Gabapentin Flashcards
What are the indications of gabapentin?
Adjunctive treatment/monotherapy in focal seizures with or without secondary generalisation
Peripheral neuropathic pain
Menopausal symptoms, especially hot flushes, in women with breast cancer
Oscillopsia/spasticity in multiple sclerosis
Muscular symptoms in MND
What is the pharmacodynamic of gabapentin?
A GABA analogue
Inhibits the release of excitatory neurotransmitters
What is the pharmacokinetic of gabapentin?
Oral bioavailability = 27(at 4800mg/day)-60(900mg/day)% (dose dependent)
Protein binding = <3%
Half-life = 5-7 hours (in patients with normal renal function)
Metabolism = not appreciably metabolized
Excretion = 100% in urine as unchanged drug (kidney)
What are the cautions for gabapentin?
Diabetes
Elderly
High doses of oral solution in adolescents and adults with LBW
Hx of substance abuse
Respiratory depression
Seizures (may be exacerbated)
In which group of patients may gabapentin exacerbate seizures?
Absence or myoclonic seizures (including juvenile myoclonic epilepsy)
Tonic/atonic seizures
Dravet syndrome
Lennox-Gastaut syndrome
Myoclonic-atonic seizures
What are the different strengths of gabapentin capsules?
100mg
300mg
400mg
What are the different strengths of gabapentin tablets?
600mg
800mg
What is the liquid gabapentin equivalent to?
100mg tablet or capsule
Usually 2ml
What is the usual dose of gabapentin for epilepsy in adults/older children (aged 12-17 years) and neuropathic pain in adults?
900-3600mg
given in 3 divided doses
What is the usual dose of gabapentin for epilepsy in younger children (aged 6-12 years)?
Usually 25-35mg/kg given in 3 divided doses
Max 70mg/kg given in 3 divided doses
How would you advice patients to take gabapentin?
Swallow capsules and tablets whole with a drink of water or juice - do not chew them
Gabapentin can be taken with/without food
Space dose evenly throughout the day (e.g., first thing in the morning, early afternoon and at bedtime)
For liquid form, use the provided plastic syringe or spoon to measure the dose (ask pharmacist for one if they do not have it?
What should patients do if they forget to take a dose of gabapentin?
Take it as soon as they remember
If its within 2 hours of the next dose, they should skip the missed dose and take the next dose as normal
Never take 2 doses at the same time
Never take an extra dose to make up for a missed one
If they forget regularly, set an alarm to help remind them. They could also ask their pharmacists for advice on ways to help them remember
What should patients do if they forget to take a dose of gabapentin?
Take it as soon as they remember
If its within 2 hours of the next dose, they should skip the missed dose and take the next dose as normal
Never take 2 doses at the same time
Never take an extra dose to make up for a missed one
If they forget regularly, set an alarm to help remind them. They could also ask their pharmacists for advice on ways to help them remember
Can patients stop taking gabapentin even if they feel fine?
Important that they do not stop taking gabapentin suddenly even if they feel fine
For those with epilepsy, stopping gabapentin suddenly can cause status epilepticus
They may have severe withdrawal syndrome if stopped suddenly
What are the symptoms in severe withdrawal syndrome after sudden withdrawal of gabapentin?
Anxiety
Difficulty sleeping
Feeling sick
Pain
Sweating
How can withdrawal syndrome/seizures be prevented?
By gradually reducing the dose of gabapentin
What are the common side effects of gabapentin?
Feeling sleepy, tired or dizzy
N+V
Diarrhoea
Mood changes
Swollen arms and legs
Blurred vision
Dry mouth
Difficulty getting an erection
Weight gain
Memory problems
Headaches
Leucopenia (increased susceptibility to infections)
Vertigo
Tremor
Dyspnoea/cough
What are the serious side effects of gabapentin? What should patients do if they experience them?
Self-harm/suicidal thoughts
High temperature, lymphadenopathy that does not go away, jaundice, unusual bruises/bleeding, severe tiredness/weakness, unexpected muscle pain or weakness with or without a rash - could be symptoms of a serious reaction
Long-lasting stomach pain, N/V - pancreatitis
Muscle pain/weakness and having dialysis for renal failure
Hallucinations
Advice patient to call a doctor or 111 immediately
What is the advice around taking gabapentin in pregnancy and breastfeeding?
Pregnancy = avoid unless benefits outweigh risks
Breastfeeding = can continue taking gabapentin if baby is healthy
If woman is on gabapentin whilst breastfeeding and notices that their baby is not feeding well as usual, seems unusually sleepy, has a stomach upset of if they have any other concerns they should talk to their doctor, pharmacists, health visitor or midwife
TRUE OR FALSE
Gabapentin negatively affects fertility
FALSE
No evidence to suggests gabapentin reduces fertility in either men or women
What are the dose adjustments for those that have renal impairment?
600‒1800 mg daily in 3 divided doses if creatinine clearance 50‒79 mL/minute.
300‒900 mg daily in 3 divided doses if creatinine clearance 30‒49 mL/minute.
150‒600 mg daily in 3 divided doses if creatinine clearance 15‒29 mL/minute (150 mg daily dose to be given as 300 mg in 3 divided doses on alternate days).
150‒300 mg daily in 3 divided doses if creatinine clearance is less than 15 mL/minute (150 mg daily dose to be given as 300 mg in 3 divided doses on alternate days)
What are the interactions for gabapentin?
No significant drug interaction but:
Antacids + gabapentin = reduced amount of gabapentin in the body - to prevent this take the antacid at least 2 hours before of after gabapentin dose
Strong analgesics (e.g., morphine) + gabapentin = increased tiredness and dizzy
Antidepressants (e.g., amitriptyline, fluoxetine) + gabapentin = increased risk of hyponatraemia
Antipsychotics (e.g., clozapine, quetiapine, risperidone) + gabapentin = CNS depressant effects - can impair ability to perform skilled tasks e.g., driving
What effect can gabapentin have on lab tests?
False +ve readings for some urinary protein tests
Sources
https://bnf.nice.org.uk/drugs/gabapentin/
https://go.drugbank.com/drugs/DB00996
https://www.nhs.uk/medicines/gabapentin/taking-gabapentin-with-other-medicines-and-herbal-supplements/
