Subconjunctival injections

Subconjunctival injection-75 mg/0.25 ml injected subconjunctivally results in ocular fluid levels of antibiotic (lasting for 5 hours or more) with MICs sufficient for most susceptible pathogens. 

Creams, ointments, and solutions containing 0.1-0.3% gentamicin sulfate have been used for the treatment of infected burns, wounds, or skin lesions and the prevention of intravenous catheter infections. Topical gentamicin is partly inactivated by purulent exudates. Ten mg can be injected subconjunctivally for treatment of ocular infections. 

A 63-year-old woman underwent phacoemulsification and lens implantation under sub-tenon block. After the local anesthetic was injected, the eye was prepared with an aqueous solution of povidone iodine and the surgery proceeded uneventfully. At the end, gentamicin and betamethasone were injected subconjunctivally. Over the next few days she developed orbital cellulitis, requiring intravenous antibiotics. 

In the horse, 5-10 mg miconazole is well tolerated when injected subconjunctivally. However, results assessing the clinical efficacy of subconjunctivally administered miconazole in animal models are equivocal, although the route is thought to have some therapeutic advantage in the horse (Hamor Whelan 1999). 

Periocular injections, subconjunctival, subtenons, and retrobulbar injection of drugs have been frequently investigated as a means to increase ocular availability. Subtenon injections of steroids, such as triamcinolone acetonide, are frequently used to control inflammatory conditions of the posterior segment such as cystoid macular edema, although this delivery route carries a risk of inadvertent intraocular injection (45). 

In-depth discussions of the anatomy of the eye and adnexa have been adequately covered elsewhere in the pharmaceutical literature [13-17] and in recent texts on ocular anatomy. Here a brief overview is presented of the critical anatomical features that influence the nature and administration of ophthalmic preparations. In this discussion, consideration will be given primarily to drugs applied topically, that is, onto the cornea or conjunctiva or into the palpebral fornices. Increasingly, drugs are being developed for administration by parenteral-type dosage forms subconjunctivally, into the anterior and posterior chambers, the vitreous chamber, Tenon s capsule, or by retrobulbar injection. 

Very few injectable dosage forms have been specifically developed and approved by FDA for intraocular use. However, the ophthalmologist uses available parenteral dosage forms to deliver antiinfectives, corti-costerioids, 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. However, these drugs are usually administered by subconjunctival or retrobulbar injection and rarely are they injected directly in the eye [301]. 

Keywords Ocular drug delivery Noncorneal route Transporters Iontophoresis Endocytosis Dry eye Inflammation Subconjunctival injections... 

Only solutions of lipophilic antibiotics are able to cross the external barrier of the cornea (drops) and the internal blood-retina barrier (systemic administration) to yield sufficient concentrations in the internal eye (vitreous). Keratitis and ulceration of the cornea can be treated by frequent administration of highly concentrated (fortified) antibiotic drops. In endophtalmitis, emergency vitreous aspirate and in-travitreal and subconjunctival injection of antibiotic solutions with a long half-life is the cornerstone of treatment. These solutions should be prepared by the hospital pharmacy. Empiric topical treatment of minor external eye infections consists of antibiotic containing gels or ointments. 

Local or topical administration of amphotericin has been used with success. Mycotic corneal ulcers and keratitis can be cured with topical drops as well as by direct subconjunctival injection. Fungal arthritis has been treated with adjunctive local injection directly into the joint. Candiduria responds to bladder irrigation with amphotericin B, and this route has been shown to produce no significant systemic toxicity. 

Barza, M., Doft, B., and Lynch, E. (1993), Ocular penetration of ceftriaxone, ceftazidime, and vancomycin after subconjunctival injection in humans, Arch. Ophthalmol., Ill, 492 194. 

Van der Veen, G., Broersma, L., Dijkstra, C. D., et al. (1994), Prevention of corneal allograft rejection in rats treated with subconjunctival injections of liposomes containing dichloromethylene diphosphonate, Invest. Ophthalmol. Vis. Sci., 35, 3505-3515. 

Transcomeal iontophoresis is superior to subconjunctival injection and simple immersion in drug solutions in producing earlier and higher peak levels in the aqueous humor and in the cornea [31,37]. 

Subconjunctival injections of sustained-release matrix materials or microparticles have produced significant levels in the vitreous cavity. Although the kinetics of transscleral drug delivery to the retina and choroid are... 

When higher concentrations of drugs, particularly corticosteroids and antibiotics, are required in the eye than can be delivered by topical administration, local injections into the periocular tissues can be considered. Periocnlar drug delivery includes subconjunctival, snb-Tenon s, retrobulbar, and peribulbar administration. 

Drugs can be injected at the conclusion of surgery to avoid the necessity of topical or systemic drug therapy. Subconjunctival injection involves passing the needle... 

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

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. 

Adverse reactions to topical application of polymyxin B include irritation and allergic reactions of the eyelids and conjunctiva but are infrequent and typically mild. However, when administered by subconjunctival injection, polymyxin B can cause pain, chemosis, and tissue necrosis. 

Periocular injection of steroids should be reserved for those situations requiring an anti-inflammatory effect greater than that obtainable with topical or systemic administration. Concurrent administration of steroid by both topical and subconjunctival routes does appear to produce an additive therapeutic effect in severe inflammations, but periocular injection alone does not necessarily result in greater anti-inflammatory effects.These fects suggest that topical administration should be the primary route of steroid therapy for anterior segment inflammations. Table 12-3 compares the achmitages and disachmitages of the three routes of steroid administration. 

Occasional development of Probable development of some adrenal adrenal suppression suppression Aggravation of a dendritic ulcer Discomfort with injection White residue possible Occasional white material, which is Epithelial keratopathy from cosmetically objectionable frequent applications Subconjunctival adhesions Occasional conjunctival infections Allergy to diluent Occasional orbital infection Occasional intraocular injection of steroid Ulceration of conjunctiva after repeated injections if not given behind the eye Exophthalmos and rugae in fundus Papilledema Adrenal suppression Occurrence of systemic side effects more likely... 

Corneal debridement Punctal plug insertion Subconjunctival injection Superficial foreign body removal Suture barb removal... 

Various ocular conditions may benefit from medication delivered via a subconjimctival injection. Applications include recalcitrant uveitis, cystoid macular edema, felling trabeculectomy, and severe corneal ulcer in a noncompli-ant patient. One to two drops of topical anesthesia should be instilled. Additionally, an anesthetic-soaked pledget of 4% lidocaine applied to the area of injection may enhance comfort, particularly if the conjunctiva is to be lifted with forceps before introducing the needle into the subconjunctival space (Figure 19-4). 

Figure 19-4 Lifting the conjunctiva with tissue forceps exposing the subconjunctival space before injection is better tolerated if an anesthetic-soaked cotton pledget is applied to the area first.

Figure 19-10 A retrotarsal block is performed by injecting anesthetic subconjunctivally along the proximal tarsal border.

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