Terbinafine Oral Suspension
Terbinafine Oral Suspension contains NLT 90.0% and NMT 110.0% of the labeled content of terbinafine hydrochloride (C21H25N·HCl). Prepare Terbinafine Oral Suspension (28.1 mg/mL as hydrochloride) equivalent to 25 mg of Terbinafine per mL as follows (see Pharmaceutical Compounding—Nonsterile Preparations 795).
Terbinafine (as Hydrochloride) 2500 mg (2810 mg)
Vehicle: A mixture of Vehicle for Oral Solution, NF, and Vehicle for Oral Suspension, NF, (1:1), a sufficient quantity to make 100 mL
Calculate the required quantity of each ingredient for the total amount to be prepared. If using tablets, place the required number of tablets in a suitable mortar, and comminute the tablets to a fine powder or add Terbinafine Hydrochloride powder. Add the Vehicle in small portions, and triturate to make a smooth paste. Add increasing volumes of the Vehicle to make a terbinafine suspension that is pourable. Transfer the contents of the mortar, stepwise and quantitatively, to a calibrated bottle. Add enough of the Vehicle to bring to final volume, and mix well.
•  Procedure
Mobile phase:  Acetonitrile and water (2:3), with 0.15% triethylamine and 0.15% phosphoric acid. Make adjustments if necessary.
Standard stock solution:  1.0 mg/mL USP Terbinafine Hydrochloride RS in methanol
Standard solution:  Transfer 0.5 mL of Standard stock solution to a 100-mL volumetric flask, dilute with Mobile phase to volume to obtain a solution containing 5 µg/mL of terbinafine hydrochloride, and pass through a suitable filter of 0.22-µm pore size.
Sample solution:  Shake thoroughly by hand each bottle of Oral Suspension. Accurately pipet 1.0 mL to a 25-mL volumetric flask. Dilute with methanol to volume to obtain a nominal concentration of 1 mg/mL of terbinafine hydrochloride. Mix the sample again. Accurately pipet 1.0 mL of the diluted terbinafine hydrochloride solution to a 10-mL volumetric flask, and dilute with Mobile phase to volume to obtain a nominal concentration of 5 µg/mL of terbinafine hydrochloride.
Chromatographic system 
Mode:  LC
Detector:  UV 224 nm
Column:  4.6-mm × 15-cm; 3.5-µm packing L1
Flow rate:  0.4 mL/min
Injection size:  10 µL
System suitability 
Sample:  Standard solution
[Note—The retention time of the terbinafine peak is 5.1 min. ]
Suitability requirements 
Relative standard deviation:  NMT 5.8%
Samples:  Standard solution and Sample solution
Calculate the percentage of the labeled amount of C21H25N·HCl in the volume of Oral Suspension taken:
Result = (rU/rS) × (CS/CU) × 100
rU== peak response from the Sample solution
rS== peak response from the Standard solution
CS== concentration of terbinafine hydrochloride in the Standard solution (µg/mL)
CU== nominal concentration of terbinafine hydrochloride in the Sample solution (µg/mL)
Acceptance criteria:  90.0%–110.0%
•   pH 791: 5.3–5.7
•  Packaging and Storage: Package in tight, light-resistant containers. Store at controlled room temperature or controlled cold temperature.
•  Labeling: Label it to state that it is to be well shaken before use, and to state the Beyond-Use Date.
•  Beyond-Use Date: NMT 30 days after the date on which it was compounded when stored at controlled room temperature or at controlled cold temperature.
•   USP Reference Standards 11
USP Terbinafine Hydrochloride RS Click to View Structure
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Jeanne H. Sun
Assistant Scientific Liaison
(CMP2010) Compounding
Reference Standards RS Technical Services
USP35–NF30 Page 4790
Pharmacopeial Forum: Volume No. 35(1) Page 96