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The next class of antibiotics are the protein synthesis inhibitors. What is the general MOA for these patients?

Attacks the 70S ribosome (remember that mammalian cells have 80S ribosome)
--so this forms the basis for the selective toxicity of these drugs against microorganisms without causing major effects on protein synthesis in mammals


First up are the tetracyclines (Doxycycline, minocycline, and tetracycline) what are their MOA?

Enter microorganisms in part via passive diffusion and in part via an energy dependent transport that is unique to the bacterial inner cytoplasmic membrane
Once inside the cell, these drugs bind reversibly to the 30S subunit of the bacterial ribosome, preventing binding of aminoacyl-tRNA to the acceptor site on the mRNA-ribosome complex
--this prevents addition of amino acids to the growing peptide.


What are the three main mechanisms of tetracycline resistance?

1. Impaired influx or increased efflux by an active transport protein pump, thus preventing accumulation of the drug within the bacterial cell
2. Production of proteins that interfere with tetracycline binding to the ribosome
3. Enzymatic inactivation


What is the spectrum of activity for the tetracyclines?

Broad spectrum
Bacteriostatic drugs
Aerobic and Anaerobic Gram Positive and Gram Negative


Tetracyclines are used in the treatment of what?

Resp Tract
Middle Ear
Urinary Tract
most current use: severe acne and rosacea


Tetracyclines are the drug of choice for what?

Mycoplasma Pneumoniae
Lyme Disease
Anthrax (prophylaxis)
Rickettsia (rocky mountain spotted fever, typhus)
(Also recommended for the use in the tx of syphilis in patient who are allergic to penicillin)


In combination regimens they have found use in the treatment of what?

Duodenal Ulcer (H. pylori)
Prophylaxis and Tx of Malaria
Tx of plague, tularemia and brucellosis


What is the main problem with the use of tetracyclines?

High level of resistance


Moving on to the pharmacokinetics of tetracyclines, what are some features?

Oral absorption
Absorption in Upper Small Intestine
Impaired by food (except doxy and mino)
Absorption of all oral tetracyclines is impaired by multivalent cations (Ca2+, Mg 2+, Fe2+) or any dairy products
Widely distributed (except CSF) and cross both the placental barrier and enters the breast milk


What are some pharmacokinetic features of doxy?

Lipid soluble and is preferred IV
Good choice for tx of STDs and prostatitis
Excreted in the feces
SID due to their high oral absorption and slow excretion


What are some pharmacokinetic features of mino?

Reaches very high concentration in tears and saliva (useful for eradication of the meningococcal carrier state)
SID due to their high oral absorption and slow excretion


Finally Adverse Effects with Tetracyclines. Hypersensitivity reactions are uncommon. Most adverse effects are due to direct toxicity of the drug or to alteration in microbial flora. What are the adverse effects?

GI effects: n/v/d (direct irritation of the intestinal tract)
Discoloration and hyperplasia of teeth and stunting of growth: bound to calcium deposited in newly formed bone and teeth in young children. In pregnancy, deposited in the fetal teeth = discoloration and in bone = deformities. AVOIDED IN PREGNANCY AND CHILDREN LESS THAN 8
Hepatotoxicity: impair hepatic function esp during pregnancy
Nephrotoxicity: acute renal failure/damage
Photosensitization: esp with systemic administration
Dizziness and Vertigo: concentrate in the endolymph of the ear


Moving on to the next class of Protein Synthesis Inhibitors are the Glycylcyclines (tigecycline). What is the MOA/

Bind to the 30S bacterial ribosome
--but 5 times more tightly than the tetracyclines
Designed to overcome two mechanisms of resistance:
--acquired efflux pumps and/or ribosomal protection


What two microorganisms are intrinsically resistant to glycylcyclines?

P. aeruginosa


What is the spectrum of activity and clinical applications for glycylcyclines?

Activity against MRSA, VISA and VRE
--recommended use is for the tx of complicated skin, soft tissue and intra-abdominal infections
--licensed for use of community-acquired pneumonia


What are some pharmacokinetic features of glycylcyclines?

Only given IV
Wide distribution and tissue and intracellular penetration
Elimination is primarily biliary
No dosage adjustment is needed for renal insufficiency patients


What are some adverse effects of glycylcyclines?

Same adverse effects as tetracyclines
--therefor do not give in pregos or kids under 8
Most common adverse effects are n/v


Next drug class for protein synthesis inhibitors are the Aminoglycosides. What is the MOA?

Amikacin, Gentamicin, Tobramycin, Streptomycin and Neomycin
--act irreversibly by inhibiting protein synthesis
-initially cross the outer membrane of the bacteria via passive diffusion before being actively transported across the cell membrane into the cytoplasm
--once inside these drugs bind to the 30S subunit prior to ribosome formation leading to misreading of the genetic code and inhibition of translocation -- cell lysis


Aminoglycosides have stability against the development of resistance. Tx-emergent resistance is rare. What three mechanisms does resistance occur?

1. Plasmid-associated synthesis of enzymes that modify and inactivate the drugs by phosphorylation, adenylylation and acetylation
2. The receptor protein on the 30S ribosomal subunit may be deleted or altered due to mutation
3. Decreased accumulation of the drug. Either impaired entry into the cell or increased efflux


There are two important pharmacodynamic properties of aminoglycosides. First is the Postantibiotic Effect, what is this?

Postantibiotic Effect (PAE): persistent suppression of bacterial growth that occurs after the drug has been removed. Thought to be due to the drugs strong irreversible binding of the 30S ribosome


The second pharmacodynamic property of aminoglycosides is Concentration-dependent killing, what is this?

Ability of higher concentrations of aminoglycosides to induce more rapid and complete killing of the microorganism
--greater efficacy when given as a single large dose than as multiple small doses.
(contrast to time dependent killing like penicillins when in vivo efficacy is directly related to time above MIC and becomes independent of concentration once the MIC has been reached)
Toxicity to these drugs depends on both a critical plasma concentration and on the time that such a level is exceeded.


What is the spectrum of activity of aminoglycosides?

Aerobic Gram - microorganisms
Activity against MRSA in vitro
BUT, Not adequate therapy as monotherapy for serious infections caused by MRSA
Synergistic effect has been demonstrated for selected organisms when aminoglycosides are used in combination with other ABX, most often with cell wall inhibitors. (used against strep and staphy)


What are the clinical uses of aminoglycosides?

Commonly used in combo with other drugs
--empiric therapy of serious infections such as septicemia, nosocomial resp tract infections, complicated UTIs, complicated intra-abdominal infections, endocarditis, and osteomyelitis caused by aerobic gram negative bacilli


What is the drug combination of choice in the empiric treatment of infective endocarditis?

Gentamicin plus either a penicillin or vancomycin


What is the most useful drug in treating plague (Yersinia Pestis)?



Oral Neomycin is used for what?

Hepatic Encephalopathy
--second line tx due to risk of serious side effects
-lactulose is commonly used as first line tx (acidifying the gut lumen, lactulose traps NH4 in the colon, reducing plasma ammonia concentrations)


What are the pharmacokinetics for aminoglycosides?

Not absorbed after oral administration (Excluding neomycin which is a topical agent)
Well distributed but show poor penetration into the CSF, biliary tree and bronchial secretions
99% of the dose is eliminated unchanged in the urine and doses must be reduced in patients with renal insufficiency


Moving on to the adverse effects of aminogylcosides. There are serious toxicities associated with aminoglycosides and therefore not used for minor infections. What are these side effects?

Nephrotoxicity: continued therapy for more than 5 days at higher doses and in patients with renal insufficiency
Ototoxicity: therapy is continued for more than 5 days at higher doses and in patients with renal insufficiency. (neomycin, kanamycin and amikacin are the most ototoxic). May be increased by using loop diuretics.
Neuromuscular Blockade: patient experiencing such reactions have disease states and or concomitant drug therapy that interfere with neuromuscular transmission. Myasthenia gravis is an absolute contraindication


What are contraindications for aminoglycosides?

Pregnancy: due to risk of ototoxicity
Myasthenia gravis


The last drug set for this deck of cards are the macrolides (Erythromycin, Clarithromycin, Azithromycin, Telithromycin). What is their MOA and resistance?

--bind to the 50S subunit of bacterial ribosomes
Resistance: (becoming more of a problem)
-reduced membrane permeability or active efflux
--production of an esterase that results in hydrolyzation of the drugs
--modifiction of the ribosomal binding site, either by chromosomal mutation or by a methylase
There is complete cross resistance between erythromycin, azithromycin, and clarithromycin for gram + organisms by alteration in ribosomal RNA mechanism.

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