Benzodiazepines

Diazepam 5mg (rapid onset; high lipid solubility; half-life 24hrs)

= Chlordiazepoxide 12.5mg

= Clobazam 10mg (slow onset; half-life 36hrs)

= Clonazepam 250mcg (slow onset; half-life 36hrs)

= Lorazepam 1mg (intermediate onset; low lipid solubility; longer anti-seizure action; half-life 12hrs)

= Midazolam 2.5mg (only available buccal/SC/IM/IV/intranasal; ; half-life 4hrs)

Short half-life better for avoiding side-effects; low lipid solubility prevents redistribution from brain

Carbamazepine

Carbamazepine 100mg oral incl liquid (is given 3 times daily)

= Carbamazepine MR 100mg oral (is given 2 times daily)

= Carbamazepine 125mg rectal suppository (is given 4 times daily)

= Eslicarbazepine 150mg (is given 1 time daily)

= Oxcarbazepine 150mg (is given 2 times daily)

Carbamazepine, eslicarbazepine and oxcarbazepine can be switched from one another overnight.

Sodium valproate

Sodium valproate 500mg

= Semisodium valproate 433mg (divalproex sodium in US; Depakote)

= Valproic acid 433mg

= Sodium valproate MR 500mg

This difference has been noted by Sanofi and others

• Alcohol (and withdrawal)
• Aminophylline
• Amphetamine
• Barbiturates (withdrawal)
• Benzodiazepines (withdrawal)
• Bupropion – 20% of those with overdose, else <1% on modified-release preparation
• Anti-epileptic drugs – paradoxical worsening at high doses; may worsen certain seizure types
• Carbapenems – at high doses; may reduce valproate levels too
• Cephalosporins – at high doses
• Chloroquine, mefloquine – use Malarone instead for malaria prevention
• Clomipramine
• Clozapine – occur in 5%; could start with sodium valproate in those at risk of seizures
• Isoniazid – treat with pyridoxine and benzodiazepines
• Local anesthetics – lidocaine, bupivacaine
• Opioids – fentanyl and pethidine particularly but also others at high doses
• Penicillins – at high doses
• SSRIs – only in serotonin syndrome
• Theophylline
• Tramadol – at high doses
• Venlafaxine – only in toxicity

The Medicines and Healthcare products Regulatory Agency has provided the following guidance on switching between brands of  drugs when the drugs are being used for seizures.

Do not switch between brands (Category 1)

Carbamazepine, Phenobarbital, Phenytoin, Primidone

May be clinical difference between brands (Category 2)

Clobazam, Clonazepam, Eslicarbazepine, Lamotrigine, Oxcarbazepine, Perampanel, Retigabine, Rufinamide, Topiramate, Valproate, Zonisamide

Unlikely clinical difference between brands (Category 3)

Brivaracetam, Ethosuximide, Gabapentin, Lacosamide, Levetiracetam, Pregabalin, Tiagabine, Vigabatrin