Special Dosing Considerations

• Learn which vulnerabilties may affect patients when prescribing medications such as age, pregnancy, organ function, body size, etc.
• Understand why medication is minimized during different parts of prgnancy and which medications must be still be prescribed.
• Review how prescriptions should be altered for immunocomprimised patients, alcholoci patients, or amputee patients.

While prescribing medications, the dose may vary from person to person depending on if they are vulnerable. In this blog, we will discuss the population in which special dosing considerations are required to protect the patient and improve clinical outcomes.  

As a nurse, knowing the dosing considerations is essential as they play a crucial role in the patient’s well-being.  

Pediatric Population

Drugs not recommended for children by the Food and Drug Administration are not tested in them and do not have any safety profile. Prescribing those drugs to children is not wrong, but they do not have any safety profile for children. Therefore, giving such drugs to children with a lack of pediatric data can result in patient harm or death, similar to what happened with chloramphenicol, leading to Gray Baby Syndrome.  

The main reason for adjusting doses in the pediatric population is body size, which is measured by body surface area or body weight.  

Weight-based pediatric drug dosages are expressed in the number of milligrams per kilogram of body weight (mg/kg), while dosages calculated on body surface areas (BSA) are expressed in the number of milligrams per meter squared (mg/m2). 

Neonates and infants also need dosage adjustments because they do not have well-developed body functions. For example, drug absorption can be hindered or incomplete because of the differences in gastric pH or motility. In the same way, distribution may be altered because of varying amounts of total body water. Excretion and metabolism can be delayed due to immature kidney and liver function. 

Moreover, you need to monitor and make careful dosage adjustments because of rapid weight changes and progressive maturation of hepatic and renal function. Sometimes, gestational age and weight may also play a role in calculating the dose for the neonate or infant.  

The Older Aged Patients

In patients over 65 years of age, the absorption, distribution, metabolism, and excretion are altered, putting them at risk of developing toxic reactions. Therefore, make dosage adjustments while giving them drugs, especially the narrow therapeutic index drugs.  

The reasons for a delay in the pharmacokinetic profile in the elderly are as follows: 

• They have diminished gastrointestinal motility and blood flow, delaying absorption.  
• Their altered body fat percentage, lean muscle mass, and total body water alter distribution.  
• If they have decreased plasma protein due to malnourishment or cachexia, distribution alters. It happens because this allows a larger proportion of free or unbound drugs to circulate and exert toxic drug reactions.  
• Their diminished hepatic function can lead to slowed metabolism, and altered renal function affects excretion.  

When prescribing drugs to older people, give the lowest possible dose and titrate accordingly. Monitor them closely for any adverse drug events.  

Another concern in the older population is polypharmacy because often, they receive different medications for various conditions that puts them at risk of drug interactions even more. One drug can potentiate the effect of another drug, leading to drug-drug interaction.  

In general, doses of most medications, especially digoxin, sedatives, hypnotics, anticoagulants, nonsteroidal anti-inflammatory agents, antibiotics, and antihypertensives, should be given in low doses in the older population to prevent adverse drug events.  

Pregnant Women

Medication use should be minimized as much as possible in pregnant women, especially in the first and the third trimesters, considering the health of the mother and the fetus because, in the first trimester, vital organs are being formed.  

In the third trimester, the baby’s body might not be able to excrete the ingested drug properly after delivery because they do not have a placenta that can help in the metabolism and excretion of the drug. The placenta protects the fetus only from extremely large molecules.  

However, the mother might need to take medications for conditions such as asthma, gastrointestinal disorders, diabetes, heart failure, mental illness, and various other problems. In those cases, give the drugs for the shortest possible time, in the lowest possible doses.  

Renal Impairment

Kidneys play an essential role in drug excretion. When the renal function is compromised, the drug does not eliminate well from the body, leading to adverse drug reactions. Therefore, to prevent it, give the drugs in lower doses in renal compromised patients.  

You can measure renal function through creatinine clearance. Drug serum concentrations can also help in gauging the adequate dose for the patient, considering their renal function.  

Patients with underlying renal impairment, premature infants with immature renal function, and older adults with an age-related decrease in renal function require careful dose adjustments. However, renal function may fluctuate over time and must be re-assessed periodically. 

Hepatic Impairment

The major drug metabolism occurs in the liver. It changes the drug from a relatively fat-soluble substance to a more water-soluble substance in order for the kidneys to excrete it. Knowing about renal function is easy.  

On the contrary, knowing about hepatic function is not that easy. Therefore, it is hard to calculate the dose required for a patient with hepatic impairment.  

Examples of drugs that need careful dosing in patients with hepatic impairment are as follows: 

• Theophylline 
• Diuretics  
• Phenytoin 
• Sedatives and hypnotics 
• Some drugs, such as enalapril and carisoprodol, must be activated in the liver to exert their effect – called prodrugs. In patients with hepatic impairment, these drugs may not be converted to the active component, leading to decreased efficacy. Therefore, you need to give them in higher doses than usual.  

Heart Failure

Heart failure leads to passive congestion of blood vessels in the gastrointestinal tract, which can lead to impaired drug absorption. Heart failure also slows drug delivery to the liver, delaying metabolism.  

In patients with heart failure, sometimes renal function is compromised, leading to delayed elimination and prolonged action of the drug. Patients with chronic heart failure should have their doses well adjusted, especially for those drugs metabolized through the liver and excreted through the kidneys.  

Body Size

Drug dosing is based on total body weight. Some drugs penetrate fatty tissues only, while some do not, such as gentamycin and digoxin. Therefore, dosages for obese patients or those with cachexia should be calculated based on the total body surface.  

Be careful while making dosing adjustments in the following: 

• Older adults 
• Chronic alcoholics 
• Patients with acquired immune deficiency 
• Patients who are terminally ill from cancer or other debilitating illnesses 
• Patients with limb amputation  

The Bottom Line

As a healthcare provider, be vigilant about the dose the patient receives. Make dose adjustments timely, depending on the patient’s condition. In patients with renal or hepatic impairment, pregnant mothers, and children, dose adjustments help prevent adverse drug events. Compel the patient to attend follow-up visits so you can monitor them closely. 

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