Understanding Drug Absorption, Interactions, and Reactions
Antacids and Drug Absorption Timing
Rationale for Separating Doses: It is fundamental to separate the administration of antacids and other drugs by an interval of at least 2 hours.
Absorption Explained: Absorption refers to the phenomenon of selective accumulation of particles on a surface. Certain substances, like antacids, possess the ability to attract molecules to their surface, generating a new compound whose physical and chemical characteristics prevent it from being absorbed effectively in the intestine.
Delayed Drug Effect Example: Morphine and Paracetamol
Scenario: Consider a person undergoing treatment with oral morphine. They develop a fever spike and are administered oral paracetamol. The paracetamol takes longer than usual to produce its effect.
Possible Cause: A slowing (elentecimiento) in peristalsis and gastric emptying, potentially induced by morphine, causes a drug to take longer to reach the small intestine. Consequently, it takes longer to be absorbed and exert its effect.
Dietary Advice for Iron Complex Treatment
Recommendation: For individuals treated with iron complexes, the recommendation is to take the iron compounds on an empty stomach, accompanied by a glass of orange juice.
Rationale: Vitamin C enhances iron absorption. Other foods high in vitamin C that can aid the absorption of this mineral include green leafy vegetables and tomatoes.
CYP450 Enzyme Interactions: Induction and Inhibition
Understanding how drugs interact with the Cytochrome P450 (CYP450) enzyme system is crucial for safe medication use.
Enzyme Induction
This is a relatively unusual mechanism where certain drugs have the capacity to accelerate the functioning of CYP450 enzyme groups. This acceleration speeds up the metabolism and elimination of other drugs processed by the same enzymes.
Enzyme Inhibition
This is the more common mechanism. Numerous drugs and substances can reduce the action of CYP450 enzyme groups. This slows down the metabolism of affected drugs, potentially leading to higher-than-expected plasma concentrations and an increased risk of toxicity.
Clinical Significance: Both enzyme induction and inhibition can significantly alter a drug’s efficacy and safety profile, potentially necessitating dose adjustments or the selection of alternative medications.
General Recommendations for Preventing Drug Interactions
- Monitor individuals taking drugs with a narrow therapeutic index closely to detect the occurrence of toxicity or sub-therapeutic levels.
- Be aware of medications known to be significant enzyme inducers or inhibitors.
- Know the basic pharmacology of commonly managed drugs.
- Recognize that elderly patients and infants often have decreased liver and renal functions, making them more susceptible to drug interactions.
- Pay particular attention to potential interactions at the level of absorption, biotransformation (metabolism), and pharmacodynamics.
- Advise patients to avoid consuming grapefruit juice with certain medications, as it can inhibit intestinal CYP3A4 enzymes, significantly affecting drug absorption and levels.
Understanding Different Types of Adverse Drug Reactions (ADRs)
Adverse Drug Reactions (ADRs), sometimes referred to as RAM (Reacciones Adversas a Medicamentos), vary in their nature and predictability.
Type A (Augmented) ADRs
These reactions are expected based on the known pharmacological characteristics of the drug, and their intensity is typically dose-related. Type A reactions are the most common (approximately 80%). They can potentially affect any individual receiving the drug, are usually not severe, and are often identified before marketing through preclinical animal models.
Type B (Bizarre) ADRs
These reactions are unexpected and cannot be foreseen based on the drug’s known pharmacology. They appear unrelated to the intended action of the drug, are not reproducible in experimental animals, and their intensity is independent of the administered dose. Type B reactions occur due to a specific patient’s susceptibility to the drug and are often severe. Their inherent unpredictability is why they are termed ‘not predictable’.
ADRs from Chronic Administration
These reactions are associated with long-term drug use and include phenomena such as rebound effects or withdrawal symptoms that can occur after the abrupt cessation of certain medications (e.g., antihypertensives, steroids).
Deferred ADRs
These adverse reactions manifest only after a prolonged period, sometimes long after the drug exposure has ceased.