CLINICAL PHARMACOLOGY
Distribution
Biologically inactive clindamycin phosphate is converted to active clindamycin. By the end of short-term intravenous infusion, peak serum concentrations of active clindamycin are reached.
After intramuscular injection of clindamycin phosphate, peak concentrations of active clindamycin are reached within 3 hours in adults and 1 hour in pediatric patients.
Serum concentrations of clindamycin can be maintained above the in vitro minimum inhibitory concentrations for most indicated organisms by administration of clindamycin phosphate every 8 to 12 hours in adults and every 6 to 8 hours in pediatric patients, or by continuous intravenous infusion. An equilibrium state is reached by the third dose.
No significant concentrations of clindamycin are attained in the cerebrospinal fluid even in the presence of inflamed meninges.
Metabolism
In vitro studies in human liver and intestinal microsomes indicated that clindamycin is predominantly metabolized by Cytochrome P450 3A4 (CYP3A4), with minor contribution from CYP3A5, to form clindamycin sulfoxide and a minor metabolite, N-desmethylclindamycin.
Excretion
Biologically inactive clindamycin phosphate disappears from the serum with 6 minutes of the average elimination half-life; however, the average serum elimination half-life of active clindamycin is about 3 hours in adults and 2½ hours in pediatric patients.
Specific Populations
Patients with Renal/Hepatic Impairment
The elimination half-life of clindamycin is increased slightly in patients with markedly reduced renal or hepatic function. Hemodialysis and peritoneal dialysis are not effective in removing clindamycin from the serum. Dosage schedules do not need to be modified in patients with renal or hepatic disease.
Geriatric Patients
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, the average 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.
Pharmacokinetics in Pediatric Patients with PMA ≤32 weeks, or >32 to ≤40 weeks
Systemic clearance (CL) in premature infants increases with increases in body weight (kg) and post-menstrual age (PMA). The dosing regimens for pediatric patients ≤32 weeks PMA (5 mg/kg) and >32 to ≤40 weeks PMA (7 mg/kg), both administered intravenously every 8 hours, achieve exposures comparable to therapeutic exposures in adults (weighing 70 kg) administered clindamycin 600 mg every 8 hours (Table 1).
| Age | Adult (70 kg) | PMA ≤32 weeks | PMA>32 – ≤40 weeks |
|---|---|---|---|
| PMA: post-menstrual age; AUCss,0–8 hour: area under the concentration-time curve during a dosing interval at steady state; Cmax,ss: maximum drug concentration at steady state; Cmin,ss: minimum or trough drug concentration at steady state. | |||
| Dose (every 8 hours) | 600 mg | 5 mg/kg | 7 mg/kg |
| AUCss,0–8 hour (mcg∙h/mL) | 50.5 (30.95) | 52.5 (17.0) | 55.9 (23.55) |
| Cmax,ss (mcg/mL) | 12.0 (3.49) | 9.0 (2.02) | 10.5 (2.79) |
| Cmin,ss (mcg/mL) | 3.1 (3.34) | 4.6 (2.00) | 4.4 (2.77) |
Obese Pediatric Patients Aged 2 to Less than 18 Years and Obese Adults Aged 18 to 20 Years
An analysis of pharmacokinetic data in obese pediatric patients aged 2 to less than 18 years and obese adults aged 18 to 20 years demonstrated that clindamycin clearance and volume of distribution, normalized by total body weight, are comparable regardless of obesity.
Microbiology
Mechanism of Action
Clindamycin inhibits bacterial protein synthesis by binding to the 23S RNA of the 50S subunit of the ribosome. Clindamycin is bacteriostatic.
Resistance
Resistance to clindamycin is most often caused by modification of specific bases of the 23S ribosomal RNA. Cross-resistance between clindamycin and lincomycin is complete. Because the binding sites for these antibacterial drugs overlap, cross-resistance is sometimes observed among lincosamides, macrolides and streptogramin B.Macrolide-inducible resistance to clindamycin occurs in some isolates of macrolide-resistant bacteria. Macrolide-resistant isolates of staphylococci and beta-hemolytic streptococci should be screened for induction of clindamycin resistance using the D-zone test.
Antimicrobial Activity
Clindamycin has been shown to be active against most of the isolates of the following microorganisms, both in vitro and in clinical infections [see Indications and Usage ]:
Gram-positive bacteria
- Staphylococcus aureus (methicillin-susceptible strains)
- Streptococcus pneumoniae (penicillin-susceptible strains)
- Streptococcus pyogenes
Anaerobic bacteria
- Clostridium perfringens
- Fusobacterium necrophorum
- Fusobacterium nucleatum
- Peptostreptococcus anaerobius
- Prevotella melaninogenica
The following in vitro data are available, but their clinical significance is unknown. At least 90 percent of the following bacteria exhibit an in vitro minimum inhibitory concentration (MIC) less than or equal to the susceptible breakpoint for clindamycin against isolates of a similar genus or organism group. However, the efficacy of clindamycin in treating clinical infections due to these bacteria has not been established in adequate and well-controlled clinical trials.
Gram-positive bacteria
- Staphylococcus epidermidis (methicillin-susceptible strains)
- Streptococcus agalactiae
- Streptococcus anginosus
- Streptococcus mitis
- Streptococcus oralis
Anaerobic bacteria
- Actinomyces israelii
- Clostridium clostridioforme
- Eggerthella lenta
- Finegoldia (Peptostreptococcus) magna
- Micromonas (Peptostreptococcus) micros
- Prevotella bivia
- Prevotella intermedia
- Cutibacterium acnes