Pharmacokinetics of pradofloxacin and doxycycline in serum, saliva, and tear fluid of cats after oral administration

Performance and overview of clinically relevant areas of application of saliva testing in the cat

Introduction

The cat represents an important model in order to investigate basic physiological knowledge of salivary secretion as well as pharmacokinetics of active substances.

Objective

The aim of the study was to review in which diagnostic application areas saliva testing is routinely used and in which areas it could be further explored in the future.

Materials and methods

Literature relevant to the research question was collected in March 2022 using the Pubmed database.

Results

The diagnosis of infectious diseases in cat saliva is one of the most important fields of application. Saliva diagnostics may also indicate dental diseases, allergies or kidney and other metabolic diseases. Sexual and stress hormones can also be measured in cat saliva. A number of clinically relevant allergens in cat saliva that may cause allergies in humans has been investigated and described, in addition to infectious agents that can be transmitted from cats to humans.

Conclusions

Saliva testing in cats can be useful in many areas, including the detection of infectious diseases, allergies and dental disease. However, it is far from being used to its full potential within veterinary medicine.

Kinetics and minimal inhibitory concentrations of ceftiofur in tear film following extended-release parenteral administration (Excede®) in dogs

Purpose

Describe the pharmacokinetics of extended-release parenteral ceftiofur (Excede^®) in canine tear film and compare these concentrations to minimal inhibitory concentrations (MICs) of ceftiofur against common ocular pathogens in dogs.

Method

Six dogs of various breeds were enrolled. Disruption of blood-tear barrier was achieved with histamine-induced conjunctivitis to ensure clinical relevance of the results. Each dog received a single subcutaneous injection of 5 mg/kg Excede^®, followed by tear collection with Schirmer strips at times 0, 0.25, 0.5, 1, 2, 4, 8, 12, 24, 36, 48, 72, 96, 120, 144, 168, 192, 216 and 240 h. Drug quantification was performed with liquid chromatography-mass spectrometry. MICs were determined for Staphylococcus pseudintermedius, Streptococcus canis and Pseudomonas aeruginosa by assessing bacterial growth (n = 10 per bacterial species) in the presence of ceftiofur at increasing concentrations.

Results

Blood-tear barrier breakdown provided tear film concentrations of ceftiofur 3.2–28.9-fold higher than in the contralateral healthy eye (n = 1 dog, pilot experiment). In all six dogs, ceftiofur concentrations in tears varied from 2.3 to 637.5 ng/mL and were detectable up to 10 days (240 h) after subcutaneous injection. However, tear levels always remained below MICs for common ocular isolates (≥640 ng/mL).

Conclusions

Ceftiofur reached the tear compartment (for up to 10 days) after a single parenteral injection, however tear concentrations were extremely variable and too low to be effective against common bacterial pathogens in dogs. Further studies with different ceftiofur dosage or other long-acting injectable antibiotics are warranted.

Doxycycline pharmacokinetics in mammalian species of veterinary interest – an overview

Doxycycline is a broad-spectrum tetracycline antibiotic widely used in veterinary medicine. The current review aims to summarise the available data about pharmacokinetics in mammalian species of veterinary interest and to indicate the basic strategies for refining dosage regimens in order to use this antibiotic reasonably. Additionally, the available data about population pharmacokinetics are reviewed as this approach exhibits a number of benefits in terms of determination of drug phar­ma­cokinetics, prediction of drug disposition and interpretation of the variations in the pharmacokinetic parameters. Further research with animal species of veterinary interest and pathogens causing diseases in animals is needed to clarify the pharmacokinetics and pharmacodynamics of doxycycline.

In Vitro Effects of Doxycycline on Replication of Feline Coronavirus

Feline infectious peritonitis (FIP) is a sporadic fatal disease of cats caused by a virulent variant of feline coronavirus (FCoV), referred to as FIP virus (FIPV). Treatment options are limited, and most of the affected cats die or are euthanized. Anecdotally, doxycycline has been used to treat FIP-affected cats, but there are currently no data to support or discourage such treatment. The aim of this study was to establish whether doxycycline inhibits replication of FIPV in vitro. The virus was cultured in Crandell-Rees feline kidney cells with various concentrations of doxycycline (0 to 50 µg/mL). The level of FIPV in cultures was determined by virus titration and FCoV-specific reverse-transcription quantitative PCR. Cell viability was also monitored. There was no difference in the level of infectious virus or viral RNA between doxycycline-treated and untreated cultures at 3, 12- and 18-hours post-infection. However, at 24 h, the growth of FIPV was inhibited by approximately two logs in cultures with >10 µg/mL doxycycline. This inhibition was dose-dependent, with inhibitory concentration 50% (IC₅₀) 4.1 µg/mL and IC₉₀ 5.4 µg/mL. Our data suggest that doxycycline has some inhibitory effect on FIPV replication in vitro, which supports future clinical trials of its use for the treatment of FIP-affected cats.

Metabolism and pharmacokinetics of pharmaceuticals in cats (Felix sylvestris catus) and implications for the risk assessment of feed additives and contaminants

In animal health risk assessment, hazard characterisation of feed additives has been often using the default uncertainty factor (UF) of 100 to translate a no-observed-adverse-effect level in test species (rat, mouse, dog, rabbit) to a 'safe' level of chronic exposure in farm and companion animal species. Historically, both 10-fold factors have been further divided to include chemical-specific data in both dimensions when available. For cats (Felis Sylvestris catus), an extra default UF of 5 is applied due to the species' deficiency in particularly glucuronidation and glycine conjugation. This paper aims to assess the scientific basis and validity of the UF for inter-species differences in kinetics (4.0) and the extra UF applied for cats through a comparison of kinetic parameters between rats and cats for 30 substrates of phase I and phase II metabolism. When the parent compound undergoes glucuronidation the default factor of 4.0 is exceeded, with exceptions for zidovudine and S-carprofen. Compounds that were mainly renally excreted did not exceed the 4.0-fold default. Mixed results were obtained for chemicals which are metabolised by CYP3A in rats. When chemicals were administered intravenously the 4.0-fold default was not exceeded with the exception of clomipramine, lidocaine and alfentanil. The differences seen after oral administration might be due to differences in first-pass metabolism and bioavailability. Further work is needed to further characterise phase I, phase II enzymes and transporters in cats to support the development of databases and in silico models to support hazard characterisation of chemicals particularly for feed additives.

Tear film concentrations of topically applied 0.5% oxytetracycline ointment in normal canine eyes

OBJECTIVE

To determine the tear film levels of oxytetracycline in normal canine eyes after application of the ophthalmic ointment, Terramycin™ (0.5% oxytetracycline, polymyxin B sulfate), to guide appropriate treatment frequency.

ANIMALS STUDIED

Ten research beagles.

PROCEDURES

Ten research beagles with confirmed normal eyes were administered 0.02 mL of Terramycin™ ophthalmic ointment onto the dorsal bulbar conjunctival surface of the right eye. Tear samples were collected via dye-less Schirmer tear strips at 2, 4, 6, 8, and 12 hours post-administration. The sample for each timepoint was collected on a separate day, and concentrations of oxytetracycline were determined using high-performance liquid chromatography (HPLC).

RESULTS

There was a semi-logarithmic decline in the median tear concentration of oxytetracycline. The median (2.5th and 97.5th percentiles) tear concentrations of oxytetracycline at 2, 4, 6, 8, and 12 hours were 43.5 μg/mL (11.1-302.2 μg/mL), 28.7 μg/mL (8.04-113.7 μg/mL), 16.1 μg/mL (4.96-37.7 μg/mL), 9.2 μg/mL (4.52-28.1 μg/mL), and 6.11 μg/mL (4.36-26.7 μg/mL), respectively. Mean (±SD) drug recovery via HPLC was 88% (±7.5%).

CONCLUSIONS

Ophthalmic Terramycin™ achieves a substantially higher tear level than the MIC for common bacterial corneal pathogens up to 12 hours post-administration in normal eyes. Anti-collagenolytic tear levels were not achieved at the timepoints evaluated or with the manufacturer-prescribed dosing frequency. HPLC can be used to analyze tear concentrations of ophthalmic ointment formulations.

Utility of systemic voriconazole in equine keratomycosis based on pharmacokinetic-pharmacodynamic analysis of tear fluid following oral administration

Objective

To clarify the detailed pharmacokinetics (PK) of orally administered voriconazole in tear fluid (TF) of horses for evaluating the efficacy of voriconazole secreted into TF against equine keratomycosis.

Animals studied

Five healthy Thoroughbred horses.

Procedures

Voriconazole was administrated through a nasogastric tube to each horse at a single dose of 4.0 mg/kg. TF and blood samples were collected before and periodically throughout the 24 hours after administration. Voriconazole concentrations in plasma and TF samples were analyzed using liquid chromatography‐electrospray tandem‐mass spectrometry. The predicted voriconazole concentration in both samples following multiple dosing every 24 hours was simulated by the superposition principle.

Results

The mean maximum voriconazole concentrations in plasma and TF were 3.3 μg/mL at 1.5 h and 1.9 μg/mL at 1.6 h, respectively. Mean half‐life in both samples were 16.4 and 25.2 h, respectively. The ratio of predicted AUC_0–24 at steady state in TF (51.3 μg∙h/mL) to previously published minimum inhibitory concentration (MIC) of Aspergillus and Fusarium species was >100 and 25.7, respectively.

Conclusions

This study demonstrated the detailed single‐dose PK of voriconazole in TF after oral administration and simulated the predicted concentration curves in a multiple oral dosing. Based on the analyses of PK‐PD, the simulation results indicated that repeated oral administration of voriconazole at 4.0 mg/kg/d achieves the ratio of AUC to MIC associated with treatment efficacy against Aspergillus species. The detailed PK‐PD analyses against pathogenic fungi in TF can be used to provide evidence‐based medicine for equine keratomycosis.

Oral doxycycline pharmacokinetics: Lambs in comparison with sheep

The pharmacokinetics of doxycycline was investigated in lactating sheep and lambs after oral administration at a dose of 10 mg/kg. Concentrations in plasma and milk were assayed with HPLC-PDA analysis. Doxycycline penetrates into the milk, and levels (0.38 ± 0.21 μg/ml) were found 0.5 hr after the treatment. The results suggest that the lambs can be exposed to doxycycline by suckling milk from their treated mothers. Population pharmacokinetic analysis showed a positive relationship between age, which reflects the stage of development of rumen function, and clearance. Possible explanations for the observed differences include the undeveloped rumen in lambs, the differences in the feed and liver function as evidenced by the blood biochemical parameters aspartate aminotransferase (AST) and alanine aminotransferase (ALT), which were significantly lower in lambs (62.67 ± 27.83 U/L and 8.50 ± 6.80 U/L) than in sheep (114.33 ± 20.77 U/L and 18.00 ± 3.16 U/L).

Pharmacokinetic/Pharmacodynamic Integration of Doxycycline Against Mycoplasma hyopneumoniae in an In Vitro Model

Doxycycline is a broad-spectrum antibacterial drug. It is used widely to treat diseases caused by Mycoplasma species. We investigated the antibacterial activity of doxycycline against the Mycoplasma hyopneumoniae strain ATCC25934. The minimum inhibitory concentration (MIC) of doxycycline against M. hyopneumoniae determined by a microdilution method was 0.125 μg/ml. Static time-kill curves with constant drug concentrations (0-64 MIC) showed that a bacteriostatic effect occurred if the doxycycline concentration reached 4 MIC. Doxycycline produced a maximum antimycoplasmal effect (reduction of 2.76 log₁₀CFU/ml) at 64 MIC within 48 h. The effect of doxycycline against M. hyopneumoniae was analyzed by a sigmoid E _max model, and there was high correlation between the kill rate and doxycycline concentration (R ² = 0.986). A one-compartment open model with first-order absorption was adopted and was used to simulate doxycycline pharmacokinetics in porcine plasma. The dynamic time-concentration curve showed that the area under the curve at 24 h (AUC_{24 h}) and C _max (peak concentration) after each drug administration was 1.78-48.4 μg h/ml and 0.16-3.41 μg/ml, respectively. The reduction of M. hyopneumoniae (log₁₀CFU/ml) for 1, 2.5, 5, 7.5, 10, 15, 20, and 30 mg/kg body weight was 0.16, 1.29, 1.75, 2.94, 3.35, 3.91, 4.35, and 5.77, respectively, during the entire experiment, respectively. When the dose was >10 mg/kg body weight, continuous administration for 3 days could achieve a bactericidal effect. The correlation coefficient of AUC_{24 h}/MIC, C _max/MIC, and %T > MIC (the cumulative percentage of time over a 24-h period that the drug concentration exceeds the MIC) with antibacterial effect was 0.917, 0.923, and 0.823, respectively. Doxycycline showed concentration-dependent activity, and the value of AUC_{24 h}/MIC and C _max/MIC required to produce a drop of 1 log₁₀CFU/ml was 164 h and 9.89, respectively.

Medical management of deep ulcerative keratitis in cats: 13 cases

CASE SERIES SUMMARY

Described are 13 cats diagnosed with deep ulcerative keratitis and successfully managed medically without grafting procedures. Typical treatment involved frequent topical application of serum and antibiotics (usually a fluoroquinolone and a cephalosporin). Seven cats also received systemic antibiotics. Analgesia was achieved using various combinations of topical atropine and systemic buprenorphine, robenacoxib or corticosteroids. Six cats were hospitalized for a median (range) period of 2.5 (1-8) days, typically because of frequent medication administration. Median (range) follow-up time was 41.5 (9-103) days. Median (range) number of recheck examinations was 4 (2-6). Median (range) time to corneal re-epithelialization was 21 (9-103) days. Median (range) topical antibiotic course was 29.5 (16-103) days. Median (range) duration of Elizabethan collar use was 28 (13-73) days. At the time of writing, no further recheck examinations were recommended for 10 cats; median (range) time between initial to final examinations in these cats was 35 (20-103) days. All cats retained the affected globes and were apparently comfortable and visual at the latest recheck examination.

RELEVANCE AND NOVEL INFORMATION

These cases reveal that aggressive medical management is highly successful in select cats with deep ulcerative keratitis, and can result in a cosmetically acceptable, apparently comfortable and visual globe. However, therapy is intensive with frequent administration of multiple topical and sometimes systemic medications, and requires multiple veterinary visits over many weeks. Referral to a veterinary ophthalmologist for consideration of surgical stabilization is recommended, as not all cases may be amenable to the medical therapy described here.

Impact of Flow Rate, Collection Devices, and Extraction Methods on Tear Concentrations Following Oral Administration of Doxycycline in Dogs and Cats

Purpose: Compare the precision of doxycycline quantification in tear fluid collected with either Schirmer strips or polyvinyl acetal (PVA) sponges following oral drug administration.

Methods: Three dogs and 3 cats were administered doxycycline orally at a dose of 4.2–5 mg/kg every 12 h for 6 consecutive days. At day 5 and 6, blood and tear fluid were sampled to capture doxycycline trough and maximal concentrations. Tear fluid was collected 3 times (spaced 10 min apart) at each session with the absorbent material placed in the lower conjunctival fornix until the 20-mm mark was reached (Schirmer strip, one eye) or for 1 min (PVA sponge, other eye). Tear extraction was performed with either centrifugation or elution in methanol. Doxycycline concentrations were measured with liquid chromatography–mass spectrometry. Low (100 ng/mL) and high (1,000 ng/mL) tear concentrations measured in vivo were spiked into each absorbent material in vitro to evaluate percentage drug recovery.

Results: After oral administration of doxycycline, the drug reached the tear compartment at concentrations of 45.1–900.7 ng/mL in cats and 45.4–632.0 ng/mL in dogs, representing a tear-to-serum ratio of 12% and 16%, respectively. Doxycycline tear concentrations were significantly more precise when tear collection was performed with Schirmer strips rather than PVA sponges (P = 0.007), but were not correlated with tear flow rate. In vitro doxycycline recovery was poor to moderate (<75%).

Conclusions: Schirmer strips represent a good option for lacrimal doxycycline quantification, although the collection and subsequent extraction have to be optimized to improve drug recovery.

In vitro selection of resistance to pradofloxacin and ciprofloxacin in canine uropathogenic Escherichia coli isolates

This study explored and compared the mechanisms and selective concentration of resistance between a 3rd (pradofloxacin) and 2nd (ciprofloxacin) generation fluoroquinolone. Pradofloxacin- and ciprofloxacin-resistant mutants were selected by stepwise exposure of Escherichia coli (E. coli) to escalating concentrations of pradofloxacin and ciprofloxacin. The sequence of the quinolone resistance determining region (QRDR) and the transcriptional regulator soxS were analyzed, and efflux pump AcrAB-TolC activity was measured by quantitative real-time reverse transcription-PCR (qRT-PCR). First-step mutants reduced the fluoroquinolone sensitivity and one mutant bore a single substitution in gyrA. Four of six second-step mutants expressed ciprofloxacin resistance, and displayed additional mutations in gyrA and/or parC, while these mutants retained susceptibility to pradofloxacin. All the third-step mutants were fluoroquinolone resistant, and each expressed multidrug resistance (MDR) phenotypes. Further, they displayed resistance to all antibacterials tested except cefotaxime, ceftazidime and meropenem. The number of mutations in QRDR of gyrA and parC correlated with fluoroquinolone MICs. Mutations in parC were not common in pradofloxacin-associated mutants. Moreover, one second- and one third-step ciprofloxacin-associated mutants bore both mutations at position 12 (Ala12Ser) and 78 (Met78Leu) in the soxS gene, yet no mutations in the soxS gene were detected in the pradofloxacin-selected mutants. Altogether, these results demonstrated that resistance emerged relatively more rapidly in 2nd compared to 3rd generation fluoroquinolones. Point mutations in gyrA were a key mechanism of resistance to pradofloxacin, and overexpression of efflux pump gene acrB played a potential role in the emergence of MDR phenotypes identified in this study.

Development of microextraction by packed sorbent for toxicological analysis of tricyclic antidepressant drugs in human oral fluid

The aim of this study was to apply microextraction by packed sorbent (MEPS) to the isolation of six tricyclic antidepressants (TCADs): nordoxepin, doxepin, desipramine, nortriptyline, imipramine, and amitriptyline from human oral fluid. Samples were collected from healthy volunteers via free spillage from the oral cavity to disposable test tubes. A method of oral fluid sample pretreatment was developed and optimized in terms of suitability for MEPS extraction and removing of interfering agents (protein, food debris, or air bubbles). Moreover, it was short and simple to perform with limited sample consumption (150μL). Extracts were analysed by UHPLC-MS. The MEPS/UHPLC-MS method was validated at three concentration levels (2.00, 4.00 and 8.00ng/mL) of all analytes in the range 1.25-10.0ng/mL. The following parameters were determined: limit of detection, limit of quantification, precision, and accuracy. For all tested concentration levels, the intra- and inter-day repeatability did not exceeded 8.1% and 12.2%, respectively. Gained LOQ value, 0.50ng/mL, made the MEPS/UHPLC-MS method to be a useful tool in clinical and forensic laboratories, which was demonstrated on the basis of analysis of real samples.

Pharmacokinetics of doxycycline in tilapia (Oreochromis aureus × Oreochromis niloticus) after intravenous and oral administration

The pharmacokinetics of doxycycline was studied in plasma after a single dose (20 mg/kg) of intravenous or oral administration to tilapia (Oreochromis aureus × Oreochromis niloticus) reared in fresh water at 24 °C. Plasma samples were collected from six fish per sampling point. Doxycycline concentrations were determined by high-performance liquid chromatography with a 0.005 μg/mL limit of detection, then were subjected to noncompartmental analysis. Following oral administration, the double-peak phenomenon was observed, and the first (Cmax1 ) and second (Cmax2) peaks were 1.99 ± 0.43 μg/mL at 2.0 h and 2.27 ± 0.38 μg/mL at 24.0 h, respectively. After the intravenous injection, a Cmax2 (12.12 ± 1.97 μg/mL) was also observed, and initial concentration of 45.76 μg/mL, apparent elimination rate constant (λz) of 0.018 per h, apparent elimination half-life (t1/2λz) of 39.0 h, systemic total body clearance (Cl) of 41.28 mL/h/kg, volume of distribution (Vz) of 2323.21 mL/kg, and volume of distribution at steady-state (Vss) of 1356.69 mL/kg were determined, respectively. While after oral administration, the λz, t1/2λz, and bioavailability of doxycycline were 0.009 per h, 77.2 h, and 23.41%, respectively. It was shown that doxycycline was relatively slowly and incompletely absorbed, extensively distributed, and slowly eliminated in tilapia, in addition, doxycycline might undergo enterohepatic recycling in tilapia.

Utility of noninvasive biomatrices in pharmacokinetic studies

Blood and plasma are the biomatrices traditionally used for drug monitoring and their pharmacokinetic profiling. Blood is the circulating fluid in contact with all organs and tissues of body and thus is the most representative fluid for measuring systemic drug levels. However, venipuncture suffers from the caveat of being an invasive technique which often makes people reluctant to participate in clinical studies. Thus, there is a need for noninvasive bio-fluids that are ethically appropriate, cost-efficient and toxicologically relevant. These alternate bio-fluids may prove clinically useful as alternatives to plasma/serum in therapeutic drug monitoring, pharmacokinetic and toxicokinetic studies, doping control in sports medicine and to monitor local adverse effects. These may be of particular interest in the case of special population groups such as neonates, children, the elderly, terminally ill patients and pregnant or lactating women, and offer the advantage of circumvention of the demand for specialized personnel for sample collection. This review describes such noninvasive bio-fluids (saliva, sweat, tears and milk) that have been considered for pharmacokinetic drug analysis, emphasizing their sample preparation, its associated difficulties and their correlation with plasma.

Pharmacokinetics, pharmacodynamics and therapeutics of pradofloxacin in the dog and cat

Pradofloxacin is a third-generation fluoroquinolone, licensed in the EU for use in a range of indications in the dog and cat and authorized more recently in the USA for one therapeutic indication (skin infections) in the cat. This review summarizes and appraises current knowledge on the physico-chemical, pharmacological [pharmacokinetics (PK) and pharmacodynamics (PD)], safety and therapeutic properties of pradofloxacin in the target species. Pradofloxacin contains two centres of asymmetry and is the pure SS enantiomer. After oral dosing of tablets (dog) or tablets and oral suspension (cat), maximum plasma concentrations (Cmax ) are achieved in less than 3.0 h, and terminal half-life is of the order of 5-10 h. Accumulation is slight or absent with once daily oral dosing. Free drug concentrations in plasma are in the range of 63-71% of total concentration. As for other fluoroquinolones, antibacterial activity is attributable to inhibition of bacterial replication at two sites, subunit A of topoisomerase II and topoisomerase IV. The antimicrobial spectrum includes gram-negative and gram-positive organisms, anaerobes, Mycoplasma spp. and some intracellular organisms (Rickettsia spp. and Mycobacterium spp.). The killing action is of the concentration-dependent type. Pradofloxacin has high potency (low MIC values) in comparison with first- and second-generation fluoroquinolones. Integration of in vivo PK and in vitro PD data provides values of Cmax /MIC and area under plasma concentration-time curve (AUC24 h )/MIC ratios predictive of good clinical efficacy against sensitive organisms, when administered at recommended dose rates. Clinical trial evaluation of pradofloxacin, in comparison with other authorized antimicrobial drugs, has demonstrated either noninferiority or superiority of pradofloxacin. Data indicating clinical and, in some instances, bacteriological cure have been reported: (i) in cats, for wound infections, abscesses, upper respiratory tract infections, conjunctivitis, feline infectious anaemia and lower urinary tract infections and (ii) in dogs, for wound infections, superficial and deep pyoderma, acute urinary tract infections and adjunctive treatment of infections of gingival and periodontal tissues. At clinical dose rates pradofloxacin was well tolerated in preclinical studies and in clinical trials. Among the advantages of pradofloxacin are (i) successful treatment of infections caused by strains resistant to some other fluoroquinolones, as predicted by PK/PD data, but depending on the specific MIC of the target strain and (ii) a reduced propensity for resistance development based on MPC measurements. The preclinical and clinical data on pradofloxacin suggest that this drug should commonly be the fluoroquinolone of choice when a drug of this class is indicated. However, the PK/PD data on pradofloxacin, in comparison with other fluoroquinolones, are not a factor that leads automatically to greater clinical efficacy.

Pharmacokinetics of famciclovir and penciclovir in tears following oral administration of famciclovir to cats: a pilot study

OBJECTIVE

To validate a means of collecting tears from cats, develop an assay for quantifying famciclovir and penciclovir in tears, and to assess famciclovir and penciclovir concentrations and pharmacokinetics in the tears of cats being treated orally with famciclovir for suspected herpetic disease.

ANIMALS

Seven client-owned cats.

PROCEDURES

Cats were treated orally with a median (range) dose of 40 (39-72) mg of famciclovir/kg three times daily for at least 24 h. At various time points following famciclovir administration, tear samples were collected using Schirmer tear test strips. Tear famciclovir and penciclovir concentrations were measured using liquid chromatography-mass spectrometry, and concentration-time profiles were analyzed noncompartmentally. The relationship between famciclovir dose and tear penciclovir concentration near its maximum was evaluated using least squares linear regression.

RESULTS

Maximum tear famciclovir concentration of 0.305 μg/mL occurred at 2.64 h; elimination half-life was 2.28 h. Maximum tear penciclovir concentration (0.981 μg/mL) occurred 2.25 h following oral administration of famciclovir; elimination half-life was 2.77 h. A significant positive correlation was noted between famciclovir dose and tear penciclovir concentration at various time points between 0.5 and 3.75 h following drug administration (P = 0.025). Tear penciclovir concentration exceeded the concentration shown to have in vitro efficacy against feline herpesvirus (FHV-1) (0.304 μg/mL) in about half of samples collected.

CONCLUSIONS

Oral administration of 40 mg of famciclovir/kg to cats resulted in a tear penciclovir concentration-time profile that approximated the plasma penciclovir concentration-time profile and frequently achieved a penciclovir concentration at the ocular surface likely to be effective against FHV-1.

Treatment of corneal ulcers: what are the medical options?

PRACTICAL RELEVANCE

Corneal ulcers in cats (ulcerative keratitis) are a common presenting complaint, and are a frequent sequela to feline herpesvirus (FHV-1) infection. In fact, it is fair to assume an FHV-1 aetiology until proven otherwise. In practice, therefore, many cases of corneal ulceration can be treated medically, but treatment can frequently be challenging, with the need to tailor therapy carefully to the type of ulcer, the individual cat and its temperament.

PATIENT GROUP

All age groups and breeds can suffer with ulcerative keratitis although some breeds are over-represented for some types of corneal ulceration.

EVIDENCE BASE

The scientific literature on feline ulcerative keratitis is extensive, particularly that related to FHV-1 infection. This article reviews the medical treatment options for corneal ulceration in cats with reference to the current evidence base.