EFPIA Comments to the Draft WFD Dossier for Clarithromycin
Summary
After review of the draft WFD dossiers prepared for Clarithromycin, we offer asummary of the available ecotoxicological information available for Clarithromycin. This document also provides an environmental assessment, a short discussion on blue green algae data and a short discussion on suggested endpoint to determine an annual average concentration (AA-QS) to protect against the occurrence of prolonged exposure and a maximum acceptable concentration (MAC-QS) to protect against possible effects from short term concentration under the Draft Technical Guidance for Environmental Quality Standards, Water Framework Directive (Draft, January 29,2010).
Introduction
Clarithromycin is a semisynthetic 14membered ring macrolide antibiotic originally synthesized as a 6Omethyl derivative of erythromycinA.
Pharmaceutical Data
Mode of Action
Clarithromycin is an antibiotic belonging to the macrolide antibiotics group. It exerts its antibacterial action by inhibiting the intracellular protein synthesis of susceptible bacteria. It selectively binds to the 50S subunit of bacterial ribosomes and thus prevents the translocation of activated amino acids.
Dose range, DDD, Route of Administration and Plasma Concentrations
The recommended dose for the Clarithromycin extended-release tablet, 500mg, ranges from 500mg to 1000mg once daily according to the indication.
The WHO Defined Daily Dose (DDD) is determined to be 0.5 g (oral route).
Human metabolism profile
The pharmacokinetics of orally administered IR clarithromycin has been studied extensively in a number of animal species and adult humans. These studies have shown clarithromycin is readily and rapidly absorbed with an absolute bioavailability of approximately 50% (Abbott, marketing authorization application, clarithromycin tablets).
Clarithromycin is excreted via the liver and kidney.
Radio-labeled substances excreted by human adults given single oral doses of 250mg or 1200mg IR clarithromycin were measured.
Urinary excretion products after five days accounted for 37.9% of the lower dose and 46.0% of the higher dose. Parent drug (18.4% and 29,4%) and 14(R)hydroxyclarithromycin (13,7% and 9,9%) comprised the majority of the urinary radioactivity after the 250mg and 1200mg doses, respectively.
In the same study, fecal elimination accounted for 40,2% (250mg) and 29,1% (1200mg) of the doses. Parent drug and represented 4,4% and 10,6% while 14(R)hydroxyclarithromycin represented 6,0% and 2,8% of the 14C dose after the low and high doses, respectively (Ferrero, 1990).
Consistent with these experimental data, the proportion of a clarithromycin dose excreted as unchanged clarithromycin was reported as about 25% (Calamari, 2003; Goebel, 2005).
Under the same conditions, the proportion of 14(R)hydroxyclarithromycin, the only microbiologically active metabolite, would likely be around 10%.
Excretion and Metabolites
The relevant emission patterns of oral medicinal products are mainly related to a diffuse release into wastewater systems due to the excretion by patients of the parent drug substance, clarithromycin, and its key metabolites of (namely M1 – desmethyl-, M4 – descladinosyl- and M5 – 14(R)hydroxyclarithromycin). Among identified metabolites, only M5 shows a bacteriological activity.
Environmental Fate
Information on the occurrence, stability, biodegradability of clarithromycin in the environment was gathered from the scientific literature for inclusion in this evaluation.
Biodegradability
It is assumed clarithromycin may degrade in aqueous media through acidic, alkali, or oxygen degradation processes.
Degradation Test
Investigation of 18 antibiotics in the Close Bottle Test reported biodegradation <60% for erythromycin and clarithromycin after 28 days (OECD 301), thus potentially qualifying these drugs as ‘not readily biodegradable’ (Alexy, 2004). However, it should be noted that elimination in the environment involves more than one mechanism.
Persistence
Based on the results of a Closed Bottle Test reported by Alexy (2004), clarithromycin could be designated as ‘not readily biodegradable’. However, based on other scientific reports gathered from the literature, clarithromycin appears to slowly degrade in the environment. Like erythromycin, clarithromycin is unstable in acidic environments. At pH 3,0, the half-life of clarithromycin was reported as about 76.5 hours (Nakagawa, 1992).
Rate of elimination in wastewater treatment plants
The rate of elimination of antibiotics in wastewater treatment plants (WWTP) is not well documented for clarithromycin. In the literature, the information is equally sparse, mainly for the reason that concentrations are often measured either in effluents from WWTPs, or in effluents from hospitals or in municipal waste waters, but are generally not directly compared.
In a study of final wastewater effluents from five Canadian cities, the median concentration of clarithromycin was reported as 0.087g/l (Miao, 2004). A second study examined the primary effluents from two wastewater treatment facilities in cities in Switzerland (Goebel, 2005) and found that the median concentration of clarithromycin in the influent was about 0.38g/l and the concentrations of clarithromycin in the primary, secondary and tertiary effluents were 0.33g/L, 0.26g/l, and 0.24g/l, respectively. Another study reported on the occurrence of macrolideantibiotics in wastewater treatment plants and in the Glatt Valley Watershed in Switzerland(McArdell, 2003). While the concentrations of clarithromycin ranged from 0.057 to 0.328g/l in the treated effluents, the concentration of clarithromycin in the river Glatt ranged from 0.004 to 0.032g/l. In addition, a survey of clarithromycin was conducted for the secondary effluent from STPs in Japan (Yamashita, 2006). Conventional activated sludge process are applied in these STPs and clarithromycin levels ranged from 0,303 to 0,596 g/l
Together, these studies suggest a modest reduction of clarithromycin in sewage effluents at the WWTPs.
Clarithromycin – Environmental Risk Assessment
Release of clarithromycin and its metabolites into the environment will affect only one medium, the surface water. Transport from surface water to the atmosphere via volatilization is not an operative process. Clarithromycin has been found to be irreversibly bound to some surface water sediments. As discussed earlier, unchanged parent drug is the primary moiety excreted by patients into the environment. However, clarithromycin does undergo significant metabolism by patients.
Only one metabolite, 14(R)hydroxyclarithromycin, appears to have some anti-microbial activity; this metabolite appears to be excreted in an amount approximating 10% of the administered dose. This metabolite does not appear to be stable in the environment as its presence has never been reported in numerous survey studies of surface waters from EU member states (e.g.Italy, United Kingdom, and Germany) or the United States. For these reasons, this assessment will focus on the impact of the parent compound, clarithromycin, on the environment.
Surface Water – Predicted Environmental Concentration/Predicted No-Effect Concentration
The initial step in the environmental exposure assessment was to estimate the concentration of the medicinal product (PEC) in the aquatic environment. The initial PECsurface water was estimated using the following equations[1]:
Where:
PECsurface waterpredicted environmental surface water concentration [mgl-1]
DOSEaimaximum daily dose of the active ingredient (i.e. the highest recommended dose) per inhabitant [mginhab-1d-1]
Fpenpercentage of market penetration (default is 0,01)
WASTEWinhabamount of wastewater per inhabitant per day [linhab-1d-1],
(default is 200l)
DILUTION10
and
Fpenpercentage of market penetration (default is 1) [%]
Consumptionestimated consumption of active ingredient in geographic region per year based on statistics and/or epidemiological studies [mgyear-1]
DDD WHO’s Defined Daily Dose value [mgd-1inhab-1]
Inhabitantsnumber of inhabitants in a geographical area
Refinement of the initial PECsurfacewater
Using the default Fpen estimate of 1%, and a DDD of 500mg (oral route), the initial PECsurfacewater for clarithromycin was calculated to be 0,0025mg/l, or 2.5g/l.
However, the EMEA guidance allows for refinement of the PECsurface water based on a variety of considerations including metabolism of the parent drug by the patient, hydrolysis, photodegradation, biodegradation, and the estimated efficiency of removal of the drug by the wastewater treatment plant (WTP).
Adjustment of Fpen
Based on the guideline the EMEA guidelines Fpen of 1% or 0.01 will be used for the purposes of this review.
Metabolism by the patient
Following oral administration, clarithromycin undergoes metabolism resulting in the formation of several metabolites. The proportion of clarithromycin excreted unchanged was reported as 25%. Based on this information, the estimated PECsurfacewater was adjusted to reflect that only about 25% of the maximum daily dose of clarithromycin (1000mg, oral route) is likely to be released into the aquatic environment.
Thus, the initial estimate of the PECsurface water was refined by i) correcting for the metabolism of clarithromycin by the patient, and ii) using the refined Fpen estimate.
By implementing these refinements, the PECsurface water was adjusted to a value of 0,00000125 mg/l, or 0,00125g/l.
Comparison of the refined PEC with the Measured Environmental Concentration (MEC)
Estimates for the removal of clarithromycin due to wastewater treatment plants (WWTP) have not been fully documented. Based on the findings of a published survey study of surface waters in Italy (Calamari, 2003), the refined PECsurface water still over-estimates the concentration of clarithromycin in several rivers in Italy. More specifically, based on the results of a survey of clarithromycin at several locations in the rivers Po and Lambro in Northern Italy, the highest measured environmental concentration (MEC) of clarithromycin was reported as 0,02g/l at one location; the MEC values for clarithromycin at seven other locations were less than 0.01g/l. This study also noted this discrepancy between the estimated PEC values and the MEC values by reporting that the ratios of the MEC values to the (estimated) PEC values ranged from 0.00002 to 0.00078. These ratios suggest that for clarithromycin, the calculated PEC value over-estimates the environmental concentration of clarithromycin in surface waters, and that clarithromycin may subject to further degradation in the environment.
Predicted No-Effect Concentration (PNEC), PEC/PNEC ratio, and MEC/PNEC ratio
PNEC values were estimated based on acute and chronic environmental test results reported in the scientific literature.
Acute Studies
A PNEC value of 1000g/l was calculated for Danio rerio on the basis of a Lethal Concentration 50 value (LC50) of greater than 1000mg/l (Isidori, 2005) and an Assessment Factor (AF) of 1000. Using a PEC value of 0.00125g/l,the PEC/PNEC ratio for fish was estimated to be 0,00000125.
Using a MEC value of 0.02g/l,the MEC/PNEC ratio for fish was estimated to be 0,00002.
A PNEC value of 100g/l was calculated for O. Latipes on the basis of a Lethal Concentration 50 value (LC50) of greater than 100mg/l (Harada, 2008) and an Assessment Factor (AF) of 1000. Using a PEC value of 0.00125g/l,the PEC/PNEC ratio for fish was estimated to be 0,0000125.
Using a MEC value of 0.02g/l,the MEC/PNEC ratio for fish was estimated to be 0,002.
A PNEC value of 35.5g/l was calculated for the rotifer Brachionus calyciflorus, on the basis of a LC50 value of 35.46mg/l (Isidori, 2005) and an AF of 1000. Using a PEC value of 0.00125g/l,the PEC/PNEC ratio for B.calyciflorus was estimated to be 0,0000352.
Using a MEC value of 0.02g/l,the MEC/PNEC ratio was estimated to be 0,00056.
A PNEC value of 33.6g/l was calculated for the anostracan crustacean Thamnocephalus platyurus, on the basis of a LC50 value of 33.64mg/l (Isidori, 2005) and an AF of 1000.
Using a PEC value of 0.00125g/l,the PEC/PNEC ratio for T.platyurus was estimated to be 0,000037.
Using a MEC value of 0.02g/l,the MEC/PNEC ratio was estimated to be 0,00059.
A PNEC value of 0,9423 g/l was calculated for the anostracan crustacean Thamnocephalus platyurus, on the basis of a LC50 value of 94,23mg/l (Harada, 2008) and an AF of 1000.
Using a PEC value of 0.00125g/l,the PEC/PNEC ratio for T.platyurus was estimated to be 0,001326.
Using a MEC value of 0.02g/l,the MEC/PNEC ratio was estimated to be 0,0212.
A PNEC value of 25,7g/l was calculated for Daphnia magna, on the basis of an Effective Concentration (EC50) value of 25,72mg/l (Isidori, 2005) and an AF of 1000.
Using a PEC value of 0.00125g/l,the PEC/PNEC ratio for D.magna was estimated to be 0,000049.
Using a MEC value of 0.02g/l,the MEC/PNEC ratio was estimated to be 0.00078.
A PNEC value of 18,7g/l was calculated for Ceriodaphnia dubia, on the basis of an EC50 value of 18,66mg/l (Isidori, 2005) and an AF of 1000.
Using a PEC value of 0.00125g/l, the PEC/PNEC ratio for C.dubia was estimated to be 0,000067.
Using a MEC value of 0,02g/l,the MEC/PNEC ratio was estimated to be 0,00011.
In the report from Isidoriet al. (2005), no effects on the luminescent bacterium Vibrio fischeri were reported at a clarithromycin concentration of 100mg/l.
Chronic Studies
A PNEC value of 163g/l was calculated for Ceriodaphnia dubia, on the basis of an EC50 value of 8,16mg/l (Isidori, 2005) and an AF of 50.
Using a PEC value of 0.00125g/l,the PEC/PNEC ratio for C.dubia was estimated to be 0,0000077.
Using a MEC value of 0.02g/l,the MEC/PNEC ratio was estimated to be0,000123.
A PNEC value of 0,04g/l was calculated for Pseudokirchneriella subcapitata, on the basis of an EC50 value of 0,002mg/l (Isidori, 2005) and an AF of 50.
Using a PEC value of 0.00125g/l,the PEC/PNEC ratio for P. subcapitata was estimated to be0,03125.
Using a MEC value of 0.02g/l,the MEC/PNEC ratio was estimated to be0.5.
A PNEC value of 0,24g/l, was calculated for Pseudokirchneriella subcapitatia (7 Day), on the based of an EC50 valued of 0,012 mg/L (Harada, 2008) and an AF of 50
Using a PEC value of 0.00125g/l, the PEC/PNEC ratio was for P. Sucapitata was estimated to be 0,0052
Using a MEC value of 0.02g/l,the MEC/PNEC ratio was estimated to be 0,0833.
A PNEC value of 0,8g/l , was calculated for Dapnia Magna, 21 day (Reproduction) on the basis of an EC50 value of 0,040mg/l (Yamashita, 2006) and an AF of 50.
Using a PEC value of 0.00125g/l,the PEC/PNEC ratio for D. Magana was estimated to be 0,0001562.
Using a MEC value of 0.02g/l,the MEC/PNEC ratio was estimated to be 0,025
In conclusion, using assessment factors applied to the ecotoxicity data in accordance with the PEC/PNEC ratios for clarithromycin from both acute and chronic effects studies are significantly less than 1.0. The MEC values for clarithromycin are significantly lower than the estimated PECsurfacewater values, resulting in a MEC/PNEC ratio of 0.5. Since this MEC/PNEC ratio is less than 1.0, in consideration of the 50-fold safety margin used to estimate the PNEC, but with additional published studies the findings in the chronicstudy in algae, this assessment factor can be lowered due to availability of long-term data. The calculated MEC/PEC ratios suggested that the predictive calculations overestimated the actual concentrations of clarithromycin in surface waters. This might be explained by the fact that several factors were not accurately captured in the prediction equations, such as the percentage of unchanged excreted drug and the existence of multiple degradation routes. Overall, these studies and assessment suggest the ecotoxicity potential for clarithromycin is small.
Proposed Clarithromycin AA-QS Derivation
Therefore, an assessment factor (AF) of 20 is recommended to be used to derive the annual average concentration AA-QS freshwater eco in freshwater for clarithromycin, due to robust dataset available for multiple long term studies in multiple trophic levels. In this case, Harada et al, 2008, the lowest NOEC = 0.0052 mg/l with AF 20 would give an AA-QS freshwater eco of 0,26 g/l. The duration of study in the Harada, 2008 was twice as long as the Isidori, 2005 study. The maximum acceptable concentration MAC freshwater eco can be derived from Isidori et al, 2005 short term study in Ceriodaphnia dubia, with EC50 value of 18.66mg/l. An AF of 100 would account for at least 1 short term from each trophic level including fish, crustaceans and algae for clarithromycin. This would yield a MAC freshwater eco of 180 g/l.
Comment on Testing Clarithromycin in Blue Green Algae
In review by Brain et al, summarized that all toxicity data for pharmaceuticals in aquatic plants reported to data generally indicate the risk of adverse effects from exposures at environmentally relevant concentrations is generally low, but there are few exceptions. The current risk assessments for pharmaceuticals typically rely on hazard or risk quotient approaches, where predicted environmental concentrations (PEC) or measured environmental concentration (MEC) is divided by statically derived toxicological benchmark concentration (NOEC or ECx value), usually under worst case circumstances. HQ or RQ ratios greater than 1 indicate potential hazard or risk and values less than 1 indicate low potential hazard or risk as we showed in the assessment for Clarithromycin. Based on the Brain et al analysis of over 50 antibiotics, there are no instances of significant hazard or risk for aquatic higher plants, although 12% of the toxicity values indicate a potential for hazard or risk for algae, largely blue-green algae exposed to antibiotics. Blue green algae are consistently the most sensitive, accounting for 80% of the HQ exceedence incidences, where M. Aeurginaose indicated potential risk from exposure to aminoglycoside, pleurosmutilin, macrolide, B-lactam, quinolone, and tetracycline antibiotics and A. flos-aquae indicated potential risk from exposure to triclosan, as well one macrolide compound (clarithromycin) in the case of S. capricornutum.
The authors indicated that it is not surprising the blue-green algae display the greatest sensitivity across the spectrum of antibiotics because they are the most bacterial in nature with rudimentary barriers for uptake and metabolic capacity. However, the generally consensus based on this review by authors, is that of low risk, even with higher tier (microcosm) studies and probalistic approaches and pathway/receptor specific receptors are employed.
References
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