GPAT cheat sheet

Bioavailability (F) = (AUC_oral × D_iv) / (AUC_iv × D_oral); absolute F compares oral to IV, relative F compares two non-IV routes.

Noyes–Whitney: dissolution rate ∝ (D·A/h)·(Cs − C); reducing particle size raises surface area A and thus dissolution, but too-fine powders may aggregate and reduce wetting.

Higuchi square-root law for matrix release: Q = kH·t^0.5; zero-order release gives Q = k0·t; first-order gives log remaining vs t linear.

Stokes' law sedimentation: v = d²(ρs − ρl)g / 18η; smaller diameter and higher viscosity slow settling in suspensions.

HLB scale: 3–6 W/O emulsifier, 8–18 O/W emulsifier, 13–15 detergents, 15–18 solubilizers; required HLB of oil must be matched by blend.

Dose uniformity by content uniformity: 10 units, acceptance value (AV) ≤ 15.0; if 10-unit AV fails, test 20 more units and AV ≤ 15.0 with no unit outside 0.75–1.25 of label.

Micromeritic Carr's index = (ρtapped − ρbulk)/ρtapped × 100; <15% excellent flow, 16–20% good, >25% poor flow; Hausner ratio = ρtapped/ρbulk, >1.25 indicates poor flow.

Sustained release: loading dose = (Css × Vd)/F; maintenance rate = (Css × CL)/F, where CL = clearance of the drug.

Sterilization by moist heat: 121 °C, 15 psi, 15–20 min; F0 value is equivalent time at 121 °C with z = 10 °C; SAL target for terminally sterilized products is 10^-6.

Henderson–Hasselbalch: pH = pKa + log([A−]/[HA]) for acids; percent ionized of a weak acid = 100/(1 + 10^(pKa − pH)); bases ionize inversely.

pKa of a carboxylic acid ≈ 4–5; protonated amine (conjugate acid) pKa ≈ 9–10; these govern absorption in stomach (pH 1–3) vs intestine (pH 6–8).

Bioisosterism: replacement of a group with similar size/electronics (e.g., –H/F, –OH/NH2, –COOH/tetrazole) to retain activity while altering metabolism or solubility.

Stereochemistry: R/S assigned by CIP priority; enantiomers differ in biological activity (e.g., S-(−)-propranolol is far more beta-blocking than R).

Prodrug design: ester prodrugs of carboxyl drugs (e.g., enalapril to enalaprilat) improve oral absorption; hydrolysis by esterases releases active drug.

Lipinski's Rule of Five for oral drug-likeness: MW ≤ 500, logP ≤ 5, H-bond donors ≤ 5, H-bond acceptors ≤ 10; one violation tolerated.

Michaelis–Menten: v = Vmax[S]/(Km + [S]); at [S] = Km velocity is half Vmax; Lineweaver–Burk plot is 1/v vs 1/[S] with slope Km/Vmax.

Nucleophilic aromatic substitution requires electron-withdrawing groups ortho/para to leaving halide; SN2 is favored by primary halides and polar aprotic solvents.

Receptor occupancy: effect = (Emax·[D])/(Kd + [D]); Kd is concentration at half-maximal occupancy; competitive antagonists raise apparent Kd without changing Emax.

Therapeutic index = TD50/ED50; low TI (e.g., digoxin, warfarin, lithium) requires therapeutic drug monitoring.

First-order elimination half-life t½ = 0.693·Vd/CL; after 4–5 half-lives ≈ 94–97% of steady state is reached.

Loading dose = (Vd × target concentration)/F; maintenance dose rate = (CL × target concentration)/F.

Sympathetic receptors: α1 → vasoconstriction; β1 → tachycardia and increased contractility; β2 → bronchodilation and vasodilation; β-blockers reduce heart rate and renin release.

NSAIDs inhibit COX-1/COX-2, reducing prostaglandin synthesis; COX-1 inhibition explains gastric ulceration and bleeding risk.

Aminoglycosides bind the 30S ribosomal subunit, causing misreading of mRNA; they are bactericidal and require monitoring for nephrotoxicity and ototoxicity.

Anticholinergic adverse effects: dry mouth, mydriasis, urinary retention, constipation, tachycardia; opioid triad: miosis, respiratory depression, coma.

Alkaloids: plant bases containing nitrogen; examples include morphine (Papaver somniferum), quinine (Cinchona), atropine (Atropa belladonna), and reserpine (Rauwolfia serpentina).

Glycosides: cardiac glycosides such as digoxin (Digitalis purpurea) contain a steroid aglycone plus a sugar; aglycone determines activity and sugar affects solubility.

Tannins are polyphenols that precipitate proteins; they are detected by ferric chloride (blue-black) and gelatin/salt tests.

Volatile oils are steam-distillable; examples are clove (eugenol), peppermint (menthol), eucalyptus (cineole), and cinnamon (cinnamaldehyde).

Gums and mucilages are polysaccharides; gum acacia is an emulsifier, gum tragacanth is a suspending agent, and agar is a gelling agent.

Standardization of crude drugs uses marker compounds (e.g., glycyrrhizin in liquorice, hypericin in St John's wort) and pharmacopoeial assays.

Biosynthetic classes: shikimate pathway → aromatic amino acids and phenylpropanoids; mevalonate pathway → terpenes and steroids; alkaloids derive largely from amino acids.

Beer–Lambert law: A = ε·b·c; absorbance is directly proportional to concentration; A = log(I0/I) = 2 − log(%T).

UV–Vis selection rules: conjugated systems absorb in the 200–400 nm range; a chromophore is the absorbing group and an auxochrome shifts λmax.

HPLC resolution R = 2(t2 − t1)/(w1 + w2); baseline separation is generally R ≥ 1.5; capacity factor k' = (tR − t0)/t0.

Column efficiency: N = 16(tR/w)² = 5.54(tR/w½)²; higher N gives sharper peaks; HETP = L/N.

Titration: equivalence point for a weak acid with strong base is basic; phenolphthalein (pH 8.2–10) is suitable, methyl orange (pH 3.1–4.4) is not.

Karl Fischer titration measures water content; it is suitable for moisture in hygroscopic APIs and uses iodine, sulfur dioxide, and a base in methanol.

ICH Q2 validation parameters: accuracy, precision (repeatability, intermediate, reproducibility), specificity, LOD/LOQ, linearity, range, and robustness.

Mass spectrometry: molecular ion gives molecular weight; ESI is a soft ionization method for polar and thermolabile compounds; GC-MS requires volatile analytes.

Glycolysis yields net 2 ATP and 2 NADH per glucose; complete oxidation to CO2 and H2O yields about 30–32 ATP depending on shuttle.

TCA cycle: per acetyl-CoA, 3 NADH, 1 FADH2, and 1 GTP are produced; oxidative phosphorylation uses the electron transport chain and ATP synthase.

Enzyme kinetics: Km is the substrate concentration at half Vmax; a competitive inhibitor raises Km without changing Vmax; a noncompetitive inhibitor lowers Vmax.

Vitamin deficiencies: thiamine (B1) → beriberi/Wernicke; niacin (B3) → pellagra (dermatitis, diarrhoea, dementia); cobalamin (B12) → megaloblastic anaemia and neuropathy.

Therapeutic drug monitoring is indicated for narrow-TI drugs (digoxin, phenytoin, lithium, vancomycin, aminoglycosides); trough sampling is usual for vancomycin.

Liver function tests: ALT/AST for hepatocellular injury, ALP/GGT for cholestasis, albumin and INR for synthetic function; Child–Pugh class guides dosing.

Renal dosing: estimate creatinine clearance by Cockcroft–Gault = [(140 − age) × weight]/(72 × SCr), ×0.85 for females; adjust doses for CrCl < 60 mL/min.

Diabetes: HbA1c reflects 2–3 months of glycaemia; metformin reduces hepatic gluconeogenesis and is first-line unless contraindicated by severe renal impairment.

Schedule H drugs require a prescription and a warning label; Schedule X drugs require prescriptions in duplicate retained by the pharmacy, with records kept for two years.

Schedule M specifies Good Manufacturing Practices for premises, plant, and equipment; Schedule Y governs clinical trials and new drug approval.

Drug Price Control Order: scheduled formulations have ceiling prices fixed under the National Pharmaceutical Pricing Authority; non-scheduled drugs may increase by no more than 10% per year.

Drugs and Cosmetics Act: misbranded, adulterated, and spurious drugs are separately defined offences; spurious drugs attract the most severe penalties.

Pharmacopoeia of India is the official book of standards; the Drug Technical Advisory Board and Drug Consultative Committee are statutory bodies under the Act.

Inventory control: economic order quantity EOQ = √(2DS/H), where D is annual demand, S is ordering cost, and H is holding cost per unit per year.

ABC analysis classifies inventory by annual consumption value; VED analysis classifies by criticality (vital, essential, desirable), and both are used together for stock control.

Clinical trial phases: Phase I (20–80 subjects, safety), Phase II (100–300, efficacy), Phase III (300–3,000, confirmatory), Phase IV (post-marketing surveillance).