Isoniazid

Abstract

The chemical stability of isoniazid in an oral liquid dosage form was studied by means of a specially developed stability-indicating high-performance liquid chromatographic assay method. The concentrations of the drug were directly related to peak heights, and the percent relative standard deviation based on five injections was 0.93. The products of decomposition and excipients present in the dosage forms did not interfere with the developed assay method. The preparation was stable for at least 42 days when stored in amber-colored glass bottles at room temperature. The pH value of the preparation decreased from 5.9 to 5.6 after 42 days of storage. The physical appearance of the preparation changed from almost colorless to light brown.

Introduction

Isoniazid (Figure 1) is used for the treatment of tuberculosis. The oral liquid dosage form of isoniazid is no longer available.1 A formula for compounding an oral liquid dosage form has been reported.1 The beyond-use date for this formulation was estimated to be 30 days based on the guidelines reported in the United States Pharmacopeia-National Formulary (USP-NF).; It has been reported that isoniazid has a maximum stability at pH 6.1 Furthermore, it has been reported that sugar has an adverse effect on the stability of isoniazid.1 Because of this adverse effect, the use of sorbitol as a sweetening agent has been recommended.3 Hald4 reported that the adverse effect of sugar can be prevented by adding 0.3% of sodium citrate. It has been reported that isoniazid should not be mixed with lactose or magnesium ions.3

The purpose of this investigation was (1) to develop a stability-indicating high-performance liquid chromatographic (HPLC) assay method for the quantitation of isoniazid and (2) to study the stability of isoniazid in an oral liquid dosage form.

Materials and Methods

Chemicals and Reagents

All chemicals and reagents were USP-NF- or American Chemical Society-grade and were used without further purification. Isoniazid powder (Lot C101217) was generously supplied by Professional Compounding Centers of America, Houston, Texas.

Equipment

An HPLC system (ALC 202 pump and Model 484 multiple wavelength detector, Waters Corporation, Milford, Massachusetts) equipped with an injector (Model 7125, Rheodyne, Cotati, California) and a recorder (Omniscribe 5213-12, Houston Instruments, Austin, Texas) were used. The column used (Beckman ultrasphere, CIS, 15 cm, 4.6 mm ID, 5 pm) is available from Phenomenex, Inc., Torrence, California. All pH values were measured with a Beckman SS-3 Zeromatic pH meter (Beckman Instruments, Fullerton, California).

Chromatographic Conditions

The mobile phase contained 3% (v/v) acetonitrile in water that contained 0.02 M potassium dihydrogen phosphate buffer. The pH of the mobile phase was approximately 4.9. The flow rate was 1.0 mL/minute, the sensitivity was 0.28 AUFS at 265 nm, the chart speed was 30.5 cm/hour, and the temperature was ambient.

Preparation of an Oral Liquid Dosage Form of Isoniazid

The oral liquid dosage form (10 mg/mL) was prepared according to the directions reported by Alien.1 The initial pH of the formulation was 5.9. The ingredients were (per 100 mL) isoniazid (1 g), sorhitol 70% (50 mL), methylparaben (200 nig), propylparaben (20 mg) and purified water (qs to 100 mL).

Preparation of Standard Solution

The stock solution of isoniazid (10 mg/mL) in water was prepared fresh daily using a simple solution method. The stock solution was used to prepare solutions of lower concentrations as needed by diluting with water. The most commonly used standard solution of the drug contained 50 µg/mL of isoniazid.

Preparation of Assay Solution

A 5.0-mL quantity of the assay mixture was diluted to 50 mL with water; 2.5 mL of this solution was further diluted to 50 mL with water.

Decomposition of Isoniazid

A 25-mL quantity of the standard solution (50 µg/mL) was transferred to a 150-mL beaker, and 0.5 mL of either 1 N sodium hydroxide solution or 1 N sulruric acid solution was added. The mixtures were boiled on a hot plate. More water was added as needed. After 5 minutes the mixtures were allowed to cool, neutralized and brought to volume (25 mL) with water. The mixtures were then injected into the chromatograph and assayed using the method described in the Assay Procedure and Calculations section.

Assay Procedure and Calculations

An 80-µL quantity of assay solution was injected into the chromatograph under the described conditions. For comparison, a similar volume of the standard solution containing the same concentration of the drug (based on the label claim) was injected. Since peak heights of the drug were directly related to the concentrations (range tested, 40 to 55 µg/mL), the results were calculated using a simple equation:

(Ph)^sub a^/(Ph)^sub s^ × 100 = Percentage of the label claim found

where (Ph)^sub a^ is the peak height of drug of the assay solution and (Ph)^sub s^ is the peak height of the standard solution. The results are presented in Table 1.

Results and Discussion

The assay method developed is stability-indicating since the product(s) of decomposition eluted out before the drug peak (Figure 2C). Furthermore, there was no interference with the assay procedure from the inactive ingredients present in the dosage form (ie, sorbitol, methylparaben, propylparaben). On decomposition, the loss of potency was approximately 3% when the sample was treated with an acid and 64% when it was treated with a base (Table 1). The concentrations of the drug were directly related to the peak heights (range tested, 40 to 55 µg/mL). The assay method developed is precise and accurate, with a percent relative standard deviation of 0.93 based on five readings.

Conclusion

The assay results indicate that the drug in the oral liquid dosage form was stable for at least 42 days when stored in an amber-colored glass bottle at room temperature (Table 1). The pH value of the preparation decreased from 5.9 to 5.6 after 42 days of storage. The physical appearance of the preparation changed from almost colorless to light brown.

References

1. Allen LV Jr. Isoniazid 10-mg/mLoral solution. IJPC 2003; 7(5): 376.

2. US Pharmacopeial Convention, Inc. United States Pharmacopeia 26National Formulary 21. Rockville, MD: US Pharmacopeial Convention, Inc.; 2003: 967-993, 2197-2201, 2214, 2564.

3. Brewer GA. Isoniazid. In: Florey K, ed. Analytical Profiles of Drug Substances. New York, NY: Academic Press; 1977; 6:165-231.

4. Hald JG. The stability of isoniazid in aqueous solutions containing sucrose or sorbitol. Dan Tidsskr Farm 1969; 43(7): 156-159.

Vishnu D. Gupta, PhD

Pharmaceutics Division

University of Houston

Arun Sood

Holland High School

Tulsa Oklahoma

Address correspondence to: Vishnu D. Gupta, PhD, Pharmaceutics Division, University of Houston, 1441 Moiirsund Street, Houston, TX 77030. E-mail: vgupta@uh.edu

Copyright International Journal of Pharmaceutical Compounding Mar/Apr 2005
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