Desired properties of antibiotics (ideal antibiotic)
- Selective toxicity.
- Bacteriocidal rather than bacteriostatic.
- Narrow spectrum – does not kill normal flora
- Pharmacokinetics properties : Good absorption ,Water soluble and stable. Soluble in body- Good tissue distribution – BBB.
- Long plasma half-life. Remains in body long enough to be effective - resists excretion and breakdown.
- Cost not excessive.
- Various routes of administration – IV, IM, oral
- Few adverse reactions – toxicity, allergy.
- Do not develop antibacterial resistance.
- High therapeutic index – ratio of toxic level to therapeutic level
Other factors for selection of therapy
HOST FACTORS
- Allergy
- Age
- Pregnancy
- Organ dysfunction :consideration e.g. the state of hepatic and renal functions of the patient.
- Concomitant use of drugs
- Comorbid disease states
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Antimicrobials should only be given when necessary and after antimicrobials susceptibility test whenever possible.
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The pharmacokinetics of the drug should be taken into In serious infection it is better to start with a parenteral loading of a bactericidal agent to avoid emergence of resistant strains by giving adequate dosage for sufficient duration and adapting proper combination regimens.
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Antimicrobials should be continued for 3 days after apparent cure is achieved to avoid relapse.