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ePaper created 2016-11-22, 09:52:12 | version 1.38.0
| CE article antibiotics 12 roots 4 2016 portant is to expose the host to the antimicrobial agentforasshortadurationoftherapyaspossible. The shorter the duration of therapy the lower the risktothepatientforthedevelopmentofantibiot- ic-induced toxicity and/or allergy, and a reduced risk of developing resistant microorganisms. 2. Thegoalofantibioticdosingistoachievedruglev- els in the infected tissue equal to or exceeding the minimal inhibitory concentration of the target or- ganism. Serum levels of antibiotics do not neces- sarilyreflectthoseintissues.Bloodconcentrations of the antibiotic should exceed the MIC by a factor of two to eight times in order to offset the tissue barriers that restrict access of the drug to the in- fected site. 3. It is advisable to initiate antibiotic therapy with a loading dose (an initial dose higher than the main- tenancedose).Anantibioticloadingdoseshouldbe used whenever the half-life of the drug is longer than three hours or whenever a delay of 12 hours or longer to achieve a therapeutic blood level is expected.Mostantibioticsusedinthetreatmentof orofacial infections have a half-life shorter than three hours but, due to their acute nature, most orofacialinfectionsrequiretherapeuticdrugblood levels sooner than 12 hours. Steady-state blood levels of any drug are usually achieved in a time equal to three to five times the drug’s half-life. Amoxicillinhasahalf-lifeofonetoone-and-a-half hours. A steady-state blood level would then be achieved in three to seven-and-a-half hours, thereby leading to a substantial delay in achieving therapeutic antibiotic blood levels. A loading dose of two times the maintenance dose is recom- mendedforacuteorofacialinfections,whichbetter achieves the goal of rapid, high blood levels rather thaninitiatingtherapywiththemaintenancedose. 4. Anoralantibioticshouldideallybeadministeredat dosing intervals of three to four times its serum half-life, particularly if steady-state blood levels are desired (as may be indicated with beta-lactam agents). For example, the serum half-life of Pen-V- Kis 0.75 hours. Higher continuous blood levels of this antibiotic are more likely to be obtained with four-hour rather than six-hour dosing intervals. The shorter the serum half-life of the drug, the shorter the dosing interval will need to be in order to maintain continuous therapeutic blood levels of the drug. When determining the appropriate dosing interval, it is also important to consider the following: 1) The post antibiotic effects of the drug; and 2) the relative merits of continuous or pulse dosing. PAEs are more persistent (two to seven hours) with antibiotics that act intracel- lularly within the microbial cytoplasm (erythro- mycin, clindamycin and tetracycline) or by sup- pression of nucleic acid synthesis (metronidazole, quinolones).As a result, these antibiotics are more effective with pulse dosing (high antibiotic dosing at widely spaced intervals). The beta-lactam anti biotics,however,haveaslow,time-dependentkill- ing activity and demonstrate very little PAE. Be- ta-lactammicrobialkillingrequiresmicrobesinthe process of cell division (interference with cell wall development); hence, they must be continuously present (steady-state blood levels) because bacte- ria divide at different rates or times. Myth No. 8: Bacterial infections require a “complete course” of antibiotic therapy There is no such thing as a “complete course” of antibiotic therapy.3 The only guide for determining theeffectivenessofantibiotictherapy,andhence,the duration of treatment, is the clinical improvement of the patient.16 A common misconception asserts that prolonged(afterclinicalremissionofthedisease)an- tibiotic therapy is necessary to prevent “rebound” in- Medical Conditions for Which Endocarditis Prophylaxis is Recommended: Premedication is recommended ONLY for patients with the following conditions associated with the highest risk of adverse outcomes from endocarditis: 1.Prosthetic cardiac/heart valve. 2.History of IE. 3.Cardiac transplant recipients who develop valve pathology. 4.One of the following congenital heart diseases: – Unrepaired cyanotic CHD,including palliative shunts and conduits. – Completely repaired congenital heart defects with prosthetic material or device, whether placed by surgery or by catheter intervention,during the first six months after placement of the material or device (because endothelialization of prosthetic material occurs within six months after the procedure). – Repaired CHD with residual defects at,or adjacent to,the site of a prosthetic patch or prosthetic device (which inhibits endothelialization). 5.Special situations and circumstances: – Patients already receiving antibiotics—Occasionally,a patient may be taking an antibiotic when coming for a dental appointment.If the patient is taking an antibiotic normally used for endocarditis prophylaxis,it is prudent to select a drug from a different class rather that increase the dose of the current antibiotic.If possible,you should delay the dental procedure until at least 10 days after completion of the antibiotic.This will allow for the usual oral flora to be re-established.If an individual receiving long-term parenteral antibiotic therapy for IE requires dental treatment,the treatment should be timed to occur 30 to 60 minutes after the parenteral antibiotic therapy has been delivered. – Failure to administer pretreatment antibiotic dose—If the dosage of an antibiotic is inadvertently not administered before the procedure,the dosage may be adminis- tered up to two hours after the procedure.However,administration of the dosage after the procedure should be considered only when the patient did not receive the preprocedure dose. –Individualswithkidneydialysisshunts—Individualswithpermanentkidneydialysis shuntsshouldbeplacedonprophylacticantibioticsusingthesameprotocolasforIE. Table 2 42016