliferation of dermatophytes responsible for infections of keratinized tissues such as skin, hair, and nails. The drug's affinity for keratin precursor cells facilitates its accumulation where fungi are embedded, thereby concentrating the antifungal action directly within the infected tissue.

Biochemically, griseofulvin also affects nucleic acid and protein synthesis indirectly through its impact on cytoskeletal elements. This leads to abnormal fungal cell morphology and apoptosis. Unlike other antifungals that target ergosterol synthesis, griseofulvin's unique mechanism makes it especially useful in treating dermatophyte infections resistant to other agents.

Clinical implications of this mechanism include the requirement for prolonged therapy to allow replacement of infected keratin with new, uninfected keratin containing the drug. Comparative studies show that griseofulvin is less effective against yeast and non-dermatophyte fungi, underscoring its selective mechanism. Ongoing research investigates analogs with improved bioavailability and reduced side effects, as well as combination regimens to enhance antifungal efficacy.

Pharmacological Actions

Inhibits fungal cell mitosis by binding to tubulin, disrupting mitotic spindle formation.
Prevents replication of dermatophyte fungi causing superficial skin, hair, and nail infections.
Accumulates in keratin precursor cells, targeting sites of fungal infection directly.
Exerts fungistatic and fungicidal effects dependent on concentration and fungal species.
Induces abnormal nucleic acid and protein synthesis in fungal cells indirectly.
Selectively active against dermatophyte species such as Trichophyton, Microsporum, and Epidermophyton.
Demonstrates prolonged antifungal activity due to keratin binding and slow release.
Metabolized hepatically with potential to induce hepatic microsomal enzymes.
May interact with cytochrome P450 system leading to altered metabolism of concurrent drugs.
Minimal antibacterial activity, with primary focus on fungal pathogens.
Requires fatty meals for optimal absorption, enhancing its systemic availability.
Not effective against systemic fungal infections or yeast like Candida species.
Can penetrate hair shaft and nail beds, thereby effective for onychomycosis and tinea capitis.
May induce hypersensitivity reactions through its metabolites in susceptible individuals.
Has a relatively long half-life supporting once or twice daily dosing regimens.

Therapeutic Or Clinical Uses

Treatment of dermatophytosis including tinea corporis (ringworm) affecting skin.
Management of tinea pedis (athlete's foot) involving interdigital and plantar surfaces.
Therapy for tinea cruris (jock itch) involving groin and inner thigh regions.
Treatment of tinea capitis (fungal scalp infections), especially in children.
Management of onychomycosis of fingernails and toenails caused by dermatophytes.
Used for chronic or recurrent superficial fungal infections unresponsive to topical therapy.
Prophylaxis of fungal infections in certain immunocompromised patient populations.
Adjunctive therapy for difficult-to-treat dermatophyte infections.
Treatment option for patients allergic or intolerant to other antifungal agents.
Used in veterinary medicine for fungal infections of skin and hair in animals.
Off-label uses include some uncommon cutaneous mycoses as dictated by clinical judgment.
Control of fungal infections in settings where topical treatment is impractical or poorly tolerated.
As a systemic antifungal for infections localized within keratinized tissues requiring oral therapy.
Useful in patients where resistance to azole antifungals is suspected or confirmed.

Side Or Adverse Effects

Nausea, vomiting, and gastrointestinal upset including diarrhea are common adverse effects.
Headache and fatigue may occur during therapy, potentially impacting compliance.
Cutaneous reactions including rash, photosensitivity, and pruritus have been reported.
Central nervous system effects such as dizziness, confusion, and insomnia observed.
Rare but serious allergic reactions including anaphylaxis and angioedema documented.
Hepatotoxicity risk manifesting as elevated liver enzymes, jaundice, and hepatic failure.
Neuropathy presenting as numbness, tingling, or burning sensations in extremities.
Hematological abnormalities such as leukopenia, neutropenia, and rarely pancytopenia.
Systemic lupus erythematosus-like syndrome with muscle and joint pain linked to treatment.
Photosensitivity reactions increase risk of severe sunburn and skin damage.
Potential for staining and discoloration of nails during extended therapy.
Rare kidney dysfunction with symptoms of oliguria and peripheral edema.
Oral mucosal changes including soreness, white patches, and stomatitis in susceptible patients.
Drug hypersensitivity reactions with fever, sore throat, and malaise may necessitate discontinuation.
Gastrointestinal bleeding signals emergency conditions associated with this drug.

Precautions

Avoid use in patients with known hypersensitivity to griseofulvin or related compounds.
Screen patients for liver disease before initiation due to risk of hepatotoxicity.
Use caution in patients with porphyria as griseofulvin may trigger exacerbations.
Not recommended during pregnancy, particularly in the first trimester, due to teratogenicity.
Advise females of reproductive age to use effective non-hormonal contraception during therapy.
Monitor hepatic and renal function periodically during prolonged therapy courses.
Adjust dosage or discontinue use in patients exhibiting signs of peripheral neuropathy.
Avoid concomitant alcohol consumption due to enhanced risk of adverse effects.
Use cautiously in patients with a history of systemic lupus erythematosus or autoimmune disease.
Instruct patients to avoid excessive exposure to sunlight and apply broad-spectrum sunscreen.
Not approved for use in children under 2 years of age due to insufficient safety data.
Inform patients about potential decreased efficacy of hormonal contraceptives.
Monitor for signs of hypersensitivity reactions, especially during initial treatment phase.
Advise to maintain proper skin hygiene and dryness to enhance treatment outcomes.
Use appropriate measuring devices for pediatric oral suspension to ensure accurate dosing.

Warnings

Contraindicated in patients with porphyria due to risk of triggering severe disease attacks.
Avoid use in individuals with severe hepatic failure or significant liver impairment.
Contraindicated during pregnancy because of risk of birth defects and fetal harm.
Potential for serious skin reactions, including Stevens-Johnson syndrome, necessitating immediate discontinuation.
May induce systemic lupus erythematosus-like reactions warranting cessation if symptoms develop.
Risk of hepatotoxicity mandates periodic liver function monitoring during therapy.
Photosensitivity risk requires avoidance of direct sunlight and use of protective measures.
Not recommended during breastfeeding because of drug excretion in breast milk and infant risk.
Use with caution in patients taking other hepatotoxic or cytochrome P450-inducing agents.
Potential interaction with anticoagulants increases bleeding risk; monitor coagulation parameters.
Risk of serious allergic reactions including anaphylaxis, though rare, requires prompt recognition.
Avoid in patients with known hypersensitivity to penicillin due to possible cross-reactivity.
Long treatment duration increases risk of cumulative toxicity and adverse effects.
Patients should be advised to report any signs of jaundice, dark urine, or abdominal pain immediately.
Drug-induced hematological abnormalities warrant baseline and regular blood counts during prolonged use.

Contraindication

Known hypersensitivity to griseofulvin or any component of the formulation.
Patients with porphyria, a genetic enzymatic disorder affecting skin and nervous system.
Active liver failure or severe hepatic impairment preventing safe metabolism.
Pregnant women, especially during the first trimester, due to teratogenic effects.
Patients with a history of allergic reactions to penicillin, due to potential cross-sensitivity.
Children under 2 years of age, as safety and efficacy in this group are not established.
Individuals with severe renal impairment without appropriate dose adjustment.
Concurrent use with certain medications contraindicated by physician due to severe interactions.
Patients with pre-existing systemic lupus erythematosus or autoimmune disorders exacerbated by the drug.
Use in breastfeeding mothers, as griseofulvin passes into breast milk causing potential infant harm.
Patients with active gastrointestinal bleeding or disorders predisposing to bleeding complications.
Individuals with previous severe skin reactions to antifungal agents should avoid use.
Those with impaired ability to swallow tablets without alternative formulation availability.
Contraindicated in patients receiving other hepatotoxic drugs without close monitoring.
Patients with documented severe photosensitive dermatoses exacerbated by UVA/UVB exposure.

Drug Interactions

Griseofulvin induces hepatic microsomal enzymes (CYP450), leading to decreased efficacy of oral contraceptives.
Concurrent use with anticoagulants such as warfarin may alter blood clotting parameters and bleeding risk.
May reduce plasma levels of cyclosporine, potentially reducing immunosuppressive effects.
Interaction with barbiturates or other enzyme inducers may accelerate griseofulvin metabolism.
Use with corticosteroids might alter metabolism and clinical effects of both drugs.
Antacids may reduce griseofulvin absorption and plasma concentrations if taken simultaneously.
Concomitant use with disulfiram can increase risk of neurological side effects.
Griseofulvin may enhance hepatotoxicity when used with other liver-metabolized drugs.
Potential reduction in plasma levels and efficacy of certain benzodiazepines.
May interfere with phenytoin metabolism leading to altered seizure control.
Usage with alcohol can potentiate adverse reactions such as flushing and gastrointestinal upset.
Herbal supplements inducing CYP450 (e.g., St John's Wort) can decrease griseofulvin effectiveness.
Drugs metabolized by CYP3A4 may have altered plasma concentrations during co-administration.
Simultaneous use with macrolide antibiotics may affect absorption and pharmacodynamics.
Careful monitoring required during combination with other antifungal agents for additive toxicities.

Preparations Of The Drug

Oral suspension, microcrystalline griseofulvin, 125 mg per 5 mL for pediatric and adult dosing flexibility.
Oral tablet, microcrystalline, 500 mg strength for adult and adolescent dosing.
Oral tablet, ultramicrocrystalline, 125 mg strength, enhancing absorption and bioavailability.
Oral tablet, ultramicrocrystalline, 250 mg strength, allowing dose adjustments for intermediate dosing needs.
Various branded preparations include Grifulvin V, Fulvicin P/G, Fulvicin U/F, Gris-PEG, Grisactin variants.
Formulations designed for improved patient compliance including coated tablets to mask taste.
Liquid suspension formulated for accurate dosing in children and those unable to swallow tablets.
Tablets that can be crushed and mixed with food such as applesauce to facilitate ingestion in some patients.
Standard packaging in bottles for suspension and blister packs for tablets to ensure stability and dosing accuracy.
Products manufactured under strict quality standards with detailed prescribing information available.
Preparation and storage instructions recommend room temperature, protected from moisture and heat.
Availability varies by country and may be subject to regulatory approvals affecting formulations.
Supplemental educational materials and dosage syringes often provided with suspension formulations.
Generics and brand-name products available to provide cost-effective treatment options.
Some formulations specifically designed to optimize pharmacokinetic profiles and reduce side effects.