Antimicrobial drugs
Lecture 1. Antimicrobial or anti-infective: drugs have the ability to injure or kill an invading m.o without harming the cell of the host. Include antibacterial, antiviral, and antifungal drugs. . Antibiotics: are chemicals produced by one kind of microorganism that inhibit the growth of or kills another.
Antimicrobial therapy takes advantage of the biochemical differences that exist between microorganisms and human beings:
Antimicrobial drugs are effective in the treatment of infections because of their selective toxicity they have the ability to injure or kill an invading microorganism without harming the cells of the host In most instances.
Antibacterial
Antibacterial / antimicrobial drugs - Substances that inhibit the growth of or kill bacteria . Bacteriostatic = Inhibits growth of bacteria and replication thus limiting the speared of infection while the immune system attacks , immobilize and eliminate the pathogen . Bactericidal = Kills bacteriaCHEMOTHERAPEUTIC SPECTRA
A. Narrow-spectrum antibiotics Chemotherapeutic agents acting only on a single or a limited group of microorganisms. For example, eg . Penicillin & erythromycin B. Extended-spectrum antibiotics Antibiotics that are effective against gram-positive organisms and also against a significant number of gram-negative bacteria. For example, ampicillin is considered to have an extended spectrum because it acts against gram-positive and some gram-negative bacteria .C. Broad-spectrum antibiotics Drugs such as tetracycline and chloramphenicol affect a wide variety of microbial species and are referred to as broad-spectrum antibiotics . Administration of broad-spectrum antibiotics can drastically alter the nature of the normal bacterial flora and precipitate a superinfection of some organism.
Advantages of combinations of antimicrobial agents
1-Therapy of sever infection in which a cause is unknown. 2-treatment of polymicrobial infection 3-enhancement of antibacterial activity of drug (synergism) 4-prevention of emergence of resistance microorganisms.Disadvantages of combination of antimicrobial agents
1- increased risk of toxicity 2-eradication of normal host flora. 3-increase cost.
Antibiotics misuses
1- Rx of nonresponsive infections:90%of antibiotic therapy of UTI and GIT is ineffective (self limiting infections) 2-therapy of fever of unknown origin: fever of short duration in the absence of localizing signs is usually associated with undefined viral infection and resolve spontaneously 3-improperd dosages: increased dose ------------ toxic decreased dose ------------ failure of treatment (Short or too long treatment)4-inappropriate reliance of chemotherapy alone: infection complicated by abscesses , necrotic tissues , foreign bodies can not cure by antibiotics alone. 5- lack of adequate bacteriological examination
Antimicrobial Resistance
Relative or complete lack of effect of antimicrobial against a previously susceptible microbe.Enzymatic destruction of drug Prevention of penetration of drug Alteration of drug's target site Rapid ejection of the drug
Mechanisms of Antibiotic Resistance
Super infection: a new or secondary infection that can produce over growth of organism that are differ from original infection resist to agent being used and these infection are difficult to treat . Over growth of Candida albican.
SELECTION OF ANTIMICROBIAL AGENTS
Selection of the most appropriate antimicrobial agent requires knowing1) the organism’s identity 2) the organism’s susceptibility to antibiotic. 3) the site of the infection 4) patient factors5) the safety of the antibiotic.6) the cost of therapy.ROUTE OF ADMINISTRATION
The oral route of administration is chosen for infections that are mild . Parenteral administration is used: for drugs that are poorly absorbed from the G.IT.for treatment of patients with serious infections. 2.it is necessary to maintain higher serum concentrations of antimicrobial agents