Systemic anti-microbial agents used in periodontal therapy

Abstract

Periodontitis is an infectious disease with marked inflammatory response, leading to destruction of underlying tissues. The aim of periodontal therapy is to eradicate the pathogens associated with the disease and attain periodontal health. This is achieved by non-surgical and surgical therapy; however, mechanical debridement and topical application of antiseptics may not be helpful in all cases. In such cases, adjunctive systemic antibiotic therapy remains the treatment of choice. It can reach micro-organisms at the base of the deep periodontal pockets and furcation areas via serum, and also affect organisms residing within gingival epithelium and connective tissue. Before advising any anti-microbial agent, it is necessary to have knowledge of that agent. The aim of this review article is to provide basic details of each systemic anti-microbial agent used in periodontal therapy. The points discussed are its mode of action, susceptible periodontal pathogens, dosage, its use in treatment of periodontal disease, and mechanism of bacterial resistance to each anti-microbial agent. It might be of some help while prescribing these drugs.

INTRODUCTION

Destructive periodontal disease appears to be caused by subgingival infection by specific microbial agent(s). Traditional therapy for these diseases has involved elimination or suppression of subgingival microbial complexes by mechanical debridement such as scaling and root planning or surgical procedures.

An increased interest in antibiotic therapy as an adjunct to standard periodontal treatment regime began in the late 1970's with the realization that certain bacteria are frequently associated with the disease process. Thus, emerging evidence of bacterial specificity in certain types of periodontitis has led to treatment strategies, which are primarily aimed at suppression or elimination of specific periodontal pathogens. These therapeutic rationales rely heavily on systemic or local administration of anti-microbial agents.

Even though systemic antibiotics have some disadvantages such as inability of systemic drugs to achieve high gingival crevicular fluid concentration,[1] an increased risk of adverse drug reactions,[2] increased selection of multiple antibiotic-resistant micro-organisms,[3] and uncertain patient compliance.[4] Systemic antibiotics do have certain advantages over topical application of anti-microbial agents. It enables simple, easy administration of the drug to multiple sites of disease activity. They may also eliminate or reduce pathogens colonizing on oral mucosa and on other extra-dental sites including tongue and tonsilar areas.[5,6,7] Thus, the chances of the micro-organism to translocate to periodontal sites and rekindle the disease reduces. Since the group of periodontal pathogens exhibit diverse anti-microbial susceptibility, microbiological analysis is necessary for proper selection of antibiotic therapy.

The different anti-microbial agents used in periodontal therapy are tetracycline, macrolides, nitroimidazole compounds, quinolones, penicillins, and cephalosporins.

The following points of each anti-microbial agent are focused on. They are its mode of action, micro-organisms susceptible, dosage, and its use in treatment of periodontal diseases and lastly, mechanism of bacterial resistance to each anti-microbial agent. The anti-microbial agents are divided depending upon their mode of action, they act by one of the following mechanisms,[1,2] the first is reversible inhibition of protein synthesis (bacteriostatic) e.g., tetracycline and macrolides (erythromycin, clindamycin, and azithromycin), the second is inhibition of DNA synthesis (bactericidal) e.g., nitroimidazole compounds (metronidazole, tinidazole, and ornidazole) and quinolones, the third mechanism is inhibition of cell wall synthesis (bacteriostatic) e.g., penicillins and cephalosporins, and the fourth is by increasing cell wall permeability e.g., chlorhexidine and triclosan (These agents are used locally.)

Tetracyclines (Agents that act by reversible inhibition of protein synthesis)

The popularity of tetracycline for treatment of non-dental infections has declined and has frequently been used for periodontal therapy. Tetracyclines are bacteriostatic in nature. They exert their anti-bacterial activity by inhibiting microbial protein synthesis. This requires access to inside of bacterial cell. Doxycycline and minocycline are more lipid-soluble than tetracycline HCL and thus pass directly through the lipid bi-layer of bacterial cell wall. Once through this layer, an energy-dependent mechanism pumps the drug through the inner cytoplasmic membrane. Within the cell, tetracycline binds specifically to 30S sub-unit of ribosome. This binding appears to prevent attachment of aminoacyl tRNA to receptor site of mRNA ribosome, which in turn prevents the addition of amino group to growing peptide chain.[8] There is also evidence that tetracycline may cause alterations in bacterial cytoplasmic membrane, facilitating leakage of nucleotides and other compounds from the cell. This action would explain the rapid inhibition of DNA replication that occurs when cells are exposed to concentrations of tetracycline in excess of that needed for protein inhibition. Doxycycline has highest protein binding capacity and the longest half-life. Minocycline has the best absorption and tissue penetration.

Tetracycline, minocycline, and doxycycline are greatly effective in inhibition of gram-negative facultative anaerobes[1] i.e., Actinobacillus Actinomycetemcomitants (Aggregatibacter Actinomycetemcomitans), Campylobacter rectus, Eikenella Corrodens, and Capnocytophaga. However, minocycline appears to be more effective than tetracycline in its inhibition of gram-negative facultative anaerobes. Tetracycline is administered orally, its absorption from GI tract is fairly rapid; however, it is reduced if the drug is taken with milk or with substances containing calcium, magnesium, iron, or aluminum, all of which chelate with tetracyclines. The chelate formed between tetracyclines and the metallic ions is not absorbed. Its dosage is 250 mg 04 times daily. The gingival fluid concentration achieved is 4-8 μg/ml,[9] and plasma concentration achieved is 1.9-2.5 μg/ml.[9] The dosage of minocycline is 100 mg twice-daily. The gingival fluid concentration achieved is 6.0 μg/ml,[9] and plasma concentration achieved is 2.6-3.3 μg/ml.[9] The dosage of doxycycline is 100 mg stat followed by 100 mg once-daily. The gingival fluid concentration achieved is 1.2-8.1 μg/ml,[9] and plasma concentration achieved is 2.1-2.9 μg/ml.[9] However, Sakkelari et al. (2000)[10] found that the average concentration of systemically administered tetracyclines in GCF was less than in plasma and varied widely among individuals (between 0 and 8 μg/ml).

Apart from anti-bacterial activity, tetracycline also exhibit additional pharmacological properties, which are of significance in management of periodontal disease. They are, (a) Collagenase inhibition:[11] Tetracycline has anti-collagenase property. However, the anti-collagenase activity appears to be related to source of enzyme and tetracycline used. Interstitial collagenases are proteinase-type enzymes, which degrade connective tissues. These enzymes are derived from a number of sources including fibroblast, epithelial cells, macrophages (MMP-1), and neutrophils (MMP-8). Tetracycline is less active against fibroblast-type collagenase and most active against neutrophil-derived collagenase. Doxycycline is the most potent tetracycline for collagenase inhibition. Inhibition of collagenase activity is related to the drugs ability to bind with calcium (present on enzymes) and zinc ions. Tetracycline can also scavenge reactive oxygen radicals (e.g., hypochlorous acid and hydroxyl groups) produced by PMNs. It has been found that these oxygen radicals activate latent collagenase, thus tetracyclines can prevent the oxidative activation of latent collagenase.[12](b) Anti-proteolytic property:[13] Tetracycline inhibition of neutrophil collagenase may also prevent other proteolytic events because neutrophil collagenase (MMP-8) as well as neutrophil-derived reactive oxygen species, i.e., hypochlorous acid, hydrogen peroxide, and hydroxyl radicals, can degrade and inactivate α-1 proteinase inhibitor. (c) Inhibition of bone resorption:[14] Bone anti-collagenase and anti-proteolytic activity has been resulted in application of these drugs to inhibit bone resorption. Tetracyclines inhibit bone resorption induced by parathyroid hormone.[15] It inhibits osteoblast collagenase and may also have a modifying effect on osteoclasts. (d) Anti-inflammatory actions:[16] Potential anti-inflammatory properties include the ability of tetracycline to suppress PMN activity, in particular, by scavenging action on reactive oxygen metabolites. Drug may block eicosanoid synthesis (especially PGE₂) by inhibiting phospholipase A2 activity. (e) Enhance fibroblast attachment - Pre-treatment of dentin with tetracycline enhances fibroblast attachment and colonization.[17,18] (f) Property of sub-stantivity.[19] (g) Sub-inhibitory concentrations have been shown to reduce adherence and co-aggregation of species including P. gingivalis and P. intermedia.[20,21] The side effects of tetracyclines are: It should not be prescribed in children below age of 08 years and in pregnant patients as it gets deposited in teeth and bone.

Tetracyclines have been used in the treatment of localized juvenile Periodontitis,[22,23,24,25,26] generalized juvenile periodontitis,[27] early onset periodontitis,[28] and adult periodontitis.[29] The different mechanisms of bacterial resistance to tetracyclines are either by acquisition of R-plasmid which carry genes which are resistant to antibiotics (Plasmid is extra-chromosomal genetic material that can replicate independently and freely in cytoplasm) or by acquisition of transposon-associated genetic material (Transposon are DNA segments that cannot self-replicate but can self-transfer between plasmids or from plasmid to chromosomes; during this transfer or co-integration, transposon can replicate, and the each new plasmid contains r-gene, which results in resistance). Also, efflux pump is another mechanism of resistance (Efflux pumps are cytoplasmic membrane transport proteins, which protect bacterial cell from foreign chemical invasion and are regulated by a number of genes) and lastly by resistance genes, which encode ribosomal protection proteins. These proteins release ribosome-bound tetracycline and, at the same time, increase the apparent dissociation constant of the tetracycline ribosome interaction, thereby reducing the possibility of a further interaction between the ribosome and the released drug. Currently, 38 tetracycline resistance genes have been identified, of which 23 encode efflux pumps, 11 encode ribosomal protection proteins, 3 encode inactivating enzymes, and 1 is of unknown function.[30]

Macrolides (Agents that act by reversible inhibition of protein synthesis)

Erythromycin was the 1^st macrolide used. Newer macrolides include clindamycin and azithromycin. All macrolides act by inhibition of protein synthesis. They are bacteriostatic in nature. Bacterial ribosome containing 50S subunit contains peptide forming catalytic site. There is peptidyl transferase center (the active site) and a protein exit tunnel, through which nascent polypeptide exits the ribosome. The macrolides bind to close sites in the region of entrance to the exit tunnel; this plugs the tunnel, leading to peptidyl tRNA drop off.[31]

Erythromycin was the first macrolide used. It is extremely safe drug. Erythromycin has a wide range of activity against both gram-positive facultative and anaerobic bacteria. However, most gram-negative micro-organisms are resistant to erythromycin due to its inability to penetrate the lipopolysaccharide-cell wall complex. The dosage of Erythromycin is 250 mg 3 times a day. The gingival crevicular fluid concentration achieved is 0.4-0.8 μg/ml.[9]

Its use is not indicated as an adjunct in the treatment of periodontitis due to the incidence of gram-negative anaerobes associated with such sites. The limitation of erythromycin is that its tissue absorption is poor, so preparations for systemic administrations are provided as pro drugs to facilitate absorption. This pro drug has little anti-bacterial activity until hydrolyzed by serum esterases.[1]

Clindamycin is an antibiotics, which may be helpful in the treatment of patients who do not respond to conventional treatments consisting of scaling and root planning and surgery. It is particularly useful in penetrating bone.[32]

Clindamycin is active against gram-positive cocci, including many penicillin-resistant staphylococci and anaerobic species such as bacteroides species.

It is very effective against most putative periodontal pathogens with important exception of Aa, and Eikenella Corrodens Walker (1990)[33] found marked reduction in percentages of peptostreptococcus, β - hemolytic streptococci, various oral gram-negative anaerobic rods. The adult dosage of Clindamycin is 300 mg 3-4 times a day. The gingival crevicular fluid concentration achieved is 1-2 μg/ml,[9] and plasma concentration achieved is 1-9 μg/ml.[9] Clindamycin has been used for the treatment of refractory periodontitis[34,35,36] and rapidly progressing periodontitis.[37]

Clindamycin should be prescribed with caution because of potential for pseudomembranous colitis as a result of intestinal overgrowth with Clostridium difficile.[38]

Azithromycin is the 1^st of a subclass of macrolides called azalides. It shows good bacteriostatic in vitro activity against a wide variety of organisms found in mouth. It has long half-life, and it provides higher drug concentrations in the tissues than in blood or serum. In addition, azithromycin is preferentially taken up by phagocytes, and so, its level in infected tissues is much higher than in similar non-infected sites.[39] The adult dosage of azithromycin is 250-500 mg dose once a day for 5 days, following an initial loading dose of 500 mg as opposed to erythromycin.[40] Azithromycin should be taken 01 hour before or 02 hours after food intake. It exhibits excellent ability to penetrate into both normal and pathological periodontal tissues.[41] It is active against gram-negative anaerobes, and the drug has been found to be highly effective against all serotypes of Actinobacillus acti-nomycetemcomitans[42] and against Porphyromonas gingiualis.[43] There is a significantly greater decrease in number of black pigmented bacteroides in patients taking azithromycin. Also, spirochete count is found to be less.[44] Azithromycin has been used for the treatment of chronic periodontitis.[45,46]

The different mechanisms of bacterial resistance to all macrolides are either by target modification. It can be either by methylation or by mutation of nucleotide 2058 of the 23S ribosomal RNA. Mutations have also been described in ribosomal proteins L4 and L22, which also affect macrolide interaction with the ribosome.

Resistance can be by inactivation of the antibiotic by enzymes (e.g., esterases inactivate erythromycin and phosphorylases, which inactivate macrolides.)[47] or by efflux pumps

Nitroimidazole compounds (Agents that act by inhibition of DNA synthesis)

It includes metronidazole, tinidazole, and ornidazole. Metronidazole has broad in vitro activity against anaerobic organisms. Following systemic administration relatively high peak plasma concentrations are attained within 1-3 hours. Ornidazole, has higher level of half-life elimination from plasma (14.4 hrs) than metronidazole (8.4 hrs), therefore, require less frequent intake, that is twice-daily. Metronidazole act by inhibiting DNA synthesis. There is general agreement that inactive form passively diffuses into cell where it is activated by chemical reduction. The nitro group reduced to anion radical targets DNA, which it oxidizes, leading to strand breakage and cell death.[48] Hence, metronidazole has both anti-microbial and mutagenic effect. It exerts its anti-bacterial effect primarily on obligate gram-positive and gram-negative anaerobes. The gram-negative obligate anaerobes are P. Gingivalis, P. Intermedia, Fusobacterium, Selenomonas sputigina, Bacteroides Forsythus, The gram-positive obligate anaerobes are Peptosteptococcus also. C. Rectus, a facultative anaerobe and probable periodontal pathogen, is susceptible to low concentration of metronidazole.

The adult dosage of metronidazole is 200-400 mg 3 times a day. The dosage of tinidazole is 300-500 mg 2 times a day and that of ornidazole is 500 mg 2 times a day. The gingival fluid concentration achieved is 13.7 μg/ml,[9] and plasma concentration achieved is 14.3 μg/ml.[9] Also, according to Liew V et al. (1991),[49] metronidazole can readily attain effective anti-bacterial concentrations in gingival tissue and crevicular fluid. Nitroimidazole compounds have been used for the treatment of ANUG (metronidazole),[50,51] refractory periodontitis (metronidazole)[52,53] (ornidazole),[54] adult periodontitis (metronidazole,)[55,56] and early onset periodontitis (ornidazole).[57] Metronidazole resistance is uncommon.[58] However, when present, it is most likely to be the result of a lack of reducing potential, leading to impairment of pro-drug activation. A different resistance mechanism has also been described in bacteroides, in which the nitro group is reduced as far as an amine.

A unique side-effect of metronidazole is a disulfiram (antabuse) effect. This effect causes cramps, nausea, and vomiting following alcohol consumption.[59] Also, patients undergoing anti-coagulant therapy and patients taking lithium should avoid metronidazole. It should not be used in pregnant patients. It should not be used in patients with a history of seizures.[60]

Quinolones (Agents that act by inhibition of DNA synthesis)

Fluoroquinolones are a group of broad-spectrum agents that are based upon nalidixic acid. Ciprofloxacin is the most widely used of this category of antibiotics.

Quinolones act on DNA gyrase, the enzyme responsible for unwinding and supercoiling of bacterial DNA prior to its replication. Quinolones thus inhibit bacterial replication and transcription. It also inhibits topoisomerase IV in gram-positive bacteria[61] and thus interferes with the separation of replicated chromosomal DNA into the respective daughter cells during cell division.

Ciprofloxacin is effective against a wide range of both gram-positive and gram-negative micro-organisms. Clinically, ciprofloxacin is best used for infections caused by facultative and aerobic gram negative rods and cocci. The adult dosage of ciprofloxacin is 500 mg twice-daily. It should be taken 01 hour before or 02 hours after food intake. It penetrates readily into periodontal tissue and GCF and may reach even higher concentrations than in serum. According to Conway TB (2000),[62] mean gingival fluid ciprofloxacin levels observed were 2.5-2.7 μg/ml, which were well in excess of ciprofloxacin MIC for A actinomycetemcomitans (0.010 μg/ml). Fluoroquinolones are effective against the pasteurellaeae family, to which Actinobacillus actinomycetemcomitans belongs;[63] therefore, it can be used in Aa-associated periodontitis. Kleinfelder et al. (2000)[64] reported that systemic ofloxacin in conjunction with open flap surgery was able to suppress A. actinomycetemcomitans below detectable levels in 22 study patients for a period of 12 months. It has been used in Papillon Lefevre syndrome patients with A. actinomycetemcomitans infection.[65] and advanced periodontal disease.[66] It should not be prescribed to children and young individuals due to potential joint problems observed for ciprofloxacin in growing animals. The different mechanisms of bacterial resistance to quinolones are first is alteration in the target enzymes brought about by mutations in gyr A/gyrB and parC/pare, which encode for the A/B and C/E subunits of DNA-gyrase and topoisomerase IV, respectively. GyrA mutations generally relate to a specific region of the chromosome linked with quinolone resistance called the QRDR region.[67] Another mechanism is mutations in outer-membrane porins (OmpF) causing reduced drug uptake. It is not considered to be of major significance clinically, unless occurring in the presence of other resistance factors.[68] Less significant resistance mechanism is the plasmid-associated qnr gene product in E Coli.[69]

Penicillins (Agents that act by inhibition of cell wall synthesis)

They are natural and semi-synthetic derivatives of broth cultures of Penicillium mold. Penicillin act by inhibition of cell wall synthesis.[1] It is bactericidal in nature. It possesses substantial anti-bacterial activity for gram-negative species. It has been found to be ineffective against Aa, even if Augmentin is used. Amoxicillin exhibits high anti-microbial activity at levels that occur in GCF for all gram-positive periodontal pathogens, except E. Corrodens, S. Sputigena, and Aa. It inhibits growth of gram-positive facultative anaerobes such as Streptococcous and Actinomyces, except Peptostreptococcus, which is an obligate Gram-positive anaerobe. The different mechanisms of bacterial resistance to Penicillins are first is mutations in the genes encoding the porins, resulting in either loss of porin or structural change resulting in impaired drug uptake, have been reported in numerous bacterial species. Structural studies suggest that β -lactamases arose from one, or a number of, low-molecular-mass penicillin-binding proteins which, in response to naturally occurring β -lactam antibiotics, initially lost the signal-like peptide, thereby enabling them to function as β -lactam detoxifiers or secreting agents, and which underwent further mutations, resulting in transformation into β-lactam hydrolyzing enzymes.[70] Thus, administration of beta-lactamase sensitive penicillins is not generally recommended and in some cases, may accelerate periodontal destruction.[71,72] The mechanism can be circumvented by the use of a β- lactamase inhibitor such as clavulanic acid, and this is used in the combination of amoxycillin with clavulanic acid in Augmentin. Augmentin is available as 375 mg or 625 mg, tablet which contain 250 mg and 500 mg of amoxicillin, respectively, and 125 mg clavulanic acid (Same amount of clavulanic acid is present in 375 mg and 625 mg tablets). The concentrations achieved in GCF[73] are 14.05 μg ml⁻¹ (amoxicillin) and 0.40 μg ml⁻¹ (clavulanic acid). Effective levels well above minimal inhibitory concentration of some susceptible periodontal anaerobes (P. intermedia) are achieved. Augmentin has been used in the treatment of refractory periodontitis[35,36,74,75] and rapidly progressing periodontitis.[73]

As A. actinomycetemcomitans shows resistance to penicillins and to erythromycin and clindamycin, to prevent bacterial endocarditis in susceptible individuals, a pre-treatment course of 3 weeks of tetracycline has been recommended for these patients.

Penicillin may be associated with hypersensitivity reactions (anaphylaxis). It may develop resistance and may result in diarrhea.

Cephalosporins (Agents that act by inhibition of cell wall synthesis)

They are most commonly used antibiotics. Their use is often for infections that might otherwise be treated with penicillin. It is available as cephalexin for oral use. It acts by inhibition of cell wall synthesis. Thus, bactericidal.[1] It can effectively inhibit growth of gram-negative obligate anaerobes but may fail to inhibit gram-negative facultative anaerobes.[1] Gram-negative obligate anaerobes are P. Gingivalis, P. Intermedia, Fusobacterium. Sputigena, B. Forsythus. Cephalosporins are effective in the treatment of gram-positive infections. Newer cephalosporins with extended gram-negative effectiveness could be of value in the treatment of periodontal conditions. No clinical trials in periodontal therapy have been conducted.

Combination therapy

It may help to broaden the anti-microbial range of therapeutic regimen beyond that attained by any single antibiotic. It may prevent or forestall the emergence of bacterial resistance by using agents with overlapping anti-microbial spectra, and it lowers the dose of individual antibiotic by exploiting possible synergy between 2 drugs against targeted organisms. Disadvantages are there can be increased adverse reactions, and antagonistic drug interactions with improperly selected antibiotics may occur. Bactericidal antibiotic (β Lactam drugs or metonidazole) should not be used with bacteriostatic agents (tetracyclines), because the bactericidal agent exerts activity during cell division that is impaired by bacteriostatic drug. Neither erythromycin nor azithromycin should be given concurrently with clindamycin, because they have similar modes of action. Different combinations are used for treatment of periodontal diseases. Metronidazole – amoxicillin combination is used in Aa-associated localized juvenile periodontitis, Papillon Lefevre syndrome periodontitis, adult type periodontitis, rapidly progressing periodontitis, generalized advanced periodontitis, and refractory periodontitis,[76,77,78,79] in P. intermedia infected sites,[76,77,78] and in generalized aggressive periodontitis.[80] Metronidazole – ciprofloxacin combination is used in recurrent adult periodontitis.[81] Metronidazole – Augmentin combination has been used in refractory periodontitis.[82]

CONCLUSION

Systemic anti-microbial therapy can thus be used as an adjunct to mechanical therapy in patients with aggressive periodontitis, who do not respond to mechanical treatment, who has acute or severe periodontal infection and who is systemically compromised. However, systemic anti-microbial agents should be used with caution in patients on long-term medication for cardiovascular disease, asthma, seizures, or diabetes as there can be drug interaction. Also, it should be prescribed in indicated patients as it has some side-effects. All systemic anti-microbial agents, if used in proper dosage, can achieve effective levels to be effective against periodontal pathogens. Since the group of periodontal pathogens exhibit diverse anti-microbial susceptibility, microbiological analysis is sometimes necessary for proper selection of antibiotic therapy, and as antibiotic resistance constitutes an increasing problem, anti-microbial susceptibility testing of isolated pathogens is important. If microbiological testing is unavailable, combination therapy is preferred. Also, as periodontitis lesions often harbor a mixture of pathogenic bacteria, drug combinations have gained interest.