2. PERHITUNGAN FORMULA TABLET VITAMIN C
Satu tablet effervescent dibuat dengan bobot 1,5 gram.
Formula untuk 1 buah tablet effervescent :
Vitamin C 500 mg
Pyridoxine 20 mg
PVP 3% 45 mg
Sukrosa 15% 225 mg
Asam sitrat monohidrat qs
Asam tartrat qs
Natrium bikarbonat qs
PEG 8000 30 mg
3. PERHITUNGAN FORMULA
Bobot tablet effervescent 1500 mg
• Fasa dalam (98%)
Bobot = 98/100 x 1500 mg = 1470 mg
Fasa dalam terdiri dari
– zat aktif
– asam
– basa
– pengikat
– pengisi
• Fasa luar (2%)
Bobot = 2/100 x 1500 mg = 30 mg
Fasa luar terdiri dari pelincir
• Bobot asam dan basa = fasa dalam – (zat aktif + pengikat + pengisi)
= 1470 mg – ( 520 + 45 + 225 ) mg
= 680 mg
4. BOBOT MOLEKUL DAN BOBOT EKIVALEN
Asam sitrat monohidrat:BM = 210,13
C6H8O7.H2O Bilangan ekivalen = 3 (jumlah gugus COOH)
Bobot ekivalen = 210,13/3 = 70,04
Asam tartrat: BM = 150,09
C4H6O6 Bilangan ekivalen = 2 (jumlah gugus COOH)
Bobot ekivalen = 150,09/2 = 75,05
Natrium bikarbonat: BM = 84,01
NaHCO3 Bilangan ekivalen = 1 (jumlah kation Na+ atau
Anion HCO3
-)
Bobot ekivalen = 84,01/1 = 84,01
5. PERSAMAAN REAKSI ASAM DAN BASA
Supaya reaksi sempurna antara asam sitrat dengan natrium
bikarbonat dan asam tartrat dengan natrium bikarbonat maka :
3 NaHCO3 + C6H8O7.H2O → 4 H2O + 3 CO2 + Na3C6H5O7
84,01 70,04
2 NaHCO3 + C4H6O6 → 2 H2O + 2 CO2 + Na2C4H4O6
84,01 75,05
(84, 01 mol ekivalen +70,04 mol ekivalen) + (84,01 mol ekivalen + 75,05 mol ekivalen) 680 mg
313,11 mol ekivalen 680 mg
6. PERHITUNGAN ASAM DAN BASA
Asam sitrat monohidrat
= ( 70,04 / 313,11 ) x 680 = 152,10 mg
Asam tartrat
= ( 75,05 / 313,11 ) x 680 = 162,99 mg
Natrium bikarbonat
= (( 84,01+84,01 ) / 313,11 ) x 680= 364,91 mg
7. Effervescent Granules
Granules are dosage forms that consist of particles ranging from about 4
to 10 mesh in size (4.76 to 2.00 mm), formed by moistening blended
powders and passing through a screen or a special granulator.
These moist granules are either air- or oven-dried. A special form of
granules can be used to provide a pleasant vehicle for selected drug
products, especially those with a bitter or salty taste. This special
formulation, an effervescent granule, may consist of mixtures of citric acid
and/or tartaric acid and/or sodium biphosphate combined with sodium
bicarbonate.
EXAMPLE
Rx
Active drug 500 mg/5 g tsp
in effervescent granule qs 120 g
Sig: Dissolve 1 teaspoonful in one-half glass of cool water and drink.
Repeat this every 8 h.
8. Calculate
• Sig: Dissolve 1 teaspoonful in one-half glass of cool water and
drink. Repeat this every 8 h.
• It is desired to dispense this as a granule, so that the patient will
measure out a teaspoonful (5 g) dose, mix, and administer.
• Since each dose weighs 5 g and the prescription consists of 120
g, there are 24 doses. Each dose contains 0.5 g of the active
drug, which comes to 12 g of the active drug for the entire
prescription.
• This requires 120 g − 12 g = 108 g of effervescent vehicle.
• A good effervescent blend consists of both citric acid and tartaric
acid (1:2 ratio), since the former is rather sticky and the latter
produces a chalky, friable granule.
• It is necessary to calculate the amount of each ingredient
required to prepare 108 g of the granulation.
9. Acid and Base
CITRIC ACID
3NaHCO3 + C6H8O7.H2O → 4 H2O + 3 CO2 + Na3C6H5O7
3 × 84 210
Citric acid 1 g (MW = 210) of citric acid reacts with 1.2 g (MW = 84) of sodium
bicarbonate as obtained from the following:
1 𝑔
210
=
𝑋
3 𝑥 84
𝑋 = 1,2 𝑔
TARTARIC ACID
2 NaHCO3 + C4H6O6 → 2 H2O + 2CO2 + Na2C4H4O6
2 × 84 150
Since it is desired to use a 1:2 ratio of citric acid to tartaric acid, 2 g (MW = 150) of
tartaric acid reacts with sodium 2.24 g of bicarbonate according to the following
calculation:
2 𝑔
150
=
𝑋
2 𝑥 84
𝑋 = 2,24 𝑔
10. Ratio adn Quantity
• Therefore, the ratio of the effervescent ingredients is
1:2:3.4 for the citric acid:tartaric acid:sodium bicarbonate.
• Since the prescription requires 108 g of the effervescent
mix, the quantity of each ingredient can be calculated as
follows:
1 + 2 + 3.4 = 6.4
1/6.4 × 108 g = 16.875 g of citric acid
2/6.4 × 108 g = 33.750 g of tartaric acid
3.4/6.4 × 108 g = 57.375 g of sodium Bicarbonate
Total = 108 g
• The prescription will require 12 g of the active drug and
108 g of this effervescent vehicle.
