Pentazocine Hydrochloride and Acetaminophen

PENTAZOCINE HYDROCHLORIDE AND ACETAMINOPHEN — pentazocine hydrochloride and acetaminophen tablet
GAVIS Pharmaceuticals, LLC

Hepatotoxicity

Pentazocine Hydrochloride and Acetaminophen Tablets contain acetaminophen and pentazocine hydrochloride. Acetaminophen has been associated with cases of acute liver failure, at times resulting in liver transplant and death. Most of the cases of liver injury are associated with the use of acetaminophen at doses that exceed 4000 milligrams per day, and often involve more than one acetaminophen-containing product.

DESCRIPTION

Pentazocine Hydrochloride and Acetaminophen Tablets are a combination of pentazocine hydrochloride, USP, equivalent to 25 mg base and acetaminophen, USP, 650 mg.

Pentazocine is a member of the benzazocine series (also known as the benzomorphan series). Chemically, pentazocine is (2R*,6R*,11R*)1,2,3,4,5,6-hexahydro-6,11-dimethyl-3-(3-methyl-2-butenyl)-2,6-methano-3-benzazocin-8-ol, a white, crystalline substance soluble in acidic aqueous solutions, and has the following structural formula:

fc01cb97-figure-01
(click image for full-size original)

C19 H27 NO HCl M.W. 321.88

Chemically, acetaminophen is Acetamide, N -(4-hydroxyphenyl)-, and has the following structural formula:

fc01cb97-figure-02

C8 H9 NO2 M.W. 151.16

Pentazocine is an analgesic and acetaminophen is an analgesic and antipyretic.

Inactive ingredients: colloidal silicon dioxide, FD&C Blue # 1 aluminum lake, microcrystalline cellulose, sodium lauryl sulfate, sodium starch glycolate, and stearic acid.

CLINICAL PHARMACOLOGY

Pentazocine is a Schedule IV opioid analgesic with agonist/antagonist action which when administered orally is approximately equivalent on a mg for mg basis in analgesic effect to codeine.

Acetaminophen is an analgesic and antipyretic.

Pentazocine weakly antagonizes the analgesic effects of morphine, meperidine, and phenazocine; in addition, it produces incomplete reversal of cardiovascular, respiratory, and behavioral depression induced by morphine and meperidine. Pentazocine has about 1/50 the antagonistic activity of nalorphine. It also has sedative activity.

Onset of significant analgesia with pentazocine usually occurs between 15 and 30 minutes after oral administration, and duration of action is usually three hours or longer.

Pentazocine is well absorbed from the gastrointestinal tract. Plasma levels closely correspond to the onset, duration, and intensity of analgesia. The time to mean peak concentration in 24 normal volunteers was 1.7 hours (range 0.5 to 4 hours) after oral administration and the mean plasma elimination half-life was 3.6 hours (range 1.5 to 10 hours).

The action of pentazocine is terminated for the most part by biotransformation in the liver with some free pentazocine excreted in the urine. The products of the oxidation of the terminal methyl groups and glucuronide conjugates are excreted by the kidney. Elimination of approximately 60% of the total dose occurs within 24 hours. Pentazocine passes into fetal circulation.

Onset of significant analgesic and antipyretic activity of acetaminophen when administered orally occurs within 30 minutes and is maximal at approximately 2 1/2 hours. The pharmacological mode of action of acetaminophen is unknown at this time.

Acetaminophen is rapidly and almost completely absorbed from the gastrointestinal tract. In 24 normal volunteers the time to mean peak plasma concentration was 1 hour (range 0.25 to 3 hours) after oral administration and the mean plasma elimination half-life was 2.8 hours (range 2 to 4 hours).

The effect of pentazocine on acetaminophen plasma protein binding or vice versa has not been established. For acetaminophen there is little or no plasma protein binding at normal therapeutic doses. When toxic doses of acetaminophen are ingested and drug plasma levels exceed 90 mcg/mL, plasma binding may vary from 8% to 43%.

Acetaminophen is conjugated in the liver with glucuronic acid and to a lesser extent with sulfuric acid. Approximately 80% of acetaminophen is excreted in the urine after conjugation and about 3% is excreted unchanged. The drug is also conjugated to a lesser extent with cysteine and additionally metabolized by hydroxylation.

If pentazocine hydrochloride and acetaminophen tablets are taken every 4 hours over an extended period of time, accumulation of pentazocine and to a lesser extent, acetaminophen, may occur.

INDICATIONS AND USAGE

Pentazocine Hydrochloride and Acetaminophen Tablets are indicated for the relief of mild to moderate pain.

CONTRAINDICATIONS

Pentazocine hydrochloride and acetaminophen tablets are contraindicated in patients who are hypersensitive to either pentazocine or acetaminophen.

WARNINGS

Hepatotoxicity

Pentazocine hydrochloride and acetaminophen tablets contain acetaminophen and pentazocine hydrochloride. Acetaminophen has been associated with cases of acute liver failure, at times resulting in liver transplant and death. Most of the cases of liver injury are associated with the use of acetaminophen at doses that exceed 4000 milligrams per day, often involve more than one acetaminophen-containing product. The excessive intake of acetaminophen may be intentional to cause self-harm or unintentional as patients attempt to obtain more pain relief or unknowingly take other acetaminophen-containing products.

The risk of acute liver failure is higher in individuals with underlying liver disease and in individuals who ingest alcohol while taking acetaminophen.

Instruct patients to look for acetaminophen or APAP on package labels and not to use more than one product that contains acetaminophen. Instruct patients to seek medical attention immediately upon ingestion of more than 4000 milligrams of acetaminophen per day, even if they feel well.

Hypersensitivity/anaphylaxis

There have been post-marketing reports of hypersensitivity and anaphylaxis associated with use of acetaminophen. Clinical signs included swelling of the face, mouth, and throat, respiratory distress, urticaria, rash, pruritus, and vomiting. There were infrequent reports of life-threatening anaphylaxis requiring emergent medical attention. Instruct patients to discontinue pentazocine hydrochloride and acetaminophen tablets immediately and seek medical care if they experience these symptoms. Do not prescribe pentazocine hydrochloride and acetaminophen tablets for patients with acetaminophen allergy.

Drug Dependence

Pentazocine can cause a physical and psychological dependence. (See DRUG ABUSE AND DEPENDENCE.)

Use In Head Injury and Increased Intracranial Pressure

In the presence of head injury, intracranial lesions or a preexisting increase in intracranial pressure, the possible respiratory depressant effects of pentazocine and its potential to elevate cerebrospinal fluid pressure (resulting from vasodilation following CO2 retention) may be markedly increased. Furthermore, pentazocine can produce effects on pupillary response and consciousness, which may obscure neurologic signs of further increases in intracranial pressure in patients with head injuries. In such patients, pentazocine hydrochloride and acetaminophen tablets must be used with extreme caution and only if its use is deemed essential.

Interactions with Alcohol and Drugs of Abuse

Pentazocine may be expected to have additive effects when used in conjunction with alcohol, other opioids, or illicit drugs that cause central nervous system depression because respiratory depression, hypotension, profound sedation, coma or death may result.

Patients Receiving Narcotics

Pentazocine is a mild narcotic antagonist. Some patients previously given narcotics, including methadone for the daily treatment of narcotic dependence, have experienced withdrawal symptoms after receiving pentazocine.

Respiratory Depression

Respiratory depression occurs more frequently in elderly or debilitated patients and in those suffering from conditions accompanied by hypoxia, hypercapnia, or upper airway obstruction, in whom even moderate therapeutic doses may significantly decrease pulmonary ventilation. Use pentazocine hydrochloride and acetaminophen tablets with extreme caution in patients with chronic obstructive pulmonary disease or cor pulmonale and in patients having a substantially decreased respiratory reserve (e.g., severe kyphoscoliosis), hypoxia, hypercapnia, or pre-existing respiratory depression. Alternative non-opioid analgesics should be considered, and pentazocine hydrochloride and acetaminophen tablets should be employed only under careful medical supervision at the lowest effective dose in such patients.

Acute CNS Manifestations

Patients receiving therapeutic doses of pentazocine hydrochloride and acetaminophen tablets have experienced hallucinations (usually visual), disorientation, and confusion which have cleared spontaneously within a period of hours. The mechanism of this reaction is not known. Such patients should be closely observed and vital signs checked. If the drug is reinstituted, it should be done with caution since these acute CNS manifestations may recur.

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