Flucytosine, Griseofulvin, and Terbinafine

In addition to the 3 other major classes of antifungal agents ( azoles Azoles Azoles are a widely used class of antifungal medications inhibiting the production of ergosterol, a critical component in the fungal cell membrane. The 2 primary subclasses of azoles are the imidazoles, older agents typically only used for topical applications, and the triazoles, newer agents with a wide spectrum of uses. Azoles, polyenes Polyenes Polyenes are a class of fungicidal agents that consist of 2 primary drugs in current use, namely, nystatin and amphotericin B. Both these drugs exert their effects by binding to ergosterol (a critical component of fungal cell membranes) and creating pores in the membrane, leading to the leakage of intracellular components and ultimately cell lysis. Polyenes, and echinocandins Echinocandins Echinocandins are a group of fungicidal agents that target the fungal cell wall. Echinocandins inhibit β-glucan synthase, which in turn inhibits the production of β-glucan, a key structural component of fungal cell walls. The 3 primary drugs in this class include caspofungin, micafungin, and anidulafungin. Echinocandins), several other clinically important antifungal agents are used, including flucytosine, griseofulvin, and terbinafine. Each drug has a distinct mechanism of action and unique characteristics and indications. Flucytosine is a pyrimidine analog that disrupts fungal DNA DNA The molecule DNA is the repository of heritable genetic information. In humans, DNA is contained in 23 chromosome pairs within the nucleus. The molecule provides the basic template for replication of genetic information, RNA transcription, and protein biosynthesis to promote cellular function and survival. DNA Types and Structure and RNA RNA Ribonucleic acid (RNA), like deoxyribonucleic acid (DNA), is a polymer of nucleotides that is essential to cellular protein synthesis. Unlike DNA, RNA is a single-stranded structure containing the sugar moiety ribose (instead of deoxyribose) and the base uracil (instead of thymine). RNA generally carries out the instructions encoded in the DNA but also executes diverse non-coding functions. RNA Types and Structure synthesis. Flucytosine is always used in combination with other antifungal agents and is primarily used to treat cryptococcal meningitis Meningitis Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Meningitis. Both griseofulvin and terbinafine act within the stratum corneum of the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin and are used to treat dermatophyte infections of the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin, hair, and nails.

Last update:

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Table of Contents

Share this concept:

Share on facebook
Share on twitter
Share on linkedin
Share on reddit
Share on email
Share on whatsapp

Classification and Chemistry

Classification

In addition to the 3 major classes of antifungal agents ( azoles Azoles Azoles are a widely used class of antifungal medications inhibiting the production of ergosterol, a critical component in the fungal cell membrane. The 2 primary subclasses of azoles are the imidazoles, older agents typically only used for topical applications, and the triazoles, newer agents with a wide spectrum of uses. Azoles, polyenes Polyenes Polyenes are a class of fungicidal agents that consist of 2 primary drugs in current use, namely, nystatin and amphotericin B. Both these drugs exert their effects by binding to ergosterol (a critical component of fungal cell membranes) and creating pores in the membrane, leading to the leakage of intracellular components and ultimately cell lysis. Polyenes, and echinocandins Echinocandins Echinocandins are a group of fungicidal agents that target the fungal cell wall. Echinocandins inhibit β-glucan synthase, which in turn inhibits the production of β-glucan, a key structural component of fungal cell walls. The 3 primary drugs in this class include caspofungin, micafungin, and anidulafungin. Echinocandins), there are several other clinically important antifungals agents. These drugs include:

  • Flucytosine (also known as 5-fluorocytosine (5-FC))
  • Griseofulvin
  • Terbinafine

Chemical structures

  • Flucytosine: a pyrimidine analog
  • Griseofulvin: an oxaspiro compound (a cyclic structure in which 1 of the ring components is an oxygen molecule)
  • Terbinafine:
    • An allylamine: contains a nitrogen atom and carbon-carbon double bond
    • Contains an alkynyl functional group (carbon-carbon triple bond)

Pharmacodynamics: Mechanisms of Action

Flucytosine

Flucytosine is a pyrimidine analog that disrupts both DNA DNA The molecule DNA is the repository of heritable genetic information. In humans, DNA is contained in 23 chromosome pairs within the nucleus. The molecule provides the basic template for replication of genetic information, RNA transcription, and protein biosynthesis to promote cellular function and survival. DNA Types and Structure and RNA RNA Ribonucleic acid (RNA), like deoxyribonucleic acid (DNA), is a polymer of nucleotides that is essential to cellular protein synthesis. Unlike DNA, RNA is a single-stranded structure containing the sugar moiety ribose (instead of deoxyribose) and the base uracil (instead of thymine). RNA generally carries out the instructions encoded in the DNA but also executes diverse non-coding functions. RNA Types and Structure synthesis.

  • Enters fungal cells via a protein known as cytosine permease
  • Inside the fungal cell, flucytosine is converted to its active form 5-fluorouracil (5-FU) by the enzyme cytosine deaminase.
    • Mammals lack cytosine deaminase → selective effects on microbial cells
    • Conversion to 5-FU by intestinal flora is thought to be responsible for toxicity in humans.
  • 5-FU:
    • Competes with uracil → incorporated into RNA RNA Ribonucleic acid (RNA), like deoxyribonucleic acid (DNA), is a polymer of nucleotides that is essential to cellular protein synthesis. Unlike DNA, RNA is a single-stranded structure containing the sugar moiety ribose (instead of deoxyribose) and the base uracil (instead of thymine). RNA generally carries out the instructions encoded in the DNA but also executes diverse non-coding functions. RNA Types and Structure strands, disrupting RNA RNA Ribonucleic acid (RNA), like deoxyribonucleic acid (DNA), is a polymer of nucleotides that is essential to cellular protein synthesis. Unlike DNA, RNA is a single-stranded structure containing the sugar moiety ribose (instead of deoxyribose) and the base uracil (instead of thymine). RNA generally carries out the instructions encoded in the DNA but also executes diverse non-coding functions. RNA Types and Structure synthesis → inhibits fungal protein synthesis
    • Irreversibly inhibits thymidylate synthases → inhibition of thymine production → inability to synthesize or correct DNA DNA The molecule DNA is the repository of heritable genetic information. In humans, DNA is contained in 23 chromosome pairs within the nucleus. The molecule provides the basic template for replication of genetic information, RNA transcription, and protein biosynthesis to promote cellular function and survival. DNA Types and Structure DNA DNA The molecule DNA is the repository of heritable genetic information. In humans, DNA is contained in 23 chromosome pairs within the nucleus. The molecule provides the basic template for replication of genetic information, RNA transcription, and protein biosynthesis to promote cellular function and survival. DNA Types and Structure damage
  • May exert fungistatic or fungicidal effects depending on the organism
  • Synergistic effects with amphotericin B and azoles Azoles Azoles are a widely used class of antifungal medications inhibiting the production of ergosterol, a critical component in the fungal cell membrane. The 2 primary subclasses of azoles are the imidazoles, older agents typically only used for topical applications, and the triazoles, newer agents with a wide spectrum of uses. Azoles
  • Resistance:
    • Primary/intrinsic resistance: due to mutations in cytosine permease → ↓ 5-FC uptake into fungal cells
    • Secondary/acquired resistance:
      • Due to mutations in cytosine deaminase
      • Resistance is significant when flucytosine is used as monotherapy.
    • Resistance among C. albicans: approximately 10%
Antifungal agents and mechanisms of action

Antifungal agents and mechanisms of action

Image by Lecturio. License: CC BY-NC-SA 4.0

Griseofulvin

The exact mechanisms of griseofulvin are not completely understood, but 2 general mechanisms of action have been suggested:

  • Binds to keratin in newly forming skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin, rendering new human cells resistant to invasion
    • Prevents infection of new skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin structures → fungistatic agent
    • Over time (weeks to months), the new, uninfected hair/ skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin/nail structures will have replaced the old, infected ones.
  • Inhibits cell replication in dermatophytes Dermatophytes Tinea infections are a group of diseases caused by fungi infecting keratinized tissue (hair, nails, and skin). These infections are termed dermatomycoses and are caused by the dermatophyte fungi. There are approximately 40 dermatophyte fungi that are part of 3 genera, including Trichophyton, Epidermophyton, and Microsporum. These infections can affect any part of the body but occur most often in warm, moist regions like the groin and the feet. Dermatophytes/Tinea Infections:
    • Binds to tubulin, inhibiting microtubule assembly 
    • Leads to inhibition of the formation of the mitotic spindle → prevention of mitosis at metaphase

Terbinafine

Terbinafine exerts its effects by causing deterioration of the fungal cell membrane Cell Membrane A cell membrane (also known as the plasma membrane or plasmalemma) is a biological membrane that separates the cell contents from the outside environment. A cell membrane is composed of a phospholipid bilayer and proteins that function to protect cellular DNA and mediate the exchange of ions and molecules. The Cell: Cell Membrane by inhibiting the production of squalene epoxide, a precursor to ergosterol.

  • Ergosterol synthesis:
    • Squalene is converted to squalene epoxide by the enzyme squalene epoxidase.
    • Squalene epoxide is converted to lanosterol.
    • Lanosterol is converted to ergosterol by the enzyme lanosterol 14-α-demethylase (14-α-demethylase is inhibited by azoles Azoles Azoles are a widely used class of antifungal medications inhibiting the production of ergosterol, a critical component in the fungal cell membrane. The 2 primary subclasses of azoles are the imidazoles, older agents typically only used for topical applications, and the triazoles, newer agents with a wide spectrum of uses. Azoles).
  • Terbinafine noncompetitively inhibits squalene epoxidase.
  • Effects include:
    • ↓ Squalene epoxide production → ↓ ergosterol
    • Fungi are unable to synthesize or maintain their cell membranes without ergosterol.
    • ↑ Fungal cell membrane Cell Membrane A cell membrane (also known as the plasma membrane or plasmalemma) is a biological membrane that separates the cell contents from the outside environment. A cell membrane is composed of a phospholipid bilayer and proteins that function to protect cellular DNA and mediate the exchange of ions and molecules. The Cell: Cell Membrane permeability → cell lysis
  • Terbinafine exerts fungicidal effects in dermatophytes Dermatophytes Tinea infections are a group of diseases caused by fungi infecting keratinized tissue (hair, nails, and skin). These infections are termed dermatomycoses and are caused by the dermatophyte fungi. There are approximately 40 dermatophyte fungi that are part of 3 genera, including Trichophyton, Epidermophyton, and Microsporum. These infections can affect any part of the body but occur most often in warm, moist regions like the groin and the feet. Dermatophytes/Tinea Infections.

Pharmacokinetics

Table: Pharmacokinetics Pharmacokinetics Pharmacokinetics is the science that analyzes how the human body interacts with a drug. Pharmacokinetics examines how the drug is absorbed, distributed, metabolized, and excreted by the body. Pharmacokinetics and Pharmacodynamics of azoles Azoles Azoles are a widely used class of antifungal medications inhibiting the production of ergosterol, a critical component in the fungal cell membrane. The 2 primary subclasses of azoles are the imidazoles, older agents typically only used for topical applications, and the triazoles, newer agents with a wide spectrum of uses. Azoles
Drugs Flucytosine Griseofulvin Terbinafine
Absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption
  • Well absorbed
  • Bioavailability: 75%‒90%
  • Not absorbed topically
  • Very poor water solubility
  • Improved oral absorption with fatty foods
  • Well absorbed
  • Bioavailability: 40% (due to 1st-pass metabolism)
Distribution
  • Minimal protein binding
  • Penetrates well into all body fluid compartments Body fluid compartments The adult human body is made up of 60% water and is divided into extracellular and intracellular fluid compartments. Extracellular fluid is present outside the cells and makes up two-thirds of the total body water. Intracellular fluid is present inside the cells and makes up two-thirds of the total body water. Body Fluid Compartments, including CSF
  • Stratum corneum (keratin layer) of skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin, hair and nails
  • Also concentrates in:
    • Liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver
    • Fat
    • Skeletal muscle
  • Stratum corneum
  • Protein binding: > 99%
Metabolism Metabolized intracellularly by yeasts to its active form, 5-FU
  • Extensive hepatic metabolism
  • CYP450 inducer (drug-drug interactions)
  • Hepatic metabolism via CYP450 enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body's constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes to inactive metabolites
  • Moderate inhibitor of CYP2D6
Excretion
  • Renal elimination via glomerular filtration Glomerular filtration The kidneys are primarily in charge of the maintenance of water and solute homeostasis through the processes of filtration, reabsorption, secretion, and excretion. Glomerular filtration is the process of converting the systemic blood supply into a filtrate, which will ultimately become the urine. Glomerular Filtration, primarily as unchanged drug
  • T1/2: 3‒6 hours
  • Adjust dose in renal impairment.
  • Elimination:
    • Fecal (33%)
    • Perspiration
  • T1/2: 9‒24 hours
  • Elimination:
    • Urine: 80%, primarily as inactive metabolites
    • Feces: 20%
  • Effective T1/2: approximately 36 hours
  • Terminal T1/2: 200‒400 hours (very slow drug release from skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin and adipose tissue Adipose tissue Adipose tissue is a specialized type of connective tissue that has both structural and highly complex metabolic functions, including energy storage, glucose homeostasis, and a multitude of endocrine capabilities. There are three types of adipose tissue, white adipose tissue, brown adipose tissue, and beige or "brite" adipose tissue, which is a transitional form. Adipose Tissue)
CYP450: cytochrome P450
5-FU: 5-fluorouracil
T1/2: half-life
Layers of the skin

Layers of the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin:
Griseofulvin and terbinafine are distributed to the stratum corneum.

Image by Lecturio. License: CC BY-NC-SA 4.0

Flucytosine

Indications

Flucytosine has a narrow spectrum of activity. Owing to its demonstrated synergy with other antifungal agents and the high risk for secondary resistance when used as monotherapy, flucytosine is not used as a single agent.

  • Active against:
    • Cryptococcus Cryptococcus Cryptococcosis is an opportunistic, fungal infection caused by the Cryptococcus species. The principal pathogens in humans are C. neoformans (primary) and C. gattii. Cryptococcus neoformans is typically found in pigeon droppings and acquired by inhaling dust from contaminated soil. The majority of affected patients are immunocompromised. Cryptococcus/Cryptococcosis neoformans
    • Some Candida Candida Candida is a genus of dimorphic, opportunistic fungi. Candida albicans is part of the normal human flora and is the most common cause of candidiasis. The clinical presentation varies and can include localized mucocutaneous infections (e.g., oropharyngeal, esophageal, intertriginous, and vulvovaginal candidiasis) and invasive disease (e.g., candidemia, intraabdominal abscess, pericarditis, and meningitis). Candida/Candidiasis spp.
    • Chromoblastomycosis
  • Not active against:
    • Endemic mycoses: Histoplasma Histoplasma Histoplasmosis is an infection caused by Histoplasma capsulatum, a dimorphic fungus. The fungus exists as a mold at low temperatures and as yeast at high temperatures. H. capsulatum is the most common endemic fungal infection in the US and is most prevalent in the midwestern and central states along the Ohio and Mississippi River valleys. Histoplasma/Histoplasmosis, Blastomyces Blastomyces Blastomycosis is an infection caused by inhalation of the spores of the fungus, Blastomyces. Blastomyces species thrive in moist soil and decaying material and are common in the Ohio and Mississippi River valleys and the Great Lakes regions of the United States and Canada. Although most patients are asymptomatic, some can develop pneumonia. Blastomyces/Blastomycosis, Coccidioides Coccidioides Coccidioidomycosis, commonly known as San Joaquin Valley fever, is a fungal disease caused by Coccidioides immitis or Coccidioides posadasii. When Coccidioides spores are inhaled, they transform into spherules that result in infection. Coccidioidomycosis is also a common cause of community-acquired pneumonia and can cause severe disease in the immunocompromised. Coccidioides/Coccidioidomycosis
    • Aspergillus
    • Zyomycetes
    • Most dermatophytes Dermatophytes Tinea infections are a group of diseases caused by fungi infecting keratinized tissue (hair, nails, and skin). These infections are termed dermatomycoses and are caused by the dermatophyte fungi. There are approximately 40 dermatophyte fungi that are part of 3 genera, including Trichophyton, Epidermophyton, and Microsporum. These infections can affect any part of the body but occur most often in warm, moist regions like the groin and the feet. Dermatophytes/Tinea Infections
  • Clinical uses:
    • Used in combination with amphotericin B to treat cryptococcal meningitis Meningitis Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Meningitis and pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia (primary use)
    • Used in combination with itraconazole to treat chromoblastomycosis
    • Used in combination with other agents for systemic, susceptible fungal infections, including:
      • Septicemia
      • Endocarditis Endocarditis Endocarditis is an inflammatory disease involving the inner lining (endometrium) of the heart, most commonly affecting the cardiac valves. Both infectious and noninfectious etiologies lead to vegetations on the valve leaflets. Patients may present with nonspecific symptoms such as fever and fatigue. Endocarditis
      • Urinary tract infections Urinary tract infections Urinary tract infections (UTIs) represent a wide spectrum of diseases, from self-limiting simple cystitis to severe pyelonephritis that can result in sepsis and death. Urinary tract infections are most commonly caused by Escherichia coli, but may also be caused by other bacteria and fungi. Urinary Tract Infections
      • Peritonitis
      • Pulmonary infections

Adverse effects

Flucytosine is often administered with the highly nephrotoxic agent amphotericin B. Amphotericin B-induced renal impairment can lead to the accumulation of 5-FC (which is renally cleared) and direct 5-FC toxicity, which includes:

  • Hematologic effects: due to bone marrow Bone marrow Bone marrow, the primary site of hematopoiesis, is found in the cavities of cancellous bones and the medullary canals of long bones. There are 2 types: red marrow (hematopoietic with abundant blood cells) and yellow marrow (predominantly filled with adipocytes). Composition of Bone Marrow toxicity
    • Leukopenia
    • Thrombocytopenia Thrombocytopenia Thrombocytopenia occurs when the platelet count is < 150,000 per microliter. The normal range for platelets is usually 150,000-450,000/µL of whole blood. Thrombocytopenia can be a result of decreased production, increased destruction, or splenic sequestration of platelets. Patients are often asymptomatic until platelet counts are < 50,000/µL. Thrombocytopenia
    • Anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview
  • GI and hepatic effects:
    • GI distress (6% of individuals): nausea, vomiting, and/or diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
    • ↑ Serum transaminases
    • Hepatic necrosis has been reported, but is rare.

Contraindications

  • Hypersensitivity to flucytosine (only absolute contraindication)
  • Use with extreme caution in individuals with:
    • Bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Structure of Bones marrow depression
    • Hepatic impairment
    • Renal impairment
  • Avoid use as monotherapy.

Monitoring

  • CBC with differential: to monitor for signs of hematologic toxicity
  • Liver function tests Liver function tests Liver function tests, also known as hepatic function panels, are one of the most commonly performed screening blood tests. Such tests are also used to detect, evaluate, and monitor acute and chronic liver diseases. Liver Function Tests: to monitor for signs of hepatotoxicity
  • BUN and creatinine: to monitor for signs of renal dysfunction, which may necessitate dosing adjustments
  • Serum flucytosine concentrations: narrow therapeutic window

Griseofulvin

Indications

Griseofulvin is primarily used to treat dermatophyte infections of the hair, skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin, or nails. However, griseofulvin is being replaced by newer agents such as terbinafine or itraconazole for many of its indications.

  • Active against:
    • Trichophyton spp.
    • Microsporum spp.
    • Epidermophyton floccosum
  • Clinical indications:
    • Tinea pedis: “athlete’s foot Foot The foot is the terminal portion of the lower limb, whose primary function is to bear weight and facilitate locomotion. The foot comprises 26 bones, including the tarsal bones, metatarsal bones, and phalanges. The bones of the foot form longitudinal and transverse arches and are supported by various muscles, ligaments, and tendons. Foot
    • Tinea cruris: “jock itch,” typically affecting the groin
    • Tinea corporis: “ringworm,” anywhere on the body
    • Tinea barbae: an infection of the beard and mustached areas of the face, typically seen in adult men
    • Tinea capitis: infection of the scalp and hair shaft
      • Efficacy is improved when combined with a shampoo containing selenium sulfide.
    • Tinea unguium (onychomycosis): infection of the nails
  • Note: Griseofulvin is not effective for the treatment of tinea versicolor.

Adverse effects

Overall, griseofulvin has a relatively low level of toxicity. Adverse effects may include:

  • GI symptoms: nausea, vomiting, and/or diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
  • Headaches
  • Histamine reactions:
    • Fever
    • Rash
    • Flushing
  • Skin reactions:
    • Photosensitivity
    • Rash
    • Stevens-Johnson syndrome Stevens-Johnson syndrome Stevens-Johnson syndrome (SJS) is a cutaneous, immune-mediated hypersensitivity reaction that is commonly triggered by medications, including antiepileptics and antibiotics. The condition runs on a spectrum with toxic epidermal necrolysis (TEN) based on the amount of body surface area (BSA) involved. Stevens-Johnson Syndrome
  • Porphyria crisis
  • Systemic lupus erythematosus Systemic lupus erythematosus Systemic lupus erythematosus (SLE) is a chronic autoimmune, inflammatory condition that causes immune-complex deposition in organs, resulting in systemic manifestations. Women, particularly those of African American descent, are more commonly affected. Systemic Lupus Erythematosus ( SLE SLE Systemic lupus erythematosus (SLE) is a chronic autoimmune, inflammatory condition that causes immune-complex deposition in organs, resulting in systemic manifestations. Women, particularly those of African American descent, are more commonly affected. Systemic Lupus Erythematosus) exacerbation
  • Hepatotoxicity (rare, but may be severe)
  • Possible cross-allergenicity with penicillins Penicillins Beta-lactam antibiotics contain a beta-lactam ring as a part of their chemical structure. Drugs in this class include penicillin G and V, penicillinase-sensitive and penicillinase-resistant penicillins, cephalosporins, carbapenems, and aztreonam. Penicillins

Contraindications

  • Hypersensitivity to griseofulvin
  • Hepatic failure
  • Porphyria
  • Pregnancy Pregnancy Pregnancy is the time period between fertilization of an oocyte and delivery of a fetus approximately 9 months later. The 1st sign of pregnancy is typically a missed menstrual period, after which, pregnancy should be confirmed clinically based on a positive β-HCG test (typically a qualitative urine test) and pelvic ultrasound. Pregnancy: Diagnosis, Maternal Physiology, and Routine Care

Terbinafine

Indications

  • Dermatophyte infections, especially onychomycosis
  • More effective than griseofulvin or itraconazole for onychomycosis
  • Available in both oral and topical forms (unlike griseofulvin, which is only available as an oral formulation)

Adverse effects

Adverse effects are usually mild and self-limiting.

  • GI distress: nausea, vomiting, and/or diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
  • Histamine reactions:
    • Fever
    • Rash
    • Flushing
  • SLE SLE Systemic lupus erythematosus (SLE) is a chronic autoimmune, inflammatory condition that causes immune-complex deposition in organs, resulting in systemic manifestations. Women, particularly those of African American descent, are more commonly affected. Systemic Lupus Erythematosus exacerbation
  • Rare cases of hepatic and hematologic toxicity have been reported.

Contraindications

  • Hypersensitivity to terbinafine or other allylamines (e.g., naftifine)
  • Chronic or active liver disease
  • Use with caution in individuals with renal impairment.

Comparison of Antifungal Medications

Table: Comparison of antifungal medications
Drug class (examples) Mechanism of action Clinical relevance
Azoles (Fluconazole, Voriconazole) Inhibits the production of ergosterol (a critical component of the fungal cell membrane Cell Membrane A cell membrane (also known as the plasma membrane or plasmalemma) is a biological membrane that separates the cell contents from the outside environment. A cell membrane is composed of a phospholipid bilayer and proteins that function to protect cellular DNA and mediate the exchange of ions and molecules. The Cell: Cell Membrane) by blocking the lanosterol 14-α-demethylase enzyme
  • Widely used antifungals with a relatively broad spectrum of activity
  • Many drug-to-drug interactions due to effects on the CYP450 system
  • Hepatotoxicity
  • Overall less toxic than amphotericin B
Polyenes (Amphotericin B, Nystatin) Binds to ergosterol in the fungal cell membrane Cell Membrane A cell membrane (also known as the plasma membrane or plasmalemma) is a biological membrane that separates the cell contents from the outside environment. A cell membrane is composed of a phospholipid bilayer and proteins that function to protect cellular DNA and mediate the exchange of ions and molecules. The Cell: Cell Membrane creating artificial pores in the membrane → results in leakage of cellular components and leads to cell lysis (death) Amphotericin B:
  • Reserved for life-threatening fungal infections
  • Broad spectrum of activity
  • Relatively ↑ toxicity (especially nephrotoxicity)
  • Overall less toxic than amphotericin B

Nystatin:
  • Topical use only: skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin, mucous membranes, GI lumen
Echinocandins (Caspofungin, Micafungin, Anidulafungin) Inhibits β-glucan synthase (the enzyme synthesizing β-glucan and an important structural component of the fungal cell wall) → weakened cell wall → cell lysis
  • Treats Candida Candida Candida is a genus of dimorphic, opportunistic fungi. Candida albicans is part of the normal human flora and is the most common cause of candidiasis. The clinical presentation varies and can include localized mucocutaneous infections (e.g., oropharyngeal, esophageal, intertriginous, and vulvovaginal candidiasis) and invasive disease (e.g., candidemia, intraabdominal abscess, pericarditis, and meningitis). Candida/Candidiasis and Aspergillus infections in critically ill and neutropenic patients
  • Minimal toxicity
  • Minimal drug-to-drug interactions
Griseofulvin
  • Binds to the keratin in newly forming skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin, making the human cells resistant to invasion → over time the new, uninfected hair/ skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin/nail structures replace the old, infected structures
  • Inhibits the assembly of microtubules in dermatophytes Dermatophytes Tinea infections are a group of diseases caused by fungi infecting keratinized tissue (hair, nails, and skin). These infections are termed dermatomycoses and are caused by the dermatophyte fungi. There are approximately 40 dermatophyte fungi that are part of 3 genera, including Trichophyton, Epidermophyton, and Microsporum. These infections can affect any part of the body but occur most often in warm, moist regions like the groin and the feet. Dermatophytes/Tinea Infections → inhibits fungal cell replication
  • Treats dermatophyte infections of the hair, skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin, and nails
  • Oral medication only (not topically active)
  • Affects the CYP450 system (more drug-to-drug interactions)
  • Largely replaced by newer agents (e.g., terbinafine)
Terbinafine Inhibits the squalene epoxidase enzyme → blocks the production of squalene epoxide, which is a precursor to ergosterol and a critical component of the cell membrane Cell Membrane A cell membrane (also known as the plasma membrane or plasmalemma) is a biological membrane that separates the cell contents from the outside environment. A cell membrane is composed of a phospholipid bilayer and proteins that function to protect cellular DNA and mediate the exchange of ions and molecules. The Cell: Cell Membrane
  • Treats dermatophyte infections of the hair, skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin, and nails
  • Agent of choice for onychomycosis
  • Relatively low toxicity
Flucytosine A pyrimidine analog with metabolites:
  • Competing with uracil and disrupting RNA RNA Ribonucleic acid (RNA), like deoxyribonucleic acid (DNA), is a polymer of nucleotides that is essential to cellular protein synthesis. Unlike DNA, RNA is a single-stranded structure containing the sugar moiety ribose (instead of deoxyribose) and the base uracil (instead of thymine). RNA generally carries out the instructions encoded in the DNA but also executes diverse non-coding functions. RNA Types and Structure synthesis
  • Irreversibly inhibiting thymidylate synthase → fungus is unable to synthesize or correct DNA DNA The molecule DNA is the repository of heritable genetic information. In humans, DNA is contained in 23 chromosome pairs within the nucleus. The molecule provides the basic template for replication of genetic information, RNA transcription, and protein biosynthesis to promote cellular function and survival. DNA Types and Structure
  • Always used in combination with other agents due to:
    • Positive synergistic effects
    • ↑ Resistance with monotherapy
  • Major indications:
    • Cryptococcal meningitis Meningitis Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Meningitis
    • Chromoblastomycosis
  • Toxicity: myelosuppression

References

  1. Sheppard, D., Lampiris, H.W. (2012). Antifungal agents. In Katzung, B.G., Masters, S.B., and Trevor, A.J. (Eds.), Basic and Clinical Pharmacology, 12th Ed., pp. 852‒853, 855‒856.
  2. Drew, R.H. (2020). Pharmacology of flucytosine (5-FC). In Bogorodskaya, M (Ed.), UpToDate. Retrieved July 23, 2021, from https://www.uptodate.com/contents/pharmacology-of-flucytosine-5-fc 
  3. Nivoix, Y., Ledoux, M., Herbrecht, R. (2020). Antifungal therapy: New and evolving therapies. Semin Respir Crit Care Med. 2020, 41, 158-174. Retrieved July 23, 2021, from https://www.medscape.com/viewarticle/924712_7 
  4. Padda, I. (2021). Flucytosine. In StatPearls. Retrieved July 23, 2021, from https://www.statpearls.com/articlelibrary/viewarticle/21829/ 
  5. Olson, J. (2020). Griseofulvin. In StatPearls. Retrieved July 23, 2021, from https://www.statpearls.com/articlelibrary/viewarticle/22435/ 
  6. Maxfield, L. (2021). Terbinafine. In StatPearls. Retrieved July 23, 2021, from https://www.statpearls.com/articlelibrary/viewarticle/42970/ 
  7. Lexicomp Drug Information Sheets (2021). In UpToDate. Retrieved July 22, 2021, from:

USMLE™ is a joint program of the Federation of State Medical Boards (FSMB®) and National Board of Medical Examiners (NBME®). MCAT is a registered trademark of the Association of American Medical Colleges (AAMC). NCLEX®, NCLEX-RN®, and NCLEX-PN® are registered trademarks of the National Council of State Boards of Nursing, Inc (NCSBN®). None of the trademark holders are endorsed by nor affiliated with Lecturio.

Study on the Go

Lecturio Medical complements your studies with evidence-based learning strategies, video lectures, quiz questions, and more – all combined in one easy-to-use resource.

Learn even more with Lecturio:

Complement your med school studies with Lecturio’s all-in-one study companion, delivered with evidence-based learning strategies.

User Reviews

0.0

()

¡Hola!

Esta página está disponible en Español.

🍪 Lecturio is using cookies to improve your user experience. By continuing use of our service you agree upon our Data Privacy Statement.

Details