Use of Prefabricated Dosage Forms in Extemporaneous Compounding

Abstract

Extemporaneous drug compounding as the best option and most of the times the only option available to provide medicine to patients with special needs is discussed in this chapter with creative calculations implicated in the preparation of commonly compounded dosage forms such as suspensions, powders, capsules, and suppositories.

Exercises

• 9.1. The physician who treated the bipolar and ADHD 5-year-old, 44 lb child described in Example 9.1 contacted you to ask whether you could prepare a liquid formulation, written below, because the child had trouble to swallow the capsules.

  Rx
  Risperidone	1 mg/10 mL
  Quetiapine fumarate	50 mg/5 mL
  Atomoxetine HCl	0.25 mg/kg/5 mL
  Sig. 2 times a day for 30 days. 1 tsp at 8 am and 1 tsp at 7 pm

  Having studied the physicochemical properties of all the ingredients, you decided to compound the medication order as a suspension:

  Rx
  Risperidone		1 mg/10 mL
  Quetiapine fumarate		50 mg/5 mL
  Atomoxetine HCl		0.25 mg/kg/5 mL
  Cherry syrup	q.s. ad.	?
  M.et. ft. suspension
  Sig. 2 times a day for 30 days. 1 tsp at 8 am and 1 tsp at 7 pm

  In Stock:

  • Risperdal tablets (contain risperidone): 1 mg strength

  • Weight of 30 Risperdal tablets = 1950 mg

  • Seroquel tablets (contain Quetiapine fumarate): 200 mg strength

  • Weight of 23 Seroquel tablets = 8050 mg

  • Strattera capsules (contain atomoxetine hydrochloride): 40 mg strength

  • Contents weight of 12 Strattera capsules = 1500 mg

  • (a) How much syrup should you prepare?

  • (b) How many tablets and capsules are required to compound the prescription?

  • (c) Calculate the ratio strength of atomoxetine HCl in two doses?

    • (Answer: (a) 300 mL; (b) 30, 15, and 8; (c) 1: 1000 g/mL)

• 9.2. The following medication order was recommended for a 3-year-old, 16.5 lb child who suffered from acute malaria:

  Rx
  Artemether		0.75 mg/kg
  Lumefantrine		4.5 mg/kg
  Sulfadoxine		100 mg
  Pyrimethamine		5 mg
  Dry milk	q.s. ad.	45 g
  M.et. ft. powder #1. D.T.D #6
  Sig. Empty contents in a glass of water, stir, and drink 3 times a day for 2 days

  In stock:

  • Coartem tablets: 20 mg artemether and 120 mg lumefantrine

  • Weight of 5 Coartem tablets = 1125 mg

  • Fansidar tablets: 500 mg sulfadoxine and 25 mg pyrimethamine

  • Weight of 5 Fansidar tablets = 4375 mg

  • (a) How many tablets of each drug are required to compound the prescription?

  • (b) What is the total weight of dry milk required for this prescription?

  • (c) Calculate the % w/v concentration of artemether in each dose assuming that a glass of water is 225 mL.

    • (Answer: (a) 2 Coartem and 2 Fansidar tablets; (b) 268.570 g; (c) 0.0025%w/v)

• 9.3. The following prescription was for a 7-year-old autistic child:

  Rx
  Paroxetine hydrochloride		5.25 mg/5 mL
  Buspirone hydrochloride		1.15 mg/mL
  Sucrose	q.s. ad.	195 g
  Purified water	q.s. ad.
  M.et. ft. suspension
  Sig. I tsp b.i.d. for 30 days

  In stock:

  • Paxil tablet strength: 10 mg paroxetine

  • Weight of 10 Paxil tablets = 760 mg

  • BuSpar tablet strength: 10 mg buspirone

  • Weight of 10 BuSpar tablets = 450 mg

  • (a) How much syrup should you prepare?

  • (b) How many tablets of each drug are required to compound the prescription?

  • (c) How much sucrose is required to fill the prescription?

  • (d) Calculate the percentage strength of buspirone HCl in each dose?

    • (Answer: (a) 300 mL; (b) 32 Paxil and 35 BuSpar tablets; (c) 191.054 g; (d) 0.115%w/v)

• 9.4. Given the following prescription:

  Rx
  Drug D		2.5 mg
  Drug Z		50 mg
  Starch	q.s. ad.	0.250 g
  M.et. ft. caps#1. D.T.D #12
  Sig. Take 1 capsule q.am

  In stock:

  • Drug D is available in powder form

  • Drug Z is available as tablets 50 mg strength

  • Weight of 5 Drug Z tablets = 625 mg

  • (a) Describe how you should compound the prescription with a 5% maximum potential error in the dose of drug D, if the balance available in the premises has an SR of 5 mg.

  • (b) How many tablets of drug Z are required to compound the medication order?

  • (c) How many grams of starch are required to fill the prescription?

    • (Answer: (a) aliquot = 1500 mg of mixture containing 30 mg of drug Z and 1470 mg of starch; (b) 12; (c) 9.178 g)

• 9.5. Given the following prescription for inflammatory acne:

  Rx
  Benzoyl peroxide		1.5%w/w
  Erythromycin		0.5%w/w
  Retinoic acid		0.25%w/w
  Glycerin		0.5 mL
  Eucerin cream	q.s. ad.	60 g
  M.et. ft. cream
  Sig. Apply on clean dry face every night

  In stock:

  • Benzoyl peroxide 10%w/w gel

  • Erythromycin capsules : 500 mg strength

  • Weight of 3 erythromycin capsules (including the shell) = 2436 mg

  • Weight of 3 empty capsule shells = 153 mg

  • Retinoic acid cream 5%w/w

  • Glycerin (specific gravity) = 1.25

  • (a) What is the purpose of glycerin in the formula?

  • (b) How many erythromycin capsules are required to compound the prescription?

  • (c) How many grams of Eucerin are required to fill the prescription?

    • (Answer: (a) levigating agent for erythromycin; (b) 1; (c) 46.918)

• 9.6. The drugs included in the prescription below are against the HIV reverse transcriptase:

  Patient’s name:	Olu, Nicole	Age: 8 years	Weight: 17.6 lb
  	Rx
  	Tenofovir disoproxil fumarate		7.5 mg/kg
  	Emtricitabine		5 mg/kg
  	Efavirenz		15 mg/kg
  	Lactose	q.s. ad.	0.350 g
  	M.et. ft. caps#1. D.T.D #14
  	Sig. Take 1 capsule q.am

  In stock:

  • Tenofovir disoproxil fumarate: Viread tablets 300 mg strength

  • Weight of 6 Viread tablets = 2490 mg

  • Emtricitabine: Emtriva capsules 200 mg strength

  • Weight of 5 Emtriva capsules (shell included) = 1755 mg

  • Weight of 5 empty Emtriva capsule shells = 255 mg

  • Efavirenz: Sustiva capsules 200 mg strength

  • Weight of 5 Sustiva capsules (shell included) = 1619 mg

  • Weight of 5 empty Sustiva capsule shells = 245 mg

  • (a) How many tablets and capsules of each drug are required to compound the prescription?

  • (b) How many grams of lactose are required to fill the prescription?

  • (c) Calculate the maximum potential error in emtricitabine dose if the balance available in the premises is a class III prescription balance that has an SR of 5 mg.

    • (Answer: (a) 3 Viread, 3 Emtriva, and 9 Sustiva; (b) 589.7 mg; (c) ±2%)

• 9.7. You wish to prepare 12, 0.625% w/w promethazine suppositories. You have on hand commercially available 2 g–25 mg/g promethazine suppositories. Your intention is to melt the commercial promethazine suppositories and mix them with a polyethylene glycol (PEG) melt (used as a base for suppositories). Assuming that each suppository weighs 2 g:

  • (a) How many commercial suppositories you should melt?

  • (b) How much PEG should you use?

    • (Answer: (a) 3; (b) 18 g)