Page 233 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Disorders of Magnesium: Magnesium Deficit and Excess 223

intracellular calcium induced by ischemia and LPC pro- dosages for administration. The safety of administration
duction may also benefit from magnesium administra- of magnesium salts, however, is great. Doses several-fold
tion. 122 The other high-risk population is patients outside the normal therapeutic range were required to
diagnosed with diabetes mellitus and in particular dia- produce significant adverse effects in a normal
betic ketoacidosis. In diabetic patients, more rapid cor- anesthetized dog model of magnesium administra-
rection of electrolyte disturbances should be expected tion. 108 As a result of its relative safety, patients with
when magnesium is used as an adjunctive therapeutic normal renal function, clinical use of magnesium should
agent. Improved speed of correction of metabolic and not be discouraged due to the lack of study evaluating
electrolyte disturbances in this condition should result appropriate dosing. Patients most likely to have
in a decreased length and cost of hospitalization. There hypermagnesemia are patients that have an impaired renal
is also some evidence from human medicine to suggest ability to excrete or clear magnesium, so magnesium
that magnesium may improve insulin sensitivity and thus should be used with extreme caution in such patients,
glycemic control in diabetic patients. 21,65,116,131 and only after assessing magnesium levels. The published
Magnesium therapy could also be considered experi- dose range for magnesium in dogs has been extrapolated
mental or unproved therapy for conditions such as bron- from human medicine and tested empirically. 40 Paren-
chial asthma, pain, tetanus infections, neuroprotection teral magnesium generally is administered intravenously
and cardioprotection following ischemia, hyperkalemia, using either the chloride or sulfate salt, both of which
sepsis, and hypertension (especially related to pheochro- are available commercially in several concentrations.
mocytoma). Very little research has been conducted in Doses for magnesium supplementation can be found in
veterinary patients related to magnesium’s effect on any Table 8-1. A rapid loading dose can be administered over
of these conditions. Limited research has been conducted minutes in severe cases or when required in emergency
on a dog model showing magnesium to have a positive situations. Alternatively, in patients who do not require
effect on bronchoconstriction and pulmonary hyperten- emergent therapy, the same emergency loading dose
sion. 73,191 An in vitro study of the effects of magnesium can be administered over the first 24 hours followed by
on hyperkalemia has also been performed on canine a slower administration on subsequent days. A continu-
myocardial cells revealing a significant attenuation of ous intravenous infusion is usually given following
the electrophysiologic effects of hyperkalemia. 87 In addi- the loading dose until the patient’s dietary intake is suffi-
tion, an anesthesia study has shown premedication with cient to maintain adequate magnesium levels.
magnesium sulfate reducing the minimal alveolar concen- Severely depleted animals can be maintained on a fast
tration of halothane and the dose of thiopental required replacement dose for multiple days. Magnesium salt solu-
to induce anesthesia in a group of 46 dogs undergoing tion concentrations greater than 20% should not be
8
ovariohysterectomy. While none of these results is sub- administered. Magnesium salt solutions are not compati-
stantial enough to justify the routine clinical use of mag- ble with calcium or bicarbonate containing solutions.
nesium for these conditions at this time, they are One human magnesium research group has strongly
significant enough to stimulate further study in these recommended the use of the chloride versus the sulfate
areas. In fact, further research related to the therapeutic salt, citing a greater risk of toxicity from magnesium sul-
use of magnesium in any of the conditions mentioned fate. 45,49 Widespread clinical use of magnesium sulfate
above could easily be conducted in veterinary patients salt has continued, however, perhaps due to the lack of
and could serve as a valuable model for human diseases. evidence in human studies to support the allegation of
Administration of magnesium in dogs and cats has not toxicity.
been studied sufficiently to determine appropriate

TABLE 8-1 Dose Ranges for Magnesium Salts

Rapid Replacement mEq/g mEq/kg/day mEq/kg/hr mg/kg/hr
8.12 0.75-1 0.03-0.04 3.7-4.9
MgSO 4
9.25 0.75-1 0.03-0.04 3.2-4.3
MgCl 2
Slow Replacement mEq/g mEq/kg/day mEq/kg/hr mg/kg/hr
8.12 0.3-0.5 0.013-0.02 1.6-2.5
MgSO 4
9.25 0.3-0.5 0.013-0.02 1.4-2.2
MgCl 2
Emergency/ Loading mEq/kg mg/kg Duration
0.15-0.3 19-37 5 min-1hr/24 hr
MgSO 4
0.15-0.3 16-32 5 min-1hr/24 hr
MgCl 2
Oral mEq/kg/day
Several 1-2