Erythromycin is a type of antibiotic which belongs to drugs family known as macrolides. This antibiotic is a first type of macrolides which was isolated in 1952 from a strain of the Streptomyces erythraeus (S.erythraea spp). It used to inhibit the bacterial reproduction by reducing the production of important proteins needed by bacteria to survive. Erythromycin is known to be particularly effective against gram-positive bacteria such as pneumococci, streptococci and some staphylococci. This antibiotic also is less effective against gram-negative bacteria as well as some fungi because erythromycin has large hydrophobic molecules and cannot penetrate both the inner and outer membrane of gram-negative bacteria. This antibiotic is very prevalent against many different types of bacterial infections including respiratory infections such as pneumonia and bronchitis, mouth infections such as throat and tonsillitis infections, skin long term infections such as acne and rosacea, ear infections, urinary tract infections, and ect. In order to treat patient who are allergic to penicillin erythromycin is an alternative option.
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Erythromycin is available as tablets, capsules, intravenous infusion and oral liquid medicine. This antibiotic can be administrated intravenously for systemic therapy; this is due to the molecule size not allowing the drug to be absorbed by the intestine. IV erythromycin is preferable regarding to slower infusion rate and lower concentration of the drug but IV route should be replace by oral route as soon as possible. Erythromycin like all medicines does have its adverse effects but the side effects that each person experiences depends to the person sensitivity and the type of route it has been administered. The most common side effects for this antibiotic are nausea, abdominal pain, vomiting and diarrhea. To reduce the side effects, administration of erythromycin will usually be monitored.
Figure 1 shows chemical structure of erythromycin:
Generally the chemical structure of macrolids contains one or more sugars and a large lacton ring which is attached to 12-16 atoms through glycosidic bonds. Erythromycin molecule contains a 14-membered lactone ring with10 asymmetric centers and two sugars called L-cladinose and D-desosamine.
Mechanism of action:
Mainly macrolides are bacteriostatic (capable of inhibiting the growth or reproduction of bacteria) but depending on bacterial sensitivity and antibiotic concentration they can be bactericidal (capable of killing bacteria outright). Generally macrolids inhibit the protein synthesis by preventing the elongation of the polypeptide chain. They interfere with protein synthesis by reversibly binding to the 50S subunit of the ribosome. They bind at the donor site to prevent the translocation and avoid the peptide chain growing. Macrolides are more active at higher pH ranges (7.8-8). They also inhibit the formation of peptide bond between amino acids by inhibiting enzyme peptidyltransfrase.
Erythromycin in high concentration is bacteriostatic. This drug binds to the 50S subunit of the bacterial 70S rRNA complex to inhibit the growth or reproduction of bacteria. Erythromycin interferes with aminoacyl translocation, to prevent the transfer of the tRNA bound at the A-site of the rRNA complex to the P-site of the rRNA complex. By not having this translocation, the A-site remains occupied thus the addition of an incoming tRNA and its attached amino acid to the elongation polypeptide chain is inhibited. Moreover, erycthromycin can inhibit protein synthesis only at, or just after initiation of mRNA translation because the nascent peptide chains have overlapping binding sites in the ribosome. Since the affinity of peptidy-tRNAs with long peptide chains to the ribosome is very high, the drugs may be unable to compete for these binding sites when the peptides are long.
Optimization of the drug:
According to the genetic engineering study in 2008 final concentration of erythromycin in fermentation process was very low. However, there have been some significant improvements in relation with productivity of erythromycin. Therefore, combined DNA techniques were applied on few strains of this drug (those which produced from Streptomyces erythraeus). At some points, during the optimization process and specifically genetic modification, genetic instability of strains was increased. The main achievements regarding to this experiment was about high production rate of erythromycin and high concentration of Streptomyces erythraeus Vitreoscilla hemoglobin gene ( S.erythraea vhb). Comparing the result with previous studies shows the final concentration of erythromycin enhanced by 70% when Vitreoscilla hemoglobin gene chromosomes were integrated. Also maximum rate of biosynthesis found to be 57.5 mg for erythromycin and 24.3 mg for the combined strain S.erythraeus vhb and Streptomyces erythraeus (S.erythraea spp).In terms of overall space-time yield, a comparison can be made between S.erythraea vhb and S.erythraea spp fermentations. S.erythraea spp fermentation is 0.56g of erythromycin/(L/day) and for S.erythraea vhb fermentation is1.1 g of erythromycin/(L/day), this quantity is 100% higher for S.erythraea vhb. Moreover, other advantages of this combined product are: higher genetic stability and it does not need any selective pressure throughout the farming.
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The erythromycin breath test (EBT) is a putative in vivo probe for drug metabolism by cytochrome P450 3A4 (CYP3A4). Because many anticancer drugs are metabolized by this system, we sought to further develop the EBT as a tool for predicting the clearance, in cancer patients, of drugs metabolized by CYP3A4. Sixteen adult patients with incurable cancer were studied. The EBT was performed on day 1 and breath sampled after the i.v. injection of 4 microCi of 14C-erythromycin. The breath 14CO2 flux (CERt) was estimated at 11 time points over 2 h. On day 2, the EBT was repeated midway through a 10-min infusion of 100 mg of erythromycin lactobionate, and the plasma pharmacokinetics of erythromycin were determined. The infusion of 100 mg of erythromycin did not modify the EBT results significantly. The values of the conventional EBT parameter CER20 min obtained on day 1 were comparable for most subjects (0.03-0.06% dose/min), with the exception of an individual receiving the known CYP3A4 inducers dexamethasone and phenytoin who returned a value of 0.14% dose/min. There was no significant correlation between any of the conventional EBT parameters and erythromycin clearance. However, two parameters reflecting early emergence of breath radioactivity (1/TMAX and CER3 min/CERMAX) correlated significantly with erythromycin clearance (P = 0.005 and 0.006, respectively). Novel parameters derived from the EBT are significantly correlated with the clearance of erythromycin even in the presence of confounding factors, such as metastatic liver disease, altered protein binding, and comedication. These parameters may enable dose optimization of cytotoxics metabolized by CYP3A4.