Liquid Section
Syrup and suspension have used as the oral administration, as the dose of
liquid medicine in earlier. In the modem century, the therapeutic use of syrup
and suspension is modernized by the discovery of new therapeutic agents with
the help of chemistry.
Syrup
Syrup is the concentrated aqua solution of sucrose and other sugars or
sweetening agents to which small quantities of suitable polyhydric alcohols may
be added to retard crystallization or to increase the solubility of the other
ingredients. It usually contains aromatic or other flavoring materials. It
should keep in well-closed containers and stored at temperatures not exceeding 90°c.
Manufacturing of syrup
To solve the formulation problems encountered with pharmaceutical liquid,
an interesting dichotomy of investigate skills is required. On the one hand,
solubility and stability factors can be approached with the precision long
associated with the exact science; on the other hand, flavoring and other
organoleptic characteristics remain subjective factors for which the
application of the scientific method still plays a distressingly minor role.
Thus, the successful formulation of liquids as well as other dosage forms
requires a blend of scientific acuity and pharmaceutical art.
Quality Control of Syrup
Whether or not a substance dissolves in a given system and the extent to
which it dissolves depends largely on nature and intensity of the forces
presents in the interaction energies and the interplay of electronic and steric
factors in determining the solubility of substances in various classes of
solvents. The solubility is the factors of the following important terms:
A. pH
The solubility of a large number of modem chemotherapeutic agents can be
marketedly influenced by the pH of their environment. The pH that satisfies the
solubility requirements, mast not conflict with product requirements, such as
stability and physiological compatibility. In addition to this if pH is
critical to maintaining drug solubility; the system must be adequately
buffered. The selection of a buffer must be consistent with the following
criteria:
1. The buffer must have adequate capacity in the desired pH range
2. The buffer must be biologically safe for the intended use
3. The buffer should have little or no deleterieres effect on the
stability of the final product
4. The buffer should permit acceptable flavoring and coloring agents
B. Co solvency
Weak electrolytes and monopolar molecules frequently have poor water
solubility. Their solubility usually can be increased by the addition of
water-miscible solvent in which the drug has good solubility. This process is
known as Co solvency.
C. Dielectric constant
A more practical approach to the solubility problem may be found in what
has come to be known as the dielectric requirement. According to this theory
every solute shows a maximum solubility in any given solvent system at one or
more specific dielectric constants. The absolute solubility of a solute may
vary considerably in two different solvents of the same dielectric constant,
but the solubility profile, as a function of dielectric constants appears to be
similar for a solute in a wide variety of solvent systems.
D. Hydrotropy
The term hydtropy has been used to designate the increased in solubility
in water of various substances due to the presence of large amount of
additives. The mechanism by which this effect occurs is not clear. Some workers
have speculated that hydrotropy is simply another type of solubiization with
the solute dissolved in oriented clusters of the hydrotropic agent.
D. Stability
It consists chemical stability and physical stability to the existence of
liquid solution.
• Chemical stability
Techniques for prediction chemical stability of homogenous drug systems
are well defined. Chemical instability of drug invariably is magnified in
solution, opposed to solid or suspension systems. This liability, however, is
to a large extent offset by the rapid and accurate stability predictions which
are possible with homogeneous system but are extremely risk with heterogeneous
dosage forms studies involving evaluation of stability in liquid drug system
includes the effect of amino acids on the stability of aspirin in propylene
glycol solution, and a systematic of the auto oxidation of polysorbates.
• Physical stability
A physically stable oral liquid retain its viscosity, color clarity,
taste and odor throughout its self-life. All of these characteristics can and
should be evaluated subjectively and objectively if possible, during the course
of stability assessment.
Suspensions
Suspensions are heterogeneous systems containing two phases. The
continuous or external phase is generally liquid or semisolid and the dispersed
or internal phase is made up of particulate matter that is essentially
insoluble but dispersed throughout the continuous phase; the insoluble matter
may be intended for physiologic absorption. Understanding of wetting, particle
interaction, electro-kinetics aggregation and a sedimentation concept
facilitates the making of good formulation for suspensions.
