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On the seventh day after the dose the mucosae were still slightly bronzed,
especially above the teeth, the urine was still red and the bowels loose, but
the animal was feeding well and in quite good condition.
By the eighth day after the dose, when the spectroscopic blood examina-
tion showed that very little methaemoglobin was left, the urine was still red.
It did not become normal till the tenth day when the mucosae were also normal
and the animal had fully recovered.
This history is interesting because it shows that a second large dose of 0. 5
gramme per lb. body weight given to a young horse was definitely toxic,
whereas the previous dose had had little toxic effect. The interpretation of
this result is difficult, but it is worth noting, because it may indicate that
successive doses must be given with care. It is possible that one dose may
sensitise an animal for some time. On the other hand, the dose given to this
horse was excessively large and its very bulk may have caused most of the
trouble. There is no record of ill-effects in horses from repetition of the small
doses and there is evidence in the literature that, in other animals, repeated
small doses do not have toxic effects and may be more effective than larger
single doses. The experiments with pigs recorded below suggest that the age
of animals dosed is an important factor. A note on the effects of relatively
large doses recently given to young foals by F. Day, F.R.C.V.S., will be sent
to the Veterinary Record as soon as possible.
Thoroughbred 1.—Another mare, 9 years old, and weighing 1,232 lb., was
given 1,000 grammes of phenothiazine powder obtained by crushing up in
water tablets each of which contained 1 gramme of phenothiazine. The sus-
pension was given by stomach tube, the object of the very large dose being to
test the toxicity of the drug. There were so few eggs in the faeces that this
animal was not suitable for observation of the anthelmintic efficiency of the
drug. The day after the dose was given, this animal would not feed and was
passing red urine and its mucosae were bronzed. It was restless and in some
pain all day. On the second day after the dose it seemed better and one dead
Ascaris was found in the faeces. Early on the third day after the dose, the
animal was very restless and still would not feed. At 2-30 P.M. she was down
and struggling for breath with staring eyes and was obviously in great distress.
She was got up, but walked very stiffly. The temperature was 103°, the pulse
rapid and weak, she was sweating a little and the ears were cold. At 4-30 P. M.
she was destroyed.
The following extract from the note published by Innes and Whittick on
this horse shows that, in their opinion, most of the symptoms shown by this
animal were due to a thrombo-angiitis, rather than to the phenothiazine. It is
difficult, however, to resist the conclusion that the condition found in the
stomach and kidneys was caused by the drug. The case must remain incon-
clusive, but it is clear that a dose as high as 1 gramme per lb. body weight
should not be given to horses. It is not likely ever to be given, because the
experiments done with other horses show that 0.1 gramme per lb. body weight
is an efficient anthelmintic dose.
Extracts from—INNES, J. R. M., and WHITTICK, J. W. (1940.) J. Path.
and Bact. 50. 377-381. " Thrombo-angiitis obliterans in a Horse."