Pharmacology Review: Pharmacokinetics and Reproduction Notes

Administration Routes and Absorption

• Intravenous (IV): works very quickly; rapid entry into systemic circulation.
• Subcutaneous: administration under the skin; slower onset than IV.
• Topical: applied to skin; transdermal routes deliver medication through the skin for systemic or local effect.
• Absorption routes: drugs enter the blood after absorption through the intestinal wall or alveoli in the lungs or after direct or indirect injection.

Distribution

• Distribution is the movement of a drug through the circulatory system to its site of action.
• Areas with rich blood supply (e.g., liver, kidneys, heart) receive higher drug levels.
• Areas with limited blood supply (e.g., bones) or barriers (e.g., brain blood–brain barrier) receive less drug.
• Most pharmacology test questions come from distribution concepts.

Metabolism

• Metabolism is how the body breaks down a drug, converting it into more or less potent forms.
• The liver is responsible for most drug metabolism.
• Biotransformation is the chemical alteration of a drug during metabolism.
• The altered form of the drug is called a metabolite (a byproduct of metabolism).
• Metabolites can be distributed to various parts of the body after formation.

Excretion

• Excretion is the elimination of a drug from the body.
• The kidneys are a major route of drug elimination (urine).
• The kidneys may reabsorb some drugs before excretion occurs.
• Other excretion routes include the gastrointestinal tract, skin, and lungs.

Key Pharmacokinetic Concepts

• Onset: the time it takes for a drug to produce an effect after administration.
• Peak: the time at which the drug reaches its maximum therapeutic effect.
• Duration: how long the drug's effect lasts.
• Half-life: the time it takes for the drug amount in the body to decrease by half; some drugs have short half-lives and wear off quickly (e.g., propofol, often used for anesthesia).
• Short-half-life drugs may require more frequent dosing; long-half-life drugs may be given less frequently.
• In patients with organ dysfunction (liver or kidneys), dosages may need adjustment to avoid toxicity.
• Therapeutic drug monitoring may be needed for drugs that must maintain a therapeutic level in the blood (e.g., vancomycin).

Therapeutic Levels and Monitoring

• Onset, peak, and duration are used to time dosing and effect.
• For drugs that must maintain a therapeutic level, blood work is used to monitor levels (e.g., peak and trough levels for vancomycin).
• Peak level measures maximum drug concentration; trough level measures minimum drug concentration just before the next dose.
• Example: vancomycin monitoring relies on maintaining an appropriate peak/trough to ensure efficacy while avoiding toxicity.

Adverse Effects vs. Side Effects; Reactions, Tolerance, Cumulative Effect, and Toxicity

• Adverse drug reaction: a harmful or unintended reaction (e.g., anaphylaxis).
• Side effect: an expected but undesirable secondary effect (e.g., nausea).
• Anaphylaxis: severe, life-threatening allergic reaction requiring rapid treatment.
• Treatment of anaphylaxis: establish airway, provide oxygen, administer epinephrine to raise blood pressure and dilate airways; antihistamines may be used to block further histamine release.

Example Question Focus: Peak and Trough

• Concept: peak is the highest drug level; trough is the lowest drug level.
• Some test items may ask to identify peak vs trough.

Expected Pharmacologic Action and Therapeutic Uses

• For each drug, know the intended pharmacologic action and the therapeutic use for that action.

Oral Contraceptives (Oral Contraception)

• Example: ethinyl estradiol combined with a progestin (various formulations such as norethindrone or others).
• Expected action: mimic natural estrogen and progesterone to prevent pregnancy.
• Adverse reactions and side effects: not all adverse reactions are common; many patients experience side effects such as nausea, breast tenderness, etc.
• Safety alert: patients on oral contraceptives should monitor blood pressure regularly.
• Blood pressure effects: combination oral contraceptives can increase blood pressure via increased levels of angiotensin and aldosterone.
• Angiotensin and aldosterone: natural substances with vasoconstrictive properties and kidney water reabsorption effects.
• When blood pressure increases significantly, actions may include discontinuation of medication or addition of antihypertensive therapy.
• Thrombotic risk: smoking, age (especially around 40), and obesity increase the risk of blood clots.
• Monitoring and education: emphasize taking pills at the same time every day; missing doses can reduce effectiveness.
• Contraindications and interactions:
  • Drospirenone is similar to a potassium-sparing diuretic.
  • Interactions with certain antidepressants and blood thinners; St. John's Wort can reduce effectiveness.
  • Other interactions include grapefruit juice, ketoconazole, certain antibiotics, and anticonvulsants.
• Combination oral contraceptives with ethinyl estradiol and progestin should be used with caution in patients with diabetes due to potential effects on glucose metabolism.
• Emergency oral contraception (Plan B):
  • Action: prevents fertilization and increases cervical mucus viscosity to slow sperm.
  • Dosing: two doses, 12 hours apart; should be taken within 72 hours of unprotected intercourse.
  • Not a routine birth control method and does not protect against STIs.
  • Side effects may include abdominal pain and breast tenderness.
  • Interactions: anticonvulsants, St. John’s Wort, certain antibiotics; may interact with substances that induce CYP3A4 (grapefruit juice, ketoconazole products).

Transdermal Contraception and Other Reproductive Therapies

• Transdermal contraception (patch) is another long-acting method.
• Depo-Provera (depo-shot): long-acting injectable contraception lasting about 3\text{ months}.
• Menopause therapies can involve hormone treatment; details vary by patient.
• Endometriosis and ovulation stimulants: discussed as part of reproductive therapies.

Labor and Fetal Metal Pharmacology

• Oxytocin: a stimulant to promote uterine contractions (labor induction/stimulation).
• Terbutaline: historically used to suppress preterm labor by relaxing uterine smooth muscle; related to beta-adrenergic agonist activity (though the content includes some confusion about receptor type).
• Magnesium sulfate: another tocolytic used to relax uterine contractions in some preterm labor scenarios; often compared with terbutaline.
• Fetal lung maturity and surfactant:
  • Glucocorticoids (e.g., betamethasone, dexamethasone) are given to accelerate fetal lung maturity and surfactant production.
  • Benefits: reduces respiratory distress syndrome, neonatal complications, and intraventricular hemorrhage.
  • Possible adverse effects in the mother include hypertension; monitor lung sounds, dyspnea, crackles, cyanosis.
• Precautions/considerations:
  • If immunizations are given, inform the client.
  • Monitor for signs of maternal or fetal distress.

Uro-genital Pharmacology and Common Medications

• Testosterone therapy for men with low testosterone.
• Sildenafil (Viagra): a vasodilator used for erectile dysfunction; should not be taken with nitrates (e.g., nitroglycerin) due to risk of severe hypotension.

Sexually Transmitted Infections (STIs) and Public Health Notes

• STIs covered in clinical settings include HIV and gonorrhea.
• Discussed outbreaks in elderly populations (e.g., nursing homes), highlighting transmission risk across age groups and the need for awareness.

Quick Review for Exam

• Distinguish distribution, metabolism, and excretion as pharmacokinetic phases.
• Understand half-life and how it influences dosing frequency and duration of action.
• Recognize the difference between adverse drug reactions and side effects.
• Be able to explain peak and trough concepts and why some drugs require monitoring (e.g., vancomycin).
• Know key interactions and contraindications for oral contraceptives, including St. John’s Wort, antibiotics, anticonvulsants, and grapefruit juice.
• Recall emergency contraception usage, dosing, timing, and limitations.
• Understand the basics of tocolytics (terbutaline, magnesium sulfate) and strategies to enhance fetal lung maturity (glucocorticoids, surfactant).
• Remember the cautions with common drugs like sildenafil and nitrates.
• Be aware of public health considerations around STIs and elder care.

End of Notes