PENTOTHAL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PENTOTHAL (PENTOTHAL).
Potentiates GABA-A receptor activity, enhancing inhibitory neurotransmission; also reduces excitatory glutamate signaling.
| Metabolism | Hepatic; primarily via CYP2C9 and other CYP450 enzymes. |
| Excretion | Hepatic metabolism (approx. 80%), renal excretion of metabolites (20-30%) and unchanged drug (0.3-1%). Biliary/fecal elimination is negligible. |
| Half-life | Terminal elimination half-life is 5-12 hours (mean 8 hours) in adults. Prolonged with hepatic impairment, obesity, or high doses due to saturation of redistribution and metabolism. |
| Protein binding | Approximately 72-86% bound, primarily to albumin (with some binding to lipoproteins). |
| Volume of Distribution | Vd = 1.0-2.5 L/kg (mean 1.5 L/kg). High Vd due to extensive tissue distribution, including brain and fat; correlates with high lipid solubility. |
| Bioavailability | IV: 100%. Rectal: approximately 60-80% (with variability). IM: approximately 60-70%. Oral: negligible due to extensive first-pass metabolism (not used clinically). |
| Onset of Action | IV: 30-60 seconds (rapid loss of consciousness). Rectal: 5-10 minutes (sedation/hypnosis). IM: 10-15 minutes (hypnosis). |
| Duration of Action | IV: 5-10 minutes for single induction dose (due to redistribution); after repeated doses or infusion, prolonged (hours) due to accumulation. T1/2 context: single dose effect ends by redistribution; elimination half-life relevant for recovery after prolonged use. |
| Molecular Weight | 264.33 |
| Action Class | Barbiturate |
| Brand Substitutes | Anesthal 500mg Injection, Thipen 500mg Injection, Pentone 500mg Injection, THIOSOL 500 MG INJECTION, Thiopental 500mg Injection |
Induction: 3-5 mg/kg IV; Maintenance: 25-75 mg IV as needed; Rectal: 25 mg/kg (max 1.5 g) for induction.
| Dosage form | SUSPENSION |
| Renal impairment | No specific GFR-based adjustment; use with caution in severe renal impairment due to prolonged effects. |
| Liver impairment | Reduce dose by 50% in Child-Pugh B and C; monitor for prolonged sedation. |
| Pediatric use | Induction: 5-6 mg/kg IV; Maintenance: 1-2 mg/kg IV as needed; Rectal: 25 mg/kg (max 1.5 g). |
| Geriatric use | Reduce induction dose to 2-3 mg/kg IV; use lower maintenance doses; increased risk of hypotension and respiratory depression. |
| 1st trimester | Avoid. Pentothal (thiopental) crosses the placenta and may be associated with fetal depression. Use only if clearly needed. |
| 2nd trimester | Use with caution. Risk of fetal respiratory depression and decreased placental perfusion. Limited data. |
| 3rd trimester | Use with caution during labor; may cause neonatal respiratory depression and decreased Apgar scores. Can accumulate with repeated doses. |
Clinical note
Comprehensive clinical and safety monograph for PENTOTHAL (PENTOTHAL).
| Placental transfer | Rapidly crosses the placenta, achieving fetal concentrations approximately 70-80% of maternal levels within minutes. |
| Breastfeeding | Thiopental is excreted into breast milk in small amounts. Single doses are unlikely to affect the infant, but repeated or high doses could cause sedation. Monitor infant for drowsiness and feeding difficulties. |
■ FDA Black Box Warning
WARNING: RESPIRATORY DEPRESSION AND APNEA; RESUSCITATIVE EQUIPMENT AND PERSONNEL MUST BE IMMEDIATELY AVAILABLE. INTRA-ARTERIAL INJECTION MAY CAUSE ARTERIAL SPASM, THROMBOSIS, AND GANGRENE.
| Serious Effects |
History of acute intermittent porphyriaHypersensitivity to barbituratesStatus asthmaticusSevere hemorrhagic shock or uncompensated cardiac disease
| Precautions | Respiratory depression, hypotension, laryngospasm, bronchospasm, cardiac arrhythmias, extravasation risk, and acute porphyria exacerbation. |
| Food/Dietary | No specific food interactions. However, avoid alcohol for at least 24 hours due to additive CNS depression. |
Loading safety data…
| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | PENTOTHAL (thiopental) crosses the placenta. First trimester: limited human data, animal studies show no consistent teratogenicity. Second trimester: no specific malformation risk. Third trimester: prolonged maternal administration may cause neonatal respiratory depression, hypotonia, and withdrawal. Use only if clearly needed. |
| Fetal Monitoring | Monitor maternal vital signs (heart rate, blood pressure, respiratory rate) continuously. Fetal heart rate monitoring is recommended during administration near delivery. Assess neonatal Apgar scores and respiratory effort at birth. Observe for maternal and fetal hypotension. |
| Fertility Effects | No known direct effects on human fertility. Animal studies show no impairment of fertility at clinically relevant doses. Use during labor does not impact long-term fertility. |
| Clinical Pearls |
| Pentothal (thiopental) is an ultra-short-acting barbiturate used for induction of anesthesia. It causes dose-dependent respiratory depression and hypotension. Administer only in a controlled setting with resuscitation equipment. Note that it is highly alkaline (pH 10-11) and extravasation causes severe tissue necrosis. Also, it is contraindicated in porphyria. |
| Patient Advice | You will receive this medication only under the supervision of an anesthesiologist. · It will cause you to fall asleep quickly and you may feel drowsy for several hours after the procedure. · Do not drive or operate machinery for at least 24 hours after receiving this medication. · Inform your doctor if you have a history of porphyria, liver disease, or allergies to barbiturates. · You may experience a bad taste or cough upon injection. |