Erythromycin used for feeding intolerance in young infants has not been associated with hypertrophic pyloric stenosis.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. Some evidence suggests similar hepatotoxicity in other populations.It can also affect the central nervous system, causing psychotic reactions, nightmares, and night sweats. Interactions
Erythromycin is metabolized by enzymes of the cytochrome P450 system, in particular, by isozymes of the CYP3A superfamily. The activity of the CYP3A enzymes can be induced or inhibited by certain drugs (e.g., dexamethasone), which can cause it to affect the metabolism of many different drugs, including erythromycin. If other CYP3A substrates — drugs that are broken down by CYP3A — such as simvastatin (Zocor), lovastatin (Mevacor), or atorvastatin (Lipitor)—are taken concomitantly with erythromycin, levels of the substrates increase, often causing adverse effects. A noted drug interaction involves erythromycin and simvastatin, resulting in increased simvastatin levels and the potential for rhabdomyolysis. 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. Earlier case reports on sudden death prompted a study on a large cohort that confirmed a link between erythromycin, ventricular tachycardia, and sudden cardiac death in patients also taking drugs that prolong the metabolism of erythromycin (like verapamil or diltiazem) by interfering with CYP3A4. Hence, erythromycin should not be administered to people using these drugs, or drugs that also prolong the QT interval.
Anything that causes further narrowing has the tendency to impinge the tendon and cause an inflammatory response, resulting in impingement syndrome. Such causes can be  bony structures such as subacromial spurs (bony projections from the acromion), osteoarthritic spurs on the acromioclavicular joint, and variations in the shape of the acromion. Thickening or calcification of the coracoacromial ligament can also cause impingement. Loss of function of the rotator cuff muscles, due to injury or loss of strength, may cause the humerus to move superiorly, resulting in impingement. Inflammation and subsequent thickening of the subacromial bursa may also cause impingement.Weight training exercises where the arms are elevated above shoulder height but in an internally rotated position such as the upright row have been suggested as a cause of subacromial impingement. Another common cause of Impingement syndrome is restrictions in the range movement of the scapulo-thoracic surfaces. Commonly, one or more ribs between rib 2 and rib 7/8 on the side of the impingement may jut out slightly and/or feel hard when the person springs on it or them. When this occurs, the scapula is raised and anteverted (angled forwards). This in turn pushes the acromion and the humeral head out of its usual anatomical position placing pressure downwards at the head of the humerus at the position of the nerve thus causing the impingement syndrome. This is visibly demonstrated by a slightly raised and protracted shoulder girdle.