Milbemycin D

Moxidectin or F28249α is a potent endectocide and semisynthetic methoxime derivative of naturally occurring nemadectin. It is well known for the novel mode of action against a broad range of nematode and anthropod animal parasites. In this work, physicochemical and pharmaceutical aspects of moxidectin are described including stability, semisynthesis, purification processes, formulation compositions, impurities, and degradation pathways. Additional experiments such as DSC, XRD, and CHN analysis were carried out to complete the profile of moxidectin. The importance of safety and quality of drug substances was highlighted by chronological developments involving moxidectin and its analogues. The information gathered from the literature was used to trace the origins of moxidectin-related substances presented in the European Pharmacopeia (EP) compendial monograph. During the review, it was noticed that majority of impurities presented in the EP does not have any potential to increase with time in drug substance or formulated products; therefore, they do not require monitoring during stability studies. This also showed the requirement for further characterization of the impurities observed during long-term storage and development of stability indicating methods distinguishing between process impurities and the true degradation products. Furthermore, the stability of moxidectin in formulations is also reviewed in conjunction with known degradation routes and innovative ways to formulate products that are stable and effective at intended shelf life.

Canine demodicosis, a disease caused by a proliferation of Demodex mites, typically leads to alopecia, comedones, follicular papules and pustules, scaling, and crusting. It may be treated with either amitraz rinses or macrocyclic lactones. Amitraz rinse is approved for application every 2 weeks at a concentration of 0.025%. Higher concentrations and more frequent applications increase the success rate but also increase the risk for adverse effects. Ivermectin is used at 0.3 to 0.6 mg/kg/d PO and moxidectin at 0.2 to 0.5 mg/kg/d PO. Both drugs may cause adverse neurologic effects in sensitive dogs. Milbemycin oxime at 1 to 2 mg/kg/d PO is a safer treatment option. A weekly spot-on combination of 2.5% moxidectin and 10% imidacloprid is recommended for milder forms of the disease.

A non-producing strain, the so-called strain RNBC-5-51 SANK 60198, was isolated during a screening program of strain improvement in the milbemycin production. Strain RNBC-5-51 indicated almost the same characteristics as those in the parent strain, that is, the abundant spore formation on agar media and the good growth in liquid media. But it does not produce any kind of milbemycins. In addition, strain RNBC-5-51 accumulated precursor-like compounds of milbemycin-polyketide, the production of which were inhibited by the addition of cerulenin. In the bioconversion experiments, strain RNBC-5-51 converted milbemycin beta6 and A4 to milbemycin alpha14, and milbemycin beta7 and A3 to milbemycin alpha11, respectively. This strain also converted milbemycin D and avermectin B1a, to 26-(3-methyl-2-butenoyloxy)milbemycin D and 26-(3-methyl-2-butenoyloxy)avermectin B1a, respectively. These results suggest that milbemycin alpha11 is biosynthesized through the same route as milbemycin alpha14, and the mutated step in strain RNBC-5-51 might be in the polyketide synthetic pathway of milbemycins. Strain RNBC-5-51 loses the ability for de novo synthesis of milbemycins, but it retains the ability to bioconvert the milbemycin skeleton. This strain might be useful for C-26 modification of milbemycin-related compounds.