Oral and Systemic Medications In Eyecare: Part III
BY WILLIAM TOWNSEND, OD
My previous two columns in this series about oral medications and eye care discussed management of pain and inflammation and the use of beta lactams (penicillins and cephalosporins) in treating soft tissue infections. In this issue I will continue to explore the use of antibiotics in eye care.
Tetracyclines are usually bacteriostatic; they inhibit the synthesis of protein in bacterial cell cytoplasm. Tetracyclines do affect human protein synthesis, but their effect on bacterial cells is much greater.
Administer tetracycline qid because it is excreted rapidly via the kidneys. Dose newer tetracyclines (docycycline, minocycline) less frequently. All drugs in this group interfere with bone and tooth development, so do not prescribe them to pregnant or lactating females or children under 8 years of age. They also cause increased light sensitivity, so warn patients on these medications to limit UV exposure or use high SPF (greater than 30) sun protection.
Tetracyclines are useful for treating lid infections, and they also treat meibomian gland dysfunction and acne rosacea. This group of medications has successfully treated adult inclusion conjunctivitis (AIC). Typically dose active infections for seven to 10 days as follows: tetracycline 250 mg qid, doxycycline 50 mg bid, minocycline 50 mg bid. For lid infections, prescribe the medications for seven to 10 days. Treat AIC for 21 days; all the patient's sexual partners must also be treated. Tetracyclines should not be taken with dairy products or vitamins that contain calcium. Do not give tetracyclines concurrently with beta lactams because they interfere with the bactericidal action of beta lactams.
Macrolides also inhibit protein synthesis. They are excreted by the liver, so avoid them in patients with hepatic failure. Erythromycin and azithromycin are two excellent examples of this class of drug. Both are good for lid infections (some resistant strains of staph exist) and AIC. Erythromycin ethysuccinate, one of several forms of the drug, is available in 400 mg tablets usually taken tid.
Azithromycin (Zithromax) is a relatively new macrolide that is available in either a 1 gram monodose that is commonly used for AIC, or in Z-Pak, with a 500 mg loading dose on day one and 250 mg qd for four days thereafter. Patients taking this drug may experience nausea, vomiting, abdominal pain, diarrhea and decreased appetite.
Fluroquinolones kill bacteria by inhibiting DNA gyrase, an enzyme that allows "super-coiling" of bacterial chromosomes. Fluroquinolones do not affect similar enzymes in mammalian cells. They are bactericidal, and newer fluoroquinolones are very active against Gram-negative organisms such as Pseudomonas. However, these medications are expensive and often cause gastric upset.
We prefer more commonly-used antibiotics for most conditions we treat. In severe lid infections or situations where you encounter resistance to other antibiotics, oral ciprofloxacin (Cipro) (available in 100 mg, 250 mg, 500 mg and 750 mg film-coated tab-lets) is an effective antibacterial agent. Treat skin and lid infections with 500 mg every 12 hours.
Levofloxacin is a newer fluoroquinolone with activity similar to Cipro, but conveniently dosed in 250 mg or 500 mg qd. Levaquin can elevate blood glucose, so closely monitor diabetics taking this medication. Patients taking this medication should also avoid antacids with magnesium, alumi-num and zinc, which can reduce the efficacy of the antibiotic.
Dr. Townsend is in private practice in Canyon, Texas, and consults at the Amarillo VA Medical Center. E-mail him at firstname.lastname@example.org.