Relagesic

• International Ethical Labs.

Rx only

Acetaminophen, 4'-hydroxyacetanilide, a slightly bitter, white, odorless, crystalline powder, is a non-opiate, non-salicylate analgesic and antipyretic. It has the following structural formula:

1. Acetaminophen

C8H9NO2                                        MW=151.17

Phenyltoloxamine citrate is an antihistamine having the chemical name N,N-dimethyl-2-(∝-phenyl-o-tolyloxy) ethylamine dihydrogen citrate with the following structure:

2. Phenyltoloxamine citrate

C17H21NO•C6H8O7                                        MW=447.48

Inactive Ingredients: Each tablet contains povidone, microcrystalline cellulose, sodium starch glycolate and magnesium stearate.

The analgesic action of acetaminophen involves peripheral influences, but the specific mechanism is as yet undetermined. Antipyretic activity is mediated through hypothalamic heat regulating centers. Acetaminophen inhibits prostaglandin synthetase. Therapeutic doses of acetaminophen have negligible effects on the cardiovascular or respiratory systems; however, toxic doses may cause circulatory failure and rapid, shallow breathing.

Pharmacokinetics

The behavior of the individual components is described below.

Acetaminophen is rapidly absorbed from the gastrointestinal tract and is distributed throughout most body tissues. The plasma half-life is 1.25 to 3 hours, but may be increased by liver damage and following overdosage. Elimination of acetaminophen is principally by liver metabolism (conjugation) and subsequent renal excretion of metabolites. Approximately 85% of an oral dose appears in the urine within 24 hours of administration, most as the glucuronide conjugate, with small amounts of other conjugates and unchanged drug.

See OVERDOSAGE for toxicity information.

Phenyltoloxamine is an H1 blocking agent which interferes with the action of histamine primarily in capillaries surrounding mucous tissues and sensory nerves of the nasal and adjacent areas. It has the ability to interfere with certain areas of acetylcholine-inhibiting secretions in the nose, mouth and pharynx. It commonly causes CNS depression.

Following an acute overdosage, toxicity may result from phenyltoloxamine citrate or acetaminophen.

Acetaminophen

In acetaminophen overdosage: dose-dependent, potentially fatal hepatic necrosis is the most serious adverse effect. Renal tubular necrosis, hypoglycemic coma, and thrombocytopenia may also occur.

Early symptoms following a potentially hepatotoxic overdose may include: nausea, vomiting, diaphoresis and general malaise. Clinical and laboratory evidence of hepatic toxicity may not be apparent until 48 to 72 hours post-ingestion.

In adults, hepatic toxicity has rarely been reported with acute overdoses of less than 10 grams or fatalities with less than 15 grams.

Treatment

A single or multiple overdose with phenyltoloxamine citrate or acetaminophen is a potentially lethal overdose, and consultation with a regional poison control center is recommended. Immediate treatment includes support of cardiorespiratory function and measures to reduce drug absorption. Vomiting should be induced mechanically, or with syrup of ipecac, if the patient is alert (adequate pharyngeal and laryngeal reflexes).

If the dose of acetaminophen may have exceeded 140 mg/kg, acetylcysteine should be administered as early as possible. Serum acetaminophen levels should be obtained, since levels four or more hours following ingestion help predict acetaminophen toxicity. Do not await acetaminophen assay results before initiating treatment. Hepatic enzymes should be obtained initially, and repeated at 24-hour intervals. Methemoglobinemia over 30% should be treated with methylene blue by slow intravenous administration. The toxic dose for adults for acetaminophen is 10 g.