CLINICAL PHARMACOLOGY
Mechanism Of Action
Telithromycin is a ketolide antibacterial drug. [see Microbiology]
Pharmacokinetics
The pharmacokinetics of telithromycin after
administration of single and multiple (7 days) once daily 800-mg doses to
healthy adult subjects are shown in Table 4.
Table 4: Pharmacokinetics of Telithromycin in Healthy
Subjects
Parameter |
Mean (SD) |
Single dose
(n=18) |
Multiple dose
(n=18) |
Cmax (pg/mL) |
1.9 (0.80) |
2.27 (0.71) |
Tmax (h)* |
1.0 (0.5-4.0) |
1.0 (0.5-3.0) |
AUC(0-24) (μg•h/mL) |
8.25 (2.6) |
12.5 (5.4) |
Terminal t ½ (h) |
7.16 (1.3) |
9.81 (1.9) |
C24h (μg/mL) |
0.03 (0.013) |
0.07 (0.051) |
SD=Standard deviation ; Cmax =Maximum plasma
concentration ; Tmax =Time to Cmax; AUC=Area under concentration vs. time
curve; t ½ =Terminal plasma half-life; C24h =Plasma concentration at 24 hours
post-dose
*Median (min-max) values |
In patients, mean peak and trough plasma concentrations
were 2.9 μg/mL (±1.55), (n=219) and 0.2 μg/mL (±0.22), (n=204),
respectively, after 3 to 5 days of KETEK 800 mg once daily. Steady-state plasma
concentrations are reached within 2 to 3 days of once daily dosing with KETEK
800 mg.
Absorption
Following oral administration, telithromycin reached
maximal concentration at about 1 hour (0.5 – 4 hours). KETEK has an absolute
bioavailability of 57% in both young and elderly subjects.
The rate and extent of absorption are unaffected by food
intake, thus KETEK tablets can be given without regard to food.
Distribution
Total in vitro protein binding is approximately 60% to
70% and is primarily due to human serum albumin.
Protein binding is not modified in elderly subjects or in
patients with hepatic impairment.
The volume of distribution of telithromycin after
intravenous infusion is 2.9 L/kg.
Telithromycin concentrations in bronchial mucosa,
epithelial lining fluid, and alveolar macrophages after 800 mg once daily dosing
for 5 days in patients are displayed in Table 5.
Table 5
|
Hours postdose |
Mean concentration (μg/mL) |
Tissue/ Plasma Ratio |
Tissue or fluid |
Plasma |
Bronchial mucosa |
2 |
3.88* |
1.86 |
2.11 |
12 |
1.41* |
0.23 |
6.33 |
24 |
0.78* |
0.08 |
12.11 |
Epithelial lining fluid |
2 |
14.89 |
1.86 |
8.57 |
12 |
3.27 |
0.23 |
13.8 |
24 |
0.84 |
0.08 |
14.41 |
Alveolar macrophages |
2 |
65 |
1.07 |
55 |
8 |
100 |
0.605 |
180 |
24 |
41 |
0.073 |
540 |
*Units in mg/kg |
Metabolism
In total, approximately 70% of the telithromycin dose is
metabolized. In plasma, the main circulating compound after administration of
an 800-mg radio-labeled dose was parent compound, representing 56.7% of the
total radioactivity. The main metabolite represented 12.6% of the AUC of
telithromycin. Three other plasma metabolites were quantified, each
representing 3% or less of the AUC of telithromycin.
It is estimated that approximately 50% of its metabolism
is mediated by CYP3A4 and the remaining 50% is CYP -independent.
Excretion
The systemically available telithromycin is eliminated by
multiple pathways as follows: 7% of the dose is excreted unchanged in feces by biliary
and/or intestinal secretion; 13% of the dose is excreted unchanged in urine by
renal excretion; and 37% of the dose is metabolized by the liver. Following
oral dosing, the mean terminal elimination half-life of telithromycin is 10
hours.
Specific Populations
Gender: There was no significant difference
between males and females in mean AUC, Cmax, and elimination half-life in two
studies; one in 18 healthy young volunteers (18 to 40 years of age) and the other
in 14 healthy elderly volunteers (65 to 92 years of age), given single and
multiple once daily doses of 800 mg of KETEK.
Hepatic impairment: Telithromycin is excreted via
the liver and kidney. [see DOSAGE AND ADMINISTRATION]
In a single-dose study (800 mg) in 12 patients and a
multiple-dose study (800 mg) in 13 patients with mild to severe hepatic
insufficiency (Child Pugh Class A, B and C), the Cmax, AUC and t ½ of telithromycin
were similar to those obtained in age- and sex-matched healthy subjects. In
both studies, an increase in renal elimination was observed in hepatically
impaired patients indicating that this pathway may compensate for some of the
decrease in metabolic clearance.
Renal impairment: Telithromycin is excreted via
the liver and kidney. [see DOSAGE AND ADMINISTRATION]
In a multiple-dose study, 36 subjects with varying
degrees of renal impairment received 400 mg, 600 mg, or 800 mg KETEK once daily
for 5 days. There was a 1.4-fold increase in Cmax,ss and a 1.9-fold increase in
AUC (0–24)ss at 800 mg multiple doses in the severely renally impaired group
(CLCR less than 30 mL/min) compared to healthy volunteers. Renal
excretion may serve as a compensatory elimination pathway for telithromycin in
situations where metabolic clearance is impaired. Patients with severe renal impairment
are prone to conditions that may impair their metabolic clearance.
In a single-dose study in patients with end-stage renal
failure on hemodialysis (n=10), the mean Cmax and AUC values were similar to
normal healthy subjects when KETEK was administered 2 hours postdialysis. However,
the effect of dialysis on removing telithromycin from the body has not been
studied.
Combined Renal and Hepatic Impairment: The effects
of co-administration of ketoconazole in 12 subjects (age 60 years and older),
with impaired renal function were studied (CLCR = 24 to 80 mL/min). In
this study, when severe renal insufficiency (CLCR less than 30
mL/min, n=2) and concomitant impairment of CYP3A4 metabolism pathway were
present, telithromycin exposure (AUC0-24) was increased by approximately 4- to
5-fold compared with the exposure in healthy subjects with normal renal
function receiving telithromycin alone. In the presence of severe renal
impairment (CLCR less than 30 mL/min), with coexisting hepatic
impairment, a reduced dosage of KETEK is recommended. [see DOSAGE AND
ADMINISTRATION]
Geriatric: Pharmacokinetic data show that there is
an increase of 1.4-fold in exposure (AUC) in 20 patients 65 years and older
with community acquired pneumonia in a Phase 3 study, and a 2.0-fold increase
in exposure (AUC) in 14 subjects 65 years and older as compared with subjects
less than 65 years of age in a Phase I study. No dosage adjustment is required
based on age alone. [see Use In Specific Populations]
Drug Interactions
CYP3A4 Inducers
Rifampin
During concomitant administration of rifampin and KETEK
in repeated doses, C and AUC of telithromycin were decreased by 79%, and 86%,
respectively. [see DRUG INTERACTIONS]
CYP3A4 Inhibitors
Itraconazole: A multiple-dose interaction study
with itraconazole showed that C of telithromycin was increased by 22% and AUC
by 54%. [see DRUG INTERACTIONS]
Ketoconazole: A multiple-dose interaction study
with ketoconazole showed that C of telithromycin was increased by 51% and AUC
by 95%. [see DRUG INTERACTIONS]
Grapefruit juice: When telithromycin was given
with 240 mL of grapefruit juice after an overnight fast to healthy subjects,
the pharmacokinetics of telithromycin were not affected.
CYP3A4 Substrates
Simvastatin: When simvastatin was co-administered
with telithromycin, there was a 5.3-fold increase in simvastatin Cmax, an
8.9-fold increase in simvastatin AUC, a 15-fold increase in the simvastatin
active metabolite Cmax, and a 12-fold increase in the simvastatin active
metabolite AUC. In another study, when simvastatin and telithromycin were
administered 12 hours apart, there was a 3.4-fold increase in simvastatin Cmax,
a 4.0-fold increase in simvastatin AUC, a 3.2-fold increase in the active
metabolite Cmax, and a 4.3-fold increase in the active metabolite AUC. [see
WARNINGS AND PRECAUTIONS; DRUG INTERACTIONS]
Midazolam: Concomitant administration of
telithromycin with intravenous or oral midazolam resulted in 2- and 6-fold
increases, respectively, in the AUC of midazolam due to inhibition of
CYP3A4-dependent metabolism of midazolam. [see DRUG INTERACTIONS]
Other Drugs
Digoxin
The plasma peak and trough levels of digoxin were
increased by 73% and 21%, respectively, in healthy volunteers when
co-administered with KETEK. However, trough plasma concentrations of digoxin (when
equilibrium between plasma and tissue concentrations has been achieved) ranged
from 0.74 to 2.17 ng/mL. There were no significant changes in ECG parameters
and no signs of digoxin toxicity. [see DRUG INTERACTIONS]
Theophylline
When theophylline was co-administered with repeated doses
of KETEK, there was an increase of approximately 16% and 17% on the
steady-state Cmax and AUC of theophylline. [see DRUG INTERACTIONS]
Sotalol
KETEK has been shown to decrease the Cmax and AUC of
sotalol by 34% and 20%, respectively, due to decreased absorption.
Oral Contraceptives
When oral contraceptives containing ethinyl estradiol and
levonorgestrel were co-administered with KETEK, the steady-state AUC of ethinyl
estradiol did not change and the steady-state AUC of levonorgestrel was
increased by 50%. The pharmacokinetic/pharmacodynamic study showed that telithromycin
did not interfere with the antiovulatory effect of oral contraceptives
containing ethinyl estradiol and levonorgestrel.
Metoprolol
When metoprolol was co-administered with KETEK, there was
an increase of approximately 38% on the Cmax and AUC of metoprolol; however,
there was no effect on the elimination half-life of metoprolol. Telithromycin
exposure is not modified with concomitant single-dose administration of metoprolol.
[see DRUG INTERACTIONS]
Ranitidine/Antacid
There was no clinically relevant pharmacokinetic
interaction of ranitidine or antacids containing aluminum and magnesium
hydroxide on telithromycin.
Paroxetine
There was no pharmacokinetic effect on paroxetine when
KETEK was co-administered.
Cisapride
Steady state peak plasma concentrations of cisapride (an
agent with the potential to increase QT interval) were increased by 95% when
co-administered with repeated doses of telithromycin, resulting in significant
increases in QTc. [see CONTRAINDICATIONS]
OATP1B1 and OATP1B3
In vitro studies using a model compound have shown that
telithromycin may act as an inhibitor for the hepatic uptake transporters
OATP1B1 and OATP1B3. Although the clinical relevance of this finding is unknown,
it is possible that concomitant administration of KETEK with drugs that are
substrates of OATP family members could result in increased plasma
concentrations of the co-administered drug.
Microbiology
Mechanism Of Action
Telithromycin belongs to the ketolide class of
antibacterials and is structurally related to the macrolides. Telithromycin
blocks protein synthesis by binding to domains II and V of 23S rRNA of the 50S
ribosomal subunit. Telithromycin may also inhibit the assembly of nascent
ribosomal units.
Telithromycin concentrates in phagocytes where it
exhibits activity against intracellular respiratory pathogens. In vitro,
telithromycin has been shown to demonstrate concentration-dependent
bactericidal activity against isolates of Streptococcus pneumoniae (including
multi-drug resistant isolates [MDRSP2]).
Mechanism Of Resistance
Production of Erm dimethyltransferases may cause
telithromycin resistance in some Gram-positive bacteria.
List Of Microorganisms
Telithromycin has been shown to be active against most
strains of the following microorganisms, both in vitro and in clinical settings
[see INDICATIONS AND USAGE].
Gram-Positive Bacteria
Streptococcus pneumoniae (including MDRSP)
Gram-Negative Bacteria
Haemophilus influenzae
Moraxella catarrhalis
Other Microorganisms
Chlamydophila pneumoniae
Mycoplasma pneumonia
The following in vitro data are available, but their
clinical significance is unknown.
At least 90% of the following microorganisms exhibit in
vitro minimum inhibitory concentrations (MICs) less than or equal to the
susceptible breakpoint for telithromycin. However, the safety and efficacy of
KETEK in treating clinical infections due to these microorganisms have not been
established in adequate and well-controlled clinical trials.
Gram-Positive Bacteria
Staphylococcus aureus (methicillin and
erythromycin susceptible isolates only)
Streptococcus pyogenes (erythromycin susceptible
isolates only)
Beta-hemolytic streptococci (Lancefield groups C
and G)
Other Microorganisms
Legionella pneumophila
Susceptibility Test Methods
When available, the clinical microbiology laboratory
should provide cumulative results of in vitro susceptibility test results for antimicrobial
drugs used in local hospitals and practice areas to the physician as periodic
reports that describe the susceptibility profile of nosocomial and
communityacquired pathogens. These reports should aid the physician in
selecting the most effective antimicrobial.
Dilution Techniques
Quantitative methods are used to determine antimicrobial
minimum inhibitory concentrations (MICs). These MICs provide estimates of the
susceptibility of bacteria to antibacterial compounds. The MICs should be
determined using a standardized procedure. Standardized procedures are based on
dilution methods (broth or agar dilution)1,3 or equivalent with
standardized inoculum and concentrations of telithromycin powder. The MIC
values should be interpreted according to criteria provided in Table 6.
Diffusion Techniques
Quantitative methods that require measurement of zone
diameters also provide reproducible estimates of the susceptibility of bacteria
to antibacterials. One such standardized procedure2,3 requires the
use of standardized inoculum concentrations. This procedure uses paper disks
impregnated with 15 μg telithromycin to test the susceptibility of
microorganisms to telithromycin. Disc diffusion zone sizes should be
interpreted according to criteria in Table 6.
Table 6 : Susceptibility Test Result Interpretive
Criteria for Telithromycin
Pathogen |
Minimum Inhibitory Concentrations (μg/mL) |
Disk Diffusion Zone Diameter (mm) |
S |
I |
R |
S |
I |
R |
Streptococcus pneumoniae |
≤ 1 |
2 |
≥ 4 |
≥ 19 |
16-18 |
≤ 15 |
Haemophilus influenzae |
≤ 4 |
8 |
≥ 16 |
≥ 15 |
12-14 |
≤ 11 |
A report of “Susceptible” indicates that the
antimicrobial is likely to inhibit growth of the pathogen if the antibacterial
compound in the blood reaches the concentrations usually achievable. 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 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 in the blood reaches the
concentrations usually achievable; other therapy should be selected.
Quality Control
Standardized susceptibility test procedures require the
use of quality control microorganisms to determine the performance of the test
procedures1,2,3. Standard telithromycin powder should provide the
MIC ranges for the quality control organisms in Table 7. For the disk diffusion
technique, the 15-μg telithromycin disk should provide the zone diameter
ranges for the quality control organisms in Table 7.
Table 7 : Acceptable Quality Control Ranges for
Telithromycin
Quality Control Organism |
Minimum Inhibitory Concentrations (μg/mL) |
Disk Diffusion (zone diameter in mm) |
Haemophilus influenzae ATCC 49247 |
1.0-4.0 |
17-23 |
Streptococcus pneumoniae ATCC 49619 |
0.004-0.03 |
27-33 |
ATCC = American Type Culture Collection |
Animal Toxicology And/Or Pharmacology
Repeated dose toxicity studies of 1, 3, and 6 months'
duration with telithromycin conducted in rat, dog and monkey showed that the
liver was the principal target for toxicity with elevations of liver enzymes and
histological evidence of damage. There was evidence of reversibility after
cessation of treatment. Plasma exposures based on free fraction of drug at the
no observed adverse effect levels ranged from 1 to 10 times the expected clinical
exposure.
Phospholipidosis (intracellular phospholipid
accumulation) affecting a number of organs and tissues (e.g., liver, kidney,
lung, thymus, spleen, gall bladder, mesenteric lymph nodes, GI-tract) has been observed
with the administration of telithromycin in rats at repeated doses of 150
mg/kg/day ( 2Ã the human dose on a body surface area basis) or more for 1
month, and 50 mg/kg/day (0.6Ã the human dose) or more for 3–6 months.
Similarly, phospholipidosis has been observed in dogs with telithromycin at repeated
doses of 150 mg/kg/day (6Ã the human dose on a body surface area basis) or more
for 1 month and 50 mg/kg/day (2Ã the human dose) or more for 3 months. The
significance of these findings for humans is unknown.
Pharmacology/toxicology studies showed an effect both in
prolonging QTc interval in dogs in vivo and in vitro action potential duration
(APD) in rabbit Purkinje fibers. These effects were observed at concentrations
of free drug at least 8.8 (in dogs) times those circulating in clinical use. In
vitro electrophysiological studies (hERG assays) suggested an inhibition of the
rapid activating component of the delayed rectifier potassium current (IKr)
as an underlying mechanism.
Clinical Studies
KETEK was studied in four randomized, double-blind,
controlled studies and four open-label studies for the treatment of
community-acquired pneumonia (CAP). Patients with mild to moderate CAP who were
considered appropriate for oral outpatient treatment were enrolled in these
trials. Patients with severe pneumonia were excluded based on any one of the
following: ICU admission, need for parenteral antibacterials, respiratory rate
greater than 30 per minute, hypotension, altered mental status, less than 90%
oxygen saturation by pulse oximetry, or white blood cell count less than 4000
per mm³. There were 2016 clinically evaluable patients in the KETEK group.
Table 8: CAP: Clinical Cure Rate at Post-Therapy
Follow-Up (17–24 days)
Controlled Studies |
Patients (n) |
Clinical Cure Rate |
KETEK |
Comparator |
KETEK |
Comparator |
KETEK vs. clarithromycin 500 mg twice a day for 10 days |
162 |
156 |
88.3% |
88.5% |
KETEK vs. trovafloxacin* 200 mg daily for 7 to 10 days |
80 |
86 |
90.0% |
94.2% |
KETEK vs. amoxicillin 1000 mg three times a day for 10 days |
149 |
152 |
94.6% |
90.1% |
KETEK for 7 days vs. clarithromycin 500 mg twice a day for 10 days |
161 |
146 |
88.8% |
91.8% |
*This study was stopped prematurely after trovafloxacin
was restricted for use in hospitalized patients with severe infection. |
Clinical cure rates by pathogen from the four CAP
controlled clinical trials in microbiologically evaluable patients given KETEK
for 7–10 days or a comparator are displayed in Table 9.
Table 9: CAP: Clinical Cure Rate by Pathogen at Pos
t-Therapy Follow-Up (17–24 days )
Pathogen |
KETEK |
Comparator |
Streptococcus pneumoniae |
73/78 (93.6%) |
63/70 (90%) |
Haemophilus influenzae |
39/47 (83%) |
42/44 (95.5%) |
Moraxella catarrhalis |
12/14 (85.7%) |
7/9 (77.8%) |
Chlamydophila pneumoniae |
23/25 (92%) |
18/19 (94.7%) |
Mycoplasma pneumoniae |
22/23 (95.7%) |
20/22 (90.9%) |
Clinical cure rates for patients with CAP due to Streptococcus
pneumoniae were determined from patients in controlled and uncontrolled
trials. Of 333 evaluable patients with CAP due to Streptococcus pneumoniae,
312 (93.7%) achieved clinical success. Blood cultures were obtained in all
patients participating in the clinical trials of mild to moderate
community-acquired pneumonia. In a limited number of outpatients with
incidental pneumococcal bacteremia treated with KETEK, a clinical cure rate of
88% (67/76) was observed. KETEK is not indicated for the treatment of severe
community-acquired pneumonia or suspected pneumococcal bacteremia.
Clinical cure rates for patients with CAP due to multi-drug
resistant Streptococcus pneumonia (MDRSP3) were determined
from patients in controlled and uncontrolled trials. Of 36 evaluable patients with
CAP due to MDRSP, 33 (91.7%) achieved clinical success.
Table 10: Clinical Cure Rate for 36 Evaluable KETEK-Treated
Patients with MDRSP in Studies of Community-Acquired Pneumonia
Screening Susceptibility |
Clinical Success in Evaluable MDRSP Patients |
n/N* |
% |
Penicillin-resistant |
20/23 |
86.9 |
2nd generation cephalosporin-resistant |
20/22 |
90.9 |
Macrolide-resistant |
25/28 |
89.3 |
Trimethoprim/ sulfamethoxazole-resistant |
24/27 |
88.9 |
Tetracycline-resistant† |
11/13 |
84.6 |
*n = the number of patients successfully treated; N = the
number with resistance to the listed drug of the 36 evaluable patients with CAP
due to MDRSP.
†Includes isolates tested for resistance to either tetracycline or doxycycline. |
REFERENCES
2MDRSP=Multi-drug resistant Streptococcus
pneumoniae includes isolates known as PRSP (penicillin-resistant Streptococcus
pneumoniae), and are isolates resistant to two or more of the following
antimicrobials: penicillin, 2 generation cephalosporins (e.g., cefuroxime),
macrolides, tetracyclines, and trimethoprim/sulfamethoxazole.
3MDRSP: Multi-drug resistant Streptococcus
pneumoniae includes isolates known as PRSP (penicillin-resistant Streptococcus
pneumoniae), and are isolates resistant to two or more of the following
antibacterials: penicillin, 2 generation cephalosporins, e.g., cefuroxime,
macrolides, tetracyclines and trimethoprim/sulfamethoxazole.
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19087, USA, 2012.
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