Drug Administration Routes: Bioavailability and Safety Insights

Oral Drug Bioavailability: Unpredictable Factors

The bioavailability of oral drugs can be unpredictable because drug absorption depends on many factors, including:

• Gastrointestinal functional status: How well the digestive system is working.
• Food intake: Presence or absence of food can affect absorption rates.
• pH level: The acidity or alkalinity within the gastrointestinal tract.

Sublingual Drug Administration: Key Benefits

The sublingual route is particularly useful for certain drugs, such as nitroglycerin, for two main reasons:

• It allows for rapid administration in emergency situations.
• It bypasses first-pass metabolism in the liver. Drugs that are extensively metabolized in the liver may not reach therapeutic plasma levels if administered orally.

Rectal Drug Absorption: Speed and Variability

While the absorption and bioavailability of rectally administered drugs can be unpredictable, the systemic effect may sometimes be very fast. This is because the drug comes into contact with highly vascular hemorrhoidal veins, allowing it to pass quickly into the bloodstream and produce a systemic effect.

Subcutaneous Absorption: Factors Affecting Speed

Several factors influence the speed of absorption when drugs are administered subcutaneously:

• Drug Solubility: More soluble drugs are absorbed faster.
• Aqueous Solutions: Drugs in aqueous solutions are absorbed more quickly than those in suspensions.
• Blood Flow: Increased blood flow to the injection site leads to faster absorption.
• Subcutaneous Tissue Modification: Fibrous nodules resulting from repeated injections at the same site can cause erratic absorption.

Subcutaneous Injections: Why Rotate Sites?

It is necessary to rotate injection sites in patients who receive continuous subcutaneous medication, such as diabetic patients, to prevent the tissue from developing fibrosis, which can impair absorption.

Epidural Morphine: Monitoring Respiratory Depression

Patients receiving epidural morphine require long-term monitoring for respiratory depression (typically 6-10 hours after administration). Although administered in the epidural space, morphine has a significant ability to spread rostrally (upwards) and can reach the respiratory centers in the brain, potentially causing severe respiratory depression.

Inhaled Drug Bioavailability: Speed and Limitations

The bioavailability of drugs administered by the inhaled route is immediate, though it is almost always less than 100%. Only intravenous administration typically achieves higher concentrations. This is because effective bioavailability depends on the drug properly reaching the lower airways.

Inhaled Dose Accuracy: Challenges and Variables

Ensuring the accuracy of the dose that reaches the lower airways via inhalation can be challenging due to several factors:

• Particle Size: The size of the drug particles.
• Inhalation Technique: The person's ability to perform deep inhalations and correctly follow the steps of the inhalation technique.
• Lung Disease: The type of lung disease the person has can also affect drug delivery.

Inhaled Drugs: Potential for Systemic Effects

Drugs administered by the inhaled route have the potential to cause systemic effects because the lungs possess a high capacity to absorb drugs and transfer them into the bloodstream.

General Drug Administration Safety Rules

Adhering to general safety rules is crucial for the administration of any drug:

• Correct Patient: Verify the patient's identity.
• Correct Drug: Ensure it is the prescribed medication.
• Correct Dose: Administer the exact prescribed amount.
• Correct Route: Use the specified administration pathway.
• Correct Time/Frequency: Administer at the correct time and frequency.
• Allergy Check: Always check for patient allergies.
• Administration Protocol: Follow specific rules for each dosage form and administration route.
• Side Effect Monitoring: Monitor for any adverse effects.
• Interaction Monitoring: Be aware of possible interactions with other drugs.

Preventing IV Fluid Incompatibility: Key Rules

To prevent incompatibility in blends of intravenous fluids, follow these rules:

• Do not mix different drugs in the same system (syringe, catheter, or IV bag) unless their compatibility is confirmed.
• Irrigate the intravenous line with saline between the administration of different drugs.
• Review the indications for each drug administration prior to reconstitution or dilution.
• Monitor for the appearance of precipitates, which indicate incompatibility.
• Do not mix drugs with blood products.
• Use opaque equipment for photosensitive drugs to protect them from light.