Telithromycin clinical pharmacology

# 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 g/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.
In a patient population, mean peak and trough plasma concentrations were 2.9 g/mL (1.55), (n=219) and 0.2 g/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.
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 g/mL at 6 hours, and remained at 14.1 g/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 g/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 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 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 (024)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 (024)) 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.