This information is intended for use by health professionals
Phenobarbital Thornton & Ross 15mg/5ml Elixir
Phenobarbital 0.3% w/v
For the full list of excipients, see section 6.1
As an anticonvulsant in the treatment of all forms of epilepsy except absence seizures
RECOMMENDED DOSE AND DOSAGE SCHEDULE
| Usual adult daily dose:
|| 60-200mg phenobarbital taken in 2 or 3 divided portions.
|| initially 3-6mg per kg body weight per day taken in 2 or 3 divided portions.
| Label states:
|| for use as directed by the practitioner
Contra-indicated in patients with known hypersensitivity to barbiturates or any other ingredient, with severe respiratory depression, with severely impaired hepatic or renal function, and in cases of acute intermittent porphyria. Also in hyperkinetic children
Suicidal ideation and behaviour have been reported in patients treated with anti-epileptic agents in several indications. A meta-analysis of randomised placebo controlled trials of anti-epileptic drugs has shown a small increased risk of suicidal ideation and behaviour. The mechanism of this risk is not known and the available data do not exclude the possibility of an increased risk for Phenobarbital Elixir.
Therefore patients should be monitored for signs of suicidal ideation and behaviours and appropriate treatment should be considered. Patients (and caregivers of patients) should be advised to seek medical advice should signs of suicidal ideation or behaviour emerge.
Barbiturates are frequently used in suicidal attempts. In the presence of severe pain, barbiturates may fail to exert their hypnotic action and may cause wakefulness, excitement and delirium unless accompanied by an analgesic. Phenobarbital should be used with caution in the young, the elderly, debilitated patients, those with depressive disorders, those with renal impairment, existing liver disease or respiratory depression (should be avoided if severe).
Prolonged use may result in the dependence of the alcohol-barbiturate type and particular care should be taken in treating patients with a history of drug abuse or alcoholism. Avoid sudden withdrawal to prevent rebound seizures.
Phenobarbital Elixir contains 38% v/v ethanol (alcohol), i.e. up to 20g alcohol per adult daily dose, equivalent to 513ml beer or 214ml wine per day This amount of alcohol may alter the effects of other medicines taken at the same time. Harmful to those suffering from alcoholism. To be taken into account in pregnant or breast feeding women, children and high risk groups such as patients with liver disease or epilepsy. Care should be taken when giving to neonates as regular dosing could result in alcohol toxicity. Patients are advised to avoid other sources of alcohol while using this medicine. The concomitant administration of barbiturates and alcohol may lead to an additive CNS depressant effect, serious respiratory depression and a lowering of the lethal dose (see section 4.5).
There is still some debate on the effects of antiepileptics, including Phenobarbital, on bone metabolism. It is therefore recommended that Vitamin D supplementation is considered in patients who are immobilised for long periods or who have inadequate sun exposure or dietary intake of Vitamin D or calcium.
Phenobarbital increases the rate of metabolism of many drugs by induction of drug-metabolising enzymes in liver microsomes. This may result in a reduction in activity.
The following list is not exhaustive; the metabolism may be increased (and activity decreased) of any drug metabolised by hepatic enzymes, during concomitant use with phenobarbital.
The concomitant administration of barbiturates and alcohol may lead to an additive CNS depressant effect, may produce very serious respiratory depression and a lowering of the lethal dose of phenobarbital (see section 4.4).
Phenobarbital reduces plasma concentrations of methadone. Opioid withdrawal syndrome has been reported in patients maintained on methadone when phenobarbital was added to their regimen. Opioid analgesics can also be expected to have additive CNS effects. Plasma levels of phenobarbital may be increased when used in conjunction with dextropropoxyphene. Plasma levels of fenoprofen may be reduced by phenobarbital. Enhanced CNS depressant effects with pethidine, including reports of prolonged sedation. Cases of hepatotoxicity have been reported in patients on phenobarbital after taking paracetamol.
Clearance of disopyramide, lidocaine, propafenone, dronedarone and quinidine increased, leading to increased dosage requirements.
Phenobarbital accelerates the metabolism of chloramphenicol, doxycycline and metronidazole and may reduce plasma levels of rifampicin. There is a possibility of increased phenobarbital levels during concomitant use of chloramphenicol. Plasma concentrations of telithromycin are reduced by phenobarbital (avoid concomitant use and use for two weeks after phenobarbital withdrawal). A marked increase in serious skin reactions has been seen in children given cefotaxime and phenobarbital.
Metabolism of coumarin anticoagulants increased leading to reduced effect.
Possible antagonism of effect of phenobarbital by SSRIs, tricyclic and tricyclic-related antidepressants, by lowering of seizure threshold. Increased metabolism and therefore reduced plasma levels of paroxetine, fluoxetine, mianserin, bupropion, MAOIs, tricyclic antidepressants (e.g. imiptamine, amitriptyline) and tricyclic-related antidepressants. Possible increased lithium toxicity. The effect of phenobarbital can be reduced by concomitant use of the herbal remedy St. John's Wort (Hypericum perforatum).
Interactions between antiepileptics are complex. Concomitant administration of phenobarbital with other antiepileptics may enhance toxicity (increased sedative effects are possible with phenytoin and sodium valproate) without a corresponding increase in antiepileptic effect. Such interactions are very variable and unpredictable and plasma monitoring is often advisable with combination therapy. Plasma concentrations of carbamazepine, clonazepam, diazepam, lamotrigine, tiagabine and zonisamide reduced. Plasma concentration of phenytoin usually reduced, but may be raised. Plasma concentration of ethosuximide possibly reduced. Plasma concentration of phenobarbital increased by oxcarbazepine, phenytoin, valproate, and possibly felbamate, whereas plasma concentrations of oxcarbazepine and its active metabolite, and valproate may be reduced. Plasma concentration of phenobarbital increased by stiripentol and reduced by vigabatrin. As primidone is substantially converted into phenobarbital within the body elevated phenobarbital levels will arise if they are given concurrently.
Phenobarbital possibly reduces plasma concentrations of itraconazole, posaconazole and voriconazole (avoid concomitant use) and may reduce the absorption of griseofulvin.
Anticonvulsant effect of phenobarbital antagonised by antipsychotics (lowered seizure threshold). Phenobarbital accelerates metabolism of haloperidol. Plasma concentrations of both drugs reduced when phenobarbital given with chlorpromazine. Possible interaction with other phenothiazines (mesoridazine, thiodorazine). Plasma levels of aripiprazole possibly reduced by phenobarbital. The clinical effect of interactions with antipsychotics has not been consistent; worsening, improvement or no change in psychotic symptoms have all been noted.
Phenobarbital possibly reduces plasma concentrations of abacavir, amprenavir, darunavir, fosamprenavir, lopinavir, indinavir, nelfinavir and saquinavir. Plasma concentration of phenobarbital possibly increased by indinavir. Manufacturer of etravirine recommends avoidance of phenobarbital. There are potential interactions with ritonavir and tipranavir.
• Anxiolytics and Hypnotics
Phenobarbital reduces plasma concentrations of clonazepam.
Plasma concentrations possibly reduced by phenobarbital.
Plasma concentration of metoprolol and timolol and possibly propranolol reduced by phenobarbital.
• Calcium-channel blockers
Effects of felodipine and isradipine, and possibly dihydropyridines (nimodipine, nifedipine may require an increase in dosage), diltiazem, and verapamil reduced by phenobarbital.
• Cardiac glycosides
Metabolism of digitoxin accelerated by phenobarbital.
• CNS depressants
(also see Alcohol) Increased sedative effects when used in combination with anaesthetics, antihistamines, narcotic analgesics and other sedatives/tranquilisers.
- Plasma levels may be reduced, leading to reduced efficacy.
Phenobarbital reduces plasma concentrations of irinotecan and its active metabolite, and possibly plasma concentrations of doxorubicin, teniposide and etoposide. Phenobarbital may enhance the effects of cyclophosphamide. Phenobarbital may increase the risk of hypersensitivity reactions with procarbazine. Avoidance of barbiturates is advised by manufacturer of Gefitinib.
Phenobarbital reduces plasma concentrations of eplerenone (avoid concomitant use). Increased risk of osteomalacia (see section 4.8) when phenobarbital used in conjunction with carbonic anhydrase inhibitors. Furosemide may increase plasma phenobarbital levels, leading to adverse effects.
• Hormone Antagonists
Accelerated metabolism of gestrinone and toremifene.
Reduced effect of ciclosporin due to acceleration of metabolism by phenobarbital. Plasma concentrations of tacrolimus possibly reduced by phenobarbital
• Leukotriene Receptor Antagonists
Reduced plasma concentration of montelukast.
increased sedative effect when phenobarbital given with lofexidine.
Effects of phenobarbital possibly reduced by memantine.
• Sex hormones
Increased clearance of oestrogens and progestogens, possibly leading to oral contraceptive failure and breakthrough bleeding. Avoidance of phenobarbital advised by the manufacturer of Ulipristal.
• Sodium Oxybate
- Enhanced effects (avoid concomitant use).
Plasma concentrations of phenobarbital possibly increased by methylphenidate.
Phenobarbital accelerates metabolism of theophylline, leading to reduced effect.
• Thyroid Hormones
Phenobarbital accelerates metabolism of thyroid hormones (levothyroxine) and may increase requirements in hypothyroidism. Prescribers should be alert for changes in thyroid status if barbiturates are added or withdrawn from patients being treated for hypothyroidism.
Phenobarbital accelerate metabolism of tibolone leading to reduced plasma levels.
Increased phenobarbital levels may occur when used concomitantly with the influenza vaccine.
Antiepileptic therapy, including treatment with phenobarbital, is associated with folic acid deficiency, possibly by increased metabolism. Phenobarbital possibly increases the requirements for Vitamin D (see 4.4 Special warnings and precautions for use.). Pyridoxine (Vitamin B6), folic acid and folinic acid may reduce serum concentrations of phenobarbital.
The use of phenobarbital in pregnancy, especially the first and third trimesters should be avoided unless it is considered to be essential. Phenobarbital can cross the placental barrier and there is an increased risk of teratogenicity. Congenital craniofacial and digital abnormalities, and cleft lip and palate have been reported with antiepileptics including phenobarbital Neonatal bleeding may occur and prophylactic treatment with vitamin k1
for mother before delivery (as well as for the neonate) is recommended. Neonates exposed in utero during late pregnancy may experience sedation and withdrawal symptoms following delivery.
Patients taking phenobarbital should be adequately supplemented with folic acid before conception and during pregnancy.
Phenobarbital is excreted into breast milk and there is a small risk of neonatal sedation and methaemoglobinaemia in nursing infants. Breast-feeding is therefore not advisable.
May cause drowsiness. Phenobarbital may impair the mental and/or physical abilities required for the performance of potentially hazardous tasks such as driving or operating machinery. If patients are affected they should not drive or operate machinery.
The following adverse effects have been associated with use of phenobarbital. The most frequent adverse effect is sedation.
Blood and lymphatic system disorders
Agranulocytosis, macrocytic anaemia, megaloblastic anaemia, hypoprothrombinaemia, thrombocytopenia. Methaemoglobinaemia in infants nursed by mothers receiving phenobarbital.
Serum concentrations of thyroid hormones may be reduced (see section 4.5).
Metabolism and nutrition disorders
Folate deficiency, hypocalcaemia, hypophosphataemia, abnormal Vitamin D metabolism (see section 4.4), vitamin K deficiency.
Abnormal behaviour, aggression and hyperactivity (particularly in children), agitation, confusional state, delirium, dependence. depression, hallucination, insomnia, mood altered, paradoxical excitement, restlessness, suicidal ideation (see section 4.4), withdrawal syndrome.
Nervous system disorders
Ataxia, cognitive impairment, dizziness, drowsiness, Grand Mal convulsion. headache, irritability, lethargy, memory impairment, nystagmus, sedation.
Respiratory, thoracic and mediastinal disorders
Respiratory depression.Hepato-biliary disorders
Cholestasis, abnormal hepatic function, hepatitis.
Skin and subcutaneous tissue disorders
Exfoliative dermatitis, drug eruption, erythema multiforme, macropapular rash, mobilliform rash, photosensitivity, purpura, scarlatiniform rash, Stevens-Johnson syndrome, toxic epidermal necrolysis.
Musculoskeletal, connective tissue and bone disorders
Bone metabolism disorder, Dupuytren's contracture, frozen shoulder, Ledderhose's syndrome, Peyronie's disease, fibromas, general joint pain, osteomalacia, rickets.
There have been reports of decreased bone mineral density, osteopenia, osteoporosis and fractures in patients on long-term therapy with Phenobarbital. The mechanism by which Phenobarbital affects bone metabolism has not been identified.
Pregnancy, puerperium and perinatal conditions
Neonatal sedation, neonatal drug dependence and withdrawal syndrome, neonatal bleeding due to vitamin K deficiency.
Congenital and familial/genetic disorders
Cleft lip and palate, congenital anomaly
General disorders and administration site conditions
Antiepileptic hypersensitivity syndrome (including fever, rash, lymphadenopathy, lymphocytosis, eosinophilia, liver and other organ involvement). Symptoms generally occur between 1 and 8 weeks after first exposure, or within 1 day of rechallenge in sensitised individuals, with potential cross reactivity to other antiepileptics.
The toxic effects of overdosage include drowsiness, prolonged coma, respiratory depression and cardiovascular depression, with hypotension and shock leading to renal failure. The duration and depth of cerebral depression varies with the dose and tolerance of the patient. Absent bowel sounds are a sign of severe poisoning. Hypothermia is common, with associated pyrexia during recovery. Characteristic erythematous or haemorrhagic blisters occur in about 6% of patients. Death is usually due to respiratory and circulatory failure. The chronic effects of phenobarbital on neurological and psychic functions closely resemble those of alcohol. The symptoms of chronic poisoning include disorientation, mental confusion, ataxia, dizziness, depression and skin rashes. The aims in treating poisoning with phenobarbital are to maintain respiration, treat shock and prevent further absorption of the drug. Supportive measures alone may be sufficient if symptoms are mild.
Oral doses of activated charcoal can be considered in those presenting within 1 hour of ingesting more than 10mg/kg, with the aim of preventing absorption and aiding elimination. Analeptics should generally be avoided. However a single dose of nikethamide may be given in an emergency. If within 4 hours of ingestion, gastric aspiration or lavage may be of benefit in adults. The stomach should be emptied by lavage with warm water to leave the stomach empty, but only after precautions have been taken to avoid aspiration. Apomorphine induced emesis evacuates the stomach more rapidly and reliably than doses of ipecacuanha. After lavage, a saline cathartic should be administered and repeated every 1 to 2 hours, as long as bowel sounds are present. The prime objective of treatment is to maintain vital functions while the majority of the drug is metabolised by hepatic enzymes. Given normal renal function, forced alkaline diuresis (maintaining the urinary pH at approximately 8 by intravenous fusion) may enhance the excretion of the drug from the kidneys. The potentially fatal dose of phenobarbital is 6 to 10g. Attention should be paid to maintenance of a patient's airway and to the prevention of hypostatic pneumonia. Measures should be taken to prevent further loss of body heat.
In severe acute intoxication circulatory collapse is a major threat. Dehydration is often severe. Hypovolemia must be corrected and if necessary the blood pressure can be supported with dopamine.
Should renal failure occur, haemodialysis or charcoal haemoperfusion may be used to dispose of the poison. Charcoal haemoperfusion is the treatment of choice for the majority of patients with very severe barbiturate poisoning who fail to improve, or who deteriorate despite good supportive care.
The barbiturates reversibly depress the activity of all excitable tissues. Not all tissues are affected at the same dose or concentration and when barbiturates are given in sedative or hypnotic doses there is very little effect on skeletal, cardiac or smooth muscle.
Phenobarbital is a barbiturate drug which has selective anticonvulsant activity and is used to control tonic-clonic seizures in the treatment of epilepsy. In a dose that has only minor effects on the reticular system, phenobarbital elevates the threshold for the initiation of afterdischarges, shortens the period of afterdischarge, and suppresses the spread of seizures
Oral absorption of phenobarbital is complete but slow, peak plasma concentrations occur several hours after a single dose. It is about 40% bound to plasma proteins and bound to a similar extent in tissues. The volume of distribution is approximately 0.9 lkg-1
. About 25% of phenobarbital is eliminated by pH-dependent renal excretion, the remainder is inactivated by the hepatic microsomal enzymes.
The major metabolite is the para hydroxyphenyl derivative, which is inactive and is excreted in the urine partly as the sulphate conjugate.
Phenobarbital has a plasma half-life of up to about 75 hours in children and 100 hours in adults. This is increased in the elderly, in overdosage and in renal or hepatic disease.
No data of relevance, which is additional to that included in other sections of the SPC
Orange oil terpeneless
Lemon oil terpeneless
Yellow Dye Sunset (E110)
No major incompatibilities known.
500ml: 36 months unopened.
Once opened use within 28 days
Store below 25°C.
Protect from light.
500ml: amber glass bottle with plastic cap with EPE/Saranex liner or white plastic child resistant cap with EPE/Saranex liner.
THORNTON & ROSS LTD