Gabapentinoids
From WikiMSK
Gabapentin
- First discovered in 1970s in an attempt to create a GABA analogue
- Whilst it resembles GABA, it does not act on the GABA receptor.
- Later discovered to act on ฮฑ2ฮด subunits of voltage-dependent calcium channels to reduce calcium influx
- Precise mechanism of analgesia unclear
- Inhibits release of excitatory neurotransmitters: glutamate, NA, substance P
- Medsafe licenced for: neuropathic pain, adjunct anti-epileptic
- Pharmacokinetics
- Absorption: Saturable transporter so delayed peak levels at higher doses. Drugs that reduce motility (e.g opiates) increase bioavailability. Peak serum conc 3 hours
- Distribution: Less lipophilic so requires active transport across the BBB
- Metabolism: minimal
- Elimination: Renal excretion, half life 5-7 hours. Dose adjustment in renal impairment
Pregabalin
- Similar to gabapentin. Binds to ฮฑ2ฮด subunits of voltage-dependent calcium channels to reduce calcium influx
- Inhibits release of excitatory neurotransmitters: glutamate, NA, substance P
- Medsafe licenced for: neuropathic pain, adjunct anti-epileptic
- Pharmacokinetics
- Absorption: Rapid absorption after oral administration. Peak serum conc 1h
- Distribution: Less lipophilic so requires active transport across the BBB
- Metabolism: minimal, no active metabolites
- Elimination: Renal excretion, half life 6.3 hours. Dose adjustment in renal impairment
Recommended prescribing: NZF
Gabapentin
- Day 1 300mg nocte
- Day 2 300mg bd
- Day 3 300mg tds
- Then increase by 300mg every 2-3 days to max dose 3600mg daily
Pregabalin
- Initially 75mg bd
- 150mg bd after 3-7 days
- Max dose 300mg bd after further 7 days
Titrate upwards until pain relief, side effects, or max dose reached
Remember to dose adjust for renal impairment: gabapentin if <80mL/min, pregabalin if <60mL/min
Caution in pregnancy (category B1); no clear data available, use if benefits outweigh risks
Evidence
Post-herpetic neuralgia, diabetic peripheral neuropathy and fibromyalgia