Learn — General pharmacology & nursing responsibilities

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Routes of drug administration

The route of administration decides how much of a drug reaches the systemic circulation and how quickly, that is its bioavailability and its onset, and therefore whether the drug works, works too slowly, or kills. Intravenous administration is by definition 100 per cent bioavailable and immediate, while every other route trades speed for safety, convenience, or the avoidance of first-pass metabolism in the liver.

Enteral routes: oral, which is safest and cheapest but slow, needs a cooperative patient and loses drug to first-pass metabolism; sublingual and buccal, which are rapid and drain into veins that bypass the liver, so sublingual nitroglycerin 0.5 mg acts within 1 to 2 minutes; and rectal, useful in vomiting, unconscious patients and children, with partial bypass of the first pass but erratic absorption.
Parenteral routes: intravenous, immediate and titratable but irretrievable once given; intramuscular, acting in 10 to 20 minutes, with the ventrogluteal site safest in adults for up to about 3 mL, the deltoid taking 1 to 2 mL and the vastus lateralis used in infants; subcutaneous, 0.5 to 1 mL at 45 to 90 degrees for insulin and heparins, which are never aspirated or massaged; and intradermal, 0.1 mL at 5 to 15 degrees bevel up to raise a wheal, for the Mantoux test and BCG.
Specialised parenteral routes: intrathecal and epidural for anaesthesia and some chemotherapy, intraosseous when intravenous access fails in an emergency, intra-articular, intraperitoneal for dialysis, and the now obsolete intracardiac route.
Other routes: inhalation gives a rapid, lung-targeted effect from a small dose, as with salbutamol, budesonide and volatile anaesthetics; transdermal patches give steady levels and bypass the first pass, as with fentanyl, nitroglycerin and hyoscine, and must be rotated, never cut, with the old patch removed before a new one is applied; and topical, ophthalmic, otic, nasal and vaginal routes act locally.
First-pass metabolism explains why the same drug needs a different dose by different routes: morphine, propranolol, nitroglycerin and lignocaine are extensively metabolised on their first passage through the liver, so the oral dose is far larger than the parenteral one.
Order of onset, fastest first: intravenous, then inhalation and intraosseous, then intramuscular, subcutaneous, oral and finally transdermal. In cardiac arrest the accepted order of access is intravenous and then intraosseous, with the endotracheal route only as a last resort for a few drugs.
The Z-track technique is used for irritant intramuscular drugs such as iron dextran, to seal the drug into the muscle and prevent staining and leakage, and needle length must be chosen for the patient's build so that the drug is not deposited in fat.
Route-specific nursing checks matter as much as the drug: the correct diluent, concentration and rate for an intravenous drug, the maximum volume and correct site for an intramuscular dose, and the rights of medication administration confirmed at the bedside with two patient identifiers.
Wrong-route errors are among the deadliest in medicine: undiluted potassium chloride given as an intravenous push causes cardiac arrest, and vincristine given intrathecally instead of intravenously is almost always fatal, which is why vincristine is dispensed in a minibag labelled for intravenous use only.

Dose calculation — adult and paediatric

Dose calculation is the arithmetic that turns a prescription into what is actually drawn into the syringe — the desired dose divided by the stock strength, multiplied by the volume of that stock — with weight-based (mg/kg) and body-surface-area (mg per square metre) rules used for children and for drugs with a narrow margin of safety. It matters at the bedside because a misplaced decimal point is a tenfold error, and because in paediatrics and chemotherapy the entire safety of the drug rests on the calculation being right and independently checked.

The working formula is dose to give = (desired dose divided by stock strength) multiplied by the stock volume, and every calculation begins by converting both figures into the same unit: 1 g is 1000 mg, 1 mg is 1000 micrograms, and 1 litre is 1000 mL.
Weight-based dosing multiplies the ordered mg/kg by the patient's measured weight in kilograms, and the weight is taken on the day rather than copied from old notes, because a paediatric dose calculated from a remembered weight is a classic source of error.
Body surface area is used for cytotoxics and some paediatric drugs because it follows metabolic rate better than weight; the Mosteller formula gives BSA in square metres as the square root of (height in cm multiplied by weight in kg, divided by 3600), and the dose is the ordered figure per square metre multiplied by that number.
The old age-based rules still appear in examinations: Young's rule is adult dose multiplied by age in years divided by (age plus 12), Clark's rule is adult dose multiplied by weight in pounds divided by 150, and Fried's rule for infants is adult dose multiplied by age in months divided by 150 — all are approximations that a proper mg/kg order replaces in practice.
A calculated paediatric dose never exceeds the adult dose: when the mg/kg arithmetic in a large adolescent gives a figure above the adult maximum, the adult dose is the ceiling.
For a reconstituted powder, calculate from the strength after reconstitution rather than from the amount on the vial label, allow for the displacement volume of the powder itself, and label the vial with the resulting concentration, the date and the time.
The error that decides nursing action is the tenfold error: never write a trailing zero after a decimal point (write 5 mg, not 5.0 mg), always write a leading zero before one (write 0.5 mg, not point five), spell out the word units instead of U, and read the concentration on the ampoule rather than assuming the usual stock.
High-alert drugs — insulin, heparin, opioids, concentrated potassium chloride, cytotoxics, digoxin and every neonatal or paediatric infusion — need an independent double check in which the second nurse recalculates from the prescription rather than agreeing with the first nurse's figure.
Before giving the dose confirm the rights of medication administration — right patient by two identifiers, right drug, right dose, right route, right time, with right documentation, right reason and right response — and afterwards check the parameter the drug was meant to move.

Flow rate and drops/min calculations

Flow-rate calculation converts a prescribed volume and time into the two numbers a nurse actually sets — millilitres per hour on a pump, or drops per minute on a gravity set. It matters at the bedside because the same bag of fluid is safe over eight hours and dangerous over one in a patient with heart failure or in a neonate, and because the drop factor printed on the giving set changes the answer completely.

The two formulas are all that is needed: millilitres per hour equals the total volume in mL divided by the time in hours, and drops per minute equals the volume in mL multiplied by the drop factor in drops per mL, divided by the time in minutes.
The drop factor is printed on the giving-set packet: an adult macrodrip set delivers 15 or 20 drops per mL (blood administration sets are usually 15) and a microdrip or paediatric set delivers 60 drops per mL, so using the wrong factor changes the delivered rate three or four times over.
The microdrip shortcut is worth memorising: with a 60 drops per mL set the drops per minute equal the millilitres per hour exactly, so an order for 50 mL/hour is simply 50 drops per minute.
Worked example: 500 mL of normal saline over 4 hours with a 15 drops per mL set gives (500 multiplied by 15) divided by 240 minutes, which is 31 drops per minute, or 125 mL per hour on a pump.
Round the drops per minute to a whole drop because a fraction of a drop cannot be delivered, and verify the setting by counting drops against a watch for a full minute rather than for fifteen seconds.
For a drug infusion the same arithmetic runs through the concentration: the pump rate in mL per hour equals the ordered dose per hour divided by the concentration in the bag in mg or micrograms per mL, and an order written in micrograms/kg/min is first multiplied by the weight and by 60 to get the hourly dose.
The complication that decides nursing action is circulatory overload from a rate set too high — breathlessness, a rising respiratory rate, basal crackles, distended neck veins, a bounding pulse and sudden weight gain — with the opposite failure being a line that has slowed, tissued or clotted.
There is no antidote for over-infusion: slow the infusion to a rate that keeps the vein open, sit the patient up, give oxygen and inform the doctor, who will usually order a loop diuretic, and continue hourly observation with a strict intake-output chart afterwards.
Monitoring: check the volume infused against the volume that should have gone in at every round, keep an hourly intake-output chart for any controlled infusion, expect a urine output above 0.5 mL/kg/hour in an adult and 1 to 2 mL/kg/hour in a child, and inspect the cannula site at each check for swelling, coolness, pain or leaking.
Gravity flow is never constant — it varies with the height of the bag, the position of the limb, the patency of the cannula and the viscosity of the fluid — so a gravity set is recounted at every check, and a volumetric pump or a burette holding only the next hour's volume is used for children, potent drugs and any patient who cannot tolerate a swing in volume.

Drug of choice table

A drug-of-choice list is the shortest possible answer to the question every emergency asks: for this diagnosis, in an average adult with no contraindication, which single agent is given first. It matters at the bedside because the recall has to be automatic — a nurse who has to stop and think about what goes into the syringe in anaphylaxis or eclampsia has already lost the time that mattered — and it is a list examinations test directly.

Anaphylaxis: adrenaline 0.5 mg of the 1 in 1000 solution intramuscularly into the anterolateral thigh, repeated every 5 minutes as needed, before any antihistamine or steroid and never as an intravenous push of that strength.
Cardiac arrest: adrenaline 1 mg of 1 in 10000 intravenously every 3 to 5 minutes in every rhythm, with amiodarone 300 mg after the third shock in a shockable rhythm; atropine has no place in the current arrest algorithm and belongs instead to symptomatic bradycardia at 1 mg intravenously repeated to a maximum of 3 mg.
Status epilepticus: a benzodiazepine first — intravenous lorazepam where there is a line, intramuscular or buccal midazolam where there is not — followed by a second-line agent such as levetiracetam, sodium valproate or fosphenytoin.
Eclampsia and severe pre-eclampsia: magnesium sulfate for both the fit and its prevention, with calcium gluconate kept at the bedside as its antidote; the antihypertensives of choice in pregnancy are labetalol, nifedipine and methyldopa.
Torsades de pointes: intravenous magnesium sulfate. Paroxysmal supraventricular tachycardia: adenosine by rapid intravenous push with an immediate saline flush, after vagal manoeuvres have failed.
Poisoning: organophosphates need atropine titrated until secretions dry, with pralidoxime; paracetamol needs N-acetylcysteine; opioids need naloxone; benzodiazepines need flumazenil (avoided in a mixed or tricyclic overdose and in chronic users); warfarin needs vitamin K with prothrombin complex concentrate; heparin needs protamine; iron needs desferrioxamine; and methanol or ethylene glycol needs fomepizole or ethanol.
Infections: tuberculosis under the National TB Elimination Programme is treated with daily fixed-dose combination isoniazid, rifampicin, pyrazinamide and ethambutol in the intensive phase followed by isoniazid, rifampicin and ethambutol in the continuation phase; bacterial meningitis and meningococcal disease need ceftriaxone; uncomplicated falciparum malaria in India needs an artemisinin-based combination; anaerobes and amoebiasis need metronidazole; MRSA needs vancomycin.
Other standing answers: diabetic ketoacidosis is treated with fluid resuscitation and an intravenous regular insulin infusion; acute severe asthma with nebulised salbutamol, oxygen and a systemic corticosteroid; thyroid storm with propylthiouracil or carbimazole plus a beta-blocker; absence seizures with ethosuximide or valproate; trigeminal neuralgia with carbamazepine; bipolar disorder maintenance with lithium; and neuroleptic malignant syndrome with dantrolene and bromocriptine.
Every drug of choice bends to the patient in front of you: pregnancy, renal or hepatic failure, a documented allergy or a resistant organism each change the answer, so the list is where thinking starts and not where it stops.

Look-alike sound-alike (LASA) drugs

Look-alike sound-alike (LASA) drugs are pairs whose names read or sound similar, or whose packaging and vial size look similar, so that one is picked up, transcribed or dispensed in place of the other. They matter because name and packaging confusion is one of the commonest causes of medication error worldwide, and the whole defence sits with the nurse at the point of preparation — tall-man lettering, separated storage, readback of verbal orders and an independent double check.

Tall-man lettering capitalises the letters that differ so that the eye catches them: DOBUTamine and DOPamine, NIFEdipine and NIMOdipine, predniSONE and predniSOLone, chlorproMAZINE and chlorproPAMIDE, vinCRIStine and vinBLAStine, hydrALAZINE and hydrOXYzine.
Sound-alike pairs that change the outcome: hydralazine (an antihypertensive vasodilator) and hydroxyzine (an antihistamine); metformin and metronidazole; amiodarone and amlodipine; losartan and valsartan; cefotaxime and cefoxitin; clonidine and clonazepam.
Look-alike strengths are as dangerous as look-alike names: insulin U-100 and U-40 vials with their matched syringes, heparin 1000 IU/mL and 5000 IU/mL vials, adrenaline 1:1000 and 1:10,000 ampoules, and concentrated potassium chloride ampoules standing beside normal saline.
The reference lists are the WHO High 5s look-alike sound-alike medication names action and the ISMP list of confused drug names; each hospital keeps its own LASA list, reviews it annually, and displays it at the drug trolley and in the pharmacy.
Verbal and telephone orders are taken only in an emergency: write it down, read it back with the dose and units spelt out letter by letter and digit by digit, and have the prescriber countersign within 24 hours.
Storage controls: separate the pair physically, do not shelve them alphabetically side by side, add a shelf-edge warning label, and keep concentrated electrolytes and neuromuscular blockers out of open floor stock.
Never use error-prone abbreviations — write units in full rather than U, write micrograms rather than a handwritten µg, avoid trailing zeros (10 mg, not 10.0 mg) and always use a leading zero (0.5 mg, not .5 mg).

High alert medications

High-alert medications are drugs that carry a heightened risk of causing significant harm when they are used in error; the error rate is not necessarily higher than for other drugs, but the consequence of a single mistake is catastrophic. They matter because the defence is systemic rather than personal — standardised concentrations, limited floor stock, an independent double check before administration, and a smart pump with a drug library.

The core list is insulins, anticoagulants (heparin, low-molecular-weight heparin, warfarin, direct oral anticoagulants), opioids and other sedatives, concentrated electrolytes (potassium chloride, hypertonic saline of 3% and above, magnesium sulphate), neuromuscular blockers, chemotherapeutic agents, and intravenous adrenergic agonists and antagonists.
Concentrated potassium chloride is never given by intravenous push; it is always diluted into an infusion bag to no more than 40 mEq/L for a peripheral line, and the rate does not exceed 10 mEq per hour peripherally or 20 mEq per hour by central line with continuous ECG monitoring.
Insulin is drawn up only in an insulin syringe or given by pen — never a tuberculin or 1 mL syringe — the order is written with units spelt out in full, and a second nurse independently verifies the patient, the insulin type, the concentration and the volume in the syringe before it is given.
Heparin: keep a single vial strength on the ward, monitor the activated partial thromboplastin time at a target of 1.5 to 2.5 times the control, and keep protamine sulphate available — 1 mg neutralises about 100 units of heparin, to a maximum of 50 mg in one dose.
Neuromuscular blockers (succinylcholine, vecuronium, rocuronium) are removed from general floor stock and kept in a sealed container labelled as a paralysing agent that causes respiratory arrest, because giving one to a patient who is not ventilated is fatal.
The independent double check is genuinely independent: two nurses check separately, without prompting each other, against the original prescription — patient, drug, concentration, dose, route, rate, pump setting and line — and both sign the chart.
Other controls: pharmacy-prepared standard concentrations, smart infusion pumps with dose limits, bar-code scanning at the bedside, auxiliary warning labels, and removal of concentrated electrolytes from ward stock altogether.
Antidotes are stored where the drug is used: naloxone with opioids, protamine with heparin, vitamin K with warfarin, calcium gluconate with magnesium sulphate, and 25% dextrose with insulin.

Safe syringe disposal

Safe syringe disposal is the handling of a used needle and syringe from the second the injection ends until the sharp has been destroyed, so that nobody is pricked and no syringe can be reused. It matters because needle-stick injury is the commonest occupational exposure in nursing and carries a real risk of hepatitis B, hepatitis C and HIV, and because the Bio-Medical Waste Management Rules 2016 make the destruction of the sharp at the point of generation a legal duty, not a preference.

Sharps go into the white translucent, puncture-proof, leak-proof container of Schedule I: needles, syringes with fixed needles, needles cut from cutters or burners, scalpels, blades and any other contaminated item that can puncture or cut.
The needle is cut with a needle cutter or hub cutter (or destroyed with a needle burner) at the point of generation and dropped straight into the container; a used needle is never recapped, bent or broken by hand, and if recapping is unavoidable the one-handed scoop technique is used.
The white container is treated by autoclaving or dry-heat sterilisation followed by shredding, mutilation or encapsulation in a metal container or cement concrete, with final disposal to iron foundries, a sanitary landfill or a designated concrete sharps pit.
Fill limit: bags and containers are filled to no more than three-fourths of their capacity, then tied or sealed and labelled with the bar code before transport — never pressed down by hand to make room.
The rest of the colour code places the syringe correctly: the plastic barrel without its needle is contaminated recyclable plastic and goes in the red bag with IV sets, catheters and gloves; anatomical and soiled waste and expired medicines go in the yellow bag; broken ampoules and vials are glassware and go in the puncture-proof, leak-proof box or container with blue marking.
Untreated human and animal anatomical waste, soiled waste and biotechnology waste must not be stored beyond 48 hours, and every accident, spill and needle-stick injury is reported at once to the prescribed authority in Form I, with the annual report filed in Form IV.
After a needle-stick the wound is washed with soap and running water — not squeezed, not sucked and not treated with bleach or a caustic antiseptic — then reported the same shift so that the source and the exposed worker can be tested.
HIV post-exposure prophylaxis is a three-drug antiretroviral regimen taken for 28 days under NACO guidance, started as early as possible and ideally within 2 hours, and of no proven use beyond 72 hours; an unimmunised worker also receives hepatitis B immunoglobulin and the hepatitis B vaccine series.

Reconstitution of drugs

Reconstitution is the aseptic addition of a specified volume of a specified diluent to a powdered drug so that it becomes a solution of a known concentration. It matters because everything the nurse then measures depends on which fluid went in and how much of it: the wrong diluent can precipitate the drug or make it unsafe for the intended route, and an unlabelled reconstituted vial is a dose of unknown strength and unknown age.

Read the package insert for three things before touching the vial: which diluent, what volume, and how long the reconstituted solution keeps and at what temperature.
Displacement volume matters in paediatrics — the powder itself occupies space, so 10 mL added to a vial may yield more than 10 mL of solution; for small doses work from the final volume printed in the insert, not from the volume you added.
Ceftriaxone is the worked example: reconstitute the 1 g vial with about 10 mL of sterile water for injection for intravenous use and give it over 2 to 4 minutes, or with about 3.5 mL of 1% lignocaine for the intramuscular route — and a lignocaine-containing solution is never given intravenously.
Compatibility is checked before the line is connected: ceftriaxone must not meet a calcium-containing fluid such as Ringer's lactate in the same line, an aminoglycoside is never mixed in the same syringe as a beta-lactam, and the line is flushed with normal saline between drugs.
Asepsis: scrub the rubber septum with 70% alcohol and let it dry for 30 seconds, use a fresh sterile needle and syringe for each vial, do not touch the septum after cleaning, and reject any solution that is cloudy, discoloured or contains particles.
Label the vial the moment it is mixed with the drug, the final concentration, the date, the time of reconstitution, the expiry of the reconstituted solution and the initials of the person who mixed it.
A single-dose vial is discarded after one use even if fluid remains; a preserved multi-dose vial is dated at first entry and used within the manufacturer's stated period at the stated temperature.
Some powders are dissolved by gentle rolling rather than shaking — shaking a protein or a suspension causes foaming and denaturation — so follow the insert rather than habit.

Drug-drug interaction basics

A drug–drug interaction is a change in the effect of one drug caused by another given with it, and it is either pharmacokinetic — the second drug changes how much of the first reaches its site — or pharmacodynamic, where the two act on the same system. It matters because the serious ones are silent until they present as a bleed, a fall, an arrhythmia or an unintended pregnancy, so the nurse who reconciles the complete medicine list, including over-the-counter and herbal products, is the one who catches them.

Absorption: antacids, calcium, iron, milk and sucralfate chelate tetracyclines and fluoroquinolones and cut their absorption — separate the two by at least 2 hours; a proton pump inhibitor reduces the absorption of ketoconazole and itraconazole.
Distribution: two highly protein-bound drugs compete for albumin (warfarin with sulphonamides, phenytoin with valproate), transiently raising the free and therefore active fraction of the displaced drug.
Enzyme inhibitors act within days and raise the level of the other drug: erythromycin and clarithromycin, the azole antifungals, ciprofloxacin, cimetidine, metronidazole, ritonavir, amiodarone, sodium valproate and grapefruit juice.
Enzyme inducers act over 1 to 2 weeks and lower the level of the other drug: rifampicin, rifabutin, phenytoin, carbamazepine, phenobarbitone, griseofulvin and St John's wort. Rifampicin with a combined oral contraceptive is the classic cause of an unintended pregnancy, and it also lowers warfarin and several antiretrovirals.
Excretion: probenecid blocks the tubular secretion of penicillin and raises its level; an NSAID with an ACE inhibitor and a diuretic — the triple whammy — precipitates acute kidney injury; and lithium is retained when a thiazide, an NSAID or an ACE inhibitor is added, which is a common route to lithium toxicity.
Pharmacodynamic interactions to know: additive respiratory depression from an opioid with a benzodiazepine, additive bleeding from warfarin with aspirin or an NSAID, serotonin syndrome when an SSRI meets tramadol, linezolid or an MAO inhibitor, and QT prolongation when two QT-prolonging drugs such as ondansetron, a macrolide, haloperidol or a fluoroquinolone are given together.
Food interactions count as well: tyramine-rich food with an MAO inhibitor causes a hypertensive crisis, and vitamin K in green leafy vegetables opposes warfarin — the advice there is a consistent intake, not avoidance.
The monitoring parameter is chosen by the interaction: INR for warfarin, potassium and creatinine for the triple whammy, a serum lithium level (therapeutic 0.6–1.2 mEq/L) when a diuretic or NSAID is added, and an ECG for the QT.

Medication error reporting

Medication error reporting is the systematic, non-punitive recording of any preventable event that leads to, or could lead to, inappropriate medication use or patient harm, whether or not it actually reached the patient. It matters because a reported near miss is free information — it exposes the system fault, a look-alike vial, an ambiguous abbreviation or an understaffed shift, while nobody has yet been hurt — and a ward that punishes the reporter simply stops hearing about errors.

Keep the definitions apart: a medication error is preventable and may or may not reach the patient; an adverse drug reaction is a noxious unintended response at a normal dose and is usually not preventable; an adverse drug event is any harm from a drug, from either cause; a near miss is an error caught before it reached the patient.
Everything is reported, including the near miss and the error that caused no harm, because the near miss is the commonest and by far the cheapest lesson the system will ever get.
Adverse drug reactions are reported in India through the Pharmacovigilance Programme of India: the suspected ADR reporting form goes to the nearest ADR Monitoring Centre, or the report is made through the national toll-free helpline or the ADR PvPI mobile application, with the Indian Pharmacopoeia Commission at Ghaziabad as the National Coordination Centre.
Medication errors additionally go into the hospital's own incident reporting system within the time the policy sets, commonly 24 hours; the incident form records facts and is never filed in the patient's case sheet.
The report states what was prescribed, what was actually given, the dose, route, time and the people involved, what happened to the patient and what was done — and no opinion about who was at fault.
Root cause analysis asks why until the answer is a system fault: the five whys, a fishbone diagram and a timeline. The output is a corrective action such as separating two vials, changing a label or adding a double check, not a warning letter.
Just culture separates three things: human error is consoled and the system fixed, at-risk behaviour (drifting from a rule because it is inconvenient) is coached, and only reckless behaviour — knowingly ignoring a safety rule — attracts sanction.
Severity is graded on the NCC MERP index from Category A (circumstances capable of causing an error) through B to D (an error occurred but no harm resulted) and E to H (harm) to Category I, an error that contributed to the patient's death.
The nurse's first duty when an error is discovered is clinical, not clerical: assess and stabilise the patient, inform the prescriber, monitor for the predictable effect, disclose honestly to the patient, and only then complete the report.

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