Page 228 - PG 101-Course notes مذكرة النظري 24-25 with spec

Medicinal plants (PG 101) Level 1 Clinical Pharmacy-PharmD

III. Drying chambers: It is a controlled and most preferable method,

where drugs are put on shelves in chambers having openings to allow

entrance of a warm stream of air through an inlet near the floor and the exit of

the moist warm air through an outlet near the roof.

IV. Vacuum drying: It is used for the drugs sensitive to high temperature.

The chambers are airtight and connected to an efficient vacuum pump. As the

pressure is lowered, the water content of the drug is removed at higher rate

at lower temperature. e.g., Digitalis leaves.

V. Freeze drying (lyophilization): This method is generally used for drying the

extremely delicate product such as serum and for foodstuffs such as orange

juice and coffee extracts. The principle of this process is the removal of water

content of the drug when present in the frozen state under vacuum at which it

sublimes into vapors directly without passing through the liquid state. A solid

is capable of sublimation if its vapor pressure is below the triple point (T).

This triple point may be defined as "the specific temperature and pressure at

which the solid, liquid and vapor phases can coexist in equilibrium". Frozen

water sublimes at temperature below 0°C and at pressure below 3 mm of

mercury.

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