T he smallest quantity that should be weighed on the balance:
100 6
5 120
%
%
× mg =
mg
(a) Q uantity of mixture required to prepare 25 capsules each containing the weigh- able quantity of 120 mg:
120 mg × 25 (capsules) = 3000 mg
Q uantity of lactose required equals the quantity of mixture required less the weight of the crushed tablets:
300 mg − 280 mg = 2720 mg or 2.72 g of lactose required (b) Q uantity of mixture to fill each capsule:
3000 mg ÷ 25 (capsules) = 120 mg (c) Proof of 4 mg of drug per capsule:
Amount of drug in mixture:
25 mg (per tablet) × 4 (tablets) = 100 mg Amount of drug per capsule:
100 mg ÷ 25 (capsules) = 4 mg or,
100
3000 120
mg mg
x mg ( )
( ) ( )
drug
mixture = mixture
= 4 mg
50 Pharma uti al c al ulations
Practice Problems
Aliquot Parts by W ighing
1. Weigh 150 mg chlorpheniramine maleate
Dilute with 450 mg lactose
to make 600 mg mixture
Weigh/use 200 mg mixture
2. Weigh 120 mg drug
Dilute with 1380 mg inert powder
to make 1500 mg mixture
Weigh/use 150 mg mixture
3. Weigh 80 mg hydromorphone hydrochloride
Dilute with 1520 mg lactose
to make 1600 mg mixture
Weigh/use 100 mg mixture
4. Weigh 160 mg substance
Dilute with 3840 mg inert powder
to make 4000 mg mixture
Weigh/use 200 mg mixture
5. Weigh 400 mg substance
Dilute with 7600 mg inert powder
to make 8000 mg mixture
Weigh/use 400 mg mixture
Aliquot Parts by M asuring volum
6. Weigh 90 mg tartar emetic
Dilute to 12 mL cherry syrup
Measure/use 2 mL mixture
7. Measure 3 mL coloring agent
Dilute to 10 mL water
Measure/use 2 mL solution
8. Measure 5 mL dye
Dilute to 8 mL water
Measure/use 2 mL solution
9. Measure 3 mL orange oil
Dilute to 8 mL alcohol
Measure/use 2 mL solution
P r ntag of e rror 10. 5%
11. 8%
12. 6.32%
13. 1.4%
14. 0.1%
15. 6.67%
3 • Pharmaceutical Measurement 51
References
1. Prescription balances and volumetric apparatus. United States Pharmacopeia 32 N ational Formulary 27. Rockville, MD: United States Pharmacopeial Convention, 2009;1:691–692.
2. Young L, Allen LV Jr, eds. T he Art, Science, and Technology of Pharmaceutical Compounding. 2nd Ed. Washington, D C: American Pharmaceutical Association; 2002.
3. H ormone replacement therapy. Secundum Artem 8(1):4. Available at: http://www.paddocklabs.com. Accessed June 6, 2012.
4. Pharmaceutical Service Division, Ministry of H ealth Malaysia. Extemporaneous Formulary. Putrajaya, Malaysia.
Available at: http://www.moh-extemporaneous-formulary-2011.pdf. Accessed April 15, 2014.
16. (a) An analytical balance
(b) Weigh 200 mg carvedilol and mix with 20 mL of purified water. Measure 10 mL of the mixture to provide 100 mg of carvedilol.
(c) Eight 12.5-mg carvedilol tablets may be pulverized in a mortar with the purified water and a portion of Ora-Blend SF suspension, as needed, until smooth. T he remaining portion of the suspension vehicle may then be added and blended until a uniform product results.
52
By def nition, a prescr iption is an order or medication issued by a physician, dentist, or other properly licensed medical practitioner. A prescription designates a specif c medication and dosage to be prepared and dispensed by a pharmacist and administered to a particular patient.
A prescription may be written on preprinted prescription orms (traditional prescrip- tions) or transmitted to a pharmacy by computer (e-prescription), telephone, or acsimile (FAX). As shown in Figure 4.1, a typical preprinted prescription orm contains the tradi- tional symbol (meaning “recipe,” “take thou,” or “you take”), name, address, telephone number, and other pertinent in ormation regarding the prescriber. Blank areas are used by the prescriber to provide patient in ormation, the medication desired, and directions or use. A prescription written by a veterinarian generally includes the animal species and/or the pet’s name and the name o the owner.
In hospitals and other institutions, the orms are somewhat di erent and are re erred to as medication order s. A medication order may be written (paper) or transmitted elec- tronically. A typical paper medication order sheet is shown in Figure 4.2.
A prescription or medication order or an in ant, child, or an elderly person may include the age, weight, and/or body sur ace area (BSA) o the patient. T his in ormation is applicable in dose calculation (as discussed in Chapter 8). An example o a prescription or a pediatric patient is shown in Figure 4.3.
A prescription may call or a pre abricated dosage orm (e.g., tablet) or it may call or multiple components and require compounding by a pharmacist.a A medication may
a T he extemporaneous compounding o prescriptions is an activity or which pharmacists are uniquely quali ied by virtue o their education, training, and experience. “Traditional” pharmacy compounding involves the mixing, packaging, labeling, and dispensing o a medication upon receipt o a prescription or medication order or a speci ic patient. Extended compounding activities involve the outsourcing o compounded medications to other health care providers. Pharmaceutical manufacturing is the large-scale production o product or the marketplace.
A distinction between these di erent activities is provided by legislation, guidelines, and regulations o state boards o pharmacy and the ederal Food and D rug Administration.1,2
Ob j e c t ive s
Upon successful completion of this chapter, the student will be able to:
D mon ra an und r and ng of h forma and ompon n of rad onal pr r p- on and -pr r p on .
D mon ra an und r and ng of h forma and ompon n of a yp al n u onal m d a on ord r.
in rpr ommon a r a on and ym ol u d on pr r p on and m d a on ord r and apply h m orr ly n pharma u al al ula on .
Apply al ula on o nd a m d a on adh r n .
4
Interpretation of Prescriptions
and Medication Orders
4 • interpretat on of Prescr pt ons and Med cat on Orders 53
be prescribed by its brand name or by the nonproprietary (generic) name.b In some cases, the product selection may be affected by pharmacy regulations and/or by provider–payer options.
Prescriptions requiring compounding include the name and quantities of each ingredi- ent, the form into which they are to be prepared (e.g., syrup, capsules), and directions for patient use. Definitions and descriptions of dosage forms and drug delivery systems are presented in Appendix B.
bA brief overview of the designation of nonproprietary and brand names may be found in Authors’ Extra Point A at the end of this chapter.
(1)
(2) (3)
(1) (4)
(5) (6) (7)
(8)
Jo hn M. Brown, M.D.
100 Main Stre e t Libe rtyville , Maryland
Phone 123-4567
Na me Da te
Addre s s
Re fill time s Labe l: Ye s No
Ge ne ric if ava ila ble : Ye s No
DEA No. 1234563
Sta te Lice ns e No. 65432
FIGURE 4 .1 • Components of a typical prescription. Parts labeled are as follows:
(1) Prescriber information and signature.
(2) Patient information.
(3) Date prescription was written.
(4) symbol (the Superscription), meaning “take thou,” “you take,” or “recipe.”
(5) Medication prescribed (the Inscription).
(6) Dispensing instructions to the pharmacist (the Subscription).
(7) Directions to the patient (the Signa).
(8) Special instructions. It is important to note that for any Medicaid or Medicare prescription and according to individual state laws, a handwritten language by the prescriber, such as “Brand necessary,” may be required to disallow generic substitution.
NOTE: When filling the prescription, the pharmacist adds a prescription number for identification.
54 Pharma euti al c al ulations
CITY HOSP ITAL Athe ns, GA 30600
PHYSICIAN'S ORDER
Unle s s “No s ubs titution pe rmitte d” is cle a rly writte n a fte r the orde r, a gene ric or the ra pe utic e quiva le nt drug may be dis pe ns e d according to the Formula ry policies of this hos pita l.
DATE TIME ORDERS
02/01/yy 1200 1. Pro pranolo l 40 mg po QID 2. Furos e mide 20 mg po q AM
3. Fluraze pam 30 mg at HS prn s le e p 4. D-5-W + 20 mEq KCl/L at 84 mL/hr Hardme r, MD
PATIENT NAME:
ADDRES S:
CITY, S TATE:
AGE/SEX:
P HYSICIAN:
HOS P.NO:
S ERVICE:
ROOM:
Thomps on, Linda 2345 Oa k Circle Athe ns, GA 35y/Fe ma le J. Ha rdme r 900612345 Medicine 220 Ea s t
FIGURE 4 .2 • Typical hospital medication order sheet.
Mary M. Brown, M.D.
Pediatric Clinic 110 Main Stre e t Libe rtyville , Maryland
Phone 456-1234
Na me Age Weight lb
Addre s s Date
Re fill time s La be l: Ye s No
Ge neric if available: Ye s No Sig:
DEA No. MB5555555 Sta te Lice ns e No. 23456
Suzie Smith 5 39.4
123 Broad Street Jan 9, 20yy
Mary Brown, M.D . tsp q 12 h
Omnicef Oral Suspension 125 mg/ 5 mL
D isp. 100 mL
Give 14 mg/ kg/ day x 10 days
0
FIGURE 4 .3 • Example of a prescription for a pediatric patient.
4 • interpretat on of Prescr pt ons and Med cat on Orders 55
Examples are shown or prescriptions calling or trade name products (Figs. 4.1 and 4.3), a generic drug (Fig. 4.4A), and compounding (Fig. 4.5). Figure 4.4B shows the label o a product that may be used by the pharmacist in illing the medication order as prescribed in Figure 4.4A.