PMDC NRE flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Half-life formula

t½ = 0.693 × volume of distribution divided by clearance. It determines the time to steady state (about 4–5 half-lives) and the dosing interval for most maintenance regimens.

Loading dose calculation

Loading dose equals volume of distribution times target plasma concentration, divided by bioavailability. It fills the distribution volume rapidly without waiting for steady state to develop.

Anion gap

Anion gap equals sodium minus the sum of chloride and bicarbonate, normally 8–12 mEq/L. It rises with unmeasured anions such as ketones, lactate, uremic toxins, or salicylate.

Winter formula

Expected PaCO2 equals 1.5 times serum bicarbonate plus 8, with a range of plus or minus 2. It detects inadequate respiratory compensation in metabolic acidosis.

Sensitivity and specificity

Sensitivity is the proportion of diseased patients who test positive; specificity is the proportion of healthy patients who test negative. Highly sensitive tests are useful for ruling out disease.

Number needed to treat

NNT is the reciprocal of absolute risk reduction. An NNT of 20 means 20 patients must be treated for one additional patient to benefit compared with control.

Volume of distribution

Vd equals the total amount of drug in the body divided by its plasma concentration. Values above about 1 L/kg indicate extensive tissue binding and limited removal by dialysis.

Phase I versus phase II metabolism

Phase I reactions use cytochrome P450 to oxidize, reduce, or hydrolyze drugs, often creating reactive intermediates. Phase II conjugations such as glucuronidation increase water solubility for biliary or renal excretion.

First-pass metabolism

Orally absorbed drug passes through portal circulation and liver before reaching systemic circulation. Drugs with high hepatic extraction, such as nitrates and propranolol, have low oral bioavailability.

Starling equation

Net filtration equals capillary hydrostatic pressure minus interstitial hydrostatic pressure, minus the reflection coefficient times the oncotic pressure difference. It explains edema from raised pressure or low albumin.

Laplace law for wall tension

Wall tension equals pressure times radius divided by twice wall thickness. Dilated ventricles face higher tension and oxygen demand, which is why afterload reduction improves efficiency.

Proximal tubule reabsorption

The proximal convoluted tubule reabsorbs roughly 65% of filtered sodium and water, plus glucose and amino acids via cotransport. Its high permeability makes it the workhorse of isosmotic reabsorption.

Thick ascending limb function

This nephron segment reabsorbs sodium via the NKCC2 cotransporter but is impermeable to water, diluting tubular fluid. Loop diuretics block NKCC2 here and abolish the medullary concentrating gradient.

Glomerular filtration rate determinants

GFR equals the filtration coefficient times the net filtration pressure across the glomerular capillary. Autoregulation keeps GFR stable across mean arterial pressures of roughly 80 to 180 mmHg.

Cardiac output equation

Cardiac output equals heart rate multiplied by stroke volume. Stroke volume is set by preload, afterload, and contractility, so tachycardia or volume loss can lower output.

Fick principle

Cardiac output equals oxygen consumption divided by the arteriovenous oxygen content difference. It underlies thermodilution and direct Fick measurement in hemodynamic assessment.

Microcytic anemia differential

Mean corpuscular volume below 80 fL suggests iron deficiency, thalassemia, anemia of chronic disease, or sideroblastic anemia. Ferritin, iron studies, and hemoglobin electrophoresis separate the causes.

Macrocytic anemia differential

Mean corpuscular volume above 100 fL points to vitamin B12 or folate deficiency, alcohol use, hypothyroidism, or myelodysplasia. B12 deficiency also causes neurologic deficits and elevated methylmalonic acid.

COPD physiology

Chronic obstructive pulmonary disease shows airflow obstruction with reduced FEV1/FVC ratio, air trapping, and increased residual volume. Emphysema destroys alveolar septa, lowering surface area and elastic recoil.

Therapeutic index

Therapeutic index equals toxic dose divided by effective dose at the 50% response points. A narrow index, as with warfarin, digoxin, and lithium, requires therapeutic drug monitoring.

CYP450 inhibitors

Macrolide antibiotics, azole antifungals, grapefruit juice, and cimetidine inhibit cytochrome P450 enzymes. They raise levels of co-administered substrates and can precipitate toxicity.

CYP450 inducers

Rifampin, carbamazepine, phenytoin, phenobarbital, and St. John's wort induce cytochrome P450 enzymes. They lower levels of co-administered substrates and can cause treatment failure.

Acetaminophen antidote

N-acetylcysteine replenishes glutathione and detoxifies the reactive metabolite NAPQI. It is most effective when given within 8–10 hours of acetaminophen overdose.

Opioid antidote

Naloxone is a competitive opioid receptor antagonist that reverses respiratory depression and sedation. Its short half-life may require repeat dosing or infusion because opioids can outlast it.

Warfarin reversal

Vitamin K restores synthesis of clotting factors II, VII, IX, and X. For major bleeding, prothrombin complex concentrate or fresh frozen plasma is added for immediate factor replacement.

Heparin antidote

Protamine sulfate neutralizes unfractionated heparin by binding it electrostatically. It only partially reverses low-molecular-weight heparin, which lacks a complete antidote.

Type A adverse drug reaction

Type A reactions are dose-dependent and predictable extensions of a drug's known pharmacology. Examples include bleeding with anticoagulants and bradycardia with beta-blockers.

Type B adverse drug reaction

Type B reactions are idiosyncratic, unpredictable, and often immune-mediated, such as anaphylaxis to penicillin or agranulocytosis from clozapine. They are unrelated to the drug's therapeutic action.

Informed consent elements

Valid consent requires decision-making capacity, disclosure of risks, benefits, and alternatives, comprehension by the patient, and voluntariness. Imminent harm creates an emergency exception.

Substituted judgment standard

Surrogate decisions should reflect what the patient would have chosen based on prior statements and values. Best interests applies only when the patient's wishes are unknown.

Mandatory reporting exceptions

Confidentiality yields to legal reporting duties for gunshot and stab wounds, suspected child or elder abuse, and certain communicable diseases. Reporting is required even without patient consent.

Screening test criteria

A condition should be common, serious, and detectable in a preclinical phase, with effective treatment available. The screening test must be sensitive, specific, safe, and acceptable to the population.