Drugs Used in Ophthalmology

Anti-Biotics

𝑷𝒓𝒂𝒕𝒚𝒖𝒔𝒉 𝑫𝒉𝒂𝒌𝒂𝒍 DOA,FOOptometristAdvanced Eye Hospital and InstituteSanpada,Navi Mumbai

Definition

• Type of antimicrobial used specifically against bacteria, and are often used in medical treatment of bacterial infections.

• They may either kill or inhibit the growth of bacteria.

• Several antibiotic agents are also effective against a number of fungi, protozoans and some are toxic to humans and animals

• Antibiotics are not effective against viruses such as the common cold or influenza, and may be harmful when taken inappropriately.

Anti-Biotics

• Broad classifications

• Bacteriostatic and Bactericidal

• Narrow/intermediate/Broad spectrums

• Tab/cap/syr/ed/eo/iv/im/ivit

• Gram-Negative and Gram-Positive

Gram Positives• Gram-positive bacteria are those that are

stained dark blue or violet by Gram staining. The examples for gram-positive bacteria are Bacillus, Nocardia, Clostridium, Propionibacterium, Actinomyces, Enterococcus, Cornyebacterium, Listria, Lactobacillus, Gardnerella, Mycobacterium, Mycoplasma, Staphylococcus, Streptomyces, and streptococcus

• Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol and The examples for Gram-negative bacteria are Escherichia coli (E.coli), Helicobcater, Hemophilus, Neisseria, Cyano bacteria, Klebsiella, Acetobacter, Enterobacter, Chlamydia, Vibrio, Pseudomona, Salmonella, Thiobacter, Borrelia, Burkholderia, Serratia, Treponema

6 groups of Anti-Biotics

• Sulfonamides:In bacteria, antibacterial sulfonamides act as competitive inhibitors of the enzyme dihydropteroate synthetase (DHPS), an enzyme involved in folate synthesis. Sulfonamidesare therefore bacteriostatic and inhibit growth and multiplication of bacteria, but do not kill them. Humans, in contrast to bacteria,

aquire folate (vitamin B9) through the diet.

• E.g Sulfadizine, Sulfacetamide, Sulfadimidineetc

Beta-lactam antibiotics

• These antibiotics have a beta-lactam ring. The two important groups are penicillins, and cephalosporins.All beta-lactam antibiotics act by interfering with the synthesis of bacterial cell wall.

• A. Penicillins. These are produced by growing one of the penicillium moulds in deep tanks. These may be categorised as: natural penicillins and

semisynthetic penicillins.

PENICILLIN

• Benzyl penicillin

• Procaine penicillin

• Methicillin, cloxacillin and flucloxacillin

• Carbenicillin.

• Ampicillin Its dosage is 0.25-2 g oral/i.m./i.v. depending

upon the severity of infection every 6 hours. Paediatric dose is 25-50 mg/kg/day

• Amoxycillin

cephalosporin's• 1.First-generation (narrow spectrum) cephalosporins.These

are very active against grampositive cocci and thus have useful antistaphylococcalactivity. These include cefazolin,cephradine, cephalexin and cephadroxyl.

• 2. Second-generation (intermediate spectrum)

cephalosporins. These have antistaphylococcal activity and are also effective against certain gram-negative organisms. They comprise cefuroxime, cefamandole and cefoxitin.

• 3. Third-generation (wide spectrum) cephalosporins.

These are mainly effective against gramnegative organisms but not against staphylococci.These include: cefotaxime, cefiximeand cefotetan.

Aminoglycosides• These are bactericidal and act primarily against gramnegative

bacilli. These are not absorbed orally, distributed mainly extracellularly and are excreted unchanged in the urine. These are ototoxic and nephrotoxic. Certain aminoglycosides are too toxic for systemic use and hence used only topically.

• Commonly used preparations are as follows:

• 1. Streptomycin. It is used mainly in tuberculosis.

• 2. Gentamicin. It has become the most commonly used aminoglycoside for acute infections. It has a broader spectrum of action and is effective against Pseudomonas aeruginosa. It is nephrotoxic, therefore, its dose must be precisely calculated according to body weight and renal function. For an average adult with normal renal function, the dose is 1-1.5 mg/kg intramuscularly 8 hourly. Topically, it is used as 0.3% eyedrops.

• 3. Tobramycin. It is 2-4 times more active against Pseudomonas aeruginosa and Proteus as compared to gentamicin. Topically, it is used as 1% eyedrops.

• 4 Amikacin. It is recommended as a reserve drug for hospital acquired gram-negative bacillary infections where gentamicin resistance is increasing.

• 5. Neomycin. It is a widespectrum aminoglycoside,activeagainst most gram-negative bacilli and some gram-positive cocci. However, Pseudomonas and Streptococcus pyogenesare not sensitive to it. It is highly toxic to internal ear and kidney and hence used only topically (0.3-0.5%).

• 6. Framycetin. It is very similar to neomycin. It is also too toxic for systemic use and hence used only topically. It is available as 1 percent skincream; 0.5 percent eye ointment and eyedrops.

• Tetracyclines

• These are broad-spectrum bacteriostatic agents with a considerable action against both gram-positive and gram-negative organisms as well as some fungi,rickettsiae and chlamydiae. This group includes tetracycline, chlortetracycline and oxytetracycline.

• Chloramphenicol

• It is also a broad-spectrum antibiotic, primarily bacteriostatic, effective against gram-positive as well as gram-negative bacteria, rickettsiae, chlamydiae and mycoplasma.Its molecule is relatively small and lipid soluble.Therefore, on systemic administration, it enters the eye in therapeutic concentration. Topically it is used as 0.5% eyedrops.

Polypeptides

• These are powerful bactericidal agents, but rarely used systemically due to toxicity. Clinically used polypeptides are polymyxin B, bacitracin, colistinand tyrothricin.

• 1. Polymyxin B and colistin. These are active against most gram-negative bacteria, notably Pseudomonas.

• 2. Neosporin (neomycin-polymyxin-bacitracin). It is an effective broad-spectrum antimicrobial but suffers the disadvantage of a high incidence (6-8%) of sensitivity due to neomycin.

Fluoroquinolones

• Fluoroquinolones are potent synthetic agents having broad spectrum of activity against gram-positive and gram negative-organisms.

• Mechanism of action. Fluoroquinolones are

bactericidal drugs. These inhibit the bacterial DNA synthesis.

Common use in Eyes

• To treat Bacterial Conjunctivitis

• Prophylactic pre-operatively

• Bacterial and Fungal keratitis

• To prevent secondary infections