Which Antibacterial Agent Performs Best for the Treatment and Clearance of Chlamydophila Felis Infection in Cats ?

Clinical bottom line: Based on the current evidence, oral doxycycline (10mg/kg PO q24h or 5mg/kg PO q12h) for at least 21 days represents the most efficacious treatment, both in terms of clinical improvement and permanent clearance of Chlamydophila felis infection in cats. In chronic infections, or where the duration of disease is unknown, a longer treatment course of 28 days is indicated. There is limited evidence that co-amoxiclav (12.5-22.5mg/kg q12h PO) may be used as an alternative, though a treatment period of at least 30 days is required.

and asymptomatic. All cats infected with cultured C. psittaci via cornea and after 6 days split into one of three treatment groups: o 4 cats treated with doxycycline 5mg/kg PO q12h for 21 days.o 4 cats left untreated. Monitoring of response to treatment: o PCR and culture from conjunctival swabs daily (objective).

Clinical bottom line
Based on the current evidence, oral doxycycline (10mg/kg PO q24h or 5mg/kg PO q12h) for at least 21 days represents the most efficacious treatment, both in terms of clinical improvement and permanent clearance of Chlamydophila felis infection in cats.In chronic infections, or where the duration of disease is unknown, a longer treatment course of 28 days is indicated.There is limited evidence that coamoxiclav (12.5-22.5mg/kgq12h PO) may be used as an alternative, though a treatment period of at least 30 days is required.
o Clinical signs of infection (non-blinded except for day 9 when an outside clinician blinded to treatment groups used). Separate rooms for each group. All treated cats euthanised on day 41, all untreated on day 64, and tissue submitted for chlamydial DNA PCR analysis.
Outcome studied:  Comparison of PCR versus culture in diagnosis.
 Investigate whether shorter course of doxycycline for 28-42 days is sufficient to clear infection with C psittaci. Investigate possible sites of persistent infections following conjunctival clearance.

Main findings: (relevant to PICO question):
 Doxycycline-treated cats: o Rapid improvement in clinical signs, average duration of signs 9.3 days.o PCR negative after 8 days on average.o Remained PCR/culture negative and disease free following treatment end until euthanasia on day 42. Untreated cats showed signs for 30 days on average, PCR positive for 30.5 days on average.
Limitations:  Insufficient numbers to answer all three questions. Very small study numbers (4 treated cats) which preclude the strong conclusion that 21 days of doxycycline is sufficient. Short follow-up of 14 days post-treatment cessation. Clinical signs reported in untreated groups correlate poorly with natural infections, with cats in the study developing a severe rhinitis.This suggests a particularly virulent experimental strain and the study does not detail whether the inoculum was a field or experimental isolate.Limits extrapolation to field cases. Use of experimental colony cats limits extrapolation to field or natural infection.This represented a mono-infection, compared to field infections, where multiple infections, infectious dose, strain variation, genetic diversity of the cats and nutritional plane could impact on severity of infection and response to treatment. Only a single blinding event at day 9 with an outside clinicianrest of clinical sign logging was by unblinded investigators. Questionable use of an untreated group -these cats lost weight, had reduced appetite and generally suffered for an extended period with the disease.The authors' aims regarding treatment were to ascertain a shorter course of doxycycline so different treatment length groups could have been used.
Sample size: 24 (21 entire females, 3 neutered males). Use of clinical scoring is subject to subjective bias, especially as the treatment groups were not blinded to the investigators. Culture of chlamydial organisms is less sensitive for detecting chlamydial organisms than PCR, but has the advantage of only identifying live bacteria. No long-term follow-up, so the persistence of freedom from infection in the doxycycline/fusidic acid and chlortetracycline groups could not be assessed. Funded in part by producers of fusidic acid eye ointment at that time (Leo Laboratories) -theoretically fusidic acid (working on primarily gram-positive organisms) would have no effect on gram-negative chlamydial organisms.
Intervention details:  Inoculated with a field strain of C. psittaci via the cornea. Co-amoxiclav showed efficacy in acute infections, but with high rate of recurrence (62.5%) between 14-20 days after treatment end. Co-amoxiclav given for 30 days in chronic disease model cats (formerly placebo) and recurrent cats (following initial 19 days treatment) cleared infection with no recurrence.
Limitations:  Small number of participants per treatment group (8) make statistical tests less valid, especially with no confidence intervals stated. Randomisation method for assigning treatment groups not detailed. Use of experimental colony cats limits extrapolation to field or natural infection.This represented a mono-infection, compared to field infections, where multiple infections, infectious dose, strain variation, genetic diversity of the cats and nutritional plane could impact on severity of infection and response to treatment. Culture is less sensitive than PCR for the detection of chlamydial organisms -the 5 cats from the co-amoxiclav treated group that showed recrudescence were likely still infected by the end of treatment, which was not detected by culture. Clinical scoring is subject to subjective bias, though this was reduced by blinding the investigator to the treatment group. Author conclusions describe co-amoxiclav as an effective treatment in acute and chronic stages of chlamydiosis, but with the proviso that a further 30 day treatment course may be required after treatment of acute phase.This would mean a 49 day treatment course versus 19 days for doxycycline. Co-amoxiclav is a time-dependent antibiotic, so treating at 0900 and 1700 is likely suboptimal in maintaining MIC values in conjunctivae for sufficient periods. No investigation into the effects of doxycycline in chronic chlamydophilosis. Funded by Pfizer Animal Health, manufacturers of a licensed coamoxiclav preparation for cats.

Owen (2003)
Population: Pathogen-free experimental colony cats aged 5-6 months.Limitations:  Small numbers precluded statistical analysis. Randomisation method for assigning treatment groups and housing not detailed. Experimental colony cats, due to their husbandry, may possess a less robust immune system than free-living domesticated cats. Housing treated and untreated cats together can lead to crosscontamination and affect culture results. Culture is less sensitive than PCR for the detection of chlamydial organisms -it is likely the azithromycin cats that were negative on culture remained persistently infected. Clinical scoring is subject to subjective bias, though this was reduced by blinding the investigator to the treatment group. Dosage and dosing regime for azithromycin is poorly characterised in cats and the regime used in this study may have negatively affected the results Outcome studied: Assess efficacy of 7-day and 14-day doxycycline treatment courses on the treatment and elimination of C felis using real-time PCR to monitor course of infection and response to treatment.

Main findings: (relevant to PICO question):
 Doxycycline treated groups: o Rapid decrease in PCR copy numbers and clinical scores within 2 days of treatment and apparent clinical cure by the end of treatment.o All cats showed recurrence of disease after treatment end: 7-day cats within 4-7 days and 14-day cats within 14-21 days. All cats underwent 21-day rescue treatment: o 8/11 cleared the infection.o 3/11 required second rescue treatment of 28 days.One of these cats was from the 7-day doxycycline group and two of these cats were from the 14-day doxycycline group.o All cats showed no recurrence in the following 6 months since last treatment. Authors' recommendation is a 28-day course of doxycycline at 10mg/kg PO q24h required for elimination.
Limitations:  Small number of participants means statistical analysis could not be applied. Use of an untreated group is questionable given previous studies. Randomisation method for assigning treatment groups and housing is not detailed. Experimental colony cats, due to their husbandry, may possess a Limitations:  Small numbers make statistical analysis less useful.
 No details on randomisation procedure. Apart from the 2 cats in the pradofloxacin group that remained PCR positive throughout, no indication which cats were hospitalised or treated at home, so compliance or chances of reinfection could not be assessed. No long-term follow up (trial stopped at 42 days). Rationale for 42 days' treatment is a textbook reference. PCR is the most sensitive method of finding chlamydial DNA but does not differentiate between live and dead organisms. Clinical scoring subject to subjective bias. Modified Kanorfsky scoring for quality of life scores to track clinical improvement is not widely used or well established, and subject to operator bias. Use of pradofloxacin as a first-line treatment in the treatment of C felis is not compliant with best antibacterial prescribing guidelines. The recommendation to use pradofloxacin in young cats and those with liver disease as an alternative to doxycyline is not supported by the results.The implied contraindication in young cats is predicated on tooth discolouration which is infrequent and of no obvious clinical significance. Funded by Bayer Healthcare, who make a licensed pradofloxacin for cats and dogs.

Ploneczka-Janeczko (2008)
Population: Privately-owned cats, aged 3-10 years, which had undergone doxycycline therapy and developed vomiting or diarrhoea within the first 3 days of treatment.
Intervention details:  Cats treated with roxithromycin 5mg/kg PO q12h for 28 days then had a treatment-free period of 28 days. Monitoring of response to treatment: o PCR from conjunctival swabs (objective).
o Clinical scoring and weekly change in clinical signs (same/increased/decreased).
Study design: Case series.
Outcome studied: Evaluate the clinical efficacy of systemic roxithromycin in treating tetracycline-intolerant cats with chronic conjunctivitis caused by C felis.

Main findings: (relevant to PICO question):
 All cats showed improvement in clinical scores with treatment. No cats cleared infection, and 9/14 showed increase in DNA copy numbers by end of the study (day 56).
Limitations:  Case series with no controls. Rare to see C felis in cats of these ages, normally a disease of cats <12 months old so the possibility of co-morbidities is high. Cats were chronically infected -8 cats had shown signs for >12months, 5 for 6-12 months and 1 for 3-6 months. PCR is the most sensitive method of finding chlamydial DNA but does not differentiate between live and dead organisms. Conjunctival samples only taken at beginning and end of trial, so difficult to ascertain if ever PCR-negative. Clinical scoring subject to subjective bias and a change determined by increase/decrease/same lacks sensitivity. Relied on owners for compliance.

Appraisal, application and reflection
In all of the studies presented, systemic doxycycline therapy shows consistent efficacy against C felis both in bringing about rapid clinical improvement (however measured) within the first week of treatment, and, when given for a sufficient time period, has the most evidence for permanently eliminating infection.It is this latter aspect that makes it currently the most useful therapy versus other compounds studied (co-amoxiclav, pradofloxacin, enrofloxacin, azithromycin, roxithromycin), which, whilst bringing about clinical improvement appear insufficiently consistent at clearing infection.This is especially pertinent for shelter or stray cats, where C felis is commonplace, and infectious diseases require effective and reliable treatment to prevent spread within the facility.
However, the question of how long a course of doxycycline needs to be is more difficult to answer from the studies available.The different course lengths can be summarised as follows: One of the main weaknesses with the evidence presented here is the use of experimental cats, as their use limits extrapolation of results to field-infected free-living cats.Field infections may occur with greater doses of infectious agent, of different pathogenecity, in the face of multiple infections with other agents or against a background of other disease processes, in cats with greater genetic variation and on a variable nutritional plane.Therefore disease presentation, severity, and response to treatment may not match that seen in the field.For example, in stray or unowned animals, the chronicity of disease is unknown and response to treatment in these cases may be suboptimal, especially where secondary sequelae such as tear-duct scarring has occurred.Cats commonly present with C felis in addition to other pathogens of the upper respiratory tract disease complex (Hartmann et  providing food or water after administration may reduce potential gastrointestinal side effects, whilst others (liver enzyme increase, tooth discolouration) appear clinically insignificant and do not represent valid reasons for not using the drug.Total relevant papers when duplicates removed

Strategy
Databases searched and dates covered: CAB Abstracts and PubMed from January 1973 to September 2016 Search terms: (cat OR cats OR feline OR kitten) AND (chlamydia OR chlamydophila OR chlamydiosis OR chlamydophilosis OR psittaci) AND (treat* OR manag*) Dates searches performed: 3 rd August and 4 th September 2016 Exclusion / Inclusion Criteria Inclusion and exclusion criteria were defined before searching and are detailed below.Exclusion: Review articles, single case reports, textbook chapters, conference proceedings.Papers not available in English or not accessible.Papers that described supportive treatment measures without concurrent antibiotic treatment assessment.Papers that described C felis infection in animals other than Felis catus.Inclusion: Papers published between 1973 and present that evaluated the efficacy of antibiotic compounds for the treatment of clinical (experimental or natural) C felis infection in cats.Studies which had more than one aim, such as diagnostic modality investigation, were included.

p a g e | 5 total pages: 16
VeterinaryEvidence ISSN:2396-9776 Vol 1, Issue 2 DOI: http://dx.doi.org/10.18849/ve.v2i1.55 next review date: 20 March 2019 p a g e | 4 total pages: 16 Intervention details:  Inoculated with field strain of C. psittaci via cornea Outcome studied: Comparison of topical and systemic therapies for the treatment of experimental chlamydiosis.

7 total pages: 16 azithromycin
10-15mg/kg PO q24 for 25 days as a model of chronic disease. At the end of the trial the 2 initially untreated cats and 5 azithromycin cats were given a 28-day course of doxycycline to eradicate infection. Monitoring of response to treatment: o Culture from conjunctival swabs (objective).o Clinical scoring of disease (subjective, but investigator blinded to treatment group). Cats housed in 2 rooms, with one cat from the untreated group and one from doxycycline group in each room and the rest from azithromycin group. Monitored for 6 months post-trial for recurrence.Determination of the efficacy of azithromycin compared to doxycycline-treated controls for the treatment of C felis infection in experimentally infected cats.
Sample size: 9 (3 entire females, 6 neutered males). After initial treatment period the 2 untreated cats were given Veterinary Evidence ISSN:2396-9776 Vol 1, Issue 2 DOI: http://dx.doi.org/10.18849/ve.v2i1.55 next review date: 20 March 2019 p a g e |  Doxycycline group: o Culture negative 7 days after starting treatment.o Rapid decrease in clinical scores from day 2. o No recurrence after initial treatment course.o Cleared infection in chronically infected cats (5 azithromycin group cats and 2 untreated cats) at end of study with 28-day course. Azithromycin group: o Culture negative 7 days after starting treatment.o Rapid drops in clinical scoring from day 2. o Infection cleared in only 1 out of 5 cats (20%).Rest either remained positive or became positive again whilst still on treatment or after treatment end. Azithromycin failed to clear chronic infection in the two untreated cats given azithromycin daily for 25 days.
Inoculated with field strain of C. felis via the cornea. 7 days post-infection all cats were showing clinical signs and randomly assigned to one of three groups: o 4 cats untreated o 6 cats doxycycline 10mg/kg PO q24h for 7 days o 5 cats doxycycline 10mg/kg PO q24h for 14 days  If treatment was ineffective at eliminating infection (continued/ recurrence of clinical signs, or PCR-positive), rescue treatment 21-day course doxycycline 10mg/kg PO q24h was initiated. Monitoring of response to treatment: o PCR copy numbers from conjunctival swabs (objective).o Clinical scoring of disease (subjective but investigator blinded to treatment group). Cats were housed in rooms according to treatment group. Monitored for 6 months post-trial for recurrence.Randomised, single-blinded controlled trial.

9 total pages: 16 less
robust immune system than free-living domesticated cats. Clinical scoring is subject to subjective bias, though this was reduced by blinding. PCR does not necessarily detect active infection as it can also pick up dead bacterial material. Authors' recommendation is not fully supported by the results.Modified Karnofsky quality of life scores (subjective).Compare efficacy of enrofloxacin and doxycycline in the treatment of conjunctivitis and C felis infection in naturally infected cats, and investigate the pharmacokinetics of enrofloxacin.Cats randomly assigned to one of two groups: o 17 cats pradofloxacin 5mg/kg PO q24h and placebo q12h o 22 cats doxycycline 5mg/kg PO q12h and placebo q24h. Treatment for 42 days. Monitoring of response to treatment: o PCR for C felis, FHV and Mycoplasma spp.from conjunctival swabs PCR for FCV and Mycoplasma spp.from pharyngeal swabs (objective).o Clinical scoring (subjective but investigators blinded to treatment group).o Modified Kanorfsky quality of life score (subjective).Investigate efficacy of pradofloxacin in the treatment of cats with clinical signs of upper respiratory tract disease and its ability to eliminate C felis and Mycoplasma infection in these cats.
Veterinary Evidence ISSN:2396-9776 Vol 1, Issue 2 DOI: http://dx.doi.org/10.18849/ve.v2i1.55 next review date: 20 March 2019 p a g e | Population: Owned cats presented to University of Munich teaching hospital suffering with conjunctivitis.All were negative for FIV/FeLV, had not been pre-treated with antibacterial agents, and were not showing clinical signs of central nervous system or renal disease.Sample size: 25 cats.Intervention details:  Randomly assigned to one of two treatment groups: Veterinary Evidence ISSN:2396-9776 Vol 1, Issue 2 DOI: http://dx.doi.org/10.18849/ve.v2i1.55 next review date: 20 March 2019 p a g e | 11 total pages: 16 Intervention details:  o Ineffective at predictably clearing C felis infections.

Table 1 :
Dean et al (2005)d received either 7 or 14 day courses before the 21 day course.The 3/11 cats (27%) which recurred after 21 day treatment cleared infection with a subsequent 28-day course.The evidence available indicates that a 14-day course is insufficient, whilst a 21-day course may be sufficient in acute-stage infections which the experimental trials model.However, in field-infected cats, especially those in which the duration of infection is unknown, such as strays, a longer course may be indicated.In the study byDean et al (2005), all the cats required rescue treatment after 7 or 14-day courses of treatment, and could therefore be considered chronically infected -in these, a 28-day course was required to eliminate infection from all cats (though 73% or 8/11 cleared the infection with a 21-day course).In shelters without finances to test for organism clearance, a 28-day course may be considered more appropriate; equally, in owned cats with acute infection, a 21-day course is likely to suffice.However, without more trials with greater participant numbers involving naturally infected cats, firm conclusions cannot be drawn.
(Sturgess et al 2001)Hartmann et al 2008)-amoxiclav has shown similar efficacy to doxycycline in improving clinical signs(Sturgess et al 2001)and pradofloxacin and enrofloxacin have shown a mildly better rate of clinical improvement(Gerhardt et al 2006;Hartmann et al 2008).However, only co-amoxiclav has been shown to consistently (that is, in all cats) clear infection, though a 30-day course was required for chronically infected cats, and a 19-day course given to acutely-infected cats that showed a high rate (62.5%) of recurrence(Sturgess et al 2001).Whilst doxycycline should remain the first-line treatment, co-amoxiclav, if given for a sufficient length of time (30 days), is a reasonable alternative.
(Schulz et al 2013) bacterial infection may complicate the clinical picture and delay resolution especially as tetracyclines appear to have only moderate efficacy against studied isolates(Schulz et al 2006).However, doxycycline has well-documented anti-inflammatory effects (e.g.Krakauer and Buckley 2003) which may help with improvement of clinical signs associated with viral co-infections Several side-effects of oral doxycycline have been described.In a retrospective study of 168 cats, 13% developed vomiting, 11% diarrhoea, and 6% decreased appetite, and 36-40% showed increases in ALT or ALP during therapy(Schulz et al 2013).Oesophagitis, oesophageal stricture and tooth discolouration, whilst described elsewhere, (e.g.McGrotty and Knottenbelt 2002; German et al 2005) were absent.Gastrointestinal side effects may be attributable to the use of the doxycycline-hyclate salt which is acidic in solution, and is the compound present in the UK licensed veterinary agent (Ronaxan; Merial).Administration with food, or Veterinary Evidence ISSN:2396-9776 Vol 1, Issue 2 DOI: http://dx.doi.org/10.18849/ve.v2i1.55 next review date: 20 March 2019 p a g e | 14 total pages: 16