Therapeutic Doses: From Minimum to Maximum
In clinical practice, therapeutic effects are achieved using therapeutic doses. Depending on the potency of the developing effect, they are divided into several grades:
- Minimum effective (threshold) doses. This is the smallest amount of a substance capable of producing a detectable therapeutic effect. They are usually 2–3 times smaller than standard values.
- Average therapeutic doses. These doses produce the desired therapeutic effect in the vast majority of patients. Due to individual biological variability and disease severity, the average dose is often expressed as a working range (e.g., 0.025–0.05 g for diclofenac). Depending on timing, a single dose (pro dosi — per administration) and a daily dose (pro die — total amount taken over 24 hours) are distinguished.
- Maximum therapeutic doses. These are the upper limits. Physicians prescribe them only if average doses fail to yield the desired result. Exceeding this threshold is extremely dangerous and risks severe toxic effects. There are maximum single and maximum daily doses. When prescribing potent or hazardous substances, strict regulatory rules apply: if a prescription exceeds the maximum dose without proper medical documentation, the pharmacist cannot dispense the medication.
Dose-Response Curve
To analyze drug kinetics and dynamics, pharmacologists use specialized graphs (coordinates: abscissa $X$ — dose $D$ or $\log D$; ordinate $Y$ — effect intensity $E$).
The curve shape depends on the coordinate system:
- In arithmetic (linear) coordinates, the graph forms a hyperbola.
- In semi-logarithmic coordinates, the curve has a characteristic S-shaped (sigmoid) form.
Key pharmacological parameters determined from the graph include:
- $E_{max}$ — the maximal effect that the drug can theoretically produce. This metric measures the intrinsic efficacy of the drug.
- $ED_{50}$ (Median Effective Dose) — the dose that produces an effect equal to half of the maximal possible effect ($1/2 E_{max}$). This parameter evaluates drug affinity (potency).
Specialized Dosage Regimens
Depending on the chosen treatment strategy, various administration regimens are used:
- Loading dose. This always exceeds the average therapeutic dose. Its primary goal is to rapidly establish a high drug concentration in the blood (saturation). This approach is frequently used in antimicrobial therapy (e.g., initial doses of antibiotics or sulfonamides).
- Maintenance dose. Administered immediately after a loading dose or after the target clinical response has been achieved with standard doses. Its purpose is to maintain the required drug concentration in the body to sustain the therapeutic effect.
- Cumulative dose. The total amount of a drug substance administered to a patient over an entire course of treatment.
Toxicity, Lethality, and Safety Parameters
Globally, based on their biological effects, all doses are divided into three categories: therapeutic, toxic, and lethal. If the administered amount exceeds maximum therapeutic values, dangerous consequences ensue.
- Toxic doses — the amount of a substance that causes toxic effects, leading to poisoning and organ damage.
- Lethal doses (from Latin Letum — death) — the amount of a drug leading to a fatal outcome. These values are always established exclusively during preclinical studies.
The main indicator of drug safety is the therapeutic window (or therapeutic range). This is the range between the minimum effective dose and the maximum therapeutic dose. The clinical significance of this parameter is immense: the wider the therapeutic window, the safer the drug and the lower the risk of accidental overdose.