What should I know before I take Fioricet ?

Do not use Fioricet if you have taken an MAO inhibitor in the past 14 days. A dangerous drug interaction could occur. MAO inhibitors include isocarboxazid, linezolid, phenelzine, rasagiline, selegiline, and tranylcypromine.

You should not use Fioricet if you are allergic to acetaminophen, butalbital, or caffeine, if you have porphyria, or if you have recently used alcohol, sedatives, tranquilizers, or other narcotic medications.

To make sure Fioricet is safe for you, tell your doctor if you have:

  • liver disease, cirrhosis, a history of alcoholism or drug addiction, or if you drink more than 3 alcoholic beverages per day;
  • kidney disease;
  • asthma, sleep apnea, or other breathing disorder;
  • stomach ulcer or bleeding;
  • a history of skin rash caused by any medication;
  • a history of mental illness or suicidal thoughts; or
  • if you use medicine to prevent blood clots.

It is not known whether Fioricet will harm an unborn baby. If you use butalbital while you are pregnant, your baby could become dependent on the drug. This can cause life-threatening withdrawal symptoms in the baby after it is born. Babies born dependent on habit-forming medicine may need medical treatment for several weeks. Tell your doctor if you are pregnant or plan to become pregnant.

This medicine can pass into breast milk and may harm a nursing baby. Tell your doctor if you are breast-feeding a baby.

Pharmacology

Mechanism of Action

Butalbital: Barbiturate; elicits generalized CNS depressant effects; depresses sensory cortex; decreases motor activity

Acetaminophen: Nonopioid, nonsalicylate analgesic; acts on hypothalamus to produce analgesia and antipyresis

Caffeine: Vasoconstrictive properties of cerebral blood vessels may be helpful when treating headaches; improves skeletal muscle contraction and medullary respiratory center sensitivity; stimulates central inspiratory drive

Absorption

Butalbital and caffeine: Well absorbed

Bioavailability: 100% acetaminophen

Distribution

Protein bound: Butalbital (45%); acetaminophen (20-50%)

Metabolism

Butalbital

  • Metabolized in liver by CYP450 enzyme system
  • Induces hepatic enzymes, but to lesser degree than phenobarbital

Acetaminophen

  • Metabolized in liver by microsomal enzyme systems
  • 80-85% conjugated principally with glucuronic acid and to a lesser extent with sulfuric acid and cysteine
  • 4% metabolized by CYP450 to toxic metabolite (N acetyl-p-benzoquinoneimine, N-acetylimidoquinone [NAPQI]), which is detoxified by conjugation with glutathione; high doses may deplete fixed amount of glutathione in body, causing NAPQI accumulation

Caffeine

  • Metabolized in liver via CYP1A2 to paraxanthine, theobromine, and theophylline

Elimination