Once-daily Gabapentin 450 Mg Oral Tablet

Titrate gabapentin tablet to an 1,800 mg dose taken orally once daily with the evening meal. Gabapentin tablets should be swallowed whole. Do not split, crush, or chew the tablets.

If gabapentin dosing is reduced, discontinued, or substituted with an alternative medication, this should be done gradually over a minimum of one week or longer (at the discretion of the prescriber).

In adults with postherpetic neuralgia, gabapentin therapy should be initiated and titrated as follows:  

For females C_Cr=(0.85)(140-age)(weight)/[(72)(S_Cr)]

For males C_Cr=(140-age)(weight)/[(72)(S_Cr)]

where age is in years, weight is in kilograms and S_Cr is serum creatinine in mg/dL.

The dose of gabapentin should be adjusted in patients with reduced renal function, according to Table 2. Patients with reduced renal function must initiate gabapentin at a daily dose of 300 mg. Gabapentin should be titrated following the schedule outlined in Table 1. Daily dosing in patients with reduced renal function must be individualized based on tolerability and desired clinical benefit.

There is a pregnancy exposure registry that monitors pregnancy outcomes in women exposed to gabapentin, including gabapentin, during pregnancy. Encourage women who are taking gabapentin during pregnancy to enroll in the North American Antiepileptic Drug (NAAED) Pregnancy Registry by calling the toll free number 1-888-233-2334 or visiting https://www.aedpregnancyregistry.org/.

Risk Summary

Available data from published prospective and retrospective cohort studies, and case reports over decades of use with gabapentin during pregnancy have not identified a drug-associated risk of major birth defects. The available data are insufficient to evaluate a drug-associated risk of miscarriage and other maternal or fetal outcomes. In nonclinical studies in mice, rats, and rabbits, gabapentin was developmentally toxic (increased fetal skeletal and visceral abnormalities, and increased embryofetal mortality) when administered to pregnant animals at doses similar to those used clinically (see Data).

Postmarketing data suggest that extended gabapentin use with opioids close to delivery may increase the risk of neonatal withdrawal versus opioids alone [see Clinical Considerations]. Although there is at least one report of neonatal withdrawal syndrome in an infant exposed to gabapentin alone during pregnancy, there are no comparative epidemiologic studies evaluating this association. Therefore, it is not known whether exposure to gabapentin alone late in pregnancy may cause withdrawal signs and symptoms.

The estimated background risk of major birth defects and miscarriage for the indicated populations is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2% to 4% and 15% to 20%, respectively.

Clinical Considerations

Fetal/Neonatal Adverse Reactions

Neonatal withdrawal syndrome has been reported in newborns exposed to gabapentin in utero for an extended period of time when also exposed to opioids close to delivery. Neonatal withdrawal signs and symptoms reported have included tachypnea, vomiting, diarrhea, hypertonia, irritability, sneezing, poor feeding, hyperactivity, abnormal sleep pattern and tremor. Reported signs and symptoms that may also be related to withdrawal include tongue thrusting, wandering eye movements while awake, back arching, and continuous extremity movements. Observe neonates exposed to gabapentin tablets and opioids for signs and symptoms of neonatal withdrawal and manage accordingly.

Data

Animal Data

When pregnant mice received oral doses of gabapentin (1,000 or 3,000 mg/kg/day, approximately 3 to 8 times the maximum recommended dose of 1,800 mg on a mg/m² basis) during the period of organogenesis, embryofetal toxicity (increased incidences of skeletal variations) was observed. The no effect level was 500 mg/kg/day, representing approximately the maximum recommended human dose [MRHD] on a mg/m² basis.

When rats were dosed prior to and during mating, and throughout gestation, pups from all dose groups (500, 1,000 and 2,000 mg/kg/day) were affected. These doses are equivalent to approximately 3 to 11 times the MRHD on a mg/m² basis. There was an increased incidence of hydroureter and/or hydronephrosis in rats in a study of fertility and general reproductive performance at 2,000 mg/kg/day with no effect at 1,000 mg/kg/day, in a teratology study at 1,500 mg/kg/day with no effect at 300 mg/kg/day, and in a perinatal and postnatal study at all doses studied (500, 1,000 and 2,000 mg/kg/day). The doses at which the effects occurred are approximately 3 to 11 times the maximum recommended dose of 1,800 mg on a mg/m² basis; the no-effect doses were approximately 5 times (Fertility and General Reproductive Performance study) and approximately equal to (Teratogenicity study) the MRHD on a mg/m² basis. Other than hydroureter and hydronephrosis, the etiologies of which are unclear, the incidence of malformations was not increased compared to controls in offspring of mice, rats, or rabbits given doses up to 8 times (mice), 10 times (rats), or 16 times (rabbits) the human daily dose on a mg/m² basis.

When pregnant rabbits were treated with gabapentin during the period of organogenesis, an increase in embryofetal mortality was observed at 60, 300, and 1,500 mg/kg/day (0.6 to 16 times the MRHD on a mg/m²basis).

In a published study, gabapentin (400 mg/kg/day) was administered by intraperitoneal injection to neonatal mice during the first postnatal week, a period of synaptogenesis in rodents (corresponding to the last trimester of pregnancy in humans). Gabapentin caused a marked decrease in neuronal synapse formation in brains of intact mice and abnormal neuronal synapse formation in a mouse model of synaptic repair. Gabapentin has been shown in vitro to interfere with activity of the α2δ subunit of voltage-activated calcium channels, a receptor involved in neuronal synaptogenesis. The clinical significance of these findings is unknown.

Gabapentin is present in human milk following oral administration. Adverse effects on the breastfed infant have not been reported. There are no data on the effects of the drug on milk production. The developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for gabapentin and any potential adverse effects on the breastfed infant from gabapentin or from the underlying maternal condition.

Gabapentin is known to be substantially excreted by the kidney. Reductions in gabapentin dose should be made in patients with age-related compromised renal function [see Dosage and Administration (2.2)].

discontinuation or a significant dose reduction of a drug.

After discontinuation of short-term and long-term treatment with gabapentin, withdrawal symptoms have been observed in some patients. Withdrawal symptoms may occur shortly after discontinuation, usually within 48 hours. In the postmarketing setting, reported adverse reactions have included, but not been limited to, seizures, depression, suicidal ideation and behavior, agitation, confusion, disorientation, psychotic symptoms, anxiety, insomnia, nausea, pain, sweating, tremor, headache, dizziness, and malaise. The abuse and dependence potential of gabapentin tablets has not been evaluated in human studies.

Gabapentin is structurally related to the neurotransmitter GABA (gamma-aminobutyric acid), but it does not modify GABA_A or GABA_B radioligand binding, it is not converted metabolically into GABA or a GABA agonist, and it is not an inhibitor of GABA uptake or degradation. In radioligand binding assays at concentrations up to 100 μM, gabapentin did not exhibit affinity for a number of other receptor sites, including benzodiazepine, glutamate, N-methyl-D-aspartate (NMDA), quisqualate, kainate, strychnine-insensitive or strychnine-sensitive glycine; alpha 1, alpha 2, or beta adrenergic; adenosine A1 or A2; cholinergic, muscarinic, or nicotinic; dopamine D1 or D2; histamine H1; serotonin S1 or S2; opiate mu, delta, or kappa; cannabinoid 1; voltage-sensitive calcium channel sites labeled with nitrendipine or diltiazem; or at voltage-sensitive sodium channel sites labeled with batrachotoxinin A20-alpha-benzoate. Gabapentin did not alter the cellular uptake of dopamine, noradrenaline, or serotonin.

In vitro studies with radiolabeled gabapentin have revealed a gabapentin binding site in areas of rat brain including neocortex and hippocampus. A high-affinity binding protein in animal brain tissue has been identified as an auxiliary subunit of voltage-activated calcium channels. However, functional correlates of gabapentin binding, if any, remain to be elucidated. It is hypothesized that gabapentin antagonizes thrombospondin binding to α2δ-1 as a receptor involved in excitatory synapse formation and suggested that gabapentin may function therapeutically by blocking new synapse formation.

Gabapentin is absorbed from the proximal small bowel by a saturable L-amino transport system. Gabapentin bioavailability is not dose proportional; as the dose is increased, bioavailability decreases.

When gabapentin (1,800 mg once daily) and gabapentin immediate release (600 mg three times a day) were administered with high fat meals (50% of calories from fat), gabapentin has a higher C_max and lower AUC at steady state compared to gabapentin immediate release (Table 5). Time to reach maximum plasma concentration (T_max) for gabapentin is 8 hours, which is about 4 hours to 6 hours longer compared to gabapentin immediate release.

As renal function decreases, renal and plasma clearances and the apparent elimination rate constant decrease, while C_max and t_1/2 increase.

In patients (N=60) with creatinine clearance of at least 60, 30 to 59 or less than 30 mL/min, the median renal clearance rates for a 400 mg single dose of gabapentin immediate release were 79, 36 and 11 mL/min, respectively, and the median t_1/2 values were 9.2, 14, and 40 hours, respectively.

Dosage adjustment is necessary in patients with impaired renal function [see Dosage and Administration (2.2)].

Hemodialysis

In a study in anuric adult subjects (N=11), the apparent elimination half-life of gabapentin on nondialysis days was about 132 hours; during dialysis the apparent half-life of gabapentin was reduced to 3.8 hours. Hemodialysis thus has a significant effect on gabapentin elimination in anuric subjects. Gabapentin should not be administered in patients undergoing hemodialysis. Alternative formulations of gabapentin products should be considered in patients undergoing hemodialysis.

Elderly

Apparent oral and renal clearances of gabapentin decrease with increasing age, although this may be related to the decline in renal function with age. Reductions in gabapentin dose should be made in patients with age-related compromised renal function [see Dosage and Administration (2.2)].

Hepatic Impairment

Because gabapentin is not metabolized, studies have not been conducted in patients with hepatic impairment.

Pediatrics

The pharmacokinetics of gabapentin have not been studied in patients less than 18 years of age.

Gender

Although no formal study has been conducted to compare the pharmacokinetics of gabapentin in men and women, it appears that the pharmacokinetic parameters for males and females are similar and there are no significant gender differences.

Race

Pharmacokinetic differences due to race have not been studied. Because gabapentin is primarily renally excreted and there are no important racial differences in creatinine clearance, pharmacokinetic differences due to race are not expected.

Gabapentin was given in the diet to mice at 200, 600, and 2,000 mg/kg/day and to rats at 250, 1,000 and 2,000 mg/kg/day for 2 years. A statistically significant increase in the incidence of pancreatic acinar cell adenoma and carcinomas was found in male rats receiving the high dose; the no-effect dose for the occurrence of carcinomas was 1,000 mg/kg/day. Peak plasma concentrations of gabapentin in rats receiving the high dose of 2,000 mg/kg/day were more than 10 times higher than plasma concentrations in humans receiving 1,800 mg per day and in rats receiving 1,000 mg/kg/day peak plasma concentrations were more than 6.5 times higher than in humans receiving 1,800 mg/day. The pancreatic acinar cell carcinomas did not affect survival, did not metastasize and were not locally invasive. The relevance of this finding to carcinogenic risk in humans is unclear.

Studies designed to investigate the mechanism of gabapentin-induced pancreatic carcinogenesis in rats indicate that gabapentin stimulates DNA synthesis in rat pancreatic acinar cells in vitro and, thus, may be acting as a tumor promoter by enhancing mitogenic activity. It is not known whether gabapentin has the ability to increase cell proliferation in other cell types or in other species, including humans.

Mutagenesis

Gabapentin did not demonstrate mutagenic or genotoxic potential in 3 in vitro and 4 in vivo assays. It was negative in the Ames test and the in vitro HGPRT forward mutation assay in Chinese hamster lung cells; it did not produce significant increases in chromosomal aberrations in the in vitro Chinese hamster lung cell assay; it was negative in the in vivo chromosomal aberration assay and in the in vivo micronucleus test in Chinese hamster bone marrow; it was negative in the in vivo mouse micronucleus assay; and it did not induce unscheduled DNA synthesis in hepatocytes from rats given gabapentin.

Impairment of Fertility

No adverse effects on fertility or reproduction were observed in rats at doses up to 2,000 mg/kg (approximately 11 times the maximum recommended human dose on an mg/m²basis).