Drug reference

Pentazocine

Opioid Analgesic · Analgesic

Also known as Pentazocine hydrochloride

Opioid AnalgesicAnalgesic

CDSCO approvedSchedule X

EXCRETION

—

not curated

INTERACTIONS

12 major

SEVERE in our sources

PREGNANCY

—

not curated

Top interactionssee all 12 →

AcetaminophenSevereTextbookHarrison 22e · p98-99
BarbituratesSevereTextbookKDT 7e · p401
BenzodiazepinesSevereTextbookKDT 7e · p383
Chlordiazepoxide HydrochlorideSevereTextbookG&G 14e

Mechanism

Pentazocine is a mixed opioid agonist-antagonist: it is a partial agonist or weak antagonist at mu-opioid receptors and an agonist at kappa-opioid receptors. Kappa receptor activation provides analgesia (particularly visceral) with less respiratory depression than pure mu agonists, but also produces dysphoria and psychotomimetic effects at higher doses. In opioid-dependent patients, its mu-antagonist activity can precipitate withdrawal, and its analgesic efficacy has a ceiling effect — increasing doses beyond 30-60 mg provides no additional analgesia.

Indications

Moderate or severe painSevere painmild-to-moderate painpreoperative medicationsupplement to anesthesiapostoperative painmoderately severe pain (in burns, trauma, fracture, cancer, etc.)

Dosing

Adult: Moderate or severe pain: 30 mg every 3–4 hours as required by subcutaneous injection, intramuscular injection, or intravenous injection. Severe pain: 45–60 mg every 3–4 hours as required by subcutaneous injection, intramuscular injection, or intravenous injection.
Renal adjustment: Avoid use or reduce dose; opioid effects increased and prolonged and increased cerebral sensitivity occurs.
Hepatic adjustment: Manufacturer advises caution in severe impairment (risk of increased bioavailability); consider dose reduction in severe impairment.
Max dose: 360 mg per day

Pharmacokinetics

Duration

Duration of action of a single dose is 4–6 hours.

Half-life

Plasma t½ is 3–4 hours.

Bioavailability

Effective orally, though considerable first pass metabolism occurs; oral: parenteral ratio is 1:3.

Metabolism

Oxidized and glucuronide conjugated in liver.

Excretion

Excreted in urine.

Contraindications

Acute porphyrias
Heart failure secondary to chronic lung disease
Patients dependent on opioids (can precipitate withdrawal)
coronary ischaemia and myocardial infarction (may increase cardiac work)
chronic (cancer) pain (due to frequent side effects and potential for dysphoric/psychotomimetic effect)

Side effects

Common

Biliary spasmBlood disorderChillsCirculatory depressionFace oedemaFacial plethoraGeneralised tonic-clonic seizureHypertensionHypothermiaIntracranial pressure increasedMood alteredMyalgiaParaesthesiaSexual dysfunctionSleep disordersSyncopeToxic epidermal necrolysisTremorUreteral spasmsedationrespiratory depression (1/3 to 1/2 of morphine at lower doses, with a lower ceiling)tachycardia (at higher doses)rise in BP (at higher doses, due to sympathetic stimulation)less severe biliary spasmless severe constipationless frequent vomitingsweatinglightheadednesspleasurable subjective effects (morphine-like at lower doses)

Serious

Potentially fatal respiratory depression
dysphoric and psychotomimetic effects (at high doses)
increase in blood pressure and heart rate (at high doses)
precipitation of withdrawal (in patients dependent on morphine or other mu-opioid agonists)
psychotomimetic effects (nalorphine-like, at > 60 mg i.m.)
dysphoric effects
precipitation of withdrawal (in morphine dependent subjects)
local fibrosis on repeated injection (due to irritant property)

Pregnancy & lactation

Lactation

Use with caution—limited information available.

Drug interactions

Acetaminophen

Severe

Textbook

Acetaminophen-related hepatotoxicity, a significant cause for liver failure.

Many practitioners have moved away from opioid-acetaminophen combination analgesics to avoid the risk of excessive acetaminophen exposure.

Source: Harrison 22e · p98-99

Barbiturates

Severe

Textbook

Exaggerated CNS depression.

Source: KDT 7e · p401

Benzodiazepines

Severe

Textbook

Marked depression of respiration, cardiac contractility, and blood pressure.

Carefully monitor respiratory and cardiovascular functions when co-administering benzodiazepines with opioids due to increased risk of severe depression of vital signs.

Source: KDT 7e · p383

Chlordiazepoxide Hydrochloride

Severe

Textbook

Increased rates of accidental overdose and death.

Caution is advised, especially for patients with a history of drug abuse.

Source: G&G 14e

Clomethiazole

Severe

Textbook

Increased rates of accidental overdose and death.

Caution is advised, especially for patients with a history of drug abuse.