Download April 4, 1968, Number 14, Page Number 774

is rarely given. Since digitalis intoxication is sometimes
observed in the presence of a normal serum potassium,
magnesium depletion may be involved in this setting,
and
measurements
of'the
serum
magnesium
concentration should be obtained. Increased sensitivity
to the development of arrhythmias occurs when cardiac
glycosides are administered to magnesium-deficient
animals.76-77
EXCESSIVE LACTATION
An unusual case of magnesium deficiency manifesting as the tetany syndrome occurred in a woman
with excessive lactation.204 The patient had been lactating
(approximately 2400 ml per day) for three months and
when first seen had painful cramping carpopedal spasms
and a positive Chvostek sign. The serum calcium
concentration was 4.8 mEq, and the magnesium 0.4
mEq per liter. Intravenous calcium therapy failed to
relieve the symptoms. With cessation of lactation and
maintenance of a normal diet symptoms abated as the
serum magnesium concentration rose spontaneously to
normal.
PORPHYRIA WITH INAPPROPRIATE
SECRETION OF
ADH
During attacks of acute intermittent porphyria
hyponatremia, hypomagnesemia and hypocalcemia have
been seen in circumstances under which there is
evidence for inappropriate secretion of antidiu-retic
hormone (ADH).205-206 In most of these patients the
lowering of serum magnesium has been in accord with
hemodilution and proportional to the decrease in the
other serum electrolytes. The situation is complicated
by the observation that arginine and lysine vasopressin
enhance the renal excretion of magnesium and calcium207
in normal human subjects; moreover, in one patient
tetany developed and responded to the combination of
parenteral calcium and magnesium.205 The relative role
of overhydra-tion versus extraordinary losses in this
disease awaits clarification.
IDIOPATHIC HYPOMAGNESEMIA
A number of patients with documented but otherwise
unexplained hypomagnesemia have recently been
described, and it has been suggested that this defect
may occur on a familial basis.181'208'209 Three of these
patients, all newborn infants, had convulsions
associated with hypocalcemia and hypomagnesemia. The
seizures could not be prevented by calcium
administration; on oral magnesium supplements
symptoms were controlled, and both hypomagnesemia
and hypocalcemia disappeared.209'211 In each case
withdrawal of magnesium therapy led to recurrent
seizures. Maintaining supplemental magnesium
therapy permitted the infants to be free of seizures and
to develop normally. Renal conservation of the mptfll was
normal in fVie.ro fU>-^^ ^.,4-,-«-,4-^
frequency and identity of this disorder must awa more
widespread measurement of serum magnesiui
concentrations in children with seizure disordei along
with a definition of the specific predisposin pathologic
defects.
Disordered magnesium metabolism has also bee
reported in hypertension,213 cardiomyopathy an
congestive heart failure,214'215 myocardial infan tjon2i6-2i8
219
In most c these reports in the
ancj muscular dystrophy.
literature the data are eithe conflicting or not
convincing
proof
that
disordere
magnesium
metabolism has a primary or significar role in the
process. None of these patients have ha symptoms
attributable to magnesium deficiency c excess.
THERAPEUTIC USE OF MAGNESIUM
Magnesium administration is specifically indicate
when- symptoms of magnesium depletion develo and
the depletion is documented by measurement of
serum or tissue concentrations. This situation i
being recognized increasingly often, and the fore
going discussion should serve as a guideline to th
circumstances in which magnesium deficiency migfc
appear.
Magnesium deficiency tetany and related syn dromes
may safely be treated parenterally if th calculated
extracellular deficit is replaced in divide! doses over
a 48-hour period. Ampoules of the sul fate salt in 10,
25 and 50 per cent concentration specifying the
magnesium content in mEq are gen erally available.*
The rate of intravenous injectio should not exceed
1.5 ml of a 10 per cent solutio (or equivalent) per
minute.
Use of magnesium in other situations is empirica
Magnesium derivatives are most widely employe in
antacids and purgatives. Although these prepara tions
are relatively inert they are absorbed suffi ciently well
to contraindicate their use in patient with renal
failure. Magnesium intoxication has bee observed to
result from magnesium sulfate ene mas24; at least one
fatal case, in a child with megs colon, has been
reported.220
Experience with parenteral magnesium has bee
most extensive in the treatment of the toxemias c
pregnancy — particularly fulminant pre-eclampsi and
eclampsia. Magnesium sulfate has been en ployed in
this complication of pregnancy for nearl half a
century.1>la It is still regarded as "the singl most
important drug in the empirical managemer of the
convulsive toxemias of pregnancy,"221 and it use is
widely endorsed.222-223 Optimal sedative el fects are
obtained when the serum concentration i held
between 4 and 7 mEq per liter.1'10 Howev^i the use
of magnesium sulfate alone will not alwaj stop
eclamptic convulsions.224 Magnesium therap should not
be used when eclampsia is accompanie