Gabapentin 100 mg/mL Oral Suspension

US Pharm. 2013;38(1):33-34.

Method of Preparation: Calculate the quantity of each ingredient for the amount to be prepared. Accurately weigh or measure each ingredient. Incorporate the Ora-Plus into the gabapentin and mix into a smooth paste. Add sufficient Ora-Sweet in portions, with mixing to final volume, and mix well. Package and label.

Use: Gabapentin oral suspension is used in the treatment of seizures, bipolar disorder, social phobia, and chronic pain.

Packaging: Package in tight, light-resistant containers.

Labeling: Shake well before taking. Keep out of reach of children. Discard after ____ [time period].

Stability: A beyond-use date of up to 56 days at room temperature or 91 days at refrigerated temperature may be used for this preparation.^1,2

Quality Control: Quality-control assessment may include weight/volume, pH, specific gravity, active drug assay, color, rheologic properties/pourability, physical observation, and physical stability (discoloration, foreign materials, gas formation, mold growth).³

Discussion: Gabapentin is an anticonvulsant that is structurally related to gamma-aminobutyric acid. It is used in combination with other anticonvulsants in the management of seizure disorders, neuropathic pain, and vasomotor symptoms. It is also used in the treatment or management of ciguatera poisoning, epilepsy, headache, hiccups, hot flushes, Lesch-Nyhan syndrome, amyotrophic lateral sclerosis, multiple sclerosis, parkinsonism, postoperative pain, some psychiatric disorders, restless legs syndrome, soft-tissue rheumatism, stiff-person syndrome, and tremor.⁴

Gabapentin is available as oral capsules of 100 mg, 300 mg, and 400 mg; tablets of 100 mg, 300 mg, 400 mg, 600 mg, and 800 mg; and an oral solution of 50 mg/mL. However, the need often exists for a higher-concentration oral liquid, and if tablets or capsules are used as the drug source, a suspension will result. In the literature, the 100 mg/mL concentration used in this formula also used an alternative second vehicle: simple syrup and methylcellulose 1% solution 1:1. Both formulations had the same stability and beyond-use dates, so the alternative formula could be used if desired.¹ In the event that tablets are used as the drug source, the 600-mg tablets also may contain hydroxypropyl cellulose, copovidone sodium, and calcium stearate. The capsules also may contain lactose, cornstarch, and talc, and the oral solution may contain glycerin, xylitol, purified water, and strawberry-anise flavor. Gabapentin may be compounded into numerous dosage forms, including topical gels, transdermal gels, creams, and injections.

Gabapentin (cyclohexaneacetic acid, Neurontin, C₉H₁₇NO₂, MW 171.24) occurs as a white to off-white, crystalline solid that is freely soluble in water and in alkaline and acidic solutions. A 2% aqueous solution has a pH of 6.5 to 8.0.

Ora-Plus is an oral suspending vehicle that accepts dilution of up to 50% or more with water, flavoring agents, or syrups while still retaining its suspending properties. It has a pH of approximately 4.2 and an osmolality of about 230 mOsm/kg. Ora-Plus is a thixotropic vehicle with a viscosity of approximately 1,000 cps at 25°C. It contains purified water, microcrystalline cellulose, sodium carboxymethylcellulose, xanthan gum, carrageenan, sodium phosphate, and citric acid as buffering agents, simethicone as an antifoaming agent, and potassium sorbate and methylparaben as preservatives.⁵

Ora-Sweet syrup vehicle is a flavoring vehicle for oral extemporaneous preparations. It is flavored with a citrus-berry flavor blend and contains glycerin and sorbitol to prevent cap lock, a problem associated with many syrups. Ora-Sweet is buffered to a pH of approximately 4.2 and has an osmolality of about 3,240 mOsm/kg. It contains purified water, sucrose, glycerin, sorbitol (5%), flavoring, sodium phosphate, and citric acid as buffering agents and potassium sorbate and methylparaben as preservatives.⁶

Methylcellulose (Methocel) is a practically odorless and tasteless, white to yellowish-white granule or powder that is widely used in both oral and topical formulations. The pH of a 1% solution ranges from 5.5 to 8.0. Methylcellulose is hygroscopic and practically insoluble in acetone, ethanol, saturated salt solutions, and hot water, but is soluble in glacial acetic acid. Its solutions are stable to alkalis and dilute acids with pH values between 3 and 11.⁷

Syrup (simple syrup) is a clear, sweet vehicle used as a sweetening agent and as the base for many flavored and medicated syrups. It contains 85% w/v sucrose in water and has a specific gravity of not less than 1.30.¹

REFERENCES

1. U.S. Pharmacopeia 35/National Formulary 30. Rockville, MD: U.S. Pharmacopeial Convention, Inc; 2012:344-350,350-386,2003,3296-3300.
2. Trissel LA. Trissel’s Stability of Compounded Formulations. 4th ed. Washington, DC: American Pharmacists Association; 2009:254-255.
3. Allen LV Jr. Standard operating procedure for performing physical quality assessment of oral and topical liquids. IJPC. 1999;3:146-147.
4. Sweetman SC, ed. Martindale: The Complete Drug Reference. 36th ed. London, England: Pharmaceutical Press; 2009:482-484.
5. Ora-Plus product information. Minneapolis, MN: Paddock Laboratories, Inc; 2010.
6. Ora-Sweet product information. Minneapolis, MN: Paddock Laboratories, Inc; 2010.
7. Allen LV Jr, Luner PE. Methylcellulose. In: Rowe RC, Sheskey PJ, Quinn ME, eds. Handbook of Pharmaceutical Excipients. 6th ed. Washington, DC: American Pharmaceutical Association; 2009:438-441.

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