Phenytoin;

My patient with long standing hypertension and obesity with significant weight loss while on a glucagon-like peptide-1 receptor agonist (GLP-1RA), now has a “borderline” blood pressure. Should I consider adjusting his antihypertensive medication(s)?

FA Manian MD, MPH, , , , , , , , , , , , , , , , Leave a comment

Yes, you may very well need to adjust antihypertensive regimen of patients who have experienced significant weight loss while on GLP-1RAs.1,2  

In the STEP-1 trial evaluating the impact of semaglutide on cardiometabolic risk factors in adults who were overweight or obese, 34.3% of the group receiving semaglutide had either reduction in the dose or cessation of antihypertensive medications, compared to 15.6% in the placebo group.2  In SURMOUNT-1 trial examining the impact of tirzepatide on blood pressure reduction, a significant net reduction of 6.8 mm Hg systolic and 4.2 mm Hg diastolic blood pressure compared to placebo over 72 weeks was found; weight loss accounted for ~70% of systolic or diastolic blood pressure reduction. 2

The need to lower the dose of or discontinue antihypertensive medications in the setting of significant weight loss should not come as a surprise since this phenomenon predates the widespread use of GLP-1RA in obesity. 1,3 However, in addition to their impact on blood pressure through weight loss, GLP-1RAs may  lower blood pressure through alternative  mechanisms, including natriuresis, direct vasodilation and reduction in sympathetic nervous system activity.4  It’s also important to remember that GLP-1RAs may reduce both systolic and diastolic blood pressures in patients with hypertension even before significant weight loss is observed! 5

But it’s not just about antihypertensive medications!  The use of GLP-1RAs with its attendant weight loss may also require dosage adjustment or discontinuation of several other commonly prescribed medications (eg, insulin, levothyroxine, and anticonvulsants, phenytoin, warfarin, lithium carbonate, and digoxin).2 So don’t forget to regularly review the medication list of patients who have experienced recent weight loss on GLP-1RAs!

Bonus Pearl:  Did you know that the concept of incretin effect was first proposed in the 1970s based on observations that insulin secretion was 2-3 times higher after oral glucose intake than that after intravenous glucose administration? 5

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References

  1. Manian FA. Antihypertensive medications in patients with weight loss. JAMA Intern Med 2025;185:475. Antihypertensive Medications in Patients With Weight Loss | JAMA Internal Medicine | JAMA Network
  2. Karakus KE, Shah VN, Akturk HK. Tirzepatide-induced rapid weight loss-related thyrotoxicosis. JAMA Intern Med 2024;184:1246-1247. Tirzepatide-Induced Rapid Weight Loss–Related Thyrotoxicosis | Lifestyle Behaviors | JAMA Internal Medicine | JAMA Network
  3. Shantha GPS, Kumar AA, Kahan S, et al. intentional weight loss and dose reductions of antihypertensive medications: a retrospective cohort study. Cardiorenal Med 2013;3:17-25. Intentional weight loss and dose reductions of antihypertensive medications: a retrospective cohort study – PubMed
  4. Lingway I, Mosenzon O, Brown K, et al. Systolic blood pressure reduction with tirzepatide in patients with type 2 diabetes: insights from SURPASS clinical program. Cardiovasc Diabetol 2023;22:66. Systolic blood pressure reduction with tirzepatide in patients with type 2 diabetes: insights from SURPASS clinical program – PubMed
  5. Liu QK. Mechanisms of action and therapeutic applications of GLP-1 and dual GIP/GLP-1 receptor agonists. Front Endocrinol 2024; 15:1431292. Frontiers | Mechanisms of action and therapeutic applications of GLP-1 and dual GIP/GLP-1 receptor agonists

Disclosures/Disclaimers: Reference 1 was written by this contributor. The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy Hospital-St. Louis, Massachusetts General Hospital, Harvard Catalyst, Harvard University, their affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

My patient with long standing hypertension and obesity with significant weight loss while on a glucagon-like peptide-1 receptor agonist (GLP-1RA), now has a “borderline” blood pressure. Should I consider adjusting his antihypertensive medication(s)?

Despite taking higher doses of warfarin, my patient’s INR won’t budge. What am I missing?

FA Manian MD, MPH, , , , , , , , , , , , , , , , , , , Leave a comment

Poor compliance is probably the most common and least “exciting” explanation for low INRs despite seemingly adequate or high warfarin doses.  Otherwise, consider the following: 

Increased vitamin K intake: Since warfarin acts by inhibiting vitamin K recycling by VKORC1 (Vitamin K epOxide Reductase Complex), find out if your patient takes multivitamins or loves foods or products rich in vitamin K, ranging from leafy green vegetables to nutritional supplements( eg, Ensure) and even chewing tobacco!1 

Drug interactions: Warfarin is notorious for interacting with many drugs, although its effect is more often enhanced than counteracted. Run the patient’s med list and look for “counteractors” of warfarin,  including carbamazepine, phenobarbital, phenytoin, rifampin, and dexamethasone.2 

Hypothyroidism: Thyroid hormone seems to be necessary for efficient clearance of the vitamin K-dependent clotting factors (II, VII, IX, and X). Thus, larger doses of warfarin may be needed when patients are hypothyroid.3 

Hyperlipidemia and obesity: High lipid levels may allow for high vitamin K levels (since it’s lipid-soluble and carried in VLDL), especially at the start of therapy.4,5 

What if the INR is falsely low? This is usually not the problem although one major trial took a lot of heat for using a point of care INR device that gave low readings in anemic patients.6  When in doubt, check a chromogenic factor Xa test to confirm; 20-30% activity correlates with a true INR of 2-3.7

If none of these explanations fit the bill, consider genetic testing for warfarin resistance.8,9

Bonus Pearl: Did you know that use of warfarin (introduced in 1948 as a rodenticide) has already led to some selective pressure for VKORC1 mutations in exposed rat populations.10

References

  1. Kuykendall JR, et al. Possible warfarin failure due to interaction with smokeless tobacco. Ann Pharmacother. 2004 Apr;38(4):595-7. https://www.ncbi.nlm.nih.gov/pubmed/14766993
  2. Zhou SF, et al. Substrates, inducers, inhibitors and structure-activity relationships of human Cytochrome P450 2C9 and implications in drug development. Curr Med Chem. 2009;16(27):3480-675. https://www.ncbi.nlm.nih.gov/pubmed/19515014
  3. Bucerius J, et al. Impact of short-term hypothyroidism on systemic anticoagulation in patients with thyroid cancer and coumarin therapy. Thyroid. 2006 Apr;16(4):369-74. https://www.ncbi.nlm.nih.gov/pubmed/16646683
  4. Robinson A, et al. Lipids and warfarin requirements. Thromb Haemost. 1990;63:148–149. https://www.ncbi.nlm.nih.gov/pubmed/16646683
  5. Wallace JL, et al. Comparison of initial warfarin response in obese patients versus non-obese patients. J Thromb Thrombolysis. 2013 Jul;36(1):96-101. https://www.ncbi.nlm.nih.gov/pubmed/23015280
  6. Cohen D. Rivaroxaban: can we trust the evidence? BMJ 2016;352:i575. https://www.bmj.com/content/352/bmj.i575/rapid-responses
  7. Sanfelippo MJ, et al. Use of Chromogenic Assay of Factor X to Accept or Reject INR Results in Warfarin Treated Patients. Clin Med Res. 2009 Sep; 7(3): 103–105. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2757431/
  8. Rost S, et al. Mutations in VKORC1 cause warfarin resistance and multiple coagulation factor deficiency type 2. Nature. 2004;427:537–41. https://www.ncbi.nlm.nih.gov/pubmed/14765194
  9. Schwarz UI, et al. Genetic determinants of response to warfarin during initial anticoagulation. N Engl J Med. 2008 Mar 6;358(10):999-1008. https://www.ncbi.nlm.nih.gov/pubmed/18322281
  10. Rost S, et al. Novel mutations in the VKORC1 gene of wild rats and mice–a response to 50 years of selection pressure by warfarin? BMC Genet. 2009 Feb 6;10:4. https://bmcgenet.biomedcentral.com/articles/10.1186/1471-2156-10-4

Contributed by Nicholas B Bodnar, Harvard Medical School student, Boston, MA.

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Despite taking higher doses of warfarin, my patient’s INR won’t budge. What am I missing?

My patient with no known liver disease appears to have bilateral asterixis. What other causes should I consider?

FA Manian MD, MPH, , , , , , , , , , , , Leave a comment

Although originally described in 1949 in patients with liver disease and labelled as “liver flap”, numerous other causes of asterixis exist aside from severe liver disease (1,2). As early as 1950s, asterixis was observed among some patients with heart failure and pulmonary insufficiency but without known significant liver disease (3). Azotemia has also been associated with asterixis.

Don’t forget about medication-associated asterixis . Commonly used drugs such as gabapentin, pregabalin, phenytoin, and metoclopramide have been associated with asterixis (1,4) . Even antibiotics such as ceftazidime and high dose trimethoprim-sulfamethoxazole may be culprits (1,5). There are many psychiatric drugs including lithium, carbamazepine, clozapine, and valproic acid that have been implicated (1,6) as well. Some reviews have also included hypomagnesemia and hypokalemia on the list of causes of asterixis (1).

Although asterixis is essentially a negative myoclonus with episodic loss of electrical activity of muscle and its tone, its exact pathophysiology remains unclear (7). 

 

Bonus Pearl: Did you know that the origin of the word asterixis is An (negative)-iso (equal)-sterixis (solidity) which was shortened by Foley and Adams, its original discoverers, to what we now refer to as “asterixis” (1).

 

References
1. Agarwal R, Baid R. Asterixis. J Postgrad Med 2016;62:115-7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4944342/

2. Pal G, Lin MM, Laureno R. Asterixis: a study of 103 patients. Metab Brain Dis; 2014:29:813-24. https://link.springer.com/article/10.1007%2Fs11011-014-9514-7
3. Conn HO. Aterixis—Its occurrence in chronic pulmonary disease, with a commentary on its general mechanism. N Engl J Med 1958;259:564-569. https://www.nejm.org/doi/full/10.1056/NEJM195809182591203
4. Kim JB, Jung JM, Park MH. Negative myoclonus induced by gabapentin and pregabalin: a case series and systemic literature review. J Neurol Sci 2017;382:36-9. https://www.sciencedirect.com/science/article/pii/S096758681830225X
5. Gray DA, Foo D. Reversible myoclonus, asterixis, and tremor associated with high dose trimethoprim-sulfamethoxazole: a case report. J Spinal Cord Med 2016; Vol. 39 (1), pp. 115-7. https://www.ncbi.nlm.nih.gov/pubmed/26111222
6. Nayak R, Pandurangi A, Bhogale G, et al. Aterixis (flapping tremors) as an outcome of complex psychotropic drug interaction. J Neuropsychiatry Clin Neurosci 2012;24: E26-7. https://neuro.psychiatryonline.org/doi/pdf/10.1176/appi.neuropsych.101102667.

7.Ugawa Y, Shimpo T, Mannen T. Physiological analysis of asterixis: silent period locked averaging. J Neurol Neurosurg Psych 1989;52:89-9. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1032663/pdf/jnnpsyc00523-0104.pdf

 

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My patient with no known liver disease appears to have bilateral asterixis. What other causes should I consider?