Penthiobarbital

Uses

Penthiobarbital 500 mg injection: Each box contains 1 vial of 500 mg Penthiobarbital Sodium for Injection (a sterile mixture of Penthiobarbital Sodium and anhydrous Sodium Carbonate as a buffer) & 1 ampoule of 10 ml Water for Injection.

Penthiobarbital 1 gm injection: Each box contains 1 vial of 1 gm Penthiobarbital Sodium for Injection (a sterile mixture of Penthiobarbital Sodium and anhydrous Sodium Carbonate as a buffer) & 2 ampoules of 10 ml Water for Injection.

Penthiobarbital Sodium for Injection is used-

• As the sole anesthetic agent for brief (15 minutes) procedures,
• For induction of anesthesia prior to administration of other anesthetic agents,
• To supplement regional anesthesia,
• To provide hypnosis during balanced anesthesia with other agents for analgesia or muscle relaxation,
• For the control of convulsive states during or following inhalation anesthesia, local anesthesia, or other causes,
• In neurosurgical patients with increased intracranial pressure, if adequate ventilation is provided, and
• For narcoanalysis and narcosynthesis in psychiatric disorders.

Penthiobarbital is also used to associated treatment for these conditions: Seizures

How Penthiobarbital works

Penthiobarbital binds at a distinct binding site associated with a Cl^- ionopore at the GABA_A receptor, increasing the duration of time for which the Cl^- ionopore is open. The post-synaptic inhibitory effect of GABA in the thalamus is, therefore, prolonged.

Dosage

Penthiobarbital dosage

Penthiobarbital Injection is administered intravenously normally as a 2.5% w/v solution. On occasions it may be administered as a 5% w/v solution (500 mg in 10 ml). The intravenous injection preparation should be used after reconstitution of the sterile powder with Water for Injections, usually to produce a 2.5% w/v solution.

Premedication: Premedication usually consists of atropine or scopolamine to suppress vagal reflexes and inhibit secretions. In addition, a barbiturate or an opiate is often given. Ideally, the peak effect of these medications should be reached shortly before the time of induction.

Test dose: It is advisable to inject a small "test" dose of 25 mg to 75 mg of Penthiobarbital Sodium for Injection to assess tolerance or unusual sensitivity to Penthiobarbital Sodium for Injection, and pausing to observe patient reaction for at least 60 seconds. If unexpectedly deep anesthesia develops or if respiratory depression occurs, consider these possibilities:

1. The patient may be unusually sensitive to Penthiobarbital Sodium for Injection,
2. The solution may be more concentrated than had been assumed, or
3. The patient may have received too much.

Use in anaesthesia: Normal dosage for the induction of anesthesia is 100 mg to 150 mg injected over 10 to 15 seconds. If necessary, a repeat dose of 100 mg to 150 mg may be given after one minute. No fixed dosage recommendations for the intravenous injection can be given, since the dosage will need to be carefully adjusted according to the patient's response. Factors such as age, sex, and weight of the patient should be taken into consideration. Penthiobarbital Sodium reaches effective concentrations in the brain within 30 seconds and anesthesia is normally produced within one minute of an intravenous dose.

• Adult: 100 mg to 150 mg intravenously over 10 to 15 seconds, normally as a 2.5% w/v solution. A repeat dose of 100 mg to 150 mg may be given after one minute. The intravenous injection should be given slowly and the amount given titrated against the patient's response to minimize the risk of respiratory depression or the possibility of over dosage. The average dose for an adult of 70 kg is roughly 200 mg to 300 mg (8 mls to 12 mls of a 2.5% w/v solution) with a maximum of 500 mg.
• Children: 2 mg/kg to 7 mg/kg bodyweight, intravenously over 10 to 15 seconds, normally as a 2.5% w/v solution. A repeat dose of 2 mg/kg to 7 mg/kg may be given after one minute. The dose is 2 mg/kg to 7 mg/kg based on the patient's response. The dose for children should not exceed 7 mg/kg.
• Elderly: Smaller adult doses are advisable.

Use in convulsive states: 75 mg to 125 mg (3 mls to 5 mls of a 2.5% w/v solution) should be given as soon as possible after the convulsion begins. Further doses may be required to control convulsion following the use of a local anesthetic. Other regimens, such as the use of intravenous or rectal diazepam, may be used to control convulsive states.

Side Effects

Hypersensitivity reactions have been reported. Other adverse reactions to thiopental sodium include the followings: respiratory depression, myocardial depression, cardiac arrhythmias, prolonged somnolence and recovery, hypotension, tachycardia, sneezing, coughing, bronchospasm, laryngospasm and shivering. Anaphylactic reactions have been reported. Symptoms, e.g., urticaria, bronchospasm, vasodilation and edema.

Toxicity

Overdosage may occur from rapid or repeated injections. Too rapid injection may be followed by an alarming fall in blood pressure even to shock levels. Apnea, occasional laryngospasm, coughing and other respiratory difficulties with excessive or too rapid injections may occur. Lethal blood levels may be as low as 1 mg/100 mL for short-acting barbiturates; less if other depressant drugs or alcohol are also present.

Precaution

A person competent in anesthesia management should be in constant attendance and adequate facilities for support of respiration and circulation should be available when Penthiobarbital Sodium for injection is being used. Penthiobarbital Sodium for Injection should be administered with caution to patients with preexisting hypotension or in conditions where the hypnotic effect may be prolonged or intensified, such as in the presence of liver disease and renal disease.

This product may be habit forming. Keep resuscitative and endotracheal intubation equipment and oxygen readily available. Maintain patency of the airway at all times. Only persons qualified in the use of anesthetics should administer this drug. Avoid extravasations or intra-arterial injection.

Interaction

Possible increase in difficulty in producing anaesthesia in patients taking alcohol or CNS depressants. Additive action with other CNS depressants including sedatives, hypnotics, nitrous oxide or alcohol. Increased hypotension and excitatory effects with phenothiazine antipsychotics. Increased hypnotic effect with antipsychotic. Decreased requirement of thiopental sodium with metoclopramide, sulfisoxazole, aspirin, meprobamate, probenecid and other highly protein bound drugs.

Food Interaction

Penthiobarbital Alcohol interaction

[Major] GENERALLY AVOID:

Concurrent acute use of barbiturates and ethanol may result in additive CNS effects,

including impaired coordination, sedation, and death.

Tolerance of these agents may occur with chronic use.

The mechanism is related to inhibition of microsomal enzymes acutely and induction of hepatic microsomal enzymes chronically.

The combination of ethanol and barbiturates should be avoided.

Penthiobarbital Drug Interaction

Moderate: morphine, acetaminophenMinor: pyridoxineUnknown: aspirin, epinephrine, amoxicillin, RHO Immunoglobulin , azithromycin, multivitamin, calcium / vitamin d, dexamethasone, heparin, ferrous sulfate, procaine penicillin, valproic acid, thiamine, cyanocobalamin, ascorbic acid, cholecalciferol, phytonadione

Penthiobarbital Disease Interaction

Major: Addison disease, asthma, liver disease, myasthenia gravis, porphyria, renal impairment, severe anemia, thyroid disorder

Elimination Route

Rapidly absorbed.

Half Life

3-8 hours

Pregnancy & Breastfeeding use

Pregnancy Category C. Animal reproduction studies have not been conducted with Penthiobarbital. It is also not known whether Penthiobarbital can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. Penthiobarbital should be given to a pregnant woman only if clearly needed. Penthiobarbital sodium readily crosses the placental barrier and small amounts may appear in the milk of nursing mothers following administration of large doses.

Contraindication

Absolute Contraindication:

• Absence of suitable veins for intravenous administration
• Hypersensitivity (allergy) to barbiturates
• Variegate porphyria (South African) or acute intermittent porphyria
• Status asthmaticus

Relative Contraindication:

• Severe cardiovascular disease
• Hypotension or shock
• Conditions in which the hypnotic effect may be prolonged or potentiated, eg, excessive premedication, Addison's disease, hepatic or renal dysfunction, myxedema, increased blood urea, severe anemia, asthma, myasthenia gravis

Acute Overdose

Overdosage may occur from too rapid or repeated administration. Too rapid injection may be followed by an alarming fall in blood pressure even to shock levels. Apnoea, occasional laryngospasm, coughing and other respiratory difficulties with excessive or too rapid injections may occur. In the event of suspected or apparent overdosage, the agent should be discontinued.

Storage Condition

Store at controlled room temperature of 15° C to 30° C. Solutions should be freshly prepared and used immediately. Any portion of the contents remaining should be discarded.

Innovators Monograph

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