Pharmacokinetic Mnemonic (ADME, ABCD)

Traditionally, the pharmacokinetic mnemonic, ADME, described the processes of a drug's journey through the body:

• Absorption: How the drug enters the bloodstream.
• Distribution: How the drug spreads through the body.
• Metabolism: How the body breaks down the drug, often in the liver.
• Excretion: How the drug leaves the body, usually via urine or feces.

It’s a simple way to recall how a drug moves through the body!

In modern pharmacokinetics, another helpful acronym is ABCD, which focuses on the key steps in the drug's pathway:

• Administration: How the drug is introduced into the body (e.g., oral, intravenous).
• Bioavailability: How much of the drug reaches the bloodstream and is available for use.
• Clearance: How the drug is removed from the body, typically through the liver or kidneys.
• Distribution: How the drug moves to its target sites within the body.

While ADME emphasizes mechanisms, ABCD highlights practical considerations like dosage, adherence, and therapeutic effects, making it particularly useful for clinical applications. Mnemonics like these, much like those for SSRIs, help simplify complex pharmacological concepts for easier recall.

Pharmacokinetic equations

Pharmacokinetic equations help explain how a drug's dosage and timing affect its concentration in the bloodstream over time. These equations are essential for understanding drug absorption, distribution, metabolism, and excretion, ensuring safe and effective dosing for patients.

Elimination Rate Constant Formula

The elimination rate constant (k) is calculated using the formula:

k = (ln(C1) - ln(C2)) / (t2 - t1)

Where C1 and C2 are the drug concentrations at times t1 and t2.

This tells you the rate at which a drug is cleared from the body.

First Order Pharmacokinetic Model Equation

The equation for a first-order pharmacokinetic model is:

Ct = C0 . e ^ (-kt)

Where Ct is the drug concentration at time t, C0 is the initial concentration, k is the elimination rate constant, and t is time.

Henderson Hasselbalch Equation

The Henderson-Hasselbalch equation is used to calculate the pH or ionization of a drug:

pH = pKa + log ([A-] / [HA])

Here, pKa is the acid dissociation constant, and [A−] and [HA] are the concentrations of the ionized and unionized forms of the drug.

It helps predict how a drug will behave in different pH environments.

How to Calculate Pharmacokinetic Parameters

How to Calculate f in Pharmacokinetics?

The bioavailability (𝑓) of a drug is calculated as:

f = AUC oral / AUC iv 

Where AUC is the area under the concentration-time curve.

This shows how much of the drug reaches systemic circulation.

How to calculate drug clearance?

Clearance (CL) is calculated using the formula:

Clearance (CL) = Rate of Elimination ÷ Plasma Concentration

Clearance is equal to the rate at which a drug is removed from plasma(mg/min) divided by the concentration of that drug in the plasma (mg/mL).

How to calculate half-life pharmacokinetics?

The formula to calculate half-life (t½) is:

t½ = 0.693 × Vd /CL

The calculation requires the volume of distribution (Vd) and clearance (CL). The constant 0.693, which is the natural logarithm of 2, represents the exponential rate of elimination, assuming the drug follows first-order kinetics.

This tells you how long it takes for the drug concentration to decrease by half.

How do you remember Pharmacodynamics and pharmacokinetics?

Use this simple distinction:

• Pharmacodynamics focuses on what the drug does to the body (effects and mechanisms).
• Pharmacokinetics is the study of what the body does to the drug (ADME).

Think of dynamics = effects and kinetics = movement.

Understanding the difference between MOA and pharmacodynamics can further clarify drug interactions by distinguishing the precise molecular actions from broader drug effects.

How to remember drugs in pharmacology?

Here are some tips to remember drugs:

1. Use mnemonics for drug classes (e.g., “ABCD” for antihypertensives: ACE inhibitors, Beta-blockers, Calcium channel blockers, Diuretics).
2. Group drugs by their suffix (e.g., -olol for beta-blockers).
3. Create flashcards or use spaced repetition apps.
4. Associate drugs with their primary use or side effect.

Check out our 12 tips to memorize drugs easily!