Pharmacokinetics and Pharmacodynamics

Pharmacokinetics and Pharmacodynamics
Pharmacokinetics deals with the absorption of drugs, their distribution as well as excretion. Clearance of the drug from the body is considered the fundamental concept in pharmacokinetics (Rosenbaum, 2016). Drug clearance on the other side involves elimination of the drug metabolites from the body. Usually, drug clearance rhymes with creatinine clearance. Time taken the drug takes to be absorbed, distributed, metabolized, and excreted is essential in pharmacokinetics. On the other side, pharmacodynamics deals with the concentration of drug at the site of action as well as the effect, time course, and intensity of therapeutic and adverse effects (Rosenbaum, 2016). Pharmacodynamics depends on the drug binding with the receptors. Pharmacokinetics and pharmacodynamics principles are applied in ensuring effective and safe therapeutic management of patients using drugs.

How would the difference in pharmacokinetics and pharmacodynamics factor alter the patient’s anticipated response to a psychiatric medication

In the course of my psychiatric rotation, I encountered so many cases. But this particular case attracted my attention. It was a male patient aged 25 years’ old who had been admitted with chief complains of being violent, having visual hallucinations and suicidal attempts. History of drug abuse was positive. The patient was being managed on I.M 50mg modecate start, chlorpromazine P.O. 300mg, P.O carbamazepine 200mg twice a day each. After some days, it was realized that the patient remained drowsy all days long and later developed priapism which did not resolve even with cold massages with ice packs. The excessive effects of the drug such as daylong drowsiness and unexpected body response; priapism were related to pharmacokinetics and pharmacodynamics of the administered drugs.


Factors that might impact the patient\’s pharmacokinetics and pharmacodynamics

Factors that would have contributed to the mentioned response is majorly nutrition, gender as well as other underlying conditions. In terms of nutrition, the patient starved most of the days he was in the ward. He refused to feed. He could not drink enough water too. This lead to physiological mechanisms of the body, such as drug metabolism and elimination drop. Reduced drug metabolism as well as elimination led to the accumulation of drug metabolites in the body hence concentration the effect of the drugs over time, leading to the mentioned effects. The patient complained of reduced urine output. This was a clear sign of acute kidney injury. Failure of the kidney to perform its function reduced drug clearance from the body hence leading to side effects. Being a male predisposed him to contract priapism a condition that only affects male.

Plan of care for the patient based on factors that influence pharmacokinetics and pharmacodynamics

To counteract the effects of psychotic drugs, I would add per Oral Artane 50 mg to be administered twice a day. This will reduce the drowsiness so as the patient can be able and be able to feed. In terms of nutrition, I would ensure the visiting relatives bring the food the patient likes and ensures he feeds adequately. This will facilitate drug metabolism, transportation, and even elimination. Priapism being side effects of chlorpromazine as a result of anti-serotonin effects, I will change the patient to olanzapine, which only has anti-dopamine effects (Werner, & Covenas, 2016). To improve the kidney function of drug elimination amongst other metabolites, I will administer I.V furosemide 20mg on top of encouraging the patient to take a lot of water.


Difference between drug agonists, partial agonist, and drug antagonists

Drug agonists are attached to the receptors to produce the same physiologic effect as the body’s chemicals. Drug antagonist bond with the receptors blocking/reversing the response that the stimulation of the receptor by the body’s chemicals would initiate (Satoskar, Rege, & Bhandarkar, 2015). Partial agonists bind to the receptors but produce effects less than that full agonists would have produced. Therefore, partial agonists block the receptors that would have otherwise been fully activated by the agonists.

Individuals have different genetic makeups others associated with mutations (Eum, Lee, & Bishop, 2016). Drug metabolism, absorption, distribution, and clearance also differ in different individuals. These factors, among others, make sensitivity and response of individuals to the same medication different.


Eum, S., Lee, A. M., & Bishop, J. R. (2016). Pharmacogenetic tests for antipsychotic medications: clinical implications and considerations. Dialogues in clinical neuroscience, 18(3), 323.

Rosenbaum, S. E. (Ed.). (2016). Basic pharmacokinetics and pharmacodynamics: An integrated textbook and computer simulations. John Wiley & Sons.

Satoskar, R. S., Rege, N., & Bhandarkar, S. D. (2015). Pharmacology and Pharmacotherapeutics-E-Book. Elsevier Health Sciences.

Werner, F. M., & Covenas, R. (2016). Serotonergic drugs: agonists/antagonists at specific serotonergic subreceptors for the treatment of cognitive, depressant and psychotic symptoms. Current pharmaceutical design, 22(14), 2064-2071.