A syringe is a simple reciprocating pump consisting of a plunger that fits tightly within a cylindrical barrel. Syringes come in a variety of sizes and are used to administer both solid and liquid medications. Understanding syringe calibration and selecting the appropriate syringe based on the prescribed volume is necessary for accurate medication administration. This document provides information on different types of syringes, their parts, calibration, and examples of calculating dosages using syringes.

1. MATH IN
PHARMACOLOGY AND
DOSAGE CALCULATION

2. USING SYRINGES
Overview
 Selecting the appropriate syringe for a given prescription is necessary to
draw up a medication appropriately.
 Understanding syringe calibration is necessary to draw up the correct
volume for a specific medication.
Syringes are widely used in clinical settings. Hypodermic syringes come in
variety of sizes from 0.5ml to 60ml. Insulin syringes have either a 0.3mls,
0.5ml or 0.1ml capacity. Syringes that are 5ml or larger are commonly used
with intravenous administration. Oral syringes come in 10mls and 60ml
capacity, have large tips to which you cannot attach needle and are used to
draw up liquid such as tube feeding and oral medications.

3. What is a syringe?
A syringe is a simple reciprocating pump consisting of a plunger that fits
tightly within a cylindrical tube called a barrel. The plunger can be linearly
pulled and pushed along the inside of the tube allowing the syringe to take in
and expel liquid or gas through a discharge orifice at the front (open) end of
the tube.
Parts of a syringe
All syringes have three main parts namely:
 The barrel
 The plunger and
 The tip

4. The barrel is the hollow tube that holds the medication. It comes in variety of
lengths and diameters. On the outside of the barrel are black calibration
markings that identify a specific solution volume. Calibrations use the metrics
system. The first marking on the calibration nearest the tip is a zero followed
by four short interim markings and then longer numbered markings; this
arrangement (four short interim markings and one longer, numbered marking)
continue for the length of the barrel.
Syringes of 1ml and 0.5ml are calibrated in hundredths. Calibration markings
in tenths include those for syringes of 2ml, 2.5ml and 3ml. Larger syringes
such as 5ml, 6ml and 10ml are calibrated in two tenth increments. Syringes
20ml and larger are calibrated in 1ml increment.

5. The plunger is the mechanism that withdraws medication from the medication
container and then is pushed by the thumb to administer the medication. The inner
tip of the plunger looks like a dome with a tip followed below by an upper ring
that touches the barrel, followed by a lower ring that is attached to the plunger and
seals the barrel to avoid leaking. The upper ring (nearest the dome) is used to
measure the correct volume
Finally, there is the tip. Some syringes come with straight slip tips however, the
safest tip is the leur-Lok tip, which allows needles to be twisted on and locked in
place. Oral syringe tips are large, A needle cannot be attached to an oral syringe tip.
NB: It is important to select the size of syringe that best allows for accurate
calibration of medication. For example drawing up 2.5ml in a 5ml syringe would
be difficult. You would be able to find 2ml marking but since the increments are in
two-tenths, finding the exact 0.5 marking would be difficult. A better choice would
be a 3ml syringe with one-tenth calibration.

6. Practice Problems
1. Choose the correct syringe size based on the following prescriptions:
 1.3ml
 0.52ml
 8.5ml
 0.25ml
 2.8ml
 16ml
 7.6ml

7. Prefilled syringes
These are single-dose syringes that come filled with sterile drug and are more designed
to be used only once. Some prefilled syringes come complete, including total dose
prescribed and either with a needle already attached or one that can be attached. Many
prefilled syringes use the same calibration markings as their hypodermic counterpart.
However with some prefilled syringes, instead of long and short markings, the four
interim makings are thin bands followed by a fifth bold wider numbered marking. With
some prefilled syringes, the entire dose of the medication is to be administered as a
single dose.
When the entire syringe volume is not required, you will need to discard(waste) in the
sink the amount of drug that is in excess of the amount prescribed prior to medication
administration. The enables you to safely administered the prescribed amount
Eg 1.
1. PRESCRIPTION: Dalteparin sodium 2500 units 2hrs before surgery, what you
have is Dalteparin sodium 5000IU per 0.2ml.

8. Questions
a. How many milliliters will be administered
b. Will there be a discard
c. If so, how many will it be
E.g. 2.
PRESCRIPTION: filgrastim (Neupogen) injection 5mcg/kg subcutaneous daily for 2weeks. Patient
weighs 60kg. What you have is filgrastin (Neupogen) injection 300mcg/0.5ml prefilled syringe
Questions
a. How many milliliters will be administered
b. Will there be a discard
c. If so, what amount will it be
E.g. 3
PRESCRIPTION: Humira (adalimumab) 0.04g subcutaneous weekly. What you have is adalimumab
40mg/0,8ml syringe
Questions
a. How many milliliters will be administered
b. Will there be a discard
c. If so, what amount will it be

9. About 0.5-ML and 1-ML Syringes
When small amount of volumes of 1ml or less are required-as with heparin, skin
testing and pediatric prescriptions-a low volume syringe offers the greatest
accuracy. The plunger on these syringes can be maneuvered very slowly and
smoothly for greater ease in accurate measurement. Increments are in hundredths,
with long hash marks equal to tenths.
Insulin syringes
Insulin syringes are only for measuring insulin. They are not to be used with any
other medication. The needle is preattached and cannot be removed. This type of
syringe is calibrated in units. Insulin is standardized to 100 units per milliliter. A 1-
ML syringe is calibrated for 100 units and each increment equals 2 units with
numbered markings every 10 unit. Low-dose insulin syringes of 0.5 ml (50 units)
and 0.3 ml (30 units) are calibrated in 1-unit increments and are numbered every 5
units.

10. ORAL MEDICATIONS
Overview
 To complete medication calculations, you must be able to read the drug label to locate necessary
computation information for clinical implementation.
 The drug label must be compared to the prescription correctly to determine whether a calculation is
necessary prior to preparing the medication for each patient
Oral medications are the most common type of prescription. They come prepared as solids (tablets,
scored tablets, chewable sublingual tablets, enteric coated tablets [dissolves in the intestine], timed-
released tablets, capsules, timed-released capsule, gelatin capsules, powders) and as liquids.
Oral medications come in different dose strengths. Scored tablets can be divided but nonscored tablets,
enteric coated tablets, extended or delayed release tablets and capsules cannot be divided and must be
given whole. In clinical settings, you will most commonly see unit dose label.

11. MEDICATION LABELS
A medication label refers to all the printed information included on the container of
any dietary supplement, over-the-counter medicine, or prescription drug.
Information that can be seen on a medication label
 Starting at the top of the label, the first line (usually in large bold print) is the
trade (brand) name of the drug which is the registered name given by the
manufacturer. The prescription may use this name.
 Under (near) the trade name is the generic name of the drug. By law, the generic
name must be on the drug label. There are some medications whose generic
name is so common that it is the only name appearing on the label. One example
is phenobarbital. Generic medications only have the generic name on the label
 Moving down the label, next is the dose strength of the medication. This refers
to the amount of that is available in the detailed unit measure list. This is the
dose that you will compare with the prescription to determine whether you need
to perform a calculation before administration. Some labels will list the
medication strength using different but comparable units of measurement.
 The label identifies the composition of the drug. E.g. are tablets, capsules, liquid
suspensions or solutions

12.  The route of administration is identified on the labels. With tablets and capsules,
the route of administration is assumed to be oral; however, because all tablets,
capsules and liquids are not always given orally, any variation from oral
administration is listed on the label.
 If the drug requires reconstitution, the instructions will be outlined on the label
 Sometimes a drug requires special handling, such as protection from light or
specific storage requirements. These directions will appear on the drug label.
Sample medication label

14. Medications may contain more than one drug (eg. Augmentin, an antibiotic that
contains both amoxicillin and clavulanate). Normally all the different drugs and
their strengths are listed on the medication label as shown in the figure below;

15. CALCULATING SOLID MEDICATION DOSAGES
Comparing the prescription with the drug you have on hand to determine that you have the
correct drug is the correct step to medication administration. This step comes before any
calculation can be started. Compare the prescribed dose with the inscribed dose on the
medication label you have to determine if they are the same drug. If they are the same drug,
decide whether a drug calculation will be required. Commonly, one tablet or capsule will be
required. When calculations are necessary, usually no more than three tablets or capsules are
required. There are some drugs-for e.g. HIV medications, steroids and potassium that exceed
this rule. With scored tablets, the calculated dose may be in half tablet increments. Compare
the route of administration. The medication you have must include the same route of
administration.
E.g. 1
PRESCRIPTION: Digoxin 0.374mg orally once. You have 250mcg (0.25mg) of digoxin
scored tablets
QUESTIONS:
a. Are the prescribed medication and the medication you have the same

16. b. Does the prescribed dose use the same system of measurement as the medication
you have?
c. Does the prescribed dose use the same equivalent measurement within the same
system?
c. Is the prescribed dose larger or smaller than the dose you have?

17. Calculation Practice Problems
1. Order: Synthroid 200 mcg po daily
Supply: Synthroid 0.4 mg per tablet
Give: tablets
2. Order: Zoloft 25 mg po twice daily
Supply: Zoloft 50 mg tablets
Give: tablets
3. Order: Doxycycline 100 mg po daily
Supply: Doxycycline 0.2 Gm. per tablet
Give: tablets
4. Order: Prednisone 40 mg po daily
Supply: Prednisone 5 mg tablets
Give: tablets
5. Order: Morphine 15 mg po every 4 hours prn
Supply: Morphine 1/2 gr per tablet
Give: tablets
6. Order: Nitroglycerin 0.4 mg po stat
Supply: Nitroglycerin 1/150 gr per tablet

18. 7. Order: metformin500mg by mouth twice a day
Supply: metformin 500mg tablet
Give: tablets
8. Order: Nitrostat 1/150gr sublingually 5 times apart for angina. Do not take more
than 3tablets in 15min
Supply: Nitrostat 0.4mg (1/150gr)
The patient said he has taken two tablets. How many milligrams has he taken?
9. Order: Lopressor 100mg by mouth
Supply: Lopressor 50mg tablet
Give: tablets
10. Order: Synthroid 50mcg
Supply: Synthroid 0.05mg
Give: tablets

19. CALCULATING LIQUID MEDICATION DOSAGES
Oral medications also come in liquid form. These are used for patients who have
difficulty swallowing; have nasogastric, gastrostomy, or jejunostomy tube; or are
an infant or young child. The medication label is similar to the tablet or capsule
labels except that the label will state if the medication is an elixir, oral suspension,
oral solution or syrup. The dose of the medication will be listed as drug strength in
a specific volume of liquid. This is the dose/volume. The label will also identify the
total volume of the bottle and may include the total strength of the entire container.
One common method for measuring liquid medications is a calibrated medicine
cup. When using a medication cup, you need to have the liquid at eye level.
Liquids have a curve (miniscus); you read the lowest point of the curve (center)
when determining the volume.

20. When the volume cannot be accurately determined by using a medication cup, an
oral syringe is used. An oral syringe has a longer tip than a hypodermic syringe and
is large enough that a needle cannot be applied. With small-volume doses, 10-mL
and 5-mL oral syringes are available. Once the medication is accurately drawn up
in the syringe, it may be easier to dispense by putting it back into a medicine cup.
Oral liquids may also be dispense by a calibrated dropper . The dropper comes with
a specific medication. This dropper is medication-specific and is not
interchangeable with other medications

21. PRACTICE PROBLEMS
1. A patient is ordered 70 mg of pethidine. Find the volume required if the stock solution
contains 10g of pethidine per 200mL
2. MD writes an order for Tylenol 160 mg by mouth as needed every 6 hours for pain for
a child. Pharmacy dispenses you with 80 mg per ml. How many ml will you administer
per dose?
3. MD writes an order for Ibuprofen 3 mg/kg by mouth every 6 hours for pain for a child.
The child weighs 73 lb. Pharmacy dispenses you with 50 mg/2 ml. How many ml will
you administer per dose?
4. MD writes an order for Lactulose 20 grams by mouth BID. Pharmacy dispenses you
with 10 gram/15 ml. How many ml will you administer per dose?
5. MD writes an order for Lortab Elixir 5mg by mouth as needed for pain every 4 hours.
Pharmacy dispenses you with 7.5mg/15ml. How many tablespoons will you administer
per dose?
6. The doctor writes an order for a liquid oral medication. The order says to administer 15
mg by mouth every 4 hours as needed for sore throat. Pharmacy dispenses you with 30
mg/3ml. How many ml will you administer per dose?
7. MD writes an order for Nystatin Oral Suspension 250,000 units by mouth every 6
hours for thrust in mouth. Pharmacy dispense you with 500,000 units/5ml. How many
ml will you administer per dose?