Pharmacology
Pharmacodynamics
Gabapentin is a ligand of the α2δ calcium channel subunit. α2δ is an auxiliary protein connected to the main α1 subunit (the channel-forming protein) of high voltage activated voltage-dependent calcium channels (L-type, N-type, P/Q type, and R-type). Gabapentin is not a direct channel blocker: it exerts its actions by disrupting the regulatory function of α2δ and its interactions with other proteins. Gabapentin prevents delivery of the calcium channels to the cell membrane, reduces the activation of the channels by the α2δ subunit, decreases signaling leading to neurotransmitters release, and disrupts interactions of α2δ with NMDA receptors, neurexins, and thrombospondins. Out of the four known isoforms of α2δ protein, gabapentin binds with similar high affinity to two: α2δ-1 and α2δ-2. Most of the pharmacological properties of gabapentin are explained by its binding to just one isoform – α2δ-1.The endogenous α-amino acids L-leucine and L-isoleucine, which resemble gabapentin in chemical structure, bind α2δ with similar affinity to gabapentin and are present in human cerebrospinal fluid at micromolar concentrations. They may be the endogenous ligands of the α2δ subunit, and they competitively antagonize the effects of gabapentin. Accordingly, while gabapentin has nanomolar affinity for the α2δ subunit, its potency in vivo is in the low micromolar range, and competition for binding by endogenous L-amino acids is likely to be responsible for this discrepancy.Gabapentin is a potent activator of voltage-gated potassium channels KCNQ3 and KCNQ5, even at low nanomolar concentrations.
A large Swedish study suggests that gabapentinoids are associated with an increased risk of suicidal behaviour, unintentional overdoses, head/body injuries, and road traffic incidents and offences. Respiratory depression
Serious breathing suppression, potentially fatal, may occur when gabapentin is taken together with opioids, benzodiazepines, or other depressants, or by people with underlying lung problems such as COPD. Gabapentin and opioids are commonly prescribed or abused together, and research indicates that the breathing suppression they cause is additive. For example, gabapentin use before joint replacement or laparoscopic surgery increased the risk of respiratory depression by 30–60%. Withdrawal and dependence
Withdrawal symptoms typically occur 1–2 days after abruptly stopping gabapentin. Agitation, confusion and disorientation are the most frequently reported, followed by gastrointestinal complaints and sweating, and more rare tremor, tachycardia, hypertension and insomnia. In some cases, users experience withdrawal seizures. All these symptoms subside when gabapentin is re-instated.On its own, gabapentin appears to not have a substantial addictive power. In human and animal experiments, it shows limited to no rewarding effects. The vast majority of people abusing gabapentin are current or former abusers of opioids or sedatives. In these persons, gabapentin can boost the opioid "high" as well as decrease commonly experienced opioid-withdrawal symptoms such as anxiety. Overdose
Through excessive ingestion, accidental or otherwise, persons may experience overdose symptoms including drowsiness, sedation, blurred vision, slurred speech, somnolence, uncontrollable jerking motions, and anxiety. A very high amount taken is associated with breathing suppression, coma, and possibly death, particularly if combined with alcohol or opioids.