Pharmacology & med administration

Learning medications by category

Medications in the same category (class) usually work the same way, so they share therapeutic effects, adverse reactions, contraindications and administration points. It's easier to learn the category than hundreds of single drugs. The prototype is the drug in the category that providers prescribe most, and it's the one to know in the most detail.

Generic vs brand (trade) names

• A drug starts out under its brand name while it's protected by a patent. Once the patent expires, other companies can make a generic form.
• Generic and brand forms have the same chemical composition and the same effects, and there's no difference in the potential for abuse or dependence. With the provider's OK, the generic can be substituted for the brand.
• On a label, the brand name is usually large and bold; the generic name is smaller, often under it or in parentheses. Drugs also have chemical names, which are rarely used.

Prescription vs over the counter

Safety decides which group a drug is in.

As more is learned about a drug over time, a prescription drug can be moved to over the counter.

Clients sometimes bring their own medications from home. Those go to the hospital pharmacist to approve before they're used.

Pharmaceutics

Pharmaceutics is the science of how a medication's form affects how it dissolves, how fast it's absorbed and so how soon it starts to work.

Routes are grouped as parenteral (by injection: IM, subcutaneous, intradermal, IV, intrathecal, epidural) and nonparenteral (oral, sublingual, buccal, topical, transdermal, eye, ear, nose, rectal, vaginal).

Oral forms that change how a drug is released

Never crush capsules or extended- or sustained-release forms. (The full do-not-crush list is in Giving oral meds.)

Injections: how fast they're absorbed

Topical and transdermal drugs deliver a steady amount over a long time: slower onset and longer duration than oral or injected drugs.

ADME

Absorption

How fast a drug is absorbed decides how soon it works; how much is absorbed decides how strong the effect is. The route changes both.

Distribution

• Circulation: anything that cuts blood flow (peripheral vascular disease, heart disease) delays distribution.
• Cell membrane permeability: the drug must pass through tissues to reach its target. The blood-brain barrier and the placenta let through drugs that dissolve in fat or that a carrier moves across.
• Plasma protein binding: drugs bind to proteins in the blood, mainly albumin. Only the unbound drug can leave and act. Two drugs competing for the same binding sites can cause toxicity, and low albumin (malnutrition, older age) leaves more free drug circulating.

Metabolism

Also called biotransformation: the drug's structure is changed, and the new form is a metabolite.

What affects metabolism

• Age: the body slows down. Liver metabolism tends to drop with age, so older adults often need smaller doses to avoid buildup. Infants also metabolize less.
• Similar metabolic pathways: two drugs broken down the same way compete, so one or both build up. Spacing them apart can help.
• Nutritional status: malnutrition (and dehydration) can leave the body short of what it needs to make metabolizing enzymes.
• More metabolizing enzymes (from some drugs): breaks the drug down faster, so the dose may need to go up.
• First-pass effect (below).

First-pass effect

Swallowed (oral):

Routes that skip the liver:

The liver gets the first pass at everything absorbed from the gut, so less active drug is left for the rest of the body.

Routes that bypass the first-pass effect: sublingual, buccal, IV, nasal, inhaled, transdermal and other injected routes. They reach the bloodstream without going through the liver first. Drugs with a high first-pass effect need one of these nonenteral routes. It's also why an oral dose is often higher than the IV dose of the same drug.

Outcomes of metabolism

• Inactivates most drugs and makes them easier for the kidneys to excrete
• Activates prodrugs into their active form
• Can raise or lower the therapeutic effect, and raise or lower toxicity

Excretion

• The kidneys are the main site (urine).
• Also the liver (bile), lungs (exhaled), intestines (bowel) and exocrine glands (sweat, saliva, breast milk).
• Excretion prevents toxic buildup and keeps the drug level balanced.
• Factors to consider: dehydration, kidney problems, bowel problems. Drugs that are harmful as they're excreted need careful handling.
• Poor kidney function makes a drug last longer and act stronger, so monitor BUN (blood urea nitrogen) and creatinine. Doses may be lowered for kidney impairment, common in older adults.
• Drugs excreted in breast milk can reach a breastfeeding infant.

Other ways drugs leave the body (besides the kidneys):

• Lungs (breathed out)
• Bile, into the stool
• Sweat and saliva
• Breast milk

Higher or lower dose?

Half-life

• Half-life (t½) is the time it takes for the amount of drug in the body to drop by 50%.
• It depends on metabolism and excretion, so liver and kidney function change it. Age and fever can change it too.
• It usually takes 4 half-lives to reach a steady (therapeutic) concentration, when intake equals what's metabolized and excreted.

Example: phenobarbital, a seizure medication, has a half-life of about 4 days, so it's given once a day.

Therapeutic range and index

• Doses aim to keep the blood level between the minimum effective concentration and the toxic concentration. In between is the therapeutic range: effective, not toxic.
• Therapeutic index (TI): the ratio of the toxic dose to the therapeutic dose, a measure of the safety margin.
  • High TI: wide safety margin; no routine blood-level checks.
  • Low TI: narrow margin; levels need close monitoring.
• Plateau: the drug's blood level during a series of doses.

Peak and trough levels

Peaks and troughs are checked for drugs that have to stay at a steady therapeutic level to work, such as some antibiotics.

Onset, peak and duration

Agonists and antagonists

• Competitive antagonists compete with the agonist for the receptor. Higher doses lower the agonist's effect but rarely block it completely.
• Noncompetitive antagonists block the agonist's access to the receptor. High enough doses can block the response completely.
• Selective drugs act on fewer receptors, so the effects are more limited; less selective drugs cause more widespread effects.
• Some drugs change the cell environment instead: penicillins stop bacteria from building cell walls; sulfa drugs stop bacteria from using folic acid to make DNA and RNA.

Expected action and therapeutic uses

• The expected pharmacologic action is what the drug does in the body. The indication is the condition it's prescribed for.
• Acetaminophen blocks the chemical messengers that tell the hypothalamus to raise core temperature, so a therapeutic use is reducing fever.
• Many drugs have more than one use:
  • Sildenafil (VIAGRA®) relaxes blood vessels and increases blood flow, so it's also used for pulmonary hypertension.
  • Diphenhydramine treats allergies (antihistamine), and is also used for motion sickness (antiemetic), sleep (sedative) and Parkinson's disease (anticholinergic).
• Whether an effect is therapeutic depends on why the drug is given. The same drowsiness from a sedating antihistamine is an unwanted effect when it's taken for allergies, but it's the therapeutic effect when it's taken for sleep.
• A drug reference's indications section lists the conditions a drug is used for, including any second uses.

Adverse drug reactions (ADRs)

• Therapeutic effect: the intended effect.
• Adverse drug reaction: a nontherapeutic, unintended effect that happens at a therapeutic dose. It can happen at any time, and ranges from annoying to life-threatening.
• Example: lisinopril for blood pressure can cause a dry, nonproductive chronic cough or angioedema (swelling of the lips, tongue and face).
• Diphenhydramine commonly causes dry mouth and drowsiness; in some older adults, confusion, poor coordination, dizziness or seizures.
• Paradoxical effect: the opposite of the intended effect, such as a sedative causing excitement.

Allergic reactions and anaphylaxis

An allergic reaction is the most severe type of ADR. It can be mild (itching, rash, hives) or life-threatening. After even a mild reaction, the client should avoid the drug: the next exposure can bring a worse reaction.

Anaphylactic shock is the body's exaggerated immune response to a drug: a massive release of histamine. It's a medical emergency that can start almost immediately and progress from mild to severe.

Treatment

1. Establish the airway
2. Oxygen
3. Epinephrine IM: raises blood pressure and opens the airways
4. Diphenhydramine (an antihistamine): blocks histamine's effects and eases hives and itching; it comes after epinephrine because it can't reverse a closing airway or low blood pressure

Tolerance, dependence and toxicity

• Ototoxic drugs harm cranial nerve VIII (hearing and balance): watch for ringing in the ears, hearing loss and dizziness.
• Hepatotoxic drugs harm the liver: watch for yellow skin or eyes (jaundice), dark urine and pain in the upper right abdomen.
• To prevent toxicity: the lowest effective dose, periodic blood levels, watching for signs of toxicity, and adjusting doses for liver or kidney problems.

Preventing complications

• Use the lowest effective dose possible
• Monitor for ADRs
• Monitor for changes in drug metabolism and excretion
• Know each drug's precautions and contraindications

Precautions, contraindications and boxed warnings

• Precaution: the drug could cause problems in certain clients or combinations, so it's used only when the benefits outweigh the risks, with extra monitoring. Example: a client with peptic ulcer disease who needs an anticoagulant after a stroke needs close assessment and labs to catch GI bleeding. A precaution can mean limiting certain foods or drugs instead of avoiding the drug.
• Contraindication: the drug should not be given because it could cause a serious or life-threatening reaction. Example: oxybutynin (for overactive bladder) is contraindicated in glaucoma.
• Boxed (black box) warning: the FDA's highest safety warning. Examples: increased risk of suicide, increased abuse potential. Celecoxib has one for heart attack, stroke and GI bleeding risk.
• Check the contraindications section of a drug reference to see whether the client can receive the drug at all; the precautions section for conditions that raise the risk or need a dose change (such as age or kidney disease); and the interactions section for other drugs, foods and herbs.

Absolute vs relative contraindications

Interactions

How one drug changes another

A medication–medication interaction happens when one drug changes how another affects the body.

• Additive (1 + 1 = 2): the combined effect equals what each drug would do alone in similar doses. Drugs with similar actions add together:
  • Two CNS (central nervous system) depressants, such as alcohol and opioids, add up to significant, possibly fatal CNS depression.
  • Two pain medications with similar actions can be given together at lower doses of each.
• Synergistic (1 + 1 = more than 2): one drug's effect is greater when it's given with another. Aspirin, which also slows clotting, given with the anticoagulant warfarin intensifies warfarin's effect, and severe bleeding can occur.
• Potentiating: one drug increases the effect of another, often on purpose, such as the drug combinations used for tuberculosis.
• Antagonistic (1 + 1 = less than 2): one drug's effect is decreased or blocked by another:
  • An antacid lowers the absorption of tetracycline (an antibiotic), so they aren't taken together.
  • An asthma medication opens the airways, but a heart medication whose adverse reaction tightens the airways works against it (1 + 1 = 0).

Food–drug interactions

Across the lifespan and the client

• Pregnancy: only drugs the provider prescribes, when benefits outweigh the risks. Many drugs cross the placenta; teratogens cause birth defects, especially in the first trimester. FDA labels now have three sections (the PLLR, Pregnancy and Lactation Labeling Rule): pregnancy, lactation, and females and males of reproductive potential. (The old A, B, C, D, X categories are being replaced; X meant fetal harm.)
• Breastfeeding: drugs can reach the infant through breast milk.
• Children: immature liver and kidneys, so doses are based on age, weight and body surface area to avoid toxicity.
• Older adults: lower cardiac output, slower GI movement, higher stomach pH, and lower liver and kidney function, so drugs absorb, metabolize and leave more slowly. Doses are often lowered; check liver and kidney labs first. Many take several drugs, so interactions are more likely.
• Genetics: genetic differences in metabolizing enzymes can make some clients more sensitive to a drug.
• Sex: females tend to have more body fat, so fat-soluble drugs can build up.
• Weight and health: overweight or underweight adults may need dose changes; kidney, liver, heart and lung problems change dosing.
• Psychosocial and cultural: beliefs about pain, Western medicine and end-of-life care affect how clients take medications.

The nurse's role

• The nurse is responsible for teaching, starting as soon as possible after admission or after the first dose, and before discharge.
• Teach in the client's preferred learning style, at their cognitive and developmental level, in their language, when they're ready to learn.
• Clients who don't speak English need a medical interpreter.
• Mix methods: talking, written handouts, videos, demonstrations (inhalers, injections), and reliable websites.
• Use plain words, not medical jargon.
• Check understanding: ask specific questions, have the client repeat it back (teach-back), or have them show you (return demonstration) for skills such as insulin injections.

What it sounds like

A sample talk with a client starting lisinopril for high blood pressure:

Medication prescriptions

Every prescription includes the client's name, date, medication name, dose, route, frequency, any special instructions, and the prescriber's signature. If it seems incorrect, inappropriate or incomplete, contact the prescriber before giving the drug.

• Electronic orders: most facilities use an EHR (electronic health record) with CPOE (computerized provider order entry), so providers enter orders directly.
• Verbal orders (prescriber present): for emergencies only. Repeat it back to the prescriber, a Joint Commission requirement.
• Telephone orders: read it back to the prescriber.
• The prescriber signs verbal and telephone orders within 24 hours (or per facility policy).
• Use only the facility's approved abbreviations. The Joint Commission has a Do Not Use list and ISMP (Institute for Safe Medication Practices) has an error-prone abbreviations list.
• If an order has to be copied onto a paper MAR, transcribe the medication, dose, route, frequency, date and when the order expires.

The MAR (medication administration record)

Paper or electronic (eMAR), every MAR has:

1. Who the client is: name, age and sex, date of birth, medical record number, admission date, the attending provider, height and weight, and allergies
2. The current date
3. The date the order was written, and a stop date if there is one
4. Scheduled medications
5. PRN medications
6. IV fluids and medications
7. Administration times, in columns for each 8- or 12-hour block
8. The nurse's signature

It can also carry instructions such as "take with food." Follow them. Administration times and the client's diagnosis are on the MAR, not the drug label.

Reading a medication label

• Brand name and generic name
• Dosage strength (your "have"), and the form (tablet, capsule, oral solution)
• Route
• Expiration date and lot number
• Bar code, manufacturer, directions, storage

• Strength: 350 mg/5 mL (the "have" is 350 mg in a quantity of 5 mL)
• Route and form: oral solution
• Directions: shake well before each use
• Reconstitution: add 80 mL of water to make 100 mL, and discard 14 days after it's mixed
• Storage: refrigerate and keep away from light

How medications reach the client

• The provider prescribes, the pharmacist prepares and sends it to the unit, and the nurse gives it.
• Unit-dose system: each dose is packaged and labeled separately (name, strength, expiration date, often a bar code). It cuts errors and is used in acute and long-term care.
• Pharmacy bulk system: one labeled container holds many doses. Liquids are best dispensed by the pharmacy in oral syringes.
• Storage: locked medication carts (a drawer for each client, filled with a 24-hour supply; keep it locked when not in use), medication rooms, locked cabinets in client rooms (all medications except controlled substances), and dispensing machines.

Automated dispensing systems (AMDS)

• Each nurse uses a personal password or fingerprint (biometric) to get in. It controls controlled substances, cuts errors and costs, and links what's removed to the client's record.
• Take out one client's medications at a time, even when there's a line.
• Compare the label with the MAR, check the expiration date, and keep the drug in its package until you're at the bedside.

Bar code scanning

At the bedside, scan the client's wristband (and your badge) and the medication label. If the system shows a mismatch, don't give the drug until the alert is resolved. Scanning doesn't replace the nurse's own checks.

The rights of medication administration

The three checks

1. When you take the drug out of storage
2. When you prepare it
3. At the bedside, before you give it

• If the client is confused or unresponsive, compare the medical record number and birth date on the MAR with the wristband.
• Check identity every time, no matter how well you know the client.
• Stay until the client takes an oral drug; don't leave it at the bedside.
• If you give a drug at a different time than ordered, note the time and the reason.
• Document and report all adverse reactions; record new allergies on the chart, the MAR and the allergy band.

Medication errors

• A medication error is anything that causes the client to get the wrong therapy, or not get it as ordered. Skipping the rights is the most basic cause.
• Report every error, whether or not the client was harmed.
• First, check the client and keep them safe. Then notify the provider and the nurse manager.
• The nurse who made the error fills out an incident (variance) report, usually within 24 hours: client information, where and when it happened, what happened and what was done, the client's condition, and the nurse's signature.
• The incident report is not part of the medical record, and you don't mention it in your charting. It's used to improve systems, not to punish.

Oral medications

The most common route.

• Assess swallowing, then sit the client upright (90°) or side-lying to prevent aspiration.
• Give irritating drugs (such as some analgesics) with a little food.
• Don't mix a drug into a large amount of food or drink, in case the client can't finish it, and avoid mixing it into favorite foods.
• Avoid interacting foods such as grapefruit juice.

Do not crush

• Split only scored tablets, with a cutting device. If it doesn't split evenly, discard it per policy (controlled substances follow the waste policy). In hospitals, the pharmacist usually splits and repackages tablets.
• Crush only when the client can't swallow and there's no liquid form. Check a drug reference or the pharmacist first; ISMP has a "Do Not Crush" list. Clean the crushing device before and after.
• Crush each pill separately and give them one at a time, each with a bite or mixed with a small amount of food (such as applesauce) or fluid. If they're all mixed into a large portion of food and the client doesn't finish it, you can't tell what they took or how much they missed.
• In report, ask how the client usually takes their medications (whole or crushed, in applesauce, one at a time). It helps them tolerate their meds.

Solid forms

Sublingual and buccal

• Keep it in place until it dissolves; don't chew or swallow it.
• Don't eat or drink until it has dissolved.
• Wear gloves if you place it in the client's mouth. NPO clients can usually still have them (check policy).

Liquids

• Follow the directions for diluting and shaking. Shake suspensions right before giving them.
• Hold the bottle with the label toward your palm so drips don't smear it.

Measuring devices

• Medicine cup: doses of 5 to 30 mL
• Oral syringe, calibrated dropper or medicine spoon: doses under 5 mL
• Teach clients to use a calibrated device, never a kitchen spoon: household spoons aren't a standard size.

Feeding tubes (nasogastric (NG), gastrostomy, jejunostomy)

• Use the liquid form when there is one, to avoid clogging.
• Ask the provider or pharmacist before crushing; don't crush the do-not-crush forms, and don't give sublingual drugs through the tube (give them under the tongue).
• Sit the client up (Fowler's, at least 30°) and verify tube placement (pH and look of the aspirate). Check residual; if it's over 250 mL, follow policy.
• Dissolve each crushed tablet or capsule's contents completely in 15 to 30 mL of water. Give each drug separately, and never mix drugs into the feeding.
• Flush with 15 to 30 mL of water before and after each drug, and finish with a final flush of 15 to 30 mL of warm sterile water.
• Let it flow by gravity or push gently with the syringe. Keep the head of the bed up for at least 1 hour afterward.
• If the tube clogs, first try irrigating gently with the right flush.

Which forms can go down the tube

• Ready as is: liquids go down the tube as they are.
• Not through the tube: buccal and sublingual tablets are still given in the mouth (cheek or under the tongue).
• Crush first: plain tablets are crushed, dissolved and given as a liquid.
• Open first: a soft gel capsule filled with liquid is punctured and squeezed out (or the contents drawn up), then diluted with water or another fluid the facility approves if needed. Some timed-release capsules can be opened into the feeding or water; check with pharmacy first.
• Never crush, ask for another form: enteric-coated tablets and timed-release tablets.

Topical and transdermal

• Lotions, creams and ointments usually act locally. Transdermal patches act systemically (through the skin into the blood).
• Wear gloves so you don't absorb the drug. Spread it with a gloved hand, a tongue blade or a cotton-tipped applicator, not bare fingers.
• Clean off old medication and debris first (soap and water, then pat dry). Use surgical asepsis on open wounds.
• Take off the old patch (or wipe off old nitroglycerin ointment, used for chest pain) before the new one goes on, so the doses don't stack into an overdose.
• Put patches on a clean, dry, hairless area and rotate sites to prevent irritation. Don't cut patches.
• Don't place a patch over an implanted device, such as a pacemaker.
• Some patches can cause burns if they aren't removed on time.
• Check for an adhesive allergy before applying one.
• Label the patch or dressing with the date, time and your initials; document where the old one came off and the new one went.
• Nitroglycerin ointment: measured in inches or centimeters on the paper strip that comes with it. Secure the strip to the skin; don't rub it in (it absorbs too fast).
• Older adults: thinner skin absorbs topical drugs faster (watch for toxicity); apply gently and remove patches slowly to avoid tearing skin.

Eye (ophthalmic)

• Eye drugs are sterile. Wipe drainage from the inner to the outer canthus first.
• Client sits up or lies supine, head tilted slightly back, looking up at the ceiling.
• Pull the lower lid down against the cheekbone to make a pocket. Hold the dropper 1 to 2 cm above and drop into the conjunctival sac, not onto the cornea. Don't touch the eye with the tip.
• Have the client close the eye gently (not squeeze). If they blink and it misses, repeat.
• Press gently on the nasolacrimal duct (inner corner) for 30 to 60 seconds to keep the drug from being absorbed into the body.
• More than one eye drug: wait at least 5 minutes between them.
• Ointment: a thin ribbon along the lower lid, from the inner to the outer canthus.

Ear (otic)

• Sterile drops are used in case the eardrum is ruptured. Warm them to room temperature (in your hands): cold drops cause dizziness and nausea.
• Clean only the outer ear; never push an applicator into the canal.
• Client sits up or lies on their side, affected ear up.
• Adults: pull the auricle (pinna) up and back to straighten the canal. Hold the dropper 1 cm above; don't touch the ear.
• Press gently on the tragus afterward (unless it hurts). Stay side-lying for 2 to 3 minutes.
• If a cotton ball is used, place it only in the outer part of the canal.

Nose (nasal)

• Have the client blow their nose gently first. Use medical asepsis.
• Drops: client lies supine, head positioned so the drug reaches the right area; breathe through the mouth, stay supine and don't blow the nose for 5 minutes. Keep the dropper from touching the nares.
• Spray: client sits upright with the head slightly back. Prime the spray if needed, aim the tip toward the outer side of the nostril (not the middle of the nose), and spray while the client breathes in through the nose. No nose-blowing for several minutes.
• Long-term decongestant spray use causes rebound congestion (swelling gets worse).

Rectal suppositories

• Not for clients after rectal surgery or with active rectal bleeding.
• Keep suppositories refrigerated. Don't cut them to split a dose: the drug may not be spread evenly.
• Position: left lateral (left Sims'). Gloves, clean technique; lubricate the rounded end with water-soluble lubricant. Have the client breathe slowly through the mouth to relax the sphincter.
• Insert it past the internal anal sphincter, against the rectal wall, not into stool.
• Client stays flat or on the left side for at least 5 minutes.

Vaginal

• Position: supine with knees bent and feet flat near the hips (dorsal recumbent). Provide perineal care if needed.
• Insert along the back (posterior) wall: suppositories 7.5 to 10 cm (3 to 4 in); creams, jellies and foams 5 to 7.5 cm (2 to 3 in).
• A perineal pad can catch extra drainage. Wash a reusable applicator with soap and water.
• Teach: use the full course, even during menstruation; no intercourse until an antifungal course is done.

Inhaled

• Corticosteroid inhaler: rinse the mouth with water (or brush teeth) afterward to prevent thrush (oral candidiasis, a fungal mouth infection).
• Nebulizer: turns liquid drug into a mist the client breathes in for a few minutes; use an aerosol mask if the client can't hold the mouthpiece.

Injections

• IM sites: ventrogluteal is preferred (and for more than 2 mL). The deltoid holds only 1 mL. The vastus lateralis is used for infants and toddlers. The dorsogluteal isn't recommended: it's close to the sciatic nerve.
• Subcutaneous sites: abdomen, upper hips, back of the upper arms, thighs (enough fat).
• Z-track for IM drugs that irritate or stain the skin (iron): keeps the drug from leaking back into the tissue.
• Use a tuberculin syringe for volumes under 0.5 mL, and an insulin syringe for insulin.
• Rotate sites and document each one. Avoid sites that are swollen, inflamed, or have moles, birthmarks or scars.
• Throw away sharps in a puncture-proof container.
• Injections: advantages are faster, more reliable absorption and depot (long-acting) forms; disadvantages are cost, pain, tissue or nerve damage, and infection.

IV

• Fastest onset; immediate absorption; precise control; large volumes; dilutes irritating drugs.
• Because it's immediate, a wrong dose or drug is dangerous: monitor the client right away. Risks: infection and embolism, phlebitis and infiltration.
• Usual catheter sizes: 16 gauge for trauma, 18 gauge for surgery and blood, 22 to 24 gauge for older adults, children and stable clients.

Epidural

Opioid analgesia (morphine, fentanyl) through a catheter in the epidural space, on an infusion pump. Watch for hypotension and respiratory depression.

What's in this section

1. Converting units (metric and household)
2. Equivalent doses (the same dose in g, mg or mcg)
3. Tablets and capsules
4. Liquids and injections
5. Weight and doses by weight
6. Splitting a daily dose
7. Checking a safe dose
8. Pump rates (mL/hr)
9. Drip rates by gravity (gtt/min, drops per minute)
10. Medication drips (units/hr, units/kg/hr)

The basics from Week 9 (the 24-hour clock, the three setup methods, rounding) are in the Week 9 guide. Each example below is worked one step at a time.

The three setup methods

Doses from a tablet or a liquid, and IV problems with several steps, are set up three ways below. You only need one: pick the method you use and follow that row. Every method gives the same answer. Converting units, equivalent doses and weight conversions are plain multiply or divide; every other type below shows all three setups.

Rounding

• Leading zero always: write 0.5, never .5.
• No trailing zero: write 5, never 5.0.
• Round only at the end. Carry the unrounded numbers (such as the weight in kg) all the way through.
• On the practice quizzes, type only the number; the unit is shown beside the box.

Conversions to know

Converting units

Check it: going to a smaller unit, the number gets bigger (0.5 g is 500 mg); going to a bigger unit, the number gets smaller.

Equivalent doses

The same dose written in a different metric unit. Use 1 g = 1,000 mg and 1 mg = 1,000 mcg: going to a smaller unit, multiply; going to a bigger unit, divide.

Tablets and capsules

Set it up with whichever of the three methods you use.

Liquids and injections

Same setup, but the quantity is the volume on the label (such as 5 mL).

Weight conversions

• kg to lb: multiply by 2.2. lb to kg: divide by 2.2. The kilogram number is always the smaller one.
• Some doses are based on the client's admission weight. Weight can change during a stay; if you aren't sure which weight the provider used, ask.

Doses by weight

• Why: the dose fits the client's size, so it's enough to work without building up to a toxic level.
• Who: most children's doses, plus some adult medications (for example the anticoagulant enoxaparin and the antibiotics vancomycin and amoxicillin).
• How: weight in kg × the ordered amount per kg.

Splitting a daily dose

1. Work out the total dose for 24 hours.
2. Divide it by the number of doses a day.

Doses a day = 24 ÷ the hours between doses: every 6 hr = 4 doses, every 8 hr = 3, every 12 hr (BID, twice a day) = 2.

Checking a safe dose

Doses can vary with age, weight, diagnosis, condition and route. Check every dose against a current drug reference:

1. Look up the recommended dose or range, and note whether it's per dose or per day.
2. If it's by weight, convert the weight to kg and multiply by the low and the high end.
3. Put the ordered dose in the same terms (per dose or per day) and compare.
4. Above the range: unsafe, hold it and contact the provider. Below the range: may not work (nontherapeutic), so check with the provider too.

Pump rates (mL/hr)

An infusion pump runs in mL per hour: Volume (mL)Time (hr). If the time is in minutes, change it to hours (÷ 60) or multiply by 60 min1 hr.

Drip rates by gravity (gtt/min)

Without a pump, the nurse sets the roller clamp and counts the drops falling in the drip chamber for 1 minute. The drop factor (gtt/mL) is on the tubing package.

gtt/min = Volume (mL) × drop factor (gtt/mL)Time (min)

Medication drips

Some drips are ordered by weight per hour (such as units/kg/hr). Work out the dose per hour, then the mL per hour from the bag's concentration.