By Nathan Wei
Tendons are ropes of tissue that connect muscles to bones and allow joint motion. When a muscle contracts, the tendon is pulled and the bone that the tendon is connected to moves.
Tendons consist of collagen (mostly type I collagen) and elastin that sit inside a matrix (framework) with collagen accounting for 65-80% and elastin approximately 1-2% of the mass of the tendon.
Collagen and elastin are produced by special cells called tenoblasts and tenocytes. Crosslinks strengthen the collagen and help them form fibrils which are thin fibers. These fibrils are bunched together to form a collagen fiber which is the basic unit of a tendon. The entire tendon is surrounded by a fine connective tissue sheath called epitenon. The actual structure of a tendon is very complex with fibers being oriented horizontally, longitudinally, and diagonally.
As mentioned above, the basic function of a tendon is to transmit the force created by the muscle to the bone, and, in this way, make joint movement possible. Normally, tendon tissue is extremely tough but it can be damaged through excessive shear forces, trauma, and, recently, with certain drugs.
The Food and Drug Administration recently notified the makers of fluoroquinolone antimicrobial drugs for systemic use of the need to add a boxed warning to the prescribing information about the increased risk of developing tendonitis and tendon rupture. In addition, a Medication Guide for patients was also mandated.
The actual wording of the FDA statement was…
‘Fluoroquinolones are associated with an increased risk of tendinitis and tendon rupture. This risk is further increased in those over age 60, in kidney, heart, and lung transplant recipients, and with use of concomitant steroid therapy. Physicians should advise patients, at the first sign of tendon pain, swelling, or inflammation, to stop taking the fluoroquinolone, to avoid exercise and use of the affected area, and to promptly contact their doctor about changing to a non-fluoroquinolone antimicrobial drug.
Tendinitis and tendon rupture most frequently involves the Achilles tendon, and rupture of the Achilles tendon may require surgical repair. Tendinitis and tendon rupture in the rotator cuff (the shoulder), the hand, the biceps, and the thumb have also been reported. Tendon rupture can occur during or after completion of fluoroquinolone use; cases occurring up to several months after completion of therapy have been reported.
Selection of a fluoroquinolone for the treatment or prevention of an infection should be limited to those conditions that are proven or strongly suspected to be caused by bacteria.’
Currently available fluoroquinolone antimicrobial drugs include ciprofloxacin (marketed as Cipro and generic ciprofloxacin), ciprofloxacin extended release (Cipro XR and Proquin XR), gemifloxacin (marketed as Factive), levofloxacin (marketed as Levaquin), moxifloxacin (marketed as Avelox), norfloxacin (marketed as Noroxin), and ofloxacin (marketed as Floxin and generic ofloxacin).
The warnings about fluoroquinolones and adverse effects on tendons applies only to fluoroquinolones for systemic use (e.g., tablets, capsules and injectable formulations); it does not apply to fluoroquinolones for eye or ear use (e.g., eye drops and ear drops).
This danger has been known to be present for approximately 14 years with case reports first surfacing in the 1990’s.
One group of investigators have stated, ‘current exposure to fluoroquinolones increases the risk of Achilles tendon disorders. This finding is in agreement with a smaller study, in which we found an association between tendinitis and fluoroquinolones’ (van der Linden PD, et al. BMJ 2002;324:1306-1307).
Researchers feel that the mechanism is due to a toxic effect on collagen fibers. This may be caused by a substance called matrix metalloproteinase.
Bottom line? Avoid these antibiotics if you have any of the above risk factors!
About the Author: Nathan Wei, MD FACP FACR is a nationally known board-certified rheumatologist. For more info:
Tendonitis and PRP