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Case 16
Case Discussion
 | This dog came in with critical systemic hypertension. Humans with this condition are
generally treated with intravenous administration of potent vasodilators such as
nitroprusside. Since at least part of this dog's systemic hypertension could be due to
volume expansion, aggressive intravenous fluid therapy and mannitol could theoretically
exacerbate the systemic hypertension in this dog. However, systemic hypertension secondary
to renal failure in dogs is generally not responsive to diuretic administration or salt
restriction. Consequently, it appears that systemic hypertension in dogs secondary to
renal failure is primarily due to constriction of systemic arterial vasculature (most
likely the systemic arterioles) and not due to volume expansion. However, one must be
careful when administering intravenous fluids to these patients. |
| Drugs that dilate systemic arterioles are generally the most effective agents for
treating systemic hypertension in dogs. Prazosin can be effective although it was not in
this dog. Hydralazine and amlodipine are the next choices. The comments below are from
when she was examined two days after her first discharge. |
Comments
Two day post discharge
| Hydralazine (7.5 mg or 1 mg/kg) was administered at 12:30 PM. Pressure was again
measured at 1:30 PM. It was 105/67 with a mean of 86. Pressure was measured at 4:30 PM. It
was 138/106 with a mean of 126. The hypertension improved
dramatically with administration of
the hydralazine indicating that vasodilation improved the problem. However, since one of
the patient's problems is chronic renal failure, hypertension is likely to be a continuing
problem, requiring continuous medication for control. The patient will be sent home
with hydralazine tablets at a dose of 7.5 mg PO BID and reevaluated tomorrow morning. |
Three days post discharge:
| Blood pressure on 7.5mg hydralazine is 147/111, with a mean of 131. This is still high,
but a dramatic improvement over previous pressures. Recommend maintain Mitzie on this dose
and recheck pressures in five days. |
Eight days post discharge:
| Mitzie's blood pressure today is 116/84 with a mean of 99.
This pressure is a little
lower than we would like, so we will decrease the hydralazine to 5mg PO BID. Recommend
recheck pressures in 7-14 days. |
| Owner feels Mitzie's neurologic signs may be improving slightly. At
this time, we are suspicious neurological signs are due to an intracranial
hemorrhage secondary to hypertension, although we cannot rule out neoplasia.
Further diagnostics for her neurological disease would include a CSF tap and
MRI; however at this time she is not a good candidate for anesthesia. Owner
elects to continue to monitor her neurological signs at home. |
Three weeks post discharge:
| She has a hypermetric gait but does not run into walls indicating that she may have
some vision. She has thick calculus on all of her teeth and she was a little snappy.
Mitzie's blood pressure was 119/87 with a mean of 101. This is a good pressure for her to
sustain so we will continue her hydralazine at 5 mg BID. Her phosphorus, creatinine and
BUN are decreased therefore therapy for renal failure is working.
Potassium is still elevated however this will just be monitored on future panels if Mitzie
continues to do well. |
Four months later:
| Mitzie developed refractory glaucoma secondary to hyphema and represented at this time
for a work-up prior to enucleation. It was noted that she had an anemia and
thrombocytopenia. The following is taken from the Comments section of her record. |
| O: CBC again showed an anemia (PCV = 16), and a thrombocytopenia of 97,000.
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| A: It is likely that the hydralazine is the cause for the anemia and thrombocytopenia.
According to Dr. Kittleson, it has been documented in human medicine that a side effect of
hydralazine is blood dyscrasia. It has not yet been documented in dogs, however the
reduction in the two cell lines (RBC & platelets) would support it in this case. The
marrow aspirate should show the evidence of decreased destruction due to the suspected
marrow suppression or demonstrate a neoplastic process. Another possible cause would be
increased destruction (AIHA, drug induced destruction, or neoplasia). The Coomb's test
does not rule out auto destruction. The CBC is necessary to evaluate the marrow. The
anemia is greater than would be suspected for an anemia of chronic disease or due to the
chronic renal failure. |
| P: Discontinue the hydralazine. 24 hours following the last
hydralazine dose begins start amlodipine 1.25 mg (0.15mg/kg) PO SID and atenolol 12.5 mg
(1.5 mg/kg) PO BID. Droncit 2 tabs PO once to treat tape worms found in the feces of Mitzie
yesterday. |
| Bone
marrow was interpreted as megakaryocytic hyperplasia. No evidence of marrow suppression is
present. The increase in megakaryocytes with a peripheral thrombocytopenia is suggestive
of a destructive process. |
| Coombs test was negative. This does not rule out a destructive process. The most likely
cause is a drug induced reaction. Other causes of destruction such as neoplasia,
parasites, or DIC can not be ruled out at this time. |
Last Comment:
| Within two weeks, Mitzie's PCV and platelet count increased while her systemic
hypertension remained controlled with the amlodipine. This clinically confirmed that her
anemia and her thrombocytopenia were secondary to the hydralazine and that the amlodipine
was effective. She lived for a little over a year after her initial presentation. During
that time she successfully underwent anesthesia for an enucleation and developed a seizure
disorder, presumably secondary to the CNS insult that occurred secondary to her systemic
hypertension. She was euthanized at the end because of worsening renal failure. |
| Hydralazine can induce a systemic lupus erythematosus - like reaction
in humans. One manifestation can be an anemia that is most commonly Comb's
positive. The combination of a hemolytic anemia and thrombocytopenia along
with elevated liver enzymes has also been described in pregnant humans with
hypertension administered hydralazine. Mitzie never had elevated
liver enzymes. The exact syndrome or mechanism of the abnormality that she
experienced is unknown but the fact that her problem resolved when the drug was
discontinued certainly implicates hydralazine. |
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