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Attention Deficit Disorder; ADD
Attention Deficit Hyperactivity Disorder; ADHD
Why your child's methylphenidate medication should be customized.
At the request of a number of physicians and parents, we recently began preparing unique strengths of methylphenidate in capsules . Parents were cutting tablets in halves and quarters in an attempt to find the dose that gave their child the most benefit for the least side effects. We investigated the problem and it became clear why concerned parents were busy cutting tablets in halves and quarters.
The manufacturer's dosing directions read "Dosage: Dosage should be individualized according to needs and responses of the patient. Children (6 years and over): methylphenidate should be initiated in small doses, (e.g. 5 to 10 milligrams three times per day) with weekly increments of 5 to 10 milligrams in the daily dosage. Dosage should be individualized on the basis of factors such as age, body weight and individual response. Timing of drug administration should be aimed to coincide with periods of greatest academic, behavioral and social difficulties for the patient."(1)
We commonly refer to a tablet strength, for example, a 10 milligram tablet, as the dose of the medication. Dose actually refers to the amount of drug per unit of body weight. The drug dose is usually expressed in milligrams divided by the body weight in kilograms or as milligrams per kilogram of body weight. Therefore, it is not a matter of just taking a 5 or 10 milligram tablet that counts, but the amount of drug per kilogram of body weight.
Children of the same age can vary widely in weight
A 10 milligram, three times per day, daily dose cannot be correct for both the child who has a 45 kilogram body weight and a child who has a 30 kilogram body weight even if they are the same age.
Let us examine in detail the case of two 12 year old children: one weighting 45 kilograms and the other weighing 30 kilograms. When the 30 kilogram child receives 5 milligrams, this child actually receives 0.16 milligram per kilogram (5 milligram/30 kilograms). The heavier 45 kilogram child taking the same amount, 5 milligrams, actually receives much less or only 0.11 milligram per kilogram(5 milligram/45 kilograms). This is illustrated in the table below:
| |
Weight in kilograms |
Amount administered |
Dose in milligrams
per kilo |
| Child A |
30 |
5 milligrams |
0.16 |
| Child B |
45 |
5 milligrams |
0.11 |
| Child B |
45 |
10 milligrams |
0.22 |
This means that child B, when administered 5 milligrams of methylphenidate, receives almost 50% less medication on a milligram per kilogram body weight basis than child A [(0.16-0.11)(0.11) X 100 = 45% ].
Giving child B 10 milligrams seems like the obvious solution. When child B ingests 10 milligrams, the dose child B receives is actually 0.22 milligrams per kilogram body weight (see table above). This is almost 40% [(0.22-0.16)(0.16) X 100 = 37.5%] higher than child A's dose. Thus what seems like a simple approach, going from 5 milligrams to 10 milligrams is in fact a very wide swing in the milligrams per kilogram body weight dose. Child B is either underdosed or overdosed when compared to child A. This may be one reason why some children do well on methylphenidate and others do not.
Problem of unwanted side effects
The patient information in the CPS makes the following statement: "Your child may experience stomach discomforts, nausea and/loss of appetite………… These problems may go away with time."(1) These side effects are an example of methylphenidate having more than just the desired effect on the central nervous system. The fact that these side effects may go away with time is a sign that the child's body is able to make a physiological adjustment.
It is our belief that these side effects can be minimized or avoided by starting at very low doses of say 1 or 2 milligrams and slowly increasing this dose in steps of 1 milligram or less. In this way the child's system is not made to cope with major and sudden physiological adjustments. A child on methylphenidate has enough problems without adding the burden of side effects due to sudden large dosage increases. Slow upward movement of the dose means that the child will get just enough medication for a positive benefit and no more! Dosing should not be based on what a manufacturer makes, but the needs of the individual child.
An exact dosage prepared by a knowledgeable pharmacist in a pharmacy equipped with the appropriate equipment is a better solution. At Pharmacy.ca we have inlicensed Exact Script ® Service capability which
allows us to prepare any medication in any strength in capsules. We use an electronic balance to monitor the accuracy of our capsule preparations.
Contact us for information on how we can provide a unique solution for your child's medications.
References
1) Ritalin® monograph page 1387, CPS Compendium of Pharmaceuticals and Specialties, 32nd edition 1997. M. Claire Gillis BSc(Pharm) Editor in Chief, Published by the Canadian
Pharmaceutical Association Ottawa Ontario Canada.
Last reviewed/updated: May 1, 2010
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311 Sherbourne St, Toronto, On M5A 3Y1 1-416-960-7768 OCP Accreditation number 17533, owner is Central Medical Pharmacy Inc. Designated manager is Veronique Koo, B Sc Phm. Pharmacists are available for counselling during operating hours.
The information provided on our site is for general information purposes only and is not intended to qualify, supplement or replace that of your medical professional. Your doctor or healthcare giver should undertake diagnosing and treating your medical condition.
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