Test: General Pharmacology - 4 - NEET PG MCQ

Cytochrome P450 enzymes are solely accountable for phase I reactions, while microsomal enzymes can also participate in phase II processes, such as glucuronide conjugation.

Acidic medications attach to albumin, while basic medications connect to α₁ acid glycoprotein.

As penicillin is classified as an acidic drug, it therefore binds to albumin.

The clearance of a medication refers to the hypothetical volume of plasma from which the drug is entirely eliminated within a specific time frame.

Drugs can exhibit either zero order or first order kinetics. This is determined by the following formula:

Rate of Elimination α {Plasma Concentration}^order

• If a drug adheres to zero order kinetics, {Plasma Concentration}⁰ equals one. In simpler terms, the rate of elimination remains constant and does not depend on plasma concentration.
• According to the formula, for drugs that follow first order kinetics, the rate of elimination is proportional to the plasma concentration.

• In contrast, the maintenance dose is determined by the clearance.
• Loading dose is particularly relevant for drugs with a very long half-life (t_½) or a high volume of distribution (V_d).
• It is computed using the formula: LD = V_d × Target PC.

• All other parameters, such as half-life, can be derived from these.

In first-order kinetics, the elimination rate is directly proportional to the plasma concentration of the drug.

Both the half-life and clearance remain constant in first-order kinetics.

The elimination of a drug is influenced by:

• Volume of distribution
• Clearance

The volume of distribution is greater for drugs that are highly lipid soluble. For drugs that adhere to first order kinetics, the rate of elimination is directly proportional to the plasma concentration.

• Total dose = 70 × 100 mg = 7000 mg
• Plasma concentration = 1.9 mg/ml

• Total dose administered = Plasma concentration × V_d
• 7000 = 1.9 × V_d

• CL = 0.693 × (V_d / t_1/2)
• t_1/2 = 0.693 / k
• k = 0.0693

• CL = 0.693 × (10 × 7000 / 1.9) = 255.3 ml/hr
• Approximately 0.2 L/hr

The maintenance dose is calculated based on clearance. The formula for the maintenance dose is:

• Maintenance dose = CL × Plasma concentration required

Dose Rate = Clearance × Steady state plasma concentration. This indicates that the plasma concentration at steady state is directly influenced by the dose rate, provided that clearance remains constant.

In first-order kinetics (where clearance is stable):

• The plasma concentration achieved is directly proportional to the dose rate.
• Consequently, increasing the dose rate from 10 to 20 mg/min results in a doubling of the steady state plasma concentration (from 2 to 4 mg/dl).

• Clearance is not a factor in calculating the loading dose.
• This information is intended to mislead you.