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All about: Ketek

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Generic Name: telithromycin
Dosage Form: Tablets

To reduce the development of drug-resistant bacteria and maintain the effectiveness of Ketek and other antibacterial drugs, Ketek should be used only to treat infections that are proven or strongly suspected to be caused by bacteria.

Ketek Description

Ketek® tablets contain telithromycin, a semisynthetic antibacterial in the ketolide class for oral administration. Chemically, telithromycin is designated as Erythromycin, 3 - de[(2,6 - dideoxy - 3 - C - methyl - 3 - O - methyl - α - L - ribo - hexopyranosyl)oxy] - 11,12 - dideoxy - 6 - O - methyl - 3 - oxo - 12,11 - [oxycarbonyl[[4 - [4 - (3 - pyridinyl) - 1H - imidazol - 1 - yl]butyl]imino]] - .

Telithromycin, a ketolide, differs chemically from the macrolide group of antibacterials by the lack of α-L-cladinose at position 3 of the erythronolide A ring, resulting in a 3-keto function. It is further characterized by a C11–12 carbamate substituted by an imidazolyl and pyridyl ring through a butyl chain. Its empirical formula is C43H65N5O10 and its molecular weight is 812.03. Telithromycin is a white to off-white crystalline powder. The following represents the chemical structure of telithromycin.

Ketek tablets are available as light-orange, oval, film-coated tablets, each containing 400 mg or 300 mg of telithromycin, and the following inactive ingredients: croscarmellose sodium, hypromellose, magnesium stearate, microcrystalline cellulose, polyethylene glycol, povidone, red ferric oxide, talc, titanium dioxide, and yellow ferric oxide.

Ketek - Clinical Pharmacology

Pharmacokinetics

Absorption

Following oral administration, telithromycin reached maximal concentration at about 1 hour (0.5 – 4 hours).

It 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.

In healthy adult subjects, peak plasma telithromycin concentrations of approximately 2 µg/mL are attained at a median of 1 hour after an 800-mg oral dose.

Steady-state plasma concentrations are reached within 2 to 3 days of once daily dosing with telithromycin 800 mg.

Following oral dosing, the mean terminal elimination half-life of telithromycin is 10 hours.

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 1.

Table 1
Mean (SD)
Parameter Single dose (n=18) Multiple dose (n=18)
*
Median (min-max) values
SD=Standard deviation
Cmax=Maximum plasma concentration
Tmax=Time to Cmax
AUC=Area under concentration vs. time curve
t½=Terminal plasma half-life
C24h=Plasma concentration at 24 hours post-dose
Cmax (µg/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 t½ (h) 7.16 (1.3) 9.81 (1.9)
C24h (µg/mL) 0.03 (0.013) 0.07 (0.051)

In a patient population, 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.

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 and 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 2.

Table 2
Mean concentration (µg/mL)
Hours post-dose Tissue or fluid Plasma Tissue/Plasma Ratio
*
Units in mg/kg
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

Telithromycin concentration in white blood cells exceeds the concentration in plasma and is eliminated more slowly from white blood cells than from plasma. Mean white blood cell concentrations of telithromycin peaked at 72.1 µg/mL at 6 hours, and remained at 14.1 µg/mL 24 hours after 5 days of repeated dosing of 600 mg once daily. After 10 days, repeated dosing of 600 mg once daily, white blood cell concentrations remained at 8.9 µg/mL 48 hours after the last dose.

Metabolism

In total, metabolism accounts for approximately 70% of the dose. In plasma, the main circulating compound after administration of an 800-mg radiolabeled 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 CYP 450 3A4 and the remaining 50% is CYP 450-independent.

Elimination

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.

Special 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 insufficiency

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 t1/2 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. No dosage adjustment is recommended due to hepatic impairment. (See PRECAUTIONS, General and DOSAGE AND ADMINISTRATION.)

Renal insufficiency

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<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. Therefore, in the presence of severe renal impairment (CLCR<30 mL/min), a reduced dosage of Ketek is recommended. (See DOSAGE AND ADMINISTRATION.)

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 post-dialysis. However, the effect of dialysis on removing telithromycin from the body has not been studied.

Multiple insufficiency

The effects of co-administration of ketoconazole in 12 subjects (age ≥60 years), with impaired renal function were studied (CLCR=24 to 80 mL/min). In this study, when severe renal insufficiency (CLCR<30 mL/min, n=2) and concomitant impairment of CYP 3A4 metabolism pathway were present, telithromycin exposure (AUC (0–24)) 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<30 mL/min), with coexisting hepatic impairment, a reduced dosage of Ketek is recommended. (See PRECAUTIONS, General and DOSAGE AND ADMINISTRATION.)

Geriatric

Pharmacokinetic data show that there is an increase of 1.4-fold in exposure (AUC) in 20 patients ≥65 years of age with community acquired pneumonia in a Phase III study, and a 2.0-fold increase in exposure (AUC) in 14 subjects ≥65 years of age as compared with subjects less than 65 years of age in a Phase I study. No dosage adjustment is required based on age alone.

Drug-drug interactions

Studies were performed to evaluate the effect of CYP 3A4 inhibitors on telithromycin and the effect of telithromycin on drugs that are substrates of CYP 3A4 and CYP 2D6. In addition, drug interaction studies were conducted with several other concomitantly prescribed drugs.

CYP 3A4 inhibitors:

Itraconazole: A multiple-dose interaction study with itraconazole showed that Cmax of telithromycin was increased by 22% and AUC by 54%.

Ketoconazole: A multiple-dose interaction study with ketoconazole showed that Cmax of telithromycin was increased by 51% and AUC by 95%.

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.

CYP 3A4 substrates:

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.)

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. (See PRECAUTIONS.)

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 PRECAUTIONS.)

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 CYP 3A4-dependent metabolism of midazolam. (See PRECAUTIONS.)

CYP 2D6 substrates:

Paroxetine: There was no pharmacokinetic effect on paroxetine when telithromycin was co-administered.

Metoprolol: When metoprolol was co-administered with telithromycin, 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 PRECAUTIONS, Drug interactions.)

Other drug interactions

Digoxin: The plasma peak and trough levels of digoxin were increased by 73% and 21%, respectively, in healthy volunteers when co-administered with telithromycin. 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 PRECAUTIONS.)

Theophylline: When theophylline was co-administered with repeated doses of telithromycin, there was an increase of approximately 16% and 17% on the steady-state Cmax and AUC of theophylline. Co-administration of theophylline may worsen gastrointestinal side effects such as nausea and vomiting, especially in female patients. It is recommended that telithromycin should be taken with theophylline 1 hour apart to decrease the likelihood of gastrointestinal side effects.

Sotalol: Telithromycin has been shown to decrease the Cmax and AUC of sotalol by 34% and 20%, respectively, due to decreased absorption.

Warfarin: When co-administered with telithromycin in healthy subjects, there were no pharmacodynamic or pharmacokinetic effects on racemic warfarin.

Oral contraceptives: When oral contraceptives containing ethinyl estradiol and levonorgestrel were co-administered with telithromycin, 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.

Ranitidine, antacid: There was no clinically relevant pharmacokinetic interaction of ranitidine or antacids containing aluminum and magnesium hydroxide on telithromycin.

Rifampin: During concomitant administration of rifampin and Ketek in repeated doses, Cmax and AUC of telithromycin were decreased by 79%, and 86%, respectively. (See PRECAUTIONS, Drug Interactions.)

Microbiology

Telithromycin belongs to the ketolide class of antibacterials and is structurally related to the macrolide family of antibiotics. 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 [MDRSP*]).

*MDRSP=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, 2nd generation cephalosporins (e.g., cefuroxime), macrolides, tetracyclines, and trimethoprim/sulfamethoxazole.

Mechanism of action

Telithromycin blocks protein synthesis by binding to domains II and V of 23S rRNA of the 50S ribosomal subunit. By binding at domain II, telithromycin retains activity against gram-positive cocci (e.g., Streptococcus pneumoniae) in the presence of resistance mediated by methylases (erm genes) that alter the domain V binding site of telithromycin. Telithromycin may also inhibit the assembly of nascent ribosomal units.

Mechanism of resistance

Staphylococcus aureus and Streptococcus pyogenes with the constitutive macrolide-lincosamide-streptogramin B (cMLSB) phenotype are resistant to telithromycin.

Mutants of Streptococcus pneumoniae derived in the laboratory by serial passage in subinhibitory concentrations of telithromycin have demonstrated resistance based on L22 riboprotein mutations (telithromycin MICs are elevated but still within the susceptible range), one of two reported mutations affecting the L4 riboprotein, and production of K-peptide. The clinical significance of these laboratory mutants is not known.

Cross resistance

Telithromycin does not induce resistance through methylase gene expression in erythromycin-inducibly resistant bacteria, a function of its 3-keto moiety. Telithromycin has not been shown to induce resistance to itself.

List of Microorganisms

Telithromycin has been shown to be active against most strains of the following microorganisms, both in vitro and in clinical settings as described in the INDICATIONS AND USAGE section.

Aerobic gram-positive microorganisms

  • Staphylococcus aureus (methicillin and erythromycin susceptible isolates only)
  • Streptococcus pneumoniae (including multi-drug resistant isolates [MDRSP*])

*MDRSP=Multi-drug resistant Streptococcus pneumoniae includes isolates known as PRSP (penicillin-resistant S. pneumoniae), and are isolates resistant to two or more of the following antimicrobials: penicillin, 2nd generation cephalosporins (e.g., cefuroxime), macrolides, tetracyclines, and trimethoprim/sulfamethoxazole.

Aerobic gram-negative microorganisms

  • Haemophilus influenzae
  • Moraxella catarrhalis

Other microorganisms

  • Chlamydophila (Chlamydia) pneumoniae
  • Mycoplasma pneumoniae

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 telithromycin in treating clinical infections due to these microorganisms have not been established in adequate and well-controlled clinical trials.

Aerobic gram-positive microorganisms

  • Streptococcus pyogenes (erythromycin susceptible isolates only)
  • Streptococci (Lancefield groups C and G)
  • Viridans group streptococci

Anaerobic bacteria

  • Prevotella bivia
  • Prevotella intermedia
  • Peptostreptococcus spp.

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 community-acquired 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 3.

Diffusion techniques

Quantitative methods that require measurement of zone diameters also provide reproducible estimates of the susceptibility of bacteria to antibiotics. 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 3.

Table 3. Susceptibility Test Result Interpretive Criteria for Telithromycin
Minimal Inhibitory Concentrations
(µg/mL)
Disk Diffusion
(zone diameters in mm)
Pathogen S                I                R* S                I                R*
*
The current absence of data on resistant isolates precludes defining any category other than "Susceptible". If strains yield MIC results other than susceptible, they should be submitted to a reference laboratory for further testing.
Staphylococcus aureus ≤0.25 ≥22
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 4. For the disk diffusion technique, the 15-µg telithromycin disk should provide the zone diameter ranges for the quality control organisms in Table 4.

Table 4. Acceptable Quality Control Ranges for Telithromycin
QC Strain Minimum Inhibitory Concentrations
(µg/mL)
Disk Diffusion
(Zone diameter in mm)
ATCC = American Type Culture Collection
Staphylococcus aureus
ATCC® 29213
0.06–0.25 Not Applicable
Staphylococcus aureus
ATCC 25923
Not Applicable 24–30
Streptococcus pneumoniae
ATCC 49619
0.004–0.03 27–33
Haemophilus influenzae
ATCC 49247
1.0–4.0 17–23

Indications and Usage for Ketek

Ketek tablets are indicated for the treatment of infections caused by susceptible strains of the designated microorganisms in the conditions listed below for patients 18 years old and above.

Acute bacterial exacerbation of chronic bronchitis due to Streptococcus pneumoniae, Haemophilus influenzae, or Moraxella catarrhalis.

Acute bacterial sinusitis due to Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, or Staphylococcus aureus.

Community-acquired pneumonia (of mild to moderate severity) due to Streptococcus pneumoniae, (including multi-drug resistant isolates [MDRSP*]), Haemophilus influenzae, Moraxella catarrhalis, Chlamydophila pneumoniae, or Mycoplasma pneumoniae.

*MDRSP, 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 antibiotics: penicillin, 2nd generation cephalosporins, e.g., cefuroxime, macrolides, tetracyclines and trimethoprim/sulfamethoxazole.

To reduce the development of drug-resistant bacteria and maintain the effectiveness of Ketek and other antibacterial drugs, Ketek should be used only to treat infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.

Contraindications

Ketek is contraindicated in patients with a history of hypersensitivity to telithromycin and/or any components of Ketek tablets, or any macrolide antibiotic.

Concomitant administration of Ketek with cisapride or pimozide is contraindicated. (See CLINICAL PHARMACOLOGY, Drug-drug Interactions and PRECAUTIONS.)

Warnings

Pseudomembranous colitis has been reported with nearly all antibacterial agents, including telithromycin, and may range in severity from mild to life-threatening. Therefore, it is important to consider this diagnosis in patients who present with diarrhea subsequent to the administration of any antibacterial agents.

Treatment with antibacterial agents alters the flora of the colon and may permit overgrowth of clostridia. Studies indicate that toxin-producing strains of Clostridium difficile are the primary cause of "antibiotic-associated colitis".

After the diagnosis of pseudomembranous colitis has been established, therapeutic measures should be initiated. Mild cases of pseudomembranous colitis usually respond to drug discontinuation alone. In moderate to severe cases, consideration should be given to management with fluids and electrolytes, protein supplementation, and treatment with an antibacterial drug clinically effective against C. difficile colitis. (See ADVERSE REACTIONS.)

Telithromycin has the potential to prolong the QTc interval of the electrocardiogram in some patients. QTc prolongation may lead to an increased risk for ventricular arrhythmias, including torsades de pointes. Thus, telithromycin should be avoided in patients with congenital prolongation of the QTc interval, and in patients with ongoing proarrhythmic conditions such as uncorrected hypokalemia or hypomagnesemia, clinically significant bradycardia, and in patients receiving Class IA (e.g., quinidine and procainamide) or Class III (e.g., dofetilide) antiarrhythmic agents.

No cardiovascular morbidity or mortality attributable to QTc prolongation occurred with telithromycin treatment in 4780 patients in clinical efficacy trials, including 204 patients having a prolonged QTc at baseline.

Exacerbations of myasthenia gravis have been reported in patients with myasthenia gravis treated with telithromycin. This has sometimes occurred within a few hours after intake of the first dose of telithromycin. Reports have included life-threatening acute respiratory failure with a rapid onset in patients with myasthenia gravis treated for respiratory tract infections with telithromycin. Telithromycin is not recommended in patients with myasthenia gravis unless no other therapeutic alternatives are available. If other therapeutic alternatives are not available, patients with myasthenia gravis taking telithromycin must be closely monitored. Patients must be advised that if they experience exacerbation of their symptoms, they should discontinue treatment of Ketek and immediately seek medical attention. Supportive measures should be instituted as medically necessary.

Precautions

General

Prescribing Ketek in the absence of a proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.

Ketek may cause visual disturbances particularly in slowing the ability to accommodate and the ability to release accommodation. Visual disturbances included blurred vision, difficulty focusing, and diplopia. Most events were mild to moderate; however, severe cases have been reported.

There have been post-marketing adverse event reports of syncope usually associated with vagal syndrome.

Patients should be cautioned about the potential effects of these visual disturbances and syncope on driving a vehicle, operating machinery or engaging in other potentially hazardous activities. (See ADVERSE REACTIONS, CLINICAL STUDIES.)

Hepatic dysfunction, including increased liver enzymes and hepatitis, with or without jaundice, has been reported with the use of Ketek. These events were generally reversible. Caution should be used in patients with a previous history of hepatitis/jaundice associated with the use of Ketek. (See ADVERSE REACTIONS, Liver and biliary system.)

Telithromycin is principally excreted via the liver and kidney. Telithromycin may be administered without dosage adjustment in the presence of hepatic impairment. In the presence of severe renal impairment (CLCR<30 mL/min), a reduced dosage of Ketek is recommended. (See DOSAGE AND ADMINISTRATION.)

Information For Patients

The following information and instructions should be communicated to the patient.

Ketek may cause problems with vision particularly when looking quickly between objects close by and objects far away. These events include blurred vision, difficulty focusing, and objects looking doubled. Most events were mild to moderate; however, severe cases have been reported. Problems with vision were reported as having occurred after any dose during treatment, but most occurred following the first or second dose. These problems lasted several hours and in some patients came back with the next dose. (See PRECAUTIONS, General and ADVERSE REACTIONS.)

If visual difficulties occur:

  • patients should avoid driving a motor vehicle, operating heavy machinery, or engaging in otherwise hazardous activities.
  • avoiding quick changes in viewing between objects in the distance and objects nearby may help to decrease the effects of these visual difficulties.
  • patients should contact their physician if these visual difficulties interfere with their daily activities.

Patients should be aware of the possibility of experiencing syncope (fainting), and its impact on the ability to drive, especially if they are experiencing vagal symptoms (severe nausea, vomiting, and/or lightheadedness).

If patients experience these symptoms, they should avoid driving a motor vehicle, operating heavy machinery, or engaging in otherwise hazardous activities.

Patients should also be advised:

  • that antibacterial drugs including Ketek should only be used to treat bacterial infections. They do not treat viral infections (e.g., the common cold). When Ketek is prescribed to treat a bacterial infection, patients should be told that although it is common to feel better early in the course of therapy, the medication should be taken exactly as directed. Skipping doses or not completing the full course of therapy may (1) decrease the effectiveness of the immediate treatment and (2) increase the likelihood that bacteria will develop resistance and will not be treatable by Ketek or other antibacterial drugs in the future.
  • that Ketek has the potential to produce changes in the electrocardiogram (QTc interval prolongation) and that they should report any fainting occurring during drug treatment.
  • that Ketek should be avoided in patients receiving Class 1A (e.g., quinidine, procainamide) or Class III (e.g., dofetilide) antiarrhythmic agents.
  • to inform their physician of any personal or family history of QTc prolongation or proarrhythmic conditions such as uncorrected hypokalemia, or clinically significant bradycardia.
  • that telithromycin is not recommended in patients with myasthenia gravis. Patients should inform their physician if they have myasthenia gravis.
  • that simvastatin, lovastatin, or atorvastatin should be avoided in patients receiving Ketek. If Ketek is prescribed, therapy with simvastatin, lovastatin, or atorvastatin should be stopped during the course of treatment.
  • that Ketek tablets can be taken with or without food.
  • to inform their physician of any other medications taken concurrently with Ketek, including over-the-counter medications and dietary supplements.

Drug Interactions

Telithromycin is a strong inhibitor of the cytochrome P450 3A4 system. Co-administration of Ketek tablets and a drug primarily metabolized by the cytochrome P450 3A4 enzyme system may result in increased plasma concentration of the drug co-administered with telithromycin that could increase or prolong both the therapeutic and adverse effects. Therefore, appropriate dosage adjustments may be necessary for the drug co-administered with telithromycin.

The use of Ketek is contraindicated with cisapride. (See CONTRAINDICATIONS and CLINICAL PHARMACOLOGY, Drug-drug interactions.)

The use of Ketek is contraindicated with pimozide. Although there are no studies looking at the interaction between Ketek and pimozide, there is a potential risk of increased pimozide plasma levels by inhibition of CYP 3A4 pathways by Ketek as with macrolides. (See CONTRAINDICATIONS.)

In a pharmacokinetic study, simvastatin levels were increased due to CYP 3A4 inhibition by telithromycin. (See CLINICAL PHARMACOLOGY, Other drug interactions.) Similarly, an interaction may occur with lovastatin or atorvastatin, but not with pravastatin or fluvastatin. High levels of HMG-CoA reductase inhibitors increase the risk of myopathy. Use of simvastatin, lovastatin, or atorvastatin concomitantly with Ketek should be avoided. If Ketek is prescribed, therapy with simvastatin, lovastatin, or atorvastatin should be suspended during the course of treatment.

Monitoring of digoxin side effects or serum levels should be considered during concomitant administration of digoxin and Ketek. (See CLINICAL PHARMACOLOGY, Drug-drug interactions.)

Patients should be monitored with concomitant administration of midazolam and dosage adjustment of midazolam should be considered if necessary. Precaution should be used with other benzodiazepines, which are metabolized by CYP 3A4 and undergo a high first-pass effect (e.g., triazolam). (See CLINICAL PHARMACOLOGY, Drug-drug interactions.)

Concomitant treatment of Ketek with rifampin, a CYP 3A4 inducer, should be avoided. Concomitant administration of other CYP 3A4 inducers such as phenytoin, carbamazepine, or phenobarbital is likely to result in subtherapeutic levels of telithromycin and loss of effect. (See CLINICAL PHARMACOLOGY, Other drug interactions.)

In patients treated with metoprolol for heart failure, the increased exposure to metoprolol, a CYP 2D6 substrate, may be of clinical importance. Therefore, co-administration of Ketek and metoprolol in patients with heart failure should be considered with caution. (See CLINICAL PHARMACOLOGY, Drug-drug interactions.)

Spontaneous post-marketing reports suggest that administration of Ketek and oral anticoagulants concomitantly may potentiate the effects of the oral anticoagulants. Consideration should be given to monitoring prothrombin times/INR while patients are receiving Ketek and oral anticoagulants simultaneously.

No specific drug interaction studies have been performed to evaluate the following potential drug-drug interactions with Ketek. However, these drug interactions have been observed with macrolide products.

 

Drugs metabolized by the cytochrome P450 system such as carbamazepine, cyclosporine, tacrolimus, sirolimus, hexobarbital, and phenytoin: elevation of serum levels of these drugs may be observed when co-administered with telithromycin. As a result, increases or prolongation of the therapeutic and/or adverse effects of the concomitant drug may be observed.

 

Ergot alkaloid derivatives (such as ergotamine or dihydroergotamine): acute ergot toxicity characterized by severe peripheral vasospasm and dysesthesia has been reported when macrolide antibiotics were co-administered. Without further data, the co-administration of Ketek and these drugs is not recommended.

Laboratory test interactions

There are no reported laboratory test interactions.

Carcinogenesis, Mutagenesis, Impairment Of Fertility

Long-term studies in animals to determine the carcinogenic potential of Ketek have not been conducted.

Telithromycin showed no evidence of genotoxicity in four tests: gene mutation in bacterial cells, gene mutation in mammalian cells, chromosome aberration in human lymphocytes, and the micronucleus test in the mouse.

No evidence of impaired fertility in the rat was observed at doses estimated to be 0.61 times the human daily dose on a mg/m2 basis. At doses of 1.8–3.6 times the human daily dose, at which signs of parental toxicity were observed, moderate reductions in fertility indices were noted in male and female animals treated with telithromycin.

Pregnancy

Teratogenic Effects

Pregnancy Category C. Telithromycin was not teratogenic in the rat or rabbit. Reproduction studies have been performed in rats and rabbits, with effect on pre-post natal development studied in the rat. At doses estimated to be 1.8 times (900 mg/m2) and 0.49 times (240 mg/m2) the daily human dose of 800 mg (492 mg/m2) in the rat and rabbit, respectively, no evidence of fetal terata was found. At doses higher than the 900 mg/m2 and 240 mg/m2 in rats and rabbits, respectively, maternal toxicity may have resulted in delayed fetal maturation. No adverse effects on prenatal and postnatal development of rat pups were observed at 1.5 times (750 mg/m2/d) the daily human dose.

There are no adequate and well-controlled studies in pregnant women. Telithromycin should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Nursing Mothers

Telithromycin is excreted in breast milk of rats. Telithromycin may also be excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when Ketek is administered to a nursing mother.

Pediatric Use

The safety and effectiveness of Ketek in pediatric patients has not been established.

Geriatric Use

In all Phase III clinical trials (n=4,780), Ketek was administered to 694 patients who were 65 years and older, including 231 patients who were 75 years and older. Efficacy and safety in elderly patients ≥65 years were generally similar to that observed in younger patients; however, greater sensitivity of some older individuals cannot be ruled out. No dosage adjustment is required based on age alone. (See CLINICAL PHARMACOLOGY, Special populations, Geriatric and DOSAGE AND ADMINISTRATION.)

Adverse Reactions

In Phase III clinical trials, 4,780 patients (n=2702 in controlled trials) received daily oral doses of Ketek 800 mg once daily for 5 days or 7 to 10 days. Most adverse events were mild to moderate in severity. In the combined Phase III studies, discontinuation due to treatment-emergent adverse events occurred in 4.4% of Ketek-treated patients and 4.3% of combined comparator-treated patients. Most discontinuations in the Ketek group were due to treatment-emergent adverse events in the gastrointestinal body system, primarily diarrhea (0.9% for Ketek vs. 0.7% for comparators), nausea (0.7% for Ketek vs. 0.5% for comparators).

All and possibly related treatment-emergent adverse events (TEAEs) occurring in controlled clinical studies in ≥2.0% of all patients are included below:

Table 5. All and Possibly Related Treatment-Emergent Adverse Events Reported in Controlled Phase III Clinical Studies (Percent Incidence)
Adverse Event* All TEAEs Possibly-Related TEAEs
Ketek
n=2702
Comparator
n=2139
Ketek
n=2702
Comparator
n=2139
*
Based on a frequency of all and possibly related treatment-emergent adverse events of ≥2% in Ketek or comparator groups.
Includes comparators from all controlled Phase III studies.
Diarrhea 10.8% 8.6% 10.0% 8.0%
Nausea 7.9% 4.6% 7.0% 4.1%
Headache 5.5% 5.8% 2.0% 2.5%
Dizziness (excl. vertigo) 3.7% 2.7% 2.8% 1.5%
Vomiting 2.9% 2.2% 2.4% 1.4%
Loose Stools 2.3% 1.5% 2.1% 1.4%
Dysgeusia 1.6% 3.6% 1.5% 3.6%

The following events judged by investigators to be at least possibly drug related were observed infrequently (≥0.2% and <2%), in Ketek-treated patients in the controlled Phase III studies.

Gastrointestinal system: abdominal distension, dyspepsia, gastrointestinal upset, flatulence, constipation, gastroenteritis, gastritis, anorexia, oral candidiasis, glossitis, stomatitis, watery stools.

Liver and biliary system: abnormal liver function tests: increased transaminases, increased liver enzymes (e.g., ALT, AST) were usually asymptomatic and reversible. ALT elevations above 3 times the upper limit of normal were observed in 1.6%, and 1.7% of patients treated with Ketek and comparators, respectively. Hepatitis, with or without jaundice, occurred in 0.07% of patients treated with Ketek, and was reversible. (See PRECAUTIONS, General.)

Nervous system: dry mouth, somnolence, insomnia, vertigo, increased sweating

Body as a whole: abdominal pain, upper abdominal pain, fatigue

Special senses: Visual adverse events most often included blurred vision, diplopia, or difficulty focusing. Most events were mild to moderate; however, severe cases have been reported. Some patients discontinued therapy due to these adverse events. Visual adverse events were reported as having occurred after any dose during treatment, but most visual adverse events (65%) occurred following the first or second dose. Visual events lasted several hours and recurred upon subsequent dosing in some patients. For patients who continued treatment, some resolved on therapy while others continued to have symptoms until they completed the full course of treatment. (See PRECAUTIONS, General and PRECAUTIONS, Information for patients.)

Females and patients under 40 years old experienced a higher incidence of telithromycin-associated visual adverse events. (See CLINICAL STUDIES.)

Urogenital system: vaginal candidiasis, vaginitis, vaginosis fungal

Skin: rash

Hematologic: increased platelet count

Other possibly related clinically-relevant events occurring in <0.2% of patients treated with Ketek from the controlled Phase III studies included: anxiety, bradycardia, eczema, elevated blood bilirubin, erythema multiforme, flushing, hypotension, increased blood alkaline phosphatase, increased eosinophil count, paresthesia, pruritus, urticaria.

Post-Marketing Adverse Event Reports

In addition to adverse

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