[1] More serious side effects may include Clostridioides difficile colitis, liver problems, prolonged QT, and allergic reactions.

[2] While generally regarded as safe during breastfeeding, its use by the mother during the first two weeks of life may increase the risk of pyloric stenosis in the baby.

[10][11] Erythromycin can be used to treat bacteria responsible for causing infections of the skin and upper respiratory tract, including Streptococcus, Staphylococcus, Haemophilus and Corynebacterium genera.

The following represents MIC susceptibility data for a few medically significant bacteria:[12] It may be useful in treating gastroparesis due to this promotility effect.

[19] Exposure to erythromycin (especially long courses at antimicrobial doses, and also through breastfeeding) has been linked to an increased probability of pyloric stenosis in young infants.

[20] Erythromycin estolate has been associated with reversible hepatotoxicity in pregnant women in the form of elevated serum glutamic-oxaloacetic transaminase and is not recommended during pregnancy.

Another group of CYP3A4 substrates are drugs used for migraine such as ergotamine and dihydroergotamine; their adverse effects may be more pronounced if erythromycin is associated.

Other examples include terfenadine (Seldane, Seldane-D),[26] astemizole (Hismanal),[27] cisapride[28] (Propulsid, withdrawn in many countries for prolonging the QT time) and pimozide (Orap).

[30] Erythromycin and doxycycline can have a synergistic effect when combined and kill bacteria (E. coli) with a higher potency than the sum of the two drugs together.

A review found that when erythromycin was given with certain oral contraceptives, there was an increase in the maximum serum concentrations and AUC of estradiol and dienogest.

[35] By binding to the 50s subunit of the bacterial rRNA complex, protein synthesis and subsequent structure and function processes critical for life or replication are inhibited.

[36] Without this translocation, the A site remains occupied, thus the addition of an incoming tRNA and its attached amino acid to the nascent polypeptide chain is inhibited.

The presence of 10 stereogenic carbons and several points of distinct substitution has made the total synthesis of erythromycin A a formidable task.

[48] Aguilar managed to isolate erythromycin from the metabolic products of a strain of Streptomyces erythreus (designation changed to Saccharopolyspora erythraea) found in the samples.

[49] Aguilar reached out to Eli Lilly again in 1993, requesting royalties from sales of the drug over the years, intending to use them to put up a foundation for poor and sickly Filipinos.

[50] The product was launched commercially in 1952 under the brand name Ilosone (after the Philippine region of Iloilo where it was originally collected).

The antibiotic clarithromycin was invented by scientists at the Japanese drug company Taisho Pharmaceutical in the 1970s as a result of their efforts to overcome the acid instability of erythromycin.

[53] In 2017, a Kaiser Health News study found that the per-unit cost of dozens of generics doubled or even tripled from 2015 to 2016, increasing spending by the Medicaid program.

Due to price increases by drug manufacturers, Medicaid paid on average $2,685,330 more for Erythromycin in 2016 compared to 2015 (not including rebates).