November 25, 2015
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Human 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 CLEOCIN HCl for up to 14 days show no evidence of accumulation or altered metabolism of drug. 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.


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). No significant levels of clindamycin are attained in the cerebrospinal fluid, even in the presence of inflamed meninges.


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.

Special Populations

Renal Impairment

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.

Use in Elderly

Pharmacokinetic studies in elderly volunteers (61–79 years) and younger adults (18–39 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 4.0 hours (range 3.4–5.1 h) in the elderly compared to 3.2 hours (range 2.1 – 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 function1.


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 -some 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 inducible resistance has been identified in macrolide-resistant staphylococci and beta-hemolytic streptococci. Macrolide-resistant isolates of these organisms should be screened for clindamycin inducible resistance using the D-zone test.

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


Prevotella melaninogenica
Fusobacterium necrophorum

Fusobacterium nucleatum

Peptostreptococcus anaerobius

Clostridium perfringens

At least 90% of the microorganisms listed below exhibit in vitro minimum inhibitory concentrations (MICs) less than or equal to the clindamycin susceptible MIC breakpoint for organisms of a similar type to those shown in Table 1. However, the efficacy of clindamycin in treating clinical infections due to these microorganisms has 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


Prevotella intermedia
Prevotella bivia

Propionibacterium acnes

Micromonas (“Peptostreptococcus”) micros

Finegoldia (“Peptostreptococcus”) magna

Actinomyces israelii

Clostridium clostridioforme

Eubacterium lentum

Susceptibility Testing Methods

When available, the clinical microbiology laboratory should provide cumulative 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 antimicrobial compounds. The MICs should be determined using a standardized procedure based on dilution methods (broth, agar, or microdilution)2,3 or equivalent using standardized inoculum and concentrations of clindamycin. 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. The standardized procedure2,4 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. Reports from the laboratory providing results of the standard single-disk susceptibility test with a 2 mcg clindamycin disk should be interpreted according to the criteria in Table 1.

Table 1: Susceptibility Interpretive Criteria for Clindamycin

Pathogen Minimal Inhibitory Concentrations (MIC in mcg/mL) Disk Diffusion (Zone Diameters in mm)
Staphylococcus spp. ≤ 0.5 1-2 ≥ 4 ≥ 21 15-20 ≤ 14
Streptococcus pneumoniae and other Streptococcus spp. ≤ 0.25 0.5 ≥ 1 ≥ 19 16-18 ≤ 15
Anaerobic Bacteria ≤ 2 4 > 8 NA NA NA
NA=not applicable

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 Control

Standardized susceptibility test procedures require the use of laboratory controls to monitor and ensure the accuracy and precision of the supplies and reagents used in the assay, and the techniques of the individuals performing the test.2,3,4,5 Standard clindamycin powder should provide the MIC ranges in Table 2. For the disk diffusion technique using the 2 mcg clindamycin disk the criteria provided in Table 2 should be achieved.

Table 2: Acceptable Quality Control Ranges for Clindamycin to be Used in Validation of Susceptibility Test Results

QC Strain Acceptable Quality Control Ranges
Minimum Inhibitory Concentration Range (mcg/mL) Disk Diffusion Range (Zone Diameters in mm)
When Testing Aerobic Pathogens
Staphylococcus aureus ATCC 29213 0.06-0.25 NA
Staphylococcus aureus ATCC 25923 NA 24-30
Streptococcus pneumoniae ATCC 49619 0.03-0.12 19-25
When Testing Anaerobes
Bacteroides fragilis ATCC 25285 0.5-2 NA
Bacteroides thetaiotaomicron ATCC 29741 2-8 NA
Eubacterium lentum ATCC 43055 0.06-0.25 NA
NA=Not applicable
ATCC® is a registered trademark of the American Type Culture Collection


1. Smith RB, Phillips JP: Evaluation of CLEOCIN HCl and CLEOCIN Phosphate in an Aged Population. Upjohn TR 8147-82-9122-021, December 1982.

2. CLSI. Performance Standards for Antimicrobial Susceptibility Testing: Twenty-fourth Informational Supplement. CLSI document M 100-S24. Wayne, PA: Clinical and Laboratory Standards Institute; 2014.

3. CLSI. Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically; Approved Standard – Ninth Edition. CLSI document M07-A9. Wayne, PA: Clinical and Laboratory Standards Institute; 2012.

4. CLSI. Performance Standards for Antimicrobial Disk Susceptibility Tests; Approved Standard – Eleventh Edition. CLSI document M02-A11. Wayne, PA: Clinical and Laboratory Standards Institute; 2012.

5. CLSI. Methods for Antimicrobial Susceptibility Testing of Anaerobic Bacteria; Approved Standard- Eighth Edition. CLSI document M11-A8. Wayne, PA: Clinical and Laboratory Standards Institute; 2012.

Last reviewed on RxList: 8/19/2015
This monograph has been modified to include the generic and brand name in many instances.

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