Pharmacology & Dosage

Drug dosing, pharmacokinetics, clearance and IV-drip calculations for clinical practice

Pharmacology & Dosage formulas help you calculate how medicines move through the body and how much to give safely and effectively, from half-life and clearance to loading doses, IV drip rates, and creatinine clearance. They’re essential for students, exam prep, and clinical practice alike, because accurate dosing supports better treatment decisions, reduces medication errors, and helps ensure drugs work as intended.

Drug Half-Life

NEWIntermediate

t_{1/2} = \frac{0.693}{k_e}

Time for the plasma concentration of a drug to fall to half its initial value.

Steady-State Concentration

NEWIntermediate

C_{ss} = \frac{F \times D}{CL \times \tau}

Average plasma drug concentration when intake and elimination are balanced.

Loading Dose

NEWIntermediate

LD = \frac{C_{target} \times V_d}{F}

Initial higher dose to rapidly achieve the desired plasma concentration.

Maintenance Dose

NEWIntermediate

MD = C_{ss} \times CL \times \tau

Recurring dose needed to sustain the steady-state concentration.

Volume of Distribution

V_d = \frac{D}{C_0}

Apparent volume into which a drug distributes — a larger Vd means the drug leaves the bloodstream and enters tissues.

Clearance

NEWIntermediate

CL = k_e \times V_d

Volume of plasma completely cleared of a drug per unit time.

Bioavailability

NEWIntermediate

F = \frac{AUC_{oral}}{AUC_{IV}} \times 100

Fraction of an oral dose that reaches systemic circulation compared with an IV dose.

IV Drip Rate

\text{Rate} = \frac{V \times gtt}{T}

Drops per minute to deliver a given volume over a set time via IV drip.

Creatinine Clearance (Cockcroft-Gault)

NEWIntermediate

CrCl = \frac{(140 - \text{age}) \times \text{weight}}{72 \times S_{cr}} \times (0.85 \text{ if female})

Estimates kidney function to guide drug dosing adjustments.

Therapeutic Index

TI = \frac{TD_{50}}{ED_{50}}

Ratio of the dose causing toxicity to the effective dose — a safety measure for drugs.

First-Order Elimination

NEWIntermediate

C(t) = C_0 \times e^{-k_e t}

Drug concentration decreases exponentially — a constant fraction is eliminated per unit time.

Weight-Based Dosing

D = d \times W

Calculate the total dose from a per-kilogram dosing rate — common in paediatrics.