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Oral Meds:  Antibiotics


The trend of simplifying dosing and administration of oral antibiotics is paralleling that of the anti-glaucoma drugs; i.e., once- or, at most, twice-daily dosing. Most older antibiotics have been reformulated to use higher dosages less frequently, and virtually all newer antibiotics are either qd or bid. Since compliance issues always loom over clinical care, we welcome these easier dosing schedules.

Summarizing the antibiotics, there are five main classes:
• Penicillins/synthetic penicillins
• Cephalosporins (1st, 2nd, and 3rd generations)
• Macrolides (erythromycin is prototype)
• Tetracyclines
• Fluoroquinolones

Penicillins/synthetic penicillins
Since most infections of the eyes and adnexal tissues are gram-positive organisms (mostly staph and some strep), we must select medicines with efficacy against these pathogens. Most staphylococcal bacteria produce an enzyme—penicillinase—that inactivates penicillins and can dampen the effect of some cephalosporins. Also, a sizeable number of patients have allergic reactions to the penicillins.

Amoxicillin is a commonly used synthetic penicillin in general medical practice; however, it is inactivated by penicillinase and therefore has no role in eye care. Over 20 years ago, researchers developed a small group of drugs known as penicillinase-resistant penicillins, such as dicloxacillin, which is highly staphylococcal. But because these drugs have to be used qid, we rarely use them in favor of antibiotics effective at bid dosing.

All physicians are familiar with Augmentin. It is a combination of amoxicillin with clavulanic acid. Now, if amoxicillin is protected from the derogatory effects of penicillinase, it becomes a highly effective killer of gram-positive bacteria. This is indeed the enabling effect of clavulanic acid.

Augmentin has traditionally been dosed at 500mg tid for one week; however, in keeping with the trend toward more patient-friendly dosing schedules, it is now commonly prescribed at 875mg bid, and at 1000mg (Augmentin XR) bid for more serious infections, and/or perhaps in larger persons.

Cephalosporins
The cephalosporins are highly useful in treating skin diseases of the ocular adnexa. Erythromycin is the choice in pregnancy. A fluoroquinolone is excellent when treating penicillin-allergic patients.

Although there are numerous antibiotics that will perform nicely, we have selected cephalexin (Keflex) 500mg bid x 1 week as our antibiotic workhorse. It has proven efficacy against the most gram-positive bacteria and should work well for most bacterial infections in and around the ocular surface.

Be aware that the cephalosporins share slight cross-allergenicity with the penicillins. This appears to be largely ignored (usually without consequence) in clinical practice. However, if a person gives a history of a life-threatening reaction to a penicillin-class drug, we would not prescribe any cephalosporin, but rather go to a macrolide (i.e., the erythromycin class) or an oral fluoroquinolone.

Macrolides
The macrolides (erythromycin, azithromycin and clarithromycin) are excellent second-line drugs in the event circumstances preclude the use of a penicillin or cephalosporin. Also, because of their pregnancy category B rating, they are preferred to treat women with bacterial infections who are, or may be, pregnant. Consult with the patient’s obstetrician in all such circumstances.

We generally prefer azithromycin (Zithromax) because it is used as two 250mg capsules on day one, followed by a 250mg capsule qd for four more days when treating skin infections. For chlamydial conjunctivitis, it is a simple single dose of four 250mg capsules (i.e., 1000mg). Pfizer also makes a 1000mg azithromycin suspension that is poured into half a glass of water and swallowed. Either approach is fine for treating chlamydia infections.

Tetracyclines
There are 3 commonly-used drugs within the tetracycline class: tetracycline itself, doxycycline, and minocycline.

We most always prescribe doxycycline because it is dosed only once or twice a day, and can be taken without regard to meals. While doxycycline is primarily an antibiotic, it has many useful secondary functions, one of which is to modify and enhance the lipid metabolism in oil producing glands. It is this role in restoring more physiological lipid production that doxycycline can have a positive effect on tear film function. We generally prescribe two 50mg capsules daily for a month (as a loading dose), then just one 50mg capsule daily x 3 to 6 months or longer, depending upon the clinical response.

Most people tolerate doxycycline very well. The main aggravation is the occasional vaginal candidiasis. Most women (and certainly their OBGYNs) are adept at handling this. We have used doxycycline with many, many patients over the years and have come to have great appreciation for its restorative power regarding tear film abnormalities with meibomian gland dysfunction.

Fluoroquinolones
Another approach when penicillin allergy is encountered is to prescribe an oral fluoroquinolone. Since the macrolides are bacteriostatic, the bactericidal fluoroquinolones may be the best choice for penicillin-contraindicated patients, especially if the infectious process is moderate to severe. Ciprofloxacin (Cipro) or ofloxacin (Floxin) have been workhorses since the late 1980s and remain good choices; however, resistance is beginning to become problematic. Our fluoroquinolone of choice is levofloxacin (Levoquin) and is dosed one 500mg tablet once daily for one week.