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Flashcards in Protein synthesis inhibitors Deck (48):

Clindamycin mechanism of action

Inhibits protein synthesis by binding exclusively to the 50S ribosomal subunit

Binds in close proximity to macrolides and Quinupristin/Daltopristin (Synercid®)– may cause competitive inhibition


clindamycin binding site

50S ribosomal subunit


is clindaycin bactericidal or bacteriostatic

bacteriostatic typically but bactericidal at high concentrations


Clindamycins main mechanism of resistance

Altered target sites – encoded by the erm gene, which alters 50S ribosomal binding site; confers high level resistance to macrolides, clindamycin and Synercid® (MLSb resistance)


erm gene

alters 50S ribosomal binding site; confers high level resistance to macrolides, clindamycin and Synercid® (MLSb resistance)


mef gene

encodes for an efflux pump that pumps macrolides out of the cell but NOT clindamycin

Confers low level resistance to macrolides, but clindamycin still remains active


clindamycin's spectrum of activity

gram + aerobes (MSSA, some MRSA and Streps not PRSP )

anaerobes: including peptostreptococcus, clostridium (except C. diff)

and a few others


clindamycin absorption

good bioavailability both IV and PO

Rapidly and completely absorbed (90%); food has minimal effect on absorption


clindamycin's distribution

Good serum concentrations with both formulations

Good tissue penetration including bone; minimal CSF penetration


Clindamcin's elmination

Clindamycin primarily metabolized by the liver (85%); enterohepatic cycling

Half-life is 2.5 to 3 hours (dosed 6 to 8 hrs)

Clindamycin is NOT removed during hemodialysis (no renal adjustments)


clindamycin clinical uses

Anaerobic Infections OUTSIDE of the CNS
Pulmonary, intraabdominal, pelvic, diabetic foot and decubitus ulcer infections

Skin & Soft Tissue Infections (good gram+ but pcn might be better)
PCN-allergic patients
Patients with infections due to CA-MRSA

Alternative therapy
C. perfringens, PCP, Toxoplasmosis, malaria, bacterial vaginosis


clindamycin's adverse effects on the GI system

Gastrointestinal – 3 to 4% (especially with oral formulation)
Nausea, vomiting, diarrhea, dyspepsia

Clostridium difficile colitis (0.01-10%)– one of worst inducers
Ranges from mild - severe diarrhea
Requires treatment with metronidazole or oral vancomycin

GI side effects occur more commonly with oral administration


clindamycin adverse effects


Hepatotoxicity - rare
Elevated transaminases

Allergy – rare (rash)

Hematological abnormalities-neutropenia and thrombocytopenia (rare)


Macrolides that are used clinically

erythromycin, clarithromycin, and azithromycin

(erythromycin is the least commonly used due to adverse effects)


Macrolide's mechanism of action

Inhibit protein synthesis by reversibly binding to the 50S ribosomal subunit

Results in suppression of protein synthesis and bacterial growth is halted


are Macrolides bacteriostatic or bactericidal?

bacteriostatic except in high concentrations


Do macrolides have time or concentration depended effects

erythromycin and clarithromycin display time dependent activity

azithromycin is concentration dependent


2 mechanisms of resistance to macrolides

1. Active efflux (accounts for 70-80% in US) – mef gene encodes for an efflux pump that pumps the macrolide out of the cell away from the ribosome; confers low level resistance to macrolides

2. Altered target sites (primary resistance mechanism in Europe) – encoded by the erm gene which alters the macrolide binding site on the ribosome; confers high level resistance to all macrolides, clindamycin, and Synercid®

Cross-resistance occurs between all macrolides


macrolides spectrum of activity compared to clindamycin

similar gram positive but macrolides also have activity against bacillus and cornynebacterium spp.

clinda has no gram negative aerobe activity but macrolides have some (NOT Enterobacteriaceae)

macrolides have anaerobe and atypical bacteria activity


which macrolide has the best gram positive activity

clarithro > Erythro > Azithro


which gram negative spp. do macrolides have activity against?

H. influenzae (not erythro), M. catarrhalis, Neisseria spp.


which macrolides have the best gram negative activity

Azithro > Clarithro > Erythro


Macrolides are mainly used for treatment of

atypical bacteria:
Legionella pneumophila – DOC*
Chlamydophila (psittacosis) and Chlamydia spp.
Mycoplasma spp.

all macrolides have excellent activity against them

others: Mycobacterium avium complex (can be used for treatment or prophylaxis


bioavailability of macrolides

Clarithro > azithro > erythro


ways to increase the absorption of Erythromycin

variable absorption (15 to 45%); food may decrease the absorption

Base: destroyed by gastric acid; enteric coated

Esters and ester salts: more acid stable


absorption of which macrolide is affected by the presence of food in the stomach



macrolide distribution

Extensive tissue and cellular distribution – clarithromycin and azithromycin with higher tissue concentrations
Minimal CSF penetration


do macrolides enter the CSF

Not really


macrolide elimination

Erythromycin is excreted in bile and metabolized by CYP450

Clarithromycin is metabolized and also partially eliminated by the kidney (18% of parent and all metabolites)


clinical uses for Macrolides

Respiratory Tract Infections
Pharyngitis/ Tonsillitis – PCN-allergic patients

Sinusitis,COPD exacerbation, Otitis Media (azithro best if H. influenzae suspected)

Community-acquired pneumonia

Uncomplicated Skin Infections

STDs – Single 1 gram dose of azithro


Alternative for PCN-Allergic Patients:


macrolide use in pneumonia

Community-acquired pneumonia – monotherapy in outpatients;

with ceftriaxone for inpatients


Macrolide use for Mycobacterium avium complex (MAC)

Azithromycin for prophylaxis;

Clarithromycin/ Azithromycin combination for treatment


Macrolide use as an Alternative for PCN-Allergic Patients

Group A Strep upper respiratory infections
Prophylaxis of bacterial endocarditis
Syphilis and gonorrhea
Rheumatic fever prophylaxis


GI adverse effects of macrolides

up to 33%
Nausea, vomiting, diarrhea, dyspepsia
Most common with erythro; less with clarithromycin and azithromycin (10%)

more common that cindamycin but less chance of sever complications from C. diff


side effects of Macrolides


Cholestatic hepatitis - rare
> 1 to 2 weeks of erythromycin estolate

Thrombophlebitis – IV Erythro and Azithro
Dilution of dose; slow administration

Allergic reactions

* Prolonged QTc; aggravated by concomitant drugs that also prolong QTc (e.g. anti‐arrhythmics)

Transient /reversible tinnitus or deafness (with long term use)

Drug‐drug: e.g., Colchicine: potentially fatal interaction


which protein inhibitors inhibit p450

macrolides: Erythromycin and clarithromycin

Quinupristin/Daltopristin (Synercid®)

potentially more drug interactions


Streptogramins what is the clinically used drug

Quinupristin/Daltopristin (Synercid®)


what was the target for Quinupristin/Daltopristin (Synercid®)

Developed in response to the need for antibiotics with activity against resistant gram-positive bacteria, namely VRE


Quinupristin/Daltopristin (Synercid®) mechanism of action

Each agent acts individually on 50S ribosomal subunits to inhibit early and late stages of protein synthesis

Binds on the 50S ribosome near where the macrolides and clindamycin binding site

Bacteriostatic (may be bactericidal against some bacteria)


Quinupristin/Daltopristin (Synercid®) mechanism of resistance

Alterations in ribosomal binding sites (erm)
Enzymatic inactivation


Quinupristin/Daltopristin (Synercid®) spectrum of activity

mainly used for gram positives
includes MRSA, PRSP, and VRE


which protein inhibitor show a post-antibiotic effect

Quinupristin/Daltopristin (Synercid®)


how is Quinupristin/Daltopristin (Synercid®) administered

only IV


Quinupristin/Daltopristin (Synercid®) distribution

penetrates into extravascular tissue, lung, skin/soft tissue

not CSF


Quinupristin/Daltopristin (Synercid®) elmination

both agents are hepatically and biliary excreted


Quinupristin/Daltopristin (Synercid®) common clinical uses

VRE (faecium) bacteremia

Complicated skin and soft tissue infections due to MSSA or Streptococcus pyogenes

Limited data in treatment of catheter-related bacteremia, infections due to MRSA, and community-acquired pneumonia


Quinupristin/Daltopristin (Synercid®) adverse effects

Venous irritation 
(66%) – especially when administered through a peripheral vein

Gastrointestinal – nausea, vomiting, diarrhea

Myalgias, arthralgias – 2%



which classes of drugs inhibit protein synethsis by binding to the 50S subunit of the ribosome

Lincosamides (clindamycin)


Streptogramins (Quinupristin/Daltopristin (Synercid®))