Physical Characteristics of Sixteen Non-Prescription Medications: Specific Gravity, Ph, Surface Tension, and Rheological Characteristics

Research Article

J Drug Discov Develop and Deliv. 2015; 2(1): 1013.

Physical Characteristics of Sixteen Non-Prescription Medications: Specific Gravity, Ph, Surface Tension, and Rheological Characteristics

Al-Achi A*, Kathuria A and Zahid Khan M

Department of Pharmacy and Health Sciences, University of Campbell, USA

*Corresponding author: Antoine Al-Achi, Department of Pharmacy and Health Sciences, University of Campbell, P.O. Box 1090, Buies Creek, NC 27506, USA

Received: August 25, 2015; Accepted: September 08, 2015; Published: September 29, 2015


The physical characteristics of Over-The-Counter (OTC) medications serve as important parameters for the compounding pharmacist in order to prepare the prescription tailored to the patient’s needs. In this study, three containers of sixteen different OTC products were tested for their pH, surface tension, specific gravity, and their rheological behavior. All measurements were recorded at room temperature and in triplicates. The specific gravity was determined by the use of two different instruments (pycnometer and Densito 30 PX), and the results obtained from both methods were in good agreement with each other. All products were found to be denser than water except Witch Hazel USP Hamamelis Water which had a specific gravity of 0.98. Tustin DM cough syrup had the highest specific gravity of 1.26.pH of all products was found to be acidic except for DIgel Antacid and Antigay which showed basic pH of 8.07. Tustin DM cough syrup was found to be the most acidic with an average pH of 2.65. All products had an apparent surface tension value similar to or less than that of water. Pediatric Electrolyte had surface tension similar to that of water while Tustin DM Cough Syrup had the smallest value for surface tension (45.74 dynes/cm).Viscosities of all Newtonian and non-Newtonian products were measured by an Ostwald viscometer and a remoter, respectively, except for DI-gel Antacid and Anti gas was measured by a Brookfield Viscometer. Most of the Newtonian products had viscosity similar to water, except for Allergy Liquid, Children’s Day Time Cough and Cold Syrup, and Tustin DM Cough syrup which showed viscosity values of 3.23, 27.02, and 27.18 cPs, respectively. Children’s Day Time Cough and Cold Syrup had the highest kinematic viscosity of 22.41cSt, whereas Podia One Oral Therapy Rehydration had the lowest value of 1.02cSt. DI-gel Antacid and Antigay was found to exhibit thyrotrophic (pseudo plastic) behavior when subjected to stress. Triple Antibiotic Ointment and the toothpastes were tested using a remoter. Rheological parameters, namely compliance factor (Jo) and ground viscosity (?o), were determined from their respective rheograms. Triple Antibiotic Ointment was found with smallest compliance factor (Jo) value of 5.7 x 10-5 Pa-1, whereas the highest value was seen with Crest Toothpaste (3.12 x 10-3 Pa-1). The viscosity value of Max Block After sun Gel was found to be the highest (2.9 x 105Pa.s). The information obtained may serve as a resource for pharmacists while compounding medications for their patients.

Keywords: Over-The-Counter (OTC) medications; Viscosity determination; Rheological properties; Specific gravity


Over-The-Counter (OTC) products are available to the public in the United States without prescription. In many countries, OTC drugs are selected by regulatory agencies to ensure that they are safe and effective when used without a physician’s advice. For the over-thecounter products consumer must be able to self-diagnose, self-treat, and self-manage [1]. In the United States, the manufacture and sale of OTC substances are regulated by the Food and Drug Administration.

The Active Pharmaceutical Ingredient (API) is considered to be the basis by which OTC drugs are regulated by the FDA regardless of the final product dosage form type [2]. The division in the FDA that oversees the OTC product is known as the Center for Drug Evaluation and Research (CDER). According to CDER, OTC drugs must be safe to use without physician supervision, properly labeled, and their benefits to the public outweigh their risk [3]. Unless the drug is Generally Regarded As Safe by the FDA (i.e., GRAS listed), the FDA requires New Drug Application (NDA) before it permits the product to be distributed in the United States, given that the product conforms to the Code of Federal Regulations (CFR) with all its labeling, warnings and doses [4].

A special class of OTC medications also exists whereas the patient is required to consult with a pharmacist prior to obtaining them. Examples of this class of medications are Schedule V controlled substances and emergency contraceptive pills. OTC class drugs may be extended in the future by the FDA to include some asthma medications and cholesterol controlling drugs [5]. Since January 2013, the FDA gave approval of several drugs to switch from prescription status to OTC class; the drugs were oxybutynin, triamcinolone actinide, esomeprazole magnesium, fluticasone propionate and, budesonide [6].

According to a study conducted in 2011, most Americans chose OTC medications for treating their common ailments such as headache, heartburn, allergies, and colds [7]. Pregnant women use 1.5 times more OTC products than medications prescribed by their physician. In The United States, around 40 % of the OTC drugs are used by the elderly patients [8]. OTC sales accrue $102 billion in value to US health care [9].

Commercially available OTC products serve as a good source of information to pharmacists to compound quality dosage forms if their physical and chemical characteristics are known. However, according to regulations governing the practice of pharmacy, pharmacists cannot exactly duplicate the commercially available formulations. Among the important physical characteristics of pharmaceutical products are specific gravity, pH, surface tension, and rheological behavior. It is known that these physical characteristics can influence the final product’s stability and palatability.

This study characterizes 16OTC products for their pH, surface tension, specific gravity, and rheological properties (i.e., flow characteristics, apparent viscosity, and compliance factor).

Material and Methods


Sixteen OTC products were selected for determining their physical characteristics (Table 1). All products (n = 3) were purchased from a local store in North Carolina.