Explore the principles of how drugs move through the body (pharmacokinetics) and their effects on the body (pharmacodynamics), including absorption, distribution, metabolism, and excretion.
Pharmacokinetics & Pharmacodynamics – Study Guide
| Aspect | Definition | Primary Question |
|---|---|---|
| Pharmacokinetics (PK) | What the body does to a drug. | How is the drug absorbed, distributed, metabolized, and eliminated? |
| Pharmacodynamics (PD) | What the drug does to the body. | How does the drug produce its therapeutic (and toxic) effects? |
Both fields are essential for dose selection, predicting drug interactions, and optimizing therapy.
| Route | Onset | Bioavailability (F) | Advantages | Limitations |
|---|---|---|---|---|
| Oral (PO) | 30 min – 2 h | 0.1–1 (first‑pass effect) | Convenient, non‑invasive | Variable F, GI irritation |
| Intravenous (IV) | Immediate | 1.0 | Precise control, 100 % F | Invasive, requires venous access |
| Intramuscular (IM) | 5–30 min | 0.5–1 | Faster than PO, depot forms | Pain, variable absorption |
| Subcutaneous (SC) | 10–30 min | 0.5–1 | Simple, can use pumps | Limited volume, variable perfusion |
| Inhalation | Seconds–minutes | 0.1–0.9 | Direct lung effect, rapid | Technique dependent |
| Transdermal | Hours | 0.5–0.9 | Steady plasma levels | Skin irritation, limited drug types |
| Phase | Main Enzymes | Typical Reactions |
|---|---|---|
| Phase I | Cytochrome P450 (CYP) isoforms, FMOs, esterases | Oxidation, reduction, hydrolysis |
| Phase II | Transferases (UGTs, SULTs, GSTs, NATs) | Conjugation (glucuronidation, sulfation, glutathione |