Tuesday, September 13, 2022



Basic characteristics

·         How drugs are absorbed into the body and distributed?

Pharmacokinetics is the study of how pharmaceuticals travel through the body, including absorption, distribution, tissue localization, biotransformation, and excretion. Pharmacodynamics refers to the study of how medications work and the impact they have on the body. Absorption and distribution in the body are prerequisites for a drug's effectiveness. Intestinal absorption of drugs taken orally can vary widely, with some taking longer to be absorbed than others. It is possible to decrease the rate of absorption of even the most rapidly absorbed medications such that they can remain effective for up to 12 hours or more. Intravenous or intramuscular administration of drugs circumvents absorption issues, however, accurate dosage calculations are still essential.

The same medicine can have various effects on different people. Drug metabolism and excretion may be slower in the elderly due to decreased renal and liver function. As a result of these and other reasons, elderly patients typically require lesser doses of medication.

The existence of the disease, nutrition, heredity, and the presence of other medicines in the system can all influence a person's response to medication. In addition, just as everyone's tolerance for pain differs, so does the body's reaction to the medication. In certain cases, bigger doses are required, while in other cases persons who are extremely sensitive to medications experience negative effects at lower amounts than others.

As intestine motility and gastric acidity decline with age, infants and children may absorb nutrients at different rates than adults. Premature newborns, who have less fat tissue and a higher proportion of water in their bodies, may have a distinct pattern of drug distribution. During childhood, metabolic rates, which influence pharmacokinetics, are substantially higher. Children's medication dosages are typically based on their weight (in milligrams per kilograms) or their surface area (in square centimeters) (milligrams per square meter). Children of the same age can have a broad range of sizes, which makes it difficult to determine how much a medicine should be given depending on the child's age. For children, drug dosages may be considerably different from those for adults because they are not miniature adults.

Taking several drugs, some of which may be incompatible with others, makes the elderly particularly vulnerable to the side effects of pharmaceuticals, and this makes them more likely to have drug interactions that are harmful to their health. Gastric acid production and arteriosclerosis restrict the arteries, reducing blood flow to the digestive tract and other organs, as we get older. It is a good example of the principle that should guide all drug therapy—drugs should be administered in the lowest effective dose, especially because adverse effects rise with concentration—in prescription medication to the elderly. Elderly people often have poorer tolerance for small side effects, which younger people may not even notice, due to illness or frailty.

Repeated dosages of medication ensure that the amount delivered and the amount excreted or metabolized are equivalent. Because of individual differences, it may be difficult to identify the correct dosage for some medications. If the therapeutic window (i.e., the concentration above which the medicine is hazardous and below which it is useless) is relatively limited, assessing the plasma level of the drug may be informative. It is common practice to keep an eye on the blood levels of drugs like phenytoin, digitalis, and lithium, which are used to treat bipolar disorder and treat seizures, in order to assure their safety.


In order to alleviate symptoms, treat infection, lower the risk of future sickness, and destroy targeted cells, such as in the chemotherapeutic treatment of cancer, medications are used. There may be no need for a medicine at all in some cases. As vital as deciding which drug to take, it is also crucial to recognize that there is no effective medication out there. In situations where more than one drug is beneficial, doctors choose the one that is most effective and least harmful to patients. A new medicine may promise better results, but it may also be more expensive and unpredictable.

In addition to the organs and systems to which it is explicitly addressed, every medication has many functions. Patients may also have idiosyncratic effects (abnormal reactions unique to that individual) and allergic reactions to some treatments, which are further indications of the need to pick drugs carefully and avoid their use altogether when simpler procedures can be implemented instead. Consider the widespread notion that antibiotics such as penicillin may treat viral infections, which simply isn't true. Antibiotics should only be used when absolutely necessary, as new antiviral medications are now being developed. There is a growing number of drug-resistant organisms that need to be countered by cautious use of these substances.

The risk of drug interactions, which can reduce a drug's effectiveness, rises when it is taken in excess. It is possible that a drug's presence in the stomach or intestines will affect the absorption of another. Tetracycline's absorption is decreased by antacids, which generate insoluble complexes. The interfering effects of one medicine on another are of increasing consequence. If a drug inhibits the metabolism of another drug, it permits the drug to accumulate in the body, increasing the risk of toxicity in the absence of a reduction in the dosage. Many medicines that require microsomal enzymes in the liver to be digested are increased in quantities after taking Cimetidine, a medication used to treat peptic ulcers. If the other medicine is warfarin, this inhibition can be dangerous. If the dosage is not lowered, bleeding may occur. A wide range of other medications are also impacted, including antihypertensives (like calcium channel blockers), antiarrhythmics (like quinidine), and anticonvulsants (like phenytoin) (e.g., phenytoin). The excretion of one drug may be reduced by the excretion of another. Penicillin's elimination is decreased when probenecid is given with it, which raises the blood level of the antibiotic as a result. The combination between quinidine and digoxin, a medication used to treat heart failure, can impede the drug's clearance, elevating the concentration to potentially lethal levels. Toxic effects can also be caused by the combination of two medications, despite the fact that either one on its own would be beneficial.

When a patient is being treated by more than one doctor, it is possible that one of those doctors is unaware of the medications that the other has given. It is not uncommon for a doctor to give medication to alleviate a side effect of another medication. It's better to stop taking the first medication than to start taking another one that has unknown negative effects. Most often, a recently started medication is suspected as the cause of a new symptom before any other possibilities are explored. Patients should notify their doctors of any new medications they are taking and speak with their pharmacists about the possibility of nonprescription medications interfering with any prescription medications they are currently taking. Patients who have a personal physician who checks all of their medications, prescription and over-the-counter, should do so.

The Food and Drug Administration (FDA) oversees the safety and efficacy of prescription pharmaceuticals in the United States (FDA). New pharmaceuticals are approved, indications are identified, formal labelling is put in place, and adverse responses are monitored. Methods of manufacture are also approved. Submission and approval by the FDA are required before INDs can be tested in humans. Clinical studies must be completed before an NDA can be filed and a medication can become available for sale. Normally, this takes years, but if the drug helps people with life-threatening illnesses when existing treatments don't, it may be approved faster. An unapproved medicine can be prescribed to a single patient with the authorization of a physician. A patient may be given emergency usage or compassionate use if there is no alternative treatment option available and the patient's life is in danger. If a life-threatening emergency warrants it, the FDA may also approve the acquisition of medications from foreign nations that are not currently available in the United States. Participating in a clinical trial is another way to get your hands on an experimental medicine. An "open study," in which the investigator is not "blinded" and knows which subjects and controls are being studied, increases the probability that the patient will be given a placebo instead of a medicine that works. Food, over-the-counter medications, and cosmetics are all subject to "truth in advertising" regulations by the Federal Trade Commission (FTC).

Other countries and governmental bodies have similar drug regulation agencies. Like the FDA in the United States, the Chinese government has its own regulatory agency for pharmaceuticals, medical devices, and cosmetics. Medicines are approved by the European Medicines Agency, which also oversees the scientific evaluation of medicines and keeps tabs on the safety and efficacy of those sold within the European Union's member countries.

As a result of the limited patient population, it is not economically feasible for pharmaceutical companies to go through the lengthy and expensive regulatory and marketing processes required for treatments for rare diseases. The Orphan Drug Act of 1983, enacted in the United States to encourage the development of treatments for uncommon diseases, makes these medications available to the public.

The term "controlled substance" refers to drugs that can lead to addiction and abuse. Their production, prescription, and dispensing are all subject to DEA regulation in the United States. Based on their misuse potential and physical and psychological dependence, controlled substances are classified into five schedules. There is no recognized medical purpose for any of the medications included in Schedule I, which includes heroin and other narcotics with a high potential for misuse. Narcotics like opium and cocaine as well as stimulants like amphetamines fall under the category of Schedule II substances because of the great potential for abuse and dependence they carry. Barbiturates, sedatives, and preparations containing only a small amount of codeine are all included in Schedule III, as is a small number of stimulants and depressants. Some sedatives, antianxiety medications, and nonnarcotic analgesics are included in Schedule IV because of their low abuse and dependence potential. Even more so than schedule IV substances, Schedule V pharmaceuticals have a lesser potential for abuse. A prescription is not required for some medications, such as cough syrups and antidiarrheal medications having a little quantity of codeine in them. Any restricted substance prescribed by a physician must have a DEA registration number on file. It is not possible to replenish a patient's supply of schedule II medicines without a fresh prescription in several states, where special triplicate prescription forms are necessary. Countries and international territories like the European Union, where the European Drug Enforcement Agency (EDA) is in charge of combating illegal drug usage and trafficking.

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