APC Written Assessment cheat sheet

First-order elimination: t½ = 0.693/k is constant; steady state is reached after about 4–5 half-lives, and loading dose = (Vd × target concentration)/F.

Zero-order elimination removes a constant amount per unit time, so half-life lengthens as concentration rises (ethanol; phenytoin at high concentrations).

Vd = Dose/C0, where C0 is the concentration extrapolated to time zero; CL = k × Vd; maintenance dosing rate = (CL × target Css)/F.

AUC = (F × Dose)/CL; oral bioavailability F = (AUC_oral × Dose_IV)/(AUC_IV × Dose_oral).

Henderson–Hasselbalch for a weak acid: pH = pKa + log([A⁻]/[HA]); the un-ionized fraction is the one that crosses lipid membranes.

Higuchi matrix release is proportional to the square root of time, whereas reservoir/membrane and osmotic pump systems give near zero-order release.

Enteric polymers such as cellulose acetate phthalate resist gastric acid and dissolve above roughly pH 5.5–6, protecting acid-labile drugs.

Prodrugs improve absorption or stability and are biotransformed to the active agent: enalapril → enalaprilat; codeine → morphine.

Michaelis–Menten: v = Vmax·C/(Km + C); first-order when C is far below Km, saturable zero-order when C is far above Km.

Competitive antagonism shifts the agonist dose–response curve right without changing Emax; noncompetitive antagonism lowers Emax.

Therapeutic index = TD50/ED50; narrow-index drugs include digoxin, lithium, warfarin, phenytoin and aminoglycosides.

β1 receptors increase heart rate and contractility; β2 receptors relax bronchial smooth muscle, so nonselective β-blockers can precipitate bronchospasm in asthma.

ACE inhibitors reduce angiotensin II and aldosterone but increase bradykinin, causing dry cough, angioedema and hyperkalemia; contraindicated in pregnancy.

Warfarin inhibits vitamin K epoxide reductase, depleting functional factors II, VII, IX and X; the effect is delayed and monitored by INR.

Unfractionated heparin potentiates antithrombin III, is monitored by aPTT, and is reversed by protamine sulfate.

Aminoglycosides bind the bacterial 30S subunit, show concentration-dependent bactericidal killing, and cause nephrotoxicity and ototoxicity.

Loop diuretics block the Na-K-2Cl cotransporter in the thick ascending limb; adverse effects include hypokalemia, hypocalcemia and ototoxicity.

CYP2D6 poor metabolizers obtain little analgesia from codeine, whereas ultrarapid metabolizers risk opioid toxicity from rapid morphine formation.

ISMP high-alert medications (insulin, heparin, opioids, concentrated electrolytes) require independent double-checks and standardized storage and labeling.

Avoid error-prone abbreviations: write 'unit' instead of U, 'daily' instead of QD, and never use a trailing zero (1 mg, not 1.0 mg).

DEA Schedule II prescriptions cannot be refilled; Schedules III–V permit up to 5 refills within 6 months of the issue date.

USP <797> requires the direct compounding area to be ISO Class 5 within an ISO Class 7 buffer room; beyond-use dates depend on the assigned risk category.

USP <800> hazardous-drug handling requires negative-pressure rooms, closed system transfer devices and appropriate personal protective equipment.

Adverse drug reactions are reported to the FDA MedWatch program; the Naranjo scale classifies causality as definite, probable, possible or doubtful.

Medication reconciliation at admission, transfer and discharge reduces omissions, duplications and dosing discrepancies across care transitions.

OBRA '90 requires prospective drug utilization review and an offer of counseling for Medicaid outpatients; many states extended this to all patients.

A valid prescription includes patient name, drug, strength, dosage form, quantity, directions, date and prescriber signature.