Question

Discuss at least three mechanisms for reduced oral availability of a drug.

Answer 1

Reduced oral availability of drug is defined as the extent and rate at which the active moiety enters systemic circulation, thereby accessing the site of action.

Bioavailability of a drug is largely determined by the properties of the dosage form, which depend partly on its design and manufacture. Differences in bioavailabilty among formulations of a given drug acan have clinical signifance; thus knowing whether drug formulations are equivalent is essention

The mechanism for reduced oral availability of drug includes

• Fast and fed stages
• Drug interactions
• Physical property of drug
• Gastric emptying
• Day and night circardian rhythm

DRUG INTERACTIONS

Drug interaction is a change in the action or side effects of a drug caused by concomitant administration with afood, beverage, supplement or another drug

A cause of a drug interaction involves one drug which alters the phramacokinetics of another medical drug.

Alternatively, drug interactions result from competition for a single receptor or signaling pathway.

Both synergism and antagonism occur during different phases of the interaction between a drug and an organism

GASTRIC EMPTYING

The rate of gastric emptying affects all drugs, even those which are well absorbed in the stomach

This is because of the fact that the small intestine has a significantly larger surface area and contributes the most to drug absorption

Gastric motility is a major determinat of oral drug absorption

Gastric emptying can be affected by food in the stomach, viscosity of the stomach content, size of the tablet or capsule, sedation, mobility etc.

CIRCADIAN RHYTHMS

Circadian rhythms are 24 hour cycles that are part of the body's internal clock, running in the bcakground to carry out essential functions and processes. One of the most important and well known circadian rhythms is the sleep-wake cycle.

Different systems of the body follow circadian rhythms that are synchronized with a master clock in the brain. This master clock is directly influenced by environment cues, especially light, which is why circadian rhythms are tied to the cycle of day and night.

When properly aligned, a circadian rhythm can promote consistent and restorative sleep. But when this circadian rhythm is thrown off, it can create significant sleeping problems, including insomnia.

Research ia also revealing that circadian rhythms play an integral role in diverse aspects of physical and mental health.