Ophthalmic preparations characteristics, Formulation, method of preparation and MCQs for GPAT, NIPER, Pharmacist and Drug Inspector exam

Ophthalmic preparations characteristics, Formulation, method of preparation and MCQs for GPAT, NIPER, Pharmacist and Drug Inspector exam

Ophthalmic preparation characteristics:

Clarity Ophthalmic solutions, by definition, contain no undissolved ingredients and are essentially free from foreign particles. Filtration can enhance clarity in some cases. It is essential that the filtration equipment be clean and well rinsed to avoid introduction of particulate matter into the solution by equipment designed to remove it. Operations performed in clean surroundings, the use of laminar-flow hoods, and proper nonshedding garments will contribute collectively to the preparation of clear solutions essentially free from foreign particles. In many instances the same filtration step can produce both clarity and sterility. If viscosity-imparting polymers are used, a polish-filtering step may be necessary before the final filtration. Both container and closure must be thoroughly clean, sterile, and non-shedding, so that neither one introduces particulate matter to the solution during prolonged contact for the duration of the shelf-life.

Stability – The stability of a drug in an ophthalmic product depends on a number of factors, including the chemical nature of the drug substance, whether it is in solution or suspension, product pH, method of preparation (particularly temperature exposure), solution additives, and type of packaging. A pharmaceutical manufacturer strives for a shelf-life measured in years at controlled room-temperature conditions, whereas the compounding pharmacist often is uncertain about the shelf-life of his or her preparation and thus provides relatively small quantities at one time, assigns a shelf-life in terms of days or weeks, and may specify refrigerated storage as a further precaution. The attainment of optimum stability often requires some compromises in the formulation, packaging, and preparation of the final product. The product’s pH is often the stability-controlling factor for many drugs.

Buffer and pH – Ideally, ophthalmic preparations should be formulated at a pH equivalent to the tear fluid value of 7.4. Practically, formulators seldom achieve this. Most active ingredients used in ophthalmology are salts of weak bases and are most stable at an acid pH. This property generally holds for suspensions of insoluble corticosteroids.

Tonicity – Tonicity refers to the osmotic pressure exerted by salts in aqueous solution. An ophthalmic solution is isotonic with another solution when the magnitudes of the colligative properties of the solutions are equal. An ophthalmic solution is considered isotonic when its tonicity is equal to that of a 0.9 percent sodium chloride solution (290 mOsm). However, the osmotic pressure of the aqueous intraocular fluid is slightly higher than that of normal tears, measuring about 305 mOsm.

Viscosity – Ophthalmic solution and suspension eyedrops may contain viscosity-imparting polymers to thicken the tear film and increase corneal contact time (i.e., reduce the rate of tear fluid drainage). The hydrophilic polymers most often used for these purposes are methylcellulose, hydroxypropyl methylcellulose, hydroxyethyl cellulose, and polyvinyl alcohol—at concentrations that produce viscosities in the range of about 5 to 100 Centipoise.

Formulation and method of preparation:

1.Formulation of eye drops –

Drug: These contains drug of various categories including antiseptic, anti-inflammatory agent, mydriatric or meiotic properties.

Preservative: Eye drop should be sterile and should contain preservatives to avoid microbial contamination when the container is open. The preservative for opthalmic use includes Benzalkonium chloride, Chlorbutanol, Phenylmercuric acetate, Phenylmercuric nitrate etc.

Sterilization: Eye drops are sterilized by autoclaving at 1210C for 15 minutes or by bacteria filter to avoid thermal degradation; for example- Preservative chlorbutanaol hydrolyzes at high temperature.

Isotonicity: All the solutes including drug contribute to the osmotic pressure of the eye drop, therefore isotonicity of the formula should be calculated and it is adjusted with sodium chloride, for example- Sodium chloride 0.9% and boric acid 1.9% are iso-osmotic.

Buffer: The buffer should be added to maintain balance between comfort, solubility, stability and activity of drug. For example-, the hydrolyzed chlorbutanol forms hydrochloride acid making the drop acidic, whereas certain drug like pilocarpine hydrochloride are acidic. On the hand certain drug such as alkaloids show precipitation at lachrymal pH. Boric acid, monobasic sodium phosphate are the common buffers for eye drop.

Viscosity: The size of drop and its residences in eye depends on viscosity of eye drops. Methylcellulose, hydroxypropyl methylcellulose and polyvinyl alcohol are common viscosity enhancer.

Method of preparation of eye drops – The eye drops are prepared in 4 stages. These stages are as under:

1.Preparation of bactericidal and fungicidal vehicle: The aqueous or oily vehicle is used in preparation of eye drops. The aqueous vehicle may support bacterial or fungal growth, so one of the following bactericide may be used to prepare the eye drops :

  • Phenyl mercuric nitrate/ acetate – 0.002%
  • Benzalkonium chloride – 0.01%
  • Chlorhexidine acetate-0.01%

2.Preparation of solution of medicaments and adjuvant: The medicaments are dissolved in the aqueous vehicle containing suitable anti microbial agent. The adjuvants are also dissolved in the vehicle at a stage to form a stable preparation.

3.Clarification: The eye drops are clarified by passing the solutions through membrane filter having pore size of 0.8µm. The clarified solution is immediately transferred in to final containers and sealed to exclude micro organisms.

4.Sterilization : the eye drops are sterilized by autoclaving or heating with bactericide at 98⁰ to 100⁰C for 30 mins., or filtration through bacteria proof filter.

2.Formulation of eye lotion –

Eye lotions are simple solution. They are iso-osmotic with tears because they cause much greater dilution of the lachrymal fluid and hence are more likely to cause discomfort if not adjusted. The eye lotion should be sterile because the large volume is used to irritation from the eye. While removing the irritation from the eye, it become more susceptible to infection. The eye lotions are sterilized by autoclaving or by passing through bacteria proof filters. Sodium chloride eye lotion and sodium bicarbonate eye lotion are commonly used to remove foreign substance from the eye.

Method of preparation of eye lotion –

EXAMPLE: To prepare and submit ml of sodium chloride eye lotion B.P.C

Sodium chloride – 9gm

Purified water to produce – 1000ml

Method:- Dissolve sodium chloride in purified water and made the final volume by adding more of purified water. Filter through sintered glass filter grade 4. The eye lotion is transfer to the bottle. Close and sealed the bottle sterilize it by autoclaving.

3.Formulation of eye ointments – The ointment based for an eye-ointment must be no-irritating to the eye. The eye ointment base should melt near to the body temperature, so as to permit the diffusion of the drug through the lachrymal secretions of the eye. For the preparation of eye-ointment the following base is used:-

  • Yellow soft paraffin 80g
  • Liquid paraffin 10g
  • Wool fat 10g

Method of preparation of eye ointment –

  • Melt wool fat, soft paraffin on a water bath. Add liquid paraffin.
  • Filter through coarse filter placed in heated funnel. It is sterilized by dry heat method (1600C for 2 hours). Incorporate the medicament with the eye ointment base. Pack in sterile containers.

Multiple choice questions:

1.Ophthalmic solutions, by definition, contain no undissolved ingredients and are essentially free from foreign particles.

a)true

b)false

2.The stability of a drug in an ophthalmic product depends on a number of factors, including

a)chemical nature of the drug substance

b)product pH

c)method of preparation

d)all of these

3.Most active ingredients used in ophthalmology are salts of weak bases and are most stable at an basic pH.

a)true

b)false

4.The osmotic pressure exerted by salts in aqueous solution is called

a)osmosis

b)tonicity

c)both of these

d)none of these

5.An ophthalmic solution is isotonic with another solution when the magnitudes of the colligative properties of the solutions are

a)equal

b)unequal

c)closer to equal

d)all of these

6.An ophthalmic solution is considered isotonic when its tonicity is equal to that of

a)0.9 percent sodium chloride solution

b)0.9 percent boric acid solution

c)0.9 percent dextrose solution

d)all of these

7.The hydrophilic polymers most often used for imparting viscosity to opthalmic products is/are

a)methylcellulose

b)hydroxyethyl cellulose

c)polyvinyl alcohol

d)all of these

8.Formulation of eye drops contain which of the following?

a)Preservative

b)Buffer

c)Antioxidant

d)a and b

9.Which of the following drugs are formulated as eye drops?

a)anti-inflammatory agent

b)mydriatric

c)meiotic

d)all of these

10.The preservative for opthalmic use includes

a)Benzalkonium chloride

b)Chlorbutanol

c)Phenylmercuric acetate

d)All of these

11.Eye drops are sterilized by

a)autoclaving

b)bacteria filter

c)filter candle

d)a and b

12.Benzalkonium chloride should be used in _____ concentration in eye drops.

a)0.002%

b)0.01%

c)0.1%

d)0.2%

13.The eye drops are clarified by passing the solutions through membrane filter having pore size of

a)0.1µm

b)0.4µm

c)0.6µm

d)0.8µm

14.For the preparation of eye-ointment the following bases is/are used

a)Yellow soft paraffin

b)Liquid paraffin

c)Wool fat

d)All of these

15.The eye lotions are sterilized by

a)autoclaving

b)bacteria filter

c)filter candle

d)a and b

Solutions:

  1. a)true
  2. d)all of these
  3. b)false
  4. b)tonicity
  5. a)equal
  6. a)0.9 percent sodium chloride solution
  7. d)all of these
  8. d)a and b
  9. d)all of these
  10. d)All of these
  11. d)a and b
  12. b)0.01%
  13. d)0.8µm
  14. d)All of these
  15. d)a and b

 References:

  1. Remington Essential of Pharmaceutics, 1st edition 2013, page no. 551-554.

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