This is an open label, randomised, balanced, two-treatment, two-period, two-sequence, single dose, crossover, oral bioequivalence study.

An open label, balanced, randomized, two-treatment, two-period, two-sequence, single dose, crossover, oral bioequivalence study of Montelukast sodium chewable tablets 4mg and 5mg of Dr. Reddy's Laboratories Limited, India comparing with that of SINGULAIR® (containing Montelukast sodium) chewable tablets 4mg and 5 mg of Merck Sharp & Dohme Ltd., USA in healthy, adult, human subjects under fasting conditions.

Inclusion Criteria:

Subjects were selected based on the following inclusion criteria:

• Provide written informed consent.
• Must be healthy, adult, human beings within 18 and 45 years of age (both inclusive) weighing at least 50 kg.
• Having a body mass index between 18.0 and 24.9 (both inclusive), calculated as weight in Kg/height in m2.
• Must be of normal health as determined by medical history, physical examination and laboratory investigation performed within 28 days prior to the commencement of the study. (Laboratory values must be within normal limits or considered by the physician I investigator to be of no clinical significance).
• Female Subjects
• Of child bearing potential practicing an acceptable method of birth control for the duration of the study as judged by the investigator(s), such as condoms, foams, jellies, diaphragm, intrauterine device (IUD), or abstinence.
• Surgically sterile (bilateral tubal ligation, bilateral oophorectomy, or hysterectomy has been performed on the subject)

Exclusion Criteria

The subjects were excluded based on the following criteria during screening and during the study:

• Incapable of understanding the informed consent.
• Systolic blood pressure less than 90 mm of Hg or more than 140 mm of Hg.
• Diastolic blood pressure less than 60 mm of Hg or more than 90 mm of Hg.
• Oral temperature is below 95.0°F or above 98.6°F.
• Pulse rate below 50/min or above 100/min.
• History of hypersensitivity or idiosyncratic reaction to investigational drug product or any other related drugs.
• Any evidence of impairment of renal, hepatic, cardiac, lung or gastrointestinal function.
• Consumption of grapefruit for the past ten days prior to the check-in, in each period.
• Regular smoker who has a habit of smoking more than nine cigarettes per day and has difficulty in abstaining from smoking during sample collection period.
• Habit of alcoholism and difficulty in abstaining from alcohol during the sample collection period.
• Difficulty in abstaining from xanthene containing food or beverages (like tea, coffee, chocolates and cola drinks) during the sample collection period.
• Intake of over the counter (OTC) or prescribed medications and enzyme modifying medication or systemic medication for the last 30 days before dosing.
• Clinically significant abnormalities and / or with significant diseases.
• Prevalence of oral candidiasis, aphthous ulcer or other oral lesions.
• Difficulty in swallowing tablets/capsules.
• Confirmed positive in alcohol screening.
• Confirmed positive in selected drug of abuse.
• Participated in any other clinical investigation using experimental drug/donated blood in past 90 days before the date of start of study.