Sub-Tenon s injection

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Anterior sub-Tenon s injection offers no significant advantages over subconjunctival dmg administration. In fact, snb-Tenon s injection delivers lower qnantities of drug to the eye and is associated with a greater risk of perfttrating the globe. Despite these disadvantages, however, anterior snb-Tenon s injections of corticosteroids are occasionally nsed in the treatment of severe nveitis. 

Figure 3-17 Relative positions of periocular injections. A, Subconjunctival B, sub-Tenon s C, retrobulbar.

Cardillo JA, Melo LA, Costa RA, et al. Comparison of intravitreal versus posterior sub-Tenon s capsule injection of triamcinolone acetonide for diffuse diabetic macular edema. Ophthalmology 2005 112 1557-1563. 

Periocular steroids can be administered by subconjimcti-val, sub-Tenon s capsule, or retrobulbar injection. A topical anesthetic often is instilled before the steroid is injected. This route of administration can be effective during surgical procedures, as a supplement to topical and systemic steroids in cases of severe inflammation, and in patients not compliant with the prescribed regimen. 

There is a preponderance of evidence that the incidence of postoperative endophthalmitis is reduced when antiseptics (povidone iodine) and antibiotics are used preoperatively.The use of balanced salt solution, to which an antibiotic has been added, to irrigate the eye during surgery is advocated by some but tempered by concerns of intraocular toxicity and questions of efficacy. Sub-Tenon s capsule injection of an antibiotic just before surgery or subconjunctival injection of antibiotic at the end of the surgery is also used to prevent infection, but risk of inadvertent intraocular injections resulting in retinal antibiotic toxicity must be considered. In addition, oral antibiotics may be used at the time of surgery and 1 day postoperatively as a prophylactic measure. 

Very few injectable dosage forms have been specifically developed and approved by the FDA for intraocular use. However, the ophthalmologist uses available parenteral dosage forms to deliver anti-infectives, corticosterioids, and anesthetic products to achieve higher therapeutic concentrations intraocularly than can ordinarily be achieved by topical or systemic administration. These unapproved or off-label uses have developed over time as part of the physician s practice of medicine and include subconjunctival, retrobulbar, sub-Tenon s, and intravitreal injections. 

Topical corticosteroids do not readily penetrate the posterior segment, and posterior sub-Tenon s steroid injections take a long time to diffuse into the posterior segment. Direct placement of corticosteroids into the vitreous cavity may be the best way to deliver corticosteroids to the posterior segment and minimize systemic side effects (16). 

Classical pharmacokinetic models of systemicaUy administered drugs (see Chapter 1) do not fuUy apply to many ophthalmic drugs. Most ophthalmic medications are formulated to be apphed topically or may be injected by subconjunctival, sub-Tenon s, and retrobulbar routes (Figure 63-1 and Table 63-1). Although similar principles of absorption, distribution, metabolism, and excretion determine drug disposition in the eye, these alternative routes of drug administration introduce other variables in compartmental analysis. 

Yoshikawa K, Kotake S, Ichiishi A, Sasamoto Y, Kosaka S, Matsuda H. Posterior sub-Tenon injections of repository corticosteroids in uveitis patients with cystoid macular edema. Jpn J Ophthalmol 1995 39 71-76. 

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