butalbital, acetaminophen

(redirected from Phrenilin Forte)

butalbital, acetaminophen†

(byoo-tal-bi-tal & a-seet-a-min-oh-fen) ,


(trade name),


(trade name),

Phrenilin Forte

(trade name)


Therapeutic: nonopioid analgesics
Pharmacologic: barbiturates
Pregnancy Category: C
† For information on acetaminophen component in formulation, see acetaminophen monograph


Relief of the symptom complex of tension (or muscle contraction) headaches (use should be short-term only as the butalbital component may be habit-forming).


Contains an analgesic (acetaminophen) for relief of pain and a barbiturate (butalbital) for its sedative effect.

Therapeutic effects

Decreased severity of pain with some sedation.


Absorption: Well absorbed.
Distribution: Widely distributed; crosses the placenta and enters breast milk.
Metabolism and Excretion: Butalbital primarily eliminated by kidneys as unchanged drug or metabolites (59–88% of dose); acetaminophen primarily metabolized by liver.
Half-life: Butalbital = 35 hr; acetaminophen = 1–3 hr.

Time/action profile

PO15–30 min1–2 hr30 hr


Contraindicated in: Hypersensitivity to individual components; Lactation: Lactation; Porphyria.
Use Cautiously in: History of suicide attempt or drug addiction; Chronic alcohol use; Severe hepatic or renal disease; Patients concomitantly receiving other CNS depressants; Geriatric: Appears on Beers list. Geriatric patients are at ↑ risk for side effects (dose ↓ recommended); Pediatric: Children <12 yr (safety not established).

Adverse Reactions/Side Effects

Central nervous system

  • drowsiness (most frequent)
  • confusion
  • delirium
  • depression
  • dizziness
  • excitation
  • headache (with chronic use)
  • irritability
  • lethargy
  • nervousness
  • numbness
  • tingling

Ear, Eye, Nose, Throat

  • earache
  • nasal congestion
  • tinnitus


  • respiratory depression


  • tachycardia


  • constipation
  • dry mouth
  • dysphagia
  • flatulence
  • heartburn


  • dermatitis
  • pruritis
  • rash
  • sweating


  • leg pain
  • muscle weakness


  • fever
  • physical dependence
  • psychological dependence
  • tolerance


Drug-Drug interaction

Additive CNS depression with other CNS depressants, including alcohol, antihistamines, antidepressants, opioid analgesics, and sedative/hypnotics.May ↑ the metabolism and ↓ the effectiveness of other drugs including amiodarone, benzodiazepines, bupropion, calcium channel blockers, carbamazepine, citalopram, clarithromycin, cyclosporine, erythromycin, fluoxetine, fluvoxamine, glipizide, hormonal contraceptives, losartan, methadone, mirtazapine, nateglinide, nefazodone, nevirapine, phenytoin, pioglitazone, promethazine, propranolol, protease inhibitors, proton pump inhibitors, rifampin, ropinirole, rosiglitazone, selegiline, sertraline, tacrolimus, theophylline, venlafaxine, voriconazole, warfarin, and zafirlukast.MAO inhibitors, felbamate, primidone, and valproic acid may ↓ metabolism and ↑ the effecta of butalbital.St. John’s wort may ↓ barbiturate effect.Concurrent use of kava kava, valerian, skullcap, chamomile, or hops can ↑ CNS depression.


Oral (Adults) 1–2 capsules or tablets (50–100 mg butalbital) every 4 hr as needed for pain (should not exceed 6 tablets or capsules/24 hr).

Availability (generic available)

Tablets: 50 mg butalbital/325 mg acetaminophen, 50 mg butalbital/650 mg acetaminophen
Capsules: 50 mg butalbital/650 mg acetaminophen

Nursing implications

Nursing assessment

  • Assess type, location, and intensity of pain before and 60 min following administration.
  • Prolonged use may lead to physical and psychological dependence and tolerance. This should not prevent patient from receiving adequate analgesia. Most patients who receive butalbital compound for pain do not develop psychological dependence.

Potential Nursing Diagnoses

Acute pain (Indications)
Risk for injury (Side Effects)


  • Explain therapeutic value of medication before administration to enhance the analgesic effect.
  • Regularly administered doses may be more effective than prn administration. Analgesic is more effective if given before pain becomes severe.
  • Medication should be discontinued gradually after long-term use to prevent withdrawal symptoms.

Patient/Family Teaching

  • Instruct patient to take medication as directed. Do not increase dose because of the habit-forming potential of butalbital. If medication appears less effective after a few weeks, consult health care professional. The dose of acetaminophen should not exceed the maximum recommended daily dose of 4 g/day. Chronic excessive use of >4 g/day (2 g in chronic alcoholism) may lead to hepatotoxicity, renal or cardiac damage.
  • Advise patients with tension headaches to take medication at first sign of headache. Lying down in a quiet, dark room may also be helpful. Medications taken for prophylaxis should be continued.
  • May cause drowsiness or dizziness. Advise patient to avoid driving and other activities requiring alertness until response to medication is known.
  • Caution patient to avoid concurrent use of alcohol or other CNS depressants.
  • Advise patient to use an additional nonhormonal method of contraception while taking butalbital compound.

Evaluation/Desired Outcomes

  • Decrease in severity of pain without a significant alteration in level of consciousness.
Drug Guide, © 2015 Farlex and Partners