CLINICAL PHARMACOLOGY
Pharmacokinetics And Metabolism
The pharmacokinetic properties
of fluconazole are similar following administration by the intravenous or oral
routes. In normal volunteers, the bioavailability of orally administered
fluconazole is over 90% compared with intravenous administration.
Bioequivalence was established between the 100 mg tablet and both suspension
strengths when administered as a single 200 mg dose.
Peak plasma concentrations (Cmax) in fasted normal
volunteers occur between 1 and 2 hours with a terminal plasma elimination
half-life of approximately 30 hours (range: 20-50 hours) after oral
administration.
In fasted normal volunteers, administration of a single
oral 400 mg dose of DIFLUCAN (fluconazole) leads to a mean Cmax of 6.72 μg/mL
(range: 4.12 to 8.08 μg/mL) and after single oral doses of 50-400 mg,
fluconazole plasma concentrations and AUC (area under the plasma
concentration-time curve) are dose proportional.
The Cmax and AUC data from a food-effect study involving
administration of DIFLUCAN (fluconazole) tablets to healthy volunteers under
fasting conditions and with a high-fat meal indicated that exposure to the drug
is not affected by food. Therefore, DIFLUCAN may be taken without regard to
meals. (see DOSAGE AND ADMINISTRATION.)
Administration of a single oral 150 mg tablet of DIFLUCAN
(fluconazole) to ten lactating women resulted in a mean Cmax of 2.61 μg/mL
(range: 1.57 to 3.65 μg/mL).
Steady-state concentrations are reached within 5-10 days
following oral doses of 50-400 mg given once daily. Administration of a loading
dose (on day 1) of twice the usual daily dose results in plasma concentrations
close to steady-state by the second day. The apparent volume of distribution of
fluconazole approximates that of total body water. Plasma protein binding is
low (11-12%). Following either single-or multiple oral doses for up to 14 days,
fluconazole penetrates into all body fluids studied (see table below). In
normal volunteers, saliva concentrations of fluconazole were equal to or
slightly greater than plasma concentrations regardless of dose, route, or
duration of dosing. In patients with bronchiectasis, sputum concentrations of
fluconazole following a single 150 mg oral dose were equal to plasma
concentrations at both 4 and 24 hours post dose. In patients with fungal
meningitis, fluconazole concentrations in the CSF are approximately 80% of the
corresponding plasma concentrations.
A single oral 150 mg dose of fluconazole administered to
27 patients penetrated into vaginal tissue, resulting in tissue:plasma ratios
ranging from 0.94 to 1.14 over the first 48 hours following dosing.
A single oral 150 mg dose of fluconazole administered to
14 patients penetrated into vaginal fluid, resulting in fluid:plasma ratios
ranging from 0.36 to 0.71 over the first 72 hours following dosing.
Tissue or Fluid |
Ratio of Fluconazole Tissue (Fluid)/Plasma Concentration* |
Cerebrospinal fluid† |
0.5-0.9 |
Saliva |
1 |
Sputum |
1 |
Blister fluid |
1 |
Urine |
10 |
Normal skin |
10 |
Nails |
1 |
Blister skin |
2 |
Vaginal tissue |
1 |
Vaginal fluid |
0.4-0.7 |
* Relative to concurrent concentrations in plasma in
subjects with normal renal function.
† Independent of degree of meningeal inflammation. |
In normal volunteers, fluconazole is cleared primarily by renal excretion, with approximately 80% of
the administered dose appearing in the urine as unchanged drug. About 11% of
the dose is excreted in the urine as metabolites.
The pharmacokinetics of
fluconazole are markedly affected by reduction in renal function. There is an
inverse relationship between the elimination half-life and creatinine
clearance. The dose of DIFLUCAN may need to be reduced in patients with
impaired renal function. (See DOSAGE AND ADMINISTRATION.) A 3-hour
hemodialysis session decreases plasma concentrations by approximately 50%.
In normal volunteers, DIFLUCAN
administration (doses ranging from 200 mg to 400 mg once daily for up to 14
days) was associated with small and inconsistent effects on testosterone
concentrations, endogenous corticosteroid concentrations, and the
ACTH-stimulated cortisol response.
Pharmacokinetics In Children
In children, the following
pharmacokinetic data {Mean (%cv)} have been reported:
Age Studied |
Dose (mg/kg) |
Clearance (mL/min/kg) |
Half-life (Hours) |
Cmax (μg/mL) |
Vdss (L/kg) |
9 Months-13 years |
Single-Oral 2 mg/kg |
0.40 (38%) N=14 |
25.0 |
2.9 (22%) N=16 |
- |
9 Months-13 years |
Single-Oral 8 mg/kg |
0.51 (60%) N=15 |
19.5 |
9.8 (20%) N=15 |
- |
5-15 years |
Multiple IV 2 mg/kg |
0.49 (40%) N=4 |
17.4 |
5.5 (25%) N=5 |
0.722 (36%) N=4 |
5-15 years |
Multiple IV 4 mg/kg |
0.59 (64%) N=5 |
15.2 |
11.4 (44%) N=6 |
0.729 (33%) N=5 |
5-15 years |
Multiple IV 8 mg/kg |
0.66 (31%) N=7 |
17.6 |
14.1 (22%) N=8 |
1.069 (37%) N=7 |
Clearance corrected for body
weight was not affected by age in these studies. Mean body clearance in adults
is reported to be 0.23 (17%) mL/min/kg.
In premature newborns
(gestational age 26 to 29 weeks), the mean (%cv) clearance within 36 hours of
birth was 0.180 (35%, N=7) mL/min/kg, which increased with time to a mean of 0.218
(31%, N=9) mL/min/kg six days later and 0.333 (56%, N=4) mL/min/kg 12 days
later. Similarly, the half-life was 73.6 hours, which decreased with time to a
mean of 53.2 hours six days later and 46.6 hours 12 days later.
Pharmacokinetics In Elderly
A pharmacokinetic study was conducted in 22 subjects, 65
years of age or older receiving a single 50 mg oral dose of fluconazole. Ten of
these patients were concomitantly receiving diuretics. The Cmax was 1.54 mcg/mL
and occurred at 1.3 hours post dose. The mean AUC was 76.4 ± 20.3
mcg•h/mL, and the mean terminal half-life was 46.2 hours. These
pharmacokinetic parameter values are higher than analogous values reported for
normal young male volunteers. Coadministration of diuretics did not
significantly alter AUC or Cmax. In addition, creatinine clearance (74 mL/min),
the percent of drug recovered unchanged in urine (0-24 hr, 22%), and the
fluconazole renal clearance estimates (0.124 mL/min/kg) for the elderly were
generally lower than those of younger volunteers. Thus, the alteration of
fluconazole disposition in the elderly appears to be related to reduced renal
function characteristic of this group. A plot of each subject's terminal
elimination half-life versus creatinine clearance compared with the predicted
half-life – creatinine clearance curve derived from normal subjects and
subjects with varying degrees of renal insufficiency indicated that 21 of 22
subjects fell within the 95% confidence limit of the predicted half-life –
creatinine clearance curves. These results are consistent with the hypothesis
that higher values for the pharmacokinetic parameters observed in the elderly
subjects compared with normal young male volunteers are due to the decreased
kidney function that is expected in the elderly.
Drug Interaction Studies
Oral Contraceptives
Oral contraceptives were administered as a single dose
both before and after the oral administration of DIFLUCAN 50 mg once daily for
10 days in 10 healthy women. There was no significant difference in ethinyl
estradiol or levonorgestrel AUC after the administration of 50 mg of DIFLUCAN.
The mean increase in ethinyl estradiol AUC was 6% (range: –47 to 108%) and
levonorgestrel AUC increased 17% (range: –33 to 141%).
In a second study, twenty-five normal females received
daily doses of both 200 mg DIFLUCAN tablets or placebo for two, ten-day
periods. The treatment cycles were one month apart with all subjects receiving
DIFLUCAN during one cycle and placebo during the other. The order of study
treatment was random. Single doses of an oral contraceptive tablet containing
levonorgestrel and ethinyl estradiol were administered on the final treatment
day (day 10) of both cycles. Following administration of 200 mg of DIFLUCAN,
the mean percentage increase of AUC for levonorgestrel compared to placebo was
25% (range: –12 to 82%) and the mean percentage increase for ethinyl estradiol
compared to placebo was 38% (range: –11 to 101%). Both of these increases were
statistically significantly different from placebo.
A third study evaluated the potential interaction of once
weekly dosing of fluconazole 300 mg to 21 normal females taking an oral
contraceptive containing ethinyl estradiol and norethindrone. In this
placebo-controlled, double-blind, randomized, two-way crossover study carried
out over three cycles of oral contraceptive treatment, fluconazole dosing
resulted in small increases in the mean AUCs of ethinyl estradiol and
norethindrone compared to similar placebo dosing. The mean AUCs of ethinyl
estradiol and norethindrone increased by 24% (95% C.I. range: 18-31%) and 13%
(95% C.I. range: 8-18%), respectively, relative to placebo. Fluconazole
treatment did not cause a decrease in the ethinyl estradiol AUC of any
individual subject in this study compared to placebo dosing. The individual AUC
values of norethindrone decreased very slightly (<5%) in 3 of the 21
subjects after fluconazole treatment.
Cimetidine
DIFLUCAN 100 mg was administered as a single oral dose
alone and two hours after a single dose of cimetidine 400 mg to six healthy
male volunteers. After the administration of cimetidine, there was a
significant decrease in fluconazole AUC and Cmax. There was a mean ± SD
decrease in fluconazole AUC of 13% ± 11% (range: –3.4 to –31%) and Cmax
decreased 19% ± 14% (range: –5 to –40%). However, the administration of cimetidine
600 mg to 900 mg intravenously over a four-hour period (from one hour before to
3 hours after a single oral dose of DIFLUCAN 200 mg) did not affect the
bioavailability or pharmacokinetics of fluconazole in 24 healthy male
volunteers.
Antacid
Administration of Maalox® (20 mL) to 14 normal male
volunteers immediately prior to a single dose of DIFLUCAN 100 mg had no effect
on the absorption or elimination of fluconazole.
Hydrochlorothiazide
Concomitant oral administration of 100 mg DIFLUCAN and 50
mg hydrochlorothiazide for 10 days in 13 normal volunteers resulted in a
significant increase in fluconazole AUC and Cmax compared to DIFLUCAN given
alone. There was a mean ± SD increase in fluconazole AUC and Cmax of 45% ± 31%
(range: 19 to 114%) and 43% ± 31% (range: 19 to 122%), respectively. These
changes are attributed to a mean ± SD reduction in renal clearance of 30% ± 12%
(range: –10 to –50%).
Rifampin
Administration of a single oral 200 mg dose of DIFLUCAN
after 15 days of rifampin administered as 600 mg daily in eight healthy male
volunteers resulted in a significant decrease in fluconazole AUC and a
significant increase in apparent oral clearance of fluconazole. There was a
mean ± SD reduction in fluconazole AUC of 23% ± 9% (range: –13 to –42%).
Apparent oral clearance of fluconazole increased 32% ± 17% (range: 16 to 72%).
Fluconazole half-life decreased from 33.4 ± 4.4 hours to 26.8 ± 3.9 hours. (See
PRECAUTIONS.)
Warfarin
There was a significant increase in prothrombin time
response (area under the prothrombin time-time curve) following a single dose
of warfarin (15 mg) administered to 13 normal male volunteers following oral
DIFLUCAN 200 mg administered daily for 14 days as compared to the
administration of warfarin alone. There was a mean ± SD increase in the
prothrombin time response (area under the prothrombin time-time curve) of 7% ±
4% (range: –2 to 13%). (See PRECAUTIONS.) Mean is based on data from 12
subjects as one of 13 subjects experienced a 2-fold increase in his prothrombin
time response.
Phenytoin
Phenytoin AUC was determined after 4 days of phenytoin
dosing (200 mg daily, orally for 3 days followed by 250 mg intravenously for
one dose) both with and without the administration of fluconazole (oral
DIFLUCAN 200 mg daily for 16 days) in 10 normal male volunteers. There was a
significant increase in phenytoin AUC. The mean ± SD increase in phenytoin AUC
was 88% ± 68% (range: 16 to 247%). The absolute magnitude of this interaction
is unknown because of the intrinsically nonlinear disposition of phenytoin.
(See PRECAUTIONS.)
Cyclosporine
Cyclosporine AUC and Cmax were determined before and
after the administration of fluconazole 200 mg daily for 14 days in eight renal
transplant patients who had been on cyclosporine therapy for at least 6 months
and on a stable cyclosporine dose for at least 6 weeks. There was a significant
increase in cyclosporine AUC, Cmax, Cmin (24-hour concentration), and a
significant reduction in apparent oral clearance following the administration
of fluconazole. The mean ± SD increase in AUC was 92% ± 43% (range: 18 to
147%). The Cmax increased 60% ± 48% (range: –5 to 133%). The Cmin increased
157% ± 96% (range: 33 to 360%). The apparent oral clearance decreased 45% ± 15%
(range: –15 to –60%). (See PRECAUTIONS.)
Zidovudine
Plasma zidovudine concentrations were determined on two
occasions (before and following fluconazole 200 mg daily for 15 days) in 13
volunteers with AIDS or ARC who were on a stable zidovudine dose for at least
two weeks. There was a significant increase in zidovudine AUC following the
administration of fluconazole. The mean ± SD increase in AUC was 20% ± 32%
(range: –27 to 104%). The metabolite, GZDV, to parent drug ratio significantly
decreased after the administration of fluconazole, from 7.6 ± 3.6 to 5.7 ± 2.2.
Theophylline
The pharmacokinetics of theophylline were determined from
a single intravenous dose of aminophylline (6 mg/kg) before and after the oral
administration of fluconazole 200 mg daily for 14 days in 16 normal male
volunteers. There were significant increases in theophylline AUC, Cmax, and
half-life with a corresponding decrease in clearance. The mean ± SD
theophylline AUC increased 21% ± 16% (range: –5 to 48%). The Cmax increased 13%
± 17% (range: –13 to 40%). Theophylline clearance decreased 16% ± 11% (range:
–32 to 5%). The half-life of theophylline increased from 6.6 ± 1.7 hours to 7.9
± 1.5 hours. (See PRECAUTIONS.)
Terfenadine
Six healthy volunteers received terfenadine 60 mg BID for
15 days. Fluconazole 200 mg was administered daily from days 9 through 15.
Fluconazole did not affect terfenadine plasma concentrations. Terfenadine acid
metabolite AUC increased 36% ± 36% (range: 7 to 102%) from day 8 to day 15 with
the concomitant administration of fluconazole. There was no change in cardiac
repolarization as measured by Holter QTc intervals. Another study at a 400 mg
and 800 mg daily dose of fluconazole demonstrated that DIFLUCAN taken in doses
of 400 mg per day or greater significantly increases plasma levels of
terfenadine when taken concomitantly. (See CONTRAINDICATIONS and PRECAUTIONS.)
Quinidine
Although not studied in vitro or in vivo, concomitant
administration of fluconazole with quinidine may result in inhibition of
quinidine metabolism. Use of quinidine has been associated with QT prolongation
and rare occurrences of torsades de pointes. Coadministration of fluconazole
and quinidine is contraindicated. (See CONTRAINDICATIONS and PRECAUTIONS.)
Oral Hypoglycemic
The effects of fluconazole on the pharmacokinetics of the
sulfonylurea oral hypoglycemic agents tolbutamide, glipizide, and glyburide
were evaluated in three placebo-controlled studies in normal volunteers. All
subjects received the sulfonylurea alone as a single dose and again as a single
dose following the administration of DIFLUCAN 100 mg daily for 7 days. In these
three studies, 22/46 (47.8%) of DIFLUCAN treated patients and 9/22 (40.1%) of
placebo-treated patients experienced symptoms consistent with hypoglycemia.
(See PRECAUTIONS.)
Tolbutamide
In 13 normal male volunteers, there was significant
increase in tolbutamide (500 mg single dose) AUC and Cmax following the
administration of fluconazole. There was a mean ± SD increase in tolbutamide
AUC of 26% ± 9% (range: 12 to 39%). Tolbutamide Cmax increased 11% ± 9% (range:
–6 to 27%). (See PRECAUTIONS.)
Glipizide
The AUC and Cmax of glipizide (2.5 mg single dose) were
significantly increased following the administration of fluconazole in 13
normal male volunteers. There was a mean ± SD increase in AUC of 49% ± 13%
(range: 27 to 73%) and an increase in Cmax of 19% ± 23% (range: –11 to 79%).
(See PRECAUTIONS.)
Glyburide
The AUC and Cmax of glyburide (5 mg single dose) were
significantly increased following the administration of fluconazole in 20
normal male volunteers. There was a mean ± SD increase in AUC of 44% ± 29%
(range: –13 to 115%) and Cmax increased 19% ± 19% (range: –23 to 62%). Five
subjects required oral glucose following the ingestion of glyburide after 7
days of fluconazole administration. (See PRECAUTIONS.)
Rifabutin
There have been published reports that an interaction
exists when fluconazole is administered concomitantly with rifabutin, leading
to increased serum levels of rifabutin. (See PRECAUTIONS.)
Tacrolimus
There have been published reports that an interaction
exists when fluconazole is administered concomitantly with tacrolimus, leading
to increased serum levels of tacrolimus. (See PRECAUTIONS.)
Cisapride
A placebo-controlled, randomized, multiple-dose study
examined the potential interaction of fluconazole with cisapride. Two groups of
10 normal subjects were administered fluconazole 200 mg daily or placebo.
Cisapride 20 mg four times daily was started after 7 days of fluconazole or
placebo dosing. Following a single dose of fluconazole, there was a 101%
increase in the cisapride AUC and a 91% increase in the cisapride Cmax.
Following multiple doses of fluconazole, there was a 192% increase in the
cisapride AUC and a 154% increase in the cisapride Cmax. Fluconazole
significantly increased the QTc interval in subjects receiving cisapride 20 mg
four times daily for 5 days. (See CONTRAINDICATIONS and PRECAUTIONS.)
Midazolam
The effect of fluconazole on the pharmacokinetics and pharmacodynamics
of midazolam was examined in a randomized, cross-over study in 12 volunteers.
In the study, subjects ingested placebo or 400 mg fluconazole on Day 1 followed
by 200 mg daily from Day 2 to Day 6. In addition, a 7.5 mg dose of midazolam
was orally ingested on the first day, 0.05 mg/kg was administered intravenously
on the fourth day, and 7.5 mg orally on the sixth day. Fluconazole reduced the
clearance of IV midazolam by 51%. On the first day of dosing, fluconazole
increased the midazolam AUC and Cmax by 259% and 150%, respectively. On the
sixth day of dosing, fluconazole increased the midazolam AUC and Cmax by 259%
and 74%, respectively. The psychomotor effects of midazolam were significantly
increased after oral administration of midazolam but not significantly affected
following intravenous midazolam.
A second randomized, double-dummy, placebo-controlled,
cross over study in three phases was performed to determine the effect of route
of administration of fluconazole on the interaction between fluconazole and
midazolam. In each phase the subjects were given oral fluconazole 400 mg and
intravenous saline; oral placebo and intravenous fluconazole 400 mg; and oral
placebo and IV saline. An oral dose of 7.5 mg of midazolam was ingested after
fluconazole/placebo. The AUC and Cmax of midazolam were significantly higher
after oral than IV administration of fluconazole. Oral fluconazole increased
the midazolam AUC and Cmax by 272% and 129%, respectively. IV fluconazole
increased the midazolam AUC and Cmax by 244% and 79%, respectively. Both oral
and IV fluconazole increased the pharmacodynamic effects of midazolam. (See PRECAUTIONS.)
Azithromycin
An open-label, randomized, three-way crossover study in
18 healthy subjects assessed the effect of a single 800 mg oral dose of
fluconazole on the pharmacokinetics of a single 1200 mg oral dose of
azithromycin as well as the effects of azithromycin on the pharmacokinetics of
fluconazole. There was no significant pharmacokinetic interaction between
fluconazole and azithromycin.
Voriconazole
Voriconazole is a substrate for both CYP2C9 and CYP3A4
isoenzymes. Concurrent administration of oral Voriconazole (400 mg Q12h for 1
day, then 200 mg Q12h for 2.5 days) and oral fluconazole (400 mg on day 1, then
200 mg Q24h for 4 days) to 6 healthy male subjects resulted in an increase in
Cmax and AUCτ of voriconazole by an average of 57% (90% CI: 20%, 107%)
and 79% (90% CI: 40%, 128%), respectively. In a follow-on clinical study
involving 8 healthy male subjects, reduced dosing and/or frequency of
voriconazole and fluconazole did not eliminate or diminish this effect.
Concomitant administration of voriconazole and fluconazole at any dose is not
recommended. Close monitoring for adverse events related to voriconazole is
recommended if voriconazole is used sequentially after fluconazole, especially
within 24 h of the last dose of fluconazole. (See PRECAUTIONS)
Tofacitinib
Co-administration of fluconazole (400 mg on Day 1 and 200
mg once daily for 6 days [Days 2-7]) and tofacitinib (30 mg single dose on Day
5) in healthy subjects resulted in increased mean tofacitinib AUC and Cmax
values of approximately 79% (90% CI: 64% – 96%) and 27% (90% CI: 12% – 44%),
respectively, compared to administration of tofacitinib alone. (See PRECAUTIONS)
Microbiology
Mechanism Of Action
Fluconazole is a highly selective inhibitor of fungal
cytochrome P450 dependent enzyme lanosterol 14-α-demethylase. This enzyme
functions to convert lanosterol to ergosterol. The subsequent loss of normal
sterols correlates with the accumulation of 14-α-methyl sterols in fungi
and may be responsible for the fungistatic activity of fluconazole. Mammalian
cell demethylation is much less sensitive to fluconazole inhibition.
Drug Resistance
Fluconazole resistance may arise from a modification in
the quality or quantity of the target enzyme (lanosterol
14-α-demethylase), reduced access to the drug target, or some combination
of these mechanisms.
Point mutations in the gene (ERG11) encoding for the
target enzyme lead to an altered target with decreased affinity for azoles.
Overexpression of ERG11 results in the production of high concentrations of the
target enzyme, creating the need for higher intracellular drug concentrations
to inhibit all of the enzyme molecules in the cell.
The second major mechanism of drug resistance involves
active efflux of fluconazole out of the cell through the activation of two
types of multidrug efflux transporters; the major facilitators (encoded by MDR
genes) and those of the ATP-binding cassette superfamily (encoded by CDR
genes). Upregulation of the MDR gene leads to fluconazole resistance, whereas,
upregulation of CDR genes may lead to resistance to multiple azoles.
Resistance in Candida glabrata usually includes
upregulation of CDR genes resulting in resistance to multiple azoles. For an
isolate where the MIC is categorized as Intermediate (16 to 32 μg/mL), the
highest fluconazole dose is recommended.
Candida krusei should be considered to be
resistant to fluconazole. Resistance in C. krusei appears to be mediated
by reduced sensitivity of the target enzyme to inhibition by the agent.
There have been reports of cases of superinfection with Candida
species other than C. albicans, which are often inherently not
susceptible to DIFLUCAN (e.g., Candida krusei). Such cases may require
alternative antifungal therapy.
Activity In Vitro And In Clinical Infections
Fluconazole has been shown to be active against most
strains of the following microorganisms  both in vitro and in clinical
infections.
Candida albicans
Candida glabrata (Many strains are intermediately
susceptible)*
Candida parapsilosis
Candida tropicalis
Cryptococcus neoformans
* In a majority of the studies, fluconazole MIC90
values against C. glabrata were above the susceptible breakpoint (≥16
μg/mL). Resistance in Candida glabrata usually includes upregulation of
CDR genes resulting in resistance to multiple azoles. For an isolate where the
MIC is categorized as intermediate (16 to 32 μg/mL, see Table 1), the
highest dose is recommended (see DOSAGE AND ADMINISTRATION). For
resistant isolates, alternative therapy is recommended.
The following in vitro data are available, but their
clinical significance is unknown.
Fluconazole exhibits in vitro minimum inhibitory
concentrations (MIC values) of 8 μg/mL or less against most (≥90%)
strains of the following microorganisms, however, the safety and effectiveness
of fluconazole in treating clinical infections due to these microorganisms have
not been established in adequate and well-controlled trials.
Candida dubliniensis
Candida guilliermondii
Candida kefyr
Candida lusitaniae
Candida krusei should be considered to be
resistant to fluconazole. Resistance in C. krusei appears to be mediated
by reduced sensitivity of the target enzyme to inhibition by the agent.
There have been reports of cases of superinfection with Candida
species other than C. albicans, which are often inherently not
susceptible to DIFLUCAN (e.g., Candida krusei). Such cases may require
alternative antifungal therapy.
Susceptibility Testing Methods
Cryptococcus Neoformans And Filamentous Fungi
No interpretive criteria have been established for Cryptococcus
neoformans and filamentous fungi.
Candida Species
Broth Dilution Techniques
Quantitative methods are used to determine antifungal
minimum inhibitory concentrations (MICs). These MICs provide estimates of the
susceptibility of Candida spp. to antifungal agents. MICs should be
determined using a standardized procedure. Standardized procedures are based on
a dilution method (broth)1 with standardized inoculum concentrations
of fluconazole powder. The MIC values should be interpreted according to the
criteria provided in Table 1.
Diffusion Techniques
Qualitative methods that require measurement of zone
diameters also provide reproducible estimates of the susceptibility of Candida
spp. to an antifungal agent. One such standardized procedure2 requires
the use of standardized inoculum concentrations. This procedure uses paper
disks impregnated with 25 μg of fluconazole to test the susceptibility of
yeasts to fluconazole. Disk diffusion interpretive criteria are also provided
in Table 1.
Table 1: Susceptibility Interpretive Criteria for Fluconazole
against Candida species
Antifungal agent |
Broth Dilution at 48 hours (MIC in μg/mL) |
Disk Diffusion at 24 hours (Zone Diameters in mm) |
Susceptible (S) |
Intermediate (I)** |
Resistant (R) |
Susceptible (S) |
Intermediate (I)** |
Resistant (R) |
Fluconazole* |
≤ 8.0 |
16-32 |
≥64 |
≥19 |
15-18 |
≤14 |
* Isolates of C. krusei are
assumed to be intrinsically resistant to fluconazole and their MICs and/or zone
diameters should not be interpreted using this scale.
** The intermediate category is sometimes called Susceptible-Dose Dependent
(SDD) and both categories are equivalent for fluconazole. |
A report of Susceptible (S)
indicates that the antimicrobial drug is likely to inhibit growth of the
microorganism if the antimicrobial drug reaches the concentration usually
achievable at the site of infection.
A report of Intermediate
(I) indicates that an infection due to the isolate may be appropriately treated
in body sites where the drugs are physiologically concentrated or when a high
dosage of drug is used.
A report of Resistant (R)
indicates that the antimicrobial is not likely to inhibit growth of the
pathogen if the antimicrobial drug reaches the concentrations usually
achievable at the infection site; other therapy should be selected.
Quality Control
Standardized susceptibility test procedures require the
use of quality control organisms to control the technical aspects of the test
procedures. Standardized fluconazole powder and 25 μg disks should provide
the following range of values noted in Table 2. NOTE: Quality control
microorganisms are specific strains of organisms with intrinsic biological
properties relating to resistance mechanisms and their genetic expression
within fungi; the specific strains used for microbiological control are not
clinically significant.
Table 2: Acceptable Quality Control Ranges for
Fluconazole to be Used in Validation of Susceptibility Test Results
QC Strain |
Macrodilution (MIC in μg/mL) @ 48 hours |
Microdilution (MIC in μg/mL) @ 48 hours |
Disk Diffusion (Zone Diameter in mm) @ 24 hours |
Candida parapsilosis ATCC 22019 |
2.0-8.0 |
1.0-4.0 |
22-33 |
Candida krusei ATCC 6258 |
16-64 |
16-128 |
---* |
Candida albicans ATCC 90028 |
---* |
---* |
28-39 |
Candida tropicalis ATCC 750 |
---* |
---* |
26-37 |
---* Quality control ranges
have not been established for this strain/antifungal agent combination due to
their extensive interlaboratory variation during initial quality control
studies. |
Clinical Studies
Cryptococcal Meningitis
In a multicenter study comparing DIFLUCAN (200 mg/day) to
amphotericin B (0.3 mg/kg/day) for treatment of cryptococcal meningitis in
patients with AIDS, a multivariate analysis revealed three pretreatment factors
that predicted death during the course of therapy: abnormal mental status,
cerebrospinal fluid cryptococcal antigen titer greater than 1:1024, and
cerebrospinal fluid white blood cell count of less than 20 cells/mm³.
Mortality among high risk patients was 33% and 40% for amphotericin B and
DIFLUCAN patients, respectively (p=0.58), with overall deaths 14% (9 of 63
subjects) and 18% (24 of 131 subjects) for the 2 arms of the study (p=0.48).
Optimal doses and regimens for patients with acute cryptococcal meningitis and
at high risk for treatment failure remain to be determined. (Saag, et al. N
Engl J Med 1992; 326:83-9.)
Vaginal Candidiasis
Two adequate and well-controlled studies were conducted
in the U.S. using the 150 mg tablet. In both, the results of the fluconazole
regimen were comparable to the control regimen (clotrimazole or miconazole
intravaginally for 7 days) both clinically and statistically at the one month
post-treatment evaluation.
The therapeutic cure rate, defined as a complete
resolution of signs and symptoms of vaginal candidiasis (clinical cure), along
with a negative KOH examination and negative culture for Candida (microbiologic
eradication), was 55% in both the fluconazole group and the vaginal products
group.
|
Fluconazole PO 150 mg tablet |
Vaginal Product ahs x 7 days |
Enrolled |
448 |
422 |
Evaluable at Late Follow-up |
347 (77%) |
327 (77%) |
Clinical cure |
239/347 (69%) |
235/327 (72%) |
Mycologic eradication |
213/347 (61%) |
196/327 (60%) |
Therapeutic cure |
190/347 (55%) |
179/327 (55%) |
Approximately three-fourths of
the enrolled patients had acute vaginitis (<4 episodes/12 months) and
achieved 80% clinical cure, 67% mycologic eradication, and 59% therapeutic cure
when treated with a 150 mg DIFLUCAN tablet administered orally. These rates
were comparable to control products. The remaining one-fourth of enrolled
patients had recurrent vaginitis (>4 episodes/12 months) and achieved 57%
clinical cure, 47% mycologic eradication, and 40% therapeutic cure. The numbers
are too small to make meaningful clinical or statistical comparisons with
vaginal products in the treatment of patients with recurrent vaginitis.
Substantially more
gastrointestinal events were reported in the fluconazole group compared to the
vaginal product group. Most of the events were mild to moderate. Because
fluconazole was given as a single dose, no discontinuations occurred.
Parameter |
Fluconazole PO |
Vaginal Products |
Evaluable patients |
448 |
422 |
With any adverse event |
141 (31%) |
112 (27%) |
Nervous System |
90 (20%) |
69 (16%) |
Gastrointestinal |
73 (16%) |
18 (4%) |
With drug-related event |
117 (26%) |
67 (16%) |
Nervous System |
61 (14%) |
29 (7%) |
Headache |
58 (13%) |
28 (7%) |
Gastrointestinal |
68 (15%) |
13 (3%) |
Abdominal pain |
25 (6%) |
7 (2%) |
Nausea |
30 (7%) |
3 (1%) |
Diarrhea |
12 (3%) |
2 (<1%) |
Application site event |
0 (0%) |
19 (5%) |
Taste Perversion |
6 (1%) |
0 (0%) |
Pediatric Studies
Oropharyngeal Candidiasis
An open-label, comparative
study of the efficacy and safety of DIFLUCAN (2-3 mg/kg/day) and oral nystatin
(400,000 I.U. 4 times daily) in immunocompromised children with oropharyngeal
candidiasis was conducted. Clinical and mycological response rates were higher
in the children treated with fluconazole.
Clinical cure at the end of
treatment was reported for 86% of fluconazole treated patients compared to 46%
of nystatin treated patients. Mycologically, 76% of fluconazole treated
patients had the infecting organism eradicated compared to 11% for nystatin
treated patients.
|
Fluconazole |
Nystatin |
Enrolled |
96 |
90 |
Clinical Cure |
76/88 (86%) |
36/78 (46%) |
Mycological eradication* |
55/72 (76%) |
6/54 (11%) |
* Subjects without follow-up
cultures for any reason were considered nonevaluable for mycological response. |
The proportion of patients with
clinical relapse 2 weeks after the end of treatment was 14% for subjects
receiving DIFLUCAN and 16% for subjects receiving nystatin. At 4 weeks after
the end of treatment, the percentages of patients with clinical relapse were
22% for DIFLUCAN and 23% for nystatin.