The half-life of
[14C]4‘‘-deoxy-4‘‘-(epi-methylamino)avermectin
B1a (MAB1a) benzoate (1 ppm)
photodegradation in buffer (pH 7), natural pond water, and sensitized
buffer (1% acetone in pH 7
buffer) determined at Three Bridges, NJ (latitude ∼40° N) during
the fall season under natural
sunlight was 22, 7, and 1 days, respectively. The half-life of
[14C]MAB1a benzoate (10−12 ppm)
photodegradation in buffer (pH 7) containing 1% (v/v) acetonitrile,
ethanol, or acetone as cosolvent
under continuous exposure with a xenon lamp was 64.5, 8.5, or 0.5 days,
respectively. The
photoisomer 8,9-Z-MAB1a, 8a-hydroxy-MAB1a, and unknown polar residues
were found in light-exposed samples of MAB1a in buffer and natural pond water. In
light-exposed sensitized buffer
samples, 8a-oxo-MAB1a and MAB1a-10,11-14,15-diepoxide were
additional products. Very polar
residues found in the organic and aqueous phases after extraction
increased with time, and their
formation followed the order sensitized buffer ≫ natural pond water
> buffer.
Keywords: MK-0244; emamectin benzoate; photodegradation;
residues
Plasma distribution and elimination of florfenicol in channel catfish were investigated after a single dose (10 mg/kg) of intravenous (i.v.) or oral administration in freshwater at a mean water temperature of 25.4 °C. Florfenicol concentrations in plasma were analyzed by means of liquid chromatography with MS/MS detection. After i.v. florfenicol injection, the terminal half-life (t(1/2)), volume of distribution at steady state (V(ss)), and central volume of distribution (V(c)) were 8.25 h, 0.9 and 0.381 L/kg, respectively. After oral administration of florfenicol, the terminal t(1/2), C(max), T(max), and oral bioavailability (F) were 9.11 h, 7.6 μg/mL, 9.2 h, and 1.09, respectively. There was a lag absorption time of 1.67 h in oral dosing. Results from these studies support that 10 mg florfenicol/kg body weight in channel catfish is an efficacious dosage following oral administration.
Cabbage was treated with a single application of [ 14 C]-MK-0244, a semisynthetic avermectin analogue, at 0.3 lb/acre and harvested 1 day after application. The wrapper leaf and exterior head surface of the cabbage were rinsed with methanol, and 12 degradates were isolated from this rinse and identified by structural analysis. Ten of these residues can be accounted for by six previously reported transformations and two are apparently formed by novel transformations. This represents the first time that avermectin residues isolated from a plant have been unequivocally identified by direct methods. The cabbage residue profile bears a strong resemblance to that seen in the photodegradation of MK-0244 thin films on glass.
Cabbage, after treatment with eight weekly applications of the
semisynthetic avermectin at a 0.015
lb a.i./acre (1×) or a 5× rate, was collected at preharvest
intervals (PHI) from 2 h to 10 d. For
foliage at 2 h to 10 d PHI: (1) the total 14C-residue
declined from 450 to 200 (1×) or 2900 to 1300
(5×) ppb, (2) the total 14C-residue was 78−92%
extractable, (3) the extractable residue consisted of
the parent as well as polar and avermectin-like residues, (4) the
parent declined from 90 to 7 ppb
(1×), and (5) polar residues in toto ranged from 120−170
ppb (1×). For the extractable residue, (1)
10 avermectin-like residues were identified with the parent accounting
for 4−38% of the total, (2)
the polar residues were found to be extremely complex, consisting of
many minor components and
no apparent conjugates, and (3) the polar residues in toto
accounted for 23−75% of the total.
Keywords: Emamectin; MK-0244; avermectin; metabolism; cabbage
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