magnesium salicylate
Backache Maximum Strength Relief, Bayer Select Maximum Strength Backache, Extra Strength Doan’s, Magan, Mobidin, Momentum Muscular Backache Formula, Nuprin Backache

Available forms
Available by prescription only
Tablets: 545 mg, 600 mg
Caplets: 467 mg, 500 mg, 580 mg

Indications and dosages
 Arthritis. Adults: 545 mg to 1.2 g t.i.d. or q.i.d.
 Analgesia, antipyresis. Adults and children older than age 11: 300 to 600 mg P.O. q 4 hours, p.r.n.
 Analgesia (self-medicated). Adults and children older than age 11: 500 mg to 1 g P.O. initially, then 500 mg q 4 hours, p.r.n., not to exceed 3.5 g in 24 hours. Absorption of buffered or enteric-coated aspirin is increased by simultaneous administration. Use cautiously in children; may receive the following doses q 4 hours, p.r.n., not to exceed five doses in 24 hours.
Children age 11: 450 mg P.O.
Children ages 9 to 10: 375 mg P.O.
Children ages 6 to 8: 300 mg P.O.
Children ages 4 to 5: 225 mg P.O.
Children ages 2 to 3: 150 mg P.O.
Children younger than age 2: Individualize dose.

Pharmacodynamics
Analgesic action: Produces analgesia by an ill-defined effect on the hypothalamus (central action) and by blocking generation of pain impulses (peripheral action). The peripheral action may involve inhibition of prostaglandin synthesis.
Anti-inflammatory action: Thought to exert anti-inflammatory effect by inhibiting prostaglandin synthesis; may also inhibit the synthesis or action of other mediators of inflammation.
Antipyretic action: Relieves fever by acting on the hypothalamic heat-regulating center to produce peripheral vasodilation. This increases peripheral blood supply and promotes sweating, which leads to loss of heat and to cooling by evaporation.

Pharmacokinetics
Absorption: Absorbed rapidly and completely from GI tract.
Distribution: Highly protein-bound.
Metabolism: Hydrolyzed in liver.
Excretion: Metabolites excreted in urine.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug, salicylates, or NSAIDs and in those with severe chronic renal insufficiency because of risk of magnesium toxicity. Also contraindicated in patients with bleeding disorders. Use cautiously in patients with hypoprothrombinemia or vitamin K deficiency.

Interactions
Drug-drug. Ammonium chloride, other urine acidifiers: Increases blood magnesium salicylate levels. Monitor patient for magnesium salicylate toxicity.
Antacids, other urine alkalizers: Decreases blood magnesium salicylate levels. Monitor patient for decreased salicylate effect.
Anticoagulants, thrombolytics: Potentiates platelet-inhibiting effects of magnesium salicylate. Monitor patient for bruising or bleeding.
Corticosteroids: Enhances magnesium salicylate elimination. Monitor patient for decreased salicylate effect.
Drugs that are highly protein-bound (such as phenytoin, sulfonylureas, warfarin): May cause displacement of either drug; possible adverse effects. Monitor patient.
Other GI-irritant drugs (antibiotics, corticosteroids, other NSAIDs): May potentiate adverse GI effects of magnesium salicylate. Use together cautiously.
Drug-lifestyle. Alcohol use: Increases risk of GI bleeding. Discourage alcohol use.

Adverse reactions
EENT: tinnitus, hearing loss.
GI: nausea, vomiting, GI distress.
Hepatic: hepatitis.
Skin: rash, bruising.
Other: hypersensitivity reactions (anaphylaxis, asthma), Reye’s syndrome.

Effects on lab test results
• May increase AST, ALT, alkaline phosphatase, bilirubin, and magnesium levels.

Overdose and treatment
Signs and symptoms of overdose include metabolic acidosis with respiratory alkalosis.
 To treat, empty stomach immediately by inducing emesis with ipecac syrup if patient is conscious, or by gastric lavage. Give activated charcoal via nasogastric tube.

Special considerations
• Drug has been linked to a lower frequency of GI disturbances.
• Drug has a less profound inhibiting effect on platelet aggregation than other salicylates.
• High doses of drug may cause false-positive urine glucose test results using copper sulfate method. Drug may cause false-negative urine glucose test results using glucose enzymatic method.
• Stop drug if patient develops dizziness, tinnitus, or hearing impairment.
• Obtain hemoglobin and PT tests periodically.
• Monitor serum magnesium levels to prevent magnesium toxicity, especially in patients with renal insufficiency.
Breast-feeding patients
• Salicylates appear in breast milk. Don’t give to breast-feeding women.
Pediatric patients
• Safety of long-term magnesium salicylate use in children hasn’t been established.
• Because of drug’s link to Reye’s syndrome, the Centers for Disease Control and Prevention recommends that children with chickenpox or flulike symptoms not be given salicylates.
• Febrile, dehydrated children can develop toxicity rapidly.
Geriatric patients
• Patients older than age 60 may be more susceptible to the toxic effects of magnesium salicylate. Use it cautiously.
• The effects of salicylates on renal prostaglandins may cause fluid retention and edema, a significant drawback for elderly patients and those with heart failure.

Patient education
• Instruct patient to follow prescribed regimen and to report problems.
• Advise patient not to take drug longer than 10 days without medical supervision.
• Caution patient to keep drug out of children’s reach.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use