Johns Hopkins ABX GuideBrand Names

Flucytosine

Janessa M. Smith, Pharm.D., BCPS, Paul A. Pham, Pharm.D.

INDICATIONS

FDA

FORMS

brand name

preparation

manufacturer

route

form

dosage^

cost*

Ancobon

Flucytosine (5-FC)

ICN Pharmaceuticals

oral

capsule

250 mg

$92.21

oral

capsule

500 mg

$178.43

Flucytosine (5-FC)

Generic manufacturer

oral

capsule

250 mg

$82.07

oral

capsule

500 mg

$158.80

*Prices represent cost per unit specified, are representative of "Average Wholesale Price" (AWP).
^Dosage is indicated in mg unless otherwise noted.

USUAL ADULT DOSING

  • 25 mg/kg PO q6h in combination with amphotericin B products
    • Sole exception: monotherapy can be used for Candida UTI, e.g. azole-resistant candiduria (e.g., C. glabrata).
  • Dosing in special populations:
    • Obesity: consider IBW for dosing of non-life-threatening infections.
    • Meningitis: consider using adjusted body weight and monitor serum concentrations.
  • Therapeutic drug monitoring recommended with renal insufficiency to limit toxicity.
    • Goal peak: 70-80 mcg/mL drawn 2 hrs post-dose after 3-5 days. Peak serum concentrations >100 mcg/mL associated with increased toxicity.

ADULT RENAL DOSING

DOSING FOR GLOMERULAR FILTRATION OF 50-80

25 mg/kg q6h

DOSING FOR GLOMERULAR FILTRATION OF 10-50

CrCl 20-40 mL/min: 25 mg/kg q12

CrCl 10-19 mL/min: 25 mg/kg q24h (monitor CBC and serum levels with appropriate dose adjustments)

DOSING FOR GLOMERULAR FILTRATION OF <10 ML/MIN

25 mg/kg q48h (monitor CBC serum levels closely with appropriate dose adjustments)

DOSING IN HEMODIALYSIS

25 mg/kg q24-48h

Dose post-dialysis on days of dialysis (monitor CBC and serum levels w/ appropriate dose adjustment)

DOSING IN PERITONEAL DIALYSIS

0.5-1.0 gm q24h (monitor CBC and serum levels w/ appropriate dose adjustments)

DOSING IN HEMOFILTRATION

CVVH and CVVHD: no data

Consider 25 mg/kg q24 for dialysis rate of 1L/hr and 25 mg/kg q12h for dialysis rate ≥1.5 L/hr (monitor CBC and serum levels with appropriate dose adjustments)

PEDIATRIC DOSING

USUAL PEDIATRIC DOSING

  • 25 mg/kg PO q6h
  • Adjust dose to maintain flucytosine concentrations (2-hour post-dose) between 40-60 mcg/mL.
  • Obtain drug levels after 3-54 days of continuous dosing.

PEDIATRIC RENAL DOSING

  • CrCL
    • 20-40 mL/min: 25 mg/kg q12h
    • 10-20 mL/min: 25mg/kg q24 h
    • < 10 ml/min: 25mg/kg q24-48h
  • Important to adjust dose to maintain 2-hour post-dose between 40-60 mcg/mL.
  • Supplemental dose needed after hemodialysis or peritoneal dialysis.

Pediatric Dosing Author: George K Siberry, MD, MPH

ADVERSE DRUG REACTIONS

OCCASIONAL

  • GI intolerance: diarrhea, dyspepsia, and abdominal pain
  • Marrow suppression: leukopenia or thrombocytopenia (with concentrations >100 mcg/mL)
  • Headache
  • Taste perversion
  • Pruritus

RARE

  • Confusion
  • Rash
  • Hepatitis (hepatic necrosis has been reported)
  • Peripheral neuropathy
  • Enterocolitis
  • Photosensitivity
  • Fatal bone marrow aplasia

DRUG INTERACTIONS

  • Drugs that cause bone marrow suppression (e.g., AZT, ganciclovir, and interferon): increased risk of bone marrow suppression

PHARMACOLOGY

MECHANISM

Flucytosine interferes with protein synthesis by incorporation into fungal RNA after being converted to 5-FU intracellularly.

PHARMACOKINETIC PARAMETERS

Absorption

75-90%

Metabolism and Excretion

Minimal metabolism; principally excreted unchanged in the urine. Unabsorbed drug excreted in feces.

Protein Binding

2-4%

Cmax, Cmin, and AUC

Cmax: 60-80 mcg/mL, Cmin: 20-40 mcg/mL after 37.5 mg/kg/dose.

T1/2

2.5-6 hrs (normal renal function). Half-life may be up to 250 hrs in patients with ESRD.

Distribution

Widely distributed into body tissues and fluids such as liver, kidney, spleen, heart, aqueous humor and bronchial secretion. Good CNS penetration (60-100% of serum concentration attained in the CSF).

DOSING FOR DECREASED HEPATIC FUNCTION

No data. Usual dose likely.

PREGNANCY RISK

Category C: Teratogenicity reported in animal studies. Partially metabolized to 5-fluorouracil, a known human teratogen. Avoid use in first trimester.

BREAST FEEDING COMPATIBILITY

No data. Breast feeding during flucytosine therapy not recommended because of concern for potential adverse effects.

COMMENTS

  • Recommended in combination with amphotericin or liposomal amphotericin for treatment of cryptococcal meningitis for at least 2 weeks.
    • Combination therapy with flucytosine results in more rapid CSF sterilization and improved mortality when compared to amphotericin alone.
    • When compared to amphotericin plus fluconazole, there was no difference in survival outcomes but combination with flucytosine resulted in more rapid CSF sterilization.
  • Levels should be considered for patients with renal insufficiency to minimize toxicity.
    • Levels >100 ng/mL for >2 weeks have been associated with increased risk of toxicity.
    • Levels < 25 ng/mL have been associated with emergence of resistance in vitro.
  • May be considered in combination with amphotericin (and surgery) in the treatment of candidal endocarditis.
  • Flucytosine should never be used as monotherapy due to the rapid development of resistance, with the exception of candiduria without systemic infection.

References

  1. Coelho C, Casadevall A: Cryptococcal therapies and drug targets: the old, the new and the promising. Cell Microbiol 18:792, 2016  [PMID:26990050]

    Comment: Authors highlight difficulties with cryptococcus and that emergence of resitance occurs so frequently with 5-FC monotherapy, hence why it is not used except in compination.

  2. Yao ZW et al: Comparison of flucytosine and fluconazole combined with amphotericin B for the treatment of HIV-associated cryptococcal meningitis: a systematic review and meta-analysis. Eur J Clin Microbiol Infect Dis Feb 20  [PMID:24550039]

    Comment: Group exmained primary outcomes using mortality d14 and d70 with secondary outcome as early fungicidal activity (EFA) at 2 weeks. Four trials were identified. Meta-analysis found lower mortality in patients given AmB + 5-FC at the 2 weeks point--combination group 44% [risk ratio (RR) 0.56, 95% confidence interval (CI) 0.33-0.95, p = 0.03]. EFA was significantly shorter in patients receiving AmB plus 5-FC [mean difference (MD) -0.10 log10 colony-forming units (CFU) per day, 95 % CI -0.11-0.09, p <  0.00001]. Mortality was no different between the 5-FC and fluconazole groups at the 3 months time point (p = 0.15) Adverse events occurred with similar frequency between the two treatment groups. There was no statistically significant difference in the survival rate between AmB in combination with high-dose fluconazole and the current standard of AmB plus 5-FC therapy for HIV-associated cryptococcal meningitis.

  3. Day JN et al: Combination antifungal therapy for cryptococcal meningitis. N Engl J Med 368:1291, 2013  [PMID:23550668]

    Comment: Amphotericin B (1 mg/kg/day) plus flucytosine (100 mg/kg/day) was associated with improved survival at day 70 as compared with amphotericin B (1 mg/kg/day) alone. Combination therapy with flucytosine also resulted in more rapid yeast clearance from CSF when compared to amphotericin monotherapy or amphotericin B plus fluconazole (800 mg/kg/day). There was no survival benefit found for those treated with amphotericin B plus fluconazole.

  4. Perfect JR et al: Clinical practice guidelines for the management of cryptococcal disease: 2010 update by the infectious diseases society of america. Clin Infect Dis 50:291, 2010  [PMID:20047480]

    Comment: Flucytosine plus AmphoB, liposomal AmB, or AmB lipid complex (for a minimum of 2 weeks) is recommended for the treatment of cryptococcal meningoencephalitis. Without flucytosine, the recommended amphoB treatment duration is 4-6 weeks. Fluconazole 1200 mg/day plus flucytosine x 6 weeks can be considered as an alternative in patients unable to tolerate amphoB.

  5. Vermes A, Guchelaar HJ, Dankert J: Flucytosine: a review of its pharmacology, clinical indications, pharmacokinetics, toxicity and drug interactions. J Antimicrob Chemother 46:171, 2000  [PMID:10933638]

    Comment: Focused review on pharmacological aspects of this antifungal drug, originally developed in 1957 as an antimetabolite

  6. Saag MS et al: A comparison of itraconazole versus fluconazole as maintenance therapy for AIDS-associated cryptococcal meningitis. National Institute of Allergy and Infectious Diseases Mycoses Study Group. Clin Infect Dis 28:291, 1999  [PMID:10064246]

    Comment: Fluconazole superior to itraconazole for maintenance therapy of cryptococcal meningitis. Factor best associated with relapse was having not received flucytosine during the initial 2 wks of primary treatment for cryptococcal disease (relative risk = 5.88; 95% confidence interval, 1.27-27.14; p=0.04).

  7. van der Horst CM et al: Treatment of cryptococcal meningitis associated with the acquired immunodeficiency syndrome. National Institute of Allergy and Infectious Diseases Mycoses Study Group and AIDS Clinical Trials Group. N Engl J Med 337:15, 1997  [PMID:9203426]

    Comment: Addition of 5FC to amphotericin resulted in faster CSF sterilization but did not improve clinical outcome.

  8. Gillum JG et al: Flucytosine dosing in an obese patient with extrameningeal cryptococcal infection. Pharmacotherapy 15:251, 1995 Mar-Apr  [PMID:7624273]

    Comment: A case report of a morbidly obese patient who received 150 mg/kg/day IBW for treatment of extrameningeal cryptococcal infection. Pharmacokinetic parameters were similar as those reported in non-obese patients receiving the same dose.

  9. Pappas PG, et al: Clinical Practice Guideline for the Management of Candidiasis: 2016 Update by the Infectious Diseases Society of America. Clin Infect Dis. 2016 Feb 15;62(4):e1-50.

    Comment: Updated IDSA guidelines on the treatment of candidiasis.

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Last updated: March 1, 2017