Antibacterial Drugs:
**Mechanisms of action ( site of action )1. Nucleic acid synthesis inhibition: e.g Sulphonamides, trimethoprim, quinolones, nitrofurantoin, refampicin.
2.Protein synthesis inhibition:e.g. Macrolides, aminoglycosides, Chloramphenicol, tetracycline
3. Cell wall synthesis inhibition: e.g Vancomycin, cephalosporins, penicillins
** The β – lactam antibiotics: These are the pencillines and cephalosporines whose basic structure include β – lactam ringResistance is commonly due to bacterial enzyme called β – lactamases (( pencillinase and cephalosporinase )) which can cleave the ring and inactivate the antibiotic.
** The penicillins:
All penicillins are bactericidal with wide range of activity for both gram +ve and certain gram –ve organismIt should never given interathecallyTheir adverse effects include:
skin rash anaphylaxis drug fever interstitial nephritis haemolysis** Benzylpenicllin:
It is rapidly absorbed following intramuscular injection and excreted by the kidneys withen few hours and addition of probenecid will delay its excreation and allow smaller doses with less frequent** Procain Penicillin:
addition of procainamide, given i.m, Active against: streptococci, meningococci, anthrax, tetanus, syphilis and diphtheria.** Phenoxymethyl penicillin (( Penicillin V ))
Incompletely absorbed from the stomach Active against: streptococci.
** Cloxacillin & flucloxacillin
They are stable to staphylococcal β – lactimasesFor oral therapy flucloxacillin is superior to cloxacillin** Temocillin:
It is active against pencillinase producing gram –ve bacilli.** Ampicillin;
It has a bactericidal action against both gram +ve and certain gram –ve organismsIt is susceptible to degradation by β – lactimase and not well absorbed with food.Skin rash in patients with infectious mononucleosis** Amoxycillin:
It is an analog of ampicillin which has similar antibacterial spectrum but it is more reliably absorbed from GIT
** Augmentin
It is a combination of amoxicillin and sodium clavulanateClavulanic acid is a potent inhibitors for many β – lactemases and it can protect amoxicillin from inactivation by them.** Ticarcillin:
It is an analogue of carbencillin with more activity against Pseudomonus spp. A combination of ticarcillin and clavulanic acid is called Timentin.** Mezlocillin, azlocillin and pipracillin;
They have a wider range of activity and more effective against many gram –ve bacilli.The Cephalosporins;
1st generation e.g cephalexin, cephradin 2nd generation e.g cephaclor, cefuroxime 3rd generation e.g cefotaxime, cephitrixone 4th generation e. g cefepime, cefpirome Wide range of activity 10 % of penicillin sensitive may als allergic to them** Imipenem:
Β- lactam antibiotic with a very broad spectrum which include aerobic and anaerobic gram +ve and gram –ve organisms.The Macrolide antibiotics
** Erythromycin:
Used in treatment of infection caused by gram +ve organisms in penicillin allergic patients. It is effective in Whooping cough, pneumonia, mycoplasma and Chlamydia. S/E : diarrhea, vomiting, abdominal pain, and cholestatic jaundice.**Clarithromycin:
Greater activity than erythromycin and higher tissue concentration** Azithromycin:
More activity against gram –ve organisms including H. Influenzae.** Spiromycin:
A macrolide used in treatment of Txoplasmosis.The Tetracyclines: is a bacteriostatic agent used in Brucellosis, mycoplasma, typhus fever, Q – feverIt should not prescribed for pregnant female, children and patients with renal failure.The aminoglycosides:
They include gentamycin, streptomycin, amikacinActive against gram –ve bacilliStreptomycin has anti TB and used in treatment of BrucellosisThey are nephrotoxic and ototoxicNeomycin is too toxic to be given parantraly and used orally in hepatic encephalopathy.*** Chloramphenicol:
It is effective in enteric fever and against H. Influenzae It may cause pancytopenia It should never be given to premature infant or to the newborn because of the risk of development of gray baby syndrome.*** Clindamycin / Lincomycin
Effective against most gram +ve organisms including penicillin resistant staphylococci It pentrate well into bones so it is useful for osteomyelitis and effective in lung abscess Common cause of pseudomembranous colitis** Sodium fusidate
It is useful in infection caused by penicillin resistant staphylococci It is well absorbed and the oral rout can be used instead the parenteral rout** Spectinomycin
Used for treatment of gonorrhoea if penicillin is contraindicated because of allergy or bacterial resistance.Vancomycin and teicoplanin:
Used for serious staphylococcal infection including methicillin resistant and it is used in antibiotic associated colitis. They are nephrotoxic and ototoxic** Sulphonamides/ Trimethoprim / Co – trimoxazol Used in treatment of cystitis, UTI, typhoid fever and pneumonia S/E skin rash, nephritis and haemolysis
*** Quinolone antibiotics
Ciprofloxacin is the most important oneEffective against aerobic gram –ve bacilli.Used in treatment of typhoid fever, UTI, gonorrhoeaThey are contraindicated in children and pregnancy** Metronidazole
Effective against anaerobic bacteria and intestinal protozoa e.g Giardia Lambelia and Entameba histilytica.