CLINICAL PHARMACOLOGYHuman Pharmacology
Serum level studies with a 150 mg oral dose of clindamycin
hydrochloride in 24 normal adult volunteers showed that clindamycin was rapidly
absorbed after oral administration. An average peak serum level of 2.50 mcg/mL
was reached in 45 minutes; serum levels averaged 1.51 mcg/mL at 3 hours and 0.70
mcg/mL at 6 hours. Absorption of an oral dose is virtually complete (90%), and
the concomitant administration of food does not appreciably modify the serum
concentrations; serum levels have been uniform and predictable from person to
person and dose to dose. Serum level studies following multiple doses of
clindamycin hydrochloride for up to 14 days show no evidence of accumulation or
altered metabolism of drug.
Serum half-life of clindamycin is increased slightly in patients with
markedly reduced renal function. Hemodialysis and peritoneal dialysis are not
effective in removing clindamycin from the serum.
Concentrations of clindamycin in the serum increased linearly with increased
dose. Serum levels exceed the MIC (minimum inhibitory concentration) for most
indicated organisms for at least six hours following administration of the
usually recommended doses. Clindamycin is widely distributed in body fluids and
tissues (including bones). The average biological half-life is 2.4 hours.
Approximately 10% of the bioactivity is excreted in the urine and 3.6% in the
feces; the remainder is excreted as bioinactive metabolites.
Doses of up to 2 grams of clindamycin per day for 14 days have been well
tolerated by healthy volunteers, except that the incidence of gastrointestinal
side effects is greater with the higher doses.
No significant levels of clindamycin are attained in the cerebrospinal fluid,
even in the presence of inflamed meninges.
Pharmacokinetic studies in elderly volunteers (61 to 79 years) and younger
adults (18 to 39 years) indicate that age alone does not alter clindamycin
pharmacokinetics (clearance, elimination half-life, volume of distribution, and
area under the serum concentration-time curve) after IV administration of
clindamycin phosphate. After oral administration of clindamycin hydrochloride,
elimination half-life is increased to approximately 4 hours (range 3.4 to 5.1 h)
in the elderly compared to 3.2 hours (range 2.1 to 4.2 h) in younger adults. The
extent of absorption, however, is not different between age groups and no dosage
alteration is necessary for the elderly with normal hepatic function and normal
(age-adjusted) renal function.
Microbiology
Clindamycin inhibits bacterial protein synthesis by binding to
the 50S subunit of the ribosome. It has activity against Gram-positive aerobes
and anaerobes as well as the Gram-negative anaerobes. Clindamycin is
bacteriostatic. Cross-resistance between clindamycin and lincomycin is complete.
Antagonism in vitro has been demonstrated between
clindamycin and erythromycin.
Clindamycin has been shown to be active against most of the isolates of the
following microorganisms, both in vitro and in
clinical infections, as described in the INDICATIONS AND
USAGE section.
Gram-positive aerobes
Staphylococcus aureus (methicillin-susceptible
strains)
Streptococcus pneumoniae (penicillin-susceptible
strains)
Streptococcus pyogenes
Anaerobes
Prevotella melaninogenica
Fusobacterium necrophorum
Fusobacterium nucleatum
Peptostreptococcus anaerobius
Clostridium perfringens
The following in vitro data are available, but
their clinical significance is unknown. At least 90% of the following
microorganisms exhibit an in vitro minimum inhibitory
concentration (MIC) less than or equal to the susceptible breakpoint for
clindamycin. However, the safety and effectiveness of clindamycin in treating
clinical infections due to these microorganisms have not been established in
adequate and well-controlled clinical trials.
Gram-positive aerobes
Staphylococcus epidermidis
(methicillin-susceptible strains)
Streptococcus agalactiae
Streptococcus anginosus
Streptococcus oralis
Streptococcus mitis
Anaerobes
Prevotella intermedia
Prevotella bivia
Propionibacterium acnes
Micromonas ("Peptostreptococcus") micros
Finegoldia ("Peptostreptococcus") magna
Actinomyces israelii
Clostridium clostridioforme
Eubacterium lentum
SUSCEPTIBILITY TESTING METHODS
NOTE: Susceptibility testing by dilution
methods requires the use of clindamycin susceptibility powder.
When available, the results of in vitro
susceptibility tests should be provided 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 antimicrobial compounds. The MICs should be
determined using a standardized procedure. Standardized procedures are based on
a dilution method (broth and agar)1,2,3 or equivalent
with standardized inoculum concentrations and standardized concentrations of
clindamycin powder.The MIC values should be interpreted according to the
criteria provided in Table 1.
Diffusion Techniques
Quantitative methods that require the measurement of zone
diameters also provide reproducible estimates of the susceptibility of bacteria
to antimicrobial compounds. One such standardized procedure2,3 requires the use of standardized inoculum concentrations.
This procedure uses paper disks impregnated with 2 mcg of clindamycin to test
the susceptibility of microorganisms to clindamycin.
A report of "Susceptible" indicates that the pathogen is likely to be
inhibited if the antimicrobial 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 pathogen is not
likely to be inhibited if the antimicrobial compound in the blood reaches the
concentrations usually achievable; other therapy should be selected.
Quality ControlStandardized susceptibility test procedures require the use of
quality control microorganisms to control the technical aspects of the test
procedures. NOTE: Quality control
microorganisms are specific strains of organisms with intrinsic biological
properties relating to resistance mechanisms and their genetic expression within
bacteria; the specific strains used for microbiological quality control are not
clinically significant.