CLINICAL PHARMACOLOGY
Pharmacokinetics And Drug Metabolism
Absorption
Oral Bioavailability
Maximal plasma cefdinir concentrations occur 2 to 4 hours
postdose following capsule or suspension administration. Plasma cefdinir
concentrations increase with dose, but the increases are less than
dose-proportional from 300 mg (7 mg/kg) to 600 mg (14 mg/kg). Following
administration of suspension to healthy adults, cefdinir bioavailability is
120% relative to capsules. Estimated bioavailability of cefdinir capsules is
21% following administration of a 300 mg capsule dose, and 16% following
administration of a 600 mg capsule dose. Estimated absolute bioavailability of
cefdinir suspension is 25%. Cefdinir oral suspension of 250 mg/5 mL strength
was shown to be bioequivalent to the 125 mg/5 mL strength in healthy adults
under fasting conditions.
Effect of Food
The Cmax and AUC of cefdinir from the capsules are
reduced by 16% and 10%, respectively, when given with a high-fat meal. In
adults given the 250 mg/5 mL oral suspension with a high-fat meal, the Cmax and
AUC of cefdinir are reduced by 44% and 33%, respectively. The magnitude of
these reductions is not likely to be clinically significant because the safety
and efficacy studies of oral suspension in pediatric patients were conducted
without regard to food intake. Therefore, cefdinir may be taken without regard
to food.
Cefdinir Capsules
Cefdinir plasma concentrations and pharmacokinetic
parameter values following administration of single 300- and 600-mg oral doses
of cefdinir to adult subjects are presented in the following table:
Mean (± SD) Plasma Cefdinir Pharmacokinetic Parameter
Values Following Administration of Capsules to Adult Subjects
Dose |
Cmax (μg/mL) |
tmax (hr) |
AUC (μg•hr/mL) |
300 mg |
1.6 (0.55) |
2.9 (0.89) |
7.05 (2.17) |
600 mg |
2.87 (1.01) |
3 (0.66) |
11.1 (3.87) |
Cefdinir Suspension
Cefdinir plasma concentrations
and pharmacokinetic parameter values following administration of single 7- and
14-mg/kg oral doses of cefdinir to pediatric subjects (age 6 months-12 years)
are presented in the following table:
Mean (± SD) Plasma Cefdinir Pharmacokinetic Parameter
Values Following Administration of Suspension to Pediatric Subjects
Dose |
Cmax(μg/mL) |
tmax(hr) |
AUC(μg•hr/mL) |
7 mg/kg |
2.3 (0.65) |
2.2 (0.6) |
8.31 (2.5) |
14 mg/kg |
3.86 (0.62) |
1.8 (0.4) |
13.4 (2.64) |
Multiple Dosing
Cefdinir does not accumulate in
plasma following once- or twice-daily administration to subjects with normal
renal function.
Distribution
The mean volume of distribution
(Vdarea) of cefdinir in adult subjects is 0.35 L/kg (± 0.29); in pediatric subjects
(age 6 months-12 years), cefdinir Vdarea is 0.67 L/kg (± 0.38). Cefdinir is 60%
to 70% bound to plasma proteins in both adult and pediatric subjects; binding
is independent of concentration.
Skin Blister
In adult subjects, median
(range) maximal blister fluid cefdinir concentrations of 0.65 (0.33-1.1) and
1.1 (0.49-1.9) μg/mL were observed 4 to 5 hours following administration
of 300- and 600mg doses, respectively. Mean (± SD) blister Cmax and AUC
(0-∞) values were 48% (± 13) and 91% (± 18) of corresponding plasma
values.
Tonsil Tissue
In adult patients undergoing
elective tonsillectomy, respective median tonsil tissue cefdinir concentrations
4 hours after administration of single 300- and 600-mg doses were 0.25
(0.220.46) and 0.36 (0.22-0.80) μg/g. Mean tonsil tissue concentrations
were 24% (± 8) of corresponding plasma concentrations.
Sinus Tissue
In adult patients undergoing
elective maxillary and ethmoid sinus surgery, respective median sinus tissue
cefdinir concentrations 4 hours after administration of single 300- and 600-mg
doses were < 0.12 ( < 0.12-0.46) and 0.21 ( < 0.12-2.0) μg/g. Mean
sinus tissue concentrations were 16% (± 20) of corresponding plasma
concentrations.
Lung Tissue
In adult patients undergoing
diagnostic bronchoscopy, respective median bronchial mucosa cefdinir
concentrations 4 hours after administration of single 300- and 600-mg doses
were 0.78 ( < 0.06-1.33) and 1.14 ( < 0.06-1.92) μg/mL, and were 31%
(± 18) of corresponding plasma concentrations. Respective median epithelial
lining fluid concentrations were 0.29 ( < 0.3-4.73) and 0.49 ( < 0.3-0.59)
μg/mL, and were 35% (± 83) of corresponding plasma concentrations.
Middle Ear Fluid
In 14 pediatric patients with acute bacterial otitis
media, respective median middle ear fluid cefdinir concentrations 3 hours after
administration of single 7- and 14-mg/kg doses were 0.21 ( < 0.09-0.94) and
0.72 (0.14-1.42) μg/mL. Mean middle ear fluid concentrations were 15% (±
15) of corresponding plasma concentrations.
CSF
Data on cefdinir penetration into human cerebrospinal
fluid are not available.
Metabolism and Excretion
Cefdinir is not appreciably metabolized. Activity is
primarily due to parent drug. Cefdinir is eliminated principally via renal
excretion with a mean plasma elimination half-life (t½) of 1.7 (± 0.6) hours.
In healthy subjects with normal renal function, renal clearance is 2.0 (± 1.0)
mL/min/kg, and apparent oral clearance is 11.6 (± 6.0) and 15.5 (± 5.4)
mL/min/kg following doses of 300- and 600-mg, respectively. Mean percent of
dose recovered unchanged in the urine following 300- and 600-mg doses is 18.4%
(± 6.4) and 11.6% (± 4.6), respectively. Cefdinir clearance is reduced in
patients with renal dysfunction (see Special Populations - Patients
with Renal Insufficiency).
Because renal excretion is the predominant pathway of
elimination, dosage should be adjusted in patients with markedly compromised
renal function or who are undergoing hemodialysis (see DOSAGE AND
ADMINISTRATION).
Special Populations
Patients with Renal Insufficiency
Cefdinir pharmacokinetics were investigated in 21 adult
subjects with varying degrees of renal function. Decreases in cefdinir
elimination rate, apparent oral clearance (CL/F), and renal clearance were
approximately proportional to the reduction in creatinine clearance (CLcr). As
a result, plasma cefdinir concentrations were higher and persisted longer in
subjects with renal impairment than in those without renal impairment. In
subjects with CLcr between 30 and 60 mL/min, Cmax and t½ increased by
approximately 2-fold and AUC by approximately 3-fold. In subjects with CLcr <
30 mL/min, Cmax increased by approximately 2-fold, t½ by approximately 5fold,
and AUC by approximately 6-fold. Dosage adjustment is recommended in patients
with markedly compromised renal function (creatinine clearance < 30 mL/min;
see DOSAGE AND ADMINISTRATION).
Hemodialysis
Cefdinir pharmacokinetics were studied in 8 adult
subjects undergoing hemodialysis. Dialysis (4 hours duration) removed 63% of
cefdinir from the body and reduced apparent elimination t½ from 16 (± 3.5) to
3.2 (± 1.2) hours. Dosage adjustment is recommended in this patient population
(see DOSAGE AND ADMINISTRATION).
Hepatic Disease
Because cefdinir is predominantly renally eliminated and
not appreciably metabolized, studies in patients with hepatic impairment were
not conducted. It is not expected that dosage adjustment will be required in
this population.
Geriatric Patients
The effect of age on cefdinir pharmacokinetics after a
single 300-mg dose was evaluated in 32 subjects 19 to 91 years of age. Systemic
exposure to cefdinir was substantially increased in older subjects (N = 16), Cmax
by 44% and AUC by 86%. This increase was due to a reduction in cefdinir
clearance. The apparent volume of distribution was also reduced, thus no
appreciable alterations in apparent elimination t½ were observed (elderly: 2.2
± 0.6 hours vs young: 1.8 ± 0.4 hours). Since cefdinir clearance has been shown
to be primarily related to changes in renal function rather than age, elderly
patients do not require dosage adjustment unless they have markedly compromised
renal function (creatinine clearance < 30 mL/min, see Patients with Renal
Insufficiency, above).
Gender and Race
The results of a meta-analysis of clinical
pharmacokinetics (N = 217) indicated no significant impact of either gender or
race on cefdinir pharmacokinetics.
Microbiology
Mechanism of Action
As with other cephalosporins, bactericidal activity of
cefdinir results from inhibition of cell wall synthesis. Cefdinir is stable in
the presence of some, but not all, β-lactamase enzymes. As a result, many
organisms resistant to penicillins and some cephalosporins are susceptible to
cefdinir.
Mechanism of Resistance
Resistance to cefdinir is primarily through hydrolysis by
some β-lactamases, alteration of penicillin-binding proteins (PBPs) and
decreased permeability. Cefdinir is inactive against most strains of Enterobacter
spp., Pseudomonas spp., Enterococcus spp., penicillin-resistant streptococci,
and methicillin-resistant staphylococci. β-lactamase negative,
ampicillin-resistant (BLNAR) H. influenzae strains are typically
non-susceptible to cefdinir.
Antimicrobial Activity
Cefdinir has been shown to be active against most strains
of the following microorganisms, both in vitro and in clinical infections as
described in INDICATIONS AND USAGE.
Gram-Positive Bacteria
Staphylococcus aureus (methicillin-susceptible
strains only)
Streptococcus pneumoniae (penicillin-susceptible
strains only)
Streptococcus pyogenes
Gram-Negative Bacteria
Haemophilus influenzae
Haemophilus parainfluenzae
Moraxella catarrhalis
The following in vitro data are available, but their
clinical significance is unknown.
Cefdinir exhibits in vitro minimum inhibitory
concentrations (MICs) of 1 mcg/mL or less against ( ≥ 90%) strains of the
following microorganisms; however, the safety and effectiveness of cefdinir in
treating clinical infections due to these microorganisms have not been
established in adequate and well-controlled clinical trials.
Gram-Positive Bacteria
Staphylococcus epidermidis (methicillin-susceptible
strains only)
Streptococcus agalactiae
Viridans group streptococci
Gram-Negative Bacteria
Citrobacter koseri
Escherichia coli
Klebsiella pneumoniae
Proteus mirabilis
Susceptibility Test Methods
When available, the clinical microbiology laboratory
should provide periodic reports that describe the regional/local susceptibility
profile of potential nosocomial and community-acquired pathogens. These reports
should aid the physician in selecting an antibacterial drug for treatment.
Dilution Techniques
Quantitative methods are used to determine antimicrobial
minimum inhibitory concentrations (MICs). These MICs provide estimates of the
susceptibility of bacteria to antimicrobial compounds. The MICs should be
determined using a standardized test method1 (broth and/or agar). The
MIC values should be interpreted according to criteria provided in Table 1.
Diffusion Techniques
Quantitative methods that require measurement of zone
diameters also provide reproducible estimates of the susceptibility of bacteria
to antimicrobial compounds. The zone size should be determined using a
standardized method.2 The procedure uses paper disks impregnated
with 5 mcg cefdinir to test the susceptibility of bacteria. The disk diffusion
interpretive criteria are provided in Table 1.
Table 1: Susceptibility Test Interpretive Criteria for
Cefdinir
Microorganismsa |
Minimum Inhibitory Concentration (mcg/mL) |
Zone Diameter (mm) |
S |
I |
R |
S |
I |
R |
Haemophilus influenzae |
≤ 1 |
— |
— |
≥ 20 |
— |
— |
Haemophilus parainfluenzae |
≤ 1 |
— |
— |
≥ 20 |
— |
— |
Moraxella catarrhalis |
≤ 1 |
2 |
≥ 4 |
≥ 20 |
17 - 19 |
≤ 16 |
Streptococcus pneumoniaeb |
≤ 0.5 |
1 |
≥ 2 |
— |
— |
— |
Streptococcus pyogenes |
≤ 1 |
2 |
≥ 4 |
≥ 20 |
17 - 19 |
≤ 16 |
aStreptococci other than S. pneumoniae that are
susceptible to penicillin (MIC ≤ 0.12 mcg/mL), can be considered
susceptible to cefdinir.
bS. pneumoniae that are susceptible to penicillin (MIC
≤ 0.06 mcg/mL) can be considered susceptible to cefdinir. Isolates of S.
pneumoniae tested against a 1-μg oxacillin disk with oxacillin zone sizes
≥ 20 mm are susceptible to penicillin and can be considered susceptible
to cefdinir. Testing of cefdinir against penicillin-intermediate or
penicillin-resistant isolates is not recommended. Reliable interpretive
criteria for cefdinir are not available. |
Susceptibility of staphylococci
to cefdinir may be deduced from testing penicillin and either cefoxitin or
oxacillin. Staphylococci susceptible to oxacillin (cefoxitin) can be considered
susceptible to cefdinir.3
A report of “Susceptible”
indicates that antimicrobial is likely to inhibit growth of the pathogen if the
antimicrobial compound reaches the concentrations at the site of infection
necessary to inhibit growth of the pathogen. A report of “Intermediate”
indicates that the result should be considered equivocal, and, if the
microorganism is not fully susceptible to alternative, clinically feasible
drugs, the test should be repeated. This category implies possible clinical
applicability in body sites where the drug is physiologically concentrated or
in situations where a high dosage of drug can be used. This category also
provides a buffer zone that prevents small uncontrolled technical factors from
causing major discrepancies in interpretation. A report of “Resistant” indicates
that the antimicrobial is not likely to inhibit growth of the pathogen if the
antimicrobial compound reaches the concentrations usually achievable at the
infection site; other therapy should be selected.
Quality Control
Standardized susceptibility test procedures require the
use of laboratory controls to monitor and ensure the accuracy and precision of
supplies and reagents used in the assay, and the techniques of the individual
performing the test.1,2,3 Standard cefdinir powder should provide
the following range of MIC values as noted in Table 2. For the diffusion
technique using a 5 mcg disk the criteria in Table 2 should be achieved.
Table 2: Acceptable Quality Control Ranges for
Cefdinir
QC Strain |
Minimum Inhibitory Concentration (mcg/mL) |
Zone Diameter (mm) |
Escherichia coli ATCC 25922 |
0.12 - 0.5 |
24 - 28 |
Haemophilus influenzae ATCC 49766 |
0.12 - 0.5 |
24 - 31 |
Staphylococcus aureus ATCC 25923 |
-- |
25 - 32 |
Staphylococcus aureus ATCC 29213 |
0.12 - 0.5 |
-- |
Streptococcus pneumoniae ATCC 49619 |
0.03 - 0.25 |
26 - 31 |
Clinical Studies
Community-Acquired Bacterial Pneumonia
In a controlled, double-blind study in adults and
adolescents conducted in the US, cefdinir BID was compared with cefaclor 500 mg
TID. Using strict evaluability and microbiologic/clinical response criteria 6
to 14 days posttherapy, the following clinical cure rates, presumptive
microbiologic eradication rates, and statistical outcomes were obtained:
US Community-Acquired Pneumonia Study Cefdinir vs
Cefaclor
|
Cefdinir BID |
Cefaclor TID |
Outcome |
Clinical Cure Rates |
150/187 (80%) |
147/186 (79%) |
Cefdinir equivalent to control |
Eradication Rates Overall |
177/195 (91%) |
184/200 (92%) |
Cefdinir equivalent to control |
S. pneumoniae |
31/31 (100%) |
35/35 (100%) |
|
H. influenzae |
55/65 (85%) |
60/72 (83%) |
|
M. catarrhalis |
10/10 (100%) |
11/11 (100%) |
|
H. parainfluenzae |
81/89 (91%) |
78/82 (95%) |
|
In a second controlled,
investigator-blind study in adults and adolescents conducted primarily in
Europe, cefdinir BID was compared with amoxicillin/clavulanate 500/125 mg TID.
Using strict evaluability and clinical response criteria 6 to 14 days
posttherapy, the following clinical cure rates, presumptive microbiologic
eradication rates, and statistical outcomes were obtained:
European Community-Acquired
Pneumonia Study Cefdinir vs Amoxicillin/Clavulanate
|
Cefdinir BID |
Amoxicillin/ Clavulanate TID |
Outcome |
Clinical Cure Rates |
83/104 (80%) |
86/97 (89%) |
Cefdinir not equivalent to control |
Eradication Rates Overall |
85/96 (89%) |
84/90 (93%) |
Cefdinir equivalent to control |
S. pneumoniae |
42/44 (95%) |
43/44 (98%) |
|
H. influenzae |
26/35 (74%) |
21/26 (81%) |
|
M. catarrhalis |
6/6 (100%) |
8/8 (100%) |
|
H. parainfluenzae |
11/11 (100%) |
12/12 (100%) |
|
Streptococcal
Pharyngitis/Tonsillitis
In four controlled studies
conducted in the United States, cefdinir was compared with 10 days of
penicillin in adult, adolescent, and pediatric patients. Two studies (one in
adults and adolescents, the other in pediatric patients) compared 10 days of
cefdinir QD or BID to penicillin 250 mg or 10 mg/kg QID. Using strict
evaluability and microbiologic/ clinical response criteria 5 to 10 days
posttherapy, the following clinical cure rates, microbiologic eradication
rates, and statistical outcomes were obtained:
Pharyngitis/Tonsillitis Studies Cefdinir (10 days) vs
Penicillin (10 days)
Study |
Efficacy Parameter |
Cefdinir QD |
Cefdinir BID |
Penicillin QID |
Outcome |
Adults/ Adolescents |
Eradication of S. pyogenes |
192/210 (91%) |
199/217 (92%) |
181/217 (83%) |
Cefdinir superior to control |
|
Clinical Cure Rates |
199/210 (95%) |
209/217 (96%) |
193/217 (89%) |
Cefdinir superior to control |
Pediatric Patients |
Eradication of S. pyogenes |
215/228 (94%) |
214/227 (94%) |
159/227 (70%) |
Cefdinir superior to control |
|
Clinical Cure Rates |
222/228 (97%) |
218/227 (96%) |
196/227 (86%) |
Cefdinir superior to control |
Two studies (one in adults and
adolescents, the other in pediatric patients) compared 5 days of cefdinir BID
to 10 days of penicillin 250 mg or 10 mg/kg QID. Using strict evaluability and
microbiologic/clinical response criteria 4 to 10 days posttherapy, the
following clinical cure rates, microbiologic eradication rates, and statistical
outcomes were obtained:
Pharyngitis/Tonsillitis
Studies Cefdinir (5 days) vs Penicillin (10 days)
Study |
Efficacy Parameter |
Cefdinir BID |
Penicillin QID |
Outcome |
Adults/ Adolescents |
Eradication of S. pyogenes |
193/218 (89%) |
176/214 (82%) |
Cefdinir equivalent to control |
|
Clinical Cure Rates |
194/218 (89%) |
181/214 (85%) |
Cefdinir equivalent to control |
Pediatric Patients |
Eradication of S. pyogenes |
176/196 (90%) |
135/193 (70%) |
Cefdinir superior to control |
|
Clinical Cure Rates |
179/196 (91%) |
173/193(90%) |
Cefdinir equivalent to control |
REFERENCES
1. Clinical and Laboratory
Standards Institute (CLSI). Methods for Dilution Antimicrobial Susceptibility
Tests for Bacteria That Grow Aerobically; Approved Standard – Tenth Edition. CLSI
Document M07-A10 [2015], Clinical and Laboratory Standards Institute, 950 West
Valley Road, Suite 2500, Wayne, Pennsylvania 19087, USA.
2. Clinical and Laboratory
Standards Institute (CLSI). Performance Standards for Antimicrobial Disk
Diffusion Susceptibility Tests; Approved Standard – Twelfth Edition. CLSI
Document M02-A12 [2015], Clinical and Laboratory Standards Institute, 950 West
Valley Road, Suite 2500, Wayne, Pennsylvania 19087, USA.
3. Clinical and Laboratory Standards Institute (CLSI). Performance
Standards for Antimicrobial Susceptibility Testing; Twenty-fifth Informational
Supplement, CLSI Document M100-S25 [2015], Clinical and Laboratory Standards
Institute, 950 West Valley Road, Suite 2500, Wayne, Pennsylvania 19087, USA.
4. Cockcroft DW, Gault MH. Prediction of creatinine
clearance from serum creatinine. Nephron 1976;16:31-41.
5. Schwartz GJ, Haycock GB, Edelmann CM, Spitzer A. A
simple estimate of glomerular filtration rate in children derived from body
length and plasma creatinine. Pediatrics 1976;58:259-63.
6. Schwartz GJ, Feld LG, Langford DJ. A simple estimate
of glomerular filtration rate in full-term infants during the first year of
life. J Pediatrics 1984;104:849-54.