phenobarbital

CLINICAL USE

Anti-epileptic agent

DOSE IN NORMAL RENAL FUNCTION

Oral: 60–180 mg at nightStatus epilepticus: 10 mg/kg, max 1 g IV

PHARMACOKINETICS

Molecular weight :232.2 (254.2 as sodium salt)

%Protein binding :45–60

%Excreted unchanged in urine : 25

Volume of distribution (L/kg) :1

half-life – normal/ESRD (hrs) :75–120/Unchanged

DOSE IN RENAL IMPAIRMENT

GFR (mL/MIN)

20 to 50 : Dose as in normal renal function

10 to 20 : Dose as in normal renal function, but avoid very large doses

<10 : Reduce dose by 25–50% and avoid very large single doses

DOSE IN PATIENTS UNDERGOING RENAL REPLACEMENT THERAPIES

CAPD :Dialysed. Dose as in GFR

<10 : mL/min

HD :Dialysed. Dose as in GFR

<10 : mL/min

HDF/high flux :Dialysed. Dose as in GFR

<10 : mL/min

CAV/VVHD :Not dialysed. Dose as in GFR=10–20 mL/min

IMPORTANT DRUG INTERACTIONS

Potentially hazardous interactions with other drugs

Antibacterials: reduced concentration of chloramphenicol, doxycycline, metronidazole, telithromycin and possibly rifampicin – avoid with telithromycin

Anticoagulants: increased metabolism of coumarins (reduced effect)

Antidepressants: antagonise anticonvulsant effect; reduces concentration of paroxetine, mianserin and tricyclics; concentration reduced by St John’s wort – avoid concomitant use

Antifungals: possibly reduced concentration of itraconazole, posaconazole and voriconazole – avoid concomitant use with voriconazole; reduced absorption of griseofulvin (reduced effect)

Antipsychotics: antagonise anticonvulsant effect; metabolism of haloperidol increased; possibly reduces aripiprazole concentration – increase aripiprazole dose; concentration of both drugs reduced with chlorpromazine

Antivirals: concentration of abacavir, amprenavir, darunavir, indinavir, lopinavir, nelfinavir and saquinavir possibly reduced

Calcium-channel blockers: effect of felodipine, isradipine and probably dihydropyridines, diltiazem and verapamil reduced

Ciclosporin: reduced ciclosporin levels Corticosteroids: metabolism of corticosteroids accelerated, reduced effect

Diuretics: concentration of eplerenone reduced – avoid concomitant use; increased risk of osteomalacia with carbonic anhydrase inhibitorsOestrogens and progestogens: metabolism accelerated, reduced contraceptive effectSodium oxybate: enhanced effects of sodium oxybate – avoid

Tacrolimus: concentration of tacrolimus reduced

ADMINISTRATION

Reconstition

–

Route

IV, oral

Rate of Administration

Not more than 100 mg/minute

Comments

For IV administration, dilute 1 in 10 with water for injectionPhenobarbital (phenobarbitone).578 PhEnoBArBiTAL (PhEnoBArBiTonE)

OTHER INFORMATION

Aim for plasma concentration of 15– 40 mg/L (65–170 µmol/L) for optimum responseMay cause excessive sedation and increased osteomalacia in ERFCharcoal haemoperfusion and haemodialysis more effective than peritoneal dialysis for poisoningUp to 50% unchanged drug excreted in urine with alkaline diuresis.

See how to identify renal failure stages according to GFR calculation

See how to diagnose irreversible renal disease

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