Metabolism of aceclofenac to diclofenac in the domestic water buffalo Bubalus bubalis confirms it as a threat to Critically Endangered Gyps vultures in South Asia

Vulture declines in South Asia were caused by accidental poisoning by the veterinary non-steroidal anti-inflammatory drug (NSAID) diclofenac. Although veterinary use of diclofenac has been banned, other vulture-toxic NSAIDs are legally available, including aceclofenac, which has been shown to metabolise into diclofenac in domestic cattle. We gave nine domestic water buffalo the recommended dose of aceclofenac (2 mg kg^-1 body weight), collected blood at intervals up to 48 h, and carried out a pharmacokinetic analysis of aceclofenac and its metabolite diclofenac in plasma. Aceclofenac was rapidly converted to diclofenac, and was barely detectable in plasma at any sampling time. Diclofenac was present within 20 min, and peaked 4-8 h after dosing. Aceclofenac is a prodrug of diclofenac, and behaves similarly in domestic water buffalo as it did in domestic cattle, posing the same risk to vultures. We recommend an immediate ban on the veterinary use of aceclofenac across vulture-range countries.

Experimental safety testing shows that the NSAID tolfenamic acid is not toxic to Gyps vultures in India at concentrations likely to be encountered in cattle carcasses

Population declines of Gyps vultures across the Indian subcontinent were caused by unintentional poisoning by the non-steroidal anti-inflammatory drug (NSAID) diclofenac. Subsequently, a number of other NSAIDs have been identified as toxic to vultures, while one, meloxicam, is safe at concentrations likely to be encountered by vultures in the wild. Other vulture-safe drugs need to be identified to reduce the use of those toxic to vultures. We report on safety-testing experiments on the NSAID tolfenamic acid on captive vultures of three Gyps species, all of which are susceptible to diclofenac poisoning. Firstly, we estimated the maximum level of exposure (MLE) of wild vultures and gave this dose to 40 Near Threatened Himalayan Griffons G. himalayensis by oral gavage, with 15 control birds dosed with benzyl alcohol (the carrier solution for tolfenamic acid). Two birds given tolfenamic acid died with elevated uric acid levels and severe visceral gout, while the remainder showed no adverse clinical or biochemical signs. Secondly, four G. himalayensis were fed tissues from water buffaloes which had been treated with double the recommended veterinary dose of tolfenamic acid prior to death and compared to two birds fed uncontaminated tissue; none suffered any clinical effects. Finally, two captive Critically Endangered vultures, one G. bengalensis and one G. indicus, were given the MLE dose by gavage and compared to two control birds; again, none suffered any clinical effects. The death of two G. himalayensis may have been an anomaly due to i) the high dose level used and ii) the high ambient temperatures at the time of the experiment. Tolfenamic acid is likely to be safe to Gyps vultures at concentrations encountered by wild birds and could therefore be promoted as a safe alternative to toxic NSAIDs. It is manufactured in the region, and is increasingly being used to treat livestock.

Metabolism of aceclofenac in cattle to vulture-killing diclofenac

The nonsteroidal anti-inflammatory drug (NSAID) diclofenac is highly toxic to Gyps vultures, and its recent widespread use in South Asia caused catastrophic declines in at least 3 scavenging raptors. The manufacture of veterinary formulations of diclofenac has since been banned across the region with mixed success. However, at least 12 other NSAIDs are available for veterinary use in South Asia. Aceclofenac is one of these compounds, and it is known to metabolize into diclofenac in some mammal species. The metabolic pathway of aceclofenac in cattle, the primary food of vultures in South Asia, is unknown. We gave 6 cattle the recommended dose of aceclofenac (2 mg/kg), collected blood thereafter at intervals for up to 12 h, and used liquid chromatography with mass spectrometry in a pharmacokinetic analysis of aceclofenac and diclofenac in the plasma. Nearly all the aceclofenac administered to the cattle was very rapidly metabolized into diclofenac. At 2 h, half the aceclofenac had been converted into diclofenac, and at 12 h four-fifths of the aceclofenac had been converted into diclofenac. Therefore, administering aceclofenac to livestock poses the same risk to vultures as administering diclofenac to livestock. This, coupled with the risk that aceclofenac may replace diclofenac in the veterinary market, points to the need for an immediate ban on all aceclofenac formulations that can be used to treat livestock. Without such a ban, the recovery of vultures across South Asia will not be successful.