01-11-2016, 02:26 PM
Single- and multiple-dose pharmacokinetics of linezolid and co-amoxiclav in healthy human volunteers
1463037648-J.Antimicrob.Chemother.2002Burkhardt707121.pdf (Size: 144.88 KB / Downloads: 7)
In an open, randomized, two-period crossover study the pharmacokinetics of linezolid and
co-amoxiclav were investigated after single- and multiple-dose administration in 12 healthy
volunteers (six females and six males). Linezolid was given in tablets of 600 mg twice a day for
7 days and co-amoxiclav in tablets of 1000 mg (875 + 125 mg) once a day for 7 days. The wash-out
period was 4 weeks between the administration of the two antibacterial agents. Blood and urine
samples were collected on days 1 and 7 before and at different time points up to 24 h after
medication. The concentrations of the antibiotics in serum and urine were measured by
validated high-performance liquid chromatography methods. Linezolid exhibited a mean Cmax of
14.5 ± 4.6 mg/L after Tmax of 47.5 ± 20.1 min on day 1, with a significant increase to 24.0 ± 6.9 mg/L
on day 7 (P < 0.01). The AUDtot (total area under the data) revealed a significant increase from
140.5 ± 28.3 mg·h/L on day 1 to 220.2 ± 42.6 mg·h/L on day 7 (P < 0.01). There were no significant
differences in terminal elimination half-life between days 1 and 7 (9.53 ± 2.87 versus 7.97 ± 3.08 h)
or in total clearance (71.6 ± 17.6 versus 81.5 ± 14.7 ml/min·1.73 m2). Results are in agreement
with the assumption of a limited accumulation of linezolid under the dosage regimen given.
Serum linezolid concentrations in females were always higher than those in males. The
volume of distribution Vss/f differed significantly between females and males (41.6 ± 4.2 versus
52.2 ± 3.3 L/70 kg; P < 0.01). Pharmacokinetic parameters of amoxicillin and clavulanic acid found
in this study were similar to previously published data. No accumulation was found with
co-amoxiclav. No serious adverse event was observed with the study drugs.
Introduction
With a worldwide increasing incidence of infections due to
Gram-positive organisms, which are resistant to standard
therapies, there is a need for new antimicrobial agents with a
new and different mode of action compared with currently
available agents. Linezolid belongs to a new class of antibacterial
agents, the oxazolidinones,1 which are active against
a variety of Gram-positive pathogenic bacteria, including
methicillin-resistant strains of Staphylococcus aureus and
Staphylococcus epidermidis, vancomycin-resistant strains of Enterococcus spp. and penicillin-resistant pneumococci.2
Linezolid acts as a protein synthesis inhibitor.3 It binds to
the 23S ribosomal RNA of the 50S ribosomal subunit on the
bacterial ribosome and prevents formation of an initiation
complex in protein synthesis in a fashion similar to macrolides,
lincosamides, chloramphenicol and streptogramins.
Although linezolid has been the subject of several review
studies,4,5 only two reports on multiple-dose kinetics, in six
male subjects, have been published so far.6,7 In our investigations
on the ecological effects of linezolid versus coamoxiclav
on the normal intestinal microflora,8 we also evaluated the pharmacokinetics of linezolid and co-amoxiclav
after single and multiple oral doses in six male and six female
volunteers.
Materials and methods
Volunteers
Six male and six female healthy Caucasians, between 23 and
39 years old (mean 32.2 ± 4.3 years for females and 31.3 ± 6.1
for males), average body height 166.7 ± 7.1 cm for females and
182.3 ± 4.3 cm for males, average body weight 65.2 ± 4.5 kg
for females and 82.2 ± 8.1 kg for males and average body
surface 1.73 ± 0.06 m2 for females and 2.03 ± 0.11 m2 for
males, participated in the study. All had normal renal and
hepatic function, the mean creatinine clearance was 101.6 ±
21.1 ml/min·1.73 m2. All volunteers included in the study had
normal findings from physical examination, electrocardiogram
and laboratory tests (including haematological and biochemical
parameters, hepatitis and human immunodeficiency
virus serological tests, tests for drug abuse, urinalysis and
negative pregnancy test). Further exclusion criteria were
regular use of medications, abuse of alcoholic beverages,
symptoms of significant illness within 3 months before the
study period, history of gastrointestinal, liver or kidney
disease potentially interfering with absorption, metabolism or
excretion of drugs, history of central nervous system disorders,
allergy or hypersensitivity to the study drugs, blood
donation of more than 500 mL during the previous 3 months,
participation in a clinical trial within 3 months before the
study period, and pregnancy. Written informed consent was
obtained from all volunteers prior to the study. The study was
approved by the Ethics Committee of University Medical
Centre Benjamin Franklin, Free University of Berlin, Berlin,
Germany.
Study design and protocol
The study was performed in an open, randomized, two-period
crossover design and was divided into two periods of 35 days.
The treatment regimens were (i) one 600 mg linezolid tablet
(Pharmacia & Upjohn, Kalamazoo, MI, USA) in the morning
and one 600 mg linezolid tablet in the evening for 6 days; and
(ii) one 1000 mg co-amoxiclav tablet in a new formulation
(875 mg amoxicillin and 125 mg clavulanic acid; SmithKline
Beecham, Harlow, UK) each morning for 7 days. Each volunteer
received first one treatment regimen and then the crossover
regimen. The wash-out period was 4 weeks between the
administration of the two antibiotic regimens. Strenuous
physical activity, smoking, intake of alcohol and of stimulating
beverages containing xanthine derivatives (tea, coffee and
soft drinks containing caffeine) were prohibited from 24 h before until 48 h after drug administration, the latter in order
to avoid analytical interference.
Oral drug administration was done at 8:00 a.m. and at
8:00 p.m., in a sitting position with 100 mL of carbon dioxidefree
water at ambient temperature. The test drug was taken
after fasting for 12 h and in fasting conditions on days 1–7 in
the morning and 2 h after dinner for the evening administration.
Breakfast was served 2 h after drug administration on
days 1 and 7. Drug intake was observed directly in each volunteer
on day 1 and on the morning of days 2 and 7; all other
medications had to be confirmed directly by telephone calls
from the volunteer to the responsible physician and each
volunteer recorded a diary protocol with the exact time of
each medication, possible adverse event and stools, including
the quality of faeces. All diaries were checked for possible
differences with the protocol made when receiving the
phone calls. In the case of adverse events, the investigating
physician performed a precise interview and, if necessary,
initiated consultations or additional diagnostic or therapeutic
procedures.
Sampling
Blood samples (10 mL) were taken from a peripheral vein on
days 1 and 7 before and 30, 60, 90, 120, 180, 240, 360, 480,
720 and 1440 min (day 7) after medication through an
indwelling venous cannula. The samples were allowed to clot
at room temperature for ∼30 min. The samples were subsequently
centrifuged at 1300g for 10 min at 4°C. The serum
samples were stored at –80°C until analysis.
Urine samples were collected on days 1 and 7. On both days,
urine fractions were collected pre-dose and over the following
intervals: 0–3, 3–6, 6–12 and 12–24 h after administration.
The urine volumes were measured after each collection interval
and two 5 mL aliquots were saved. The samples were
stored without preservatives in closed sterile tubes at –80°C.
Specimens were protected against light and heat during
collection, storage and analysis.
High-performance liquid chromatography (HPLC)
Concentrations of linezolid, amoxicillin and clavulanic acid
in serum and urine were determined by validated HPLC
methods.9,10,11 Validation of the method for linezolid gave
the following results for serum (and urine): detection limit
0.07 mg/L (2.4 mg/L), lower limit of quantification 0.14 mg/L
(4.7 mg/L), linear range 20 mg/L (500 mg/L), intra-assay
variability (CV) 1.8–2.5% (0.8–1.0%), inter-assay variability
(CV) 1.8–2.3% (0.4–2.3%), recovery 99–102% (93–103%).
Validation of the method for amoxicillin yielded the following
results for serum (and urine): detection limit 0.15 mg/L
(1.6 mg/L), lower limit of quantification 0.5 mg/L (15.6 mg/L),
linear range 20 mg/L (1500 mg/L), intra-assay variability
(CV) 1.1–3.7% (0.7–1.1%), inter-assay variability (CV)
1.7–11.2% (1.7–2.4%), recovery 96.2–101.5% (100.7–
101.3%). Validation of the method for clavulanic acid yielded
the following results for serum (and urine): detection limit
0.06 mg/L (3.9 mg/L), lower limit of quantification 0.12 mg/L
(7.8 mg/L), linear range 5 mg/L (200 mg/L), intra-assay variability
(CV) 1.5–5.9% (1.2–6.4%), inter-assay variability
(CV) 3.6–4.8% (4.5–19.6%), recovery 98.8–101% (89.5–
105.3%).
Pharmacokinetic calculations and statistical evaluations
The serum concentrations of linezolid were analysed
assuming an open two-compartment model and the data of
amoxicillin and clavulanic acid with a one-compartment
model. Models were selected using the Schwarz criterion.12
These models were used to calculate time between drug administration
and start of absorption (Tlag), terminal half-life
and total area under the curve (AUCtot) by integration of the
regression curve. The highest observed serum concentration
was taken for peak concentration (Cmax) and time to peak
concentration (Tmax). All other parameters [total area under
the data (AUDtot), volume of distribution at steady state (Vss/f),
mean residence time (MRT) and urinary recovery] were
analysed non-compartmentally. The AUD was calculated
with the trapezoidal rule. AUCtot and AUDtot of linezolid on
each day were calculated up to 12 h after administration and
on day 7 up to 24 h. Residual areas were calculated by integration
of the compartmental regression line from the last data
point to infinity and added to the areas from zero to 12 or 24 h
(day 7). The dose-dependent parameters (AUCtot, AUDtot, Vss/f
and Cmax) were adjusted to a body weight of 70 kg. Clearance
values were normalized to a body surface of 1.73 m2. Recoveries
in urine were extrapolated to infinity. The pharmacokinetic
determinations were made using REVOL software as
previously described.13 Student’s t-test and Wilcoxon’s rank
test were used for statistical analysis and P values <0.05 were
considered significant.