non-surgical periodontal therapy (3): antibiotics in periodontal therapy

lecture given 3/31/2026

generally, why are antibiotics used in conjunction with SRP?

to increase the effect of treatment- SRP leads to a reduction in the level of periodontal pathogens but does not modify the composition of subgingival biofilm sufficiently to create a new, beneficial bacterial community

antibiotics (broadly)

naturally occuring, semisynthetic, or syntheic type that eliminates or inhibits the growth of selective microorganisms at a low concentration that is harmless to host tissues

do not remove calculus and plaque so it is used only as an adjunct to mechanical therapy

what are the ideal requirements of an antibiotic?

specific for periodontal pathogens, do not cause allergic and hypersensitive reactions, active in plasma and other body fluids, desired levels should be achieved rapidly and maintained for an adequate time, not cause drug resistance, inexpensive

what are the classifications of antibiotics?

basis of chemical structure/side chain

basis of spectrum of activity (narrow or broad)

basis of mechanism of action

basis of type of action

classification of antibiotics based on chemical structure/side chain

sulfonamides, beta lactam, tetracyclines, macrolides, lincosamides, quinolones, glycopeptide, nitroimidazole, aminoglycosides

classification of antibiotics based on spectrum of activity

narrow- penicillin G, penicillin V/VK

broad- tetracycline, clinidamycin, azithromycin, fluoroquinolones, cephalosporin, metronidazole, sulfonamides

classification of antibiotics based on mechanism of action

inhibit cell wall synthesis- penicillin, vancomycin, cephalosporin

inhibit protein synthesis- tetracyclines, clindamycin, azithromycin

inhibit DNA synthesis- fluoroquinolones, metronidazole

interfere with intermediary metabolism- sulfonamides

classification of antibiotics based on type of action

bactericidal- agent eliminates bacteria population / penicilin, vancomycin, cephalosporin, metronidazole, fluoroquinolones

bacteriostatic- agent prevents the growth of bacteria / tetracyclines, clindamycin, erythromycin, sulfonamides

why do you need to consider age when prescribing antibiotics?

patients at young and ol dage take drugs differently by affecting pharmacokinetics of antibiotics

children- all antibiotic doses need to be adjusted, tetracycline can cause staining of teeth and depressed skeletal growth, fluoroquinolones cause cartilage toxicity in young animals

eldery adults- all antibiotic doses need to be adjusted for altered pharmacokinetics, clindamycin can cause p. colitis, penicillins can cause increased anaphylaxis due to prior exposure

why do you need to consider renal or liver dysfunction when prescribing antibiotics?

modification in type and dosage of antibiotics is necessary when liver or kidney become defective

why do you need to consider impaired host defense when prescribing antibiotics?

bacteriostatic- patients with normal host defence

bactericidal- patients with impaired host defense

why do you need to consider drug allergy when prescribing antibiotics?

allergy to antibiotics can cause severe and life threatening allergic reaction, history should be obtained

why do you need to consider local factors when prescribing antibiotics?

increase activity of antibitoics like biotransformation to more active molecule and elevated temperature

decreased activity of antibiotics like decrease in pH and barriers to drug entry in presence of pus and necrotic material

why do you need to consider organism identification when prescribing antibiotics?

culture and sensitivity tests

in cases not responding to conventional therapy

why do you need to consider drug factors when prescribing antibiotics?

spectrum of activity, type of activity

how can you measure antimicrobial activity?

MIC90- minimum inhibitory concentration which inhibit growth of 90% of bacterial strains

Cgcf- gingival fluid concentration by systemic delivery for periodontal pathogens in pocket

antimicrobial activity %: 100 (Cgcf x MIC90)

lower MIC90 value indicates…

less of drug is required to inhibit growth of pathogens indicating more effective antimicrobial agents

why do you need to consider pregnancy when prescribing antibiotics?

to be avoided to prevent risk of fetal abnormalities

how should you dose antibiotics?

use high loading doses for a short duration to achieve maximum blood and tissue levels by oral route quickly

use doses 2 to 8 times the MIC to compensate tissue barriers to reach site of infection

use frequent dosing intervals to maintain constant blood levels

how should you determine the duration of antibiotics?

antibiotic therapy should be terminated as soon as patient host defenses gained control of the infection

no difference in effect of short vs standard duration

avoid side effects and development of resistant bacteria

systemically administered bacteriostatic require longer periods to be effective as compared to bactericidal counterparts

what are the indications for antibiotics in periodontal therapy?

chronic periodontitis, refractory periodontitis, aggressive periodontitis, necrotizing ulcerative gingivitis/periodontitis (NUG/NUP), patients with acute periodontal infections (periodontal abscess) with systemic manifestations

what are some reasons for failure of antibiotic therapy?

patient noncompliance of not taking antibiotics, incorrect choice of antibiotic (antibiotic antagonism like tetracycline and milk), emergence of antibiotic resistant pathogens, low antibiotic concentration in blood due to low dosage, restricted blood flow or vascularity, failure to penetrate site of infection (pus) and low pH, failure to drain all infection after incision to remove source of infection, failure to eradicate pathogens due to low growth rate (beta lactams require organisms to divide to eliminate, old abscess have slow growth rate of pathogens), impaired host immune defense system

how can antibiotics be administered?

systemic administration, local administration

what are the pros of systemic antibiotics?

simple and easy administration of drug to multiple disease sites

eradicate pathogens on both oral mucosa and extra-oral sites

what are the cons of systemic antibiotics?

multiple antibiotic resistance

risk of adverse drug reactions

difficult to achieve high GCF concentration

unpredictable patient compliance

what are the systemic antibiotic treatment options for periodontal disease?

penicillin (amoxicillin), clindamycin, metronidazole, tetracyclines (doxycycline), azithromycin, fluoroquinolones (ciprofloxacin)

penicillin

bactericidal

natural derivative of penicillium mold

major activity in g+

amoxicillin is semisynthetic penicillin with extended spectrum that includes both G+ and - bacteria

clinical use: adjunct to SRP

what are the pharmacokinetic/dynamic properties of penicillin?

interfere with synthesis of bacteria cell wall by inhibiting cross linking by transpeptidases

usual daily adult oral dosage is 500mg tid for 7 days

side effects of hypersensitivity (rash), diarrhea, nausea/vomiting

drug interaction with probenecid (tx of gout), inhibits excretion of penicillin and increase plasma penicillin drug levels

augmentin (amoxicillin clavulanic acid)

clavulanic acid is an inibitor of beta lactamases

makes effective against antibiotic resistant due to beta lactamase activity

spectrum increases to cover beta lactamase producing pathogens

usual daily adult oral dosase is 875mg bid for 7 days

does systemic penicillin administration work with severe periodontitis pts?

haffajee et all found amox/cla improved PD and CAL compared to placebo or ibuprofen

clindamycin

bacteriostatic

used for patients allergic to penicillin

effective against G+ and - anaerobic bacteria

clinical use: adjunct to SRP for pts allergic to penicillin (no longer recommended due to increased risk of p. colitis), refractory periodontitis

what are the pharmacokinetic/dynamic properties of clindamycin?

inhibition of protein synthesis by binding to 50s ribosome

usual adult dosage is 300mg tid for 8 days

side effects of diarrhea, p. colitis (aka c. dif), nausea/vomiting

drug interactions with anti-diarrheals (decreases absorption), muscle relaxants (increases frequency and duration of respiratory paralysis), erythromycin (mutual antagonism)

does systemic clindamycin administration work with severe periodontitis pts?

gordon et all found clin w scaling improved clinical variables, reduced motile organisms, ect

walker & gordon found clin w scaling improved clincal variables and reduced annual rate of sites with disease activity

metronidazole

bactericidal

synthetic nitroimidazole

major activity in G + and - obligate anaerobes

clinical uses: adjunct to SRP, for treatment of NUG/NUP, recalcitrant/refractory periodontitis with p. gingivalis or p. intermedia, it should be used in combination with other antibiotic (amox) for treatment of localized aggressive periodontitis as it does not eliminate A. a alone

what are the pharmacokinetic/dynamic properties of metronidazole?

inhibtion of DNA synthesis

usual adult dose is 500mg tid for 8 days

side effects of nausea/vomiting, possible risk of teratogenicity so avoid in 1st trimester (cat. B)
drug interactions with barbituates and hydantoins (decreased effectiveness of metronidazole), warfarin (increased anticoagulant effect), alcohol (disulfiram reaction like nausea, vomiting, headache)

does systemic metronidazole administration work with severe periodontitis pts?

loesche et all found more reduction in PD, more gain in CAL, reduced level of pathogens

tetracycline

bacteriostatic

natural derivative of strptomyces or derived semi-synthetically

broad spectrum- active against G+ and - aerobic and anaerobic bacteria

clinical use: benefit of inhibiting gingival collagenases, periodontal infections in which A. a is the prominent pathogen, in mixed infections it does not provide sufficient suppression (adjunct to SRP, treatment of localized aggressive periodontitis)