Inclusion Criteria:

1. Healthy subjects at least 18 years of age.
2. Informed of the nature of the study and provide their written informed consent.
3. Have a body mass index2 between 18 and 30 and weighing at least 110 pound.
4. In good health as determined by lack of clinically significant abnormalities in health assessments performed at screening as judged by the physician.

Exclusion Criteria:

1. Hypersensitivity to cetirizine hydrochloride (Zyrtec®) or related compounds.
2. Conditions that affect the absorption, metabolism or passage of drugs out of the body, e.g., sprue, celiac disease, Crohn's disease, colitis, liver, kidney or thyroid conditions.
3. Recent history (within 1 year) of mental illness, drug addiction, drug abuse or alcoholism.
4. A hematocrit value of ≤ 33.0 % for females and ≤ 37.0 % for males.
5. Donation of greater than 500 ml of blood in the past 4 weeks prior to study dosing or difficulty in donating blood.
6. Received an investigational drug within the 4 weeks prior to study dosing.
7. Currently taking any systemic prescription medications, except for oral/cutaneous/vaginal hormone contraceptives, within the 7 days prior to study dosing or over-the-counter medication within 3 days of study dosing. This prohibition does not include vitamins or herbal preparations taken as nutritional supplements for non-therapeutic indications as judged by the attending physician. Any nonprescription medication consumption reported will be reviewed by the investigator prior to dosing. At the discretion of the investigator these volunteers may be enrolled if the medication is not anticipated to alter study integrity.
8. Regular smoking of more than 5 cigarettes weekly or the regular daily use of nicotine-containing products beginning 3 months before study medication administration through the final evaluation.
9. If female, the subject is lactating or has a positive pregnancy test at screening and prior to each of the treatment periods. Females must use a medically acceptable method of contraception throughout the entire study period and for one week after the study is completed. Medically acceptable methods of contraception that may be used by the subject and/or her partner are: oral contraceptives/patches, progestin injection or implants, condom with spermicide, diaphragm with spermicide, IUD, vaginal spermicidal or hormonal suppository, surgical sterilization of themselves or their partner(s) or abstinence. Females taking oral contraceptives/patches must have taken them consistently for at least three months prior to receiving study medication.
10. Grapefruit beverages or foods beginning 7 days before each study medication administration and alcohol, caffeine or xanthine beverages or foods beginning 24 hours before each study medication administration through the last PK sample of each period. Such restricted items include coffee, tea, iced tea, Coke®, Pepsi®, Mountain DeW®, chocolate, brownies, etc.
11. Regular use of any drugs known to induce or inhibit hepatic drug metabolism (examples include barbiturates, carbamazepine, rifampin, phenylhydantoins, phenothiazines, cimetidine,omeprazole, macrolides, imidazoles, fluoroquinolones) within 30 days prior to study administration.
12. Positive test results for: HIV, Hepatitis B surface antigen, Hepatitis C antibody at screening.
13. Positive test results for: drugs of abuse or pregnancy at screening and prior to each dosing period.