Clindamycin is an oral and intravenous antibiotic that works by inhibiting the 50S ribosomal subunit required for bacterial protein synthesis. It has excellent activity against gram-positive cocci (e.g., Streptococcus and Staphylococcus, limited coverage of MRSA, not Enterococcus) and anaerobic organisms and is therefore used for infections involving the skin and soft tissue, oropharynx, pelvis, respiratory tract, and peritoneum.
Things to keep in mind are that clindamycin does not penetrate the blood-brain barrier and is becoming less effective against Bacteroides, so it might not be a wonderful option for peritonitis related to an infection. Furthermore, toxin-mediated infections (S. pyogenes causing toxic shock syndrome) may benefit from clindamycin due to its antitoxin effect. Compared to most other antibiotics, clindamycin also increases the risk of Clostridium difficile infection.
“D-testing” is performed to assess the therapeutic efficacy of clindamycin in patients with gram-positive infections. If these colonies are resistant to erythromycin (a macrolide antibiotic), they may also be rendered resistant to clindamycin due to an inducible methylase that alters binding to the 50S ribosomal subunit. A “positive D-test” implies that this inducible resistance exists and that clindamycin should not be used.