Page 186 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

176 ELECTROLYTE DISORDERS

because some of them require a few days before intestinal Reports of this reaction to the subcutaneous adminis-
calcium transport is maximized. Calcitriol exerts initial tration of calcium gluconate had not previously been
effects on the intestine within 3 to 4 hours. 601 Additional reported in dogs despite its extensive use by some
parenteral calcium salt administration is necessary until institutions (Feldman, personal communication, 2005).
therapy with vitamin D metabolites is effective at Unfortunately, we are aware of at least three other dogs
maintaining serum calcium concentration at an accept- with similar severe reactions to the subcutaneous admin-
able level. istration of properly diluted calcium gluconate as treat-
Multiple intermittent intravenous injections of cal- ment for primary hypoparathyroidism, resulting in
cium salts can be administered to control clinical signs, euthanasia for most (Chew, personal communications,
but this method is not recommended because wide 2003, 2004). Differences in an individual animal’s
fluctuations in serum calcium concentration are susceptibility to the effects of calcium salts on subcutane-
observed. Instead, continuous intravenous infusion of ous tissues could account for severe reactions in some
calcium is recommended at 60 to 90 mg/kg/day ele- dogs. All dogs with this severe tissue reaction were also
mental calcium (2.5 to 3.75 mg/kg/hr) until oral receiving calcitriol, which may potentiate more local
medications provide control of serum calcium concentra- dramatic effects in the subcutaneous tissues as compared
tion. 87,179,446,447 Initial doses in the higher range are with less active vitamin D metabolites (cholecalciferol,
administered to patients with more severe hypocalcemia, ergocalciferol, and dihydrotachysterol) commonly used
and the dose decreased according to the serum calcium in the past.
concentration achieved. The intravenous dose of calcium There are only two reports of cats with primary
is further reduced as oral calcium salts and vitamin D hypoparathyroidism that were treated with subcutaneous
metabolites become more effective. administration of calcium gluconate. No adverse effects
Ten milliliters of 10% calcium gluconate provides 93 were noted in one report. 195 Iatrogenic calcinosis cutis,
mg of elemental calcium. A convenient method for infus- skin necrosis, and scarring occurred at sites of diluted
ing calcium is available when intravenous fluids are given calcium gluconate injection and sites where injected
at a maintenance volume of 60 mL/kg/day (2.5 mL/ fluids pooled in one cat. 501 This cat survived. Because
kg/hr). Approximately 1, 2, or 3 mg/kg/hr elemental of the severity of adverse reactions that have recently
calcium is provided by adding 10, 20, or 30 mL of 10% been observed in dogs and a cat, the administration of
calcium gluconate, respectively, to each 250-mL bag of subcutaneous fluids containing calcium gluconate is
fluids. Calcium salts should not be added to fluids that no longer recommended as a safe and predictable
contain lactate, acetate, bicarbonate, or phosphates treatment.
because calcium salt precipitates can occur. Alkalinizing
fluids that contain or generate bicarbonate should be Subacute and Chronic Maintenance
avoided because they can decrease iCa and may unmask Supplemental elemental calcium is administered orally
the clinical signs of hypocalcemia in animals with border- (see Table 6-5) to guarantee adequate calcium for intes-
line hypocalcemia. tinal absorption after treatment with vitamin D
Subcutaneous administration of calcium gluconate has metabolites. Oral calcium administered by pill or slurry
been regarded as safe for use in dogs with hypocalcemia is most important during initial treatment, especially if
when diluted to a ratio of at least 1:1 by volume. The the animal is not eating. Active intestinal transport of cal-
use of calcium chloride is too caustic to ever be given sub- cium is under the control of calcitriol when calcium intake
cutaneously. However, a recent report raises concerns is low, but vitamin D-independent (passive) intestinal
about the safety of calcium gluconate administration sub- absorption of calcium occurs when calcium intake is high.
cutaneously. A 6-month-old border collie with hypopara- The passive mechanisms for intestinal calcium transport
thyroidism was initially treated with intravenous calcium can be used therapeutically before the actions of vitamin
gluconate, followed by oral calcitriol and calcium carbon- D take effect in the intestine. In most patients, normal
513
ate. This dog then received subcutaneous calcium dietary intake of calcium is sufficient to maintain ade-
gluconate three times daily for 2 days, and calcium gluco- quate serum calcium concentrations in the presence of
nate was diluted as previously recommended. Fever and vitamin D metabolite treatment. Consequently, oral cal-
pain, swelling, and erythema of the ventral abdomen were cium salt supplementation can be tapered and
obvious after 2 days of subcutaneous calcium gluconate discontinued in many instances as vitamin D compounds
treatments. Initial skin biopsy revealed calcinosis cutis reach maximal effect.
with pyogranulomatous dermatitis and dermoepidermal Calcium carbonate is the most widely used oral prepa-
separation. The dog’s condition worsened; ulceration ration of the calcium salts because it contains the greatest
involving about 80% of the skin developed over the trunk; percentage of elemental calcium. This approach allows
and the dog was euthanized. A second skin biopsy fewer pills to be administered. The degree of calcium ion-
revealed severe pyogranulomatous panniculitis with ization from its salt and its bioavailability for absorption
mineralization of adipocytes. vary for each calcium salt and with conditions in the